U.S. patent application number 17/503544 was filed with the patent office on 2022-02-03 for imaging probe with combined ultrasound and optical means of imaging.
The applicant listed for this patent is SUNNYBROOK HEALTH SCIENCES CENTRE. Invention is credited to Brian COURTNEY, Francis Stuart FOSTER, Nigel Robert MUNCE, Amandeep Singh THIND, Victor Xiao Dong YANG.
Application Number | 20220031165 17/503544 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-03 |
United States Patent
Application |
20220031165 |
Kind Code |
A1 |
COURTNEY; Brian ; et
al. |
February 3, 2022 |
IMAGING PROBE WITH COMBINED ULTRASOUND AND OPTICAL MEANS OF
IMAGING
Abstract
The present invention provides an imaging probe for imaging
mammalian tissues and structures using high resolution imaging,
including high frequency ultrasound and optical coherence
tomography. The imaging probes structures using high resolution
imaging use combined high frequency ultrasound (IVUS) and optical
imaging methods such as optical coherence tomography (OCT) and to
accurate co-registering of images obtained from ultrasound image
signals and optical image signals during scanning a region of
interest.
Inventors: |
COURTNEY; Brian; (TORONTO,
CA) ; MUNCE; Nigel Robert; (Toronto, CA) ;
THIND; Amandeep Singh; (Toronto, CA) ; YANG; Victor
Xiao Dong; (Toronto, CA) ; FOSTER; Francis
Stuart; (Toronto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUNNYBROOK HEALTH SCIENCES CENTRE |
TORONTO |
|
CA |
|
|
Appl. No.: |
17/503544 |
Filed: |
October 18, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14283052 |
May 20, 2014 |
11147452 |
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17503544 |
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12010208 |
Jan 22, 2008 |
8784321 |
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14283052 |
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60881169 |
Jan 19, 2007 |
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International
Class: |
A61B 5/00 20060101
A61B005/00; A61B 8/00 20060101 A61B008/00; A61B 8/12 20060101
A61B008/12; A61B 8/08 20060101 A61B008/08; A61B 1/00 20060101
A61B001/00; G10K 11/00 20060101 G10K011/00; G02B 23/24 20060101
G02B023/24 |
Claims
1. A method of displaying co-registered images, said method
comprising the steps of: obtaining a first image and a second image
from an imaging catheter configured to obtain images according to
two or more imaging modalities, wherein said first image is
obtained according to a first imaging modality and said second
image is obtained according to a second imaging modality, and
wherein said first image and said second image are spatially
co-registered; and dynamically displaying an image comprising one
or more portions of said first image and one or more portions of
said second image.
2. The method according to claim 1 wherein said one or more
portions of said first image and said one or more portions of said
second image vary with time.
3. The method according to claim 2 wherein said step of dynamically
displaying said image comprises the steps of: dividing said image
into a plurality of sectors, wherein alternating sectors are
displayed using alternating imaging modalities; and displaying said
image while varying locations of said sectors.
4. The method according to claim 3 wherein said sectors rotate over
time.
5. The method according to claim 1 wherein said one or more
portions of said first image and said one or more portions of said
second image are determined according to input from a user.
6. The method according to claim 5 wherein said user input
comprises an identification of one or more contours.
7. The method according to claim 1 wherein said step of dynamically
displaying said image comprises the steps of varying a transparency
level of one or more of said first image and said second image.
8. The method according to claim 1 further comprising the steps of:
processing one or more of said first image and said second image to
identify one or more tissue types; generating an updated image
comprising an indication of said one or more tissue types; and
displaying said updated image.
Description
CROSS REFERENCE TO RELATED U.S. APPLICATIONS
[0001] This patent application relates to, and claims the priority
benefit from, U.S. Pat. No. 11,147,452, issuing on Oct. 19, 2021,
(application Ser. No. 14/283,052, filed on May 20, 2014), in
English, entitled IMAGING PROBE WITH COMBINED ULTRASOUND AND
OPTICAL MEANS OF IMAGING which relates to, and claims priority
benefit from U.S. Pat. No. 8,784,321, issued on Jul. 22, 2014,
(application Ser. No. 12/010,208 filed on Jan. 22, 2008), in
English, entitled IMAGING PROBE WITH COMBINED ULTRASOUND AND
OPTICAL MEANS OF IMAGING, which relates to, and claims the priority
benefit from U.S. Provisional Patent Application No. 60/881,169
filed on Jan. 19, 2007, in English, entitled IMAGING PROBE, the
contents of these applications being incorporated herein by
reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the field of
imaging mammalian tissues and structures using high resolution
imaging using combined high frequency ultrasound (IVUS) and optical
imaging methods such as optical coherence tomography (OCT) and to
accurate co-registering of images obtained from ultrasound image
signals and optical image signals during scanning a region of
interest.
BACKGROUND OF THE INVENTION
[0003] High resolution imaging of the interior of the body (or for
dermatologic or ophthalmology applications not restricted to the
interior) serves multiple purposes, including any of i) assessing
tissue structures, anatomy and composition; ii) planning and/or
guiding interventions on localized regions of the body; and iii)
assessing the result of interventions that alter the structure,
composition or other properties of the localized region. High
resolution imaging in this particular case refers to high frequency
ultrasound and optical imaging methods. For the purposes of this
invention, high frequency ultrasound typically refers to imaging
with frequencies of greater than 3 MHz, and more typically in the
range of 9 to 100 MHz.
[0004] High frequency ultrasound is very useful for intravascular
and intracardiac procedures. For these applications, the ultrasound
transducers are incorporated into a catheter or other device that
can be inserted into the body. By way of example, two particularly
important implementations of high frequency ultrasound are
intravascular ultrasound (IVUS), for imaging blood vessels, and
intracardiac echocardiography (ICE) for imaging cardiac chambers.
Both ICE and IVUS are minimally invasive, and involve placing one
or more ultrasound transducers inside a blood vessel or cardiac
chamber to take high quality images of these structures.
[0005] Optical imaging methods based on fiber optic technology used
in the field of medicine include optical coherence tomography
(OCT), angioscopy, near infrared spectroscopy, Raman spectroscopy
and fluorescence spectroscopy. These modalities typically require
the use of one or more optical fibers to transmit light energy
along a shaft between an imaging site and an imaging detector.
Optical coherence tomography is an optical analog of ultrasound,
and provides imaging resolutions on the order of 1 to 30 microns,
but does not penetrate as deeply into tissue as ultrasound in most
cases. Fiber optics can also be used to deliver energy for
therapeutic maneuvers such as laser ablation of tissue and
photodynamic therapy.
[0006] Additional forms of imaging related to this invention
include angioscopy, endoscopy and other similar imaging mechanisms
that involves imaging a site inside the patient using a probe to
take pictures based on the back-reflection of light. High
resolution imaging means have been implemented in many forms for
assessing several different regions of mammalian anatomy, including
the gastrointestinal system, the cardiovascular system (including
coronary, peripheral and neurological vasculature), skin, eyes
(including the retina), the genitourinary systems, breast tissue,
liver tissue and many others. By way of example, imaging of the
cardiovascular system with high frequency ultrasound or optical
coherence tomography has been developed for assessing the structure
and composition of arterial plaque.
[0007] High-resolution imaging has been used to measure vessel or
plaque geometry, blood flow through diseased arteries, the effects
of interventions on arterial plaque (such as by atherectomy,
angioplasty and/or stenting). Attempts have also been made using
high resolution imaging to identify vascular lesions that have not
led to clinical symptoms, but are at increased risk of rupturing or
eroding and causing an acute myocardial infarction. These so-called
"vulnerable plaques" are an area of interest as the prospect of
treating such plaques to pre-empt adverse clinical events is
conceptually appealing.
[0008] Chronic total occlusions are a specific subset of vascular
lesions where the entire lumen of the vessel has been occluded
(based on the angiographic appearance of the lesion) for over
approximately one month. Most intravascular imaging modalities are
"side-viewing" and require passage of an intravascular imaging
device through a lesion. In order to image chronic total
occlusions, methods of high resolution imaging would be more useful
if they were adapted to a "forward-looking" rather than
"side-viewing" configuration.
[0009] Several of these high resolution imaging means are dependent
on the use of a rotary shaft to transmit torque to an imaging
device near the distal end of the probe. These rotary shafts are
often long, thin and flexible, such that they can be delivered
through anatomical conduits, such as the vasculature, genitourinary
tracts, respiratory tracts and other such bodily lumens. Ideally,
when a continuous torque is applied to the cable in a specified
direction the torque cable develops a property of having a close
relation between the degree of rotation at its proximal and distal
ends. This allows the simplification of the design of the
ultrasound catheter by making the angle of rotation at the distal
end of the torque cable (within the body) a reasonable
approximation of the angle of rotation at the proximal end of the
torque cable (outside of the body).
[0010] The rotation of the torque cable or shaft at the point from
which the imaging occurs may not be identical to the rotation
occurs at the proximal end of the torque cable or shaft. This
occurs especially when the flexible shaft is delivered through
tortuous passageways and is, at least in part, due to inertia and
friction between the rotating components and stationary components
of the imaging shaft. The assumption that the rotational speed of
the proximal and distal ends of the rotary shaft are equal to each
other is also less likely to be valid if the rotational speed
varies over time. The undesirable result of not knowing the true
angular velocity of the imaging probe at the point from which the
imaging beam is directed towards the tissue leads to an artifact
referred to non-uniform rotational distortion (NURD). NURD can lead
to significant distortion of the image and a concomitant reduction
in the geometric accuracy of the image. Knowledge of a more precise
estimation of the true rotary speed of the distal rotary shaft or
an imaging assembly attached to the rotary shaft can help overcome
such distortion by providing more accurate information for image
reconstruction. A better estimation of the rotary speed can also
help improve the accuracy of co-registration of images when more
than one imaging modality is implemented on the imaging probe (such
as combined ultrasound and optical imaging).
[0011] While use of more than one type of imaging technique, such
ultrasound and optical techniques, have both proved valuable in
medical applications for high resolution imaging, they are not
commonly used in tandem. As described in the Summary of the related
art below, there are some designs that exist for the combination of
optical and ultrasound technologies. However, the limitations in
these designs have prevented their acceptance.
[0012] Namely, designs that incorporate optical and ultrasound
technologies offset the ultrasound and optical imaging mechanisms,
such as disclosed in (Maschke, U.S. Pat. No. 7,289,842 resulting in
the acquisition of unaligned ultrasound and optical signals.
Alignment of the resultant data from these two imaging means
requires movement of the imaging mechanisms and is prone to
registration errors due to (i) non-uniform rotational distortion
(NURD), (ii) motion of the object occurring between successive
imaging of the same location using the two imaging means, (iii)
variability in the object being imaged, and (iv) difficulty in
accurately tracking the location of the imaging means. All these
effects result in inaccurate co-registration which limits the
usefulness of the acquisition of data from the two imaging
means.
SUMMARY OF THE RELATED ART
[0013] A catheter-based system for intravascular ultrasound is
described by Yock (U.S. Pat. No. 4,794,931) to provide high
resolution imaging of structures in blood vessels. This system
comprises an outer sheath, within which there is an ultrasound
transducer near the distal end of a long torque cable. When a motor
rotates the torque cable and ultrasound transducer assembly, 2D
cross-sectional images of anatomical structures, such as blood
vessels, can be made. Linear translation of the catheter or the
torque cable and ultrasound transducer in combination with the
rotational motion of the ultrasound transducer allows for
acquisition of a series of 2D images along the length of the
catheter.
[0014] Milo et al (U.S. Pat. No. 5,429,136) and Lenker et al (U.S.
Pat. Nos. 6,110,121 and 6,592,526) describe reciprocating and
vibrating means for scanning an ultrasound imaging beam in
circumferential or longitudinal directions at the end of the
catheter. Reciprocating or vibrating means obviates the need to use
a mechanism such as a slip ring to provide an electrical connection
to a probe that rotates more than a few rotations in a particular
direction, such as more than one or two rotations. Similarly,
certain implementations of optical imaging can avoid the use of
optical rotary joints using reciprocating or vibrating means.
[0015] Liang et al. (U.S. Pat. Nos. 5,606,975 and 5,651,366)
describe means of implementing forward-looking intravascular
ultrasound where ultrasound is directed towards a mirror that
causes the ultrasound beam to propagate at an angle from the
longitudinal axis of a rotating torque cable advanced within the
vasculature. Liang et al. also describe means of varying the angle
of deflection of the mirror using either a micromotor, a gear
clutch mechanism, steering cables or bimorph elements such a shape
memory alloys, piezoelectric files or conductive polymers. FIG. 13
of U.S. Pat. No. 5,651,366 shows a diagram of a forward looking
ultrasound probe combined with a fiber optic to deliver laser
ablation energy via a fiber and mirror in a coaxial direction to
the ultrasound imaging beam, but does not relate to combined
optical and acoustic imaging or provide for optical focusing
elements which would be of benefit for imaging purposes.
[0016] The use of intravascular ultrasound (IVUS) has since become
commonplace, with many improvements and adaptations to the
technology. A flexible torque cable (Crowley, U.S. Pat. No.
4,951,677) improves the fidelity of the transmission of rotational
torque along the length of an IVUS catheter, minimizing an artifact
known as non-uniform rotational distortion.
[0017] The center frequency of IVUS lies within the range of 3 to
100 MHz and more typically in the range of 20 to 50 MHz. Higher
frequencies provide higher resolution but result in worse signal
penetration and thus a smaller field of view. Depth of penetration
can range from less than a millimeter to several centimeters
depending on several parameters such as center frequency and
geometry of the transducer, the attenuation of the media through
which the imaging occurs and implementation-specific specifications
that affect the signal to noise ratio of the system.
