Note: Descriptions are shown in the official language in which they were submitted.
CA 02475409 2004-07-29
73236-7E
1
DESCRIPTION .
Coronary Tracking Display
This is a divisional of Canadian application,2,073,247
in respect of which national phase was entered :in Canada on
July 6, 1992. ,
Background Of The Invention
1. Field of the Invention
This invention relates to a, coronary tracking
display. More specifically, this invention relates to a
p coronary tracking display which improves .visibility of
details of coronary artery lesions in cineangiography.
2. Description of Related Art
Cineangiography for coronary arterial segments is
~ typically done by means of an x-ray image. An artery is
filled with a contrast material (for example; a large
molecule with iodine in it, such as megluamine d:iatrozoate
(sold under the name Renografin 76) or iohexal (sold under
the name Omnipaque), and its arterial segments are
30 examined. Medical personnel may examine the shape of the
inner wall of the artery and look for space where the
contrast material would be expected to fill, but does not.
CA 02475409 2004-07-29
73236-7E
la
These spaces are called "filling defects°' and commonly
indicate lesions for which a specific treatment may be
desireable.
It is advantageous to collect and display images of
coronary arterial segments for later review by medical
CA 02475409 2004-07-29
JVO 92/09184 PCT/US9. 3439
2
personnel. For example, review of such images may prove
useful in detecting and locating lesions, and thus may
assist in treatment of a patient by interventional
methods. however, one problem which has arisen in the art
is that image quality under conditions imposed by
cineangiography may be poor, making it difficult for
medical personnel to readily recognize critical features.
It may also be advantageous to insert a catheter into
an artery, appraach an arterial segment containing a
l0 lesion, and perform an interventionai therapy on that
lesion. For example, a lesion may be dilated with a
balloon or ablated with a laser. Hecause these treatments
may have adverse effects, it is desireable to identify
which lesions truly require treatment.
Another problem which has arisen in the art is that
it may be difficult to move such a catheter within the
patient°s arterial network. It would be advantageous to
superimpose an image of the catheter on the patient°s
arterial network while moving the catheter. however, the
contrast material may have adverse effects on the patient,
so it is generally not preferred to collect and display
cineangiographic images while moving a catheter.
Summary Of The Invention
The invention provides a method of displaying details
of a coronary artery lesion in a cineangiogram, by
(digitally or analog) adjusting each frame of the
cineangiogram so that the lesion is continually displayed
at a fixed location on a display. As a result, the
remaining cardiac anatomy appears to move, in background,
past a stationary arterial segment, thus making the
displayed arterial segment easier to identify and to
examine by medical personnel. In a preferred embodiment,
cineangiographic image frames are digitized and processed
by a processor and the image frames are digitally shifted
to place the arterial segment in substantially the same
viewing location in each frame.
CA 02475409 2004-07-29
73236-7E
3
In a preferred embodiment, sequential image frames
may be presented to the viewer as a stereoscopic pair, to
produce pseudostereopsis. As a result, the arterial segment
appears to the viewer in foreground, as if it was floating
in front of the remaining cardiac anatomy. Moreover, image
frames may be further processed to aid examination by
medical personnel. The processor may make quantitative
measurements of the cineangiogram and may display results of
those measurements to aid review of the cineangiogram.
Frames may be averaged to reduce quantum noise and to blur
any structure noise; frames may be compared with prior
cineangiograms to increase clarity or contrast. Coordinate
adjustments for a cineangiogram may help guide therapeutic
procedures, or may help enhance other imaging procedures
such {as fluoroscopy.
Thus in a broad aspect the invention provides a
method of displaying a fluoroscopic image, comprising the
steps of capturing said fluoroscopic image at a relatively
low frame rate; and adjusting each frame of said fluoroscopic
image so that a predetermined feature in said fluoroscopic
image is continually displayed at a substantially fixed
location on a display screen.
In another aspect the invention provides a system
for displaying a fluoroscopic image, comprising means for
capturing said fluoroscopic image at a relatively low frame
rate; and means for adjusting each frame of said fluoroscopic
image so that a predetermined feature in said fluoroscopic
image is continually displayed at a substantially fixed
location on a display screen.
CA 02475409 2004-07-29
73236-7E
3a
Brief Description Of The Drawings
Figure 1 shows a drawing of a cineangiographic
system.
