U.S. patent number RE38,209 [Application Number 09/073,876] was granted by the patent office on 2003-08-05 for diagnostic ultrasound system.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Fumiyasu Sakaguchi, Nobuo Yamazaki.
United States Patent |
RE38,209 |
Yamazaki , et al. |
August 5, 2003 |
Diagnostic ultrasound system
Abstract
A diagnostic ultrasound system is provided for displaying a
color image of a motion of a tissue scans an ultrasonic pulse
signal along a tomographic plane to acquire an electrical echo
signal, extracts a Doppler signal from the echo signal, calculates
velocity data concerning the motion of the tissue for respective
sample points on the tomographic plane on the basis of the Doppler
signal, and forms data of a B-mode tomographic image on the basis
of the echo signal. The system comprises an element for setting a
scale along which each of the velocity data over a measurable band
of frequencies of the Doppler signal is assigned to each gradation
data for color display, the measurable band of frequencies being
limited by a pulse repetition frequency of the ultrasonic pulse
signal and a given low-velocity band of the measurable frequency
band being enhanced in the gradation data than a remaining velocity
band of the measurable band, an element for converting the velocity
data into the gradation data according to the scale, an element for
blanking either one of the converted gradation data and the
calculated velocity data at every sample point when each of them
exceeds a specified threshold, and an element for displaying the
velocity color image subjected to blanking and superimposed on the
B-mode tomographic image.
Inventors: |
Yamazaki; Nobuo (Otawara,
JP), Sakaguchi; Fumiyasu (Otawara, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
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Family
ID: |
26358899 |
Appl.
No.: |
09/073,876 |
Filed: |
May 7, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
415479 |
Mar 31, 1995 |
05513640 |
May 7, 1996 |
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Foreign Application Priority Data
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Jun 24, 1994 [JP] |
|
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6-143528 |
Feb 9, 1995 [JP] |
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7-21795 |
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Current U.S.
Class: |
600/455 |
Current CPC
Class: |
G01N
29/0609 (20130101); G01S 7/52071 (20130101); G01S
7/5206 (20130101); G01S 15/8979 (20130101); G01S
15/899 (20130101) |
Current International
Class: |
G01S
7/52 (20060101); G01S 15/89 (20060101); G01S
15/00 (20060101); A61B 008/12 () |
Field of
Search: |
;600/443,437,440,441,454,458,468,465,451,455,456,457 ;348/163,29,30
;73/861.25 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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4800891 |
January 1989 |
Kim |
5148809 |
September 1992 |
Biegeleisen-Knight et al. |
5170792 |
December 1992 |
Sturgill et al. |
5215094 |
June 1993 |
Franklin et al. |
5285788 |
February 1994 |
Arenson et al. |
|
Foreign Patent Documents
Other References
"Colour Doppler Velocity Imaging of the Myocardium", W. N. McDicken
et al., Ultrasound in Med. & Biol., 18(6/7):651-654
(1992)..
|
Primary Examiner: Manuel; George
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Claims
What is claimed is:
1. A diagnostic ultrasound system for displaying a color image of a
motion of a tissue contained on a subject's tomographic plane,
comprising: means for scanning an ultrasonic pulse signal along the
tomographic plane so as to acquire an electrical echo signal
corresponding to an ultrasonic signal reflected from the
tomographic plane; means for extracting a Doppler signal from the
echo signal, said Doppler signal being Doppler-shifted by the
motion of the tissue; means for calculating velocity data
concerning the motion of the tissue for respective sample points on
the tomographic plane on the basis of the Doppler signal; means for
setting a scale along which each of the velocity data over a
measurable band of frequencies of the Doppler signal is assigned to
each gradation data for color display, said measurable band of
frequencies being limited by a pulse repetition frequency of the
ultrasonic pulse signal and a given low-velocity band of the
measurable frequency band being enhanced in the gradation data than
a remaining velocity band of the measurable band; means for
converting the velocity data into the gradation data according to
the scale; and means for displaying the color image using the
gradation data provided by the velocity converting means.
2. The diagnostic ultrasound system according to claim 1, wherein
said extracting means comprises a low-pass filter for selectively
extracting the Doppler signal.
3. The diagnostic ultrasound system according to claim 2, wherein
said scale is non-linear in a ratio between changes in the velocity
data and changes in the gradation data.
4. The diagnostic ultrasound system according to claim 3, wherein
said ratio in the given low-velocity band is higher than said ratio
in the remaining velocity band.
5. The diagnostic ultrasound system according to claim 4, wherein
said specified low-velocity band is any of
-fr/8.ltoreq.fd.ltoreq.fr/8, -fr/12.ltoreq.fd.ltoreq.fr/12, and
-fr/16.ltoreq.fd.ltoreq.fr/16, where fr represents the pulse
repetition frequency of the ultrasonic pulse signal and fd
represents a Doppler shift frequency.
6. The diagnostic ultrasound system according to claim 4, wherein
said specified low-velocity band is assigned to all of the
gradation data and said remaining velocity band is assigned to
maximum values of the gradation data.
7. The diagnostic ultrasound system according to claim 6, wherein
said ratio for said specified low-velocity band is linearly
changed.
8. The diagnostic ultrasound system according to claim 6, wherein a
scale portion of said scale in the specified low-velocity band is
changed in a bent line divided into two line segments, one of said
two line segments having higher in the ratio being assigned to a
lower side on a axis representing the velocity data.
9. The diagnostic ultrasound system according to claim 1, wherein
said gradation data consist of a plurality of color code data
representing changes in either one of color brightness and hue,
said changes expressing degrees of the velocity data in each
direction of the motion of the tissue to the ultrasonic pulse
signal.
10. The diagnostic ultrasound system according to claim 9, wherein
at least maximum data of said color code data is discontinuous in
gradation levels from a series of remaining data of said color code
data.
11. The diagnostic ultrasound system according to claim 10, wherein
said extracting means comprises a low-pass filter for selectively
extracting the Doppler signal.
12. The diagnostic ultrasound system according to claim 11, wherein
said scale is non-linear in a ratio between changes in the velocity
data and changes in the gradation data.
13. The diagnostic ultrasound system according to claim 12, wherein
said ratio in the given low-velocity band is higher than said ratio
in the remaining velocity band.
14. A diagnostic ultrasound system for displaying a color image of
a motion of a tissue contained on a subject's tomographic plane,
said color image being superposed on a B-mode tomographic image of
the subject's tomographic plane, said system comprising: means for
scanning an ultrasonic pulse signal along the tomographic plane to
acquire an electrical echo signal corresponding to a reflected
ultrasonic signal from the tomographic plane; means for extracting
a Doppler signal from the echo signal, said Doppler signal being
Doppler-shifted by the motion of the tissue; means for calculating
velocity data concerning the motion of the tissue for respective
sample points on the tomographic plane on the basis of the Doppler
signal; means for forming data of the B-mode tomographic image on
the basis of the echo signal; means for blanking the velocity data
at every sample point when each of the velocity data exceeds a
specified threshold; and means for displaying the color image by
coloring the velocity data and by superimposing the velocity data
subjected to blanking by the blanking means on the data of the
B-mode tomographic image.
15. A diagnostic ultrasound system for displaying a color image of
a motion of a tissue contained on a subject's tomographic plane,
said color image being superposed on a B-mode tomographic image of
the subject's tomographic plane, said system comprising: means for
scanning an ultrasonic pulse signal along the tomographic plane to
acquire an electrical echo signal corresponding to a reflected
ultrasonic signal from the tomographic plane; means for extracting
a Doppler signal from the echo signal, said Doppler signal being
Doppler-shifted by the motion of the tissue; means for calculating
velocity data concerning the motion of the tissue for respective
sample points on the tomographic plane on the basis of the Doppler
signal; means for forming data of the B-mode tomographic image on
the basis of the echo signal; means for setting a scale along which
each of the velocity data over a measurable band of frequencies of
the Doppler signal is assigned to each gradation data for color
display, said measurable band of frequencies being limited by a
pulse repetition frequency of the ultrasonic pulse signal and a
given low-velocity band of the measurable frequency band being
enhanced in the gradation data than a remaining velocity band of
the measurable band; means for converting the velocity data into
the gradation data according to the scale; means for blanking
either one of the converted gradation data and the calculated
velocity data at every sample point when each of said either one
exceeds a specified threshold; and means for displaying the color
image by coloring the velocity data and by superimposing the
velocity data subjected to blanking by the blanking means on the
data of the B-mode tomographic image.
16. The diagnostic ultrasound system according to claim 15, wherein
said scale setting means is a means that sets the scale in which a
ratio of changes in the gradation data to changes in the Doppler
frequency is higher than a corresponding ratio for analysis of
fluid motion within the subject and the velocity data larger than a
reference velocity data corresponding to maximums of the gradation
data are all assigned to the maximums.
17. The diagnostic ultrasound system according to claim 16, wherein
said gradation data consists of a plurality of code data
representing brightnesses of a specified color for every direction
of the motion of the tissue to the ultrasonic pulse signal.
18. The diagnostic ultrasound system according to claim 16, wherein
said gradation consists of a plurality of code data representing
hues of a specified color for every direction of the motion of the
tissue to the ultrasonic pulse signal.
19. The diagnostic ultrasound system according to claim 16, further
comprising means for setting the threshold independently of the
scale.
20. The diagnostic ultrasound system according to claim 19, wherein
said either one is the velocity data calculated by the velocity
calculating means.
21. The diagnostic ultrasound system according to claim 20, wherein
said velocity data calculating means comprises means for analyzing
frequency components of the Doppler signal, means for computing the
velocity data at each of the sample points on the basis of results
analyzed by the analyzing means and wherein said velocity data
computing means, said velocity data converting means and said data
blanking means are incorporated into a single unit.
22. The diagnostic ultrasound system according to claim 20, wherein
said specified threshold consists of values of the velocity data,
said values corresponding to maximums of the gradation data defined
by the scale.
