U.S. patent application number 14/989883 was filed with the patent office on 2016-04-28 for method for monitoring of medical treatment using pulse-echo ultrasound.
The applicant listed for this patent is Guided Therapy Systems, LLC. Invention is credited to Peter G. Barthe, T. Douglas Mast, Michael H. Slayton.
Application Number | 20160113620 14/989883 |
Document ID | / |
Family ID | 34826381 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160113620 |
Kind Code |
A1 |
Slayton; Michael H. ; et
al. |
April 28, 2016 |
Method for Monitoring of Medical Treatment Using Pulse-Echo
Ultrasound
Abstract
A method for ultrasound imaging of anatomical tissue. A first
signal is received from a first imaging ultrasound wave which has
been reflected from a location in the anatomical tissue during a
first time period. A second signal is received from a second
imaging ultrasound wave which has been reflected from the location
in the anatomical tissue during a later second time period,
following a discrete medical treatment. The second signal is
subtracted from the first signal to form a difference signal. The
difference signal may be scaled, spatially filtered, then used to
generate an indication, the indication showing the effect of the
medical treatment in the location in the anatomical tissue.
Inventors: |
Slayton; Michael H.; (Tempe,
AZ) ; Barthe; Peter G.; (Phoenix, AZ) ; Mast;
T. Douglas; (Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Guided Therapy Systems, LLC |
Mesa |
AZ |
US |
|
|
Family ID: |
34826381 |
Appl. No.: |
14/989883 |
Filed: |
January 7, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12915358 |
Oct 29, 2010 |
9261596 |
|
|
14989883 |
|
|
|
|
10721034 |
Nov 24, 2003 |
7846096 |
|
|
12915358 |
|
|
|
|
10153241 |
May 22, 2002 |
|
|
|
10721034 |
|
|
|
|
60294135 |
May 29, 2001 |
|
|
|
Current U.S.
Class: |
600/443 |
Current CPC
Class: |
A61B 8/5207 20130101;
A61B 2090/3784 20160201; A61N 2007/0078 20130101; A61B 8/08
20130101; A61B 8/5238 20130101; A61B 2090/3929 20160201; A61B 17/29
20130101; A61B 8/5276 20130101; A61B 2090/3975 20160201; A61B
17/22012 20130101; A61B 8/4488 20130101; A61B 2090/378 20160201;
A61N 7/022 20130101; A61B 8/14 20130101; A61B 8/12 20130101; A61B
10/0233 20130101; G01S 15/899 20130101; A61B 17/2202 20130101 |
International
Class: |
A61B 8/08 20060101
A61B008/08; A61B 8/14 20060101 A61B008/14 |
Claims
1. A method for ultrasound imaging of anatomical tissue, comprising
the steps of: a) receiving a first signal of a first imaging
ultrasound wave which has been reflected from a location in the
anatomical tissue during a first time period; b) receiving a second
signal of a second imaging ultrasound wave which has been reflected
from the location in the anatomical tissue at a later second time
period following a discrete medical treatment; c) subtracting the
second signal from the first signal to derive a difference signal;
d) generating an indication from the difference signal, the
indication showing the reflect of the discrete medical treatment in
the location in the anatomical tissue.
2. The method of claim 1 wherein the first and second signals are
received after the discrete medical treatment has been
completed.
3. The method of claim 1 wherein the first signal is received
before the discrete medical treatment, and the second signal is
received after the discrete medical treatment has been
completed.
4. The method of claim 1, further comprising the step of processing
the first and second signals.
5. The method of claim 4, further comprising the step of
multiplying at least one of the first and second signals by a phase
compensation function to reduce motion artifacts.
6. The method of claim 1, further comprising the step of scaling
the difference signal.
7. The method of claim 6 wherein the difference signal is scaled by
squaring the amplitude of the difference signal.
8. The method of claim 1, further comprising the step of spatially
filtering the difference signal.
9. The method of claim 1, wherein the medical treatment is
ultrasound medical treatment.
10. The method of claim 1, also including the steps a) through d)
for different locations to image the anatomical tissue, wherein the
image includes medically-treated locations and medically-untreated
locations of the anatomical tissue.