Figure 2 shows a block diagram of a digital
processing system for adjusting the image of the lesion in a
cineangiogram.
Figure 3 shows a block diagram of a digital
processing system for producing pseudostereopsis.
Figure 4 shows a block diagram and drawing of a
cineangiographic system being employed to aid in
catheterization.
Description Of The Preferred Embodiment
Figure 1 shows a drawing of a cineangiographic
system.
A cineangiographic system 101 may comprise a
table 102 on which a patient 103 is placed, with an x-ray
generating tube 104 below the table 102 for projecting
x-rays and an x-ray intensifier tube 105 placed above the
table for receiving x-rays. The x-ray intensifier tube 105
may be coupled to a motion-picture camera 106 or
CA 02475409 2004-07-29
!O 92/09184 PCT/US91~ :439
4
television camera 107, which may produce a video image
signal 108 of the patient's heart 109, as is well known in
the art. The video image signal 108 may be stored on a
storage medium such as a videotape 110, and may later be
retrieved and displayed on a video monitor 111 for review
by medical personnel, as is well known in the art.
A film 112 captured by the motion-picture camera 106
may also be displayed by a motion-picture projector 113 on
a projection screen 114. The film image may be directed
20 by the motion-picture projector 113 at an adjustable
mirror 115, which may be disposed to reflect the film
image onto the projection screen 114.
Figure 2 shows a block diagram of a digital
processing system for adjusting the image of the lesion in
a cineangiogram.
In a preferred embodiment, the video image signal 108
may be coupled to a processor system 201, which may
digitize the video image signal 108 and store a digital
signal 202 in a memory 203. The processor system 201 may
then adjust each frame of the cineangiogram so that a
lesion is continually displayed at a fixed location on a
display screen.
In a preferred embodiment, the processor. system 201
may comprise a processor, memory comprising a stored
program, memory comprising data, and input/output devices,
as is well known in the art. Although the operation of
the processor system 201 is given in terms of functions
that it performs, it would be clear to one of ordinary
skill in the art, after perusal of the specification,
drawings and claims herein, that modification and/or
programming of a standard microprocessor to achieve the
functions disclosed herein would be a straightforward task
and would not require undue experimentation.
In a preferred embodiment, the processor system 201
may comprise an ADAC computer made by ADAC Corporation, or
may be a GE DXC image acquisition system made by General
Electric Corporation.
CA 02475409 2004-07-29
~~ 92/09184 PCT/US91/0~
Collectinq Data on Lesion Location
In a preferred embodiment, the processor system 201
may operate interactively with a human operator, as is
well known in the art. First, the processor system 201
5 may retrieve a single frame 204 of the stored digital
signal 202 from memory 203, and may display that frame 204
on an operator's monitor 205. As each frame 204 is
displayed, the cineangiogram will show a motion picture of
the patient's heari_ 109. In this motion picture, an
arterial segment 20f may appear on which there is a lesion
207. However, because of the patient's heartbeat, the
lesion 207 will tend to move about on the screen.
A human operator 208 may examine the operator°s
monitor 205 and may indicate (e. g., with a pointing device
such as a light pen, mouse or trackball) the location in
the frame 204 of the lesion 207. The processor system 201
may receive the indication by the operator 208 and may
store a set of spatial coordinates 209 for the lesion 207
which it associates with the frame 204. The processor
system 201 may then repeat this interactive process for
each frame 204 of the stored digital signal 202. When
complete, the processor system 201 will have a record
stored in memory 203 of movements which the lesion 207
undergoes as a result of the patient°s heartbeat.
zn an alternative preferred embodiment, the processor
system 201 may locate the lesion 207 by edge-detection or
other automatic means. For example, the stored digital
signal 202 may comprise a set of pixels, each of which
represents a measure of light level detected by the
television camera 107. The patient's arterial. network may
have a different light level from other structure. The
processor system 201 may then trace the patient's arterial
network and determine what areas of the digital signal 202
represent arteries and what areas represent other
structure.
CA 02475409 2004-07-29
73236-7E
6
In a preferred embodiment, the technique used by the
processor system 201 for edge-detection rnay comprise a
technique based on an optimum matched filter.
description of a preferred optimum matched filter
technique is given in the Ph.D. thesis of J. Martin Pfaff,
on file with the UCLA Library System. However, it would
be clear to one of ordinary skill in the art, after
perusal of the specification, drawings and claims herein,
that other techniques for edge-detection or for otherwise
locating the lesion 207 would be workable, and~are within
the scope and spirit of the invention.