[0018] Variations of high frequency ultrasound exist, where the
signal acquisition and/or analysis of the backscattered signal is
modified to facilitate obtaining or inferring further information
about the imaged tissue exist. These include elastography, where
the strain within tissue is assessed as the tissue is compressed at
different blood pressures (de Korte et al Circulation. 2002 Apr. 9;
105(14):1627-30); Doppler imaging which assesses motion such as
blood flow within anatomic structures; virtual histology, which
attempts to infer the composition of tissue using the
radio-frequency properties of the backscattered signal combined
with a pattern recognition algorithm (Nair, U.S. Pat. No.
6,200,268); second harmonic imaging (Goertz et al, Invest Radiol.
2006 August; 41(8):631-8) and others. Each of these forms of
imaging can be improved upon by means described in the present
invention.
[0019] Ultrasound transducers themselves are improving
considerably, including the use of single crystal ultrasound
transducers and composite ultrasound transducers.
[0020] Hossack et al (WO/2006/121851) describe a forward looking
ultrasound transducer using a CMUT transducer and a reflective
surface.
[0021] Tearney et al (U.S. Pat. No. 6,134,003) describe several
embodiments that enable optical coherence tomography to provide
higher resolution imaging than is readily obtained by high
frequency ultrasound or IVUS.
[0022] Boppart et al (U.S. Pat. No. 6,485,413) describe several
embodiments of optical coherence tomography imaging, including
forward-looking implementations. Either an optical fiber or a
gradient index (GRIN) lens are displaced using a mechanism such as
a motor, a piezoelectric, a moveable wire, inflation means and
others.
[0023] Mao et al (Appl Opt. 2007 Aug. 10; 46(23):5887-94) describe
methods for creating ultrasmall OCT probes using single mode fiber,
coupled to a small length of GRIN fiber which acts as a lens.
Including an optical spacer between the fiber and the lens can
alter the working distance of the fiber-lens system. Furthermore,
adding a small length of no-clad fiber to the distal end, and
cutting the no-clad fiber at an angle can add a deflecting element
to the end of the fiber-lens system. This deflecting element
enables side-viewing imaging, which could also be accomplished
using a small prism or mirror.
[0024] Variations of optical coherence tomography (OCT) include
polarization sensitive OCT (PS-OCT) where the birefringent
properties of tissue components can be exploited to obtain
additional information about structure and composition;
spectroscopic OCT which similarly provides improved information
regarding the composition of the imaged structures; Doppler OCT
which provides information regarding flow and motion; elastography
via OCT; and optical frequency domain imaging (OFDI), which allows
for a markedly more rapid acquisition of imaging data and therefore
enables imaging to occur over a larger volume of interest in less
time. Again, each of these forms of imaging can be improved upon by
means of the present invention.
[0025] Several other forms of fiber-optic based imaging exist other
than OCT. Amundson et al describe a system for imaging through
blood using infra-red light (U.S. Pat. No. 6,178,346). The range of
the electromagnetic spectrum that is used for their imaging system
is selected to be one which optimizes penetration through blood,
allowing optical imaging through blood similar to that afforded by
angioscopy in the visible spectrum, but without the need to flush
blood away from the region being imaged.
[0026] Dewhurst (U.S. Pat. No. 5,718,231) discloses a forward
looking probe for intravascular imaging where a fiber optic travels
through an ultrasound transducer to shine light on a target tissue
straight in front of the end of the probe. The light then interacts
with the target tissue and makes ultrasound waves, which are
received by the ultrasound sensor and the images are photoacoustic
images only as the system is not configured to receive and process
optical images. The ultrasound sensor used in the Dewhurst device
is limited to thin film polymeric piezoelectrics, such as thin film
PVDF, and is used only to receive ultrasound energy, not to convert
electrical energy to ultrasound.
[0027] Angioscopy, endoscopy, bronchoscopy and many other imaging
devices have been described which allow for the visualization of
internal conduits and structures (such as vessels, gastrointestinal
lumens and the pulmonary system) in mammalian bodies based on the
principle of illuminating a region within the body near the distal
end of a rigid or flexible shaft. Images are then created by either
having a photodetector array (such as a CCD array) near the end of
the shaft or by having a bundle of fiber optics transmit the
received light from the distal end of the shaft to the proximal end
where a photodetector array or other system that allows the
operator to generate or look at an image representative of the
illuminated region. Fiber bundles are bulky and reduce the
flexibility of the shaft among other disadvantages.
[0028] Other fiber optic based modalities for minimally invasive
assessment of anatomic structures include Raman spectroscopy as
described by Motz et al (J Biomed Opt. 2006 March-April; 11(2)),
near infrared spectroscopy as described by Caplan et al (J Am Coll
Cardiol. 2006 Apr. 18; 47 (8 Suppl): C92-6) and fluorescence
imaging, such as tagged fluorescent imaging of proteolytic enzymes
in tumors (Radiology. 2004 June; 231(3):659-66).
[0029] The ability to combine ultrasound and optical coherence
tomography onto a single catheter would be extremely advantageous.
Kubo et al presented an interesting in vivo study of coronary
arteries using OCT, IVUS and angioscopy to assess the morphology of
lesions that have caused an acute myocardial infarction (Journal of
American College of Cardiology, Sep. 4, 2007, 10(50):933-39). They
demonstrate that there are benefits to imaging with each of these
modalities. However, in order to execute their study, they had to
use separate catheters for each of IVUS, OCT and angioscopy imaging
modalities as no catheters that combine these functions have been
commercialized to date. Kawasaki et al previously compared OCT,
conventional IVUS and a variant of IVUS known as integrated
backscatter IVUS on cadaveric specimens of coronary arteries using
separate probes for the OCT and IVUS components. Brezinski et al
(Heart. 1997 May; 77(5):397-403) had previously demonstrated ex
vivo studies on dissected aortic specimens where IVUS and OCT
images were compared, again using separate probes. The OCT probes
in this latter study were not suitable for in vivo use.
[0030] Optical coherence tomography generally has superior
resolution to ultrasound and has the potential to better identify
some structures or components in vascular and other tissues than
ultrasound. For example, fibrous cap thickness or the presence of
inflammatory or necrotic regions near the surface of arteries may
be better resolved with optical coherence tomography. However,
optical coherence tomography is limited by its small penetration
depth (on the order of 500 to 3000 microns) in most biologic media.
Most such media are not optically transparent.
[0031] Meanwhile, ultrasound has the ability to better penetrate
through biological media such as blood and soft tissues and has a
depth of penetration that typically extends several millimeters or
centimeters beyond that of optical coherence tomography. The
ability to image with either or both methods of imaging using a
combined imaging device provides advantages with respect to
selecting the required resolution and depth of penetration.
Furthermore, much of the information acquired by optical coherence
tomography is complementary to that acquired by ultrasound and
analysis or display of information acquired by both imaging methods
would improve the ability to better understand the interrogated
tissue, such as with respect to its composition.
[0032] These differences between IVUS and OCT are well known in the
art. Maschke (United States Patent Publication No. 2006/0116571
corresponding to U.S. patent application Ser. No. 11/291,593)
describes an embodiment of a guidewire with both OCT and IVUS
imaging transducers mounted upon it. The described invention has
several shortcomings. Guidewires are typically 0.014'' to 0.035''
in diameter (approximately 350 microns to 875 microns), yet
ultrasound transducers typically are at least 400 microns.times.400
microns and generally are larger in size for the frequencies in the
20 to 100 MHz range. If the transducer is too small, the beam is
poorly focused and has poor signal properties. In Maschke the IVUS
and OCT imaging mechanisms are located at different positions along
the length of the guidewire and a drawback to this type of
configuration having the IVUS and OCT imaging means located at
different positions along the length of an imaging shaft does not
allow for optimal co-registration of images.
[0033] U.S. Pat. No. 7,289,842) issued to Maschke describes an
imaging system that combines IVUS and OCT on a catheter where the
IVUS and OCT imaging elements are longitudinally displaced from
each other along the length of a catheter that rotates around its
longitudinal axis. Maschke also describes generating images where
the center portion of the images are substantially derived from the
output of the higher resolution OCT imaging portion of the system
while the outer portion of the images are substantially derived
from the output of the ultrasound imaging portion of the system, to
make use of ultrasound's greater depth of penetration in
combination with OCT's higher resolution for tissues close to the
catheter.
[0034] Park et al (U.S. patent application Ser. No. 11/415,848)
also briefly refers to the notion of having a catheter that
combines IVUS and OCT imaging onto a single catheter.
[0035] However, the integration of means for combined acoustic and
optical imaging, such as combined IVUS and OCT imaging, onto a
single device is not trivial. Having an optical imaging element and
an acoustic imaging element longitudinally separated from each
other on a primarily rotating catheter does not provide an ideal
configuration for combined imaging. A more ideal configuration
would enable the acquisition of high quality acoustic and optical
signals from which ultrasound and optical-based images could be
made while enabling the acoustic and optical images to be
registered with each other in a highly precise manner.
[0036] For example, by simply placing an IVUS imaging element in
line with an OCT imaging element along the length of the catheter,
the center of the imaging planes of the IVUS and OCT images will be
separated from one another by a distance of at least approximately
half the length of the ultrasound transducer and half the length of
the optical imaging elements.
[0037] Mechanical IVUS transducers for vascular imaging are
typically more than 400 microns in length. The separation between
the IVUS and OCT planes of imaging in a configuration such as that
proposed by Maschke would require at least 250 microns of
separation between the optical and acoustic imaging planes.
Typically, mechanical IVUS rotates at 30 frames per second with a
pullback rate of 0.5 mm/s, meaning that from a given time point to,
at least 15 imaging frames or 500 milliseconds would elapse between
the time that the more distally placed imaging means would
translate to the same position at which the more proximally placed
imaging means was originally positioned at time to. This separation
of several hundred milliseconds or several rotations of the imaging
probe makes it difficult to precisely register the imaging data
from one imaging means with the other.
[0038] This is particularly relevant given the fact that the
catheter can undergo significant unintentional lateral and
longitudinal displacements within body lumen in that time period,
such as those displacements that occur as a result of cardiac
contraction and pulsatile flow. Non-uniform rotational distortion
(NURD) can also have an impact on the ability to accurately
register images acquired several rotations apart from each other.
Any imprecision of the registration of the two data sets is even
more significant when one considers the scale at which important
pathologies, such as vulnerable plaques can be found. Dramatic
differences in the appearance of an arterial plaque's composition
(e.g. the thickness of a fibrous cap, the presence of a calcified
nodule or the extent of an atheromatous deposit) can be observed in
as little as a few hundreds microns along the length of a vessel.
Similarly, small but potentially relevant sidebranches of anatomic
conduits, such as blood vessels, can have dimensions on the order
of less than a hundred microns.
[0039] Previous experiments and implementations of IVUS and OCT or
other combinations of acoustic and optical imaging have not been
provided that enable significant precision in the registration of
the imaging data from the two or more imaging means in a manner
that is suitable for minimally invasive imaging, such as
intravascular imaging.
[0040] To the best of our knowledge, previous experiments and
implementations of IVUS and OCT or other combinations of acoustic
and optical imaging have not been provided that enable significant
precision in the registration of the imaging data from the two or
more imaging means in a manner that is suitable for minimally
invasive imaging, such as intravascular imaging.
[0041] It would be very advantageous to also provide high
resolution imaging probes that combine acoustic and optical imaging
onto "forward-looking" probes rather than "side-viewing" probes. It
would also be helpful to provide similar probes that can look
backwards, or from multiple angles in a generally side-viewing
configuration.
[0042] It would also be advantageous to provide high-resolution
imaging probes that combine ultrasound imaging with one or more
optical imaging means.
[0043] It would also be advantageous to provide minimally invasive
imaging probes that can be used for photoacoustic imaging or
sonoluminescent imaging.
[0044] It would also be advantageous to provide minimally invasive
imaging means where on of the imaging means provides helpful
information regarding the direction in which the other imaging
means is acquiring imaging data.
SUMMARY OF THE INVENTION
[0045] The present invention provides embodiments of imaging probes
for combining acoustic and optical imaging means in a manner that
facilitates simultaneous imaging by two or more imaging methods.
The embodiments enable methods to accurately co-register the images
obtained from each of the modalities. In some embodiments, the
current invention provides embodiments for combining acoustic
imaging means with the delivery of therapeutic energy, such as
ultraviolet light for photodynamic therapy or laser energy for
ablation procedures.
[0046] The present invention also provides embodiments where one
form of imaging is used to help with the reconstruction of the
second form of imaging. This is more specifically related to
monitoring the position or orientation of a component in the image
probe that subsequently determines the position or orientation of
the imaged region.
[0047] The present invention provides methods for combining high
frequency ultrasound and optical coherence tomography into a
combined imaging system.
[0048] The present invention provides novel means for implementing
a combined ultrasound and optical imaging system where the volume
scanned includes a region either forward of, or behind, the
location of the imaging transducers.
[0049] The present invention provides the ability to take images
similar to those produced by angioscopy, endoscopy and similar
imaging techniques using a single optic or a small number of fiber
optics, in combination with means to acquire ultrasound images.
These optical images can also be acquired using infrared and/or
visible wavelengths.
[0050] The present invention provides means for combining high
frequency ultrasound and optical coherence tomography where the
volumes scanned include regions either forward of, or behind, the
locations of the imaging transducers.