11. The method of claim 1, further comprising the step of combining
the difference signal image with a second image of the location in
the anatomical tissue.
12. The method of claim l 1 wherein the second image is generated
using a B-Mode ultrasound scan.
13. A method for ultrasound imaging of anatomical tissue,
comprising the steps of: a) receiving a first signal of a first
imaging ultrasound wave which has been reflected from a location in
the anatomical tissue during a first time period; b) receiving a
second signal of a second imaging ultrasound wave which has been
reflected from the location in the anatomical tissue at a later
second time period following a discrete medical treatment; c)
processing the first and second signals; d) subtracting the second
signal from the first signal to derive a difference signal; e)
scaling the difference signal; f) spatially filtering the
difference signal; and g) generating an indication from the
difference signal, the indication showing the effect of the
discrete medical treatment in the location in the anatomical
tissue.
14. The method of claim 13 wherein the first and second signals are
received after the discrete medical treatment has been
completed.
15. The method of claim 13 wherein the first signal is received
before the discrete medical treatment and the second signal is
received after the discrete medical treatment.
16. A method for ultrasound imaging of anatomical tissue,
comprising the steps of: a) receiving a first set of image frames
comprising a plurality of imaging ultrasound wave signals which
have been reflected from a location in the anatomical tissue during
a first period of time; b) receiving a second set of image frames
comprising a plurality of imaging ultrasound wave signals which
have been reflected from the location in the anatomical tissue
during a later second period of time following a discrete medical
treatment; c) subtracting the imaging ultrasound signals of the
second set of image frames from the imaging ultrasound signals of
the first set of image frames to derive a difference signal; and d)
generating an indication from the difference signal, the indication
showing the effect of the discrete medical treatment in the
location in the anatomical tissue.
17. The method of claim 16 wherein the first and second sets of
image frames are received after the discrete medical treatment has
been completed.
18. The method of claim 16 wherein the first set of image frames is
received before the discrete medical treatment, and the second set
of image frames is received after the discrete medical
treatment.
19. The method of claim 16, further comprising the step of
processing the first and second sets of signals.
20. The method of claim 16, further comprising the step of scaling
the difference signal.
21. The method of claim 20 wherein the difference signaled by
squaring the amplitude of the difference signal.
22. The method of claim 16, further comprising the step of
spatially filtering the difference signal.
23. The method of claim 16, wherein the medical treatment is
ultrasound medical treatment.
24. The method of claim 16, also including the steps a) through d)
for different locations to image the anatomical tissue, wherein the
image includes medically-treated locations and medically-untreated
locations of the anatomical tissue.
25. A method for ultrasound imaging of anatomical tissue,
comprising the steps of: a) receiving a first set of image frames
comprising a plurality of imaging ultrasound wave signals which
have been reflected from a location in the anatomical tissue during
a first period of time; b) receiving a second set of image frames
comprising a plurality of imaging ultrasound wave signals which
have been reflected from the location in the anatomical tissue
during a later second period of time following a discrete medical
treatment; c) processing the first and second sets of signals; d)
subtracting the imaging ultrasound signals of the second set of
image frames from the ultrasound signals of the first set of image
frames to derive a difference signal; e) scaling the difference
signal; f) spatially filtering the difference signal; and g)
generating an indication from the difference signal, the indication
showing the effect of the discrete medical treatment in the
location in the anatomical tissue.
26. The method of claim 25 wherein the first and second sets of
image frames are received after the discrete medical treatment has
been completed.
27. The method of claim 25 wherein the first set of image frames is
received before the discrete medical treatment, and the second set
of image frames is received after the discrete medical
treatment.
28. The method of claim 25 wherein the medical treatment is
ultrasound medical treatment.
29. The method of claim 25, also including the steps a) through g)
for different locations to image the anatomical tissue, wherein the
image includes medically-treated locations and medically-untreated
locations of the anatomical tissue.