In one aspect of this alternative preferred
embodiment, the operator 208 may identify the lesion 207
in one frame 204 by the same technique, but the processor
system 201 may determine the location of the lesion 207 in
the succeeding frames 204 automatically. For example, the
processor system 201 may locate the lesion 207 by noting
the distance from the lesion 207 to a reference point 210,
such as a junction of arterial segments, and by locating
the lesion 207 in the succeeding frames 204 by reference
to the reference point 21f.
In another aspect of this alternative preferred
embodiment, the processor system 201 may determine the
location of the lesion 207 by noting a point in the
arterial segment where the arterial segment is much
narrower. In this aspect, the operator 208 may identify
the lesion 207 of interest out of several possible lesions
207 which might be displayed.
Where the cineangiogram is captured on film 112, the
0 operator 208 may examine the projection screen 114 and may
indicate (e.g., with a pointing device such as an
acoustical x-y digitizer) the location on the projection
screen 114 of the lesion 207 in each frame 204 of .the
cineangiogram (prior to adjustment). The processor system
CA 02475409 2004-07-29
''O 92/09184 PCT/US91 s ...439
7
201 may receive the indication by the operator 208 and may
store the set of spatial coordinates 209 for the lesion
207 which it associates with the frame 204. The processor
system 201 may then repeat this interactive process far
each frame 204 of the film 112. When complete, the
processor system 201 will have a record stored in memory
203 of that motion which the lesion 207 undergoes as a
result of the patient's heartbeat.
Further Image Processinct
In a preferred embodiment, the processor system 201
may further process the frames 204, both t.o aid visual
examination by medical personnel and to generate medical
data.
The processor system 201 may compute quantitative
measurements of the cineangiogram. For example, edge
detection and centerline detection allow the processor
system 201 to measure or compute the length, width and
spatial orientation of arterial segments 206, size and
location of lesions 207 or other morphologies of the
arterial segments 206, and relative stenosis. The
processor system 201 may also compute roughness index,
cross-sectional area and thickness of arterial segments
206, by methods which are well known in the art. Hecause
data on lesion 207 location is collected, the processor
system 201 generally need not recompute the location of
the arterial segment 206 in each frame 204, aiding
automated quantitative measurement.
Image enhancement techniques may be applied to the
video image signal 108 and the frames 204 altered so as to
enhance their clarity. For example, the processor system
201 may locate the edges of arterial segments 206, or
other features such as the location and size of lesions
207, and may superimpose them on the video monitor 111
when displaying the frames 204. The processor system 201
may display quantitative measurements as "false color" on
the video monitor 111.
CA 02475409 2004-07-29
~'O 92/09184 PC'f/US91, .,13439
8
In a preferred embodiment, the frames 204 may be
averaged to reduce quantum noise and to blur any structure
noise, either for display or when computing quantitative
measurements of the cineangiogram. In a preferred
embodiment; after adjusting each frame 204 of the
cineangiogram so that the lesion 207 is continually found
at a fixed location, the processor system 201 may average
the adjusted frames 204 and compute quantitative
measurements on the average. The average may be over a
cardiac cycle of about thirty frames 204. In an
alternative preferred embodiment, the processor system 201
may compute quantitative measurements for each frame 204
and average the quantitative measurements over a cardiac
cycle.
In a preferred embodiment, the frames 204. may also be
processed to increase contrast, either for display or when
computing quantitative measurements of the cineangiogram.
In a preferred embodiment, these steps may be performed:
(1) A first cineangiogram may be taken, with
contrast material present, and each frame 204 adjusted
based on the set of spatial coordinates 209 which are
collected for the lesion 207.
(2) A second cineangiogram is~ taken, this time
without contrast material present, and each frame 204
adjusted based on the set of spatial coordinates 209
collected for the lesion 207 in the first cineangiogram.
(3) Each frame 204 of the second cineangiogram is
subtracted, after adjustment, from a corresponding frame
204 of the first cineangiogram, or from a corresponding
frame 204 of a third cineangiogram taken with contrast
material present. Alternatively, the frames 204 of the
second cineangiogram may be averaged, after adjustment,
over a cardiac cycle, and the average subtracted from
every frame 204 of the first cineangiogram.
