U.S. patent application number 14/635159 was filed with the patent office on 2015-06-25 for ultrasonic diagnostic apparatus and elastic evaluation method.
The applicant listed for this patent is Hitachi Aloka Medical, Ltd.. Invention is credited to Hideki YOSHIKAWA.
Application Number | 20150173720 14/635159 |
Document ID | / |
Family ID | 51866057 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150173720 |
Kind Code |
A1 |
YOSHIKAWA; Hideki |
June 25, 2015 |
ULTRASONIC DIAGNOSTIC APPARATUS AND ELASTIC EVALUATION METHOD
Abstract
An ultrasonic diagnostic apparatus and a method having a
highly-reliable elastic evaluation unit for tissues. The invention
includes a signal processing unit that processes received data
obtained after ultrasonic waves are transmitted and received
to/from an inspection target through a probe. An ROI detection unit
of the processing unit obtains a distance index indicating a region
proper for an elastic evaluation based on brightness distribution
of the received data obtained by transmitting and receiving first
ultrasonic waves to/from the probe, and sets an ROI based on the
distance index. Then, second ultrasonic waves are transmitted to
the ROI to generate shear waves. An elastic evaluation unit
calculates a shear wave velocity based on received data obtained by
transmitting and receiving third ultrasonic waves in the ROI, and
outputs the shear wave velocity and an elastic evaluation value of
the ROI as a reliability index.
Inventors: |
YOSHIKAWA; Hideki; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi Aloka Medical, Ltd. |
Tokyo |
|
JP |
|
|
Family ID: |
51866057 |
Appl. No.: |
14/635159 |
Filed: |
March 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14533198 |
Nov 5, 2014 |
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14635159 |
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Current U.S.
Class: |
600/438 |
Current CPC
Class: |
G01S 7/52074 20130101;
G01S 7/52042 20130101; A61B 8/485 20130101; A61B 8/5269 20130101;
A61B 8/463 20130101; A61B 8/469 20130101; A61B 8/5207 20130101;
A61B 8/5223 20130101; G01S 7/52063 20130101; G01S 7/52071 20130101;
A61B 8/488 20130101 |
International
Class: |
A61B 8/08 20060101
A61B008/08; A61B 8/00 20060101 A61B008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2013 |
JP |
2013-232540 |
Claims
1. An ultrasonic diagnostic apparatus comprising: a
transmission/reception unit that transmits and receives first,
second, and third ultrasonic waves to/from an inspection target
through a probe that transmits and receives ultrasonic waves; and a
processing unit that processes received data obtained from the
inspection target, wherein the processing unit calculates an index
indicating a region proper for an elastic evaluation based on
brightness distribution of the inspection target calculated using
image information formed using the received data obtained by
transmitting and receiving the first ultrasonic waves, and
determines a measurement region based on the index, transmits the
second ultrasonic waves to the determined measurement region to
generate shear waves, calculates a shear wave velocity using the
received data obtained by transmitting and receiving the third
ultrasonic waves to/from the measurement region, and outputs the
shear wave velocity and an elastic evaluation value of the
measurement region.
2. The ultrasonic diagnostic apparatus according to claim 1,
wherein the processing unit includes: an Region of Interest (ROI)
detection unit that calculates the index based on the brightness
distribution, and detects the measurement region based on the
calculated index, and an elastic evaluation unit that performs the
elastic evaluation of the measurement region using the shear wave
velocity measured at the measurement region.
3. The ultrasonic diagnostic apparatus according to claim 1,
wherein the processing unit calculates the index based on a
statistical value of brightness in a certain range of the
inspection target, and uses, as the statistical value, the average
value of brightness after an adjustment process by an s-shaped
function.
4. The ultrasonic diagnostic apparatus according to claim 1,
wherein a display unit is further provided, and the processing unit
displays the value of the index on the display unit as a color map
of the inspection target.
5. The ultrasonic diagnostic apparatus according to claim 1,
wherein a display unit is further provided, and the processing unit
displays the value of the index using the size of a frame line of
the measurement region displayed on the display unit, the type of
line, a color, or the size of a frame of the measurement
region.
6. The ultrasonic diagnostic apparatus according to claim 1,
wherein a display unit is further provided, and the processing unit
calculates the elastic evaluation value of the measurement region
based on the index, and displays the elastic evaluation value of
the measurement region on the display unit.
7. The ultrasonic diagnostic apparatus according to claim 6,
wherein the processing unit displays dispersion or standard
deviation of the elastic evaluation values calculated at the plural
measurement regions on the display unit as indexes to determine
unevenness of elasticity of the measurement target.
8. The ultrasonic diagnostic apparatus according to claim 1,
wherein the processing unit measures the wavefront characteristic
amount of the shear waves at a first measurement point and a second
measurement point using the received data obtained by transmitting
and receiving the third ultrasonic waves to/from the measurement
region, calculates a frequency distribution of peak to-times of the
shear waves at the first measurement point and the second
measurement point, and calculates the shear wave velocity and the
elastic evaluation value of the measurement region through a
correlation operation of the frequency distribution.
9. The ultrasonic diagnostic apparatus according to claim 8,
wherein a display unit is further provided, and the processing unit
displays a correlation value calculated through the correlation
operation of the frequency distribution on the display unit as the
elastic evaluation value of the measurement region.
10. The ultrasonic diagnostic apparatus according to claim 9,
wherein the processing unit displays dispersion or standard
deviation of the elastic evaluation values calculated at the plural
measurement regions on the display unit as indexes to determine
unevenness of elasticity of the measurement target.
