U.S. patent application number 10/696608 was filed with the patent office on 2005-05-05 for image plane stabilization for medical imaging.
This patent application is currently assigned to Siemens Medical Solutions USA, Inc.. Invention is credited to Chomas, James E., Sumanaweera, Thilaka S., Ustuner, Kutay F..
Application Number | 20050096538 10/696608 |
Document ID | / |
Family ID | 34550148 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050096538 |
Kind Code |
A1 |
Chomas, James E. ; et
al. |
May 5, 2005 |
Image plane stabilization for medical imaging
Abstract
A medical imaging system automatically acquires two-dimensional
images representing a user-defined region of interest despite
motion. The plane of acquisition is updated or altered adaptively
as a function of detected motion. The user-designated region of
interest is then continually scanned due to the alteration in scan
plane position. A multi-dimensional array is used to stabilize
imaging of a region of interest in a three-dimensional volume. The
user defines a region of interest for two-dimensional imaging.
Motion is then detected. The position of a scan plane used to
generate a subsequent two-dimensional image is then oriented as a
function of the detected motion within the three-dimensional
volume. By repeating the motion determination and adaptive
alteration of the scan plane position, real time imaging of a same
region of interest is provided while minimizing the region of
interest fading into or out of the sequence of images.
Inventors: |
Chomas, James E.; (San
Francisco, CA) ; Ustuner, Kutay F.; (Mountain View,
CA) ; Sumanaweera, Thilaka S.; (Los Altos,
CA) |
Correspondence
Address: |
Siemens Corporation
Intellectual Property Department
170 Wood Avenue South
Iselin
NJ
08830
US
|
Assignee: |
Siemens Medical Solutions USA,
Inc.
|
Family ID: |
34550148 |
Appl. No.: |
10/696608 |
Filed: |
October 29, 2003 |
Current U.S.
Class: |
600/437 |
Current CPC
Class: |
G01S 15/8979 20130101;
A61B 8/5276 20130101; G01S 7/52077 20130101; G01S 7/52088 20130101;
A61B 8/5284 20130101; A61B 8/469 20130101; G01S 15/8925 20130101;
G01S 7/52085 20130101; G01S 15/8993 20130101; A61B 8/543 20130101;
A61B 8/14 20130101; A61B 8/483 20130101 |
Class at
Publication: |
600/437 |
International
Class: |
A61B 008/00 |
Claims
I claim:
1. A method for stabilizing an image plane in medical imaging, the
method comprising: (a) tracking motion within a region; and (b)
automatically altering an acquisition scan plane position relative
to a transducer as a function of the motion.
2. The method of claim 1 wherein (a) comprises performing one of a
cross-correlation and a sum of absolute differences.
3. The method of claim 1 wherein (a) comprises comparing data from
a first acquisition with data from a second acquisition.
4. The method of claim 1 wherein (b) comprises translating and
rotating an acquisition scan plane to the acquisition scan plane
position.
5. The method of claim 1 further comprising: (c) scanning the
region with ultrasound energy; (d) receiving input designating a
region of interest within the region; wherein (b) comprises
maintaining the acquisition scan plane position at the region of
interest over time.
6. The method of claim 1 wherein (a) comprises tracking the motion
within the region, the region being a three-dimensional volume, and
wherein (b) comprises altering the acquisition scan plane position
relative to the transducer, the transducer being a
multi-dimensional array of elements, the alteration maintaining an
acquisition scan plane at a region of interest within the
three-dimensional volume over time.
7. The method of claim 6 further comprising: (c) electronically
steering acoustic energy across the acquisition scan plane; wherein
(a), (b) and (c) are repeated.
8. The method of claim 6 wherein (a) comprises transmitting
acoustic energy to at least three sub-regions of the
three-dimensional volume without acquiring data for the entire
three-dimensional volume.
9. The method of claim 8 further comprising: (c) scanning a
representative sample of the entire three-dimensional volume;
wherein (a) comprises comparing data responsive to the acoustic
energy transmitted to the at least three sub-regions with data
responsive to the representative sample.
10. The method of claim 8 wherein (a) comprises: (a1) transmitting
at least three grouped sets of beams spaced apart within the
three-dimensional volume; (a2) determining a direction and a
magnitude of motion from data responsive to the at least three
grouped sets of beams for each of the at least three grouped sets
of beams; wherein (b) comprises altering the acquisition scan plane
position as a function of the at least three directions and at
least three magnitudes.
11. The method of claim 1 wherein (b) comprises adaptively altering
the acquisition scan plane position in response to the motion;
further comprising: (c) repetitively scanning the adaptively
positioned acquisition scan planes; and (d) generating
two-dimensional images responsive to (c).
12. The method of claim 11 further comprising: (e) shifting the
two-dimensional images as a function of an initial position of the
region of interest.
13. The method of claim 1 further comprising: (c) identifying at
least one feature within the region; wherein (a) comprises tracking
motion of the at least one feature.
14. The method of claim 1 wherein (a) comprises tracking one of
speckle and a spatial gradient.
15. The method of claim 1 further comprising: (c) adjusting a
tracking parameter for (a) as a function of a position of a
tracking location within the region.
16. A method for stabilizing a scan plane within a volume in
medical diagnostic ultrasound imaging, the method comprising: (a)
identifying a region of interest; (b) acquiring data representing
at least portions of a three-dimensional volume positioned at least
partly around the region of interest; (c) acquiring data
representing sub-volumes of the three-dimensional volume, (c) using
fewer scan lines than (b); (d) comparing the data representing the
sub-volumes with the data representing at least the portions of the
three-dimensional volume; (e) detecting motion as a function of
(d); (f) positioning a two-dimensional scan plane within the
three-dimensional volume as a function of the region of interest
and the detected motion; and (g) acquiring a-two-dimensional image
responsive to the two-dimensional scan plane.