[0051] Embodiments of the present invention are able to scan a
region for the purposes of imaging or delivery of therapeutic
energy the region accessed by a shaft where changes in the rotation
velocity of the shaft causes changes in the direction of either an
emitter and/or receiver of acoustic and/or optical energy.
[0052] The present invention also facilitates certain forms of high
resolution imaging that use acoustic energy to create optical
energy (sonoluminescence imaging) or optical energy to create
acoustic energy (photoacoustic imaging).
[0053] An embodiment of the present invention provides an imaging
probe for insertion into bodily lumens and cavities for imaging an
interior of said bodily lumens and cavities or imaging exterior
surfaces of a body, comprising:
[0054] a) an hollow shaft having a longitudinal axis having distal
and proximal end sections and an midsection, an imaging assembly
being located in said hollow shaft, said imaging assembly being
connected to a first end of an imaging conduit, said imaging
conduit extending through the hollow shaft and being connectable at
a second end thereof to an image processing and display system
through the proximal end section, said imaging conduit including a
fiber optic having a distal end and said imaging assembly including
an optical emitter/collector including light directing and
receiving means associated with said distal end of a fiber optic
for directing light imaging energy out of a distal end of said
fiber optic and receiving reflected light imaging energy signals
and directing said received reflected light energy signals back to
said image processing and display system, said imaging assembly
including an ultrasound transducer and said ultrasound transducer
emitting and receiving reflected ultrasound imaging energy signals
and said imaging conduit including an electrical conductor for
electrically coupling the ultrasound transducer to an ultrasound
signal generator connectable to said second end of said imaging
conduit, said imaging conduit being connectable at said second end
to a source of light;
[0055] b) said imaging assembly including a scanning mechanism
configured to deliver said light from the optical emitter/collector
and ultrasound from said ultrasound transducer along pre-selected
paths out of said hollow shaft, the ultrasound transducer and the
optical emitter/collector being positioned and oriented relative to
each other to enable accurate co-registering of received reflected
light imaging energy signals and reflected ultrasound imaging
energy signals during scanning a region of interest; and
[0056] c) drive mechanism for imparting motion to said imaging
conduit and said imaging assembly, said drive mechanism being
connectable to a controller which is connectable to said image
processing and display system.
[0057] A further understanding of the functional and advantageous
aspects of the invention can be realized by reference to the
following detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] Preferred embodiments of the invention will now be
described, by way of example only, with reference to the drawings,
in which:
[0059] FIG. 1 is a schematic of an imaging system including
ultrasound and optical imaging components;
[0060] FIG. 2 is a perspective drawing of a flexible imaging probe
with an adapter, conduit and imaging assembly;
[0061] FIG. 2a is a cross sectional view of the mid section of the
imaging probe of FIG. 2 taken along the dotted line;
[0062] FIG. 2b is an expanded perspective drawing of the distal
region of the imaging probe of FIG. 2;
[0063] FIG. 2c shows a schematic of how the rotary and non-rotary
components of the imaging probe can be coupled with an adapter to
the rest of an imaging system.
[0064] FIG. 2d is a perspective drawing of an example of the
coupling of the rotary and non-rotary components of the probe to an
adapter.
[0065] FIGS. 3a to 3e are representative of general imaging
catheter configurations described in the prior art;
[0066] FIG. 3a shows one embodiment of an over-the-wire
configuration for an external sheath that may be incorporated with
the imaging probe if a guidewire lumen is included;
[0067] FIG. 3b shows a cross-section through the imaging probe to
demonstrate the guidewire lumen configuration.
[0068] FIG. 3c shows a rapid access configuration for an external
sheath that may be incorporated with the imaging probe if a
guidewire lumen is included;
[0069] FIG. 3d shows a cross-section through a portion of the
imaging probe that does not contain a guidewire lumen;
[0070] FIG. 3e shows a cross-section through a portion of the
imaging probe that does contain a guidewire lumen;
[0071] FIGS. 4a to 4l are examples of ultrasound transducers that
contain a hole for allowing transmission of optical energy through
the transducer that enables optical and acoustic imaging of regions
that are precisely aligned with each other, as well as means to
deflect the path of the imaging light;
[0072] FIGS. 5a to 5f are examples of ultrasound transducers that
contain a hole for allowing transmission of optical energy through
the transducer that enables optical and acoustic imaging of regions
that are precisely aligned with each other, without a means to
deflect the path of the imaging light;
[0073] FIGS. 6a to 6c demonstrate representative acoustic
transducer configurations, with FIG. 6a not having a hole in the
transducer. FIGS. 6d to 6f demonstrate representative simulation
results of the effects of placing a hole through an ultrasound
transducer on the acoustic beam pattern produced by the ultrasound
transducer with FIG. 6d not having a hole;
[0074] FIGS. 7a to 7e show examples of ultrasound transducers that
have an optical apparatus for transmitting and/or receiving optical
imaging energy either on top of or recessed within an acoustic
transducer;
[0075] FIG. 8a is a perspective view of an imaging assembly
suitable for side viewing with both acoustic and optical
imaging;
[0076] FIG. 8b is a side view of the imaging assembly in FIG.
8a;
[0077] FIGS. 8c to 8e are end views of the imaging assembly in FIG.
8a in different rotated positions;
[0078] FIGS. 9a to 9c depict configurations whereby an optical
imaging emitter/receiver is embedded into the backing material 435
of an acoustic transducer.
[0079] FIGS. 10a to 10e are similar to FIGS. 8b to 8e showing the
imaging assembly being rotated in a reciprocating fashion rather
than in a single rotational direction;
[0080] FIG. 11 shows a perspective view of an imaging probe where
the predominant motion is a longitudinal motion where the surface
swept by the optical beam and the acoustic beam are two co-planar
rectangles;
[0081] FIG. 12 shows a perspective view of an embodiment of an
imaging probe where the optical imaging system is configured such
that the optical imaging beams are angled such that these imaging
beams substantially converge or overlap;
[0082] FIG. 13 is a cross sectional view of an imaging assembly
suitable for side viewing with both acoustic and optical
imaging;
[0083] FIG. 14a is a cross sectional view of an imaging assembly
suitable for forward viewing with both acoustic and optical
imaging;
[0084] FIG. 14b is a cross sectional view of an imaging assembly
suitable for forward viewing with both acoustic and optical imaging
in which an artificial muscle polymer can be used to deform the
distal region of the imaging probe;
[0085] FIG. 15a is a cross sectional view of an imaging assembly
suitable for side viewing with both acoustic and optical imaging
using a reflective component to direct the optical and acoustic
beams in the sideways direction;
[0086] FIGS. 15b and 15c are similar to FIG. 15a but in which the
reflective component is mounted about a pivot point so the optical
and acoustic beams can be scanned in the sideways direction at a
variable angle;
[0087] FIG. 16a is a cross section of an embodiment of an imaging
probe using a tiltable component where the tilting action is
modulated by centripetal acceleration due to the rotational motion
of the imaging assembly around the longitudinal axis;
[0088] FIG. 16b is a view along the line 16b-16b of FIG. 16a;
[0089] FIG. 16c is a cross section of the imaging probe of FIG. 16a
but with the tiltable component at a different angle during
use;
[0090] FIG. 16d is a view along the line 16d-16d of FIG. 16c;
[0091] FIG. 17a is a perspective drawing of a deflecting component
that comprises a flat optically reflective layer and a shaped
acoustically reflective layer;
[0092] FIGS. 17b through 17d depict cross-sections of the
deflecting component of FIG. 17a;
[0093] FIG. 18a is a perspective view of an ultrasound imaging
transducer with two (2) optical imaging emitters/receivers through
two (2) separate optically transmissive channels in the acoustic
transducer;
[0094] FIG. 18b is a perspective view of an embodiment of an
imaging probe having an ultrasound imaging transducer with two (2)
optical imaging emitters/receivers arranged in a manner such that
they are aligned with the predominant rotary motion of the imaging
assembly;
[0095] FIG. 18c is a view along arrow C of FIG. 18b;
[0096] FIG. 19 is a schematic of a system where there are two
optical imaging systems that are coupled to the same optical
imaging waveguide via optical routing circuitry;
[0097] FIGS. 20a and 20b demonstrate sector-shaped patterns for
simultaneously demonstrating portions of two (2) or more images
that are co-registered with each other;
[0098] FIGS. 21a and 21b demonstrate arbitrary patterns for
simultaneously showing portions of 2 or more images that are
co-registered with each other;
[0099] FIG. 22 is a schematic of a display which transitions over
time from one image to another, co-registered image;
[0100] FIGS. 23a and 23b demonstrate how a feature in a first image
can be mapped onto a feature in another image that is co-registered
with the first image;
[0101] FIGS. 24a and 24b demonstrate how a contour feature in a
first image can be mapped into another image with is co-registered
with the first image and vice versa;
[0102] FIGS. 25a and 25b provide a schematic for how a composite
image can be constructed from two (2) or more co-registered imaging
datasets; and
[0103] FIGS. 26a to 26c shows cross sectional views of an imaging
probe with a rotary encoder.
DETAILED DESCRIPTION OF THE INVENTION
[0104] Without limitation, the majority of the systems described
herein are directed to an imaging probe that enables imaging by
both optical and acoustic means. As required, embodiments of the
present invention are disclosed herein. However, the disclosed
embodiments are merely exemplary, and it should be understood that
the invention may be embodied in many various and alternative
forms.
[0105] The Figures are not to scale and some features may be
exaggerated or minimized to show details of particular elements
while related elements may have been eliminated to prevent
obscuring novel aspects. Therefore, specific structural and
functional details disclosed herein are not to be interpreted as
limiting but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to
variously employ the present invention. For purposes of teaching
and not limitation, the illustrated embodiments are directed to an
imaging probe that enables imaging by both optical and acoustic
means.
[0106] As used herein, the term "about", when used in conjunction
with ranges of dimensions, temperatures or other physical
properties or characteristics is meant to cover slight variations
that may exist in the upper and lower limits of the ranges of
dimensions so as to not exclude embodiments where on average most
of the dimensions are satisfied but where statistically dimensions
may exist outside this region. For example, in embodiments of the
present invention dimensions of components of an imaging probe are
given but it will be understood that these are not meant to be
limiting.
[0107] As used herein, the phrase "co-registration of images"
refers to the process of identifying a subset of imaging data
acquired by one imaging means with a subset of imaging data
acquired using another imaging means where the identified imaging
data from the two means was acquired by detecting a form of imaging
energy (e.g. photons or ultrasound) from the same object (or tissue
in the case of the present invention). Each co-registered point in
the first subset can then be mapped to a corresponding point in the
second subset such that the two points from the two different
imaging means are thought to have been acquired from a similar
focal region of the imaged object (or tissue).
[0108] Successful and accurate co-registration of images, or
portions thereof, between images acquired using two (2) or more
imaging means is helpful in that it can provide multiple
opportunities to assess features of interest of the imaged object
by more than one imaging means.
[0109] FIG. 1 represents an overview of an exemplary imaging system
constructed in accordance with the present invention shown
generally at 10. It comprises an imaging probe 12, which connects
via an adapter 14 to an image processing and display system 16. The
image processing and display system 16 comprises the necessary
hardware to support one or more of the following imaging
modalities: 1) ultrasound, 2) optical coherence tomography, 3)
angioscopy, 4) infrared imaging, 5) near infrared imaging, 6) Raman
spectroscopy-based imaging and 7) fluorescence imaging.
[0110] Implementations of the optical coherence tomography,
ultrasound, angioscopy and infrared imaging circuitry have been
described in the prior art. The system herein described further
typically comprises a controller and processing unit 18 to
facilitate the coordinated activity of the many functional units of
the system, and may further comprise a display and/or user
interface and may further comprise electrode sensors to acquire
electrocardiogram signals from the body of the patient being
imaged. The electrocardiogram signals may be used to time the
acquisition of imaging data in situations where cardiac motion may
have an impact on image quality. The optical circuits and
electronics 21 forming image processing and display system, if
included in a particular implementation of the present invention,
may include any or all of the following components: interferometer
components, one or more optical reference arms, optical
multiplexors, optical demultiplexors, light sources,
photodetectors, spectrometers, polarization filters, polarization
controllers, timing circuitry, analog to digital converters and
other components known to facilitate any of the optical imaging
techniques described in the background and prior art sections. The
ultrasound circuitry 20 may include any or all of the following
components: pulse generators, electronic filters, analog to digital
converters, parallel processing arrays, envelope detection,
amplifiers including time gain compensation amplifiers and other
components known to facilitate any of the acoustic imaging
techniques described in the background and prior art sections.
[0111] The controller and processing units 18, if included in a
particular implementation of the present invention, serve multiple
purposes and the components would be markedly adapted based on the
needs of a particular imaging system. It could include one or a
combination of motor drive controller, data storage components
(such as memory, hard drives, removable storage devices, readers
and recorders for portable storage media such as CDs and DVDs),
position sensing circuitry, timing circuitry, cardiac gating
functionality, volumetric imaging processors, scan converters and
others. A display and user interface 22 is also optionally provided
for either real time display or display of data at a time later
than the time at which imaging data is acquired.
[0112] The imaging probe 12 comprises an imaging assembly 30 near
its distal end 32, an optional conduit 34 along a substantial
portion of its length, and a connector 36 at its proximal end 38.
