U.S. patent application number 14/818300 was filed with the patent office on 2015-11-26 for location tracking of a metallic object in a living body.
The applicant listed for this patent is Kyma Medical Technologies Ltd.. Invention is credited to Assaf Bernstein, Vered Cohen Sharvit, Dov Oppenheim, Uriel Weinstein.
Application Number | 20150335310 14/818300 |
Document ID | / |
Family ID | 41380646 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150335310 |
Kind Code |
A1 |
Bernstein; Assaf ; et
al. |
November 26, 2015 |
LOCATION TRACKING OF A METALLIC OBJECT IN A LIVING BODY
Abstract
A method and apparatus are provided for determining and tracking
location of a metallic object in a living body, and then directing
a second modality such as ultrasound waves to the determined
location. The metal detector may be a radar detector adapted to
operate on a living body. The adaption may include disposing a
transfer material having electromagnetic properties similar to the
body between the radar detector and the living body, ECG gating the
radar detector, and/or employing an optimal estimator with a model
of expected stent movement in a living body. Applications include
determination of extent of in-stent restenosis, performing
therapeutic thrombolysis, or determining operational features of a
metallic implant.
Inventors: |
Bernstein; Assaf; (Givat
Nilly, IL) ; Weinstein; Uriel; (Mazkeret Batia,
IL) ; Cohen Sharvit; Vered; (Jerusalem, IL) ;
Oppenheim; Dov; (Jerusalem, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kyma Medical Technologies Ltd. |
Tel Aviv |
|
IL |
|
|
Family ID: |
41380646 |
Appl. No.: |
14/818300 |
Filed: |
August 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13735512 |
Jan 7, 2013 |
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14818300 |
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12127544 |
May 27, 2008 |
8352015 |
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13735512 |
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Current U.S.
Class: |
600/424 |
Current CPC
Class: |
A61B 8/06 20130101; A61B
8/0833 20130101; A61B 5/06 20130101; A61B 2562/164 20130101; A61B
2090/378 20160201; A61B 5/05 20130101; A61B 5/6833 20130101; A61B
8/4254 20130101; A61B 2562/143 20130101; A61B 5/0507 20130101; A61B
5/062 20130101; A61B 5/0205 20130101; A61B 8/42 20130101; A61B
8/543 20130101; A61B 8/4245 20130101; A61B 5/0402 20130101; A61B
5/113 20130101 |
International
Class: |
A61B 8/00 20060101
A61B008/00; A61B 5/06 20060101 A61B005/06; A61B 5/05 20060101
A61B005/05; A61B 8/08 20060101 A61B008/08 |
Claims
1. Apparatus for use in diagnostic imaging, comprising: a metal
detector adapted for determining location of a metallic object in a
living body; an ultrasound probe; and guiding means for directing
said probe at the location determined by the metal detector.
2.-51. (canceled)
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to an apparatus and method
for determining and tracking location of a metallic object in a
living body, and for guiding a second modality, for example,
ultrasound, to the determined location. The invention has
applicability to the general field of diagnostic imaging, and, is
particularly advantageous for determining the extent of in-stent
restenosis.
BACKGROUND ART
[0002] Cardiovascular disease is today considered the main cause
for mortality in the Western world. Such cardiovascular diseases
include atherosclerosis in which plaque builds up on the inside of
arteries. Plaque is made up of fat, cholesterol, calcium and other
substances found in the blood. Over time, the plaque hardens and
narrows the arteries reducing the flow of oxygen-rich blood to
organs and other parts of the body. This can lead to serious
problems, including heart attack, stroke or even death.
[0003] Atherosclerosis can affect any artery in the body, including
arteries in the heart, brain, arms, legs and pelvis. As a result,
different diseases may develop based on which arteries are
affected. When plaque builds up in the coronary arteries reducing
or blocking blood flow to the heart, it can lead to chest pain and
heart attack. This is referred to as coronary artery disease (CAD),
also called heart disease, and it is currently the leading cause of
death in the United States. Carotid artery disease occurs when
plaque builds up in the carotid arteries that supply oxygen-rich
blood to the brain. When blood flow to the brain is reduced or
blocked, it can lead to a stroke. Peripheral arterial disease
occurs when plaque builds up in the major arteries that supply
oxygen-rich blood to the legs, arms and pelvis. When blood flow to
these parts of the body is reduced or blocked, it can lead to
numbness, pain and, sometimes, dangerous infections.