17. The method of claim 16 further comprising: (h) repeating (c),
(d), (e), (f) and (g) over time such that the two-dimensional scan
plane is adaptively positioned through the region of interest over
time.
18. The method of claim 16 wherein (b) comprises acquiring data
representing an entire spatial extent of the three-dimensional
volume, the entire spatial extent being based on an area of a
two-dimensional transducer array used for (b), (c) and (g), wherein
(c) comprises acquiring the data representing sub-volumes of the
three-dimensional volume, the sub-volumes together being
substantially less than the three-dimensional volume.
19. A method for stabilizing imaging within a volume in medical
diagnostic ultrasound imaging, the method comprising: (a)
repetitively scanning a two-dimensional area with a
multi-dimensional transducer array; (b) repetitively detecting
motion within a volume including the two-dimensional area; and (c)
adaptively re-positioning the two-dimensional area within the
volume as a function of the detected motion.
20. A system for stabilizing a scan plane within a volume in
medical imaging, the system comprising: a multi-dimensional
transducer array; a beamformer controller operative to control a
position of a data acquisition scan plane relative to the
multi-dimensional transducer array; a beamformer connected with the
multi-dimensional transducer array, the beamformer responsive to
the beamformer controller and operative to acquire data
representing tissue at the data acquisition scan plane; and a
processor operable to detect motion within a volume; wherein the
beamformer controller is operable to alter the position of the data
acquisition scan plane in response to the detected motion.
21. The system of claim 20 wherein the multi-dimensional transducer
array comprises a two-dimensional transducer array.
22. The system of claim 20 further comprising: a user interface
connected with the processor, the user interface operable to
receive input indicating a region of interest; and a display
operable to display a sequence of two-dimensional images of the
region of interest, the two-dimensional images responsive to the
data acquisition scan plane.
23. The method of claim 1 further comprising: (c) obtaining data
for motion tracking in response to different acquisition parameters
than used for imaging.
24. The method of claim 1 wherein (b) comprises automatically
altering an acquisition volume position relative to a transducer as
a function of the motion.
Description
BACKGROUND
[0001] The present invention relates to image stabilization in
medical imaging. An imaging position is stabilized with respect to
a region of interest as images are acquired over time.
[0002] In medical diagnostic ultrasound imaging, a transducer is
positioned adjacent to a patient. The sonographer attempts to
maintain the transducer in a given position relative to a region of
interest within the patient. Temporal variations in the transducer
position due to movements by the sonographer, movements by the
patient, breathing motion, heart motion or other sources of motion
cause the transducer to move relative to the patient. The scan
plane is typically fixed at least in the elevation dimension with
respect to the transducer. The undesired or unintended motion
results in scanning different tissue within the patient.
[0003] Images may be stabilized within the scan plane. Motion
between subsequent images in a sequence of images is tracked. The
acquired image data is then adjusted or shifted along the azimuth
or range dimensions so that a region of interest is maintained at
the same location on the display. Other processes, such as contrast
agent quantification, use motion tracking to reduce motion
artifacts. Previously acquired data is processed or shifted as a
function of the motion to reduce the artifacts. However, some
motion artifacts may remain despite shifts in data. The shifted
data may not optimally represent the region of interest. To provide
the maximum versatility, a large amount of unused image information
is acquired and stored for allowing shifts. Acquiring lots of
ultrasound information may reduce frame rates.
[0004] Motion tracking is also used in three-dimensional and
extended field of view imaging. A plurality of two-dimensional
scans are performed in different positions within a same plane for
extended field of view imaging. The motion between the various
acquired images is determined for assembling the images together in
an extended field of view. Similarly for three-dimensional imaging,
a plurality of two-dimensional images are acquired for a plurality
of scan planes within a three-dimensional volume. Motion tracking
is performed using ultrasound data, motion sensors on the
transducer or other techniques for determining the relative
positions of the scan planes. An image representing
three-dimensional space is then rendered from the acquired sets of
ultrasound data. However, multiple images or sets of data are
acquired to form the extended field of view or three-dimensional
representation.
[0005] Another motion adaptive process is disclosed in U.S. Pat.
No. 5,873,830. An amount of motion between different images is
detected. Where motion is not detected or minimal, the beamformer
is configured to increase spatial resolution, such as by increasing
line density or the number of transmit beams. Where motion is
detected, the frame rate is increased by decreasing the line
density or number of beams. However, changing density or number of
beams as a function of detected motion may still result in desired
tissue fading in or fading out of the image scan plane due to the
motion.
BRIEF SUMMARY
[0006] By way of introduction, the preferred embodiments described
below includes methods and systems for stabilizing a scan plane in
medical imaging. A medical imaging system automatically acquires
two-dimensional images representing a user-defined region of
interest despite motion. The plane of acquisition is updated or
altered adaptively as a function of detected motion. The
user-designated region of interest is then continually scanned due
to the alteration in scan plane position.
[0007] In one embodiment, a multi-dimensional array is used to
stabilize imaging of a region of interest in a three-dimensional
volume. The user defines a region of interest for two-dimensional
imaging. Motion is then detected for six or other number of degrees
of freedom, such as translation along each of three dimensions and
rotation about each of those three dimensions. The position of a
scan plane used to generate a subsequent two-dimensional image is
then oriented as a function of the detected motion within the
three-dimensional volume. The scan plane is positioned such that
the region of interest designated by the user is within the scan
plane. By repeating the motion determination and adaptive
alteration of the scan plane position, real time imaging of a same
region of interest is provided while minimizing the region of
interest fading into or out of the sequence of images.
[0008] In a first aspect, a method for stabilizing an image plane
in medical imaging is provided. Motion is tracked within a region.