23. The diagnostic ultrasound system according to claim 19, wherein
said either one is the gradation data converted by the velocity
data converting means and wherein said threshold setting means
includes a member for setting a gradation data threshold lower than
maximums of the gradation data.
24. The diagnostic ultrasound system according to claim 23, wherein
said data blanking means is incorporated into an independent unit
of at least the velocity data calculating means and the color image
displaying means.
25. The diagnostic ultrasound system according to claim 23, wherein
said color image displaying means has a digital scan converter for
superimposing the velocity data on the data of the B-mode
tomographic image pixel by pixel, said digital scan converter
including the data blanking means.
26. The diagnostic ultrasound system according to claim 16, wherein
said scale setting means is a means that automatically sets the
threshold in connection with setting the scale.
27. The diagnostic ultrasound system according to claim 26, wherein
said either one is the gradation data converted by the velocity
data converting means..Iadd.
28. A diagnostic ultrasound system for displaying a color image of
a motion of a tissue of a subject's tomographic plane, comprising:
means for scanning an ultrasonic pulse signal along the tomographic
plane so as to acquire an electrical echo signal corresponding to
an ultrasonic signal reflected from the tomographic plane; means
for extracting a Doppler signal from the echo signal, said Doppler
signal being Doppler-shifted by the motion of the tissue; means for
calculating velocity data concerning the motion of the tissue for
respective sample points on the tomographic plane on the basis of
the Doppler signal; means for setting a scale along which each of
the velocity data over a measurable band of frequencies of the
Doppler signal is assigned to each gradation data for color
display, a given low-velocity band of the measurable frequency band
being enhanced in the gradation data compared to a remaining
velocity band of the measurable band; means for converting the
velocity data into the gradation data according to the scale; and
means for displaying the color image using the gradation data
provided by the velocity converting means..Iaddend..Iadd.
29. A diagnostic ultrasound system for displaying a color image of
a motion of a tissue contained on a subject's tomographic plane,
comprising: means for scanning an ultrasonic pulse signal along the
tomographic plane so as to acquire an electrical echo signal
corresponding to an ultrasonic signal reflected from the
tomographic plane; means for extracting a Doppler signal from the
echo signal, said Doppler signal being Doppler-shifted by the
motion of the tissue; means for calculating velocity data
concerning the motion of the tissue for respective sample points on
the tomographic plane on the basis of the Doppler signal; means for
setting a scale along which each of the velocity data over a
measurable band of frequencies of the Doppler signal is assigned to
each gradation data for color display, said measurable band of
frequencies being limited by a pulse repetition frequency of the
ultrasonic pulse signal and a given low-velocity band of the
measurable frequency band being enhanced in the gradation data
compared to a remaining velocity band of the measurable band; means
for converting the velocity data into the gradation data according
to the scale; and means for displaying the color image using the
gradation data provided by the velocity converting
means..Iaddend..Iadd.
30. The diagnostic ultrasound system according to claim 6, wherein
a scale portion of said scale in the specified low-velocity band is
changed in a bent line divided into two line segments, the one of
said line segments having lower absolute Doppler shift frequencies
being enhanced in the gradation data..Iaddend..Iadd.
31. A diagnostic ultrasound system for displaying a color image of
a motion of a tissue contained on a subject's tomographic plane,
said color image being superposed on a B-mode tomographic image of
the subject's tomographic plane, said system comprising: means for
scanning an ultrasonic pulse signal along the tomographic plane to
acquire an electrical echo signal corresponding to a reflected
ultrasonic signal from the tomographic plane; means for extracting
a Doppler signal from the echo signal, said Doppler signal being
Doppler-shifted by the motion of the tissue; means for calculating
velocity data concerning the motion of the tissue for respective
sample points on the tomographic plane on the basis of the Doppler
signal; means for forming data of the B-mode tomographic image on
the basis of the echo signal; means for setting a scale along which
each of the velocity data over a measurable band of frequencies of
the Doppler signal is assigned to each gradation data for color
display, said measurable band of frequencies being limited by a
pulse repetition frequency of the ultrasonic pulse signal and a
given low-velocity band of the measurable frequency band being
enhanced in the gradation data compared to a remaining velocity
band of the measurable band; means for converting the velocity data
into the gradation data according to the scale; means for blanking
either one of the converted gradation data and the calculated
velocity data at every sample point when each of said either one
exceeds a specified threshold; and means for displaying the color
image by coloring the velocity data and by superimposing the
velocity data subjected to blanking by the blanking means on the
data of the B-mode tomographic image..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to diagnostic ultrasound system, or
more particularly, to a diagnostic ultrasound system adaptable to
tissue Doppler imaging based on an ultrasonic pulsed-wave Doppler
technique.
2. Description of the Related Art
In the past, a diagnostic ultrasound system having a tissue Doppler
imaging (TDI) feature has been disclosed, for example, in Japanese
Patent Laid-Open No. 6-114059 (of which title of the invention is
an "ultrasound color Doppler tomography system") proposed by the
present applicant. The diagnostic ultrasound system described in
the unexamined patent publication has a feature that uses a
pulsed-wave Doppler technique and a lowpass filter to detect the
motion velocities of tissues including the cardiac muscle and
vascular wall, compute various physical volumes relevant to motion
on the basis of the motion velocities, and display the results of
computation in appropriate modes in color. For detecting the motion
velocity of a tissue, since the motion velocity of a tissue is
markedly lower than a blood flow velocity, the pulse repetition
frequencies (PRF) of transmitted ultrasonic pulsed waves (rate
pulses) are lowered to enable measurement of super-low motion
velocities of tissues.
Various modes are available for color display of the results of
computation. In the invention described in the unexamined patent
publication, two-dimensional color display has been proposed. As
for the gradations for the color display, a procedure used for the
blood flow imaging, which is implemented in a color Doppler system
and shares concepts with tissue Doppler imaging, can be
employed.
In the blood flow imaging, a band of Doppler shift frequencies fd
ranging from -fr/2 to fr/2 (where, fr denotes a pulse repetition
frequency of an ultrasonic pulsed wave) is rendered, as shown in
FIG. 27, in 32 gradation (gray-scale)levels (fr/32 per level) with
different color brightnesses or hues. In other words, a scale whose
gradation levels associated with velocities (Doppler shifts) have a
constantly progressive change is assigned to the whole band of
Doppler shift frequencies ranging from -fr/2 to fr/2, thus defining
a color-display gradation between red (yellow) to blue (light
blue).
As mentioned above, one of the characteristics of tissue Doppler
imaging lies in that pulse repetition frequencies (lower frame
rates) of ultrasonic waves are set to lower values in order to
enable measurement of ultra-low motion velocities of tissues. Owing
to the characteristic of enabling measurement of an ultra-low
motion velocity, the band of Doppler shift frequencies required for
display images produced by tissue Doppler imaging is narrower than
that required for display images produced by blood flow imaging of
ranges, for example, from -fr/8 to fr/8.
Nevertheless, at present, the assignment of a color-display
gradation adopted for blood flow imaging cannot help applying to
tissue Doppler imaging as it is. As a result, the number of
gradation levels assigned to a low-velocity band is quite limited.
A tissue region to be observed; such as, the cardiac muscle
appears, for example, in red of almost the same hue or brightness.
It is therefore very hard to visually assess a difference in
velocity in a low-velocity band image. Even if a difference in
velocity smaller than fr/32 can be detected, since a displayed hue
or brightness is unchanged, high-precision detectability is
canceled out by poor displaying ability. There still exists an
unsolved problem that the high-precision detectability cannot be
exerted fully.
When tissue Doppler imaging is used for diagnosis, it should be
discerned promptly whether the cardiac muscle or any other tissue
region of interest is normal or abnormal. Using the conventional
display technique, the levels of a color-display gradation are
assigned uniformly between a low-velocity band and a high-velocity
band. The displaying ability for the low-velocity band is, as
described previously, poor. There is therefore difficulty in
discerning whether a diagnostic region is normal or abnormal.
Consequently, it takes too much time for diagnosis. Moreover, an
examining physician is requested to have high expertise.
SUMMARY OF THE INVENTION
The present invention attempts to solve the aforesaid unsolved
problems. The first object of the present invention is to improve
the ability to display a low-velocity band image by making the most
of the function relevant to measurements of motion concerning a
low-velocity band which is available in tissue Doppler imaging.
The second object of the present invention is to achieve the first
object and provide images that are produced by tissue Doppler
imaging (hereinafter, TDI images) and facilitate easy discernment
of whether a region of interest (hereinafter, ROI)is normal or
abnormal.
For achieving the above objects, as one aspect of the invention,
there is provided a diagnostic ultrasound system for displaying a
color image of a motion of a tissue contained on a subject's
tomographic plane, comprising: an element for scanning an
ultrasonic pulse signal along the tomographic plane so as to
acquire an electrical echo signal corresponding to an ultrasonic
signal reflected from the tomographic plane; an element for
extracting a Doppler signal from the echo signal, the Doppler
signal being Doppler-shifted by the motion of the tissue; an
element for calculating velocity data concerning the motion of the
tissue for respective sample points on the tomographic plane on the
basis of the Doppler signal; an element for setting a scale along
which each of the velocity data over a measurable band of
frequencies of the Doppler signal is assigned to each gradation
data for color display, the measureable band of frequencies being
limited by a pulse repetition frequency of the ultrasonic pulse
signal and a given low-velocity band of the measurable frequency
band being enhanced in the gradation data than a remaining velocity
band of the measurable band; an element for converting the velocity
data into the gradation data according to the scale; and an element
for displaying the color image using the gradation data provided by
the velocity converting element.