30. A method for ultrasound imaging of anatomical tissue,
comprising the steps of: a) providing a discrete medical treatment
to the anatomical tissue; b) receiving a set of image frames
comprising a plurality of imaging ultrasound wave signals which
have been reflected from a location in the anatomical tissue; c)
pairing together a plurality of image frames, each pair comprising
a first image frame and a second image frame such that the second
image frame has been reflected from a location in the anatomical
tissue at a later time than the first image frame; d) subtracting
the signals of the second image frame from the signals of the first
image frame, for each pair of image frames in the image frame set,
to derive a set of difference signals; e) using at least one
difference signal to generate an indication showing the effect of
the discrete medical treatment in the location in the anatomical
tissue; and f) repeating steps a) through e) until medical
treatment is completed.
31. The method of claim 30, further comprising the steps of: a)
computing an average of the set of difference signals; and b) using
the average of the set of difference signals to generate an
indication showing the effect of the discrete medical treatment in
the location in the anatomical tissue.
32. The method of claim 31, further comprising the steps of: a)
cumulatively summing the averages of the set of difference signals;
and b) using the cumulative sum of averages of the set of
difference signals to generate an indication showing the effect of
the discrete medical treatment in the location in the anatomical
tissue.
Description
FIELD OF THE INVENTION
[0001] This is a continuation of application Ser. No. 10/721,034,
filed Nov. 24, 2003, presently allowed, which is a
continuation-in-part of application Ser. No. 10/153,241, filed May
22, 2002, abandoned, which claims priority to provisional
application Ser. No. 60/294,135 filed May 29, 2001. The present
invention relates generally to ultrasound, and more particularly,
to an ultrasound medical imaging method.
BACKGROUND OF THE INVENTION
[0002] Ultrasound medical systems and methods include ultrasound
imaging of anatomical tissue to identify tissue for medical
treatment. Ultrasound may also be used to medically treat and
destroy unwanted tissue by heating the tissue. Imaging is done
using low-intensity ultrasound waves, while medical treatment is
performed with high-intensity ultrasound waves. High-intensity
ultrasound waves, when focused at a focal zone a distance away from
the ultrasound source, will substantially medically affect tissue
in the focal zone. However, the high-intensity ultrasound will not
substantially affect patient tissue outside the focal zone, such as
tissue located between the ultrasound source and the focal zone.
Other treatment regimes of interest include unfocused
high-intensity ultrasound, wherein the ultrasound energy is
distributed over a relatively broad region of tissue rather than
being generally concentrated within a focal zone.
[0003] Ultrasound waves may be emitted and received by a transducer
assembly. The transducer assembly may include a single element, or
an array of elements acting together, to image the anatomical
tissue and to ultrasonically ablate identified tissue. Transducer
elements may employ a concave shape or an acoustic lens to focus
ultrasound energy. Transducer arrays may include planar, concave or
convex elements to focus or otherwise direct ultrasound energy.
Further, such array elements may be electronically or mechanically
controlled to steer and focus the ultrasound waves emitted by the
array to a focal zone to provide three-dimensional medical
ultrasound treatment of anatomical tissue. In some treatments the
transducer is placed on the surface of the tissue for imaging
and/or treatment of areas within the tissue. In other treatments
the transducer is surrounded with a balloon which is expanded to
contact the surface of the tissue by filling the balloon with a
fluid such as a saline solution to provide acoustic coupling
between the transducer and the tissue.
[0004] Examples of ultrasound medical systems and methods include:
deploying an end effector having an ultrasound transducer outside
the body to break up kidney stones inside the body; endoscopically
inserting an end effector having an ultrasound transducer into the
rectum to medically destroy prostate cancer; laparoscopically
inserting an end effector having an ultrasound transducer into the
abdominal cavity to destroy a cancerous liver tumor; intravenously
inserting a catheter end effector having an ultrasound transducer
into a vein in the arm and moving the catheter to the heart to
medically destroy diseased heart tissue; and interstitially
inserting a needle end effector having an ultrasound transducer
into the tongue to medically destroy tissue to reduce tongue volume
as a treatment for snoring. Methods for guiding an end effector to
the target tissue include x-rays, Magnetic Resonance Images ("MRI")
and images produced using the ultrasound transducer itself.
[0005] Low-intensity ultrasound energy may be applied to unexposed
anatomical tissue for the purpose of examining the tissue.
