U.S. patent application number 13/906705 was filed with the patent office on 2014-07-03 for methods and systems for performing medical procedures with reference to projective image and with respect to pre-stored images.
This patent application is currently assigned to Covidien LP. The applicant listed for this patent is Covidien LP. Invention is credited to Pinhas Gilboa.
Application Number | 20140188204 13/906705 |
Document ID | / |
Family ID | 22639457 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140188204 |
Kind Code |
A1 |
Gilboa; Pinhas |
July 3, 2014 |
Methods And Systems For Performing Medical Procedures With
Reference To Projective Image And With Respect To Pre-Stored
Images
Abstract
A catheter is navigated within a body cavity of a patient. This
navigation is enabled by the provision of the transmitter of
electromagnetic radiation under platform, a receiver of
electromagnetic radiation rigidly attached to fluoroscope, and a
receiver of radiation rigidly attached to the catheter, all three
of which are connected by wires to a computer. The computer
displays, on a display unit, the image of the body cavity acquired
by the fluoroscope, with an icon representing the catheter
superposed on the image in the location and orientation of catheter
relative to the body. There is no representational imaging device
equipped with a receiver in the apparatus of the current
invention.
Inventors: |
Gilboa; Pinhas; (Haifa,
IL) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Covidien LP |
Mansfield |
MA |
US |
|
|
Assignee: |
Covidien LP
Mansfield
MA
|
Family ID: |
22639457 |
Appl. No.: |
13/906705 |
Filed: |
May 31, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12490237 |
Jun 23, 2009 |
8565858 |
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13906705 |
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10169186 |
Jun 28, 2002 |
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PCT/US01/00074 |
Jan 2, 2001 |
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12490237 |
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Current U.S.
Class: |
623/1.11 |
Current CPC
Class: |
A61B 6/504 20130101;
A61B 5/06 20130101; A61B 6/481 20130101; A61B 34/20 20160201; A61B
6/4441 20130101; A61B 5/062 20130101; A61F 2/95 20130101; A61B
6/508 20130101; A61B 5/11 20130101 |
Class at
Publication: |
623/1.11 |
International
Class: |
A61B 19/00 20060101
A61B019/00; A61F 2/95 20060101 A61F002/95 |
Claims
1-10. (canceled)
11. A method of treating a body of a patient, comprising the steps
of: simultaneously: acquiring a first image of at least a portion
of the body, using an imaging device, measuring a disposition of
said imaging device relative to a reference frame, and measuring a
disposition of the body relative to said reference frame: restoring
said imaging device and the body to respective dispositions that
are equivalent to said measured dispositions; and performing a
medical procedure on the body with reference to said first image
after said restoring of said imaging device and of the body to said
equivalent dispositions.
12. The method of claim 11, wherein said measuring of said
disposition of said imaging device is effected using a disposing
system that includes a disposition implement associated with said
imaging device and a disposing implement associated with said
reference frame.
13. The method of claim 11, wherein said measuring of said
disposition of said imaging device is effected using a disposing
system that includes a disposing implement associated with said
imaging device and a disposition implement associated with said
reference frame.
14. The method of claim 11, wherein said measuring of said
disposition of the body is effected using a disposing system that
includes a disposition implement associated with the body and a
disposing implement associated with said reference frame.
15. The method of claim 11, wherein said measuring of said
disposition of the body is effected using a disposing system that
includes a disposing implement associated with the body and a
disposition implement associated with said reference frame.
16. The method of claim 11, further comprising the step of:
acquiring a second image of said at least portion of the body,
using said imaging device, after said imaging device and the body
have been restored to said equivalent dispositions thereof; said
medical procedure being performed with reference to both said
images.
17. The method of claim 11, wherein said performing of said medical
procedure includes navigating a probe to a point-of-interest in
said at least portion of the body with reference to said first
image.
18. The method of claim 17, further comprising the steps of:
acquiring a second image of said at least portion of the body,
using said imaging device, after said imaging device and the body
have been restored to said equivalent dispositions; said navigating
being with reference to both said images.
19. The method of claim 17, wherein said navigating includes
measuring a disposition of said probe relative to said reference
frame.
20. The method of claim 17, wherein said measuring of said
disposition of said probe is effected using a disposing system that
includes a disposition implement associated with said probe and a
disposing implement associated with said reference frame.
21. The method of claim 17, wherein said measuring of said
disposition of said probe is effected using a disposing system that
includes a disposing implement associated with said probe and a
disposition implement associated with said reference frame.
22. The method of claim 19, wherein said measuring of said
disposition of said imaging device, said measuring of said
disposition of the body and said measuring of said disposition of
said probe are effected using a common disposing system that
includes a first disposition implement associated with said imaging
device, a second disposition implement associated with the body, a
third disposition implement associated with said probe and a common
disposing implement associated with said reference frame.
23. The method of claim 19, wherein said measuring of said
disposition of said imaging device, said measuring of said
disposition of the body and said measuring of said disposition of
said probe are effected using a common disposing system that
includes a first disposing implement associated with said imaging
device, a second disposing implement associated with the body, a
third disposing implement associated with said probe and a common
disposition implement associated with said reference frame.
24. A method of treating a body of a patient, comprising the steps
of: simultaneously: acquiring a first image of at least a portion
of the body, using an imaging device, measuring a disposition of
said imaging device relative to a reference frame, and measuring a
first disposition of the body relative to said reference frame;
measuring a second disposition of the body relative to said
reference frame; and performing a medical procedure on the body
with reference to said first image and with reference to all three
said dispositions.
25. The method of claim 24, wherein said measuring of said
disposition of said imaging device is effected using a disposing
system that includes a disposition implement associated with said
imaging device and a disposing implement associated with said
reference frame.
26. The method of claim 24, wherein said measuring of said
disposition of said imaging device is effected using a disposing
system that includes a disposing implement associated with said
imaging device and a disposition implement associated with said
reference frame.
27. The method of claim 24, wherein said measuring of said
dispositions of the body is effected using a disposing system that
includes a disposition implement associated with the body and a
disposing implement associated with said reference frame.
28. The method of claim 24, wherein said measuring of said
dispositions of the body is effected using a disposing system that
includes a disposing implement associated with the body and a
disposition implement associated with said reference frame.
29. The method of claim 24, wherein said performing of said medical
procedure includes navigating a probe to a point-of-interest in
said at least portion of the body.
30. The method of claim 29, wherein said navigating includes
measuring a disposition of the probe relative to said reference
frame.
31. The method of claim 30, wherein said measuring of said
disposition of said probe is effected using a disposing system that
includes a disposition implement associated with said probe and a
disposing implement associated with said reference frame.
32. The method of claim 30, wherein said measuring of said
disposition of said probe is effected using a disposing system that
includes a disposing implement associated with said probe and a
disposition implement associated with said reference frame.
33. The method of claim 30, wherein said measuring of said
disposition of said imaging device, said measuring of said
dispositions of the body and said measuring of said disposition of
said probe are effected using a common disposing system that
includes a first disposition implement associated with said imaging
device, a second disposition implement associated with the body, a
third disposition implement associated with said probe and a common
disposing implement associated with said reference frame.