For the purposes of this invention, an imaging assembly 30
generally refers to the component of the imaging probe 12 from
which the signals (acoustic or optical (or both)) are collected for
the purposes of imaging a region that is proximate to the imaging
assembly 30. The imaging assembly 30 includes at least one or more
emitters of imaging energy and at least one or more receivers of
imaging energy. For the purposes of this invention, "imaging
energy" refers to both light and acoustic energy. Specifically,
light refers to electromagnetic waves that span the ultraviolet,
visible and infrared spectrum of wavelengths. For example, for
acoustic imaging, the imaging assembly 30 contains an ultrasound
transducer that is both an emitter and receiver of acoustic
energy.
[0113] For optical imaging, the imaging assembly 30 typically
contains the distal tip of a fiber optic, as well as a combination
of optical components such as a lens (such as a ball lens or GRIN
lens), which collectively serve the purpose of acting as an optical
receiver and may also serve as an optical emitter. A mirror and/or
a prism are often incorporated as part of an optical emitter and/or
receiver. The imaging assembly 30, connector 36 and/or imaging
conduit 34 may be liquid-filled, such as with saline and may be
flushed.
[0114] The imaging probe 12 may contain ports at one or more points
along its length to facilitate flushing. For optical imaging, it is
possible to consider a gas filled imaging probe 12. Preferably, the
gas would substantially comprise carbon dioxide or another readily
dissolved gas. Alternatively, the imaging assembly may be
compartmentalized such that there is at least one gas-filled
compartment or lumen for optical imaging and at least one
fluid-filled compartment or chamber for acoustic imaging.
[0115] The imaging conduit 34 comprises at least one optical
waveguide and at least one conductive wire (preferably two or more)
that connect an emitter and/or receiver via a connector to an
adapter. The imaging conduit 34 may also act as a mechanical force
transmission mechanism for rotating or translating the imaging
assembly. For example, the imaging conduit 34 may comprise a fiber
optic, wrapped by two layers of electrical wire that are insulated
by each other. The imaging conduit 34 may further be reinforced by
other structural features, such as helically wrapped wires or other
designs used to construct imaging torque cables for rotating scan
mechanisms, as described in the prior art.
[0116] The adapter 14 facilitates transmission of signals within
any fibers and/or wires to the appropriate image processing units.
The adapter 14 may also incorporate a pullback mechanism 49 (FIG.
2d) or a reciprocating push-pull mechanism to facilitate
longitudinal translation of the imaging assembly. Such longitudinal
translation of the imaging assembly 30 may occur in conjunction
with the longitudinal translation of an external shaft that
surrounds the imaging conduit 34, or may occur within a relatively
stationary external shaft.
[0117] Additional sensors may be incorporated as part of the
adapter 14, such as position sensing circuitry, for example to
sense the angle of rotation of a rotary component within the
imaging probe 12. The imaging probe 12 may also include a memory
component such as an EEPROM or other programmable memory device
that includes information regarding the imaging probe to the rest
of the imaging system. For example, it may include specifications
regarding the identification of specifications of the imaging probe
12 and may also include calibration information regarding the probe
12.
[0118] While precise alignment of the acoustic and optical imaging
data is highly desired, it is also important to recognize the need
to optimize the geometry of a minimally invasive probe so that it
is as small as reasonably possible to achieve its desired purpose.
Current IVUS probes are approximately 0.9 to 2 mm in diameter and
the smaller sizes of probes can be delivered more distally within
the vascular tree of the coronary anatomy as the vessel size tapers
down. Thus, smaller sizes generally allow for interrogation of a
larger portion of the coronary anatomy. It is therefore desirable
to have embodiments of a probe that combines optical and acoustic
imaging in arrangements that minimize certain dimensions of the
probe, such as the diameter of the probe.
[0119] FIG. 2 is a perspective drawing of a flexible catheter
containing a fiber optic 40 and a co-axial electrical wire 50. The
proximal connector contains fiber optic 40 that can be received by
the adapter to optically couple the imaging fiber optic 40 to the
optical imaging system "back-end". There are also electrical
connectors 56 that allow the one or more electrical conduits to be
connected to the ultrasound circuitry 20 and/or controller and
processing units 18. In embodiments where the imaging conduit
rotates around its longitudinal axis, there may be a need to couple
the rotating components of the imaging fiber optic with the
relatively stationary fiber optic that connects to the optical
imaging system's back-end 21. The coupling of a rotating fiber
optic probe can be accomplished using a fiber optic rotary joint
incorporated either as part of the proximal connector of the
imaging probe 10 or as part of the adapter 14. Similarly, in
embodiments where the imaging conduit rotates around its
longitudinal axis, there may be a need to couple the conductive
wires that rotate with the imaging conduit with the relatively
stationary conductors of the ultrasound circuitry 20 and/or
controller and processing units 18, preferably by means of slip
rings. These slip rings can be incorporated as part of the proximal
connector of the imaging probe 36 or as part of the adapter 14.
[0120] FIG. 2a shows a cross sectional view of the mid section of
the imaging probe of FIG. 2 taken along the dotted line which shows
a fiber optic 40, guidewire port 44 and guide wire 42, imaging
conduit 34, imaging conduit lumen 46, external sheath 48 which is a
hollow, flexible elongate shaft made of a physiologically
compatible material and having a diameter suitable to permit
insertion of the hollow elongate shaft into bodily lumens and
cavities, and coaxial electrical wiring 50. The expanded detailed
view of the end of the imaging probe 10 shown in FIG. 2b shows the
distal end of the guidewire 42 extended beyond the end of the outer
sheath 48 and a flush port 54 at the end of the sheath 48. In FIG.
2 the proximal end of the imaging probe 10 includes another
guidewire port 55 into which guidewire 42 is inserted and the
connector assembly 36 which includes a flush port 58 and electrical
contacts 56 along the connector body.
[0121] FIG. 2c shows a schematic of how the rotary and non-rotary
components of the imaging probe can be coupled with an adapter to
the rest of an imaging system. FIG. 2d schematically shows how the
rotating components of the imaging probe can be coupled to the
rotating components of an adapter. The rotating components of each
can be electrically, optically and/or mechanically coupled using
connectors and other configurations known in the art. Similarly,
the non-rotating components of the imaging probe can be coupled to
the non-rotating components of the adapter 14. The adapter 14 can
include slip rings, optical rotary joints and other such implements
for electrically or optically coupling a rotary component to a
non-rotary component and enable communication of necessary
electrical and optical signals with the rest of the system.
[0122] Dual-fiber optical rotary joints are also available but
considerably more complex. Electrical coupling between any
conductor mounted onto a rotating component in the imaging probe 12
can be coupled to non-rotating conducting elements via metallic
slip rings and springs, metallic slip rings and brushes or other
commonly known methods of forming conductive contact between a
stationary conductor and a rotary conductor.
[0123] While the electrical, optical and mechanical connections are
shown separately in FIG. 2d, it is possible to reduce the several
connectors that must each be separately connected between the probe
and adapter with fewer connectors by combining several connectors
into combined connectors, as needed for a specific embodiment.
[0124] FIG. 3a shows one embodiment of an over-the-wire
configuration for an external sheath at 47 and FIG. 3b shows a
cross-section of sheath 47 through the portion that contains the
imaging assembly 30 along the vertical line 3b-3b in FIG. 3a.
[0125] FIG. 3c shows an embodiment at 60 that is a "rapid exchange"
configuration for the external sheath that may be incorporated with
the imaging probe if a guidewire is required. Sheath 60 in FIG. 3c
includes the entry port 55 shown in FIG. 2. FIG. 3d shows a
cross-section of the "rapid-exchange" configuration 60 through the
portion that is proximal to the entry port 55 for a guidewire along
line 3d-3d in FIG. 3c. FIG. 3e shows a cross-section along line
3e-3e in FIG. 3c.
[0126] The present invention describes several embodiments by which
precisely registered ultrasound and optical images can be formed.
The simplest conceptual approach is to have the paths of the
ultrasound and optical imaging beams be aligned collinearly with
each other.
[0127] Referring to FIG. 4a, an imaging probe 399 is provided which
is configured to allow imaging by acoustic and optical means in the
same direction, so that an acoustic transducer that allows light
energy to travel through a channel in the transducer is utilized.
Essentially, probe 399 uses an acoustic transducer 402 that is
altered to have an optically transmissive channel made through its
substrate. The acoustic transducer 402 can be any kind of
ultrasound transducer known in the art, such as piezoelectric
composition (e.g. PZT or PVDF), a composite transducer or a single
crystal transducer.
[0128] Electrical conductors 400 are directed to the conducting
layers 401 on either side of the transducer's acoustic substrate
402. A fiber optic 403 provides an optical conduit for enabling
optical imaging. One or more matching layers can be added to the
emission surfaces of the transducer, such as an epoxy layer (such
as a silver or copper conductive epoxy layer which may functionally
also serve as one or both of the electrodes that drives the
transducer), or a polymer (such as parylene or PVDF). The optically
transmissive channel 407 is made by any of several techniques, such
as precision drilling, laser ablation, photo-etching, inclusion of
a feature in a mold to create the opening and others. Precision
drilling may include the use of drill bits, such as diamond or
carbide drill bits explicitly designed for cutting through hard
materials. A high precision spindle, such as an air spindle, may be
helpful for accurate and efficient execution of the drilling
technique. A laser source can be used to ablate a channel through
the substrate. Exemplary laser sources include YAG or excimer
lasers.
[0129] Alternatively, if the acoustic transducer 402 is formed from
a substrate that is initially viscous, a sacrificial component can
be embedded in the piezoelectric during the formation of the
piezoelectric transducer 402. The sacrificial component can then be
removed by mechanical means or exposure to a solvent. For example,
a polystyrene cylinder can serve as the sacrificial component,
which can be subsequently sacrificed using dissolution in acetone.
Alternatively, if the piezoelectric material 402 is formed from a
substrate that is initially viscous, a removable mandrel can be
included in the material during the formation of the piezoelectric
transducer and removed after the piezoelectric has partially or
substantially hardened.
[0130] Conductive layers 401 on either side of the piezoelectric
material 402 are incorporated as required for applying a voltage to
the piezoelectric. The opening 407 is coupled to an optical
waveguide 403, either directly, or by means of one or more mirrors
404 or prisms 397 and one or more lenses 405. If any optical
components are included within the opening, a dampening, insulating
layer of a compliant material 406 (see FIG. 4l), such as silicon or
polymer may separate the optical components from the acoustic
substrate 402 to act as either an electrical insulator or to
minimize the transmission of stresses that are generated by the
acoustic substrate 402 to the optical components.
[0131] As in FIG. 4b, the light from the fiber can be directed
towards a mirror 404 (or prism) that causes the light from the
fiber to be deflected through the optically transmissive channel
407. Alternatively, as in FIG. 4c, a prism 397 can be used to
deflect the light through the optically transmissive channel. The
prism 397 may deflect light either as a result of total internal
reflection or be assisted by a reflective coating on its deflecting
surface 419. The prism 397 may be a separate optical component that
is affixed to the appropriate position along the optical path. For
example, it can be glued in place onto the end of a fiber, onto a
lens or onto a spacer using bonding methods such as UV cured glue.
Alternatively, attaching a no-clad optical fiber along the optical
path and cutting the segment of no-clad fiber at a desired length
can be performed to make the prism. The segment of clad fiber can
be cut and/or polished to achieve the desired angle. Mao describes
this method in the previously cited reference.
[0132] Also seen in FIG. 4c, an optically transparent window 409
may optionally be found at the end of the optically transmissive
channel 407 and any unoccupied space within the channel may be
filled with a gas, fluid or optically transparent material such as
glass or any of several transparent polymers known in the art. The
purpose of the window 409 is to prevent undesired air bubbles from
being created or retained in the channel 407 and to protect the
components in the optically transmissive channel 407.
[0133] As seen in FIG. 4d it may be desirable to have a gas instead
of fluid or solid material inside the channel 407 to improve the
refractive power of certain optical components such as a contoured
lens 424, which may be a ball lens.
[0134] As seen in FIGS. 4e to 4g, the GRIN lens 405 or other
optical component can reside adjacent to the distal dip of the
optical fiber 403, between the fiber 403 and the deflecting mirror
or prism 397 along the optical path. In this case, the opening 407
in the acoustic substrate 402 can be left free of any optical
components and simply contain an optically transparent material, or
be covered by a window 409. Alternatively, the GRIN lens 405 or
other optical component can reside in the optically transmissive
channel 407 of the acoustic substrate 402, as seen in FIGS. 4g to
4l. The sleeve of insulating material 406 mentioned above can
surround the GRIN lens 405 or other optical component within the
opening 407 as shown in FIG. 4l in order to provide either
mechanical or electrical insulation from the acoustic substrate
402.
[0135] Referring to FIG. 4f an optical spacer 433 is located
between the distal end of the optical fiber 403 and GRIN lens 405.
The optical spacer element 433 may comprise an optically
transparent medium, such as no-clad fiber, glass, plastic, a
gas-filled gap or a fluid-filled gap. The use of an optical spacer
element 433 may help reduce the required precision for the
alignment and sizes of optical components in order to achieve a
desired focal length.
[0136] Alternatively, as seen in FIG. 4g, the path length of the
prism 397 or mirror can act as all or a portion of the optical
spacer 433 in between the distal end of the optical fiber and the
lens 405. The advantage of using the distance that light must
travel through the mirror or prism 397 as a substitute for a
portion of a functional optical spacer is that the focusing element
(e.g. the GRIN lens 405 or other lens) is closer to the region
being imaged, thus improving the effective working distance of the
optical imaging system. In some situations, the lens 405 can be
offset from either edge of the optically transmissive channel to
achieve the desired depth of focus, as in FIG. 4h.
[0137] In other embodiments, it may be helpful to have one or more
optical elements of the optical path extend beyond the outer
surface of the acoustic transducer, such as element 434 as in FIG.