An acquisition scan plane position is automatically altered
relative to the transducer as a function of the motion.
[0009] In a second aspect, a method for stabilizing a scan plane
within a volume in medical diagnostic ultrasound imaging is
provided. A region of interest is identified. Data representing at
least portions of a three-dimensional volume positioned at least
partially around the region of interest is acquired. Data
representing sub-volumes of the three-dimensional volume is
acquired using fewer scan lines. The data representing the
sub-volumes is compared with the data representing the portions of
the three-dimensional volume. Motion is detected as a function of
the comparison. A two-dimensional scan plane is positioned within
the three-dimensional volume as a function of the region of
interest and the detected motion. A two-dimensional image is then
acquired using the positioned two-dimensional scan plane.
[0010] In a third aspect, a method for stabilizing imaging within a
volume in medical diagnostic ultrasound imaging is provided. A
two-dimensional area is repetitively scanned with a
multi-dimensional transducer array. Motion within a volume that
includes the two-dimensional area is repetitively detected. The
two-dimensional area is adaptively repositioned within the volume
as a function of the detected motion.
[0011] In a fourth aspect, a system for stabilizing a scan plane
within a volume in medical imaging is provided. A multi-dimensional
transducer array connects with a beamformer. The beamformer is
responsive to a beamformer controller and is operable to acquire
data representing tissue within a data acquisition scan plane. The
beamformer controller is operable to control a position of the data
acquisition scan plane relative to the multi-dimensional transducer
array. A processor is operable to detect motion within a volume.
The beamformer controller is operable to alter the position of the
data acquisition scan plane in response to the detected motion.
[0012] The present invention is defined by the following claims,
and nothing in this section should be taken as a limitation on
those claims. Further aspects and advantages of the invention are
discussed below in conjunction with the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The components and the figures are not necessarily to scale,
emphasis instead being placed upon illustrating the principles of
the invention. Moreover, in the figures, like reference numerals
designate corresponding parts throughout the different views.
[0014] FIG. 1 is a block diagram of one embodiment of a system for
stabilizing a scan plane in medical imaging;
[0015] FIG. 2 is a flow chart diagram of a method for stabilizing
an image plane in medical imaging in one embodiment;
[0016] FIGS. 3A-3C are graphical representations of one embodiment
for implementing the method of FIG. 2 for two-dimensional motion
tracking; and
[0017] FIGS. 4A-4C are graphical representations representing
another embodiment of FIG. 2 for three-dimensional motion
tracking.
DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED
EMBODIMENTS
[0018] Image movement due to respiratory motion, patient motion,
sonographer motion or other undesirable motions leading to a tissue
of interest moving into and/or out of a sequence of images is
avoided. By tracking a position of a tissue of interest, subsequent
acquisitions are aligned to insonnify the tissue, resulting in a
steady or more stable maintenance of the image plane relative to
the tissue of interest. In addition to ease of use and general
aesthetic desirability, quantification is made more stable and
consistent. Diagnosis may be improved since each image in the
sequence is more likely to represent the tissue of interest. Moving
tissues, such as associated with the fetus or cardiology imaging
may be more accurately monitored by maintaining a scan plane
relative to the moving tissue despite the tissue movement.
Perfusion measurements, such as associated with contrast agent
enhancement applications, may be improved.
[0019] FIG. 1 shows one embodiment of a medical imaging system 10
for stabilizing a scan plane within a region or volume. The system
10 includes a transducer 12, a beamformer 14, a beamformer
controller 16, a processor 18, an image processor 20, a display 22
and a user interface 24. Additional, different or fewer components
may be provided, such as not having the user interface 24, image
processor 20 or display 22. In one embodiment, the system 10 is a
medical diagnostic ultrasound system for acquiring image
information using acoustic energy. In alternative embodiments,
other medical imaging systems may be used, such as a computed
tomography, magnetic resonance, X-ray or other now known or latter
developed imaging systems. Using feedback from received data to the
scanner, such as the ultrasound beamformer 14 used for acquisition,
the position of a subsequent scan is controlled to maintain a
tissue of interest within the scan plane or acquisition region.
[0020] The transducer 12 is a multi-dimensional array of elements.
For example, a 1.5, 1.75 or two-dimensional array of elements are
provided. Annular, wobbler, or other mechanically or electrically
steerable arrays may be used. Two-dimensional array is used broadly
to include an array of N.times.M elements where N and M are equal
or non-equal, but both greater than 1. Arrays with non-square or
non-rectangular element patterns may be provided in any
multi-dimensional arrangement. The multi-dimensional transducer
array 12 is steerable in two dimensions, such as along an elevation
and azimuth dimension. In alternative embodiments, the transducer
12 is a one-dimensional linear array for scanning a two-dimensional
region.
[0021] The beamformer 14 is an analog or digital ultrasound
transmit and/or receive beamformer. In one embodiment, the
beamformer 14 is the beamformer disclosed in U.S. Pat. Nos.
5,675,554 and 5,685,308, the disclosures of which are incorporated
herein by reference. The beamformer 14 is shown in general, but in
one embodiment includes both a transmit and receive beamformers as
separate devices. The transmit beamformer generates the acoustic
energy along the acquisition scan plane. The receive beamformer
receives responsive echo signals and provides them to the image
processor 20 and the processor 18.
[0022] In one embodiment, sufficient beamformer channels are
provided on transmit and/or receive to beamform along both the
azimuth and elevation dimensions. To reduce the number of
beamformer channels, sparse array techniques may be used.