34. The method of claim 30, wherein said measuring of said
disposition of said imaging device, said measuring of said
dispositions of the body and said measuring of said disposition of
said probe are effected using a common disposing system that
includes a first disposing implement associated with said imaging
device, a second disposing implement associated with the body, a
third disposing implement associated with said probe and a common
disposition implement associated with said reference frame.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of and claims priority to
U.S. patent application Ser. No. 10/169,186 filed Jun. 28, 2002
entitled Methods And Systems For Performing Medical Procedures With
Reference To Projective Image And With Respect To Pre-Stored
Images, which claims priority to International Patent Application
No. PCT/US01/00074, International Filing Date Jan. 2, 2001,
entitled Methods And Systems For Performing Medical Procedures With
Reference To Projective Images And With Respect To Pre-Stored
Images, which claims benefit of U.S. Provisional Application Ser.
No. 60/175,226 filed Jan. 10, 2000 entitled Interventional 3D
Fluoroscope, all of which are hereby incorporated herein by
reference.
FIELD AND BACKGROUND OF THE INVENTION
[0002] The present invention relates to medical procedures that are
performed with reference to images of the patient and, more
particularly, to medical procedures performed with reference to
projective images such as fluoroscope images, and also to medical
procedures performed with reference to images acquired prior to,
and independently of, the procedures.
[0003] Images of the interiors of patients commonly arc used to
guide the performance of invasive medical procedures on the
patients. Bucholtz, in U.S. Pat. No. 5,383,454, Ferre et al., in
U.S. Pat. No. 5,829,444 and U.S. Pat. No. 5,873,822, and Bourman,
in U.S. Pat. No. 5,902,239, teach the navigation of a probe, such
as a catheter, within the body of a patient, with reference to
previously acquired images. Barrick, in U.S. Pat. No. 5,772,594,
teaches fluoroscopic imaging of a bone prior to the insertion
therein of a guide pin or screw with reference to the image.
[0004] Two kinds of imaging modalities are in common use.
Representational images, such as CT images, MR images and
ultrasound images, represent physical properties of the patient's
body at particular locations therein. For example, each pixel of a
2D digital ultrasound image of a patient represents an acoustic
impedance contrast at a corresponding point inside the patient's
body, and each voxel of a 3D CT image volume represents the density
of the patient's body tissue at a corresponding point inside the
patient's body. Projective images, such as fluoroscopic X-ray
images, represent projections of physical properties of the
patient's body into a plane. For example, each point in a
fluoroscopic X-ray image is an integral along a ray, from the X-ray
source to the X-ray image, of the density of the patient's body
tissue.
[0005] Two prior art references of particular note are Gilboa et
al., WO 00/10456 and WO 00/16684, both of which documents are
incorporated by reference for all purposes as if fully set forth
herein. WO 00/10456 teaches intra-body navigation of a probe in
conjunction with imaging by a C-mount fluoroscope. WO 00/16684
teaches the use of a representational imaging device, such as an
ultrasound probe, in conjunction with the C-mount fluoroscope of WO
00/10456, for the purpose of identifying and recording
points-of-interest, within the body of the patient, towards which
the probe subsequently is navigated. FIG. 1A, which is adapted from
FIG. 2 of WO 00/16684, shows a patient 24 lying on an operation
platform 34 and being imaged by a C-mount fluoroscope 22. A
catheter 26 is navigated within a body cavity 28 of patient 24.
This navigation is enabled by the provision of a transmitter 30 of
electromagnetic radiation under-platform 34, a receiver 40 of
electromagnetic radiation rigidly attached to fluoroscope 22, and a
receiver 32 of radiation rigidly attached to catheter 26, all three
of which are connected by wires 51 to a computer 50. Fluoroscope 22
is used to acquire an image of a portion of the body of patient 24
that includes body cavity 28. As explained in WO 00/10456,
transmitter 30 defines a reference frame, and the signals received
by computer 50 from receivers 40 and 32 in response to the
electromagnetic radiation transmitted by transmitter 30 are
indicative of the locations and orientations of fluoroscope 22 and
catheter 26 relative to the reference frame. Given these locations
and orientations, computer 50 displays, on a display unit 48, the
image of body cavity 28 acquired by fluoroscope 22, with an icon
representing catheter 26 superposed on the image in the true
location and orientation of catheter 26 relative to body cavity
28.
[0006] Because patient 24 may move, relative to platform 34, during
the medical procedure, patient 24 also is provided with a receiver
38 of electromagnetic radiation. Computer 50 computes, from the
signals received from receiver 38 in response to the
electromagnetic radiation transmitted by transmitter 30, the
location and orientation of the body of patient 24 relative to the
reference frame. This is in addition to the computation, by
computer 50, from the signals received from receiver 40, of the
location and orientation of fluoroscope 22 relative to the
reference frame, and in addition to the computation, by computer
50, from the signals received from receiver 32, of the location and
orientation of catheter 26 relative to the reference frame.
Computer 50 records the location and orientation of patient 24 when
the image of body cavity 28 is acquired. If patient 24 does moves,
computer 50 adjusts the joint display of the image and the catheter
icon on display unit 48 to reflect the movement of patient 24. so
that the catheter icon always is displayed in a manner that
reflects the true location and orientation of catheter 26 relative
to body cavity 28.
[0007] As alternatives to receivers 32 and 44, catheter 26 and
patient 24 are provided with respective imageable markers 46 and
44. Computer 50 locates the shadows of markers 46 and 44 in the
image, using standard image processing techniques, and computes,
from the locations of these shadows, the locations and orientations
of catheter 26 and patient 24.
[0008] A representational imaging device 52, equipped with a
receiver 40a of electromagnetic radiation, also is provided, to
acquire a representational image of a portion of the body of
patient 24 that overlaps with the portion of the body of patient 24
that is acquired using fluoroscope 22. Computer 50 computes, from
the signals received from receiver 40a in response to the
electromagnetic radiation transmitted by transmitter 30, the
location and orientation of imaging device 52 relative to the
reference frame. Computer 50 then displays the representational
image, on display unit 48, superposed on the image acquired by
fluoroscope 22, so that a point-of-interest, towards which catheter
26 is to be navigated, can be picked on display unit 48, even prior
to the introduction of catheter 26 into body cavity 28. Improved
methods of effecting this superposition are taught by Gilboa et al.
in PCT application US99/26826, which also is incorporated by
reference for all purposes as if fully set forth herein. Because
computer 50 tracks the movement of both patient 24 and catheter 26,
an icon representing the point-of-interest is displayed on display
unit 48 in a manner that represents the true location of the
point-of-interest in body cavity 28, so that catheter 26 can be
navigated Jo the point-of-interest with reference to the relative
locations, as displayed by display unit 48, of the icon
representing catheter 26 and of the icon representing the
point-of-interest.
[0009] Representational imaging device 52 may be external to the
body of patient 24, as illustrated in FIG. 1A, or internal to the
body of patient 24. The specific example of representational
imaging device 52 that is presented in WO 00/16684 is an
intracardiac ultrasound probe that is used to image and identify
the fossa ovalis of the cardiac septum and one or more of the
openings of pulmonary veins. These points within the heart may be
targets of ablation for treating atrial fibrillation, and so
constitute points-of-interest within the heart (as body cavity 28)
of patient 24. Following the representational imaging of these
targets by intracardiac ultrasound probe 52 and the picking of the
points-of-interest, intracardiac ultrasound probe 52 is withdrawn
and an ablating catheter 26 is navigated towards the
points-of-interest.