4i, in order to achieve the desired performance of the optical
imaging technique. This is particularly important when the acoustic
transducer 402 is quite thin (such as a for very high ultrasound
frequencies) or when the effective working distance of the optical
imaging technique is longer than can be accommodated by having all
the optical components reside below the emitting surface of the
acoustic transducer.
[0138] It is also important to realize that the optical circuit can
be distant from the surface of the acoustic transducer 402. By way
of example, as seen in the embodiment shown in FIG. 4j, it may be
desirable to have some backing material 435 interposed between the
fiber optic 403 or other optical components proximal to the
deflecting mirror or prism 397 and the acoustic transducer 402 to
minimize back-reflections from the optical components.
[0139] The direction of propagation of the acoustic and optical
imaging energy can be in a direction other than perpendicular to
the longitudinal axis of the imaging probe. In fact, a slight
angular offset of a few degrees is desired to minimize reflections
back from the sheath that surrounds the probe. FIG. 4k shows an
embodiment of a probe that combines optical and acoustic imaging
means aligned at an angle other than normal to the longitudinal
axis of the probe.
[0140] The embodiment of the probe 500 shown in FIG. 5a is
structurally configured such that both acoustic and optical imaging
sensors can be combined for viewing without components such as the
mirror 404 of FIG. 4b or prism 397 of FIG. 4c. The head section of
probe 500 containing piezoelectric material 402 for the acoustic
sensor and the conductive layers 401 on either side of the
piezoelectric material 402 is aligned along the longitudinal axis
of the fiber optic 403 and the probe is configured so that both
acoustic and optical signals are emitted axially relative to the
fiber axis, not perpendicular as in FIG. 4a.
[0141] The embodiment shown in Figure Sb is analogous to the
embodiment shown in FIGS. 4b and 4c. Figure Sc is analogous to the
embodiment shown in FIG. 4d. The embodiment shown in FIG. 5d is
analogous to the embodiment shown in FIG. 4e. The embodiment shown
in Figure Se is analogous to the embodiments shown in FIGS. 4f and
4g. The embodiment shown in FIG. 5f is analogous to the embodiment
shown in FIG. 4i.
[0142] FIG. 6a shows the geometry of an emitting surface of a
square transducer 402. It should be noted that the geometry of the
emitting surfaces of the acoustic transducers 402 are not limited
to being in square in shape and may be any of several shapes, such
as rectangular, circular, ellipsoid, and any other desirable shape.
FIG. 6b shows a square transducer with the hole 407 in the center,
while FIG. 6c shows a square transducer with a glass rod 501 in the
hole 407.
[0143] Results of a simulated beam profile using acoustic beam
simulation software are shown in FIGS. 6d through 6f, corresponding
to the transducer geometries in FIG. 6a through 6c respectively. As
can be seen, there is considerable similarity in the beam profiles
of the various configurations, providing evidence that ultrasound
transducers adapted to allow a channel for optical transmission are
capable of producing an acceptable ultrasound beam profile suitable
for imaging purposes.
[0144] A simpler method for aligning the optical and acoustic
imaging means would be to place the fiber optic adjacent to the
surface of the acoustic transducer 402 without going through the
transducer 402 itself. FIG. 7A shows an imaging probe 510 comprised
of an acoustic transducer 402 with the distal end of an optical
imaging circuit 428 placed on top of the acoustic transducer 402.
The distal end portion of the optical imaging circuit 428 comprises
the distal end of fiber 403 and any optical components, such as an
optical spacer 433, a lens, such as a GRIN lens 405, mirror 404 or
prism 397, that enable emission or collection of optical imaging
energy. The distal end of an optical imaging circuit 428 can be
affixed directly to the acoustic transducer 402 or supported by a
support next to the acoustic transducer 402. The distal end of
optical imaging circuit 428 would affect acoustic signals generated
and/or received by the acoustic transducer 402 as it lies directly
in the path of a portion of the acoustic beam emitted by transducer
402. However, a significant portion of the energy of the acoustic
beam would not travel through the optical imaging means 403 and
therefore would remain relatively unaffected.
[0145] Furthermore, the signal processing means preferably includes
signal subtraction methods for discarding the portion of the signal
that represents the early time portion of an echo signal to cancel
reflections from interfaces close to the acoustic transducer's
surface.
[0146] FIG. 7b shows a perspective view of imaging probe 512 which
is a modification of the system in FIG. 7a where the distal end of
optical imaging circuit 428 is recessed into the surface of the
transducer 402 thus rendering the recessed portion of the
transducer non-functional, so that acoustic beams transmitted or
sensed by the acoustic transducer 402 do not substantially
propagate through the overlying imaging fiber 403. A top view of
this embodiment is shown in FIG. 7c. The portion of the transducer
402 rendered non-functional can be rendered non-functional by
either removing the portion of the transducer 402 that lies
underneath the distal end of optical imaging circuit 428 as shown
in FIG. 7b, or by electrically isolating the portion of the
electrode underneath the optical imaging means. Removal may be done
by several methods, including the use of a dicing saw to cut a
channel through the transducer 402. Furthermore, removal of a
channel makes it possible to consider recessing the distal portion
of the optical imaging means within a channel.
[0147] FIG. 7c shows a top view of the emitting/receiving surface
of the probe 510 shown in FIG. 7b surrounding the distal end of
optical imaging circuit 428.
[0148] FIG. 7d shows an imaging probe 516 that employs a composite
transducer for the acoustic imaging means. In this case the
composite transducer is a transducer comprising more than one
signal generating element, or pillars 520. The composite transducer
in FIG. 7d comprises four pillars 520. The channels 522 in between
the pillars 520 leave a channel 522 for one or more distal ends of
optical imaging circuit 428 to be placed within the confines of the
composite acoustic transducer. The distal end of an optical imaging
circuit 428 need not necessarily be recessed within channels 522,
and can alternatively rest on or above the surface of the acoustic
transducer 402. Conducting connections 400 between the upper
conducting surfaces of the pillars 520 allows for the pillars to be
simultaneously activated. The channels 522 can be filled with a
filler material, such as a polymer or epoxy, to increase the
mechanical stability of the composite transducer, or to help affix
the optical imaging means in place.
[0149] FIG. 7e shows a top view of the imaging probe 516 with the
distal end of the optical imaging circuit 428 placed within the
center of the pillars 520. Any of the implementations for the
distal portion of the optical imaging circuit 428 (e.g. any
combination of fiber optics, spacers, GRIN lenses, Ball lenses, air
gaps, transparent windows), such as those shown in FIG. 4, can be
used in the implementations described in FIGS. 7a to 7e.
[0150] As part of most mechanical scanning mechanisms for imaging,
there is a predominant motion associated with the scanning
mechanism that defines the geometric path through which the imaging
beam will sweep. For example, in an imaging system that uses a
rotary motion to scan a region, there will typically be a circular
or conical surface, through which the imaging beam sweeps, with the
circular or conical surface being centered approximately on the
axis of rotation, as occurs in current implementations of
mechanical scanning intravascular ultrasound. The predominant
motion in this case is the rotational motion.
[0151] Alternatively, if the imaging emitter/receiver is translated
along the longitudinal axis, then the imaging beam will sweep
through a planar surface and the plane defined by that surface will
include the axis of translation. This predominant motion in this
case is a longitudinal translation.
[0152] If the imaging emitter/receiver is simultaneously rotated
around a longitudinal axis of a probe and translated along a path
that is generally parallel to the longitudinal axis of the probe,
then the imaging beam will sweep through a surface defined by a
helicoid geometry.
[0153] It is possible to generate co-registered images with good
precision from multiple acoustic and/optical imaging means without
having to have the two or more imaging beams be simultaneously
collinear. This can be accomplished by having one or more imaging
beams follow the path of a leading beam. Software or electronic
circuitry can use knowledge of the speed and direction of the
scanning mechanism's motions over time to then register the images
generated from one of the imaging means onto one another.
[0154] For example, if the path of one imaging beam closely follows
the path of another imaging beam (the leading beam) in a short time
period, then it is possible to assume that the region scanned by
the two means is similar enough to accurately co-register the two
images with each other. The accuracy of the registration between
the two images can be affected by the time delay in which the
second beam follows the first beam. If the time delay is relatively
small, then inaccuracies in the co-registration of the two images
that could potentially develop in that time period are likely to be
minimal. Such inaccuracies might include those caused by tissue
motion (such as that induced by cardiac or respiratory motion),
unintentional probe motion, physiologic changes such as blood flow
and imprecision in the fidelity of the scanning mechanism. The time
delay (which itself can vary over time) can be used for the process
of registering the different images.
[0155] FIG. 8a shows an example of an imaging assembly 530 that
contains both an acoustic imaging means and an optical imaging
means. The predominant scanning motion is a rotational motion
around a longitudinal axis that lies along the length of the
imaging probe. As illustrated, the acoustic imaging beam 532 and
optical imaging beam 534 sweep through a path that is circular in
nature. If the imaging beams are not aligned normal to the
longitudinal axis, but rather at an angle other than 90 degrees
from the longitudinal axis, than the path through which the imaging
beams sweep will be conical in nature. If a longitudinal
translation were to be applied in combination with the rotary
motion, the two beams would follow a roughly helicoid path.
[0156] It will be understood that the in all embodiments disclosed
herein the imaging assembly may be translationally movable within
the hollow shaft and may emit anywhere along its length and is not
restricted to the distal end of the hollow shaft.
[0157] FIG. 8b shows a side view of the combined imaging probe 530
where the acoustic beam 532 travels in one direction (upwards in
the diagram) and the optical imaging beam 534 travels out of the
page (towards the reader). In this case, the optical beam 534 and
acoustic beam 532 at any instant are oriented 90 degrees apart from
each other.
[0158] FIGS. 8c through 8e represent a time series of the
rotational motion of the imaging probe 530 as it would appear from
the distal end of the imaging probe. In this example, the optical
imaging beam 534 leads the acoustic imaging beam 532 by 90 degrees
of rotation. At a constant frame rate of 30 frames per second, the
time delay that it would take for the trailing beam to become
collinear with a prior position of the leading beam would under 9
milliseconds, which is a short period of time with respect to
artifacts that might occur due to cardiac motion experienced by an
intravascular catheter.
[0159] Given the importance of miniaturizing the space occupied by
components and assemblies in minimally invasive imaging means, it
may be desirable to recess some of the components. For example, as
seen in FIG. 9a, an imaging probe 540 has been configured to recess
the distal end of the optical imaging circuit 428 into the backing
435 of the acoustic transducer 402. Recessing may not only
accomplish efficiency of space use, but it may also provide a
method of fixing the distal end of an optical imaging circuit 428
to the acoustic transducer 402.
[0160] The purpose of the backing material 435 on the acoustic
transducer 402 is to attenuate signals generated from the back
surface of the piezoelectric 402 so that an image is not formed by
the energy that is emitted from the back surface of acoustic
transducer 402 on which the optical emitter/receiver 403 is
located, but rather only from the primary emitting surface for
acoustic signals (top surface) of the transducer 402. Recessing an
optical or other component in the backing material 435 may
potentially cause the optical or other component to reflect signals
back to the acoustic transducer 402 that would potentially create
imaging artifacts.
[0161] FIG. 9b shows a deflecting surface 544 in which the optical
emitter/receiver 403 is cradled that acts to deflect acoustic
energy that might otherwise reach the optical emitter/receiver 403
and deflects that energy laterally (substantially parallel to the
surface of the acoustic transducer 402) to minimize the amount of
energy that is reflected back towards the transducer 402. This
deflecting surface 544 may be made of a hard substance such as
glass or steel.
[0162] FIG. 9c shows an implementation where the distal end of an
optical imaging circuit 428 itself has a surface 545 that
substantially deflects acoustic energy laterally without the need
of an additional deflecting material as seen in FIG. 9b.
[0163] For embodiments of imaging probes where the imaging beams
scan as a result of rotational motion, it is not necessary that the
rotational velocity be a constant or even remains in the same
direction. It is possible to have a reciprocating motion where the
imaging assembly rotates in one direction and then stops and
rotates in the opposite direction. In this situation, the leading
and trailing beams swap roles with each other.
[0164] For example, in FIG. 10a, the acoustic beam 532 initially
follows the optical beam 534 as the imaging assembly rotates in a
counter clockwise direction. The acoustic beam 532 continues to
follow the sweep path of the optical beam 534 as shown in FIG. 10b
until the rotational velocity of the imaging probe reaches zero,
(as in FIG. 10c). Once the direction of rotation changes to the
opposite direction, the acoustic beam 532 becomes the leading beam
and the optical beam follows (as in FIGS. 10d and 10e). The motion
can change direction as many times as desired with a concomitant
change in the definition of the leading and trailing sensor
beams.
[0165] FIG. 11 shows an imaging probe 540 where the predominant
motion is a longitudinal motion back and forth along arrow 541
where the surface swept the optical beam 534 and the acoustic beam
532 are two co-planar rectangles. As the imaging assembly is
translated proximally (to the left in FIG. 11) the optical imaging
beam 534 leads the acoustic imaging beam 532. The opposite is true
for distal translation (to the right in FIG. 11). The longitudinal
motion can be reciprocated as well.
[0166] With either longitudinal or rotational predominant motions,
it is understood that additional motions can be combined with the
predominant motion. For example, a slow translation (such as 10
mm/s or less, and typically 1 mm/s or less) can be added to a rapid
rotational scanning motion (such as 360 degrees per second or more
and typically 3600 degrees per second or more) in order to acquire
2D cross-sectional images at different longitudinal positions.
