Note: Descriptions are shown in the official language in which they were submitted.
CA 02954798 2017-01-13
CARDIAC MECHANICAL ASSESSMENT USING ULTRASOUND
This is a divisional of Canadian Patent Application
No. 2,633,231, filed June 2, 2008.
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S.
Provisional Patent Application 60/941,778, filed June 4,
2007.
FIELD OF THE INVENTION
The present invention relates generally to systems and
methods for medical diagnosis, and specifically to systems
and methods for assessing the function of a moving organ,
such as the heart.
BACKGROUND OF THE INVENTION
Methods for three-dimensional (3-D) mapping of the
endocardium (i.e., the inner surfaces of the heart) are
known in the art. For example, U.S. Patent 5,738,096,
describes a method for constructing a map of the heart. An
invasive probe is brought into contact with multiple
locations on the wall of the heart. The position of the
invasive probe is determined for each location, and the
positions are combined to form a structural map of at least
a portion of the heart.
In some systems, such as the one described by U.S.
Patent 5,738,096 cited above, additional physiological
properties, as well as local electrical activity on the
surface of the heart, are also acquired by the catheter. A
corresponding map incorporates the acquired local
information.
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Some systems use hybrid catheters that incorporate
ultrasound imaging and position sensing, as well as
electrical sensing. For example, U.S. Patent 6,690,963,
describes a locating system for determining the location
and orientation of an invasive medical instrument that may
include an ultrasound imaging head, as well as an
electrode.
A catheter with acoustic transducers may be used for
non-contact imaging of the endocardium. For example, U.S.
Patents 6,716,166 and 6,773,402, describe a system for 3-D
mapping and geometrical reconstruction of body cavities,
particularly of the heart.
As another example, U.S. Patent 5,876,345, describes
an ultrasonic catheter for two-dimensional (2-D) imaging or
3-D reconstruction. The ultrasonic catheter includes at
least two ultrasonic arrays having good near and far field
resolutions. The catheter provides an outline of a heart
chamber, in order to assist in interpreting images obtained
by the catheter.
Several methods are known in the art for non-contact
reconstruction of the endocardial surface using
intracardial ultrasonic imaging. For example,
PCT Patent
Publication WO 00/19908, describes a steerable transducer
array for intracardial ultrasonic imaging. The array forms
an ultrasonic beam, which is steered in a desired direction
by an active aperture. U.S. Patent 6,004,269, describes an
acoustic imaging system based on an ultrasound device that
is incorporated into a catheter. The ultrasound device
directs ultrasonic signals toward an internal structure in
the heart to create an ultrasonic image.
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PCT Patent Publication WO 99/55233, describes a method
for delineating a 3-D surface of a patient's heart. A 3-D
mesh model is developed using training data, to serve as an
archetypal shape for a population of patient hearts.
Multiple ultrasound images of the patient's heart are taken
in different image planes. Anatomical locations are
manually identified in each of the images. The mesh model
is rigidly aligned with the images, in respect to the
predefined anatomical locations.
Other methods of contour extraction and 3-D modeling
using ultrasonic images are described in European Patent
Application EP 0961135. As another example, PCT Patent
Publication WO 98/46139, describes a method for combining
Doppler and B-mode ultrasonic image signals into a single
image using a modulated nonlinear mapping function.
U.S. Patent Application Publication 2006/0241445,
describes a method for modeling of an anatomical structure.
A plurality of ultrasonic images of the anatomical
structure are acquired using an ultrasonic sensor, at a
respective plurality of spatial positions of the ultrasonic
sensor. Location and orientation coordinates of the
ultrasonic sensor are measured at each of the plurality of
spatial positions. Contours-of-interest that refer to
features of the anatomical structure are marked in one or
more of the ultrasonic images. A three-dimensional (3-D)
model of the anatomical structure is constructed, based on
the contours-of-interest and on the measured location and
orientation coordinates.
Other patents and patent applications of relevance to
the present invention include U.S. Patent 6,139,500, U.S.
Patent Application Publication 2005/0283075, U.S. Patents
6,447,453 and 6,447,454, U.S. Patent Application
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Publication 2005/014377, U.S. Patent Application
Publication 2005/0137661, and U.S. Patent 6,556,695.
SUMMARY OF THE INVENTION
Embodiments of the present invention that are
described hereinbelow provide improved methods for modeling
and analyzing motion of organs in the body, and
particularly of the heart.
In some of these embodiments, an acoustic imaging
probe, such as an ultrasound catheter within the heart,
captures a sequence of 2-D images as the heart beats.
Contours of a heart chamber are identified, either
automatically or manually, in one of the 2-D images. An
image processor then automatically identifies these
contours in the other images in the sequence. The image
processor may analyze changes in the contours during the
heart cycle in order to determine parameters of motion of
the heart wall, such as local velocity and strain.