[0010] Transmitter 30 is an example of what is called in WO
00/16684 a "locating implement". Receivers 32, 38, 40 and 40a are
examples of what is called in WO 00/16684 "location implements".
Transmitter 30, together with receiver 32, 38, 40 or 40a constitute
what is called in WO 00/16684 a "locating system". In the present
context, the location and the orientation of an object are called
the "disposition" of the object, so what WO 00/16684 calls a
"locating system" is called herein a "disposing system". Similarly,
what WO 00/16684 calls a "locating implement" is called herein a
"disposing implement", and what WO 00/16684 calls a "location
implement" is called herein a "disposition implement". The term
"location system" is used herein to refer, not only to systems that
measure both the location and the orientation of an object, but
also to systems that measure only the location of an object; such a
system includes a locating implement and a location implement. Note
that when multiple disposing systems are used, one disposing
instrument may be shared by all the disposing systems as is the
case with transmitter 30, in which case the shared disposing
instrument defines a common reference frame for all the disposing
systems; or, alternatively, one disposition implement may be shared
by all the disposing systems, in which case the shared disposition
instrument defines a common reference frame for all the disposing
systems. Common examples of disposing systems include
electromagnetic disposing systems, magnetic disposing systems,
acoustic disposing systems and stereopair optical systems.
[0011] One invasive medical procedure for which the prior art
methods are not quite suitable is the deployment of a stent in a
partially blocked coronary artery. This procedure commonly is
performed by injecting a contrast agent into the target coronary
artery tree and then navigating a catheter that bears the stent
towards the target blockage with the help of X-ray angiographic
images acquired in real time by a fluoroscope such as fluoroscope
22. In this case, the points-of-interest are the blockage itself,
and the branches of the coronary artery tree that must be traversed
on the way to the blockage. In principle, the prior art discussed
above can be used to identify the points-of-interest, provided that
these points-of-interest can be picked on the image provided by
representational imaging device 52. For example, representational
imaging device 52 may be a CT scanner: the contrast agent, being
X-ray opaque, shows up in both the projective images acquired using
fluoroscope 22 and the representational CT scan acquired using the
CT scanner. This has the disadvantage of requiring the use of two
imaging modalities, one of which (CT) is not suitable for real-time
imaging. Furthermore, it is relatively difficult to register a CT
image volume with a fluoroscopic image.
[0012] There is thus a widely recognized need for, and it would be
highly advantageous to have, a method, of navigating a probe to a
point-of-interest in a body cavity of a patient, that is based on a
single projective imaging modality.
[0013] A CT scanner produces its representational image volume by
appropriate processing (typically, by backprojection) of a set of
projective images. In principle, then, it should be possible to use
fluoroscope 22 itself as both a projective imager and a
representational imager. Yeung, in U.S. Pat. No. 5,588,033, which
is incorporated by reference for all purposes as if fully set forth
herein, teaches the reconstruction of a binary (two-level) image
volume from a relatively small set of projective radiographic
images. In principle, a similar reconstruction should be possible
using fluoroscopic images acquired at different dispositions
relative to patient 24. In particular, in the stent deployment
discussed above, a binary representational image volume of the
contrast agent in the coronary artery tree would show the portion
of the coronary artery tree that contains the contrast agent at one
of the two display levels (e.g., "1") and the rest of the imaged
portion of the patient's body at the other level (e.g., "0"), and
so would suffice to allow picking of the points-of-interest. In
practice, however, fluoroscope 22 lacks sufficient mechanical
stability to allow accurate reconstruction of even a binary image
volume. Known successful reconstructions of image volumes from 2D
projective images all require very accurate positioning of the
imaging apparatus. Conventional CT scanners include heavy and very
accurate mechanisms for rotating their X-ray sources and detectors
and similarly heavy and accurate sliding mechanisms for moving the
platform on which the patient lies. Yeung uses a stereotactic
localizer frame to provide the required dispositional accuracy.
[0014] There is thus a widely recognized need for, and it would be
highly advantageous to have, a method of transforming a set of
projective images, acquired using a projective imager of limited
mechanical stability, into a representational image volume.
[0015] Returning to the procedure for deploying a stent in a
coronary artery, the fluoroscope commonly is placed in a
disposition relative to the patient that is expected to give the
best projective view of the target coronary artery tree. The
contrast agent is injected into the coronary tree, and the
projective image is acquired and digitized. This projective image
is used as a background "road map" for catheter navigation with the
help of other images subsequently acquired of the target coronary
artery tree, but only if the fluoroscope and the patient remain in
the same relative disposition. Movement of either the fluoroscope
or the patient renders this projective image useless as a road map.
In particular, if the disposition of the fluoroscope relative to
the patient turns out to be suboptimal, or if the patient must be
imaged from several dispositions of the fluoroscope in order to
give an adequate picture of the three-dimensional structure of the
coronary artery tree, then for each new disposition of the
fluoroscope, the contrast agent must be injected anew and a new
road map must be acquired. This exposes both the medical team and
the patient to additional X-radiation, and also exposes the patient
to the danger of liver damage from repeated injections of the
contrast agent.
[0016] There is thus a widely recognized need for, and it would be
highly advantageous to have, a method of acquiring and using X-ray
angiographic road maps without undue danger to either the patient
or the medical team.
SUMMARY OF THE INVENTION
[0017] According to the present invention there is provided a
method of navigating a probe to a target point-of-interest in a
body cavity of a patient, including the steps of: (a) acquiring a
plurality of projective images of at least a portion of the body
cavity, using a projective imaging device, each projective image
being acquired with the projective imaging device in a different
respective disposition relative to a reference frame; (b) for each
projective image, measuring the respective disposition of the
projective imaging device; (c) estimating a location of the target
point-of-interest, relative to the reference frame, from the
protective images, the estimating being based on the measured
dispositions of the projective imaging device; (d) inserting the
probe into the body cavity; (e) measuring a location of the probe
relative to the reference frame; and (f) moving the probe, within
the body cavity, so as to minimize a difference between the
measured location of the probe and the estimated location of the
target point-of-interest.
[0018] According to the present invention there is provided a
navigating system for navigating a probe to a point-of-interest in
a body, cavity of a patient, including: (a) a projective imaging
device for acquiring a plurality of projective images of at least a
portion of the body cavity; (b) a disposing system for measuring,
for each projective image, a respective disposition of the
projective imaging device relative to a reference frame; (c) a
mechanism for estimating a location of the point-of-interest,
relative to the reference frame, from the projective images, the
estimating being based on the measured dispositions of the
projective imaging device; and (d) a locating system for measuring
a location of the probe relative to the reference frame.
[0019] According to the present invention there is provided a
method of acquiring an image volume of a body, including the steps
of: (a) for each of a plurality of nominal dispositions of a
projective imaging device relative to a reference frame: (i)
measuring an actual disposition of the projective imaging device
relative to the reference frame, (ii) if the actual disposition is
not substantially the same as the each nominal disposition, moving
the projective device until the actual disposition is substantially
the same as the each nominal disposition, and (iii) acquiring a
respective projective image of the body, using the projective
imaging device at the each nominal disposition; and (b)
transforming the plurality of projective images into the image
volume.