11. The ultrasonic diagnostic apparatus according to claim 8,
wherein the processing unit calculates a histogram of peak-to-times
of the shear waves as information representing a frequency
distribution of peak to-times of the shear waves.
12. An elastic evaluation method comprising the steps of:
transmitting and receiving first ultrasonic waves to/from an
inspection target through a probe that transmits and receives
ultrasonic waves; generating brightness distribution of an
inspection target based on received data obtained from the
inspection target; calculating an index indicating a region proper
for an elastic evaluation based on brightness distribution of the
inspection target; determining a measurement region based on the
calculated index; transmitting second ultrasonic waves to the
determined measurement region to generate shear waves; calculating
a shear wave velocity using the received data obtained by
transmitting and receiving third ultrasonic waves to/from the
measurement region; and outputting the shear wave velocity and an
elastic evaluation value of the measurement region.
13. The elastic evaluation method according to claim 12, further
comprising the steps of: measuring the wavefront characteristic
amount of the shear waves at a first measurement point and a second
measurement point using the received data obtained by transmitting
and receiving the third ultrasonic waves to/from the measurement
region; calculating a frequency distribution of peak-to-times of
the shear waves at the first measurement point and the second
measurement point; and calculating the shear wave velocity and the
elastic evaluation value of the measurement region through a
correlation operation of the frequency distribution.
14. The elastic evaluation method according to claim 13, further
comprising the step of: using dispersion or standard deviation of
the elastic evaluation values calculated at the plural measurement
regions as indexes to determine unevenness of elasticity of the
measurement target.
15. An ultrasonic diagnostic apparatus comprising: a probe that
transmits and receives ultrasonic waves to/from an inspection
target; a measurement region determination unit that determines a
measurement region based on image information formed using the
received data obtained by transmitting and receiving first
ultrasonic waves to/from the inspection target by the probe; an
evaluation unit that generates shear waves by transmitting second
ultrasonic waves to the determined measurement region by the probe,
measures peak-to times of the shear waves at plural measurement
points in the determined measurement region by transmitting and
receiving the third ultrasonic waves to/from the measurement region
by the probe, calculates a frequency distribution of the
peak-to-times, and calculates a shear wave velocity and the elastic
evaluation value of the measurement region through a correlation
operation of the frequency distribution; and a display unit that
displays the shear wave velocity and/or the elastic evaluation
value.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation application of
application Ser. No. 14/533,198, filed Nov. 5, 2014; which claims
priority from Japanese patent application JP2013-232540, filed on
Nov. 8, 2013, the contents of which are hereby incorporated by
reference into this application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an ultrasonic diagnostic
apparatus, and particularly to a technique of generating shear
waves in a living body using acoustic radiation force to evaluate
the elasticity using the propagation velocity.
[0003] Medical image display apparatuses typified by ultrasonic
waves, MRI (Magnetic Resonance Imaging), and X-ray CT (Computed
Tomography) have been widely used as apparatuses that present
information in a living body that cannot be visually confirmed in
the form of values or images. Among those, an image display
apparatus using ultrasonic waves is provided with a high degree of
temporal resolution as compared to the other apparatuses, and has
performance capable of imaging a pulsating heart without
blurring.
[0004] Ultrasonic waves propagating in a living body are mainly
classified into longitudinal waves and transverse waves, and
information of the longitudinal waves (a sound velocity of about
1540 m/s) is mainly used in many techniques used in products,
namely, techniques of visualizing tissue configurations and
measuring a blood velocity.
[0005] Recently, a technique of evaluating the elastic modulus of a
tissue using transverse waves (hereinafter, referred to as shear
waves) attracts attention, and is being used for mammary tumors and
chronic liver disease in clinical practice. In the technique, shear
waves are allowed to be generated inside a tissue as a measurement
target, and the elasticity is evaluated on the basis of the
propagation velocity. The techniques of generating the shear waves
are roughly classified into a mechanical method and a radiation
pressure method. The mechanical method is a method in which a
vibration of about 1 kHz is applied to a body surface using a
vibrator or the like to generate the shear waves, and a driving
apparatus serving as a vibrating source is necessary. On the other
hand, in the radiation pressure method, acoustic radiation pressure
is applied to the inside of a living body using focused ultrasonic
waves that allow ultrasonic waves to be locally concentrated in a
tissue, and the shear waves are allowed to be generated using
following tissue displacement. Each method is a technique in which
the tissue displacement caused by propagation of the generated
shear waves is measured using ultrasonic waves to evaluate
information related to hardness of the tissue.
[0006] As prior art documents related to these techniques, for
example, U.S. Pat. No. 8,118,744B2 and US2010/0222678A1 relate to a
method of an elastic evaluation using acoustic radiation
pressure.
BRIEF SUMMARY OF THE INVENTION
[0007] In the method described in the above-described patent
documents, radiation force is allowed to be generated in a tissue
using focused ultrasonic waves to propagate shear waves in the
tissue. Plural measurement points where ultrasonic waves are
transmitted and received are provided in the propagation direction
to measure time changes of tissue displacement. Using the
measurement result of the displacement, a feature value (PT (Peak
to time), zero-cross point, and so on), to show the spatial
distribution of the shear waves at each measurement point is
measured. As a typical approach to use the PT at each measurement
point, the propagation time of the shear waves between the
measurement points is calculated to measure the velocity.