Additionally or alternatively, the image processor may
use the contours in segmenting the images and
reconstructing a "4-D" image of the heart, i.e., a 3-D
anatomical image that changes over time, showing the motion
of the heart. The moving
image may be enhanced, by
addition of pseudocolor, for example, to show changes over
time in other physiological parameters, such as local
electrical parameters measured by a catheter inside the
heart.
There is therefore provided, in accordance with an
embodiment of the present invention, a method for
diagnosis, including:
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capturing a sequence of two-dimensional ultrasound
images of a moving organ within a body of a patient;
identifying at least one contour of the organ in a
succession of the images in the sequence; and
processing the at least one identified contour to
generate an output indicative of motion of the organ over
time.
Processing the at least one identified contour may
include computing a displacement of the contour over a
period of cyclical movement of the organ, a velocity vector
of one or more segments of the contour, or a strain in the
organ responsively to a change in length of the contour.
In disclosed embodiments, the moving organ is a heart
of the patient, and processing the at least one identified
contour includes analyzing the motion of a wall of at least
one chamber of the heart over one or more cycles of the
heart. Typically,
capturing the sequence of the two-
dimensional ultrasound images includes inserting a
catheter, including an acoustic transducer and a position
sensor, into the heart, and capturing the two-dimensional
ultrasound images using the transducer while tracking
coordinates of the catheter using the position sensor. In
one embodiment, analyzing the motion of the wall includes
find a location of scar tissue in the wall responsively to
the motion. In another embodiment, analyzing the motion of
the wall includes comparing the motion of two or more
chambers of the heart so as to detect improper
synchronization of the motion of the chambers.
There is also provided, in accordance with an
embodiment of the present invention, a method for
diagnosis, including:
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capturing multiple ultrasound input images of a moving
organ within a body of a patient;
collecting data that are indicative of respective
local values of a physiological parameter at locations on a
surface of the moving organ; and
generating a sequence of three-dimensional images,
responsively to the input images and the collected data,
showing movement of the organ while superimposing an
indication of changes in the local values on the surface
in the three-dimensional images as the organ moves in the
three-dimensional images in the sequence.
In some embodiments, capturing the multiple ultrasound
input images includes capturing two-dimensional ultrasound
images from multiple different positions of an acoustic
transducer, and recording location and orientation
coordinates of the acoustic transducer in the multiple
different positions, and generating the sequence includes
combining the two-dimensional ultrasound images using the
location and orientation coordinates to reconstruct the
three-dimensional images. Typically,
capturing the two-
dimensional ultrasound images includes recording respective
times of capture of the two-dimensional ultrasound images
relative to an annotation point in a cycle of motion of the
organ, and combining the two-dimensional ultrasound images
includes grouping the two-dimensional ultrasound images
according to the respective times of capture in order to
generate the three-dimensional images corresponding to the
respective times in the cycle. In a disclosed embodiment,
the moving organ is a heart of the patient, and capturing
the two-dimensional ultrasound images includes inserting a
catheter, including the acoustic transducer and a position
sensor, into the heart, and capturing the two-dimensional
ultrasound images using the transducer while tracking
coordinates of the catheter using the position sensor.
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Typically, generating the sequence includes coloring
the surface of the moving organ in the three-dimensional
images responsively to the values of physiological
parameter. In a disclosed embodiment, the moving organ is
a heart of the patient, and collecting the data includes
collecting electrical data, and coloring the surface
includes displaying variations in electrical activity of
the heart over an area of a chamber of the heart in the
course of one or more heart cycles.
There is additionally provided, in accordance with an
embodiment of the present invention, diagnostic apparatus,
including:
an acoustic transducer, which is configured to capture
a sequence of two-dimensional ultrasound images of a moving
organ within a body of a patient; and
an image processor, which is configured to identify at
least one contour of the organ in a succession of the
images in the sequence, and to process the at least one
identified contour to generate an output indicative of
motion of the organ over time.
There is further provided, in accordance with an
embodiment of the present invention, diagnostic apparatus,
including:
an acoustic transducer, which is configured to capture
multiple ultrasound input images of a moving organ within a
body of a patient;
an invasive probe, which is configured to collect data
that are indicative of respective local values of a
physiological parameter at locations on a surface of the
moving organ; and
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an image processor which is configured to generate,
responsively to the input images and the collected data, a
sequence of three-dimensional images showing movement of
the organ while superimposing an indication of changes in
the local values on the surface in the three-dimensional
images as the organ moves in the three-dimensional images
in the sequence.