[0020] According to the present invention there is provided an
imaging system for acquiring an image volume of a body, including:
(a) a projective imaging device for acquiring projective images of
the body; (b) a disposing system for measuring dispositions of the
projective imaging device relative to a reference frame; (c) a
mechanism for moving the projective imaging device among a
plurality of nominal dispositions thereof, with reference to the
measured disposition; and (d) a processor for transforming the
projective images into the image volume, each projective image
having been acquired at a different respective nominal
disposition.
[0021] According to the present invention there is provided a
method of acquiring an image volume of a body, including the steps
of: (a) for each of a plurality of dispositions of a projective
imaging device relative to a reference frame: (i) moving the
imaging device to the disposition, as measured by a disposing
system, and (ii) acquiring a respective projective image of the
body; and (b) transforming the projective images into the image
volume according to the measurements of the dispositions.
[0022] According to the present invention there is provided an
imaging system for acquiring an image volume of a body, including:
(a) a projective imaging device for acquiring projective images of
the body; (b) a disposing system for measuring dispositions of the
projective imaging device relative to a reference frame; and (c) a
processor for transforming the projective images into the image
volume according to the measured dispositions.
[0023] According to the present invention there is provided a
method of acquiring an output image volume of a body, including the
steps of: (a) for each of a plurality of actual dispositions of a
projective imaging device: (i) moving the projecting imaging device
to the each actual disposition, and (ii) acquiring a respective
projective image of the body, using the projective imaging device
at the each actual disposition; (b) based on the projective images,
estimating the actual dispositions; and (c) based on the estimated
dispositions, transforming the projective images into the output
image volume.
[0024] According to the present invention there is provided an
imaging system for acquiring an image volume of a body, including:
(a) a projective imaging device for acquiring a plurality of
projective images of at least a portion of the body at actual
respective dispositions of the projective imaging device; and (b) a
processor for estimating the actual dispositions from the
projective images and for transforming the projective images into
the image volume, the transforming being based on the estimated
dispositions.
[0025] According to the present invention there is provided a
method of navigating a probe in a body cavity of a patient,
including the steps of: (a) acquiring a plurality of images of at
least a portion of the body cavity, using an imaging device, while
measuring, for each image, a respective disposition of the imaging
device relative to a reference frame, each image being acquired at
a different respective disposition; (b) selecting one of the first
images to use as a guide image; and (c) displaying the guide image
along with an icon representative of a disposition of the probe
within the body cavity.
[0026] According to the present invention there is provided a
method of treating a body of a patient, including the steps of: (a)
simultaneously: (i) acquiring a first image of at least a portion
of the body, using an imaging device, (ii) measuring a disposition
of the imaging device relative to a reference frame, and (iii)
measuring a disposition of the body relative to the reference
frame; (b) restoring the imaging device and the body to respective
dispositions that are equivalent to the measured dispositions; and
(c) performing a medical procedure on the body with reference to
the first image after the restoring of the imaging device and of
the body to the equivalent dispositions.
[0027] According to the present invention there is provided a
method of treating a body of a patient, including the steps of: (a)
simultaneously: (i) acquiring a first image of at least a portion
of the body, using an imaging device, (ii) measuring a disposition
of the imaging device relative to a reference frame, and (iii)
measuring a first disposition of the body relative to the reference
frame; (b) measuring a second disposition of the body relative to
the reference frame; and (c) performing a medical procedure on the
body with reference to the first image and with reference to all
three dispositions.
[0028] The patient upon whom the methods of the present invention
are practiced could be either a person or an animal. The term
"medical procedure" as used herein should be construed as including
veterinary procedures.
[0029] The term "probe" as used herein should be construed as
including any device or instrument, such as a catheter, an
endoscope or a surgical tool, that is introduced to the body of a
patient and that is navigated towards a target for the purpose of
performing a medical procedure. The medical procedures that fall
within the scope of the present invention include but are not
limited to diagnostic procedures and therapeutic procedures,
including surgical procedures.
[0030] According to a first aspect of the present invention, a
plurality of projective images of at least a portion of a body
cavity are acquired by a projective imaging device such as
fluoroscope 22 at different respective dispositions relative to a
reference frame, while measuring these dispositions, for example by
using a disposing system. Each projective image includes a point
that corresponds to a target point-of-interest in the body cavity;
these points in the projective images are termed herein
"projections" of the target point-of-interest. A location of the
point-of-interest, relative to the reference frame, is estimated,
preferably by picking the projections of the point-of-interest on
two or more projective images, constructing rays corresponding to
the picked projections, and computing the location, relative to the
reference frame, of the point-of-nearest-mutual-approach of the
rays. The projections may be picked manually. Alternatively, the
projections are picked manually on a first projective image and
automatically on subsequent projective images, for example by using
standard image processing and feature recognition techniques to
track the projection from image to image. Alternatively, the
projective images are displayed successively and repeatedly, along
with an icon that represents a point in space. The coordinates of
the point are varied until the icon substantially coincides with
all the projections. Alternatively, the projective images are
transformed into an image volume, preferably by backprojection, and
the target point-of-merest is picked directly in the image
volume.
[0031] With the location of the target point-of-interest relative
to the reference frame now known, a probe is inserted in the body
cavity. The location of the probe is measured, preferably using a
locating system, and the probe is moved towards the target
point-of-interest.
[0032] Preferably, a contrast agent is introduced to the imaged
portion of the body cavity prior to imaging.
[0033] Preferably, the location of at least one intermediate
point-of-interest, relative to the reference frame, also is
estimated from the projective images, and the probe is moved
towards the target point of interest with reference to a display of
icons that represent the estimated locations of the
points-of-interest and the measured location of the probe. This
display may be from any convenient point of view. In particular,
this display may be from a point of view different from the points
of view from which the projective images were acquired.
[0034] A system for implementing the first aspect of the present
invention includes a projective imaging device for acquiring the
projective images; a disposing system for measuring the disposition
of the projective imaging device relative to the reference frame as
the images are acquired; a mechanism for estimating the location of
the point-of-interest relative to the reference frame, based on the
acquired images; and a locating system for measuring the location
of the probe in the reference frame.
[0035] Preferably, the disposing system includes a disposition
implement associated with the projective imaging device and a
disposing implement associated with the reference frame.
Alternatively, the disposing system includes a disposing implement
associated with the projective imaging device and a disposition
implement associated with the reference frame. Preferably, the
disposing system is an electromagnetic disposing system, a magnetic
disposing system, an acoustic disposing system or a stereopair
optical system.
[0036] Preferably, the locating system includes a location
implement associated with the projective imaging device and a
locating implement associated with the reference frame.
Alternatively, the locating system includes a locating implement
associated with the probe and a location implement associated with
the reference frame. Preferably, the locating system is an
electromagnetic locating system, a magnetic locating system or an
acoustic locating system.
[0037] The accurate transformation of projective images into an
image volume is addressed by a second aspect of the present
invention, intended for use with a relatively mechanically unstable
projective imaging device such as fluoroscope 22.