[0008] In the case where tissue structures such as blood vessels
and fibrous tissues exist on a propagation route of the shear
waves, the wavefront is scattered due to affects of diffraction and
refraction, and the shape of the wavefront is disordered. In a
method of estimating the shear wave velocity using the amount of
displacement of a tissue caused by propagation, the wavefront
disorder is a major factor of increasing errors of the elastic
evaluation. Further, there is no means to evaluate the reliability
of the measurement result of the velocity measured under the
circumstances, and thus the objectivity is disadvantageously
low.
[0009] An object of the present invention is to provide an
ultrasonic diagnostic apparatus and an elastic evaluation method
having a highly-reliable elastic evaluation unit for tissues.
[0010] In order to achieve the above-described object, the present
invention provides an ultrasonic diagnostic apparatus including: a
transmission/reception unit that transmits and receives first,
second, and third ultrasonic waves to/from an inspection target
through a probe that transmits and receives ultrasonic waves; and a
processing unit that processes received data obtained from the
inspection target, wherein the processing unit can determine a
measurement region on the basis of image information formed using
the received data obtained by transmitting and receiving the first
ultrasonic waves, can transmit the second ultrasonic waves to the
determined measurement region to generate shear waves, can
calculate a shear wave velocity using the received data obtained by
transmitting and receiving the third ultrasonic waves to/from the
measurement region, and can output the shear wave velocity and an
elastic evaluation value of the measurement region.
[0011] Further, in order to achieve the above-described object, the
present invention provides an elastic evaluation method in an
ultrasonic diagnostic apparatus including the steps of:
transmitting and receiving first ultrasonic waves to/from an
inspection target through a probe that transmits and receives
ultrasonic waves; generating brightness distribution of an
inspection target on the basis of received data obtained from the
inspection target; determining a measurement region on the basis of
the generated brightness distribution; transmitting second
ultrasonic waves to the determined measurement region to generate
shear waves; calculating a shear wave velocity using the received
data obtained by transmitting and receiving third ultrasonic waves
to/from the measurement region; and outputting the shear wave
velocity and an elastic evaluation value of the measurement
region.
[0012] According to the present invention, an elastic evaluation
can be performed at a region where velocity measurement with a high
degree of accuracy can be expected, and the reliability of the
result can be determined on the basis of objective elastic
evaluation values. The highly-reliable elastic evaluation for
tissues can be realized, so that shortening of inspection time of
an ultrasonic diagnostic apparatus, lessening of a load placed on
operators and patients, and improvement of the accuracy rate of
diagnosis can be expected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block diagram for showing a configuration
example of an ultrasonic diagnostic apparatus according to a first
embodiment;
[0014] FIG. 2 is a block diagram for showing another configuration
example of the ultrasonic diagnostic apparatus according to the
first embodiment;
[0015] FIG. 3 is a diagram for showing a configuration of an
elastic evaluation unit according to the first embodiment;
[0016] FIG. 4 is a diagram for showing a flowchart in an ROI
detection unit according to the first embodiment;
[0017] FIG. 5 is a diagram for showing an example of a function
used for brightness adjustment according to the first
embodiment;
[0018] FIG. 6 is a diagram for showing an example of a distance
index according to the first embodiment;
[0019] FIG. 7 is a diagram for showing an example of setting ROIs
according to the first embodiment;
[0020] FIG. 8 is a diagram for showing determination of a position
where second ultrasonic waves are irradiated according to the first
embodiment;
[0021] FIG. 9 is a diagram for showing an example of display
configurations of setting the ROIs according to the first
embodiment;
[0022] FIG. 10 is a diagram for showing an example of a display
configuration of values of elastic evaluation results according to
the first embodiment;
[0023] FIG. 11 is a diagram for showing equations related to
processing methods according to the first embodiment;
[0024] FIG. 12 is a diagram for showing a flowchart related to
calculation of a velocity according to a second embodiment;
[0025] FIG. 13 is a diagram for explaining calculation of a
histogram according to the second embodiment;
[0026] FIG. 14 is a diagram for showing an example of a display
configuration of elastic evaluation results according to the second
embodiment; and
[0027] FIG. 15 is a diagram for showing equations related to
processing methods according to the second embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Hereinafter, embodiments of the present invention will be
described in accordance with the drawings. It should be noted that
information used for an elastic evaluation for tissues in the
specification indicates general physical properties of tissues such
as distortion, a shear wave velocity, a longitudinal wave velocity,
a Young's modulus, the modulus of rigidity, the modulus of volume
elasticity, a Poisson's ratio, and a viscosity coefficient.
However, the present invention will be described using the shear
wave velocity. Further, information used for the elastic evaluation
in an ultrasonic diagnostic apparatus according to the present
invention, for example, structural objects such as blood vessels,
local fibrous tissues, and cysts of a living body that is an
inspection target for which the shear wave velocity is measured are
referred to as tissue structures or structural objects. Further, an
elastic evaluation value in the specification means a reliability
index of a result of the elastic evaluation in a measurement
region, and is a value indicating the reliability of a result of
the elastic evaluation in each measurement region.
First Embodiment
[0029] The first embodiment is an embodiment of an ultrasonic
diagnostic apparatus and an elastic evaluation method. The
ultrasonic diagnostic apparatus includes a transmission/reception
unit that transmits and receives first, second, and third
ultrasonic waves to/from an inspection target through a probe that
transmits and receives ultrasonic waves and a processing unit that
processes received data obtained from the inspection target. The
processing unit can determine a measurement region on the basis of
image information formed using the received data obtained by
transmitting and receiving the first ultrasonic waves, can transmit
the second ultrasonic waves to the determined measurement region to
generate shear waves, can calculate a shear wave velocity using the
received data obtained by transmitting and receiving the third
ultrasonic waves to/from the measurement region, and can output the
shear wave velocity and an elastic evaluation value of the
measurement region.