[0004] A common treatment for atherosclerosis comprises insertion
of a stent into the narrowed blood vessel via angioplasty to
prevent or counteract the localized flow constriction. Stents are
typically made of metal mesh, e.g. stainless steel. After expansion
by balloon angioplasty with a stent, plaque is pushed back and the
artery wall stretches allowing increased blood flow. The stent
prevents the stretched blood vessel from reverting to its initial
size.
[0005] Unfortunately, as a result of neo-intimal tissue growth,
in-stent restenosis may occur narrowing the treated blood vessel
over time. In-stent restenosis is defined as greater than 50%
stenosis and is estimated to occur up to 30% in bare metal stents
and 7% -11% in drug eluding stents.
[0006] Existing protocols for detecting and determining extent of
in-stent restenosis include catheterization, and imaging. However,
catheterization is an invasive process with a high rate of
complications, and existing non-invasive diagnostic protocols only
provide indirect measurement. Accordingly, post stenting follow-up
is significantly impaired, being neither sensitive nor specific
enough, and not fully safe.
[0007] A need thus exists for a non-invasive tool for diagnosing
and monitoring in-stent restenosis. More particularly, there is a
need to precisely determine and track the location of a stent
within a living body and then directly measure vascular flow within
the stent.
[0008] More generally, a need exists for a non-invasive tool for
in-vivo localization and diagnosis of metallic objects, such as
artificial heart valves, orthopedic implants and screws, metallic
shrapnel, and the like.
BRIEF SUMMARY OF THE INVENTION
[0009] These and other needs are met, and additional benefits and
advantages achieved, according to one aspect of the present
invention, by the provision of apparatus for use in diagnostic
imaging. The apparatus includes a metal detector for determining
location of a metallic object in a living body, an ultrasound
probe, and guiding means for directing the probe at the location
determined by the metal detector. The metal detector may also track
the location of the metallic object in the living body. The metal
detector may comprise a magnetometer, or, preferably, a radar
detector. The radar detector preferably: operates in a bandwidth of
several Gigahertz at a frequency in the range of 1-10 GHz, is
multi-static, and employs a localization scheme based on
super-resolution techniques.
[0010] The apparatus may further comprise an interface for coupling
the radar detector to the living body. The interface can comprise a
transfer material having electromagnetic properties similar to the
body. A container may surround the transfer material, with the
container situated between and in intimate contact with the radar
detector and the body. In an advantageous embodiment, the antenna
of the radar detector may be substantially planar, and the
container rests on the substantially planar antenna with a first
surface of the container adjacent the antenna and an opposite
surface of the container adjacent and conforming to the body.
[0011] Various guiding means can be used to direct the ultrasound
probe at the location determined by the metal detector. The guiding
means may comprise a rigid attachment between the metal detector
and the ultrasound probe, or a tracking system for locating the
probe relative to the detector. The tracking system may preferably
employ electromagnetic tracking, and at least one of the metal
detector and the ultrasound probe may include a tracking
element.
[0012] The guiding means may also comprise a physical framework
substantially fixed in location relative to the body. The metal
detector and the ultrasound probe can be mounted to this framework.
Advantageously, the ultrasound probe may be mounted to the
framework by a mechanical tracking device.
[0013] The guiding means may also comprise a tracking system and
fiducial markers. The markers may be substantially fixed in
location relative to the body and detectable by both the metal
detector and the tracking system.
[0014] The guiding means may also include a component for
electronic steering of an ultrasound beam of the probe to the
location determined by the metal detector.
[0015] The apparatus may further include a display for presenting
instructions to an operator for directing the ultrasound probe to
the location determined by the metal detector. The instructions may
be textual and/or graphic and may be presented on the same or a
supplemental display screen as the ultrasound image. Auditory,
tactile or other modes of instruction may also be employed.