Ultrasound pulses are emitted, and returning echoes are measured to
determine the characteristics of the unexposed tissue. Variations
in tissue structure and tissue boundaries have varying acoustic
impedances, resulting in variations in the strength of ultrasound
echoes. A common ultrasound imaging technique is known in the art
as "B-Mode" wherein either a single ultrasound transducer is
articulated or an array of ultrasound transducers is moved or
electronically scanned to generate a two-dimensional image of an
area of tissue. The generated image is comprised of a plurality of
pixels, each pixel corresponding to a portion of the tissue area
being examined. The varying strength of the echoes is preferably
translated to a proportional pixel brightness. A cathode ray tube
or liquid crystal display can be used to display a two-dimensional
pixellated image of the tissue area being examined. The varying
strength of the echoes is preferably translated to a proportional
pixel brightness. A cathode ray tube or liquid crystal display can
be used to display a two-dimensional pixellated image of the tissue
area being examined.
[0006] When high-intensity ultrasound energy is applied to
anatomical tissue, significant beneficial physiological effects may
be produced in the tissue. For example, undesired anatomical tissue
may be ablated by heating the tissue with high-intensity ultrasound
energy. By focusing the ultrasound energy at one or more specific
focusing zones within the tissue, thermal effects can be confined
to a defined region that may be remote from the ultrasound
transducer. The use of high-intensity focused ultrasound to ablate
tissue presents many advantages, including: reduced patient trauma
and pain; potentially reduced patient recovery time; elimination of
the need for some surgical incisions and stitches; reduced or
obviated need for general anesthesia; reduced exposure of
non-targeted internal tissue; reduced risk of infection and other
complications; avoidance of damage to non-targeted tissue;
avoidance of harmful cumulative effects from the ultrasound energy
on the surrounding non-target tissue; reduced treatment costs;
minimal blood loss; and the ability for ultrasound treatments to be
performed at non-hospital sites and/or on an out-patient basis.
[0007] Ultrasound treatment of anatomical tissue may involve the
alternating use of both low-intensity imaging ultrasound and
high-intensity treatment ultrasound. During such treatment, imaging
is first performed to identify and locate the tissue to be treated.
The identified tissue is then medically treated with high-intensity
ultrasound energy for the purpose of ablating the tissue. After a
period of exposure to high-intensity ultrasound, a subsequent image
of the tissue is generated using low-intensity ultrasound energy to
determine the results of the ultrasound treatment and provide
visual guidance to the user to aid in subsequent treatments. This
process of applying low-energy ultrasound to assist in guiding the
position and focal point of the transducer, followed by high-energy
ultrasound to ablate the undesired anatomical tissue, may continue
until the undesired tissue has been completely ablated.
[0008] Although this conventional B-Mode ultrasound imaging
provides an effective means for imaging tissue that is in a static
state, imaging of the tissue becomes more problematic when used in
conjunction with thermal high-intensity ultrasound treatment. As
the tissue is ablated during treatment, the heating effects of
ultrasound upon the tissue often result in qualitative changes in
echo strength, causing brightness variations in the pixel display
that do not consistently correspond spatially to the tissue being
treated. These brightness variations result in an image display
that does not represent the actual shape and size of the region of
tissue that is being thermally modified by the treatment,
introducing some visual ambiguity to the image.
[0009] Several methods are known for monitoring thermal ablation
using B-Mode ultrasound imaging. Most of these are based on changes
in the energy of ultrasound echoes, and include simple B-Mode
displays of echo amplitude, estimates of tissue attenuation from
analysis of distal shadowing, and quantification of changes in echo
energy. Each of these methods have significant shortcomings because
the tissue being treated can appear hyperechoic for reasons other
than thermal ablation and because image changes must be
qualitatively perceived by the user.
[0010] The most successful known methods for monitoring thermal
ablation using ultrasound are based on analysis of changes in echo
energy rather than a direct analysis of the echo energy. Automatic
and quantitative displays of changes in echo energy or tissue
attenuation are possible and can help users isolate
thermally-induced changes from pre-existing echo characteristics.