[0030] Further, the embodiment is an embodiment of an ultrasonic
diagnostic apparatus and an elastic evaluation method in which an
index indicating a region proper for the elastic evaluation is
calculated on the basis of brightness distribution of the
inspection target calculated using the image information to
determine the measurement region on the basis of the index.
[0031] A configuration example of an ultrasonic diagnostic
apparatus and a measurement method of a shear wave velocity in the
first embodiment will be described using a block diagram of FIG. 1.
In the configuration of the ultrasonic diagnostic apparatus of the
embodiment, the measurement region where the shear wave velocity is
measured is referred to as an ROI (Region of Interest). A signal
processing unit 23 includes, as will be described later, an ROI
evaluation unit 21 that calculates an index indicating a region
proper for the elastic evaluation on the basis of the brightness
distribution of the image information to determine the measurement
region on the basis of the image information formed using the
received data and that detects the measurement region on the basis
of the calculated index, and an elastic evaluation unit 22 that
evaluates the elasticity of a tissue in the measurement region
using the shear wave velocity and the like measured in the
measurement region. The signal processing unit 23 is a general term
of a module that processes signals on the basis of RF (Radio
Frequency) data. In this case, the index indicating the region
proper for the elastic evaluation is, as will be described later
using equations, a distance index that is calculated on the basis
of the brightness distribution of the image information generated
using the received data and that objectively indicates a
homogeneous region with less tissue structures and with a
sufficient degree of brightness for measurement of shear waves.
[0032] First, a configuration related to generation of RF data and
image data used in the embodiment will be described. An electric
signal for a transmission pulse is transmitted, through a
digital/analog (D/A) converter (not shown in the drawing), from a
transmission beamformer (BF) 13 that generates ultrasonic signals
to a probe 11 that is placed on a body surface of the inspection
target described in FIG. 1 and that transmits and receives
ultrasonic waves. The electric signal input to the probe 11 is
converted to an acoustic signal by ceramic elements placed inside
to be transmitted to the inside of the test body. The transmission
is performed by plural ceramic elements, and predetermined time
delays are set for the respective elements to be focused at a
predetermined depth in the test body.
[0033] The acoustic signal reflected in the course of propagation
in the inspection target is received by the probe 11 again, and is
converted to an electric signal contrary to the transmission. Then,
the electric signal is transmitted as received data to a reception
beamformer (reception BF) 14 that generates complex RF data from
the received ultrasonic signals through an analog/digital (A/D)
converter (not shown in the drawing). Switching of transmission and
reception is carried out by a transmission/reception switch SW 12
on the basis of control of a control unit 15 that is a processing
unit. The reception BF 14 performs an adding process (phasing
addition) for the signals received by the plural elements in
consideration of the time delays set at the time of transmission.
Then, after an attenuation correction process and the like are
performed, the signals are transmitted, as the complex RF data, to
a Doppler image generation unit 16 that generates a Doppler image
indicating the velocity and direction of blood flow or to a B-image
generation unit 17 that generates a brightness (B)-mode image
(hereinafter, referred to as B-image) representing configuration
information of tissues from the RF data in the signal processing
unit 23 that is a processing unit. It should be noted that the
probe 11, the transmission/reception switch SW 12, the transmission
BF 13, and the reception BF 14 are collectively referred to as an
ultrasonic wave transmission/reception unit in the
specification.
[0034] The RF data input to the signal processing unit 23 from the
reception BF 14 of the ultrasonic wave transmission/reception unit
becomes element data in a specific line along the
transmission/reception direction of ultrasonic waves among plural
pieces of image data that are finally displayed on the display unit
20. The transmission and reception of the ultrasonic waves to/from
the inspection target are sequentially switched to each other in
the arrangement direction of the ceramic elements configuring the
probe 11, so that the RF data can be obtained as all received data
serving as configuration elements of image data.
[0035] For the RF data that is received data obtained from the
ultrasonic wave transmission/reception unit, image generation
processes such as gain control, logarithmic compression, and
envelope detection that are generally used in a common ultrasonic
diagnostic apparatus are performed by the B-image generation unit
17 of the signal processing unit 23, and the B-image representing
configuration information in the inspection target is
generated.
[0036] On the other hand, the Doppler image generation unit 16 of
the signal processing unit 23 calculates the velocity and direction
as blood flow information using a correlation operation to generate
the Doppler image. It should be noted that the generation of the
Doppler image is different from that of the B-image in transmission
and reception sequences of the ultrasonic waves. However, the
technical content thereof is generally known, and thus the detailed
explanation thereof will be omitted. The B-image and the Doppler
image are stored in a cine memory 18. Coordinate transformation and
pixel interpolation are performed for the generated B-image and
Doppler image by a scan converter 19 in accordance with the type of
the probe to be displayed on the display unit 20 that displays
these images, evaluated images, and values.
[0037] As shown in FIG. 1, the signal processing unit 23 further
includes an ROI detection unit 21 that detects an ROI that is a
measurement region with less tissue structures and a high degree of
brightness and an elastic evaluation unit 22 that calculates a
shear wave velocity on the basis of the received data in the
ROI.