[0016] In one preferred embodiment, the metal detector comprises a
radar detector having an antenna in the form of an adhesive
conforming patch adapted to be removably attached to the living
body. The patch may include a tracking element. The patch may be
designed as a single use disposable component.
[0017] In a preferred application, the metallic object comprises a
stent, and the ultrasound probe measures blood velocity within the
stent in order to determine extent of in-stent restenosis.
[0018] Thus, in another aspect, the present invention provides
apparatus for in-vivo determination of extent of restenosis within
a stent deployed in a body of a person or animal. This apparatus
includes a radar detector for determining and tracking location of
the deployed stent within the body, an ultrasound probe for
measuring fluid flow, and guiding means for establishing a common
geometric frame of reference for the radar detector and the
ultrasound probe, and for guiding the probe to measure fluid flow
at the location determined by the radar detector, whereby extent of
in-stent restenosis can be determined from measured fluid flow.
[0019] The radar detector may be adapted to a living body by
employing at least one of: a transfer material having
electromagnetic properties similar to the body, ECG gating, and an
optimal estimator with a model of expected stent movement in a
living body.
[0020] The present invention also contemplates a method for
locating a metallic object in a living body, comprising: adapting a
radar detector to interface with the living body, directing a radar
beam from the radar detector at the body to produce a returned
radar signal, receiving the returned radar signal, and detetinining
and tracking location of the metallic object in the living body
from the returned radar signal. This method may further include
directing ultrasound waves to the location determined from the
returned radar signal. The ultrasound waves may be directed to the
determined location for measuring fluid flow or for therapeutic
purposes.
[0021] In another application, the metallic object may comprise an
artificial heart valve, and the method may further include the step
of determining operational feature(s) of the valve from the
returned radar signal.
[0022] The radar detector may be adapted to the living body by
disposing a transfer material having electromagnetic properties
similar to the body between the radar detector and the living body,
and/or ECG gating the radar detector, and/or employing an optimal
estimator with a model of expected stent movement in a living
body.
[0023] The method may also include registering a three-dimensional
arterial map of the living body, reconstructed from angiography
images, to the determined location of the metallic object, and
guiding a modality other than radar to the determined location of
the metallic object and/or a different correlated location on the
arterial map.
[0024] In a further aspect, the current invention provides a method
for determining fluid flow within a metallic object in a living
body. This method includes metallic object localization by
determining and tracking location of the metallic object in the
body with a metal detector; guiding an ultrasound probe to the
location determined by the metal detector; and measuring fluid flow
at the location with the ultrasound probe. The guiding may include
registering the ultrasound probe and the metal detector to a common
geometric frame of reference, and such registration may be
performed automatically.
[0025] The metallic object localization may be performed
continuously online during fluid flow measurement, or periodically
or at a single instance. Fluid flow measuring may be performed at
several locations near the metallic object and/or performed at
different times and measurement results compared.
[0026] In still another aspect, the present invention provides a
method for determining extent of restenosis within a stent deployed
in a living body comprising the steps of: determining and tracking
location of the deployed stent in the body with a radar detector;
measuring fluid flow with an ultrasound probe at the location
determined by the radar detector; and determining extent of
restenosis within the deployed stent from measured fluid flow.
[0027] The present invention affords numerous benefits and
advantages. It provides a non-invasive, non-ionizing tool for
diagnosing and monitoring in-stent restenosis by combing radar and
ultrasound Doppler modalities. It enables precise determination and
tracking of location of a metallic stent or other metallic object
in a living body, and facilitates direct vascular flow measurement
within deployed stents. Post stenting follow-up is thus
significantly improved.
[0028] The present invention enables an ultrasound Doppler in-stent
flow measurement enhanced by a radar or other metallic object
locator. The radar detector may be especially adapted for in-vivo
application. Various guidance approaches and tracking systems may
be employed to guide the ultrasound probe based on the metallic
object localization. Guidance instructions can be provided to the
operator visually, audibly or otherwise, allowing simple,
efficient, and accurate real-time operation. The metallic object
locator and probe guidance components can be readily added to
existing ultrasound machines or systems.