However, since such methods require integration of echoes over
substantial regions of an image scan or "frame," the resulting
images are very limited in spatial resolution. Although energy
increases and therefore B-Mode brightness increases) correspond
roughly to lesion (i.e., the thermally treated tissue) position,
typically the shape and size of the mapped energy increases do not
always spatially correspond to actual lesions, and sometimes are
either absent or otherwise unapparent.
[0011] There is a need for an improved method of ultrasound imaging
that can be utilized in conjunction with therapeutic ultrasound
treatment that monitors the thermal effects of the treatment on
targeted tissue with greater accuracy and resolution.
SUMMARY OF THE INVENTION
[0012] The present invention overcomes the limitations of the known
art by mapping differences between a first and second echo signal,
each signal being obtained at different instants of time. The first
and second signals are typically separated by a small time
interval. The first and second signals are processed, then a
measure of the amplitude of the differences between the first and
second signals is made (as contrasted with a measure of the
differences in signal amplitude). This difference signal is then
spatially filtered and scaled to quantify echo changes associated
with changes in tissue state. Difference signals may be summed over
multiple time periods to obtain a cumulative map of the changes in
the tissue. The resulting signals may be used to generate an
ultrasound image that is more representative of the tissue as
treatment progresses, providing additional information about where
thermal effects are occurring. This allows for verification of
successful treatment and modification of unsuccessful treatment.
Known ultrasound imaging and treatment transducers may be used,
providing users with increased accuracy without a need for special
end effectors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Further features of the present invention will become
apparent to those skilled in the art to which the present invention
relates from reading the following specification with reference to
the accompanying drawings, in which:
[0014] FIG. 1 is a flow diagram providing an overview of an
ultrasound treatment method according to an embodiment of the
present invention;
[0015] FIG. 2 illustrates the relative amplitude and timing of
ultrasound image frames and ultrasound treatments of the method of
FIG. 1;
[0016] FIG. 3 is a flow diagram of a method for monitoring medical
treatment of anatomical tissue using pulse-echo ultrasound
according to an embodiment of the present invention;
[0017] FIG. 4 is a view of a first ultrasound signal on a time
scale;
[0018] FIG. 5 is a view of a second ultrasound signal on a time
scale;
[0019] FIG. 6 is a composite view of the signals of FIG. 4 and FIG.
5;
[0020] FIG. 7 is a view showing the difference signal computed from
FIG. 4 and FIG. 5;
[0021] FIG. 8 is a view showing the absolute value of the
difference signal of FIG. 7;
[0022] FIG. 9 is a view of the signal of FIG. 8 after
filtering;
[0023] FIG. 10 is a flow diagram depicting a method for monitoring
medical treatment of anatomical tissue using puke-echo ultrasound
according to an alternate embodiment of the present invention;
[0024] FIG. 11 illustrates the relative amplitude and timing of
ultrasound image frames, image frame sets and ultrasound treatments
of the method of FIG. 10;
[0025] FIG. 12 depicts a flow diagram of a method for monitoring
medical treatment of anatomical tissue using pulse-echo ultrasound
according to another alternate embodiment of the present
invention;
[0026] FIG. 13 shows the relative amplitude and timing of
ultrasound image frame sets, difference signals and ultrasound
treatments of the method of FIG. 12;
[0027] FIG. 14 is a flow diagram of a method for monitoring medical
treatment of anatomical tissue using pulse-echo ultrasound
according to yet another alternate embodiment of the present
invention; and
[0028] FIG. 15 shows the relative amplitude and timing of
ultrasound image frames and ultrasound treatments of the method of
FIG. 14.