It would be clear to one of ordinary skill in the
art, after perusal of the specification, drawings and
claims herein, that other and further signal processing
CA 02475409 2004-07-29
J 92/09184 PCT/L~S91 /0 .~9
9
may be performed on the stored digital signal 202, such as
filtering, noise-removal and other related techniques.
Such other and further signal processing would be
workable, and is within the scope and spirit of the
invention.
Displaying the Lesion
The processor system 201 may then display the stored
digital signal 202 on the video monitor 111 for review by
medical personnel. First, the processor system 201 may
retrieve a single frame 204 from memory 203, and note the
spatial coordinates 209 of the lesion 207. The processor
system 201 may then adjust that frame 204 to place the
lesion 207 in a specified location (e. g., a position near
the center of the screen). Alternatively, the processor
system 201 may adjust each frame 204 except the first to
place the lesion 207 in the same location as in the first
frame 204. As a result, the lesion 207 appears in the
same location in each screen, and the remaining cardiac
anatomy appears to move, in background, past a stationary
arterial segment.
The processor system 201 may also display the
cineangiogram, as captured on film 112, on the projection
screen 114. The processor system 201 may be coupled to
the mirror 115 and may continually adjust thE~ position of
the mirror 115 so as to continually adjust the reflection
of the film image onto the projection screen 114. In
particular, the processor system 201 may adjust the
position of the mirror 115 so that the lesion 207 appears
in the same location on the projection screen 114 in each
frame of the film 112, in like manner as if a digital
frame image had been adjusted so that the lesion 207
appears in the same location in each frame 204.
Pseudostereogsis
Figure 3 shows a block diagram of a digital
processing system for producing pseudostereopsis.
CA 02475409 2004-07-29
1V0 92/0918A PCT/US9r, x8439
In a preferred embodiment, the processor system 201
may present a pair of sequential frames 204 to medical
personnel as a stereoscopic pair, to produce
pseudostereopsis. An odd frame 301 is displayed on a left
5 half 302 of a stereoscopic display 303, while an even
frame 304 is displayed on a right half 305 of the
stereoscopic display 303. When the stereoscopic display
303 is viewed with appropriate stereoscopic Eaquipment, a
three-dimensional image will appear, as is well known in
10 the art. As a result, the arterial segment appears to the
viewer in foreground, as if it was floating in front of
the remaining cardiac anatomy.
Aid in Catheterizat:ion
Figure 4 shows a block diagram and drawing of a
cineangiographic system being employed to aid in
catheterization.
In a preferred embodiment, a catheter patient 401 may
be catheterized with a catheter 402 which is inserted into
one of the patient°s arteries (typically the femoral
artery), as is well known in the art. In a preferred
embodiment, the catheter patient 401 may be positioned on
a fluoroscope 403, which generates an x-ray image 404 of
the catheter 402. The x-ray image 404 may then be
superimposed on a frame 204 retrieved from memory 203 by
the processor system 201, to form a composite image 405.
The composite image 405 may then be adjusted so that the
catheter remains in the same location in the image.
For example, the processor system 201 may simply
"play back" the set of coordinate adjustments it made for
the cineangiogram, applying those same coordinate
adjustments to the x-ray image 404 of the catheter 402.
In this aspect of the invention, movement of the image
which is due to the patientas heartbeat may be essentially
eliminated, so that medical personnel performing the
catheterization may determine routing of the catheter in
the patient's arterial network.
CA 02475409 2004-07-29
' ~ 92/09184 PCT/US91/~ .9
11
In like manner, coordinate adjustments recorded for
the cineangiogram may help guide other therapeutic
procedures, such as balloon angioplasty, laser
angioplasty, atherectomy, stem insertion, thrombectomy,
intravascular ultrasound, radiation therapy and
pharmacologic agent delivery. In general, when invading
the body with a moving object, the progress of that object
may be viewed by means of images which are adjusted by the
techniques described herein, so that progress of the
moving object may be measured with reference to a
relatively fixed map of the patient's body. In a
preferred embodiment, these steps may be performed:
(1) A first cineangiogram may be taken, with
contrast material present, and each frame 204 adjusted
based on the set of spatial coordinates 209 which are
collected for the lesion 207. Image enhancement
techniques may be applied to enhance the clarity of the
position of the arterial segment 206 and the lesion 207,
( 2 ) A therapeutic process may be performed with a
live second cineangiogram, this time without contrast
material present. It may be quite difficult to see the
arterial segment 206 or the lesion 207 in the second
cineangiogram, so the results of image enhancement from
the first cineangiogram are used to identify them. In a
preferred embodiment, each frame 204 of the second
cineangiogram may be adjusted based on the set of spatial
coordinates 209 collected during the first cineangiogram.