[0029] In addition to diagnostic and imaging applications, the
present invention may be used for therapeutic purposes or to
monitor implanted devices such as artificial heart valves. When
combined with a 3 dimensional arterial map, other locations can be
readily targeted.
[0030] The present invention may also be advantageously applied to
in-vivo localization and diagnosis of metallic shrapnel and of
orthopedic objects such as implants and screws, and to assessing
the danger posed by metallic objects for patients expected to
undergo MRI scanning.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0031] Preferred embodiments of the present invention will now be
described in relation to the accompanying drawing figures, in
which:
[0032] FIG. 1 illustrates the combined use of a radar detector with
an ultrasound probe and a tracking system, in which an antenna of
the radar detector is substantially planar and a flexible container
filled with compatible transfer material is employed to adapt the
radar detector to a living body;
[0033] FIG. 2 depicts apparatus for determining location of a stent
in a living body which employs a rigidly connected ultrasound probe
and metal detector;
[0034] FIG. 2A is a blow-up of the combined instrument of FIG.
2;
[0035] FIG. 3 depicts an embodiment in which a radar detector and
ultrasound probe are registered by mounting to a physical framework
substantially fixed in relation to the living body;
[0036] FIG. 4A depicts a first stage in which a radar detector
determines location of a stent using fiducial markers worn by a
patient;
[0037] FIG. 4B shows a second stage in which an ultrasound probe
can be guided to the determined location of the stent using the
same fiducial markers and a tracking system;
[0038] FIG. 5 depicts an embodiment employing an antenna patch
having a tracking element;
[0039] FIG. 6 is a block diagram of one preferred embodiment of the
apparatus of the present invention; and
[0040] FIG. 7 provides a flow chart of methods that can
advantageously be implemented by the present invention.
DETAILED DESCRIPTION
[0041] The present invention is generally directed to a method and
apparatus for determining location, of a metallic object in a
living body, and directing a second modality at the determined
location or a related location. Although amenable to various
applications, specific embodiments are described herein, by way of
example and not limitation, in order to illustrate the principles
and features of the invention. In the various drawing figures,
common elements are designated by common reference numbers.
[0042] FIG. 1 shows a first approach for precisely identifying and
tracking location of a stent or other metallic object in a patient
with a radar detector, and then directing ultrasound waves to the
determined location. In this embodiment, the patient (14), shown as
transparent, reclines on a mattress (16) or other suitable
supporting surface. Embedded in, or otherwise associated with
mattress (16) is a substantially planar radar antenna (40).
Interposed between the radar antenna and the patient's body is a
container or cushion (37) having an upper surface (38) that
conforms to the shape and contour of the portion of the patient's
body in contact with the cushion. Cushion (37) is preferably filled
with a transfer material having electromagnetic properties similar
to those of the body. An exemplary transfer material might be a
solution of about 85% ethylene glycol and about 15% water. Other
materials, e.g. gel or liquid, which mimic the electromagnetic
properties of the body can be used as the transfer material.
Similarly, cushion or container (37) may be made of any suitable
material that allows for intimate contact with the antenna and
intimate conforming contact with the patient's body.
[0043] As more fully described hereinafter, antenna (40) is
preferably a multi-static, multi-element antenna constructed as a
flat panel to fit beneath the patient's back. The multi-element
antenna can be a printed or patch antenna. The radar detector
preferably operates in a bandwidth of several Gigahertz at a
frequency in the range of 1-10 GHz. The transfer material in
container (37) serves as an interface between the radar detector
and the living body that reduces radar reflection caused by a
skin-air interface, and thus comprises an adaption of the radar
detector to the living body.