[0038] According to a first variant of the second aspect of the
present invention, the projective images are transformed into the
image volume, preferably by backprojection, according to respective
nominal dispositions of the projective imaging device relative to a
reference frame. To ensure that the projective imaging device
really is in these nominal dispositions when the projective images
are acquired, the actual dispositions of the projective imaging
device are measured. If an actual disposition differs from the
corresponding nominal disposition, the projective imaging device is
moved until the actual disposition substantially coincides with the
nominal disposition, and only then is the corresponding image
acquired. The projective image device may be moved manually, or
automatically via a feedback loop. The corresponding imaging system
includes the projective imaging device, a disposing system for
measuring the dispositions of the projective imaging device, a
mechanism for moving the projective imaging device to make the
actual dispositions coincide with the nominal dispositions, and a
processor for transforming the projective images into the image
volume.
[0039] According to a second variant of the second aspect of the
present invention, the dispositions of the projective imaging
device are measured explicitly as the projective images are
acquired, and the acquired projective images are transformed into
the image volume according to the measured dispositions, preferably
by backprojection. The corresponding imaging system includes the
projective imaging device, a disposing system for measuring the
dispositions of the projective imaging device, and a processor for
transforming the projective images into the image volume according
to the measured dispositions of the protective imaging device.
[0040] Preferably, the disposing system, of the devices of the
first and second variants of the second aspect of the present
invention, includes a disposition implement associated with the
projective imaging device and a disposing implement associated with
the reference frame. Alternatively, this disposing system includes
a disposing implement associated with the projective imaging device
and a disposition implement associated with the reference frame.
Preferably, this disposing system is an electromagnetic disposing
system, a magnetic disposing system, an acoustic disposing system
or a stereopair optical system.
[0041] According to a third variant of the second aspect of the
present invention, the projective images are transformed into the
image volume, preferably by backprojection, according to respective
actual dispositions of the projective imaging device. Because these
actual dispositions are not known initially with sufficient
accuracy to effect the transformation, these actual dispositions
are estimated from the projective images themselves, and the
transformation then is based on the estimated dispositions.
Preferably, the estimating of the actual dispositions is effected
by transforming the projective images into a working image volume,
on the assumption that the images were acquired at respective
computational dispositions of the projective imaging device; and
then correcting the computational dispositions, on the basis of the
preliminary image volume, to obtain the estimated dispositions.
Preferably, the correcting of the computational dispositions is
effected by, for each computational disposition, computing a
respective synthetic projective image from the working image
volume; comparing the synthetic projective image to the
corresponding acquired protective image; estimating, based on the
comparison, the difference between the computational disposition
and the actual disposition; and adjusting the computational
disposition by subtracting this difference from the computational
disposition. This transforming of the acquired projective images
into the working image volume, and this correcting of the
computational dispositions, are iterated until the estimated
differences between the computational dispositions and the actual
dispositions are negligible.
[0042] The imaging system of the third variant of the second aspect
of the present invention includes the projective imaging device and
a processor for performing the relevant calculations.
[0043] Preferably, in all three variants of the second aspect of
the present invention, the projective imaging device is a
fluoroscope.
[0044] According to a third aspect of the present invention,
directed at navigating a probe within the body cavity of the
patient, a plurality of first images of at least a portion of the
body cavity is acquired at different respective dispositions of the
imaging device relative to a reference frame, while measuring these
dispositions. One of the first images is selected as a guide image,
and the guide image is displayed along with an icon that represents
the true disposition of the probe within the body cavity.
[0045] Preferably, the dispositions of the imaging device are
measured using a disposing system that includes a disposition
implement associated with the imaging device and a disposing system
associated with the reference frame. Alternatively, the
dispositions are measured using a disposing system that includes a
disposing implement associated with the imaging device and a
disposition implement associated with the reference frame.
Preferably, the disposing system is an electromagnetic disposing
system, a magnetic disposing system, an acoustic disposing system
or a stereopair optical system.
[0046] Preferably, a contrast agent is introduced to the portion of
the body that is to be imaged prior to acquiring the plurality of
first images.
[0047] To facilitate the correct display of the icon, the
disposition of the probe relative to the common reference frame
also is measured. Preferably, the disposition of the probe is
measured using a disposing system that includes a disposition
implement associated with the probe and a disposing implement
associated with the reference frame. Alternatively, the disposition
of the probe is measured using a disposing system that includes a
disposing implement associated with the probe and a disposition
implement associated with the reference frame. Preferably, the
disposing system is an electromagnetic disposing system, a magnetic
disposing system or an acoustic disposing system.
[0048] Also according to the third aspect of the present invention,
directed towards invasive medical procedures generally, a first
image of at least a portion of the body of a patient is acquired
while measuring both the disposition of the imaging device and the
disposition of the patient relative to a common reference frame.
Subsequently, both the body of the patient and the imaging device
are restored to dispositions that are equivalent to the
dispositions of the body of the patient and of the imaging device
when the first image was acquired, and a medical procedure is
performed on the body of the patent with reference to the first
image. "Equivalent dispositions", as understood herein, means that
the disposition of the body of the patient relative to the imaging
device (or. equivalently, of the imaging device relative to the
body of the patient) after restoration is the same as when the
first image was acquired.
[0049] Preferably, the dispositions of the body of the patient and
of the imaging device are measured using disposing systems that
include respective disposition implements associated with the
imaging device and with the body of the patient and a common
disposing system associated with the reference frame.
Alternatively, the dispositions are measured using disposing
systems that include respective disposing implements associated
with the imaging device and with the body of the patient and a
common disposition implement associated with the reference frame.
Preferably, the disposing systems are electromagnetic disposing
systems, magnetic disposing systems, acoustic disposing systems or
stereopair optical systems.
[0050] Preferably, a contrast agent is introduced to the portion of
the body that is to be imaged prior to acquiring the first
image.
[0051] Preferably, the medical procedure includes navigating a
probe to a point-of-interest in the targeted portion of the
patient's body, with reference to the first image.
[0052] Preferably, after the body of the patient and the imaging
device are restored to their equivalent dispositions, a second
image is acquired, and the medical procedure is performed with
reference to both images. If the medical procedure includes
navigating a probe to a point-of-interest in the targeted portion
of the patient's body, then the disposition of the probe relative
to the common reference frame also is measured. Preferably, the
disposition of the probe is measured using a disposing system that
includes a disposition implement associated with the probe and a
disposing implement associated with the common reference frame.
Alternatively, the disposition of the probe is measured using a
disposing system that includes a disposing implement associated
with the probe and a disposition implement associated with the
common reference frame. Preferably, the disposing system is an
electromagnetic disposing system, a magnetic disposing system or an
acoustic disposing system.
[0053] Also according to the third aspect of the present invention,
directed towards invasive medical procedures generally, a first
image of at least a portion of the body of a patient is acquired
while measuring both the disposition of the imaging device and the
disposition of the patient relative to a common reference frame.
Subsequently, the disposition of the patient is measured again, in
case the patient has moved since the first disposition
measurements, and a medical procedure is performed on the patient
with reference to both the first image and all three measured
dispositions.
[0054] Preferably, the dispositions of the body of the patient and
of the imaging device are measured using disposing systems that
include respective disposition implements associated with the
imaging device and with the body of the patient and a common
disposing system associated with the reference frame.
Alternatively, the dispositions are measured using disposing
systems that include respective disposing implements associated
with the imaging device and with the body of the patient and a
common disposition implement associated with the reference frame.
Preferably, the disposing systems are electromagnetic disposing
systems, magnetic disposing systems, acoustic disposing systems or
stereopair optical systems.
[0055] Preferably, a contrast agent is introduced to the portion of
the body that is to be imaged prior to acquiring the first
image.