There is further provided, in accordance with an
embodiment of the present invention, a diagnostic apparatus
comprising: an Invasive probe comprising a position sensor
configured to transmit signals used to determine location
and orientation coordinates of a distal end of the probe in
a 3-D coordinate frame of reference and an acoustic
transducer configured to transmit and receive signals used
to determine two-dimensional (2D) ultrasound images,
wherein the acoustic transducer is configured to capture
multiple ultrasound input images of a beating heart within
a body of a patient, wherein the invasive probe is
configured to collect data that are indicative of
respective local values of a physiological parameter at
locations on a surface of the beating heart; and an image
processor which is configured to associate each of the two-
dimensional (2D) ultrasound images with a poine in time
relative to an annotation point in a heart cycle of the
beating heart and a location and orientation coordinate of
the distal end of a catheter at the point in time relative
to the annotation point in time, and create an
electroanatomical map of a chamber of the beating heart
within the 3-D coordinate frame, wherein the image
processor is configured to:
(i) display a video of the sequence of 2D images in
succession to show motion of the beating heart and overlay
the electroanatomical map on the video of the motion of the
beating heart using the location and orientation
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coordinates of the distal end of the catheter at each point
in time relative to the annotation point in time;
(ii) freeze the video to display one of the 2D images
of the sequence;
(iii)identify at least one contour of the beating
heart on the one frozen image;
(iv) find the at least one contour in each of the
other images in the sequence of 2D images;
(v) analyze changes in the at least one contour in
the sequence of 2D images based on the motion of the
beating heart by computing a displacement of the at least
one contour over a period of cyclical movement of the
beating heart;
(vi) generate an output in response to analyzing
changes of the at least one contour;
(vii) display the output on the video of the sequence
of 2D images; and
(viii) superimpose an indication of changes in the
local values on the surface in the three-dimensional images
as the beating heart moves in the three-dimensional images
in the sequence.
The present invention will be more fully understood
from the following detailed description of the embodiments
thereof, taken together with the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic, pictorial illustration of a
system for cardiac mapping and imaging, in accordance with
an embodiment of the present invention;
k'ig. 2 is a schematic side view of the distal end of a
catheter, in accordance witl an embodiment of the present
invention;
Figs. 3 and 4 are schematic representation of
ultrasound images of a heart chamber at different,
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respective points in the heart cycle, showing a moving
contour of the heart chamber in accordance with an
embodiment of the present invention;
Fig. 5 is a flow chart that schematically illustrates
a method for heart tissue characterization, in accordance
with an embodiment of the present invention; and
Fig. 6 is a flow chart that schematically illustrates
a method for cardiac imaging, in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
SYSTEM DESCRIPTION
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Reference is now made to Figs. 1 and 2, which
schematically illustrate a system 20 for imaging and
mapping a heart 22 of a patient 23, in accordance with an
embodiment of the present invention. The system comprises
a catheter 24, which is inserted by a physician 27 into a
chamber of the heart through a vein or artery. Fig. 1 is a
pictorial view of the system as a whole, while Fig. 2 shows
details of the distal end of the catheter.
Catheter 24 is used, as described hereinbelow, to
acquire ultrasound images inside the heart and may, in some
embodiments, acquire other local physiological data, as
well, such as electophysiological data. Catheter 24
typically comprises a handle 26 for operation of the
catheter by the physician. Suitable controls (not shown) on
the handle enable the physician to steer, position and
orient the distal end of the catheter as desired.
Alternatively, the principles of the present invention may
be implemented using images captured by ultrasound probes
of other types, such as a transesophageal probe or a non-
invasive trans-thoracic probe.
System 20 comprises a positioning sub-system that
measures location and orientation coordinates of catheter
24. (Throughout this patent application and in the claims,
the term "location" refers to the spatial coordinates of
the catheter, and the term "orientation" refers to its
angular coordinates. The term "position" refers to the full
positional information of the catheter, comprising both
location and orientation coordinates.)
In one embodiment, the positioning sub-system
comprises a magnetic position tracking system that
determines the location and orientation of catheter 24. The
positioning sub-system generates magnetic fields in a
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predefined working volume its vicinity and senses these
fields at the catheter. For this purpose, the positioning
sub-system typically comprises a set of external radiators,
such as field generating coils 30, which are located in
fixed, known positions external to the patient and generate
electromagnetic fields in the vicinity of heart 22. The
generated fields are sensed by a position sensor 32 inside
catheter 24. In an
alternative embodiment, a radiator,
such as a coil, in the catheter generates electromagnetic
fields, which are received by sensors outside the patient's
body.
Position sensor 32 transmits, in response to the
sensed fields, position-related electrical signals over
cables 40 running through the catheter to a console 34.
Alternatively, the position sensor may transmit signals to
the console over a wireless link. The console comprises a
positioning processor 36, which controls coils 30 and
calculates the location and orientation of the distal end
of catheter 24 based on the signals sent by position sensor
32. Positioning processor 36 typically receives, amplifies,
filters, digitizes, and otherwise processes signals from
catheter 24.