In a preferred embodiment, the patient's electrocardiogram
may be used to synchronize the spatial coordinates 209
from the first cineangiogram with the frames 204 in the
second cineangiogram. In a preferred embodiment, the
processor system 201 may indicate the edges of arterial
segments 206, or other features such as the location and
size of lesions 207, and may superimpose them on the video
monitor 111 when displaying the frames 204, as a "roadmap"
for the therapeutic process.
CA 02475409 2004-07-29
WO 92/09184 PCT/U5. 08439
12
In a preferred embodiment, steps (1) and (2) may be
alternated in sequence, so that a first cineangiogram is
taken, then the therapeutic process is advanced some using
the results of image enhancement, then another first
cineangiogram is taken, then the therapeutic process is
advanced some more using the results of further image
enhancement, and so on.
other Medical Imag,ina Apglications
It would be clear to one of ordinary skill in the
art, after perusal of the specification, drawings and
claims herein, that the techniques described herein for
cineangiograms may also be applied to fluoroscopy. In the
art of fluoroscopy,- an x-ray generating tube (like the x
ray generating tube 104 of the cineangiographic system
101) may be disposed for projecting x-rays and an x-ray
intensifier tube (like the x-ray intensifier tube 105 of
the cineangiographic system 101) may be disposed for
receiving x-rays. The x-ray intensifier tube 105 may be
coupled to a display (like the video monitor 111 of the
cineangiographic system 101) for immediate display of an
x-ray image of the patient 103.
One problem which has arisen in the art of
fluoroscopy is that excessive exposure to x-rays can put
both the patient 103 and any nearby medical personnel
(such as those viewing the x-ray image) at risk of
radiation damage. One solution.has been to generate a
sequence of relatively still x-ray images, each using only
relatively short bursts of x-rays, at a display rate which
gives the illusion of a continuous motion picture, i.e.,
an x-ray movie similar to a cineangiogram. It would be
advantageous to reduce exposure to x-rays, e.g., by
reducing the number of frames per second which are
generated and displayed (°'frame rate°~). However, because
of the patient's heartbeat, this has the effect of
producing an x-ray image which is jumpy and difficult to
view.
CA 02475409 2004-07-29
PCT/US91 /0;
' 1 92!09184
13
Each frame of the fluoroscopic x-ray image may be
adjusted by the techniques shown herein, so that an
identified feature (e.g. an arterial segment or lesion) is
continually displayed at a fixed location on the display
screen. Because the identified feature does not move
about on the screen, jumpiness which might be induced by
a lowered frame rate is ameliorated and the image is of
acceptable quality. Accordingly, the frame rate may be
reduced from about 30 frames per second to about 3 frames
per second or fewer, while maintaining acceptable
visualization of the arterial segment or lesion.
It would be clear to one of ordinary skill in the
art, after perusal of the specification, drawings and
claims herein, that the techniques described herein for
cineangiograms may also be applied to other medical
imaging applications, including imaging applications which
use imaging signals other than x-rays. For example, the
techniques described herein may also be applied to
echocardiography (of several types, such as exercise,
transesophageal, transthoracic, intravascular ultrasound),
ultrafast computed tomography, cine magnetic resonance
imaging, and single-photon emission computed tomography.
In general, a sequence of images comprising a moving
feature may be adjusted by the techniques described herein
to continually maintain the moving feature at a relatively
fixed location in the image, and the adjusted image may be
used by personnel or processes which find advantage to
looking to a relatively fixed location for the moving
feature.
Alternative Embodiments
While preferred embodiments are disclosed herein,
many variations are possible which remain within the
concept and scope of the invention, and these variations
would become clear to one of ordinary skill in the art
after perusal of the specification,. drawings and claims
herein.