[0167] Similarly, a slow rotational motion (e.g. less than 360
degrees per second and typically less than 30 degrees per second)
can be added to a sequence of rapidly reciprocating longitudinal
motions (averaging over 0.1 mm/s and more typically more than 1
mm/s) to create a series of longitudinal images acquired at
different orientations around the longitudinal axis of the imaging
probe. The alignment of the various imaging elements at the distal
end is configured such that the one of the imaging beams will
follow the other during the predominant motion, but the ability to
accurately register the images on top of each other would not be
significantly affected by the addition of a relative slow secondary
motion. While absolute numbers for slow and rapid motions in the
rotational and translation motions are provided above, it is the
relative magnitude of these motions that is more important.
[0168] Collinear alignment of the optical and acoustic beams (as
shown in the embodiments shown from FIGS. 4a to 5f) provide very
accurate registration of the optical and acoustic images. An
alternative embodiment of the probe is configured to have the
optical and acoustic beams substantially overlap each other by
angling either the optical imaging emitters/receivers towards the
path of the acoustic beam or by angling the acoustic imaging
emitter towards the path of the optical imaging beam. FIG. 12 shows
such an embodiment of an imaging probe 546 where the distal end of
an optical imaging circuit 428 is configured such that the optical
imaging beam 534 is angled towards the acoustic imaging beam 532
and vice versa. This provides a simpler method of construction than
aligning the optical and imaging beams as seen in FIGS. 4a to 5f,
but allows the two imaging means to provide what may be a
reasonably precise overlap over a portion of the two imaging beams.
In particular, embodiments whereby the beams are aligned such that
they overlap over a substantial portion of their focal ranges would
be useful.
[0169] FIG. 13 shows an embodiment of the imaging probe 550
configured to image simultaneously in the same general orientation
and from the same general origin with both acoustic and optical
means. At least one fiber optic 410 and one electrical conduit 411,
such as a pair of coaxial conductors, reside within the imaging
conduit 560 and travel to the imaging assembly 562. The imaging
assembly 562 comprises an acoustic transducer 412 configured for
imaging in a substantially side-viewing direction indicated by
arrow 420. The imaging assembly 562 also includes distal end of an
optical imaging circuit 564 configured for imaging in a
substantially side-viewing direction indicated by arrow 421.
[0170] The acoustic transducer 412 and distal end of an optical
imaging circuit 564 are configured such that they allow imaging in
two or more separate directions at any instant within the same
cross-sectional plane that is substantially perpendicular to the
axis 423 around which the imaging assembly 562 rotates. Thus,
assuming minimal translation of the imaging assembly 562 while the
imaging assembly is rotated, the imaging data collected by the
optical emitters/receivers 564 can be co-registered with the
imaging data collected by the acoustic transducer 412. For example,
if the acoustic and optical means are configured to image in
directions that are 180 degrees opposite of each other around the
longitudinal axis, as shown in FIG. 13, then the region imaged by
the acoustic transducer 412 at one point in time will be
substantially the same region that is imaged by the distal end of
an optical imaging circuit 564 after the imaging assembly 562 has
been rotated by half a revolution. Similarly, if the imaging beams
420 and 421 have a similar angle from the longitudinal axis other
than 180 degrees, they will both sweep through paths of
substantially coincident cones, and can therefore be
co-registered.
[0171] The embodiment of the probe 570 shown in FIGS. 14a and 14b
is configured such that both IVUS and OCT can be combined for
forward viewing with a deformable component. At least one fiber
optic 410 and one electrical conduit 411, such as a pair of coaxial
conductors reside within the imaging conduit 578 and travels to the
imaging assembly 572. The acoustic transducer 412 is configured for
imaging in a substantially forward-looking direction indicated by
arrow 413. A distal end of an optical imaging circuit 574 is
configured for imaging in a substantially forward-looking direction
indicated by arrow 414.
[0172] The distal end of an optical imaging circuit 574 typically
comprises a distal end of a fiber optic 410 combined with a lens
415, such as a GRIN lens and an optional spacer (not shown). The
imaging conduit 578 comprises an artificial muscle actuator that
has the property of being able to deform upon the application of an
electrical charge. FIG. 14b illustrates how the imaging angle would
be changed if an artificial muscle actuator achieved a deformation
while FIG. 14a shows the shape of the probe without application of
a voltage to actuator.
[0173] Embodiments of the present imaging probe may be configured
to make use of a deflector to allow for a larger transducer to be
used within the imaging probe. Alternatively, the deflector may be
pivotable and coupled to a pivoting mechanism to enable an
additional degree of freedom in the scanning mechanism. For
example, the scanning mechanism may facilitate 2D imaging, or may
augment a 2D imaging system into a 3D imaging system.
Alternatively, the deflector may be translated along the
longitudinal axis in order to change the focal depth of the imaging
system.
[0174] FIG. 15a illustrates an embodiment of an imaging assembly
590 that comprises a deflector 592 used to deflect optical and/or
acoustic imaging energy into a generally radial direction. The
deflector 592 is made of one or more reflective materials.
Optically reflective materials include polished or sputtered
metals, such as stainless steel, gold, silver and platinum.
[0175] Acoustically reflective materials include stainless steel
and other metals, quartz and other crystals, glass and hard
polymers. FIG. 15b shows another embodiment of an imaging assembly
600 which comprises a deflector 602 that pivots around a pivot
point 604 and thus allows the angle between the imaging beam and
the longitudinal axis of the imaging probe to vary. The imaging
assembly 600 may be configured so that deflector 602 can change
position by being coupled to a variety of mechanisms, including
mechanisms which utilize centripetal motion, magnetic forces, cable
mechanisms, rheologic forces, piezoelectric drivers, miniaturized
motors and others.
[0176] FIG. 15c illustrates an embodiment of the arrangement in
FIG. 15b wherein a cantilever 901 mounted on a cantilever mount 902
and the deflector's range of motion is limited by a minimum stop 82
and a maximum stop 80. This embodiment has the property of having
the imaging angle change as a result of changes in the rotational
motion of the imaging assembly around the longitudinal axis of the
probe. At rest or low rotational speeds, the cantilever wire forces
the deflector 602 around its pivot point such that it comes into
contact with stop 80. At higher rotational speeds, centripetal
acceleration causes the deflector 604 to pivot away from stop 80.
As centripetal acceleration continues to overpower the restoring
force exerted by cantilever 901 on deflector 602, the deflector
eventually comes into contact with stop 82. In such an embodiment,
an imaging assembly 600 with a 3D scanning mechanism is
implemented.
[0177] FIG. 16a illustrates an embodiment of the distal portion of
an imaging probe 100 capable of both acoustic and optical imaging
in a generally forward-looking direction. FIG. 16a shows an
embodiment of a distal end 29 of an imaging probe containing an
imaging assembly 30 that includes a tiltable component 70 where the
tiltable component is a disc mounted on a pivoting mechanism such
as a pin 72 that extends through the disc 70. The pivoting
mechanism 72 defines the tilting axis of the tiltable disc 70. When
the imaging assembly 30 is at rest, the disc 70 will remain in an
arbitrary starting position. However, as the imaging assembly 30
rotates, the disc 70 will align itself such that the normal of the
planes defined by the faces of the disc 70 are substantially
parallel with the longitudinal axis 75. The disc 70 has two
preferred orientations when the imaging assembly 30 is rotated,
that are separated by a rotation around the tilting axis of 180
degrees.
[0178] For the purposes of this description, the tilt angle will be
referred to as the angle between the longitudinal axis 75 and an
imaginary axis through the tiltable component 70 that is parallel
to the longitudinal 75 axis when the tiltable component 70 is in
one of its preferred orientations. By way of example, when the
tiltable component 70 is in a preferred orientation, the tilt angle
is approximately zero. If the tiltable component 70 is tilted away
from its preferred orientation by an external force, such as
gravity, magnetic forces, electrostatic forces, friction with
another moving part or fluid, compressive forces, normal forces or
any other source of incompletely opposed torque on the tiltable
component 70 around the tilt axis, the tilt angle will
increase.
[0179] One or more mechanisms may be included in the imaging
assembly 30 that tends to cause the tiltable component 70 to have
its tilting angle increase. For the purposes of this invention,
such a mechanism is referred to as a restoring mechanism. A torsion
spring 76 (as shown in FIGS. 16a and 16c), a cantilever or a
compression spring can be used as a restoring mechanism, where one
end of the spring 76 is mechanically in contact with tiltable
component 70 and the other end is mechanically in contact with
another part of the imaging probe 100, such as the body of the
imaging assembly 30.
[0180] Alternatively, magnetic, electrostatic, hydraulic or other
mechanisms that apply a torque on the tiltable component around the
tilting axis could be applied. Other examples of mechanisms that
could be used to provide a restoring force include tension from an
elastomer (such as rubber, polyurethane, silicone,
fluoroelastomers, thermoplastics and many others) or by use of a
cantilever spring or foil, such as springs or foils made of
platinum, nitinol, steel or other suitable materials. In very small
embodiments of the imaging device, where intermolecular forces such
as electrostatic forces and Van der Waals forces between components
in the imaging assembly may become quite significant even without
the application of an external voltage. Therefore, the innate
intermolecular forces between the tiltable component and structures
close to the tiltable component, such as the stops 80 and 82
described below, may be sufficient to provide a net restoring
force. For example, a stop comprising a surface made of PVC, nylon
or LDPE could provide sufficient attraction between the tiltable
component and the stop.
[0181] One or more stops 80 and 82 may limit the range of the tilt
angle of the tiltable component 70. For example, a post or lip 80
can extend from the shell 84 of the imaging assembly 30 as a stop
to prevent the tilting component from further changing its tilt
angle while it makes contact with the stop 80. Therefore, a stop
can be used to limit the tilt angle from exceeding a maximum value
determined by the position of the stop. In many embodiments, this
maximum tilt angle is the tilt angle that is achieved when the
imaging assembly 30 is at rest and at low rotational speeds.
[0182] An additional or alternative stop 82 can be included to
create a minimum tilt angle that the tiltable component will
achieve at rotational speeds in the upper end of the operating
range. Indeed, there are many situations in which there is no
significant benefit in allowing the tilt angle to reach zero, as
will become apparent in the following descriptions of specific
embodiments. FIG. 16c shows the tiltable component hitting the
second stop to limit its range of motion at higher rotational
speeds of the imaging assembly.
[0183] The imaging assembly may include both optical emitters and
associated optics and ultrasound transducers. The ultrasound
transducer 88 is mounted at the end of small coaxial cable 89 and
lens 92 and mirror 94 are mounted at the end of a fiber optic cable
96 in the imaging assembly 30 in FIGS. 16a to 16d with the optical
and ultrasonic emitters configured to focus imaging energy onto the
tiltable component 70. The ultrasound transducer 88 and optical
emitter can direct imaging energy towards the tiltable component
70. Alternatively, one of the embodiments that enables collinear
optical and acoustic imaging, as seen in FIGS. 4a through 4k or
FIGS. 5a through 5f can direct imaging energy towards the tiltable
component 70.
[0184] The imaging energy is then deflected by an energy-deflecting
component mounted on the tiltable component 70. For ultrasound
imaging, the energy-deflecting component (the tiltable component
70) may comprise an acoustically reflective surface, such as a
solid metal surface (e.g. stainless steel) or crystalline surface,
such as quartz crystal or glass. For optical imaging, the energy
deflecting component (tiltable component 70) can comprise an
optically reflective surface such as a mirror surface made from
polished metal, metallized polymer such as metallized biaxially
oriented polyethlylene terephthalate (Mylar), sputtered or
electrochemically deposited metal or metal foil. Metals commonly
used to make mirrors include aluminum, silver, steel, gold or
chrome.
[0185] Alternatively, the energy-deflecting component could be made
of a transparent refractive material, such as glass, clear
polymers, and many others, and deflect the imaging energy in a
manner similar to a prism. Preferably, the emitter and/or receiver
is mounted on a component of the imaging assembly that rotates with
the imaging assembly. However, it is also possible that the emitter
and/or receiver is mounted on a component of the imaging probe that
does not rotate with the imaging assembly while the energy
deflecting mechanism within the imaging assembly does rotate. This
could be achieved by mounting the emitter and/or receiver on an
external sheath for example, or by having the imaging assembly
divided into two or more sub-assemblies, one of which rotates and
includes the tiltable component.
[0186] For ultrasound and optical coherence tomography, the ability
to adjust the angle of propagation of the emitted and/or received
imaging energy, when combined with the rotational motion of the
imaging assembly, allows a 3D volume to be scanned. For angioscopy
and infrared imaging, the ability to adjust the angle of
propagation of the emitted and/or received imaging energy, when
combined with the rotational motion of the imaging assembly, allows
an image to be produced using a single fiber optic rather than
requiring a bundle of fibers. Such an improvement can result in
greater flexibility and/or miniaturization of the imaging
device.
[0187] Further details of various scanning mechanisms that may be
used in the imaging probe disclosed herein are disclosed in U.S.
patent application Ser. No. 12/010,206 entitled SCANNING MECHANISMS
FOR IMAGING PROBE, filed Jan. 22, 2008, now U.S. Pat. No.
8,214,210, which his incorporated herein by reference in its
entirety.
[0188] In the case where the energy-deflecting component comprises
a reflective surface it is not necessary that the reflective
surface be planar. For example, in the case of acoustic imaging, it
may be advantageous for an acoustically reflective surface to have
a contour to it, such as a parabolic or spheroid contour, so that
the acoustic beam can be focused by the reflective surface and
improve lateral resolution of the acoustic imaging system as a
result. Furthermore, in the case where the tilting component is
used to deflect both acoustic and optical energy using reflection,
the acoustic reflector need not be the same surface that reflects
the optical energy.