Preferably, the extracting element comprises a low-pass filter for
selectively extracting the Doppler signal. Still preferably, the
scale is non-linear in a ratio between changes in the velocity data
and changes in the gradation data. For example, the ratio in the
given low-velocity band is higher than said ratio in the remaining
velocity band. For example, the specified low-velocity band is any
of -fr/8.ltoreq.fd.ltoreq.fr/8, -fr/12.ltoreq.fd.ltoreq.fr/12, and
-fr/16.ltoreq.fd.ltoreq.fr/16, where fr represents the pulse
repetition frequency of the ultrasonic pulse signal and fd
represents a Doppler shift frequency. It is preferred that at least
maximum data of the color code data is discontinuous in gradation
levels from a series of remaining data of the color code data.
A diagnostic ultrasound system in accordance with the above aspect
of the present invention is adaptable to tissue Doppler imaging.
For this imaging technique, the cardiac muscle or any other region
is scanned according to an ultrasonic pulsed-wave Doppler method.
Echoes are then obtained, whereby a motion velocity is computed for
each of sample points on a scanned tomographic plane. The motion
velocity is visualized in two-dimensional color display mode. For
the display, the slope of a scale of velocity data versus
color-display gradation data to be assigned to a low-velocity band
(for example,-fr/8.ltoreq.fd.ltoreq.fr/8) within a velocity range
measurable by the ultrasonic pulsed-wave Doppler that is equivalent
to a band of Doppler shifts; -fr/2.ltoreq.fd.ltoreq. fr/2 (where fr
denotes a pulse repetition frequency of an ultrasonic pulsed wave,
and fd denotes a Doppler shift) is larger than that of the other
velocity band. This results in an increase in display resolution
for the low-velocity band. A minute change in low-velocity motion
of the cardiac muscle is therefore visualized with high sensitivity
as a change in multi-level gradation of color brightness degrees
(luminances) or hues. Consequently, even if an attempt is made to
upgrade the function relevant to measurements of low-velocity
motion by specifying lower pulse repetition frequencies, the
function will not be impaired. Moreover, a pixel rendering a
velocity comparable to a maximum gradation level is displayed with
such a hue as making the pixel discontinuous with the other pixels
rendering lower velocities. The pixel rendering the velocity
comparable to a maximum gradation level is therefore readily
discernible. Thus, discernible efficiency improves.
As another aspect of the invention is provided by a diagnostic
ultrasound system for displaying a color image of a motion of a
tissue contained on a subject's tomographic plane, the color image
being superposed on a B-mode tomographic image of the subject's
tomographic plane, the system comprising: an element for scanning
an ultrasonic pulse signal along the tomographic plane to acquire
an electrical echo signal corresponding to a reflected ultrasonic
signal from the tomographic plane; an element for extracting a
Doppler signal from the echo signal, the Doppler signal being
Doppler-shifted by the motion of the tissue; an element for
calculating velocity data concerning the motion of the tissue for
respective sample points on the tomographic plane on the basis of
the Doppler signal; an element for forming data of the B-mode
tomographic image on the basis of the echo signal; an element for
blanking the velocity data at every sample point when each of the
velocity data exceeds a specified threshold; and an element for
displaying the color image by coloring the velocity data and by
superimposing the velocity data subjected to blanking by the
blanking element on the data of the B-mode tomographic image.
Still another aspect of the invention is provided by a diagnostic
ultrasound system for displaying a color image of a motion of a
tissue contained on a subject's tomographic plane, the color being
superposed on a B-mode tomographic image of the subject's
tomographic plane, the system comprising: an element for scanning
an ultrasonic pulse signal along the tomographic plane to acquire
an electrical echo signal corresponding to a reflected ultrasonic
signal from the tomographic plane; an element for extracting a
Doppler signal from the echo signal, the Doppler signal being
Doppler-shifted by the motion of the tissue; an element for
calculating velocity data concerning the motion of the tissue for
respective sample points on the tomographic plane on the basis of
the Doppler signal; an element for forming data of the B-mode
tomographic image on the basis of the echo signal; an element for
setting a scale along which each of the velocity data over a
measurable band of frequencies of the Doppler signal is assigned to
each gradation data for color display, said measurable band of
frequencies being limited by a pulse repetition frequency of the
ultrasonic pulse signal and a given low-velocity band of the
measurable frequency band being enhanced in the gradation data than
a remaining velocity band of the measurable band; an element for
converting the velocity data into the gradation data according to
the scale; an element for blanking either one of the converted
gradation data and the calculated velocity data at every sample
point when each of either one exceeds a specified threshold; and an
element for displaying the color image by coloring the velocity
data and by superimposing the velocity data subjected to blanking
by the blanking element on the data of the B-mode tomographic
image.
Preferably, the scale setting element is an element that sets the
scale in which a ratio of changes in the gradation data to changes
in the Doppler frequency is higher than a corresponding ratio for
analysis of fluid motion within the subject and the velocity data
larger than a reference velocity data corresponding to maximums of
the gradation data are all assigned to the maximums. It is
preferred that the diagnostic ultrasound system further comprises
an element for setting the threshold independently of the scale. It
is also preferred that the scale setting element is an element that
automatically sets the threshold in connection with setting the
scale.
In consequence, in the same way as explained above, an increase in
display resolution for the low-velocity band is provided. In
addition, sample points having velocities higher than the specified
threshold on the tomographic plane dose not display the tissue
Doppler image and, instead of it, display only the B-mode
tomographic image as the background image hidden behind the tissue
Doppler image. Properly specifying the threshold enables to exclude
or minimize the meaningless (gradation-less) velocity color region
of a tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a block diagram showing a diagnostic ultrasound system in
accordance with the first embodiment of the present invention;
FIG. 2 is a graph expressing characteristics of Doppler shift
frequencies (motion velocity) induced by tissues or blood flow and
a characteristic of a low-pass filter employed in tissue Doppler
imaging according to the first embodiment;
FIG. 3 is a graph expressing an example of a velocity conversion
scale according to the first embodiment;
FIG. 4 is a brief flowchart describing a sequence executed by an
encoding arithmetic unit in the first embodiment;
FIG. 5 shows a relationship between the motion direction of the
cardiac muscle and a color bar in the first embodiment;
FIG. 6 shows an example of display of the cardiac muscle in the
first embodiment;
FIG. 7 shows another example of a velocity conversion scale;
FIG. 8 shows yet another example of a velocity conversion
scale;
FIG. 9 shows still another example of a velocity conversion
scale;
FIG. 10 is a block diagram showing a diagnostic ultrasound system
in accordance with the second embodiment of the present
invention;
FIG. 11 is a block diagram showing a velocity arithmetic unit in
the second embodiment;
FIG. 12 is a flowchart describing an example of a sequence executed
by the velocity arithmetic unit;
FIG. 13 is an explanatory diagram concerning output data supplied
by a frequency analyzer;
FIG. 14 shows an example of a velocity conversion scale;
FIG. 15 is an explanatory diagram concerning an increase or
decrease in size of a blanking band corresponding to a change in
velocity threshold;
FIG. 16 is a block diagram showing a diagnostic ultrasound system
in accordance with the third embodiment of the present
invention;
FIG. 17 is a flowchart describing an example of a sequence executed
by a blanking control unit in the third embodiment;
FIG. 18 is a flowchart describing an example of a sequence executed
by a velocity arithmetic unit in the third embodiment;
FIG. 19 is a flowchart describing an example of a sequence executed
by a blanking unit in the third embodiment;
FIG. 20 shows an example of a velocity conversion scale in the
third embodiment;
FIG. 21 is a block diagram showing a diagnostic ultrasound system
in accordance with a variant of the present invention;
FIG. 22 is a block diagram showing a diagnostic ultrasound system
in accordance with the fourth embodiment of the present
invention;
FIG. 23 is a flowchart describing a sequence executed by a velocity
arithmetic unit in the fourth embodiment;
FIG. 24 shows an example of velocity thresholds that define
blanking bands and depend on velocity conversion scales;
FIG. 25 is a partial block diagram showing a diagnostic ultrasound
system in accordance with the fifth embodiment of the present
invention;
FIG. 26 is a flowchart partly describing an example of a sequence
executed by a blanking control unit in the fifth embodiment;
and
FIG. 27 shows a velocity conversion scale for blood flow velocity
analysis in accordance with a prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
The first embodiment of the present invention will be described in
conjunction with FIGS. 1 to 6. A diagnostic ultrasound system in
accordance with the first embodiment is a diagnostic system for
producing TDI images of the cardiac muscle (cardiac wall) that is a
tissue.
FIG. 1 is a block diagram showing a diagnostic ultrasound system.
As illustrated, a diagnostic ultrasound system 10 comprises an
ultrasound probe 11 responsible for receiving or transmitting
ultrasonic waves from or to a subject, a main unit 12 for driving
the ultrasound probe 11 and processing signals received by the
ultrasound probe 11, an electrocardiograph (hereinafter, ECG) 13
connected to the main unit 12 in order to detect
electrocardiographic information, and an operation panel 14
connected to the main unit 12 and capable of supplying instruction
information entered by an operator to the main unit,
The main unit 12 is broadly divided into an ultrasound probe
system, an ECG system, and an operation panel system according to
the type of signal line concerned, The ultrasound probe system has
an ultrasonic-wave transmitter/receiver 15 connected to the
ultrasound probe 11 and includes a B-mode digital scan converter
(hereinafter, B-mode DSC) 16, a B-mode frame memory 17, a memory
synthesizer 18, and a display unit 19 which are installed in the
output stage of the ultrasonic-wave transmitter/receiver 15. The
ultrasound probe system further includes a phase detector 20 for
use in color mapping, a filter 21, a frequency analyzer 22, an
encoding arithmetic unit 23, a tissue Doppler imaging DSC
(hereinafter, TDI DSC) 24, and a tissue Doppler imaging frame
memory (hereinafter, TDI frame memory) 25, all of which are
connected to the ultrasound probe 11. The ECG system has an ECG
amplifier 40 connected to the ECG 13 and includes a triggering
signal generator 41 and a reference data memory 42 which are
connected in the output stage of the amplifier 40. The operation
panel system includes a CPU 43 that inputs operation information
entered at the operation panel 14, and a timing signal generator 44
working under the control of the CPU 43. The CPU 43 can supply a
ROI setting signal representing a command entered at the operation
panel 14 by an operator to component elements required for setting
a ROI.