Alternatively, plane wave imaging techniques are provided. In yet
another alternative embodiment, the number of cables between the
transducer 12 and the beamformer 14 is reduced by time division
multiplexing for allowing a greater number of channels while
minimizing the size of the cable. In yet another alternative
embodiment, sufficient channels are provided for beamforming along
an azimuth dimension, and switchable connections between the
channels and elements of the arrays are used to position a linear
array of elements along any of azimuth and elevation positions on
the plane of the transducer 14. As a result, an acquisition scan
plane is always normal to at least one dimension but electronic
steering is provided for scanning along angles for another
dimension.
[0023] In one embodiment, the beamformer 14 includes a plurality of
transmit channels connectable with one or more of the elements of
the transducer 12. Each transmit channel includes a delay,
amplifier and a waveform generator. Additional, different or fewer
components may be provided. The transmit channels generate
waveforms with different apodization and delay profiles relative to
other waveforms for steering acoustic energy along one or more scan
lines. By selecting which transmit channels connect to which
elements of the transducer array 12, ultrasound scan lines are
generated along any various azimuthal and elevation locations and
angles.
[0024] The beamformer 14 is responsive to the beamformer controller
16 for positioning the acquisition scan plane. Using the
above-described electronic, mechanical or both electronic and
mechanical steering, the acquisition scan plane is positioned
within a two-dimensional or three-dimensional region. Acoustic
energy is transmitted in any of various now known or later
developed scan patterns along the scan plane for acquiring data.
The acquisition scan plane is used for acquiring data for
subsequent images.
[0025] As part of a feedback control loop, the processor 18 is a
digital signal processor, general processor, application specific
integrated circuit, control processor, detector or other now known
or latter developed processor. In one embodiment, the processor 18
is a separate component from the beamformer 14, the beamformer
controller 16 and the image processor 20. For example, the
processor 18 is a general, system control processor connected with
the user interface 24. In other embodiments, the processor 18 is a
processor within the beamformer 14, the beamformer controller 16 or
the image processor 20. In yet other embodiments, the processor 18
has multiple processors or circuits distributed at a same or
different locations throughout the system 10. The processor 18 is
operable to detect motion within a volume in response to acquired
data. The processor 18 identifies motion from the received
ultrasound data. While the processor 18 is shown connected to the
beamformer 14, in other embodiments, the processor 18 connects to
an output of the image processor 20 for processing detected
data.
[0026] The beamformer controller 16 is a general processor,
application specific integrated circuit, digital signal processor
or other now known or later developed controller for controlling
the beamformer 14. In one embodiment, the beamformer controller 16
is the controller disclosed in U.S. Pat. Nos. 5,675,554 or
5,685,308. The beamformer controller 16 is operable to control a
position of the data acquisition scan plane relative to the
multi-dimensional transducer array 12. The beamformer controller 16
receives input from the processor 18. The input indicates a desired
scan plane position, an amount of motion, a direction of motion, or
change. In response to the detected motion provided by the
processor 18 or calculated by the beamformer controller 16, the
beamformer controller 16 is operable to alter the position of the
data acquisition scan plane for transmit and/or receive operation.
For example, the beamformer controller 16 controls the apodization
and delay profile generated across the multiple channels of the
transmit beamformer 14. The connection of the channels to specific
elements within the array may also be controlled by the beamformer
controller 16, such as by controlling a multiplexer or transmit and
receive switch. As a result, the scan plane is positioned at any of
various positions and angles within three-dimensional space
relative to the transducer 12.
[0027] The image processor 20 includes one or more spatial or
temporal filters, one or more detectors and a scan converter.
Additional, different or fewer components may be provided. The
image processor 20 receives data responsive to transmission along
the acquisition scan plane. The data is then detected and converted
to a display format. A resulting image is displayed on the display
22. The detected information or image information may alternatively
or additionally be stored for later viewing or processing. In one
embodiment, the image processor 20 is operable to determine one or
more quantities as a function of the data, such as a distance
between detected data points associated with tissue features. Since
the feedback between the beamformer 14, the processor 18 and the
beamformer controller 16 provides for real time or adaptive
positioning of the acquisition scan plane, the resulting images
generated by the image processor are more likely images of a tissue
of interest despite undesired motions.
[0028] The user interface 24 is a keyboard, trackball, mouse,
touchpad, touch- screen, slider, knob, button, combinations thereof
or other now known or latter developed input device. The user
interface 24 is shown connected with the beamformer controller 16.
In alternative embodiments, the user interface 24 connects to the
beamformer controller 16 through one or more other devices, such as
the processor 18 or a system control processor. The user designates
a region of interest within a two-dimensional or three-dimensional
image using the user interface 24. The user interface 24 is
operable to receive the input indicating a region of interest and
store or otherwise communicate the spatial position within the
image to the beamformer controller 16 or processor 18. For example,
a plurality of two-dimensional images are generated. Once the user
positions the transducer 12 such that a tissue of interest is being
imaged, the user indicates the position of the tissue of interest,
such as by tracing the tissue of interest or starting an automatic
border detection function. Alternatively, the tissue of interest
may be automatically set by the system using techniques such as
automatic image segmentation.
[0029] Once a region of interest is identified by the user, the
system 10 tracks motion of the transducer 12 relative to the tissue
of interest within a three dimensional volume. As the region of
interest moves relative to the transducer 12 due to undesired
motion, the acquisition scan plane is altered to account for the
movement. As a result, the acquisition scan plane continuously or
more likely passes through the region of interest.
[0030] FIG. 2 shows one embodiment of a method for stabilizing
imaging or an image plane within a volume in medical diagnostic
ultrasound or other medical imaging. Different, additional or fewer
acts are provided in other embodiments. The method of FIG. 2 is
applicable to both two-dimensional and three-dimensional tracking.
FIGS. 3A-3C show one embodiment of stabilizing a scan region in two
dimensions. FIGS. 4A-4C show a graphic representation of an
alternative embodiment of the stabilizing a two-dimensional scan
region within a three-dimensional volume. FIG. 2 will be described
with respect to both embodiments.