[0056] Preferably, the medical procedure includes navigating a
probe to a point-of-interest in the targeted portion of the
patient's body. This navigation includes measuring the disposition
of the probe relative to the common reference frame. Preferably,
the disposition of the probe is measured using a disposing system
that includes a disposition implement associated with the probe and
a disposing implement associated with the common reference frame.
Alternatively, the disposition of the probe is measured using a
disposing system that includes a disposing implement associated
with the probe and a disposition implement associated with the
common reference frame. Preferably, the disposing system is an
electromagnetic disposing system, a magnetic disposing system or an
acoustic disposing system.
[0057] Under the third aspect of the present invention, the imaging
device may be either a protective imaging device or a
representational imaging device, so that the first image may be
either a projective image or a representational image. The
preferred projective imaging device is a fluoroscope.
[0058] An important difference between prior art computer-aided
surgery and the first and third aspects of the present invention
should be noted. In prior art computer-aided surgery, if a 3D image
volume is used to guide the navigation of a surgical tool within
the patient, then this image volume is acquired prior to surgery.
That guide image volume then must be registered to the frame of
reference of the disposing system that is used to track the
surgical tool. Because the locations of the intermediate points of
interest of the first aspect of the present invention, as well as
the guide image of the third aspect of the present invention, are
acquired with the help of location and disposition systems that
share a common component that is associated with a common reference
frame, no such registration is necessary. For example, in FIG. 1A,
the location system (under the first aspect of the present
invention) or the disposition system (under the third aspect of the
present invention) for catheter 26 includes transmitter 30 and
receiver 32; the disposition system for fluoroscope 22 includes
transmitter 30 and receiver 40; and the disposition system for the
body of patient 24 includes transmitter 30 and receiver 38, with a
common reference frame for all three receivers 32, 38 and 40 being
defined by common transmitter 30.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0060] FIG. 1A (prior art) illustrates a system for intra-body
navigation of a probe towards a point-of-interest in a body cavity
of a patient, with the help of a protective imaging device and a
representational imaging device;
[0061] FIG. 1B shows the system of FIG. 1A modified according to
the present invention by the removal of the representational
imaging device,
[0062] FIG. 2 (prior art) is a more detailed illustration of the
C-mount fluoroscope of FIGS. 1A and 1B;
[0063] FIG. 3 illustrates the near intersection of three rays;
[0064] FIG. 4 shows further details of the mechanical construction
of the fluoroscope of FIG. 1 as modified for the purposes of the
present invention;
[0065] FIG. 5 illustrates the backprojection algorithm of the
present invention;
[0066] FIG. 6 is a flow chart for iteratively estimating actual
dispositions at which the fluoroscope of FIG. 1 acquired a set of
projective images while refining an image volume constructed from
those projective images.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] The present invention is of a method of performing invasive
medical procedures with the help of a single imaging device,
particularly with the help of a single projective imaging device
such as a fluoroscope. Specifically, the present invention can be
used to facilitate intrabody navigation of a probe in a medical
procedure such as stent deployment in a coronary artery.
[0068] The principles and operation of invasive medical procedures
according to the present invention may be better understood with
reference to the drawings and the accompanying description.
[0069] The present invention is explained herein with reference to
stent deployment in a coronary artery as an example of an invasive
medical procedure. This example is merely illustrative, and should
not be construed as limiting the scope of the present invention,
which is applicable to any invasive medical procedure that requires
intra-body navigation of a probe to a point-of-interest.
[0070] Referring again to the drawings, FIG. 1B, which is identical
to FIG. 1A with representational imaging device 52 and receiver
40;* removed, illustrates a system of the present invention. In the
context of the example of deployment of a stent in a coronary
artery, body cavity 28 represents a coronary artery tree and
catheter 26 is a catheter that is used to carry the stent to the
blockage.
[0071] FIG. 2 illustrates C-mount fluoroscope 22 in .more detail,
in schematic cross-section. C-mount fluoroscope 22 is based on a
C-arm 60. At one end of C-arm 60 is an X-ray source 62 that
includes an X-ray tube 63 and a collimator 64. At the other end of
C-arm 60 is an imaging tube 66 that includes an anti-scatter grid
68, an image intensifier 70 and a CCD camera 72. Collimator 64
blocks the X-rays emerging from X-ray tube 63 except at an aperture
76. A cone 74 of X-rays emerges from aperture 76 and impinges on
anti-scatter grid 68 and imaging tube 70. The image thus created in
imaging tube 70 is captured by camera 72. Depending on the spatial
density distribution in an object such as patient 24 that is
traversed by cone 74, each element of the CCD array of camera 72
receives more or less light from imaging tube 70, and the
corresponding pixel of the protective image produced by fluoroscope
22 is correspondingly darker or lighter.
[0072] Each element of the CCD array receives X-rays in a very
narrow subcone of cone 74, corresponding to how much of cone 74 is
subtended by the portion of the image created in imaging tube 70
that is focused onto that element. The attenuation of this X-ray
subcone is proportional to the integrated density of the material
traversed by the subcone between X-ray tube 63 and imaging tube 66.
Conceptually, this subcone can be treated as a geometric ray from
X-ray tube 63 to imaging tube 66. Because the disposition of
fluoroscope 22 is measured by computer 50 with the help of
transmitter 30 and receiver 40, computer 50 knows the true location
of X-ray tube 63 and every CCD element of camera 72 for every image
acquired by fluoroscope 22. Therefore, for every pixel of an image
acquired by fluoroscope 22, computer 50 can form a mathematical
representation of the corresponding ray.
[0073] According to the first aspect of the present invention, as
applied to the deployment of a stent in a coronary artery, a
contrast agent is injected into coronary artery tree 28, and then
several images of coronary artery tree 28 are acquired, using
fluoroscope 22, from several angles. Projections of points of
interest, such as the blockage to be opened by the stent, and such
as branch points of coronary artery tree 28 that must be traversed
on the way to the blockage, appear on these images. These
projections are picked on these images as displayed on display unit
48. FIG. 3 shows, for three projections of one particular
point-of-interest, three corresponding rays 78. In general, rays 78
do not intersect; but there is a point in space, labeled in FIG. 3
by reference numeral 80, such that the sum of the distances from
point 80 to rays 78 is less than the sum of the distances from any
other point to rays 78. Point 80 is referred to herein as the
"point of nearest mutual approach" of rays 78. Given mathematical
representations of rays 78, computer 50 computes the coordinates of
point 80 in the reference frame of transmitter 30. These
coordinates are an estimate of the true spatial location of the
point-of-interest corresponding to rays 78.
[0074] A minimum of two rays 78 are required to define point 80.
Therefore, at least two images of patient 24 must be acquired in
order to estimate the locations of all the points-of-interest.
[0075] The projections of the points-of-interest may be picked
manually. The preferred method of manual picking is to acquire a
set of images at an evenly spaced series of dispositions of
fluoroscope 22 and to display the images successively and
repeatedly on display 48 as a movie. All the images are displayed
in true mutual relative spatial location orientation, on the basis
of the measured dispositions of fluoroscope 22 when the images were
acquired. Along with the images is displayed an icon representing a
point in space. Using an interactive input device such as a mouse
or a trackball, the user changes the coordinates of the point
represented by the icon until the icon coincides with the
projection of the point-of-interest on each of the images. Note
that when this has been accomplished, the coordinates of the point
are approximately the true spatial coordinates of the
point-of-interest, so that the coordinates of the point serve as an
alternative to the point of nearest approach as an estimate of the
true spatial location of the point-of-interest.