[0189] For example, while it might be advantageous to have a
contour such as a parabolic contour for the acoustically reflective
surface, it may be preferable to have a planar surface for the
redirection of the optical imaging energy. This can be accomplished
by having an acoustically reflective surface such as a stainless
steel disc with one of its faces contoured to have a parabolic
shape to it as in FIGS. 17a through 17d which show a tiltable
deflecting component that has an optically reflective surface that
is distinct from the acoustically reflective surface.
[0190] FIG. 17a is a perspective drawing of a deflector that has
holes on its side for receiving pins on which the deflector can
pivot within an imaging assembly. FIG. 17b shows a cross-section
through the deflector near the center of the deflector. The holes
for receiving pins 465 are seen. The top layer is a flat, optically
reflective layer 461. Under the optically reflective layer 461 is a
generally acoustically transparent layer 462, which lies between
the optically reflective layer 461 and an acoustically reflective
substrate 463. FIGS. 17c and 17d show cross-sectional images of
such a deflector at different points away from the center of the
disc.
[0191] Such a deflector can be constructed by taking a disc of an
acoustically reflective material such as stainless steel and
drilling the necessary holes or indentations so that the deflector
can eventually be mounted into an imaging assembly. A parabolic or
spheroid indentation can be made into one face of the disc. The
indented surface can then be filled with an acoustically
transparent medium, such as polymethylpentene (TPX). A thin layer
of gold, silver or chrome can be sputter deposited onto the exposed
planar polymer surface to act as an optically reflective surface.
Such a layer may be on the order of 300 Angstroms to 20,000
Angstroms such that it is thin enough that its mechanical
properties to allow acoustic energy to transmit through it, while
simultaneously providing an optically reflective surface.
[0192] The result of such a fabrication process is to create a
layered reflector that reflects acoustic energy from the contoured
surface to achieve the desired focusing effect, while the optical
energy is reflected from a planar surface. It is a further
advantage of this construct that the optical and acoustic imaging
can occur in a configuration where the optical and acoustic imaging
energy travels through the same general space, facilitating
co-registration of optical and acoustic images and minimizing the
amount of space required within the imaging assembly to accommodate
more than one modality of imaging.
[0193] In some embodiments, such as the assembly shown in FIGS. 16a
and 16c, it may be helpful to use one of the imaging modalities
solely to measure a parameter useful for the reconstruction of 2D
and 3D images. For example, in the case of a volumetric imaging
probe that uses a deflectable component, it may be desirable to use
OCT to accurately measure the tilt angle of the deflectable
component. Thus, an ultrasound image could be generated with
knowledge of the tilt angle derived from OCT data, such as the tilt
angle of tiltable component 70 in FIG. 16a without necessarily
using the OCT data to generate corresponding OCT images of the
region outside of the imaging probe.
[0194] In some embodiments, it will be desirable to have more than
one method for optical imaging in an intravascular imaging system.
For example, OCT and angioscopy may be a useful combination. FIG.
18a shows an ultrasound imaging transducer 402 with two (2) distal
ends of optical imaging circuits 428 through two (2) separate
optically transmissive channels in the acoustic transducer. FIGS.
18b and 18c show an acoustic imaging transducer with two (2) distal
ends of optical imaging circuits 428 arranged in a manner such that
they are aligned along the predominant rotary motion of the imaging
assembly. These are examples of using more than one optical imaging
emitter/receiver at the distal end of the imaging probe. If the
imaging probe uses extensive rotary motion around its longitudinal
axis as part of the scanning mechanism, such embodiments may
require the use of a multi-channel optical rotary joint.
[0195] Alternatively, the optical imaging light sources and/or
detectors for some of the imaging systems may be mounted on the
rotary portion of the imaging probe and be coupled to the imaging
system using electrical slip rings or wireless communication. A
battery may optionally be used as a source of electrical energy on
the rotary portion of the probe or adapter to minimize the number
of slip rings required. Illuminating sources and photodetectors can
be placed at the proximal end of the imaging probe and may be
configured such that they rotate around the longitudinal axis of
the probe with the rest of the imaging conduit 34 so that further
optical couplers are not required between the imaging probe and the
adapter. This is done because the complexity of rotary optical
joints increases substantially if more than one fiber is involved
to connect the probe to the rest of the system.
[0196] If the imaging probe uses only reciprocal rotary motion over
a short range of angles (such as less then two full revolutions),
or no rotary motion at all, then the use of an optical rotary joint
is not necessary, simplifying the task of coupling the optical
elements of the imaging probe to the image processing and display
hardware.
[0197] The imaging probe may include a motion detector for
detecting movement of the movable member (tiltable or bendable
members) relative to a remainder of the imaging assembly. The
motion detector may be based on any of optical coherence based
detection means, reflection intensity detection means, and a strain
gauge based detection means.
[0198] The pivotally mountable members may be pivotally mounted on
a low friction pivot mechanism. The restoring mechanism is provided
by any one or combination of a spring and a
magnetic/elelctromagnetic assembly as discussed above. The
restoring mechanism may also include a surface exhibiting
electrostatic properties which interact with the movable
member.
It will be understood that the hollow shaft may be an external
catheter sheath which may have memory properties.
[0199] All embodiments of the imaging probe disclosed herein may be
fitted to existing control and image processing system and display
systems to which the probe is connectable. The processing and
display system would be configured to process the received energy
signals and produce images of interior surfaces or adjacent
structures of said bodily lumens and cavities or exterior surfaces
or adjacent structures of a body.
[0200] In another embodiment, it is possible to using the same
optical imaging emitter/receiver at the distal end of the imaging
probe and use optical routing circuitry such as switches,
multiplexers, demultiplexers, prisms, diffraction gratings,
couplers and/or circulators to use the same fiber and distal
optical components for more than one imaging modality. FIG. 19
shows a schematic of a system where there are two (2) optical
imaging systems 211 that are coupled to the same optical imaging
waveguide 212 via optical routing circuitry (comprising one or more
of the components listed above). The waveguide may be coupled to
the imaging probe via an optical rotary joint 213 if the image
probe 12 requires a large range of rotary motion as part of its
scanning mechanism. The distal end of optical imaging circuit 428
may comprise any of the combinations of optical fiber, spacers,
mirrors, prisms, ball lenses, GRIN lenses, air gaps and transparent
windows mentioned elsewhere in the present invention to enable
optical imaging. While many optical imaging elements, such as the
waveguide and lenses, are designed to operate optimally for
particular ranges of wavelengths (e.g. infrared vs visible
spectrum), the performance of a fiber optic or other optical
component designed for one range is often still adequate to provide
information using light in the other spectrum.
[0201] Therefore, imaging using more than one range of wavelengths
can occur simultaneously. Alternatively, the imaging waveguide can
be used at different time intervals for different imaging
modalities by means of optical switches, multiplexers and
demultiplexers within the optical routing circuitry 210, or by
simply timing the use of the optical waveguide at different time
intervals for different imaging modalities.
[0202] While a fiber optic would be a preferred optical waveguide
212 for most embodiments, it may be desirable to use an alternative
form of optical waveguide that is potentially more space efficient
than an optical fiber. For example, a thin optical channel, on the
order of 3 to 500 microns in maximal diameter and preferably on the
order of 4 to 125 microns can be formed in a catheter at the time
of extrusion. A fluid medium with a high index of refraction can be
introduced into the optical channel, such as by means of injection.
Such a fluid medium may include an epoxy or adhesive specifically
designed for optical components.
[0203] The fluid medium may also be curable, such as in the case of
UV curable adhesives. The creation of an optically transparent
channel filled with a material with a high index of refraction
surrounded by the extruded catheter material with a lower index of
refraction would essentially replicate the functionality of
including a fiber optic, but may allow for slightly more efficient
use of space in the catheter by not requiring a separate cladding
layer. The optimal use of space in a catheter is often important
given their minimally invasive nature and the limited space
available in the regions in which these catheters are deployed.
[0204] Yet another mode of operation for the present invention is
the use of a transducer that combines acoustic transduction with an
optical transducer where the transmitted energy is of one form and
the received energy is of another. For example, photoacoustic
imaging comprises delivery of light-based energy to an imaged
region. The photons interact with the imaged region and create
acoustic energy as part of their interaction with the medium in
which they propagate. This acoustic energy is often in the form of
ultrasound waves, and can be detected by an ultrasound transducer.
It should be apparent that the use of an optical emitter aligned
and in combination with an acoustic receiver would be a good
configuration to enable photoacoustic imaging. An ultrasound
transducer with an opening for optical imaging or that allows
substantial overlap in the acoustic and optical imaging regions,
such as those shown in FIGS. 4a through 4k, 5a through SF or FIG.
12, would enable photoacoustic imaging.
[0205] Similarly, sonoluminescent imaging comprises delivery of
ultrasound-based energy to an imaged region (Daniels and Price,
Ultrasound in Medicine and Biology 1991: 17(3):297-308). The
acoustic energy interacts with the imaged region and creates
photons as part of its interaction with the medium in which it
propagates. Some of these photons are directed back toward the
source of the acoustic energy. It should be apparent that the use
of an ultrasound transducer aligned in combination with an optical
receiver would be a good configuration to enable sonoluminescent
imaging. Implementations of acoustic and optical imaging elements
where the imaging beams are collinear, or substantially overlap,
such as those shown in FIGS. 4a through 4k, 5a through 5f or FIG.
12, would enable sonoluminescent imaging.
[0206] Referring to FIG. 1 again, imaging probe 12 (which may
include any of the embodiments of the acoustic and optical sensors
discussed herein) and its components may be of several dimensions
and properties depending on the anatomic location and purpose of
use for the imaging that is enabled by the imaging probe 12. For
example, for the purposes of use in the cardiovascular system,
including the cardiac chambers, the imaging probe 12 would
preferably be elongate and flexible, with a length ranging from 5
to 3000 mm, preferably with a length ranging from 300 mm to 1600
mm. The imaging conduit 34 and imaging assembly 30 may have a
maximum cross-sectional dimension ranging from 200 microns to 10
mm, preferably ranging from 500 microns to 5 mm. An external sheath
48 may surround both the imaging conduit 34 and imaging assembly
30. This would enable the imaging conduit 34 and imaging assembly
30 to rotate within the external sheath while mechanically
isolating the rotational motion of these two components from the
surrounding tissues.
[0207] In yet another example, the use of the imaging probe 10 in
the gastrointestinal system would typically have the imaging probe
10 being elongate and flexible, with a length ranging from 100 mm
to 2000 mm and preferably in the range of 300 mm to 1500 mm. The
maximum cross-sectional dimension would typically range from 3 mm
to 20 mm.
[0208] In yet another example, the use of the imaging probe 10 to
image soft tissue via percutaneous means would have the imaging
probe with a rigid shaft. The external sheath would be replaced by
a rigid hollow shaft, such as a stainless steel tube although many
other polymers, metals and even ceramics would be functionally
suitable.
[0209] In yet another example, the use of the imaging probe 10 in
the intraoperative neurosurgical setting would typically have the
imaging probe 10 being short and semi-flexible, with a length
ranging from 50 mm to 200 mm. It would be preferable that the
surgeon can bend and shape the probe during the procedure to
provide optimal passage from extra-cranial space towards the
intracranial target being imaged. The maximum cross-sectional
dimension would range from 200 microns to 5 mm and preferably from
500 microns to 3 mm.
[0210] In yet another example, the use of the imaging probe 10 in
the interventional neurovascular setting would typically have the
imaging probe 10 being long and ultraflexible, with a length
ranging from 200 mm to 4000 mm and preferably ranging from 1300 mm
to 2000 mm. The maximum cross-sectional dimension would range from
200 microns to 5 mm and preferably from 500 microns to 3 mm. The
distal end of the probe would preferably possess shape memory to
enhance navigation through the neurovasculature.
[0211] Embodiments of the present invention can be used in
conjunction with or incorporated into devices that are used for
intervention, such as those used for cardiovascular intervention,
such as an angioplasty balloon, atherectomy device, stent delivery
system or localized drug delivery system. It can also be used in
conjunction with or incorporated into devices that facilitate
biopsies, radio-frequency ablation, resection, cautery, localized
brachytherapy, cryotherapy, laser ablation or acoustic
ablation.
[0212] In particular, using the image scanning mechanism to direct
higher powers of optical or acoustic energy to a targeted region
can facilitate the use of the current device to enable laser or
acoustic ablation of tissue. For example, while imaging a region of
a blood vessel with an OCT or ultrasound embodiment of an imaging
probe described in the present invention a region for the delivery
of therapy can be selected through a user interface. Then, powerful
pulses of energy can be delivered at times when the scanning
mechanism is oriented to delivery energy in the desired direction.
For example, pulses of laser energy can be transmitted down the
same fiber optic used for optical imaging, be deflected by a
deflecting component in those embodiments that include a deflecting
component, and travel towards the targeted tissue for the desired
effect. The timing of the pulses of laser energy is coordinated
with the scanning pattern realized by the imaging probe to direct
the energy towards the targeted region.
[0213] The opportunity to acquire accurately registered images of
two or more high resolution imaging modalities provides significant
information that is likely to be more useful than available by a
single imaging modality. Maschke et al describe the formation of a
composite image whereby the inner portion of an intravascular image
is composed of OCT imaging information while the outer portion of
an intravascular image is composed of IVUS imaging information.