[0031] Referring to FIGS. 3A-3C and FIG. 2, a region of interest 40
is identified in act 30. The region of interest 40 is identified
from a two-dimensional image of a region using a user input and/or
automated detection. The region 42 represents a two-dimensional
region for which the transducer is capable of scanning. The region
of interest 40 is within the region 42. For example, an image
representing the entirety of the region 42 or a subset of the
region 42 is acquired.
[0032] Frame of reference data, such as data representing the
entirety of the region 42 is acquired in act 32. Different or less
sample density may be provided in acquiring the frame of reference
than for subsequent imaging.
[0033] As represented in FIG. 3B, motion is tracked in act 34. A
plurality of sub-regions 44, such as areas associated with a
plurality of scan lines spaced throughout the region 42 are
acquired. In alternative embodiments, the sub-regions are
two-dimensional areas that extend less than an entirety of the
depth of the region 42. Using speckle tracking or tracking of
features (e.g., applying gradient processing and then tracking peak
gradient locations), any motion of the sub-regions or subimages 44
relative to the reference is determined. For example, any of
various constant or adaptive search processes are used to provide a
best match or a sufficient match of each of the sub-regions 44 to
the reference frame of data. A translation along two dimensions and
a rotation for each of the subimages 44 is determined. In
alternative embodiments, a translation along a single dimension,
translation along two dimensions without rotation, or translation
along a single dimension with rotation is used. The resulting
translational and rotational vectors are combined, such as through
averaging, to identify an overall motion. Since only sub-regions
are scanned for tracking motion, the frame rate is now increased
compared to scanning the whole volume for tracking.
[0034] As shown in FIG. 3C, a scan plane position is altered as a
function of the tracked motion in act 36. The scan plane 46 is less
than the entire spatial extent 42 possible by the transducer. The
scan plane 46 is sized to just encompass the region of interest 40
or to include the region of interest 40 as well as additional
information. As transducer movement relative to the region of
interest 40 occurs, the scan plane 46 is positioned to scan a
region of interest 40 based on the tracked motion.
[0035] In act 38, image data is acquired based on the shifted
acquisition scan plane position. Since the scan plane 46 is shifted
to account for motion, the region of interest 40 appears in the
displayed image at a same location for each subsequent image
regardless of motion between the region of interest 40 and the
transducer 12. For example, the region of interest 40 shifts within
the region 42 as shown in FIG. 3A as opposed to FIG. 3B. By
shifting the scan plane 46, the region of interest 40 is then moved
by the estimated motion amount in a reverse direction and shown to
the user as the region 46 shown in FIG. 3C. The region of interest
40 appears to be stabilized or stationary and is included within
each of the images. Acts 34, 36 and 38 are repeated for subsequent
images without requiring further acquisition of an entire reference
frame of data. In alternative embodiments, an entire frame of
reference data may be subsequently acquired.
[0036] FIGS. 4A-4C and 2 represent a similar process for
positioning a scan plane in a three-dimensional region 52 as
opposed to the two-dimensional region 42 of FIGS. 3A-C. The
three-dimensional region 52 corresponds to a volume that is a
subset or the entirety of the volume that the transducer is
operable to scan. As shown in FIGS. 4A, the volume region 52 is
conical but may be pyramid-shaped, cylindrical, or other shapes in
other embodiments. The volume region 52 corresponds to electric
steering of a two-dimensional array in one embodiment. The steering
is at any of various angles, such as a normal through to 45 degrees
away from normal. Other angles may be used.
[0037] In act 30, the region of interest 40 is identified. The user
moves the transducer relative to the patient or causes the system
to move the scan plane 54 to find the region of interest 40. For
example, a two-dimensional region is scanned with ultrasound
energy. As represented in FIG. 4A, the two-dimensional region is
the plane EFGH within the volume region 52. In one embodiment, the
plane 54 is positioned at a center of the transducer array, but may
be positioned any where in any orientation within the volume region
52. In alternative embodiments, a three-dimensional representation
is generated for identifying the region of interest 40.
[0038] Once an image includes the desired region of interest 40,
the user inputs information designating the region of interest 40
within the region 52. For example, the user identifies the region
of interest by tracing, by selecting two or more points, by
selecting a point, by automatic border detection, automatic
segmentation or by other now known or latter developed techniques.
Based on the position of the scan plane 54 relative to the
transducer 12 and the position of tissue designated within the
image, the system 10 determines the spatial location of the region
of interest 40 within the volume 52.
[0039] Once the region of interest 40 is identified, reference data
is acquired in act 32. The entire three-dimensional volume is
scanned. For example, a representative sample of the volume region
52 is obtained. A larger or smaller three-dimensional volume, such
as associated with greater or lesser steering angles, may be
scanned. The representative sample is acquired over the entire
spatial extent in one embodiment, but may be acquired over lesser
spatial extents in other embodiments. The entire spatial extent is
based on an area of the two-dimensional transducer array and the
steering angle. For example, the two-dimensional array used for
acquiring data defines the entire spatial extent of the scan.
[0040] The representative sample is acquired over the entire or
other spatial extent with a same or different scan line density
than for subsequent imaging. Data representing at least portions of
the three-dimensional volume are acquired for positions at least
partially around the region of interest. A lesser line density,
sample density or combinations thereof may be used. In one
embodiment, the representative data is equally or evenly spaced
throughout the volume region 52, but unequal or variations in
sample or line density may be provided. In one embodiment, the data
for the entire volume is acquired with a low resolution, such as
using a low frequency or smaller aperture. Low resolution may
result in a higher frame rate for scanning the entire spatial
extent.