In this embodiment, the ultrasound probe 11 and ultrasonic-wave
transmitter/receiver 15 constitute a scanning means in accordance
with the present invention. The phase detector 20 serves as a
sampling means. The filter 21 and frequency analyzer 22 constitute
a velocity arithmetic means in accordance with the present
invention. The TDI DSC 24, TDI frame memory 25, memory synthesizer
18, and display unit 19 constitute a display means in accordance
with the present invention. The encoding arithmetic unit 23 has the
capabilities of a scale setting means and a velocity converting
means.
A phased-array transducer in which a plurality of strip-shaped
piezoelectric oscillators are set in array is incorporated in the
ultrasound probe 11. The piezoelectric oscillators are energized in
response to drive signal sent from the ultrasonic-wave
transmitter/receiver 15. By controlling the delay times of drive
signals, scan directions can be changed to enable electronic sector
scanning. Delay-time patterns set for the ultrasonic-wave
transmitter/receiver 15 are controlled by the CPU 43 using a
reference signal sent from the timing signal generator 44, as a
representation of a reference time instant. The ultrasonic-wave
transmitter/receiver 15 supplies drive voltages, which are
generated according to the delay-time patterns controlled
dependently on scan directions, to the ultrasound probe 11. When
receiving the drive voltages, the ultrasound probe 11 allows the
transducer to transform the voltages into ultrasonic waves. The
resultant ultrasonic waves are transmitted to the heart of a
subject. The transmitted ultrasonic waves are reflected from
tissues including the heart and returned to the ultrasound probe
11. The transducer in the probe 11 then transforms the reflected
ultrasonic waves into voltages (echoes). The echoes are supplied to
the ultrasonic-wave transmitter/receiver 15.
A signal processor in the ultrasonic-wave transmitter/receiver 15
beam-forms the input echoes by delaying the echoes in the same
manner as it does for transmission, and produces an echo beam that
is equivalent to an ultrasound beam focused in the scan direction.
The echo beam resulting from beam forming is subjected to phase
detection and then supplied to the B-mode DSC 16. The DSC 16
converts echo data resulting from ultrasound scanning into standard
TV data and supplies the standard TV data into the memory
synthesizer 18. Concurrently, the B-mode DSC 16 places data of a
plurality of images produced in any cardiac phase in the B-mode
frame memory 17.
The echoes processed by the ultrasonic-wave transmitter/receiver 15
are also supplied to the phase detector 20. The phase detector 20
includes mixers and low-pass filter. Echoes reflected from a region
making motion; such as, the cardiac muscle have undergone a Doppler
shift due to the Doppler effect. The phase detector 20 performs
phase detection on the echoes to discriminate frequencies of
Doppler signals and then supplies Doppler signals alone to the
filter 21.
The filter 21 removes unnecessary signal components; such as,
valvular motion signal components returned from any region other
than the cardiac wall or blood flow signal components from the
Doppler signals resulting from phase detection on the basis of the
relationship of the magnitudes of motion velocities; the magnitude
of a motion velocity of the cardiac muscle<that of a
valve<that of blood flow (See FIG. 2). The filter 21 thus highly
efficiently detects the Doppler signals returned from the cardiac
muscle and related to the direction of an ultrasound beam. In this
case, the filter 21 plays the role of a low-pass filter.
The filter is included in even a color Doppler tomography system
that has already been put to practical use and designed for
acquiring blood flow information. For the color Doppler tomography
system for acquiring blood flow information, the filter serves as a
high-pass filter for handling echoes containing a mixture of blood
flow, cardiac wall, and valvular motion of Doppler signals, and
thus eliminates the Doppler signals other than the blood flow
Doppler signals. If the filter is designed to serve as either of
low-pass and high-pass filters according to a purpose of use, it
can enjoy the general-purpose characteristic.
The Doppler signals filtered by the filter 21 are supplied to the
frequency analyzer 22 lying in the subsequent stage. The frequency
analyzer 22 adopts fast Fourier transform (hereinafter, FFT) or
autocorrelation that is a technique of frequency analysis employed
in blood flow measurements based on an ultrasonic-wave Doppler
technique, wherein average velocities or maximum velocities to be
detected within an observation time interval (time window) at
sample points on a tomographic plane to be scanned are computed. To
be more specific, for example, the FFT or autocorrelation technique
is used to compute average frequencies of Doppler signals at
individual sample points (that is, average motion velocities to be
observed at the sample points) and variances (spectral incoherences
of Doppler signals). Furthermore, the FFT technique is used to
compute maximum frequencies of the Doppler signals (that is,
maximum motion velocities to be observed at the sample points)
substantially in real time. The results of analysis on the
frequencies of the Doppler signals are supplied as color Doppler
information concerning motion velocities to the encoding arithmetic
unit 23 in the subsequent stage.
The encoding arithmetic unit 23 has the capability of a CPU, and
encodes Doppler shift frequencies fd, which are induced at the
sample points on the tomographic plane and provided by the
frequency analyzer 22, into velocity data composed of a given
number of bits using a designated velocity conversion scale.
According to the ultrasonic pulsed-wave Doppler technique, pulse
repetition frequencies fr of ultrasonic pulsed waves correspond to
sampling rates. Based on the sampling theorem, a maximum measurable
Doppler shift frequency fdmax is determined according to the
following formula:
A doppler shift frequency fd that can be computed by the frequency
analyzer 22 and does not trigger aliasing has the following
band:
Within the Doppler shift frequency (velocity) band, a band
expressed below is quantized at a quantization factor of fr/128,
and thus encoded into velocity codes each having a data length of,
for example, 5 bits.
In this case, when the Doppler shift frequency fd ranges as
follows:
it is associated with an encoded data obtained when the fd has a
value -fr/8 comparable to a maximum gradation level for one motion
direction (for example, for a direction of receding from an
ultrasound beam). When the Doppler shift frequency fd ranges as
follows:
it is associated with an encoded data obtained when the fd has a
value fr/8 comparable to a maximum gradation level for the other
motion direction (for example, for a direction of approaching an
ultrasound beam).
As a result, a velocity conversion scale whose abscissae cover a
Doppler shift frequency band of -fr/2.ltoreq.fd.ltoreq.fr/2 and
whose ordinates indicate velocity codes expressed with changing
hues of color-display colors; red (yellow) and blue (light blue)
appears as shown in FIG. 3. That is to say, when the absolute value
of a velocity exceeds a quotient of fr/8, the colors are saturated.
Velocity display data of 5 bits long that is obtained for each
sample point and has undergone encoding is supplied to the TDI DSC
24 in the subsequent stage. The aforesaid procedure corresponds to
step S1 to S5 in FIG. 4.
The TDI DSC 24 includes a DSC circuit 24a for changing scanning
forms and a coloring circuit 24b having a look-up table for use in
converting encoded velocity display data into color data. Velocity
display data sent from the encoding arithmetic unit 23 are
converted into standard TV signals by the DSC circuit 24a, and
further converted into color data by the coloring circuit 24b. The
converted signals are supplied to the memory synthesizer 18.
Now, mention will be made of a color display form used to render a
velocity of the cardiac muscle and employed in the coloring circuit
24b. The color display form is broadly classified into (i) a form
of displaying magnitudes (absolute values) of velocities, (ii) a
form of displaying motion directions and magnitudes of velocities,
and (iii) a form of displaying motion directions. The display form
(i) falls into form (a) in which display is monochrome and
brightnesses are dependent on magnitudes and form (b) in which
colors are dependent on magnitudes. The display form (ii) includes
a form in which directions are discriminated with hues and
magnitudes are indicated with their brightnesses, and a form in
which directions are indicated with hues and magnitudes are
indicated with changes in their hues. Herein, an adaptable form of
rendering velocities is limited dependently on a velocity
information structure. The coloring circuit 24b in the TDI DSC 24
determines colors as shown in FIG. 5. Specifically, according to a
conventional method of rendering a motion approaching an ultrasound
beam in red and a motion receding from the ultrasound beam in blue,
the systolic motion of the cardiac muscle is rendered in red
(yellow) and the diastolic motion thereof is rendered in blue
(light blue). With a larger absolute value, red or blue is gradated
into yellow or light blue. As a result, velocity display data
concerning a desired low-velocity band
of-fr/8.ltoreq.fd.ltoreq.fr/8 is converted into color information
of 32 gradation levels, which represent a series of color-display
colors from light blue through blue and red to yellow, for each
motion direction.
The DSC circuit 24a places a plurality of color Doppler images
produced in any cardiac phase in the TDI frame memory 25.
The aforesaid ECG 13 detects electrocardiographic information of a
subject in respective cardiac phases of the subject. The detected
signal is supplied to each of the triggering signal generator 41
and reference data memory 42 via the ECG amplifier 40. The
reference data memory 42 stores electrocardiographic information
acquired in the respective cardiac phases and supplies required
information to the memory synthesizer 18 when it becomes
necessary.
The triggering signal generator 41 informs the timing signal
generator 44 of timing information concerning the cardiac phases.
The timing signal generator 44 operates under the control of the
CPU 43 that controls delay-time patterns to be set for the
ultrasonic-wave transmitter/receiver 15 in response to an
instruction entered at the operation panel 14. When notified of the
timing of each cardiac phases by the triggering signal generator
41, the timing signal generator 44 outputs a reference signal for
use in transmitting or receiving ultrasonic waves to or from the
ultrasonic-wave transmitter/receiver 15.