This takes advantage of the higher resolution images acquired by
OCT and the higher penetration of IVUS. However, the reliability of
this superposition of IVUS and OCT images is limited by the
inaccuracy of the registration in the IVUS and OCT images that
occurs using the arrangement of the IVUS and OCT imaging elements
as described by Maschke and are substantially overcome by many of
the embodiments in the present invention.
[0214] Alternative presentations of combined IVUS and OCT images
might include dividing the image into sectors, where alternating
sectors are displayed using alternating imaging means, as seen in
FIG. 20a. First image 231 and second image 232, where the first and
second images are co-registered with each other images and acquired
by different means, can be used to form a combined image 234 where
sectors 233 of the first image replace sectors of the second image.
Optionally, the borders 235 defining the sectors 233 can rotate
over time around the center of the image to provide a dynamic image
for identifying features in both the first and second co-registered
images. FIG. 20b shows a time progression of the rotations of the
borders 235 around the center of the combined image 234.
[0215] Alternatively, the user can specify which portions they
would like to have as one image and which they would like to see as
the other by identifying closed contours 236 in the second image as
seen in FIG. 21a or by identifying a space 237 in between two
closed contours in the second image, as seen in FIG. 21b.
[0216] Alternatively, displaying the first image 231 and second
image 232 at the same position on the screen as separate layers and
varying the transparency of the layer in the foreground can
effectively provide a means for combining the images.
Alternatively, the order of the layers can be varied over time,
such as by having the IVUS image in the foreground for one time
interval and then transitioning to having the OCT image in the
foreground for a subsequent time interval, as seen in FIG. 22.
[0217] It is an object of the present invention to be able to
identify certain features of interest in a first image 231 and
transfer knowledge of that feature (such as its position, shape,
signal properties or composition) to a second image 232 that is
accurately co-registered with the first image 231. Geometric
features include specific points, contours or 2D regions in an
image. As seen in FIG. 23a, a user can identify a point 238,
contour or region in a first image 231 manually, through the user
interface of the imaging system (such as with a mouse or keyboard)
and have that geometric point 238 appear in a second image 232
co-registered with the first image 231 as in FIG. 23b. The
availability of one or more other images that are accurately
co-registered with the first image makes it possible to superimpose
any or all of the geometric features from the first image to any of
the other images.
[0218] By way of example, the user might identify the inner
boundary of a blood vessel or the trailing edge of a fibrous cap in
an OCT image. FIG. 24a shows the contour representing the inner
border 241 identified in a schematic representation of an OCT image
(the first image). Similarly, the outer boundary 242 of the vessel
wall (usually defined by the external elastic lamina) can be
identified in an IVUS image (the second image). The contours
representing the inner boundary 241 of the blood vessel or the
trailing edge of the fibrous cap can then be superimposed onto the
corresponding IVUS image. Similarly, the outer boundary 242 of the
vessel wall (usually defined by the external elastic lamina) can be
identified in an IVUS image. The contour representing the outer
boundary as assessed in the IVUS image can be superimposed onto the
OCT image. FIG. 24b shows the inner and outer boundaries on both
the first and second images.
[0219] While the inner boundary of the blood vessel is readily
identified on most IVUS images, the OCT generated contour would be
more accurate in most circumstances. Furthermore, OCT is thought to
be much better for identifying the fibrous cap of a plaque, in part
due to its higher resolution. However, IVUS can see much further
into most vascular tissues and can provide a better assessment of
the outer vessel wall.
[0220] A geometric feature can include features observed in 3D data
sets, such as surfaces or volumes. A surface or volume observed in
a 3D imaging dataset can be superimposed into another 3D imaging
dataset if the two imaging datasets are accurately registered.
[0221] The geometric features of interest need not be manually
identified. It is possible that features in an imaging dataset can
be identified by automated or semi-automated means to minimize user
intervention. For example, there are several border detection
methods cited in the literature on IVUS (e.g. Klingensmith, IEEE
Transactions on Medical Imaging, 2000; 19:652-662). Automated
border detection methods analyze an image to identify a contour of
some pre-determined significance. Semi-automated methods are
similar, but require some user intervention to either provide a
starting point for the border detection algorithm or to refine the
results produced the algorithm.
[0222] Other feature detection algorithms can be conceived of to
identify features other than a border. For example, a
hyper-intense/bright region in an ultrasound image followed a dark
region in the same direction of the imaging beam is often referred
to as "shadowing" and occurs most commonly when the area being
imaged includes either calcium (such as from advanced
atherosclerosis or malignant processes) or metal (such as from
stents or other implants). Similarly, a highly intense region in an
OCT image of a blood vessel, followed by a rapid but continuous
attenuation of the signal acquired along the same imaging path is
suggestive of necrotic material in the vessel wall. It is possible
to detect such regions algorithmically and identify them in their
respective images. Once such features are identified in their
respective images, their position and shape can be superimposed
into other images that are accurately co-registered.
[0223] In certain embodiments of the present invention, it will be
desirable to do some adjustment to one or more of the images to
further improve the co-registration. While many of the embodiments
of the present invention improve the precision of acquiring imaging
data with one or more imaging methods, there may be some advantage
to further adjusting the images to improve the accuracy of the
co-registration process. For example, ultrasound images are
generated assuming a constant speed of sound through all tissues,
while OCT assumes a constant speed of light through all
tissues.
[0224] In reality however, there are small changes in these speeds
depending on the composition of the tissue in which each of the
imaging energies propagate.
[0225] Therefore, prior to completing the co-registration process
for one or more images, it may be desirable to morph or warp one or
more of the images by identifying certain features in the two or
more images that are to be co-registered and using those features
to guide the morphing process. Any point, contour or other feature
identified in all of the images to be co-registered can be used to
drive the morphing process. An ultrasound image is most commonly
formed by displaying a grayscale representation of the intensity of
the ultrasound signal reflected back from the approximate anatomic
location that corresponds to each pixel in the image. Similarly, an
OCT image is most commonly formed by displaying a grayscale
representation of the intensity of the light reflected back from
the approximate anatomic location that corresponds to each pixel in
the image.
[0226] Aside from the intensity information at each location in
either an ultrasound or OCT image, there are several other features
from ultrasound or OCT images that can be very helpful for analysis
derived from combined imaging.
[0227] The display of an image derived from ultrasound signals
based on a feature other than then intensity of a sample in the
image is well known in the art. Nair et al (Circulation 2002;
106(17):2200-2206 and U.S. Pat. No. 6,200,268) published results of
an algorithm that measures several parameters of an ultrasound
signal in discrete regions of IVUS images of blood vessels. Each
region was also assigned a tissue category based on histological
analysis of the vessel. The ultrasound derived parameters and the
histological classification of each region were input into a
pattern recognition engine to generate an algorithm that is
subsequently applied in an attempt to classify tissue in vivo based
on its many ultrasound signal properties. Some of the properties
used for analysis include frequency domain parameters over a
defined range of frequencies such as maximum power, frequency of
maximum power, minimum power, frequency of minimum power, slope,
.gamma.-intercept, mid-band fit and integrated backscatter. The
image generated comprises a topographical map of the vessel
cross-section and a discrete number of colors, with each color
representing a single tissue category. Wilson et al demonstrated
the use of measuring the frequency domain attenuation of an
ultrasound signal in regions of an IVUS images and overlaying a
color map of the attenuation slope onto the conventional IVUS image
to identify areas thought to correspond to specific pathological
types.
[0228] Similarly, features of interest can be measured or
identified in optical images in order to generate images other than
intensity-based images. Parameters or other features that can be
used to generate such images include attenuation, polarization
sensitivity, detected edges, spectroscopic information and
others.
[0229] As a result of the high degree of accuracy of
co-registration enabled by the present invention, it is possible to
generate images based on features or signal properties measured
with more than one imaging modality. For example, a composite image
can be made using an inner border 245 identified by OCT, an outer
border 246 identified by IVUS and a color map of the most likely
tissue components within the vessel wall using a pattern
recognition system that combines optical signal properties with
acoustic signal properties within focal regions of the imaging
datasets to generate a composite image that will improve the
ability to identify important components within the vessel wall,
such as calcified, fibrous, atheromatous, thrombotic, metallic and
non-diseased regions.
[0230] FIG. 25a shows a schematic representation of an inner border
245 identified by OCT, an outer border 246 identified in the second
image by IVUS and a region of interest 247 used for analysis of the
OCT and ultrasound signal properties. As shown in FIG. 25b, the
signal properties 248 from the more than one modalities of imaging
in the co-registered region of interest are used to generate an
assessment of the composition of one or more pixels in the
composite image that correspond to the region of interest analyzed.
The assessment may be formed by a pattern recognition system 249
trained using methods known in the art. The geometric features 249
identified in the co-registered images are also optionally included
in the composite image. The process of assessing the composition of
a region of interest can be repeated several times over for
different regions of interest to generate a composite image.
[0231] In addition, the software and image processing algorithms
that enables such analysis of the combined imaging means need not
be on the acquisition station. Once the imaging data is acquired,
the imaging data can be transferred to allow analysis to occur
offline on a separate set of one or more processing units.
[0232] The combined IVUS/OCT scanning devices disclosed herein may
include a rotary encoder. Further details of optical encoders which
may used with the combined IVUS/OCT scanning devices are disclosed
in U.S. patent application Ser. No. 12/010,207 filed Jan. 22, 2008,
now U.S. Pat. No. 8,712,506, entitled MEDICAL IMAGING DEVICE WITH
ROTARY ENCODER, which is incorporated herein by reference in its
entirety.
[0233] Briefly, referring to FIGS. 26a to 26c, the imaging probes
may incorporate an encoder which is designed be used with an
elongate imaging probe that uses a rotary shaft such as the imaging
conduit 34 as part of its scanning mechanism, its use can be
generalized for use with any device that makes use of a long,
flexible cable used for transmission of torque where non-uniform
rotational distortion may occur and an accurate estimation of
rotary motion is required. In particular, it is most suited for use
with flexible torque transmission systems where the outer diameter
of the torque cable is relatively small (e.g. less than 4 mm) and
long (e.g. longer than 5 cm) such that conventional rotary encoding
systems would not provide the desired angular resolution or be
adequately compact for the intended use.
[0234] FIG. 26a demonstrates a longitudinal cross-section of the
proximal and distal ends of an elongate imaging device 450 with a
torque transmission shaft 451, mechanically coupled to a torque
source 452. The torque source 452 can be a motor, a handle that is
manually turned by the operator or any other such device. The
torque transmission shaft 452 transmits torque to the functional
end 454 of the device, which can be an energy delivery device, a
needle, an atherectomy head or any of several other implements. In
FIG. 26c, the wall of an external sheath 453 is shown to surround
the transmission shaft and is shown to enclose the functional end
of the device although embodiments where the external sheath is
open or has openings near the functional end are possible. An
optical fiber 455 is shown to be included as part of the external
sheath 453 for the purposes of enabling either the emitting light,
detecting light or both to travel to or from the encoding interface
104 that is remote to the proximal end of the transmission sheath.
In FIG. 26a the cylindrical encoding interface body 180 in this
case is attached to a rotating portion of the device while the
fiber is relatively stationary. The optical fiber 455 may be
included as part of the extrusion of the external sheath 453, as
shown, or may be added to the inner or outer surface of the sheath
and anchored to the sheath 453 by methods well known in the art,
such as bonding or surrounding the fiber and sheath with an
additional layer of heat shrinkable material. The optical fiber 455
is terminated with any necessary distal optics 115, such as an
optical spacer, lens and/or deflecting mechanism 172 (such as a
prism or mirror) to direct light towards the encoding interface
104. The encoding interface 104 in FIG. 26a may be similar to that
on the cylindrical encoding interface body disclosed in U.S. patent
application Ser. No. 12/010,207 filed Jan. 22, 2008, now U.S. Pat.
No. 8,712,506, entitled MEDICAL IMAGING DEVICE WITH ROTARY ENCODER,
mentioned above.
[0235] The encoding interface 104 in FIG. 26b is similar to that on
the cylindrical encoding interface body in the above mentioned
copending application. As the encoding optical circuit used in the
embodiments of FIGS. 14a and 14b are not mounted onto or directly
coupled with the torque transmission shaft, there is no need for an
optical rotary joint along the optical encoding circuit.
[0236] FIG. 26c shows a cross-sectional image of a representative
cross-section through the device 450 in FIG. 26b through line
14c-14c. One or more fiber optics 455 for the encoding system may
be incorporated with the external sheath 453.
[0237] Thus the rotary encoder embodiments disclosed in U.S. patent
application Ser. No. 12/010,207 filed Jan. 22, 2008, now U.S. Pat.
No. 8,712,506, entitled MEDICAL IMAGING DEVICE WITH ROTARY ENCODER,
mentioned above can be incorporated into an imaging probe 12 by
substituting the functional end of any of the embodiments in FIGS.
26a to 26d for an imaging assembly 30 and substituting the torque
transmission shaft 451 for an imaging conduit 34 suitable for
carrying either electrical or optical signals.
[0238] As used herein, the terms "comprises", "comprising",
"includes" and "including" are to be construed as being inclusive
and open ended, and not exclusive. Specifically, when used in this
specification including claims, the terms "comprises",
"comprising", "includes" and "including" and variations thereof
mean the specified features, steps or components are included.
These terms are not to be interpreted to exclude the presence of
other features, steps or components.
[0239] The foregoing description of the preferred embodiments of
the invention has been presented to illustrate the principles of
the invention and not to limit the invention to the particular
embodiment illustrated. It is intended that the scope of the
invention be defined by all of the embodiments encompassed within
the following claims and their equivalents.
* * * * *