Some position tracking systems that may be used for
this purpose are described, for example, in U.S. Patents
6,690,963, 6,618,612 and 6,332,089, and U.S. Patent
Application Publications 2002/0065455 Al, 2004/0147920 Al
and 2004/0068178 Al. Although the positioning sub-system
shown in Fig. 1 uses magnetic fields, the methods described
below may likewise be implemented using any other suitable
positioning sub-system, such as systems based on electrical
impedance, acoustic or ultrasonic measurements.
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System 20 enables physician 27 to perform a variety of
mapping and imaging procedures, including display and
analysis of two-dimensional (2-D) ultrasound images, as
well as reconstruction of three-dimensional (3-D) images of
target structures, such as chambers of the heart, based on
the 2-D ultrasound images. The system can also register,
overlay and display a parametric map, such as an
electrophysiological information map or an electro-
anatomical map on the ultrasound images, as well as
registering the ultrasound images with a 3-D image acquired
from an external system, such as a computed tomography (CT)
or magnetic resonance imaging (MRI) system. Some of these
aspects of system 20 are described in the above-mentioned
US 2006/0241445, while other novel aspects are described
further hereinbelow.
As shown in Fig. 2, the distal end of catheter 24
comprises an ultrasonic imaging sensor 38, which typically
comprises an array of ultrasonic transducers 40, such as
piezo-electric transducers. Transducers 40
operate as a
phased array, jointly transmitting an acoustic beam.
(Although the transducers are shown arranged in a linear
array configuration, other array configurations can be
used, such as circular or convex configurations.) In one
embodiment, the array transmits a short burst of ultrasound
energy and then switches to a receiving mode for receiving
the ultrasound signals reflected from the surrounding
tissue.
Typically, transducers 40 are driven individually in a
controlled manner in order to steer the ultrasound beam in
a desired direction. By
appropriate timing of the
transducers, the ultrasound beam can produced by sensor 38
be given a concentrically curved wave front, so as to focus
the beam at a given distance from the transducer array.
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Thus, system 20 uses the transducer array as a phased array
and implements a transmit/receive scanning mechanism that
enables the steering and focusing of the ultrasound beam,
so as to produce 2-D ultrasound images.
After receiving the reflected ultrasound echoes,
transducers 30 send electric signals based on the reflected
echoes over cables 42 through catheter 24 to an image
processor 44 in console 34. The image processor transforms
the signals into 2-D ultrasound images, which are typically
sector-shaped. Image
processor 44 typically computes or
receives catheter position information from positioning
processor 36 and uses this information in performing image
reconstruction and analysis functions, which are described
in greater detail below. In some
embodiments, the image
processor uses the ultrasound images and the positional
information to produce a 3-D image or 4-D image sequence of
a target structure, which is presented to the physician as
a 2-D projection on a display 46. The
physician may
interact with the displayed image and with console 34
generally by means of a user interface device 48, such as a
trackball or other pointing device.
In some embodiments, the distal end of catheter 24
also comprises at least one electrode 49 for performing
diagnostic and/or therapeutic functions, such as electro-
physiological mapping and/or radio frequency (RF) ablation.
In one embodiment, electrode 49 is used for sensing local
electrical potentials. The electrical potentials measured
by electrode 49 may be used in mapping the local electrical
activity on the endocardial surface. When electrode 49 is
brought into contact or proximity with a point on the inner
surface of the heart, it measures the local electrical
potential at that point. The measured potentials are
converted into electrical signals and sent through the
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catheter to the image processor for processing and display.
In other embodiments, the local electrical potentials are
obtained from another probe, such as a second catheter (not
shown in the figures), comprising suitable electrodes and a
position sensor, all connected to console 34.
In alternative embodiments, catheter 24 may comprise
sensors in other configurations. For example,
although
electrode 49 is shown as being a single ring electrode, the
catheter may comprise any number of electrodes in any form.
Additionally or alternatively, the catheter may sense other
physiological parameters, such as various tissue
characteristics, temperature and/or blood flow.
Position sensor 32 is typically located within the
distal end of catheter 24, adjacent to electrode 49 and
transducers 40. Typically, the mutual locational and
orientational offsets between the position sensor,
electrode, and transducers are constant. These offsets are
used by positioning processor 36 to derive the coordinates
of ultrasonic sensor 38 and of electrode 49, given the
measured position of position sensor 32. Further
characteristics of the position sensor and its use are
described in the above-mentioned US 2006/0241445.
Typically, both the ultrasound images and the position
measurements are synchronized with the heart cycle, by
gating signal and image capture relative to a body-surface
electrocardiogram (ECG) signal or intra-
cardiac
electrocardiogram. Since features
of the heart change
their shape and position during the heart's periodic
contraction and relaxation, console 34 records the timing
of each image captured by sensor 38 relative to an
annotation point (such as the QRS peak of the ECG) in the
heart cycle, along with the corresponding position
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measurement. Thus, the images may be grouped according to
the different points in the heart cycle at which they were
captured. In some
embodiments, additional measurements
taken by the catheter, such as measurements of electrical
and other tissue characteristics, are also synchronized to
the ECG signal, as well as with the corresponding position
measurements. The results of these additional measurements
may then be overlaid on the reconstructed 3-D ultrasound
image, as described further hereinbelow.