DETAILED DESCRIPTION
[0029] An overview of an ultrasound treatment method 10 according
to an embodiment of the present invention is shown in FIG. 1. The
method begins at step 12 by positioning proximate the targeted
anatomical tissue to be medically treated a transducer capable of
transmitting and receiving ultrasound signals. Once the transducer
is in position, treatment begins at step 14 by emitting a
high-intensity ultrasound signal from the transducer. The
high-intensity ultrasound signal medically treats the targeted
tissue, such as (but not limited to) heating the tissue to ablate
the material. At step 16 a low-intensity ultrasound signal, such as
a B-Mode signal, is emitted from the transducer and the reflected
signals are received to form a first image frame It is understood
that the terminology "image" includes, without limitation, creating
an image in a visual form and displayed, for example, on a monitor,
screen or display, and creating an image in electronic form which,
for example, can be used by a computer without first being
displayed in visual form. After the first image frame F.sub.1 is
received at step 16, a predetermined waiting period is executed at
step 18 before proceeding further. It is to be understood that the
predetermined waiting period may vary in value from zero seconds
upwardly to a maximum of several seconds, but preferably is in the
range of milliseconds. After the predetermined wait period has been
completed, a low intensity ultrasound signal is again emitted from
the transducer and a second image frame F.sub.2 is received at step
20. At step 22 a difference signal is derived from the image frames
F.sub.1 and F.sub.2, as will be discussed in greater detail below.
The difference signal of step 22 is displayed as an image at step
24 to obtain a visual indication of the tissue change as a result
of the medical treatment of step 14. It should be noted that the
visual indication of the tissue change provided by the present
invention differs from the post-treatment image of the prior art in
that the present invention provides an image showing echo
differences in contrast to echos from the target tissue. The image
of echo differences can indicate whether treatment is complete. If
treatment is complete at step 26 (for example, the targeted tissue
has been fully ablated), the method is ended at step 28. However,
if the tissue requires additional treatment, the transducer may be
re-positioned at step 30. The method then returns to step 14 to
continue medical treatment of the targeted tissue.
[0030] Referring additionally to FIG. 2, the method of FIG. 1 is
illustrated in relation to a time scale t. The targeted tissue is
medically treated with a relatively high-intensity ultrasound
signal as at step 14. Then, at step 16 a relatively low-intensity
B-Mode image scan frame F.sub.1 is received. After a predetermined
off-time, as at step 18, a second image frame F.sub.2 is received,
as at step 20. The image frames F.sub.1 and F.sub.2 each contain a
signal representing the same portion of the target tissue. For each
image frame, a number of A-lines of raw echo signal data are
received, the number of each line corresponding to azimuthal
position and the signal time corresponding to depth.
[0031] Referring now to FIG. 3 in combination with FIGS. 1 and 2, a
method for monitoring medical treatment of anatomical tissue
including, but not limited to, thermal ablation according to an
embodiment of the present invention is depicted. An ultrasound
transducer is positioned proximate the targeted anatomical tissue.
The tissue may then be medically treated such as by ablation using
high-intensity ultrasound waves for a period of time as at step 14.
At step 16 a first image frame F.sub.1 (such as is illustrated in
FIG. 4) is received. The image frame may optionally be stored
electronically, such as in a computer, magnetic media and
solid-state memory. A second image frame F.sub.2, separated from
F.sub.1 by a fixed time interval of step 18, is received at step
20. An example image frame F.sub.2 is illustrated in FIG. 5. A
difference signal is then derived at step 22 by means of steps
32-38. The raw echo signals of frames F.sub.1 and F.sub.2 may be
processed at step 32, such as to obtain complex analytic signals by
means of a Hilbert transformation. A difference signal may then be
derived by subtracting the signal of image frame F.sub.2 from the
signal of F.sub.1 at step 34. The difference signal of step 34 may
take into account both phase and amplitude differences between
F.sub.1 and F.sub.2, computing the amplitude of the signal
differences (as opposed to differences in signal amplitude) of and
F.sub.2. A composite illustration of image frames F.sub.1 and
F.sub.2 is shown in FIG. 6, while the derived difference signal is
depicted in FIG. 7. At step 36 the difference signal may be scaled
to a convenient value, such as the mean squared value of the
difference signal, the mean squared value of one of the original
echo signals, or a mathematical constant. As an example, a signal
representing the scaled absolute value of the difference signal of
FIG. 7 shown in FIG. 8. Other functions of the difference signal,
such as its squared absolute value or logarithm, may similarly be
employed. Still other scaling algorithms may use the amplitude
and/or phase of the first and second signals to enhance differences
between the first and second signals. Details of such algorithms
are left to the skilled artisan. At step 38 the difference signal
is spatially filtered, as depicted in FIG. 9, to smooth small-scale
random variations. Spatial filtering of the scaled difference
signal is represented by Equation 1.