As mentioned above, a B-mode image signal sent from the B-mode DSC
16, a TDI-mode image signal sent from the TDI DSC 24, and, if
necessary, electrocardiographic information supplied from the
reference data memory 42 are fed to the memory synthesizer 18. The
memory synthesizer 18 superposes these input signals. Data
resulting from the superposition is supplied to the display unit
19. The display unit 19 includes a cathode-ray tube (hereinafter,
CRT).
As a result, since the blood flow Doppler signal and valvular
Doppler signal have already been cut off by the filter 21, a
tomographic image, in which a B-mode tomographic image
(black-and-white gradation) of the heart and a color image
rendering the motion of the cardiac muscle with colors contained in
a color bar shown in FIG. 5 according to the velocity conversion
scale shown in FIG. 3 are superposed on each other, is, as shown in
FIG. 6, displayed substantially in real time on the display unit 19
(in FIG. 6, a hatched area indicates the cardiac muscle HM). In
other words, the cardiac muscle HM in FIG. 6 appears in red
(yellow) during systole and in blue (light blue) during diastole.
The colors of red and blue reappear cyclically and in real time. A
change in motion velocity during systole or aliastole is expressed
substantially in real time as a change in hue of red or yellow, or
blue or light blue. The motion velocity of the cardiac muscle HM
can be rendered in color substantially in real time and highly
accurately. Thus, basic images for use in assessing cardiac
hypofunction quantitatively and highly accurately are made
available.
In particular, as far as tissue Doppler imaging is concerned, since
a super-low-velocity band of -fr/8.ltoreq.fd=fr/8 is rendered with
hues equivalent to 32 gradation levels (quantization rate of 5
bits), which are all of the gradation levels provided by the color
bar, for each motion direction, as very small a Doppler shift
frequency(that indicates a motion velocity) as a quotient of fr/128
is assigned each gradation level in practice. Compared with the
aforesaid conventional method in which all the 32 gradation levels
are assigned to the full band of -fr/2.ltoreq.fd.ltoreq.fr/2, the
display ability to render the super-low-velocity band of
-fr/8.ltoreq.fd.ltoreq.fr/8 is upgraded fourfold. This enables the
velocity of super-low-velocity motion of the cardiac muscle
detected with low pulse repetition frequencies to be rendered in an
unprecedentedly large number of gradation levels. A minute
difference in velocity concerning a super-low-velocity band is
rendered with a display color of a different hue. Consequently, a
difference in velocity becomes readily discernible for
evaluation,
In clinical assessment conducted by the present applicant, any
value ranging from 4 cm/s to 10 cm/s was specified as a maximum
velocity for the low-velocity band, and a velocity exceeding the
maximum velocity was rendered with a saturated color and encoded
into velocity data associated with red or blue of the highest
brightness (a change in brightness of a designated color was
adopted as color-display gradation data instead of a change in
hue). A velocity that triggers aliasing and is calculated on the
basis of a sampling rate was four times or eight times higher than
the maximum velocity rendered with a saturated color; that is,
ranged from 30 cm/s to 40 cm/s. Under this condition, the motion
velocity of the ventricle wall was measured. It was confirmed that
no aliasing occurred.
Even ultrasonic pulsed waves having the same pulse repetition
frequencies as those adopted conventionally are used for scanning,
the capacity for measuring the velocity of super-low-velocity
motion of a tissue will not be impaired but a high-performance
system can be materialized.
Since the diagnostic system in the aforesaid embodiment includes
two kinds of frame memories 17 and 25 dedicated to B and TDI modes
respectively, if necessary, the diagnostic system may perform cine
loop reproduction such as slow-motion reproduction or
frame-by-frame reproduction, animated reproduction, or independent
or parallel display of images produced in different cardiac phases
between B and CFM modes.
The aforesaid tomography system may be provided with a Doppler
filter or FFT frequency analyzer for use in rendering the motion of
the cardiac muscle on the basis of Doppler principle.
Furthermore, in the aforesaid embodiment, an image on which a TDI
image of the cardiac muscle is superposed is a B-mode tomographic
image, and a region to be diagnosed is the heart. The present
invention is not necessarily limited to this application. For
example, the B-mode image may be replaced with an M-mode image (in
this case, the component elements required for producing B-mode
images are replaced with those required for producing M-mode
images). The vascular wall may be diagnosed on behalf of the
cardiac muscle (in this case, the cutoff frequency of the filter 21
is set to a value optimal for the vascular wall). Moreover, the
B-mode images or M-mode images may not be superposed on a TDI
image, but a TDI (color Doppler) image alone may be displayed.
Furthermore, biomedical signals including electrocardiograms may be
displayed concurrently or a time lag relative to the R wave of an
electrocardiographic signal may be displayed for reference. This
display mode is employed in a normal B-mode tomography system or
blood flow (color flow) mapping, and helpful for clearly indicating
the association of biomedical signals with produced images.
An absolute velocity arithmetic unit may be interposed between the
frequency analyzer 22 and encoding arithmetic unit 23 in the
aforesaid embodiment. Absolute motion velocities of tissues
including the cardiac muscle (that is, velocities in motion
directions of tissues at sample points) may be computed by
inference, and displayed two-dimensionally in color.
On the other hand, the low-velocity band to be rendered in fine
gradation levels owing to the superb gradation rendering ability in
accordance with the present invention is not limited to the band in
the aforesaid embodiment; -fr/8.ltoreq.fd.ltoreq.fr/8. When the
encoding arithmetic unit is programmed differently, a band of
-fr/12.ltoreq.fd.ltoreq. fr/12 plotted as a velocity conversion
scale indicated with a dot-dash line in FIG. 7 or a band of
-fr/16.ltoreq.fd.ltoreq.fr/16 plotted as a velocity conversion
scale indicated with an alternate long-and-two short-dashes line
will do. Any of these frequency bands; -fr/8.ltoreq.fd
.ltoreq.fr/8, -fr/12.ltoreq.fd=fr/12, and
-fr/16.ltoreq.fd.ltoreq.fr/16 may be selected according to a manual
operation signal entered by an operator, so that the operator can
designate an appropriate band while viewing a screen on the display
unit. For this purpose, the CPU 43 in FIG. 1 should send a
selection signal concerning manual operation to the encoding
arithmetic unit 23 in response to the manual operation signal
propagating from the operation panel 14.
For enhancement of a low-velocity band in accordance with the
present invention, as shown in FIG. 8, a velocity conversion scale
having a sharp slope may be assigned to a desired low-velocity band
of, for example,-fr/12.ltoreq.fd.ltoreq.fr/12, and a velocity
conversion scale having a moderate slope may be assigned to a
middle-velocity band outside the low-velocity band. In this case,
an encoding arithmetic unit is used to control transition between
adjoining ones of a plurality of slopes of a velocity conversion
scale. Consequently, two-dimensional color images reflecting a
relationship in velocity between a low-velocity band and a
surrounding band can be produced.
For enhancement of a low-velocity band in accordance with the
present invention, a velocity conversion scale indicated with a
solid line in FIG. 9 may be employed (a dot-dash line in FIG. 9
indicates a conventional scale dedicated to blood flow analysis).
The velocity conversion scale is pre-set as, for example, a storage
table in the encoding arithmetic unit 23. Assigned to, for example,
a band of -fr/8<fd<+fr/8 defined as a low-velocity band are
velocity codes equivalent to gradation levels representing hues
that have a progressive (or continuous) change from red to yellow
and from blue to light blue for each direction of tissue motion.
However, when an averaged Doppler shift frequency fd (that is an
average velocity of tissue motion) meets the condition of
fd.gtoreq..+-.fr/8, velocity display codes associated with special
colors CL1 and CL2 whose hues are not continuous at all are
assigned uniformly to the above low-velocity band but the velocity
display codes associated with the hues having a continuous change
from red to yellow and from blue to light blue are not. The special
colors CL1 and CL2 are produced by mixing a red hue and a blue hue
with a certain hue. Needless to say, the velocity thresholds are
not limited to .+-.fr/8 but may be any values that can be modified.
The motion velocities of tissues exceeding those defined with a
predetermined low-velocity band are discernible at sight owing
discontinuous hues. With the enhancement of a low-velocity band,
interpretation of diagnostic images gets further easier.
Gradation levels equivalent to velocity display codes necessary for
color display in accordance with the present invention may be hues
dependent on magnitudes of velocities or brightnesses of red (or
blue) dependent on magnitudes of velocities as mentioned above.
The aforesaid embodiment or any variant thereof can be incorporated
into a conventional diagnostic ultrasound system capable of
performing blood flow Doppler imaging, if necessary.
Second Embodiment
Next, the second embodiment of the present invention will be
described in conjunction with FIGS. 10 to 15. The aforesaid first
embodiment aims at improving the ability to render a low-velocity
band. A diagnostic ultrasound system of the second embodiment
attempts not only to improve the rendering ability but also to
permit easy diagnosis of discerning whether a ROI is normal or
abnormal. For achieving this object, the diagnostic ultrasound
system of the second embodiment has the configuration shown in FIG.
10.
To be more specific, the diagnostic ultrasound system comprises an
ultrasound probe 100 responsible for transmitting or receiving
ultrasonic waves to or from a subject, and a main unit 101 for
driving the ultrasound probe 100 and processing signals received by
the ultrasound probe 100.
The ultrasound probe 100 is of a phased array type similarly to the
one in the first embodiment. The main unit 101 has an
ultrasonic-wave transmitter/receiver 110 connected to the
ultrasound probe 100, and includes a phase detector 111, an A/D
converter 112, a filter 113, a motion velocity analyzer 114, a DSC
115, a coloring unit 116, a D/A converter 117, and a color monitor
118 which are connected in that order in the output stage of the
ultrasonic-wave transmitter/receiver 110.
The motion velocity analyzer 114 is connected to a blanking control
unit 121 for blanking at least part of a color image of tissue
motion which will be described later. Necessary information is fed
to the blanking control unit 121 by an examining physician through
an input unit 122.