[0076] Alternatively, the projections of the points-of-interest are
picked manually on the first acquired image and are tracked
automatically to subsequent images. Standard image processing and
feature recognition techniques are used to track the projections of
each point-of-interest from image to image.
[0077] The true spatial locations of the points-of-interest having
been established, the methods of WO 00/16684 are used to navigate
the stent into position. Note that at this point in the procedure,
it is no longer necessary to display any of the acquired images;
nor is it necessary to acquire further images, with the attendant
exposure of both the medical team and the patient to additional
X-radiation, and with the attendant additional exposure of the
patient to the contrast agent. Instead, only icons representing the
locations of the points-of-interest are displayed on display unit
48, from any convenient point of view, along with an icon
representative of the true location of catheter 26 relative to the
points-of-interest, as determined using transmitter 30 and receiver
32 to measure the disposition of catheter 26.
[0078] Note further that the point of view from which the icons are
displayed need not be, and generally is not, any of the points of
view from which the images were acquired. In the present case of
the points-of-interest being the branch points of coronary artery
tree 28 and the target location in coronary artery tree 28, the set
of points-of-interest contains all the information needed to
navigate catheter 26 to the target location, and the images are
redundant. In this context, the target location in coronary tree 28
is referred to herein as the "target point-of-interest" and the
branches of coronary artery tree 28 are referred to herein as
"intermediate point-of-interest". Nevertheless, if so desired, the
points of interest may be displayed superposed on one of the
images, from the point of view at which that image was
acquired.
[0079] As an alternative to the projection picking and ray
construction discussed above, the projective images acquired using
fluoroscope 22 are transformed into an image volume, and the
points-of-interest are picked in the image volume. How this
transformation is accomplished, despite the relative mechanical
instability of fluoroscope 22, is the subject of the second aspect
of the present invention.
[0080] The mathematics of the tomographic transformation of a set
of projective images into an image volume is well-established,
being described, for example, in A. G. Ramm and A. I. Katsevich,
The Radon Transform and Local Tomography, CRC Press, 1996; in F.
Natterer, The Mathematics of Computerized Tomography, Wiley, 1989;
in G. T. Herman et al., Basic Methods of Tomography and Inverse
Problems, Hildger, 1987; and in G. T. Herman and Attila Kuba,
Discrete Tomography, Birkhauser, 1999. All four of these
publications are incorporated by reference for all purposes as if
fully set forth herein. In particular, Ramm and Katsevich, on pages
276-302, discuss backprojection reconstruction in the case of a
conical X-ray beam geometry such as X-ray cone 74.
[0081] Standard tomographic reconstruction algorithms assume that
the input projective images are acquired at regularly spaced angles
around the target being imaged, or equivalently, in the terminology
used herein, at regularly spaced dispositions of the projective
imaging device. The operator of fluoroscope 22 moves fluoroscope 22
(manually or under the control of computer 50) to successive
nominal dispositions of fluoroscope 22, as indicated by the
controls of fluoroscope 22. At each nominal disposition, the
operator acquires a corresponding projective image. Because of
inaccuracies in the construction of a typical fluoroscope 22, and
because of the inherent mechanical flexibility of components of
fluoroscope 22 such as C-arm 60, the actual disposition of
fluoroscope 22 when each projective image is acquired usually is
not quite identical to the corresponding nominal disposition of
fluoroscope 22. The difference between the actual disposition of
fluoroscope 22 and the corresponding nominal disposition of
fluoroscope 22 is sufficient to introduce artifacts in the
tomographically reconstructed image volume.
[0082] One way to overcome the mechanical instability of
fluoroscope 22 is to ignore the indications of the nominal
disposition of fluoroscope 22 as indicated by the controls of
fluoroscope 22, but instead to use transmitter 30 and receiver 40
to measure the actual disposition of fluoroscope 22. Computer 50
computes this actual disposition from signals received from
receiver 40 in response to electromagnetic radiation transmitted by
transmitter 30. Computer 50 then displays this actual disposition
on display unit 48. The operator then uses the controls of
fluoroscope 22 to move fluoroscope 22 until the actual disposition
displayed on display unit 48 is substantially identical to the
desired nominal disposition. Alternatively, computer 50 itself
moves fluoroscope 22 to the desired nominal disposition, as
illustrated schematically in FIG. 4, which shows further aspects of
the mechanical construction of fluoroscope 22 in (he context of
other components of the system of the present invention as
illustrated in FIG. 1B. As shown in FIG. 4, C-arm 60 is mounted in
a yoke 82. A motor 88 in yoke 82 rotates C-arm 60 about an axis 92
that is perpendicular to the plane of Figure 'I. Yoke 82 itself is
rigidly secured to a shaft 86 that is turned by a motor 90, so that
motor 90 rotates yoke 82 about an axis 94 that is in the plane of
FIG. 4. Motor 90 is secured to a base 84. Just as transmitter 30
and receiver 40 are connected to computer 50 by wires 51, so motors
88 and 90 are connected to computer 50 by wires 51'. As computer 50
receives signals from receiver 40 that are indicative of the actual
disposition of fluoroscope 22, computer 50 computes the actual
disposition of fluoroscope 22 and operates motors 88 and 90 to move
C-arm 60 until the actual disposition of fluoroscope 22, as
measured using transmitter 30 and receiver 40, is substantially the
same as the desired nominal disposition. The cooperative action of
computer 50, transmitter 30, receiver 40 and motors 88 and 90
constitutes a feedback loop for automatically moving fluoroscope 22
to the desired nominal disposition.
[0083] A second way to overcome the mechanical instability of
fluoroscope 22 is to move fluoroscope 22 to the nominal
dispositions for acquiring the projective images, as indicated by
the controls of fluoroscope 22; to measure the actual dispositions
of fluoroscope 22 after fluoroscope 22 has been moved to these
nominal dispositions; and to transform the acquired projective
images into an image volume, not according to the nominal
dispositions, but according to the actual dispositions. This
transformation is done by a modified backprojection algorithm, as
illustrated in FIG. 5. As noted above, for any disposition of
fluoroscope 22, computer 50 can form, for each pixel of the
projective image acquired at that disposition, a mathematical
representations of the rays from X-ray tube 63 to the corresponding
CCD element of camera 72. The space occupied by the imaged portion
of the body of patient 24 is partitioned mathematically into a set
of voxels. Some of these voxels are illustrated in FIG. 5 as
squares 96, it being understood that this illustration is
schematic, as voxels 96 actually are geometrically
three-dimensional, and in fact typically are cubes. Also shown in
FIG. 5 are some rays 98, corresponding to one disposition of
fluoroscope 22, and some other rays 100, corresponding to another
disposition of fluoroscope 22. In general, each voxel 96 is
traversed by many such rays. The value assigned to each voxel 96 in
the image volume is the sum of the pixels that correspond to the
rays that traverse the voxel, weighted by the lengths of the
portions of the rays that are inside the voxel. For example, if the
value of the pixel associated with ray 98a is v.sub.a, if the value
of the pixel associated with ray 100c is v.sub.c, and if the value
associated with ray 100d is v.sub.d, then the value assigned to
voxel 96e is
l.sub.av.sub.a+l.sub.cv.sub.c+l.sub.dv.sub.d+corresponding terms
for all the other rays that traverse voxel 96e.