[0044] Continuing with the description of FIG. 1, a console (42)
may be mounted along one side of support surface (16). Console (42)
includes a tracking transmitter (44) and a central controller (52)
(described hereinafter with reference to FIG. 6). Tracking
transmitter (44) interacts with a tracking element, sensor or
transducer 46 associated with ultrasound probe (22) and optionally,
with additional tracking elements associated with radar antenna
(40) or transfer material container (37). Transmitter (44) and the
tracking elements form part of a tracking system employed to
register the ultrasound probe to a common coordinate system with
the radar detector. Although preferably electromagnetic, the
tracking may be optical, mechanical or employ another suitable
modality. One suitable electromagnetic tracking system is sold
under the name FASTRAK by the Polhemus Company of Colchester, Vt.,
USA. A suitable optical tracking system is the Micron Tracker
available from Claron Technology Inc. of Toronto, Ontario Canada. A
useful mechanical tracking system is the MicroScribe.RTM. G2
desktop digitizing system available from Immersion Corporation of
San Jose, Calif., USA. Other available tracking systems may, of
course, also be used.
[0045] As more fully described hereinafter, the radar detector,
operating in conjunction with the tracking system, provides
instructions (36) to an operator (48) for directing the ultrasound
probe (22) at the precise location of a stent or other metallic
object in the living body, as determined by the adapted radar
detector. Instructions (36) may be presented on a supplemental
display (50) located adjacent the display (32) so that both
instructions (36) and ultrasound image (34) of the stent and its
vicinity, are within the field of view of operator (48). Display
(50) may, of course, be positioned in different locations or could
be combined with display (32) of the conventional ultrasound
machine. Instructions (36) may be textual and/or graphic or
otherwise visually presented. Such instructions can also be
presented in auditory, tactile or other fashion to the
operator.
[0046] FIG. 2 depicts an alternate embodiment of a system (10) for
locating a metal stent (12) in a living person (14) and directing
an ultrasound probe (22) to the determined location. As
illustrated, a patient having a previously implanted stent (12)
reclines on a mattress (16), bed or other suitable support surface.
A combined instrument (18) determines in-vivo the location of stent
(12) and directs ultrasound waves to the determined location.
[0047] As more clearly seen in the magnified view of FIG. 2A,
combined instrument (18) includes a standard ultrasound probe (22)
rigidly connected by any suitable physical arrangement (24) to a
metal detector (20). Metal detector (20) may comprise a
magnetometer, for example, of the pulse-induction type, or other
metal detector. The rigid connection between ultrasound probe (22)
and metal detector (20) ensures registration, i.e. both operate in
the same coordinate system. Thus, the rigid connection serves to
guide and direct the ultrasound probe at a location of the stent or
other metallic object in the living body determined by the metal
detector.
[0048] Electronic & RF cabling (26) connects ultrasound probe
(22) to an ultrasound machine (28). Optionally, metal detector (20)
can also be electrically connected by cable (26) to its operational
control unit.
[0049] Ultrasound machine (28) typically includes an operator
control and input device (30) and a display (32) for presenting an
ultrasound image (24).
[0050] In operation, metal detector (20) is used to detect,
determine location and, preferably, track location of stent (12)
within patient (14). The metal detector provides instructions (36),
overlaid on the same display screen as ultrasound image (34) or
presented on a supplemental display monitor, to guide an operator
in directing ultrasound probe (22) to the stent location determined
by the metal detector. Rigid connection (24) provides automatic
registration between the ultrasound probe (22) and metal detector
(20), thereby ensuring operation in a common coordinate system.
[0051] In FIG. 3, a physical framework (54) is associated with a
support structure (56) on which mattress (16) and patient (14)
reside. Patient (14) is preferably located in a fixed position
relative to framework (54).
[0052] Framework (54) preferably includes apertures (57) and (59)
therethrough. Framework (54) supports a radar detector (58), or
other metal detector, adjacent aperture (57), and ultrasound probe
(22) above aperture (59). Radar detector (58) is fixed in position
relative to framework (54) by a bracket (61), or other suitable
mounting hardware. Ultrasound probe (22) is preferably mounted to
framework (54) by a base (62) of a mechanical supporting and
tracking unit (60). The mechanical supporting and tracking unit can
include articulated arms facilitating three-dimensional positioning
of probe (22), and appropriate sensors for tracking the position of
the probe relative to base (62) and framework (54). For example, a
MicroScribe G2 desktop digitizing system. available from Immersion
Corporation can be used as the mechanical supporting and tracking
unit. The mechanical supporting and tracking unit (60) may also be
a robotic active element that receives direct movement commands
from the metal detector and automatically directs the ultrasound
probe to the target, thereby compensating for patient movement,
breathing and heart beat. Framework (54) with its rigid attachment
of radar detector (58) and base (62) of the mechanical supporting
and tracking device affords registration to a common coordinate
system of the radar detector and ultrasound probe. Apertures (57)
and (59) in framework (54) afford unimpeded radar and ultrasound
wave transmission, respectively.