Typically, positioning processor 36 and image
processor 44 comprise one or more general-purpose computer
processors, which are programmed in software to carry out
the functions described herein. The software
may be
downloaded to the computer in electrical form, over a
network, for example, or it may, alternatively or
additionally, be stored on tangible media, such as optical,
magnetic or electronic memory media. The positioning
processor and image processor may be implemented using
separate computers or using a single computer, or may be
integrated with other computing functions of system 20.
Additionally or alternatively, at least some of the
positioning and image processing functions may be performed
using dedicated hardware.
TRACKING AND ANALYSIS OF CONTOURS
Reference is now made to Figs. 3-5, which
schematically illustrate a method for heart tissue
characterization based on ultrasound images, in accordance
with an embodiment of the present invention. Figs. 3 and 4
show 2-D ultrasound images 50 and 52, respectively, of
heart 22, which are used in the method, while Fig. 5 is a
flow chart that presents the steps of the method itself.
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Images 50 and 52 are processed by image processor 44 to
identify contours 54 and to perform other functions that
are described hereinbelow on the basis of these contours.
As noted earlier, images for this sort of processing may be
acquired not only using an ultrasound catheter, but also
using any other suitable type of acoustic imaging system
that is known in the art.
To acquire images 50 and 52, the user (such as
physician 27) moves catheter 24 inside the heart until the
desired point of view is achieved, such as the view shown
in Figs. 3 and 4. The user
then operates system 20 to
capture a "clip," i.e., a sequence of 2-D ultrasound images
at the desired position, at an image capture step 60. The
images show a certain "slice" of a heart chamber and the
surrounding tissue at multiple points in time over the
course of one or more heart cycles. (Typically the clip is
about 2.5 seconds long.)
The user freezes an ultrasound image in the sequence
and draws contour 54 on the 2-D image, at a contour
identification step 62.
Alternatively or additionally,
processor 44 may apply automatic edge detection to locate
the contour. The image is
marked with the point in the
heart cycle at which it was captured. Typically, as noted
earlier, the timing of the image is marked relative to an
annotation point in the electrocardiogram (ECG) signal,
which is captured using skin-surface electrodes and a
suitable monitor (not shown), but any other suitable means
for identifying the annotation point may alternatively be
used. Figs. 3 and 4 show a contour of one chamber of the
heart, but the methods described herein may similarly be
applied to multiple contours of multiple chambers.
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Contour 54 is initially drawn on one of the images in
the sequence, typically (although not necessarily) the
image captured at the annotation point itself. For the
sake of illustration, it will be assumed that image 50 is
the annotation image on which the contour is initially
drawn. After contour 54 has been drawn on image 50, image
processor 44 uses this contour to find the corresponding
contours in all the other images of the image sequence
between successive annotation points, at a contour
propagation step 64. Thus, based on
contour 54 in image
50, the image processor finds the corresponding contour in
image 52. The frame
rate in the video sequence is
typically 30 frames per second, but rates up to 100 frames
per second may enable better estimation of the tissue
characteristics.
In addition to detecting the contours, image processor
44 may calculate velocity vectors, corresponding to the
movement of a contour or contours during the sequence, at a
velocity calculation step 66. To determine
the local
velocity of segments 56 of a contour, for example, the
image processor sweeps a rectangular window over the
selected contour in successive image frames. Any suitable
window size may be used, for example, 5 x 10 pixels. The
processor computes a correlation function between windows
from the successive frames as a function of displacement
between the windows. The movement
in the x and y
directions that maximizes the correlation function gives
the local displacement of the contour in the window in x
and y directions. Knowing the
time difference between
successive frames and the displacement, the local velocity
can be calculated as the quotient of the displacement
divided by the time difference. The velocity vector is the
combination of the velocity components in the x and y
directions.
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Referring to Figs. 3 and 4, it can be seen that the
segments in the central part of contour 54 have velocity
components mainly in the upward direction.
The image processor may also perform strain analysis,
at a local strain calculation step 68. To compute
the
strain along contour 54, the contour is segmented into a
number of segments 56 of known length. In the subsequent
image frame, the same contour is identified and segmented
into the same number of segments. The difference between
the lengths of two corresponding segments from the two
frames divided by the length of the segment in the first
frame gives the strain on the segment.
Further information regarding strain computations of
this sort are presented by Stoylen in a thesis entitled,
"Strain Rate Imaging of the Left Ventricle by Ultrasound,"
Norwegian University of Science and Technology (2001),
which is available at
http://folk.ntnu.no/stoylen/strainrate/thesis_AS.pdf.