The ultrasonic-wave transmitter/receiver 110 includes a
transmitter/receiver 110a for driving the ultrasound probe 100 in
cycles of a duration of a supplied rate pulse and for beam-forming
echoes sent from the ultrasound probe 100 by delaying the echoes
and adding them to each other, a rate pulse generator (RPG) 110b
for supplying necessary information such as raster addresses to the
transmitter/receiver 110a, and an envelope detector 110c for
producing a B-mode image signal. The ultrasonic-wave
transmitter/receiver 110 functions similarly to the one in the
first embodiment.
In the output stage of the transmitter/receiver 110a, the phase
detector 111, A/D converter 112, and filter 113 are connected in
that order. These units function similarly to the phase detector 20
and filter 21 (having the capability of an A/D converter) in the
first embodiment.
The motion velocity analyzer 114 includes a frequency analyzer 114a
for analyzing frequencies of Doppler signals detected at sample
points on a tomographic layer by performing autocorrelation or the
like. The motion velocity analyzer 114 further includes a velocity
arithmetic unit 114b for computing average frequencies (average
velocities) of Doppler signals at the sample points using the
results of the analysis, a variance arithmetic unit 114c for
computing variances (spectral incoherences), and a power arithmetic
unit 114d for computing the intensities (powers) of Doppler
signals.
The velocity arithmetic unit 114b in this embodiment includes, as
shown in FIG. 11, a CPU 1140 and a memory 1141. A program that runs
as described in FIG. 12 is pre-set in a given storage area in the
memory 1141. The program is run automatically with the activation
of the velocity arithmetic unit 114b. The velocity arithmetic unit
114b may be made by combining analog and digital electronic circuit
elements in such a manner that they function to execute the
sequence shown in FIG. 12.
The blanking control unit 121 interprets a signal supplied from the
input unit 122, and, on the basis of the interpretation, supplies a
threshold signal S.sub..theta.th representing a threshold
.theta..sub.th of an argument .theta. required for blanking and a
factor signal S.sub.K representing a scale conversion factor K to
the velocity arithmetic unit 11b.
The DSC 115 inputs image data of a monochrome B-mode tomographic
image sent from the envelope detector 110c as well as image data of
a TDI image sent from the velocity arithmetic unit 114b, variance
arithmetic unit 114c, and power arithmetic unit 114d, and produces
frame image data in which the TDI image is superposed (synthesized
with) on the B-mode image. The frame image data is sent to the
coloring unit 116. The coloring unit 116 colors the pixels of the
TDI image according to the velocity display codes, and sends the
color frame image data to the color monitor 118 via the D/A
converter 117.
The sequence executed by the velocity arithmetic unit 114b will be
described in conjunction with FIG. 12.
The CPU 1140 in the velocity arithmetic unit 114b first reads the
threshold signal S.sub..theta.th supplied from the blanking control
unit 121 at step 200. At step 201, the CPU 1140 stores the
threshold .theta..sub.th represented by the threshold signal
S.sub..theta.th. The velocity arithmetic unit 114b inputs, as
described later, for example, the factors Re and Im (complex
numbers) among autocorrelation factors Re, Im and P.sub.o for
average frequencies of Doppler signals (average velocities)
resulting from analysis made by the frequency analyzer 114a, and
calculates an argument .theta. indicating a point on a unit circle
on a complex plane and corresponding to a motion velocity of a
tissue (See FIG. 13). The threshold (.theta..sub.th is therefore
equivalent to a threshold V.sub.th of a motion velocity V
(indicating a Doppler shift frequency) as shown in FIG. 14.
The CPU 1140 then passes control to step 202, and reads the factor
signal SK representing the scale conversion factor K (>1) for
use in enhancing the ability to display a TDI image from the
blanking control unit 121. At step 203, the scale conversion factor
K represented by the factor signal S.sub.K is stored, When the
factor K equals to 1, blood flow velocity analysis is
designated.
At step 204, the CPU 1140 inputs, for example, the autocorrelation
factor (Re, Im) provided by the frequency analyzer 114a. At step
205, the CPU 1140 computes the argument .theta. corresponding to
the velocity V of tissue motion mentioned above. The argument
.theta. has a value indicating that the scale conversion factor K
is 1; that is, the blood flow velocity analysis is designated. The
value of the argument .theta. varies according to a straight line
(velocity conversion scale) indicated with a dot-dash line d in
FIG. 14. In FIG. 14, the abscissa indicates the motion velocity V
and the ordinate indicates the velocity display code CD.sub..nu.
(for example, logical data of 8 bits long) representing a
brightness level used as a gradation level of red (for a motion
approaching the probe) or blue (for a motion receding from the
probe). In FIG. 14, various lines or velocity conversion scales in
accordance with the present invention may be plotted as described
later. The straight line d manifests a velocity conversion scale to
be used for blood flow velocity analysis. The velocity conversion
scale d is, as already known, such that velocity display codes
CD.sub..nu. having a continuous change are assigned to all the
velocities V within aliasing-prone velocities indicated with a band
of .+-.fr/2.
At step 206, the CPU 1140 determines whether the argument .theta.
computed at step 205 exceeds the threshold .theta..sub.th set at
step 201 (that is, whether the V value exceeds the V.sub.th
threshold). When the result of the determination is in the
affirmative (.theta.>.theta..sub.th), control is passed to step
207. A blanking command is issued in order to blank pixels
rendering the motion velocity corresponding to the argument 0that
exceeds the threshold .theta..sub.th (V>V.sub.th). By performing
blanking, the velocity display codes CD.sub..nu. assigned to the
pixels concerned are forcibly set to a value of 0, 0, . . . , 0
(blank code) meaning that the V value is 0.
When the blanking command terminates or when the result of the
determination made at step 206 is in the negative
(.theta.<.theta..sub.th), control is passed to step 208. At step
208, the scale conversion factor K (>1) set at step 203 is
multiplied by the argument .theta. computed at step 205.
With the multiplication of K by .theta., the argument .theta.
corresponding to the velocity V of tissue motion is weighted to
enhance a low-velocity band of a TDI image signal. For example, a
velocity conversion scale whose scale conversion factor K equals to
a K.sub.i value (that is larger than 1 or, for example, 4) is
plotted as a line a but not plotted as the straight line d
indicating that blood flow analysis is designated. Even when the
argument .theta.(=0) having undergone blanking is multiplied by the
factor K, the product is zero. The velocity conversion scale a that
is an example of a velocity conversion scale for tissue Doppler
imaging is, as shown in FIG. 14, plotted as a characteristic line
according to which velocity codes equivalent to all set brightness
levels of display colors; red and blue are assigned to a range of
V=.+-.Va (for example, .+-.fr/8). A range of
Va.gtoreq..vertline.V.vertline..gtoreq.V.sub.th is assigned
velocity display codes .+-.CD.sub..nu.(MAX) associated with maximum
brightnesses, or in other words, saturated colors. With the V
values equal to .+-.V.sub.th, the characteristic line a falls to
the axis of abscissas indicating a color of black.
Another examples of velocity conversion scales are plotted as
characteristic lines b and c in FIG. 14, wherein the scale
conversion factor K by which the argument .theta. is multiplied is
set to a K.sub.2 value (which is larger than the K.sub.1 value and,
for example, 8) and a K.sub.3 value (which is larger than the
K.sub.2 value and, for example, 16) respectively. According to the
velocity conversion scale b, the value of the velocity display code
CD.sub..nu. increases linearly in a range of V=.+-.Vb (for example,
.+-.fr/12). A range of
Vb.gtoreq..vertline.V.vertline..gtoreq.V.sub.th is assigned
saturated colors or maximum velocity display codes
.+-.CD.sub..nu.(MAX) associated with maximum brightnesses of red
and blue. For the other velocity conversion scale c, the value of
the velocity display code CD.sub..nu. increases linearly in a range
of V=.+-.Vc (for example, .+-.fr/16). A range of
Vc.gtoreq..vertline.V.vertline..gtoreq.V.sub.th is assigned the
saturated colors or maximum velocity display codes
.+-.CD.sub..nu.(MAX) associated with maximum brightnesses. In
either of the scales b and c, the characteristic line falls with
the V value given as .vertline.V.vertline..gtoreq.Vth because of
the effect of blanking. As mentioned above, the slope of the
straight line section of a characteristic line of a velocity
conversion scale gets larger proportionally to the value of the
factor K serving as a multiplier. The ability to render a
low-velocity band according to gradations is enhanced
proportionally to the value of the scale conversion factor K.
Upon completion of multiplication to be performed for tissue
Doppler imaging using the scale conversion factor K as a
multiplier, the CPU 1140 passes control to step 209 in FIG. 12, and
converts a product of the argument .theta. (corresponding to the
velocity V) by the factor K into a velocity display code
CD.sub..nu.. The conversion is achieved by referencing a storage
table which is pre-set in the memory 1141 and in which the values
of the argument .theta. are placed in one-to-one correspondence
with velocity display codes CD.sub..nu. (each of which is, for
example, 8 bits long). At step 210, the velocity display code
CD.sub..nu. resulting from the conversion is fed to the DSC
115.
At step 211, the threshold signal S.theta.th and factor signal
S.sub.K are read again. At step 212, it is determined whether both
or either of the threshold .theta..sub.th of the argument .theta.
represented by the threshold signal S.sub..theta.th and the factor
K represented by the factor signal S.sub.K should be modified. If
the values are modified, control is returned to step 201 or 203. If
the threshold .theta..sub.th and factor K are not modified but
blanking is continued, control is returned to step 204 via step
213. Blanking is controlled as described previously.
Echoes reflected from living tissues to which an ultrasound beam is
transmitted from the ultrasound probe 100 are returned to the probe
100. The echoes are converted into received signals with magnitudes
of electricity by the probe 100, received by the
transmitter/receiver 110a, and then subjected to orthogonal phase
detection by the phase detector 111. Signal components having
Doppler shifts that are induced by tissue motion are extracted from
the detected signals by means of the filter 113. The Doppler
signals still containing clutter components are sent to the
frequency analyzer 114a. The results of the frequency analysis are
sent to the velocity arithmetic unit 114b, variance arithmetic unit
114c, and power arithmetic unit 114c, whereby intended values
relevant to tissue motion are computed. In the power arithmetic
unit 114d, the computation of Klog.sub.10 P.sub.o is carried out (K
is a constant).