[0041] Once the region of interest 40 is identified and a frame of
reference data in a known spatial relationship to the region of
interest 40 is acquired, a two-dimensional area is repetitively
scanned with the multi-dimensional transducer array. The
two-dimensional area, such as the scan plane 54, is adaptively
positioned within the volume region 52 as a function of tracked or
detected motion. The two-dimensional area can be a C-Plane, B-Plane
or any other variation of the above two planes, obtained by
rotating C-- or B-Planes. Instead of a 2D area, the transducer may
also acquire a small 3D volume enclosing the region of interest,
such as with two or more spatially distinct scan planes. By
repositioning the two-dimensional area or the scan plane 54, the
region of interest 40 is continually scanned despite relative
movement between the region of interest 40 and the transducer
12.
[0042] In act 34, motion within the three-dimensional volume region
52 is tracked. The motion within the volume is repetitively
detected for generating a plurality of images. Since the volume
region 52 where motion is detected includes the two-dimensional
scan plane 54 and associated region of interest 40, the detected
motion indicates motion of the region of interest 40 within the
volume region 52.
[0043] Motion is detected by comparing data acquired at different
times, such as comparing each subsequently acquired set of data
with the reference frame of data acquired in act 32. Rather than
acquiring data representing the entire volume region 52, such as
performed in act 32, a lesser amount of data is acquired to
maintain higher frame rate. For example, acoustic energy is
transmitted to three sub-regions of the three-dimensional volume
region 52 without acquiring data for the entire three-dimensional
volume region 52. In one embodiment, two of the sub-regions are
along a same set of scan lines. More than three sub-regions along
the same or different scan lines may be used. The data is acquired
using fewer scan lines than performed for acquiring the reference
information in act 32. As shown in FIG. 4B, three sets of scan
lines 56 are transmitted at different angles and locations within
the volume region 52. In one embodiment, each set of sub-regions
includes nine adjacent scan lines, but sets of spaced scan lines,
sparse scan lines, a greater number of scan lines or a fewer number
of scan lines may be used. In one embodiment, each of the sets of
scan lines 56 is of a same or similar scan line density, but
different densities may be provided. In one embodiment, the scan
line density and scan line positions for each of the sets of scan
lines 56 are the same density and scan lines for a sub-volume used
to acquire the reference frame data, but different densities or
scan line positions may be used.
[0044] Acquisition parameters for obtaining data for motion
tracking are the same or different than used for acquiring the
reference information. In an alternative embodiment, acquisition of
the tracking data is adaptive. For example, the size of each beam,
the number of beams or other acquisition parameter is adjusted as a
function of a previous motion estimate, the variance associated
with the motion estimate or a measure of a tissue rigidity. For
large variance motion estimates or low tissue rigidity, the beam
size is increased or the number of beams is increased. The
acquisition parameters may also be updated as a function of a
change in acquisition parameters for imaging. For example, the user
selects a different center frequency, aperture, F number, depths of
imaging or other imaging parameter. The same parameter is altered
for obtaining a tracking data. The same parameter is used for both
tracking and imaging. In alternative or additional embodiments,
different imaging parameters are used for tracking than for
imaging.
[0045] Data associated with a cubed region at two or more different
depths along each of the sets of scan lines 56 is used for
comparison and motion detection. As shown in FIG. 4B, six tracking
regions 58 are obtained. Additional or fewer sub-regions 58 may be
used. In alternative embodiments, one or three or more sub-regions
within each of the sets of scan lines 56 are used. While data
representing cubes are acquired in one embodiment, data
representing any of other various one, two or three-dimensional
shapes may be used. In another embodiment, the data along the
entire depth of each of the sets of scan lines 56 is used for
motion detection. By acquiring data in only sub-regions 58 or along
the sets of scan lines 56, a substantially lesser portion of the
volume region 52 is scanned than is performed for acquiring the
reference information or for scanning an entire volume. For
example, 50 percent fewer scan lines are acquired as compared to
scanning the entire volume 52 with a same density. A greater or
lesser percentage may be provided. As a result, the sub-volumes
also represent a substantially less total volume than the entire
three-dimensional volume region 52.
[0046] The motion vectors 60 are determined by tracking each cube
using speckle correlation. A high pass filter or other filtering
and acquisition parameters are selected to best identify or provide
speckle information. In alternative embodiments, a spatial gradient
is applied to the data to identify one or more features within each
sub-region 58. Easily identified landmarks, such a cystic areas,
blood vessels or highly echogenic specular targets are tracked
instead of tracking pixels within a sub-volume for speckle
correlation. In another embodiment, the sub-regions 58 are
adaptively placed prior to acquisition by identifying features
within the reference frame of data acquired in act 32. Filtering or
other techniques in addition to or as an alternative to a spatial
gradient function may be used to identify one or more features. A
feature pattern or volume around an identified single feature for
each sub-volume 58 is identified. Filtering or other functions may
be used in addition to or as an alternative to the spatial gradient
for identifying a tracking feature.
[0047] A motion vector 60 is determined for each of the sub-volumes
58. For example, a direction, a magnitude or both a direction and a
magnitude of the motion are determined by comparing the data from
each of the sub-volumes 58 with the reference data acquired in act
32. In one embodiment, a translation within three dimensions is
determined without determining rotation. The amount and direction
of translation of the sub-volume 58 relative to the volume region
52 indicates a motion vector 60. Data responsive to the grouped
sets of beams is used to determine the direction and magnitude of
motion of the volume region 52 relative to the transducer. A
minimum sum of absolute differences, cross correlation, or other
now known or latter developed correlation is used to match the data
for the sub-volumes 58 with the referenced data. Correlation is
performed using data prior to detection, data after detection but
prior to scan conversion, data after scan conversion, display image
data, or other data. Any of various search patterns involving
translating and/or rotating the data representing the sub- volumes
58 relative to the referenced data is used to identify a best
match. A coarse search followed by a fine search, a search adapted
to expected motion, a size of the region to be searched adapted to
previous amounts of motion, or other adaptive or efficient search
techniques may be used.