Other calculations can also be done on the identified
moving contours. For example, the displacement of contours
and segments of contours during the heart cycle may be
calculated.
Image processor 44 outputs the calculation results, at
an output step 70, typically by showing 2-D or 3-D images
on display 46. The results can
be displayed on the actual
ultrasound images in the video sequence, for example,
showing the identified contours and the calculated
parameters (velocity vectors, strain, etc.) The magnitudes
of a parameter of interest over segments 56 may be shown by
color-coding the segments accordingly.
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The parameters that are derived and output in this
manner may be used in characterizing the tissue, either
automatically by processor 44 or visually by a user of
system 20. Anomalies in the velocity and/or displacement
of certain contour segments can be used, for example, for
scar tissue identification (particularly in combination
with information provided by other imaging modalities, such
as MRI). As another
example, differences in the
instantaneous velocity between contours in different parts
of the heart (such as in different chambers) can be used to
assess the synchronization between the chamber walls, as
well as other diagnostic indicators of the mechanical
functioning of the heart. Some of these indicators may be
combined with electrophysiological diagnostic information,
which may be provided by catheter 24 or by another mapping
catheter within the heart. For example,
some of the
methods for cardiac mechanical and electromechanical
diagnosis that are described in the above-mentioned U.S.
Patent 5,738,096 may also be applied, mutatis mutandis,
using the diagnostic information provided by the moving
contours that are detected in ultrasound images as
described above.
4-D IMAGE SEQUENCES BASED ON CONTOUR MAPPING
Fig. 6 is a flow chart that schematically illustrates
a method for cardiac imaging, in accordance with an
embodiment of the present invention. In this method, the
moving contours provided by sequences of ultrasound images
are combined with electro-anatomical mapping data, such as
the type data produced by the CARTO mapping system
(Biosense Inc., Diamond Bar, California).
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A user, such as physician 27, aims catheter 24 in a
desired direction in heart 22, and captures a clip of 2-D
ultrasound images, at an image capture step 72. The user
operates the system as described above with reference to
Fig. 5 so as to identify contours in all the frames in the
clip. The user then moves the catheter, captures another
clip of images, and identifies new contours if necessary.
Alternatively, the user may move the catheter continually
while acquiring the images. In any case,
as explained
above, each of the ultrasound images is associated with a
certain point in time relative to an annotation point in
the heart cycle and the position of the catheter at which
the image was recorded. Each image is thus marked with the
time of acquisition, relative to the annotation point, and
with the catheter position coordinates at the time of
acquisition.
In addition, for each time slot in the heart cycle, a
corresponding CARTO map is generated, at a mapping step 74.
For example, at a frame rate of 30 frames per second, there
will be maps in time slots of 33 ms. For this purpose, the
user brings electrode 46 on catheter 24 (or an electrode or
electrodes on a separate mapping catheter) into contact
with points on the inner surface of one or more of the
heart chambers. Although steps 72 and 74 are shown in Fig.
6 as occurring separately and sequentially, the order of
these steps may be reversed, or the steps may be
interleaved, without any particular constraints on the
order of acquisition of ultrasound images relative to
acquisition of electrical mapping data.
When the user has finished imaging, mapping and
identifying all the desired contours, image processor 44
produces a moving image of the heart overlaid with an
electro-anatomical CARTO map for every time slot, at an
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image output step 76. The image
processor uses the
position data provided by position sensor 32 in the
catheter in order to align the ultrasound images with the
CARTO data in the same 3-D coordinate frame. Each contour
in the ultrasound images is thus associated with the CARTO
map for the corresponding time slot. The geometrical shape
of the CARTO map may be updated according to the contours,
as described, for example, in the above-mentioned US
2006/0241445, as well as in U.S. Patent Application
Publication 2007/0106146.
To reconstruct 3-D and 4-D images, the 2-D fan images
are grouped by acquisition time (relative to the heart
cycle). Typically,
the images are divided into between
fifteen and thirty time groups in this manner. The images
in each group are then combined, using the location and
orientation coordinates, into a 3-D volume matrix. In
other words, the images are stored in 3-D matrices, with a
corresponding matrix for each time slot. System 20
may
give the user an indication of the amount of data acquired
in each time slot matrix so as to assist the user in
knowing when to terminate data acquisition. To segment the
3-D images, processor 44 may select a seed point inside the
heart chamber that is to be segmented. It then spreads the
chamber volume outward from this seed point in order to
segment the chamber, using the contours that were found at
step 72.
Alternatively, other methods that are known in
the art may be used to reconstruct the surfaces of the
heart chamber. At the conclusion of this stage, for each
time slot there is a segmented CT-like image generated from
the 3-D volume.