Assuming that commands are issued to the velocity arithmetic unit
114b via the input unit 122 and blanking control unit 121 in order
to specify the threshold .theta..sub.th of the argument .theta.
(that is, the threshold V.sub.th of the velocity V of tissue
motion) as shown in FIG. 14 and to set the scale conversion factor
K required for tissue Doppler imaging to a K.sub.2 value (line b),
the characteristic line indicated with a dot-dash line mb in FIG.
14 is selected for conversion into codes.
When an average velocity (a product of K by .theta.) of tissue
motion computed for enhancement of a TDI image is within a
low-velocity range of .vertline.V.vertline.<.+-.Vb, all
permissible velocity display codes CDV are employed. When the
velocity V is within a range of
.+-.Vb.ltoreq..vertline.V.vertline.<.+-.V.sub.th, maximum
velocity display codes .+-.CDV.sub.(MAX) associated with maximum
brightnesses are assigned to saturated colors. Velocities defined
with .+-.V.sub.th.gtoreq..vertline.V.vertline. are assigned a blank
code.
As mentioned above, the results of motion velocity analysis
containing average velocity data, which have undergone blanking,
are sent to the DSC 115. The DSC 115 is also provided with B-mode
image data by the envelope detector 110c. The motion velocity
information is superposed on the B-mode image. The superposed frame
image data is colored by the coloring unit 116, and then displayed
on the color monitor 118. The display image has the motion velocity
information concerning a color image of tissue motion superposed on
the background of the monochrome B-mode image. Pixels rendering
velocities exceeding a designated V.sub.th value are blanked at
step 207 in FIG. 12 and therefore not displayed in color. In other
words, color information is not superposed on pixels rendering a
high-velocity band indicated with
.+-.V.sub.th.ltoreq..vertline.V.vertline., and only the B-mode
image serving as the background is visible to an examining
physician.
When the velocity threshold V.sub.th (practically, the threshold
.theta..sub.th of the argument .theta.) to be specified in order to
cut off a high-frequency band is set to an appropriate value,
tissue motion such as of cardiac muscle motion that is visualized
with a maximum brightness without any change in gradation can be
limited to the smallest possible area (smallest number of pixels).
This results in an easy-to-see screen. It is therefore
substantially avoidable that the maximum-brightness image
unnecessary for tissue motion analysis interferes with diagnosis.
This contributes to improvement of diagnostic efficiency (or to
reduction of time and labor required for diagnosis).
A background image (monochrome B-mode image) appears in place of
the maximum-brightness image. Thus, another information required
for diagnosis becomes available.
Since the velocity conversion scales a, b, and c (See FIG. 14)
characteristic of enhancing a low-velocity band are employed, low
motion velocities suggesting necrotic tissues are readily
discernible. This leads to improvement of the ability to diagnose
whether a ROI is normal or abnormal.
In this embodiment, the threshold V.sub.th of the motion velocity V
can be set irrespectively to the velocity conversion scale a (b or
c). The maximum brightnesses .+-.CD.sub..nu.(MAX) of red and blue
to be allowed to appear in a monitor screen can be adjusted
optimally to the same velocity conversion scale a (b or c) (or, in
other words, to the same low-velocity enhancement function).
Depending on the threshold V.sub.th and scale conversion factor K,
as indicated with a dot-dash line m.sub.1 in FIG. 15, images with
maximum brightnesses associated with maximum gradation levels may
be allowed to appear in a monitor screen. Alternatively, as
indicated with a solid line m.sub.2 in FIG. 15, a TDI color image
alone whose brightnesses have not reached to the maximum values may
be blanked.
In this embodiment, a plurality of velocity conversion scales a, b,
and c are pre-prepared for tissue motion analysis and selectively
used according to a diagnostic purpose (See steps 202 and 211 in
FIG. 12). This results in a highly general-purpose system. Virtual
lines ma and mc in FIG. 14 present another examples of velocity
conversion characteristic lines in which the velocity threshold
V.sub.th is set to a fixed value.
Third Embodiment
The third embodiment of the present invention will be described in
conjunction with FIGS. 16 to 20. In a diagnostic ultrasound system
in accordance with the third embodiment, the aforesaid blanking of
a high-velocity band of tissue motion signals is executed after
velocity display codes are computed so that a low-velocity band
will be enhanced. For the third embodiment and thereafter,
component elements identical to those in the second embodiment will
be assigned the same reference numerals. The description on the
identical component elements will be omitted or summarized.
FIG. 16 is a block diagram showing a diagnostic ultrasound system
of the third embodiment. A blanking unit 125 is interposed between
the motion velocity analyzer 114 and DSC 115. The aforesaid factor
signal S.sub.K alone is supplied from the blanking control unit 121
to the aforesaid velocity arithmetic unit 114b. A threshold signal
S.sub.CDth representing a threshold of a velocity display code is
supplied to the blanking unit 125.
The blanking control unit 121 has the capability of a computer,
including a CPU 1210 and a memory 1211. The CPU 1210 executes the
sequence described in FIG. 17. The CPU 1140 in the velocity
arithmetic unit 114b executes the sequence described in FIG. 18.
The blanking unit 125 includes a CPU 1250 and a memory 1251. The
CPU 1250 executes the sequence described in FIG. 19.
To begin with, the actions of the blank control unit 121 will be
described in conjunction with FIG. 17. The CPU 1210 calculates a
scale conversion factor K on the basis of an operation signal
entered at the input 122 at steps 250 and 251. The CPU 1210 then
outputs a factor signal S.sub.K representing the calculated scale
conversion factor K to the velocity arithmetic unit 114b (step
252). At step 253, velocities .+-.V.sub.MAX represented by velocity
display codes .+-.CD.sub..nu.(MAX) that are associated with maximum
brightnesses and derived from a velocity conversion scale which is
weighted with the K value and designed for blood flow analysis are
computed (See FIG. 20). The computation of the .+-.V.sub.MAX values
may be assigned to the velocity arithmetic unit 114b, and then the
computed values may be returned from the velocity arithmetic unit
114b.
The CPU then reads an operation signal entered at the input unit
122 at step 254, and computes the velocity threshold V.sub.th
desired by an examining physician at step 255 (See FIG. 20). The
velocity threshold has no direct relation to the argument .theta.,
for the velocity threshold V.sub.th is supposed to define
thresholds for the already-converted velocity display codes
CD.sub..nu. supplied from the velocity arithmetic unit 114b.
Based on the velocity threshold Vth, it is determined at step 256
whether .vertline.v.sub.th.vertline.>V.sub.MAX is established.
If the result of the determination is in the affirmative or if
-V.sub.MAX.ltoreq.Vth.ltoreq.+V.sub.MAX is established, a threshold
CD.sub.th of a velocity display code corresponding to the threshold
V.sub.th is computed (See FIG. 20) (step 257). A code threshold
signal S.sub.CDth representing the threshold CD.sub.th is then
supplied to the blanking unit 125 (step 258). By contrast, if the
result of the determination made at step 256 is in the negative or
if .vertline.V.sub.th.vertline.>V.sub.MAX is established, an
indication meaning that blanking is disabled is displayed on the
monitor 118 by means of the DSC 115 (See the signal S.sub.un in
FIG. 16).
After the processing of steps 259 and 258 is completed, an attempt
is made at step 260 to read an operation signal entered at the
input unit 122. At step 261, it is determined whether the examining
physician wants to modify both or either of the scale conversion
factor K and velocity threshold V.sub.th. If the result of the
determination is in the affirmative, control is returned to step
251 or 255 and the processing is rerun. If the result of the
determination made at step 261 is in the negative, it is determined
at step 262 whether the sequence terminates. If the sequence
continues, the processing of steps 260 to 262 is rerun and a
standby state is set up.
The subsequent actions of the velocity arithmetic unit 114b will be
described in conjunction with FIG. 18. The actions are identical or
equivalent to the corresponding steps bearing the same reference
numerals in FIG. 12. Steps 202,201,206, and 207 in FIG. 12 are
excluded, though. In response to a command specifying the scale
conversion factor K and being issued from the blanking control unit
121, a velocity display code CD.sub..nu. that is weighted in order
to enhance a low-velocity band is supplied to the blanking
processor 125.
The actions of the blanking unit 125 will be described in
conjunction with FIG. 19. A CPU 1250 in the blanking unit 125 first
reads a code threshold signal S.sub.CDth sent from the blanking
unit 121 at step 270, and sets the threshold CD.sub.th of a
velocity display code at step 271. The velocity display code
CD.sub..nu. sent from the velocity arithmetic unit 114b is read at
step 272, and it is determined at step 273 whether
.vertline.CD.sub..nu..vertline.>CD.sub.th is established. If the
result of the determination is in the affirmative (the absolute
value of the sent code CD.sub..nu. exceeds the threshold
CD.sub.th), control is passed to step 274. Blanking is then
performed on the velocity display code CD.sub..nu.. Thus, a blank
code is forcibly assigned to each of pixels rendering velocities V
associated with codes CD.sub..nu. whose absolute values exceed the
threshold CD.sub.th.
If the result of the determination made at step 273 is in the
negative or .vertline.CD.sub..nu..vertline..ltoreq.CD.sub.th is
established, the velocity display code CD.sub..nu. * (including the
blanking code) having undergone blanking at step 274 is supplied to
the DSC 115 (step 275).