[0038] As will be described later in detail using the drawings, the
ROI detection unit 21 of the signal processing unit 23 detects a
tissue structure that affects scattering of shear waves using the
RF data received from the reception BF 14, and further detects
whether or not the tissue structure has a sufficient degree of
brightness for measurement of the shear waves. Further, the ROI
detection unit 21 calculates an index indicating a region proper
for the elastic evaluation, in other words, a distance index to
determine properness for measurement of the shear wave velocity
using the tissue structure and brightness distribution that is
information of brightness.
[0039] The ROI detection unit 21 of the signal processing unit 23
calculates the distance index on the basis of a generally-known
index such as a statistical value of brightness in a certain range
of the inspection target, for example, an average value, standard
deviation, dispersion, entropy, an eigenvalue, a kurtosis, or the
like. The distance index is calculated in all regions of candidates
of the elastic evaluation, and an image for determination is
generated in accordance with the value of the calculated distance
index. Further, on the basis of the image for determination, the
ROI that is the optimum measurement region for measurement of the
shear wave velocity where lessening of wavefront disorder can be
expected is automatically selected. The image for determination is
preferably displayed as a color map having a color pattern as will
be described later. Specifically, the color map used as the image
for determination of the inspection target is displayed on the
display unit 20 on the basis of the value of the distance index
calculated by the signal processing unit 23.
[0040] It should be noted that the ROI detection unit 21 generates
the image for determination on the basis of the brightness
information of the image using the RF data in the configuration of
the ultrasonic diagnostic apparatus shown in FIG. 1. However, as
shown in a modified configuration example of the ultrasonic
diagnostic apparatus of FIG. 2, the image for determination can be
similarly generated on the basis of the brightness information of
the image using the image data stored in the cine memory 18. The
configuration of the ultrasonic diagnostic apparatus of FIG. 2 is
different from that of FIG. 1 only in the above-described point,
and the other configurations are the same. The elastic evaluation
unit 22 of the signal processing unit 23 transmits burst waves that
are the second ultrasonic waves in the ROI determined by the ROI
detection unit 21 and transmits and receives track pulses that are
the third ultrasonic waves to evaluate information related to the
elasticity of the tissue.
[0041] It should be noted that the control unit 15 and the signal
processing unit 23 that control entire data flows and processes in
the apparatus main body in the configuration of the ultrasonic
diagnostic apparatus of the embodiment shown in FIGS. 1 and 2 can
be realized using a general computer configuration having a CPU
(Central Processing Unit) and a memory. Specifically, the units
except the cine memory 18 and the scan converter 19 realized by
hardware as needed can be realized by program processing by the
CPU. Thus, the signal processing unit 23 together with the control
unit 15 is referred to as a processing unit in the specification.
It should be noted that when using a general computer, a display of
the computer can be used as the display unit 20.
[0042] Next, a configuration of the elastic evaluation unit 22 of
the signal processing unit 23 in the configuration of the
embodiment shown in FIG. 1 and FIG. 2 will be described in detail
using a block configuration diagram of FIG. 3. As described above,
the respective functional units included in the elastic evaluation
unit 22 can be realized by program processing by the CPU.
[0043] As shown in FIG. 3, the elastic evaluation unit 22 includes
a second ultrasonic wave control unit 31, a third ultrasonic wave
control unit 32, a displacement measuring unit 33, a velocity
measuring unit 34, and an elastic evaluation unit 35. In this case,
the second ultrasonic wave control unit 31 determines acoustic
parameters necessary for wave transmission such as a focused
position, a transmission angle, a burst length, voltage, a
frequency, and the number of driving elements that are wave
transmission conditions of the ultrasonic burst waves to generate a
radiation pressure in the ROI that is a measurement region detected
and determined by the ROI detection unit 21. Further, the third
ultrasonic wave control unit 32 determines acoustic parameters
necessary for wave transmission such as a focused position, a
transmission angle, the number of waves, voltage, a frequency, the
number of times of transmission and reception, and the number of
driving elements that are wave transmission conditions of the track
pulses that are ultrasonic pulse waves to measure the displacement
of the tissue on the basis of coordinate information. The
displacement measuring unit 33 measures the displacement of the
tissue using the RF data output from the ultrasonic wave
transmission/reception unit. The velocity measuring unit 34
measures the shear wave velocity using the result of the
displacement measuring unit 33. The elastic evaluation unit 35
evaluates elastic information of the tissue using the result of the
velocity measuring unit 34.
[0044] In this case, the elastic information for the elastic
evaluation of tissues indicates general physical properties related
to deformation and flowage of materials such as distortion, a shear
wave velocity, a longitudinal wave velocity, a Young's modulus, the
modulus of rigidity, the modulus of volume elasticity, a Poisson's
ratio, and a viscosity coefficient. It should be noted that PT
(Peak to time) of the shear waves can be calculated using the
wavefront characteristic amount such as a maximum value, a minimum
value, and an intermediate value between the maximum value and the
minimum value on the basis of time changes of displacement measured
by the displacement measuring unit 33.
[0045] In FIG. 3, the second ultrasonic wave control unit 31 first
determines the wave transmission conditions of push pulses as the
second ultrasonic waves on the basis of the position coordinate of
the ROI that is the designated measurement region. As the wave
transmission conditions under which a living body is less affected
and the shear waves can be effectively generated, a focused
condition in which the F number is about 1 to 2 (a value obtained
by dividing the width of the aperture by the focal depth) is
appropriate. In addition, as a strength and a burst length, a
strength in a range of 0.1 to 1 kW/cm.sup.2 and a burst length in a
range of 100 to 1000 .mu.s are appropriate.