Following step 76, processor 44 is able to display the
moving volumes of the heart using 3-D volume-rendering
techniques, with numbers or other visual cues to show the
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electrical activity on the inner heart surface. These 3-D
images can be displayed as a clip, showing the heart motion
and electrical activity in a "four-dimensional" (4-D - 3-D
plus time) display. By
interpolation of the electrical
activity in the CARTO maps, the electrical parameters of
interest may be interpolated over the entire heart wall
surface, and the map of the heart can be colored according
to the parameters. The colors
change and move over the
course of each heart cycle, thereby enabling the user to
visualize the interaction between the electrical and
mechanical activity of the heart. Other parameters, such
as temperature or chemical parameters, may be displayed in
4-D in a similar manner.
Alternatively, upon the user's
command, system 20 may display only the moving contours,
and optionally the calculated mechanical parameters, such
as the velocity vector and strain, that were described
above. Volume calculations can also be performed on the 4-
D images.
The user of system 20 views and analyzes the moving
images in order to identify characteristics of the heart
tissue, at a diagnosis step 78. For example, the user may
identify areas of scar tissue based on their weak
electrical parameters and deviant mechanical behavior. As
another example, the user may use the moving images to
diagnose improper coordination between different chambers
of the heart, as expressed by abnormal timing of mechanical
and/or electrical changes over the course of a heart cycle.
Such abnormalities typically occur, for example, in
congestive heart failure. The user may
then apply the
visual information provided by system 20 in deciding where
to place pacing leads in the heart for purposes of cardiac
resynchronization therapy or to meet other therapeutic
goals.
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Disclosed embodiments include:
1. A method for diagnosis, comprising:
capturing a sequence of two-dimensional ultrasound
images of a moving organ within a body of a patient;
identifying at least one contour of the organ in a
succession of the images in the sequence; and
processing the at least one identified contour to
generate an output indicative of motion of the organ over
time.
2. The method according to embodiment 1, wherein
processing the at least one identified contour comprises
computing a displacement of the contour over a period of
cyclical movement of the organ.
3. The method according to embodiment 1, wherein
processing the at least one identified contour comprises
computing a velocity vector of one or more segments of the
contour.
4. The method according to embodiment 1, wherein
processing the at least one identified contour comprises
computing a strain in the organ responsively to a change in
length of the contour.
5. The method according to embodiment 1, wherein the
moving organ is a heart of the patient, and wherein
processing the at least one identified contour comprises
analyzing the motion of a wall of at least one chamber of
the heart over one or more cycles of the heart.
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6. The method according to embodiment 5, wherein
capturing the sequence of the two-dimensional ultrasound
images comprises inserting a catheter, comprising an
acoustic transducer and a position sensor, into the heart,
and capturing the two-dimensional ultrasound images using
the transducer while tracking coordinates of the catheter
using the position sensor.
7. The method according to embodiment 5, wherein
analyzing the motion of the wall comprises find a location
of scar tissue in the wall responsively to the motion.
8. The method according to embodiment 5, wherein
analyzing the motion of the wall comprises comparing the
motion of two or more chambers of the heart so as to detect
improper synchronization of the motion of the chambers.
9. The method according to embodiment 1, wherein
capturing the sequence of the two-dimensional ultrasound
images comprises capturing the images from multiple
different positions of an acoustic transducer, and wherein
the method comprises reconstructing a sequence of three-
dimensional images showing the motion of the organ based on
the two-dimensional ultrasound images.
10. A method for diagnosis, comprising:
capturing multiple ultrasound input images of a moving
organ within a body of a patient;
collecting data that are indicative of respective
local values of a physiological parameter at locations on a
surface of the moving organ; and
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generating a sequence of three-dimensional images,
responsively to the input images and the collected data,
showing movement of the organ while superimposing an
indication of changes in the local values on the surface
in the three-dimensional images as the organ moves in the
three-dimensional images in the sequence.
11. The method according to embodiment 10, wherein
capturing the multiple ultrasound input images comprises
capturing two-dimensional ultrasound images from multiple
different positions of an acoustic transducer, and
recording location and orientation coordinates of the
acoustic transducer in the multiple different positions,
and wherein generating the sequence comprises combining the
two-dimensional ultrasound images using the location and
orientation coordinates to reconstruct the three-
dimensional images.
12. The method according to embodiment 11, wherein
capturing the two-dimensional ultrasound images comprises
recording respective times of capture of the two-
dimensional ultrasound images relative to an annotation
point in a cycle of motion of the organ, and wherein
combining the two-dimensional ultrasound images comprises
grouping the two-dimensional ultrasound images according to
the respective times of capture in order to generate the
three-dimensional images corresponding to the respective
times in the cycle.
13. The method according to embodiment 12, wherein the
moving organ is a heart of the patient, and wherein
capturing the two-dimensional ultrasound images comprises
inserting a catheter, comprising the acoustic transducer
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and a position sensor, into the heart, and capturing the
two-dimensional ultrasound images using the transducer
while tracking coordinates of the catheter using the
position sensor.