[0048] The same reference data is used to compare to each
subsequently acquired set of data representing sub-regions 58. In
alternative embodiments, data representing a subsequently acquired
sub-volume 58 is compared to data from a previously acquired
sub-volume in a same general area. Given minimal amount of motion,
the motion vector may be small enough to track from one sub-volume
to a subsequently acquired sub-volume without comparison to the
reference frame of data.
[0049] As an alternative to finding individual motion vector 60 for
each sub-volume, the sub-volumes are translated and/or rotated as a
group to find a single motion vector. Where two or more different
motion vectors are detected for a given time, a least squares fit,
an average, or other combination of the motion vectors is used to
calculate a single transformation indicating motion of the
transducer 12 relative to the volume region 52. Rigid body motion
is assumed for each sub-volume, but warping or other techniques may
be used to account for tissue deformation. Translations in three
dimensions and rotations about the three dimensions are determined
using a least squares fit, such as determined from using six
separate motion vectors shown in FIG. 4B. U.S. Pat. No. 6,306,091,
the disclosure of which is incorporated herein by reference,
discloses various techniques for identifying a rigid body
transformation from a plurality of vectors. The motion tracking,
subvector or global vector techniques disclosed in the '091 patent
are extended to three-dimensional processing. The resulting rigid
body transformation represents six degrees of freedom, such as a
translation in an X, Y and Z dimensions as well as rotation about
each of the dimensions. In alternative embodiments, fewer degrees
of freedom or motion associated with only translation, only
rotation or a subset of the six degrees of freedom is provided.
[0050] Since the characteristics of the speckle may change as a
function of position within the volume region 52, one or more
tracking parameters are adjusted as a function of a position of the
tracking location within the region 52. For example, as the speckle
is positioned deeper and deeper within the region 52, diffraction
results in larger speckle. Element factor or other factors may
change as a position of depth, steering angle or other location
within volume region 52. The correlation, cross correlation,
minimum sum of differences or other matching function is altered
based on the position. Through example, a warping, such as a one-,
two- or three-dimensional expansion or contraction of the data is
performed as part of the correlation operation as a function of the
position of the tracking location. By spatially expanding or
contracting the data, the data more likely matches the reference
data. Other warping may be used. Differences in thresholds for
identifying a best or sufficient match, differences in an algorithm
apply to track motion or other tracking parameters are altered as a
function of the location. Alternatively, the tracking parameters
are the same regardless of position. Other types of
transformations, besides rigid body transformation may be estimated
between the reference data set and the subsequent sub regions. One
such technique is image morphing as described in U.S. Pat. No.
______ (application Ser. No. 10/251,044) for Morphing Diagnostic
Ultrasound Images for Perfusion Assessment, the disclosure of which
is incorporated herein by reference.
[0051] In act 36, the position of the acquisition scan plane 54 is
automatically altered relative to the transducer 12 as a function
of the detected motion. FIG. 4C shows transformation of the
acquisition scan plane 54 to account for the detected or estimated
motion. By translating and rotating the acquisition scan plane 54,
subsequent acquisition along the scan plane 54 more likely scans
the region of interest 40. The acquisition scan plane 54 is
maintained at a position to intersect the region of interest 40
over time. The position of the acquisition scan plane 54 is altered
within the three-dimensional volume region 52 to account for
relative motion between the region of interest 40 and the
transducer 12. The motion tracking provides information on the
position of the region of interest 40 within the volume region 52
relative to the transducer 12. The acquisition scan plane (i.e.,
the transmission and/or reception plane) is adaptively
repositioned, altered or updated. The two-dimensional area of the
acquisition scan plane is positioned within the volume as a
function of and in response to the detected motion and the region
of interest 40. As shown in FIG. 4C, the acquisition scan plane 54
is positioned in a plane QPRS different than the EFGH plane of FIG.
4A as a function of the motion vectors 60 shown in FIG. 4B. The
region of interest 40 moves in a direction opposite to the detected
motion.
[0052] Using electronic or mechanical steering, the acquisition
scan plane 54 is translated and/or rotated, such as translating and
rotating within the six degrees of freedom. In alternative
embodiments, the acquisition scan plane 54 is translated and
maintained at the same angle relative to the normal to the array or
not rotated. Where a two-dimensional transducer is used, six
degrees of freedom may be provided for positioning the acquisition
scan plane 54. Fewer degrees of freedom may be provided for other
multi-dimensional or two-dimensional arrays. The scan plane 54 is
adaptively positioned using one or more degrees of freedom to more
likely scan the region of interest 40. Where motion is indicated
beyond the original extent of the volume 52 or beyond the ability
to acquire a sufficiently large acquisition scan plane 54,
stabilized imaging is ceased, imaging without the stabilization
described herein is performed or the process returns to acquire a
reference frame of data in act 32 for a new extent of the volume
region 52. In another embodiment, the reference frame of data is
acquired for every N frames of data containing the region of
interest, where N is a number such as 10. Other values may also be
used for N.
[0053] In act 38, image data is acquired. Acoustic energy is
electronically or mechanically steered across the acquisition scan
plane 54 in any of now known or later developed formats, such as
sector, vector, linear or as a plane wave. The data from acoustic
echoes represents the tissue intersected within the acquisition
scan plane 54. Received data is beamformed, image processed and
used to generate a two-dimensional or three-dimensional display.