[0046] In this case, the width of the aperture is a range of the
ceramic elements that are actually driven, and a discrete value of
the element interval is used. Apodization that sets an aperture
weight is performed for voltage applied to each element to form an
optimum focal range, and the weight is reduced from the center of
the aperture towards the corners, so that the disorder of the focal
range affected by diffraction is suppressed. However, the aperture
weight disadvantageously reduces the strength. Thus, in the case
where the evaluation position is deep and largely affected by
attenuation, the aperture weight is lessened by giving priority to
the strength over the formation of regions in some cases. Further,
the transmission frequency is effective around the center frequency
of the sensitivity bandwidth of the probe 11. The wave transmission
conditions of the push pulses determined by the second ultrasonic
wave control unit 31 are immediately transmitted to the
transmission BF 13 through the control unit 15, and irradiation to
the inside of the living body is performed from the probe 11.
[0047] Thereafter, the third ultrasonic wave control unit 32
determines the wave transmission conditions of the track pulses
that are the third ultrasonic waves. The acoustic parameters such
as a frequency, the number of waves, and an F number are almost the
same as the conditions under which the image data is generated. If
the inspection target is an abdomen, conditions in which the
frequency is 1 to 5 MHz, the number of waves is 1 to 3, and the F
number is 1 to 2 are used.
[0048] A reflected signal from the living body obtained by
transmission of the track pulses is transmitted to the reception BF
14 through the probe 11, and complex RF data is generated. The RF
data is input to the displacement measuring unit 33, and
displacement of the tissue caused by propagation of the shear waves
is measured. The displacement measuring unit 33 measures the
displacement of the tissue using a complex correlation operation
between the pieces of RF data obtained at time intervals of PRT
(Pulse Repetition Time). The displacement measuring unit 33 of the
embodiment calculates a particle velocity as displacement in a unit
of time. There is a method in which the absolute value of
displacement is calculated on the basis of the RF data before
transmission of the push pulses. However, if the particle velocity
is used, low frequency components caused by swing of the probe and
natural movement of body tissues can be effectively removed to
measure the shear waves at a high degree of sensitivity, as
compared to the absolute value of displacement.
[0049] The above-described operation by the displacement measuring
unit 33 is performed for all RF signals obtained by the ultrasonic
wave transmission/reception unit, and the shear wave velocity is
calculated by the velocity measuring unit 34 on the basis of the
particle velocity that is the calculated displacement
information.
[0050] Finally, the elastic information of the tissue, namely, the
physical properties of the tissue such as distortion, a shear wave
velocity, a longitudinal wave velocity, a Young's modulus, the
modulus of rigidity, the modulus of volume elasticity, a Poisson's
ratio, and a viscosity coefficient are evaluated by the elastic
evaluation unit 35 on the basis of the measured shear wave
velocity.
[0051] Next, the calculation of the distance index that is an index
indicating a region proper for the elastic evaluation on the basis
of the brightness distribution of the inspection target in the ROI
detection unit 21 that detects an ROI that is a measurement region
of the signal processing unit 23 in the apparatus of the embodiment
and detailed content leading to the determination of the ROI on the
basis of the distance index will be described on the basis of a
flowchart of FIG. 4. As described above, the distance index is
calculated on the basis of a generally-known index such as a
statistical value of brightness distribution in a certain range,
for example, an average value, standard deviation, dispersion,
entropy, an eigenvalue, a kurtosis, or the like. The distance index
is calculated to determine the ROI that is a region proper for the
elastic evaluation by measurement of the shear waves on the basis
of the brightness distribution. The determination conditions
include no tissue structures causing the wavefront disorder and a
sufficient signal strength for an operation of displacement
measurement. Thus, the former is evaluated using the standard
deviation of the brightness distribution, and the latter is
evaluated using the average brightness of the brightness
distribution in the configuration of the embodiment. As a value
uniquely evaluating the both, the distance index is defined.
[0052] As shown in FIG. 4, the ROI detection unit 21 first extracts
an ROI as a candidate region where the shear waves are measured
using data of the B-image obtained by transmitting and receiving
the first ultrasonic waves that are pulse signals in Step 41.
[0053] In Step 42, the average brightness of the extracted ROI is
calculated using Equation 1 shown in FIG. 11. Further, brightness
adjustment for the calculated brightness is performed in Step 43.
As the brightness adjustment, an S-shaped function is preferable.
In other words, the average brightness that is the average value of
brightness after performing the adjustment process by the S-shaped
function is used as a representative statistical value. The average
brightness serves as an index of measured sensitivity.
[0054] FIG. 5 shows a graph 51 as an example of a function in the
case where the brightness adjustment is performed for a
256-gradation image using a sigmoid function (Equation 2). In the
drawing, the horizontal axis represents input brightness of 0 to
256 gradations, and the vertical axis represents output values. As
being apparent from the shape of the sigmoid function in the
drawing, the result of the brightness adjustment lessens the
difference between the middle brightness and the high brightness,
and further defines the discrimination from the low brightness. As
described above, the input brightness is an index related to
measurement of displacement. If the input brightness is sufficient
for the measurement of displacement, the condition related to the
brightness is satisfied. Thus, it is not necessary to discriminate
the middle brightness from the high brightness. On the contrary,
there is a possibility that a high-brightness region with uneven
brightness distribution such as a superficial region or a region
including a nodule is wrongly detected.