[0084] A third way to overcome the mechanical instability of
fluoroscope 22 is to estimate the actual dispositions of
fluoroscope 22 from the acquired projective images and to then
transform the projective images into an image volume according to
the estimated actual dispositions instead of according to the
nominal dispositions. FIG. 6 shows a flow chart 110 of how this is
accomplished. The input to flow chart 110 is a set 112 of acquired
projective images and the corresponding nominal dispositions. The
output of flow chart 110 is an image volume 114 that is initialized
in flow chart 110 according to the nominal dispositions and then is
corrected iteratively. In each iteration, acquired projective
images 112 are backprojected into a working version of image volume
114 on the basis of the current estimate of the actual
dispositions, corrections to these dispositions are computed from
the working version of image volume 114 and from acquired
projective images 112, and the corrections are applied to the
current dispositions to obtain a new estimate of the dispositions
to be used in the next iteration.
[0085] In more detail, in box 116, the computational dispositions
to be used in the backprojection are initialized to the nominal
dispositions. In box 118, acquired projective images 112 are
backprojected according to the computational dispositions to obtain
image volume 114. At this stage, image volume 114 is an approximate
rendition of the image volume that would have been obtained if
acquired projective images had been acquired at the computational
dispositions. Therefore, in box 120, image volume 114 is projected
forward according to these dispositions to obtain a set 122 of
synthetic projective images, which are approximations of what
acquired projective images 112 would have been if acquired
projective images 112 had been acquired at the computational
dispositions. In box 124, synthetic projective images 122 are
compared to acquired protective images 112 to obtain estimates of
the differences between the computational dispositions and the
actual dispositions. For example, if a particular synthetic
projective image is rotated relative to the corresponding acquired
projective image, the degree of rotation is an indication of how
much the corresponding computational disposition is rotated
relative to the corresponding actual disposition. In box 126, these
differences are compared to a threshold. If the differences are
sufficiently small, the current version of image volume 114 is
accepted as the final image volume (box 128). Otherwise, the
differences are subtracted from the computational dispositions in
box 130 and steps 118, 120, 124 and 126 are repeated.
[0086] According to the third aspect of the present invention, as
applied to the deployment of a stent in a coronary artery, a
contrast agent is injected into the target coronary artery tree 28,
and then several images of coronary artery tree 28 are acquired,
using fluoroscope 22, from several angles. The best of these images
to use as a road map, for subsequent navigation of catheter 26 that
bears the stent to the target location in coronary artery tree 28,
is selected. This image is referred to herein as the "guide image".
As each image is acquired, the corresponding disposition of
fluoroscope 22 is measured using transmitter 30 and receiver 40,
and the corresponding disposition of patient 24 is measured using
transmitter 30 and receiver 38. There are two ways to navigate
catheter 26 with reference to the guide image.
[0087] The first way to navigate catheter 26 is to restore
fluoroscope 22 to the disposition of fluoroscope 22 at which the
guide image was acquired. New images of coronary artery tree 28 are
acquired using fluoroscope 22 while catheter 26 is inserted into
coronary artery tree 28. The projection of catheter 26 appears on
the newly acquired images as a shadow. The guide image is
superposed on each newly acquired image, so that the instantaneous
location of catheter 26 in coronary artery tree 28 can be seen.
Catheter 26 is directed accordingly towards the target location in
coronary artery tree 28.
[0088] The second way to navigate catheter 26 is to measure the
disposition of catheter 26, using transmitter 30 and receiver 32,"
to display the guide image on display unit 48, and to display an
icon, on display unit 48, that represents the shadow of catheter 26
that would ha-e been projected onto the guide image if the guide
image had been acquired with catheter 26 at the measured
disposition of catheter 26. Navigation of catheter 26 with
reference to the guide image then is conducted similarly to
navigation of catheter 26 with reference to both the guide image
and the newly acquired images according to the first way of
navigating catheter 26.
[0089] The first way of navigating catheter 26 minimizes the
exposure of patient 24 to the contrast agent. The second way of
navigating catheter 26 also minimizes the exposure of patient 24
and the operators of fluoroscope 22 to X-radiation.
[0090] The discussion, to this point, of the third aspect of the
present invention, has assumed that patient 24 does not move
between the acquisition of the guide image and the navigation of
catheter 26. If patient 24 move, then the new disposition of the
body of patient 24, relative to the reference frame defined by
transmitter 30, must be measured, using transmitter 30 and receiver
38, and the navigation of catheter 26 must take into account the
change in the disposition of the body of patient 24.
[0091] Under the first way of navigating catheter 26, fluoroscope
22 is moved until the relative dispositions of fluoroscope 22 and
the body of patient 24 are the same as these dispositions were when
the guide image was acquired. Let D.sub.f.sup.1 represent the
disposition of fluoroscope 22, relative to the reference frame
defined by transmitter 30, when the guide image was acquired. Let
D.sub.b.sup.1 represent the disposition of the body of patient 24,
relative to the reference frame defined by transmitter 30, when the
guide image was acquired. Let D.sub.b.sup.2 represent the present
disposition of the body of patient 24, relative to the reference
frame defined by transmitter 30. D.sub.b.sup.1 and D.sub.b.sup.2
are related by a translation T and a rigid rotation R:
D.sub.b.sup.2=RTD.sub.b.sup.1
[0092] Fluoroscope 22 must be moved to a corresponding new
disposition D.sub.f.sup.2, relative to the reference frame defined
by transmitter 30:
D.sub.f.sup.2=RTD.sub.f.sup.1
[0093] Note that dispositions D.sub.f.sup.1 and D.sub.f.sup.2 are
measured using transmitter 30 and receiver 40, and that
dispositions D.sub.b.sup.1 and D.sub.b.sup.2 are measured using
transmitter 30 and receiver 38.
[0094] Under the second way of navigating catheter 26, the icon
that represents catheter 26, on the display on display unit 48,
must be positioned in that display as though the guide image had
been acquired with fluoroscope 22 at disposition D.sub.f.sup.2
instead of at disposition D.sub.f.sup.1.
[0095] As discussed above in the context of the first aspect of the
present invention, once all the points-of-incrust have been
acquired, a display of these points-of-interest on display unit 48
may be substituted for the guide image. This has the advantage of
allowing navigation of catheter 26 with reference to a display
oriented according to whatever point of view is most convenient. Of
course, if so desired, the display may be from the point of view
from-which the guide image was acquired, and the points-of-interest
may be superposed on the guide image.
[0096] During the acquisition of the points-of-interest, the
disposition of the body of patient 21 is measured using transmitter
30 and receiver 38. If patient 24 moves between the acquisition of
the points-of-interest and the navigation of catheter 26, the
disposition of the body of patient 24 is measured again, and the
mathematical transformations described above are used to adjust the
display of the icons to ensure that the icon representing catheter
26 still is displayed correctly relative to the icons representing
the points-of-interest.
[0097] While the invention has been described with respect to a
limited number of embodiments, it will be appreciated that many
variations, modifications and other applications of the invention
may be made.
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