[0053] In FIG. 4A, patient (14) wears a vest (66), or a
partially-rigid apparel, designed to remain in the same position on
the body whenever worn, having a set of fiducial markers (64) for
registration of a radar detector (58). The fiducial markers (64)
are in a predetermined position relative to patient (14), and may,
alternatively, be applied directly to the patient's body. The
markers may take various forms provided that they are detectable
both by a radar (or other metal) detector and by a tracking
system.
[0054] In the first stage, illustrated in FIG. 4A, radar detector
(58) determines and tracks location of stent (12) within patient
(14) relative to fiducial markers (64),
[0055] In a second stage, illustrated in FIG. 4B, a tracking system
(44) determines the location of ultrasound probe (22) relative to
fiducial markers (64). To facilitate such tracking, an additional
fiducial marker (46) or other tracking element is associated with
ultrasound probe (22).
[0056] As also illustrated in FIGS. 4A and 4B, vest (66) is
preferably provided with an aperture (68) overlying the general
area in which the stent is located. Aperture (12) minimizes
interference of vest (66) with ultrasound probe (22). Optionally,
radar detector (58) may be gated by an ECG signal from
electrocardiogram machine (70), as more fully described
hereinafter.
[0057] The embodiment of FIG. 5 is similar to that of FIG. 1, but
instead of a substantially planar radar antenna placed under the
patient, the radar antenna may comprise a conforming patch (74)
adapted to be removably attached to patient (14), e.g. near the
heart. In known fashion, patch (74) may be provided with a skin
compatible adhesive coating for temporary connection to the body.
Patch (74) can be provided with a tracking element or transducer
(76) for tracking its location, and may be provided with an
electronic cable (78) for connecting the patch to the rest of the
radar detector. The patch may contain a printed radar antenna. One
advantage of this embodiment is the direct coupling of the radar
antenna to the patient's body; another advantage is that the patch
may be disposable after a single use.
[0058] FIG. 6 depicts one preferred configuration, in block diagram
form, of the apparatus of the present invention. As earlier
described, patient (14) can be located on a cushion (37) containing
transfer material (39), atop a multi-element substantially planar
antenna (40). A tracking element (43) may be associated with
cushion (38) and/or antenna (40) for tracking purposes. The
multi-static, multi-element antenna can be a printed or patch
antenna constructed and operated in know fashion. Additionally, the
antenna may be customized and adapted to a living body by creating
an electromagnetic field pattern or aperture that can be focused or
pointed at a precise location within human tissue while immersed in
or enfolded by a transfer material.
[0059] In order to reduce reflection at the air-skin interface, the
antenna is surrounded by a transfer material with electromagnetic
properties similar to that of the body. The high dielectric
constant of the transfer material also allows the antenna to be
smaller because the wavelength is significantly smaller in such a
substance as in the body. The transfer material is suspended in a
cushion or other container touching the antenna and extending above
it until the cushion snuggly touches the patient's body in a
conforming way, allowing direct line-of-sight from the entire
antenna to the metallic target, without passing through air. In
place of antenna elements, multiple coils may be used for magnetic
determination of location of the metallic object.
[0060] Outputs of the antenna elements (or magnetic coils) (41) are
acquired into the system. In order to avoid many radar receivers,
the different antenna elements can either be switched consecutively
into one or more receivers or modulated in orthogonal modulations
and summed into one or more RF signal(s) (81), in known fashion.
This modulation can be achieved by adding a printed layer to the
antenna with modulating diodes on it, or by other known
techniques.