[0055] In Step 44, the standard deviation of the ROI that is the
extracted candidate region is calculated (Equation 3). The standard
deviation serves as an index of the wavefront disorder. The average
brightness and the standard deviation are calculated in the entire
image. It should be noted that the ROI extracted as a candidate
region is extracted in all pixels on the image. In Step 45, the
standard deviation is normalized (Equation 4). By performing the
process, the standard deviation of the general population
calculated in the entire image is adjusted in a range of 0 to
1.
[0056] In Step 46, the distance index is calculated on the basis of
the average brightness and the standard deviation in accordance
with Equation 5. FIG. 6 schematically shows an example of the
distance index as a graph 61. As shown in FIG. 6, an ROI with a
smaller value of the distance index is determined as a
high-brightness region having a homogeneous tissue structure.
Specifically, the ROI is a region with less wavefront disorder
where the measurement of displacement can be performed at a high
degree of sensitivity and the measurement of the shear wave
velocity at a high degree of reliability can be expected. As the
value of the distance index is closer to 0, the region is
preferable and proper for the elastic evaluation. As the value of
the distance index is closer to 1, the region is not preferable and
proper for the elastic evaluation. As will be described later, the
value of the distance index is also used as one of values
representing elastic evaluation values as reliable indexes of the
ROI that is a measurement region.
[0057] FIG. 7 shows an example of a B-image 71 for a liver, an
image for determination 72, and an ROI setting image 73 that is a
determination result. The image for determination 72 is displayed
using a color map colored in accordance with the values of the
distance indexes, and a color scale in accordance with the values
of the distance indexes is displayed on the image for determination
72. For the convenience of illustration, FIG. 7 is shown in black
and white. However, as compared to blood vessels, a low-brightness
shadow region, and a high-brightness superficial region that can be
confirmed on the B-image 71, the image for determination 72 is
colored to indicate that the regions are improper for the
measurement, as shown in the drawing. The ROIs proper for the
measurement of the shear waves for the elastic evaluation are
automatically set in accordance with the values of the calculated
distance indexes as shown in the ROI setting image 73. It is
obvious that an operator as a user may manually set the ROIs by
reference to the values and colors of the image for determination
72 displayed on the display or the like.
[0058] When the determination of the ROIs that are measurement
regions where the shear waves are measured for the elastic
evaluation is completed, the burst waves that are the second
ultrasonic waves to generate the shear waves and the track pulses
that are the third ultrasonic waves to measure displacement are
irradiated in the ROIs. The position of the irradiation of the
burst waves that are the second ultrasonic waves is determined
using the image for determination 72 used in the detection of the
ROIs. Specifically, the image for determination 72 is displayed
using a color map colored in accordance with the values of the
distance indexes, and thus the position of the irradiation of the
burst waves that are the second ultrasonic waves is determined on
the basis of the distance indexes.
[0059] A method of determining the position of the irradiation of
the burst waves that are the second ultrasonic waves will be
described using FIG. 8. FIG. 8 shows an image for determination 81
corresponding to the image for determination 71, and an in-ROI
image for determination 82 enlarged by narrowing the display range
of the distance index in the ROI extracted on the basis of the
image for determination 81. The colors in the ROI that are
difficult to be visually determined in the image for determination
81 can be definitely and visually confirmed in the enlarged in-ROI
image for determination 82.
[0060] The burst waves to generate the shear waves need to be
irradiated on a region as homogeneous as possible. Otherwise, the
wavefront disorder occurs at the time of generation of the shear
waves, and the affect is increased together with propagation.
Further, the shear waves are attenuated dependently on frequencies.
Specifically, the affects of diffraction and refraction caused by a
tissue structure and a structural object are increased in the
upstream containing high frequency components. Thus, for the
measurement of the shear wave velocity in which the affect of the
wavefront disorder is lessened, the burst waves are desirably
irradiated on a region with a small distance index. Accordingly,
the position of the irradiation of the burst waves that are the
second ultrasonic waves in the embodiment is preferably determined
on the basis of the distance index calculated by the ROI detection
unit 21. The determination can be automatically made using the
value (0 to 1) of the distance index. Further, an operator as a
user can manually set the position of the irradiation of the burst
waves using the in-ROI image for determination 82 that is displayed
on the display and is illustrated and enlarged in FIG. 8.
[0061] The calculation of the shear wave velocity and the elastic
evaluation on the basis of the shear wave velocity are performed in
each ROI determined by the ROI detection unit 21. Specifically, the
ROI that is a measurement region can be automatically set by
determination using an index that is calculated on the basis of the
brightness distribution of the image data and that objectively
indicates a region proper for the elastic evaluation in the
ultrasonic diagnostic apparatus in the embodiment. Therefore, the
elastic evaluation with a high degree of reliability can be
realized. In addition, improvement of operability of setting the
ROI can be advantageously expected.
[0062] FIG. 9 shows an example of display configurations each
showing a relative difference of the value of the distance index of
each ROI on the display unit on the assumption that plural ROIs are
set in the ultrasonic diagnostic apparatus of the embodiment. The
relative differences of the distance indexes are shown using the
thicknesses of frame lines showing the ROIs in a first display
configuration 91 on the display of the drawing, the line types of
the frame lines showing the ROIs in a second display configuration
92, the colors of the frame lines showing the ROIs in a third
display configuration 93, and the sizes of the frames showing the
ROIs in a fourth display configuration 94. Specifically, the
distance indexes are displayed in visually-determinable
configurations such as the sizes of the frame lines, the line types
of the frame lines, the colors of the frame lines, and the sizes of
the frames of the ROIs that are measurement regions displayed on
the display unit 20. Such visual distinction can be easily used as
diagnostic information by being reflected on the result of the
elastic evaluation.