At step 276, the CPU 1250 attempts to read a code threshold signal
S.sub.CDth that may be supplied from the blanking unit 125. At step
277, the CPU 1250 determines whether the examining physician wants
to modify the threshold CD.sub.th. For modifying the threshold
CD.sub.th, control is returned to step 271. For leaving the
threshold CD.sub.th intact, it is determined at step 278 whether
the sequence terminates. If the sequence does not terminate,
control is returned to step 272. The aforesaid processing is
rerun.
The blanking unit 125 is not illustrated in particular. For
observing both or either of a velocity variance and a power
independently, these values are supplied directly to the DSC 115.
For observing the values together with a velocity V, the velocity V
(that is, a velocity display code CD.sub..nu.) is given priority,
and pixels to which velocity display codes CD.sub..nu. exceeding
the threshold CD.sub.th are assigned are blanked. The processing is
executed in response to a command signal S.sub.con entered at a
console that is not shown.
The blanking control unit 121, velocity arithmetic unit 114b, and
blanking unit 125 act as described above. As shown in FIG. 20, only
when the threshold V.sub.th, which are used for blanking and
designated by the examining physician, is within a range of
.+-.V.sub.th associated with maximum gradation levels of the
gradation scale in which a low-velocity band of tissue motion
signals is enhanced, pixels rendering velocities exceeding the
velocity thresholds .+-.V.sub.th are blanked automatically. Thus,
the same effect as the one of the second embodiment is exerted.
Even when the value of the scale conversion factor K is modified,
blanking is executed on a constant basis.
In this embodiment, however, velocity display codes CD.sub..nu.
succeeding the velocity display codes representing velocities
.+-.V.sub.MAX do not have any progressive change. When an examining
physician designates values exceeding the .+-.V.sub.MAX values as
the thresholds .+-.V.sub.th, the fact is reported to the examining
physician but blanking is not enabled. An examining physician need
not pay special attention to what .+-.V.sub.MAX values are set for
low-velocity band enhancement but can designate any values as the
thresholds .+-.V.sub.th. Thus, operation is easy.
The capability of the blanking unit 125 may, as shown in FIG. 21,
be given to the DSC 130. In this case, the code threshold signal
S.sub.CDth and other control signals S.sub.un and S.sub.con are fed
to the DSC 130. The DSC 130 blanks velocity display codes
CD.sub..nu. with respect to a code threshold CD.sub.th associated
with a velocity threshold V.sub.th in the same manner as that
described previously, and superposes image data containing tissue
motion information on B-mode data. Thus, an appropriate velocity
threshold V.sub.th (CD.sub.th) can be set for a low-velocity band
indicating velocities that are represented with velocity display
codes CD.sub..nu. having a progressive change. The same blanking
effect as that in the third embodiment can be exerted.
Fourth Embodiment
In the aforesaid second and third embodiments, thresholds for
blanking can be set irrespectively of a velocity conversion scale
for use in low-velocity band enhancement. The thresholds (that is,
blanking bands) can be determined at the same time of setting a
velocity conversion scale. Subsequent embodiments provide
diagnostic ultrasound systems in which this idea is
implemented.
The fourth embodiment of the present invention will be described
with reference to FIGS. 22 to 24.
A diagnostic ultrasound system shown in FIG. 22 has the aforesaid
velocity arithmetic unit 114b. The CPU 1140 in the velocity
arithmetic unit 114b executes the sequence shown in FIG. 23. Only
the factor signal S.sub.K representing a factor for use in
low-velocity band enhancement is fed from the blanking control unit
121.
In FIG. 23, the CPU 1140 in the velocity arithmetic unit 114b
executes the processing of steps 300 and 301 (corresponding to
steps 202 and 203 in FIG. 12), and then computes code thresholds
.+-.CD.sub..nu.(MAX) equivalent to maximum highest gradation levels
provided by a velocity conversion scale (See lines a to c in FIG.
24) at step 302. Thereafter, the processing of steps 303 and 304
(corresponding to steps 204 and 205 in FIG. 12) is executed.
According to the sequence shown in FIG. 23, as soon as an argument
.theta. is specified at step 304, the processing of steps 305 and
306 (corresponding to steps 208 and 209 in FIG. 12) is executed.
The CPU 1140 then passes control to step 307, and uses the code
thresholds .+-.CD.sub..nu..sub.(MAX) to determine whether the
absolute value of a velocity display code CD.sub..nu. is larger
than the CD.sub..nu.(MAX) value.
The determination is made on the assumption that tissue motion
signals indicating velocities exceeding those associated with
maximum gradation levels are blanked. Depending on the values of
maximum gradation levels provided by a velocity conversion scale
that has been weighted by the K value, a velocity threshold value
V.sub.th for blanking is specified automatically. In short, when a
velocity conversion scale for low-velocity band enhancement is
produced, velocity thresholds are determined at the same time. For
example, in the example shown in FIG. 24, when a velocity
conversion scale a whose scale conversion factor K is set to a
K.sub.1 value (larger than 1) is employed, velocity thresholds
.+-.V.sub.th-1 are adopted. When a velocity conversion scale b
whose scale conversion factor K is set to a K.sub.2 value (larger
than K.sub.1) is employed, velocity thresholds .+-.V.sub.th-2 are
adopted. When a velocity conversion scale c whose scale conversion
factor K is set to a K.sub.3 value (larger than K.sub.2) is
employed, velocity thresholds .+-.V.sub.th-3 are adopted.
If the result of the determination made at step 307 is in the
affirmative or if "CD.sub..nu..vertline.<CD.sub..nu.(MAx) is
established, control is passed to step 309. The velocity display
code CD.sub..nu. whose value remains unchanged is supplied to the
DSC 115. If the result of the determination is in the negative or
if .vertline.CD.sub..nu..vertline..gtoreq.CD.sub..nu.(MAX) is
established, a calculated velocity display code CD.sub..nu. is
equivalent to a maximum gradation level of a brightness of red or
blue. In this case, the value of the velocity display code
CD.sub..nu. is forcibly set to that of a blank code at step 308.
The velocity display code CD.sub..nu. having undergone blanking is
supplied to the DSC 115 at step 309. As a result, for example, when
the .+-.CD.sub..nu.(MAx) values are .+-.128, as far as a velocity
display code CD.sub..nu. has a value ranging between .+-.127,
blanking is disabled. When the velocity display code CD.sub..nu.
has a value ranging between .+-.128, blanking is enabled. This
characteristic is, as shown in FIG. 24, plotted as a line that
falls from points indicating velocity display codes
.+-.CD.sub..nu.(MAX) equivalent to maximum gradation levels to a
point indicating a velocity display code CD.sub..nu. having a value
0.
The CPU 1140 then executes the processing of steps 310 to 312 in
the same manner as steps 211 to 213 in FIG. 12.
Owing to the aforesaid blanking, any of velocity conversion scales
a to c for enhancement of a low-velocity band of tissue motion
signals can be selected freely. Pixels rendering velocities that
exceed a velocity threshold value V.sub.th determined concurrently
with a velocity conversion scale a (b, or c) are blanked
automatically, and a background image appears in place of the
pixels.
As mentioned above, this embodiment can enjoy the advantages of the
aforesaid low-velocity band enhancement and blanking. This
embodiment also has the advantage that an examining physician
should enter the scale conversion factor K alone using the input
unit 122.
Thresholds for blanking is set to maximum gradation levels
equivalent to codes .+-.CD.sub..nu.(MAX). Alternatively, the
thresholds may be set to codes having a lower value than the codes
.+-.CD.sub..nu.(MAX), if necessary. Even in this case, velocity
thresholds are automatically determined concurrently with the
codes. Only color pixels rendering velocities exceeding the
velocity thresholds are blanked.
Fifth Embodiment
The fifth embodiment of the present invention will be described in
conjunction with FIGS. 25 and 26.
In this embodiment, as shown in FIG. 25, a discrete blanking unit
131 is interposed between the tissue motion analyzer 114 and DSC
115 similarly to that in FIG. 16. A CPU (not shown) incorporated in
the blanking unit 131 executes the sequence including steps shown
in FIG. 26. The blanking control unit 121 sends the threshold
signal SCD.sub.th representing a code threshold value CD.sub.th to
the blanking unit 131.
The blanking unit 131 reads the code threshold signal SCD.sub.th as
shown in FIG. 26 and sets code thresholds CD.sub.th (similarly to
those in the previous embodiment, .+-.CD.sub..nu.(MAx)) (steps 320
and 321). Thereafter, a computed velocity display code CD.sub..nu.
is read, and it is determined whether
.vertline.CD.sub..nu..vertline.<CD.sub.th is established (steps
323 and 324). When .vertline.CD.sub..nu..vertline.=CD.sub.th is
established, blanking is enabled (step 325).
When a velocity range enabling blanking is to be specified at the
same time of production of a velocity conversion scale, even after
a velocity display code representing a velocity dependent on an
average Doppler shift has been computed, the velocity range can be
specified merely by setting code thresholds appropriately. Thus,
the procedure is simple. Nevertheless, the same effect as that
described in conjunction with FIG. 24 can be exerted.
In this embodiment, the code thresholds S.sub.CDth may be computed
by the velocity arithmetic unit 114b and then fed to the blanking
unit 131.
The DSC 115 belonging to the display system may have the capability
of the aforesaid blanking unit 131 (See FIG. 21. In this case, the
control signal S.sub.un indicating whether thresholds can be set or
not need not be issued.)
In the aforesaid second to fifth embodiments and their variants,
the velocity display codes CD.sub..nu. are expressed as gradation
levels of brightnesses (luminances) of red and blue used to
distinguish between tissue motion directions. Alternatively, the
velocity display codes CD.sub..nu. may be expressed as gradation
levels of hues.
For the sake of completeness it should be mentioned that the
embodiment examples shown above are not definitive lists of
possible embodiments. The expert will appreciate that it is
possible to combine the various construction details or to
supplement or modify them by measures known from the prior art
without departing from the basic inventive principles.
* * * * *