[0061] RF signal(s) (81) is fed into front-end module (80) of the
radar detector. The RF chain within front-end module (80) includes
switching/modulating matrix (82), amplifier (84), mixer (86) and
other conventional components, In addition to the
switching/modulation function, in front-end module (80), the RF
signal(s) from the antenna elements are amplified, using low-noise
amplifiers, band-pass filtered, and down-converted into coherent IF
signals (90). The IF signals may retain the inter-element amplitude
and phase information, and can be later used to detect, locate and
track the metallic object in the living body in different locations
in space.
[0062] The IF signals are sampled in a digital data acquisition
module (92), where they are converted into digital information
streams. If the antenna channels were modulated, they can be
de-modulated using known digital signal processing techniques.
[0063] Next, all of the antenna channels contained within the
sampled signal (94) are fed into the detection module (96) where
they are optionally integrated coherently with different
time-gating and different phase differences corresponding to the
different locations in the detection space. In measurement module
(98), super-resolution techniques are employed for interpolating a
more accurate position for the detected target. Super-resolution
techniques are well known in the radar field. Alternatively,
non-coherent processing methods may be used for detection and
measurement, using difference of time of arrival or amplitude
ratios for determining the target location.
[0064] Target information and radar signature or other
characterizing information (100) from the detection and measurement
modules is then passed onto an optimal estimator (102) for
estimating the target location, using a modified Kalman filter or
equivalent. The characterizing information and/or radar signature
may relate to orientation of the metallic object and other optional
information such as Doppler velocity, other spectral and temporal
characteristics and amplitude information. The same estimator is
also used for predicting location of the target at certain points
in time, allowing for proper control and man-machine interface. As
an adaption of the radar detector to a living body, the optimal
estimator can employ a model of expected stent movement in a living
body. Such movement is periodic, of known amplitudes, velocities
and acceleration as expected from the movement of the heart wall,
according to known measurements of these values. An optimal
estimator with a Kalman filter is a known measurement
technique.
[0065] The estimated target position from optimal estimator (102)
is then fed into a central controller (52) where it is compared to
the tracked ultrasound probe location to provide directional
guidance to the operator.
[0066] In the configuration shown in FIG. 6, a tracking transmitter
(44) is installed close to the patient, preferably in a position
least affected by metallic parts of the bed. A tracking sensor or
receiver (46) is attached to standard ultrasound probe (22).
Optionally, the tracking sensor can be removed when the ultrasound
unit is used for other procedures. Ultrasound probe (22) is
connected by cable (110) to ultrasound machine (28) in the usual
manner and the ultrasound machine is used as it is normally
used.
[0067] Tracking data (104) from ultrasound sensor (46) is fed into
standard tracking system electronics module (106). Ultrasound probe
tracked location (108) passes from module (106) to central
controller (52) where it is preferably filtered according to an
expected probe movement profile. Movement profile refers to
velocities and accelerations expected to result from normal
movement of a probe. The central controller then estimates a
"region of imaging" location from the filtered probe tracked
location signal and compares it with the estimated target location
provided by the radar detector. A difference in location between
the "region of imaging" and the predicted target location from the
radar detector is used to calculate user commands or instructions
(114) needed for the user to adjust the probe so as to see the
target. These commands are passed to the user interface display
(50) as user directions (112) or to the ultrasound display (32) as
user commands (114). The central controller can also provide
ultrasound steering information (115) to the ultrasound machine
(28) to steer the ultrasound beam to the targeted location, as
disclosed, for example, in U.S. Pat. No. 6,730,033 (which patent is
hereby incorporated by reference herein).
[0068] Optionally, an ECG trigger (88) can be used to gate
front-end module (80) of the radar detector to reduce the RF duty
cycle by transmitting the RF signal only at certain phases of the
heartbeat. ECG gating can also be used for an improved model of
target motion in the optimal estimator (102). Similarly,
optionally, an additional tracking sensor (not shown) can be
attached to the patient to measure breathing motion and then used
for improved tracking. In conventional fashion, outputs of the
ultrasound machine can be provided to a PACS system (116) for
medical archiving.