.PSI.(x,z)=.intg..sub.-.infin..sup..infin..intg..sub.-.infin..sup..infin-
.w(x-x,z-z.sub.0)|p.sub.0(x.sub.0,z.sub.0)-p.sub.1(x.sub.0,z.sub.0)|.sup.2-
dx.sub.0dz.sub.0 Equation 1
[0032] In Equation 1 .PSI. is a spatial difference map (image) of
the e scaled and filtered difference signal. The filtering may be
performed by convolution of the scaled difference signal with a
two-dimensional window w. This convolution may be efficiently
performed through the use of two-dimensional Fast Fourier Transform
("FFT") operations,
[0033] The difference signal may be normalized to have a maximum
value of 1. This approach would result in a spatial map of the echo
decorrelation, similar to measures of turbulence in color Doppler
imaging systems. However, instead of examining echo decorrelation
(a normalized measure of echo differences), a non-normalized map is
considered preferable for the present invention because the echo
difference is then enhanced in regions of greater echogenicity.
Since hyperechoicity is one correlate to tissue ablation, this
feature increases the specificity of the method for monitoring
thermal ablative medical treatment by providing an image with
greater detail.
[0034] The spatially filtered signal of FIG. 9 is then displayed as
an image at step 24 (see FIG. 3), in any manner previously
discussed.
[0035] In a second embodiment of the present invention, ultrasound
images may be generated as depicted in FIGS. 10 and 11 At step 40
the tissue is medically treated with high-intensity ultrasound
waves. At step 42 a succession of image frames, depicted as
F.sub.1, F.sub.2, . . . F.sub.n, are received. The image frames
F.sub.1, F.sub.2, . . . F.sub.n each contain a signal representing
the same portion of the target tissue. At step 44 the image frames
F.sub.1, F.sub.2, . . . F.sub.n are mathematically grouped, such as
by summing or averaging, to form a first image frame set labeled
FS.sub.1, as shown in FIG. 11. After waiting a predetermined amount
of time, as at step 46, a second set of image frames F.sub.1,
F.sub.2, . . . F.sup.n are received at step 48. At step 50 the
second set of image frames F.sub.1, F.sub.2, . . . F.sub.n are
mathematically grouped, such as by summing or averaging, to form a
second image frame set FS.sub.2 as shown in FIG. 11. The raw echo
signals of image frame sets FS.sub.1 and FS.sub.2 may be processed
at step 52, such as to derive complex analytic signals by means of
a Hilbert transformation. The signal of image frame set FS.sub.2 is
then subtracted from the signal of image frame set FS.sub.1 at step
54 to derive a difference signal. The difference signal may take
into account both phase and amplitude differences between FS.sub.1
and FS.sub.2, computing the amplitude of the signal differences (as
opposed to differences in signal amplitude) of FS.sub.1 and
FS.sub.2. At step 56 the difference signal may be scaled to a
convenient value using any scaling methods and algorithms,
previously described or otherwise. At step 58 the difference signal
is spatially filtered to smooth small-scale random variations
before being displayed as an image at step 59. This embodiment of
the present invention may provide a more robust map of the
backscatter changes by reducing the influence of random signal
variations caused by rapid transient effects such as violent bubble
activity produced during tissue ablation.