14. The method according to embodiment 10, wherein
generating the sequence comprises coloring the surface of
the moving organ in the three-dimensional images
responsively to the values of physiological parameter.
15. The method according to embodiment 14, wherein the
moving organ is a heart of the patient, and wherein
collecting the data comprises collecting electrical data,
and wherein coloring the surface comprises displaying
variations in electrical activity of the heart over an area
of a chamber of the heart in the course of one or more
heart cycles.
16. Diagnostic apparatus, comprising:
an acoustic transducer, which is configured to capture
a sequence of two-dimensional ultrasound images of a moving
organ within a body of a patient; and
an image processor, which is configured to identify at
least one contour of the organ in a succession of the
images in the sequence, and to process the at least one
identified contour to generate an output indicative of
motion of the organ over time.
17. The apparatus according to embodiment 16, wherein the
image processor is configured to compute at least one
parameter, selected from a group of parameters consisting
of a displacement of the contour over a period of cyclical
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movement of the organ, a velocity vector of one or more
segments of the contour, and a strain in the organ
responsively to a change in length of the contour.
18. The apparatus according to embodiment 16, wherein the
moving organ is a heart of the patient, and wherein the
image processor is configured to analyze the motion of a
wall of at least one chamber of the heart over one or more
cycles of the heart.
19. The apparatus according to embodiment 18, and
comprising a catheter, which contains the acoustic
transducer and a position sensor, and is configured to be
inserted into the heart so as to capture the two-
dimensional ultrasound images using the transducer while
tracking coordinates of the catheter using the position
sensor.
20. The apparatus according to embodiment 18, wherein the
image processor is configured to indicate a location of
scar tissue in the wall responsively to the motion.
21. The apparatus according to embodiment 18, wherein the
image processor is configured to display the motion of two
or more chambers of the heart so as to provide an
indication of improper synchronization of the motion of the
chambers.
22. The apparatus according to embodiment 16, wherein the
acoustic transducer is operable to capture the images from
multiple different positions of an acoustic transducer, and
wherein the image processor is configured to reconstruct a
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sequence of three-dimensional images showing the motion of
the organ based on the two-dimensional ultrasound images.
23. Diagnostic apparatus, comprising:
an acoustic transducer, which is configured to capture
multiple ultrasound input images of a moving organ within a
body of a patient;
an invasive probe, which is configured to collect data
that are indicative of respective local values of a
physiological parameter at locations on a surface of the
moving organ; and
an image processor which is configured to generate,
responsively to the input images and the collected data, a
sequence of three-dimensional images showing movement of
the organ while superimposing an indication of changes in
the local values on the surface in the three-dimensional
images as the organ moves in the three-dimensional images
in the sequence.
24. The apparatus according to embodiment 23, wherein the
ultrasound input images comprise two-dimensional ultrasound
images, which are captured from multiple different
positions of the acoustic transducer, and wherein the image
processor is coupled to receive location and orientation
coordinates of the acoustic transducer in the multiple
different positions, and to combine the two-dimensional
ultrasound images using the location and orientation
coordinates in order to reconstruct the three-dimensional
images.
25. The apparatus according to embodiment 24, wherein the
image processor is configured to record respective times of
capture of the two-dimensional ultrasound images relative
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to an annotation point in a cycle of motion of the organ,
and to group the two-dimensional ultrasound images
according to the respective times of capture in order to
generate the three-dimensional images corresponding to the
respective times in the cycle.
26. The apparatus according to embodiment 25, wherein the
moving organ is a heart of the patient, and wherein the
apparatus comprises a catheter, which comprises the
acoustic transducer and a position sensor and is configured
to be inserted into the heart so as to capture the two-
dimensional ultrasound images using the transducer while
tracking coordinates of the catheter using the position
sensor.
27. The apparatus according to embodiment 26, wherein the
catheter is the invasive probe and is configured to collect
the data from an inner surface of the heart.
28. The apparatus according to embodiment 23, wherein the
image processor is configured to color the surface of the
moving organ in the three-dimensional images responsively
to the values of physiological parameter.
29. The apparatus according to embodiment 28, wherein the
moving organ is a heart of the patient, and wherein the
data comprises electrical data, and wherein the image
processor is configured to color the surface so as to
display variations in electrical activity of the heart over
an area of a chamber of the heart in the course of one or
more heart cycles.
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It will be appreciated that the embodiments described
above are cited by way of example, and that the present
invention is not limited to what has been particularly
shown and described hereinabove. Rather, the scope of the
present invention includes both combinations and
subcombinations of the various features described
hereinabove, as well as variations and modifications
thereof which would occur to persons skilled in the art
upon reading the foregoing description and which are not
disclosed in the prior art.
29