[0069] FIG. 7 presents a flow chart of methods that can be
successfully implemented with the present invention. In an initial
step (118), a radar detector is preferably adapted to serve as a
detector and locator of a metallic object in a living body. Such
adaption may include disposing a transfer material having
electromagnetic properties similar to the body between the radar
detector and the living body, ECG gating the radar detector, and/or
employing an optimal estimator with a model of stent movement in a
living body.
[0070] Next, the radar beam is directed at the living body and
metal target, with optional ECG gating (step 120). A returned radar
signal is then received (step 122), and processed as earlier
described to detect the metallic object in the living body (step
124). The metallic object's location is then measured, preferably
using super-resolution techniques (step 126), and its location
tracked (step 128).
[0071] The ultrasound probe and radar detector (or other metallic
object detector) are registered to a common frame of reference
(step 130), by a tracking system, or otherwise. Optionally, a
3-dimensional map of the patient's arteries (arterial map)
constructed from angiograms or cardiac CT data such as provided by
Paieon Inc. of New York, N.Y., USA and including the metallic
object in the map, can also be registered to this frame of
reference (step 132). The ultrasound beam is then directed by user
guidance provided by the central controller, for example, on a
suitable display, or otherwise, to the location of the metallic
object as determined by the radar detector or to another correlated
location on the arterial map (step 134).
[0072] The directed ultrasound beam can be used to measure Doppler
velocity of the fluid at the determined location (step 136), in
known fashion. If the metallic object is a deployed stent, extent
of in-stent restenosis can be determined from measured fluid
velocity (step 138), via a look-up table or in other known fashion.
Such techniques are disclosed, for example, in "Duplex Ultrasound
Velocity Criteria For The Stented Carotid Artery" by Brajesh K Lai
et al, on the Vascular Web site provided by the Society for
Vascular Surgery at:
http://www.vascularweb.org/Annual_Meeting/Abstracts/2007/lal_duplex_ultra-
sound_velocity.html and in the Inaugural issue of the newsletter of
the Vascular Diagnostic Laboratory published by the Heart and
Vascular Institute of Morristown, N.J., at:
http://www.franklynideas.com/hvi_site/hvi2_newsevents_newsletter.html
(which publications are hereby incorporated by reference
herein).
[0073] Alternatively, the directed ultrasound beam may be employed
to perform therapeutic thrombolysis at the determined location
(step 142). Optionally the method used can be HIFU (high intensity
focused ultrasound).
[0074] If the metallic object is an artificial heart valve,
operational feature(s) of the artificial heart valve can be
determined from the radar signal, signature and characterizing
information provided by the radar detector (step 140). Such
characterizing information may be the radar Doppler velocity of a
valve along time, characterizing operational features such as the
speed and the travel distance at which a valve operates.
[0075] In other applications, a modality other than radar or
ultrasound may be directed to the determined location of the
metallic object, or to a different location on the arterial
map.
[0076] The metallic object localization of the present invention
may be performed continuously on-line during fluid flow measurement
(which is especially appropriate to the configuration depicted in
FIGS. 4A and 4B), or periodically, or at a single instance.
Similarly, the measurement of fluid flow may be performed at
several locations near the metallic object to observe blood flow
before and after obstructions. Fluid flow measurement can also be
performed at different times and measurement results compared; for
instance, one measurement immediately after stent placement as a
baseline for comparison to measurements at subsequent times.
[0077] From the foregoing description, it will be evident that the
present invention provides a unique, non-invasive tool for
precisely determining and tracking location of a metallic object,
such as a stent, within a living body. Guidance can then be
provided to direct ultrasound waves, or another modality, to the
determined location of the metallic object, or a correlated
location on a registered arterial map, for diagnostic, therapeutic
or other purposes. As such, the present invention provides a
significant advance in medical diagnosis, imaging and treatment.
Although various embodiments have been described and depicted
herein, it will be apparent to those skilled in the art that
various modifications, substitutions and additions can be made
without departing from the scope of the present invention, as
defined by the appended claims.
* * * * *
References