[0036] In a third embodiment of the present invention, smoothing of
the image signal may alternatively be accomplished by using a
plurality of image frames, as illustrated in FIGS. 12 and 13. The
tissue is medically treated at step 60, then a set of image frames
F.sub.1, F.sub.2, . . . F.sub.n are received at step 62. A
plurality of difference signals D.sub.1, D.sub.2, . . . D.sub.n are
computed at step 64. It should be noted that the difference signals
may be computed using various arrangements of pairs of image
frames. For example, difference signal D.sub.1 may be formed by
subtracting F.sub.2 from F.sub.1; likewise, D.sub.2 may be formed
by subtracting F.sub.3 from F.sub.2, as shown in FIG. 13. Other
arrangements of image frame pairs may also be used, including (but
not limited to) odd-numbered image frames (i.e., subtracting
F.sub.3 from F.sub.1, etc.) and even-numbered image frames (i.e.,
subtracting F.sub.4 from F.sub.2, etc.). The pairings may be
interlaced (i.e., subtracting F.sub.2 from F.sub.1, subtracting
F.sub.3 from F.sub.2, etc.) or sequential (i.e., subtracting
F.sub.2 from F.sub.1, F.sub.4 from F.sub.3, etc.). An indication or
image may be displayed at step 66, showing at least one of the
difference signals D.sub.1, D.sub.2, . . . D.sub.n. At step 68 the
difference signals D.sub.1, D.sub.2, . . . D.sub.n may be further
processed, such as by averaging, to reduce artifactual content. The
averaged signal, denoted as D, may also be displayed as an image,
as at step 70. The averaged signals may themselves be cumulatively
summed, as at step 72, to provide a view of the results of
successive medical treatments 60. The summed averages may be
displayed at step 74. If treatment is determined to be complete at
step 76, the method is ended at step 78. However, if the tissue
appears to require additional treatment, the transducer may be
re-positioned at step 80. The method is then repeated beginning at
step 60 to continue treatment of the targeted tissue.
[0037] A fourth embodiment of the present invention is shown in
FIGS. 14 and 15 wherein a difference signal is derived using
imaging frames generated both before and after medical treatment.
At step 82 the ultrasound transducer is positioned proximate the
targeted tissue to be medically treated. At step 84 a pre-treatment
image frame F.sub.1 is generated from received ultrasound signals.
Then, at step 86 the tissue is subject to a quantum of medical
treatment, such as by ablating the tissue. After a quantum of
medical treatment is administered, a second image frame F.sub.2 is
generated at step 88. A difference signal is derived at step 90,
using the data contained in image frames F.sub.1 and F.sub.2 in the
same manner as previously described. An indication or image of the
difference signal may be displayed at step 92. If treatment is
determined to be complete at step 94, the method is ended at step
96. However, if the targeted tissue is determined to require
additional treatment, the transducer may be re-positioned as
necessary at step 98. The method is then repeated and a subsequent
quantum of treatment is administered beginning at step 84.
[0038] An expected difficulty for the present invention is
artifactual backscatter change due to tissue motion artifacts. This
difficulty can be largely overcome by several features of the
method. First, backscatter differences can be computed between
image frames closely spaced in time. If the tissue moves only a
small amount during the interval, motion artifacts are then small.
Second, artifacts due to axial tissue motion can be removed
effectively by phase compensation during signal processing. That
is, before computation of the signal difference, one of the complex
image frames is multiplied by a phase compensation function
e.sup.-j.theta., where .theta. is the low-pass filtered phase of
the conjugate product of the two complex image frames. The
resulting signal difference is then computed, for example, using
Equation 2:
.PSI.=.intg..sub.-.infin..sup..infin..intg..sub.-.infin..sup..infin.w(x,-
z)|p.sub.0(x,z)-p.sub.1(x,z)e.sup.-iw.sup.0.sup..delta.t|.sup.2dxdz
Equation 2
[0039] which is an improved echo difference map with reduced tissue
motion artifacts.
[0040] It is understood that one or more of the
previously-described embodiments, expressions of embodiments,
examples, methods, etc. can be combined with any one or more of the
other previously-described embodiments, expressions of embodiments,
examples, methods, etc. For example, and without limitation, any of
the ultrasound transducers may be used with other methods of
medical treatment, such as producing images to aid in tissue
ablation by means of Radio Frequency (RF) and laser energy, various
non-ablative ultrasound medical treatments, and various ultrasound
imaging applications.
[0041] The foregoing description of several expressions of
embodiments and methods of the invention has been presented for
purposes of illustration. It is not intended to be exhaustive or to
limit the present invention to the precise forms and procedures
disclosed, and obviously many modifications and variations are
possible in light of the above teaching. It is intended that the
scope the invention be defined by the claims appended hereto.
* * * * *