The region of interest 40 is represented in the image due to the
shift in the scan plane position. In alternative embodiments,
spectral Doppler display associated with a range gate position or
point, continuous wave Doppler display associated with a line, or
M-mode display associated with a line are generated from a point or
line within the scan plane 54. The point or line are tracked and
adaptively positioned.
[0054] The motion tracking of act 34, the acquisition scan plane
position alteration of act 36 and the acquisition of image data of
act 38 are repeated over time such that the two-dimensional
acquisition scan plane 54 is adaptively positioned to intersect the
region of interest over time. The adaptively positioned acquisition
scan planes are repetitively scanned for generating images. Upon
viewing a sequence of images, the user perceives the region of
interest 40 as being stationary or stabilized. The region of
interest 40 is less likely to fade out of the images due to the
adapted positioning of the scan plane 54. The acquisition scan
plane 54 is maintained in a position to intersect the region of
interest 40 during multiple acquisitions accounting for relative
motion of the transducer 12 to the tissue.
[0055] By acquiring image data from the two-dimensional area of the
acquisition scan plane 54 or a one-dimensional line or point, rapid
or high frame rate imaging is provided. Since the motion tracking
uses sub-volumes, the affect on frame rate is greatly reduced as
opposed to tracking using the entire volume region 52. As a result,
real time or substantially real time two-dimensional imaging is
provided with three-dimensional motion tracking.
[0056] Further stabilization is provided by shifting the resulting
two-dimensional images as a function of an initial position of the
region of interest 40. Adaptive positioning of the acquisition scan
plane 54 results in the region of interest 40 being continually
imaged. The region of interest 40 may also or alternatively be
shifted within the display two-dimensional image by translation
along one or two dimensions and/or rotation to maintain further
stabilization. For example, as the transducer shifts to the left
relative to the tissue, the region of interest 40 may appear to
shift to the left within resulting images. The region of interest
40 is tracked or the shift is accounted for in the display
two-dimensional image. In one embodiment, the shift occurs to the
image data in range and azimuth. In another embodiment, the
acquisition scan plane 54 extends only over a portion of the width
of the volume region 52 accessible by the transducer 12. As a
result, the positioning of the acquisition scan plane automatically
shifts the region of interest 40 in the displayed image. Where
tissue is compressed due to additional pressure from the transducer
12 or extended due to a release of pressure, the region of interest
40 may appear to shift upwards or downwards on the image. Either
through changing a depth associated with the acquisition scan plane
54 or by shifting the resulting image data upwards or downwards,
the region of interest 40 is maintained in the same location on the
display.
[0057] A further shift in the acquisition scan plane position 54
may be performed as a function of time. For example, the difference
in time between acquisition of the data used for tracking motion
and the acquisition of data used for generating an image is
considered. A velocity, acceleration or both velocity and
acceleration are determined. The temporal difference is used with
the velocity or acceleration information to determine an additional
shift.
[0058] The tracking of the imaging plane is used for any B-mode,
Doppler, M-mode, spectral Doppler, continuous wave Doppler,
harmonic, contrast agent imaging or other imaging. Other
applications may benefit from tracking the position of the
acquisition scan plane 54 in three-dimensional volume region 52.
For example, tumor perfusion using contrast agents or other
radiology-based contrast quantification is performed. Contrast
agent quantification may also be performed for myocardial perfusion
or other cardiology applications. Triggered imaging of the heart is
provided so that the resulting images are acquired at a same time
during a heart cycle. Alternatively, warping or other non-rigid
motion is accounted for throughout the heart cycle. Another
application is a biopsy or surgical guidance. Better guidance may
be provided by maintaining the scan plane in position relative to
the region of interest. Yet other applications are cardiovascular
quantitative measurements, such as vascular measurements of carotid
plaque assessment, pulsatility, aortic aneurism or others.
[0059] In one embodiment, the acquisition scan plane is used for
acquiring Doppler information for both Doppler and B-mode
information. The motion is tracked using B-mode or other
information. Any of various combinations of using the same or
different data for tracking and imaging may be used. By stabilizing
the scan plane position relative to the region of interest 40, more
aggressive persistence for Doppler imaging may be used with no or
minimal decrease in resolution. Vessel structure reconstruction may
also be improved. Other high persistence imaging, such as contrast
agent imaging to identify microvascular structures, may be
improved.
[0060] By reducing the artifacts due to patient or sonographer
motion for two-dimensional imaging, work flow may be improved,
reducing the amount of acquisition data and the amount of
acquisition time. Off-line motion tracking processing is eliminated
by providing for a tracking and imaging described above in real
time or while a patient is being scanned during an imaging session.
Real time imaging is provided due to the reduced or minimal impact
of acquiring motion information using sub-volumes. Motion tracking
is performed in three dimensions without having to acquire
consecutive full three-dimensional volume representations of
data.
[0061] As an alternative to two-dimensional imaging of a region of
interest, stabilization of the acquisition scan plane is used for
acquiring a three-dimensional set of data. Using electronic
steering, the scan plane is purposefully positioned at different
locations within the volume region 52. To provide regular spacing
of the acquisition scan plane for a more uniform density of samples
throughout the three-dimensional region, motion of the transducer
12 relative to the tissue is accounted for as discussed above. The
acquisition scan plane position is adjusted as a function of both
the motion and the intended displacement for three-dimensional data
acquisition.
[0062] While the invention has been described above by reference to
various embodiments, it should be understood that many changes and
modifications can be made without departing from the scope of the
invention. For example, the same firings and data are used for both
tracking and imaging. As another example, one or more sub-volumes
58 for tracking are positioned within, as parts of, or overlapping
with the region of interest. It is therefore intended that the
foregoing detailed description be regarded as illustrative rather
than limiting, and that it be understood that it is the following
claims, including all equivalents, that are intended to define the
spirit and the scope of this invention.
* * * * *