[0063] Next, FIG. 10 shows an example of a display configuration
that displays elastic evaluation values that are reliability
indexes of the result of the elastic evaluation on the display unit
using colors in the ultrasonic diagnostic apparatus of the
embodiment. For the convenience of illustration, FIG. 10 is shown
in black and white. In the drawing, the values of the distance
indexes calculated in respective measurement regions ROI1, ROI2,
PORI3, and ROI4 are replaced by colors, and are displayed on a
graph 101 representing the result of the elastic evaluation as the
elastic evaluation values, namely, the reliability indexes.
Further, a color scale of the degrees of reliability as the
reliability indexes of the result is simultaneously displayed on
the graph 101. The colors are set depending on the degrees of
reliability in the color scale of the degrees of reliability in
accordance with the values of the distance indexes. The signal
processing unit 23 displays the elastic evaluation values that are
the reliability indexes of the result of the elastic evaluation on
the display unit 20. Accordingly, the degree of reliability of the
result of the elastic evaluation in each measurement region ROI can
be visually confirmed, and thus information used for diagnosis can
be promptly and accurately extracted.
[0064] Further, the average value and the dispersion of the elastic
evaluation values are presented as elastic evaluation values of
"all ROIs" while limiting to the ROI that is determined as a high
degree of reliability, so that the unevenness of elasticity of the
entire tissue can be evaluated. In general, the dispersion of the
measurement result represents accuracy. However, the dispersion of
the elastic evaluation values displayed as "all ROIs" after
calculating the elastic evaluation values using plural ROIs that
are set in spatially-different positions on the basis of the ROI
where the reliability is preliminarily evaluated represents the
unevenness of elasticity in the same tissue rather than the
accuracy. Thus, the dispersion can be used as diagnostic
information of, for example, distribution of the progression rates
and the sites of onset of disease.
[0065] According to the above-described configuration of the first
embodiment, it is possible to provide an ultrasonic diagnostic
apparatus with improved operability by which a highly-reliable and
high-accuracy elastic evaluation can be performed using a method of
automatically determining and setting an ROI as a measurement
region proper for the elastic evaluation. It should be noted that
the above-described configuration of the ultrasonic diagnostic
apparatus is only an example, and includes various modified
examples. For example, it is obvious that a signal processing unit
using the RF data having the configurations of FIG. 1 and FIG. 2
and the image data stored in the cine memory can be used.
Second Embodiment
[0066] The second embodiment is an embodiment related to another
method of calculating the shear wave velocity, and the like in the
ROI that is a measurement region determined in the first
embodiment. Specifically, the second embodiment is an embodiment of
an ultrasonic diagnostic apparatus and an elastic evaluation
method. The ultrasonic diagnostic apparatus includes a
transmission/reception unit that transmits and receives first,
second, and third ultrasonic waves to/from an inspection target
through a probe that transmits and receives ultrasonic waves and a
processing unit that processes received data obtained from the
inspection target. The processing unit determines a measurement
region on the basis of image information formed using the received
data obtained by transmitting and receiving the first ultrasonic
waves, transmits the second ultrasonic waves to the determined
measurement region to generate shear waves, measures the wavefront
characteristic amount of the shear waves at a first measurement
point and a second measurement point using the received data
obtained by transmitting and receiving the third ultrasonic waves
to/from the measurement region, calculates a frequency distribution
of peak-to-times (PT) of the shear waves at the first measurement
point and the second measurement point, and calculates a shear wave
velocity and an elastic evaluation value of the measurement region
through a correlation operation of the frequency distribution. A
frequency distribution can be represented by a histogram, a
frequency table, and so on.
[0067] The constitutional elements themselves of the apparatus
according to the second embodiment are the same as those of FIG. 1
and FIG. 2 provided in the first embodiment. Further, the
processing content up to irradiating the second ultrasonic waves
and the third ultrasonic waves onto the set ROI and measuring the
PT of the wavefront of the shear waves at the measurement position
that is preliminarily set in the propagation direction of the shear
waves is the same as that in the first embodiment. Thus, the
detailed explanation will be omitted.
[0068] FIG. 12 shows a flowchart of processes leading to
calculation of a shear wave velocity and an index indicating
reliability using PT (Peak to time) calculated at each of plural
measurement positions that are preliminarily set in the ultrasonic
diagnostic apparatus of the second embodiment. The description of
the embodiment assumes two measurement points, in total, of a first
measurement point and a second measurement point from the upstream
side of the propagation of ultrasonic waves along the propagation
direction of shear waves. The PT measured at each measurement point
is referred to as PT.sup.tr1 or PT.sup.tr2.
[0069] FIG. 13 shows an example of the results of measurement of
displacement at the first measurement point and the second
measurement point as a wavefront 131 at the first measurement point
and a wavefront 132 at the second measurement point. The shear
waves generated from the first ultrasonic waves are expanded in a
certain range in the depth direction. The results obtained by
measuring the propagation of the wavefronts by measurement of
displacement can be obtained as shown in FIG. 13 in which the
vertical axis represents a depth and the horizontal axis represents
time. As described in the first embodiment, the PT of the wavefront
is calculated using the wavefront characteristic amount such as a
maximum value, a minimum value, and an intermediate value between
the maximum value and the minimum value on the basis of time
changes of displacement that are results of measurement of
displacement.
[0070] In the embodiment, the explanation will be continued using a
method of using the minimum value as the wavefront characteristic
amount. In Step 122, the PT is first calculated at each point in
the depth direction, and histograms hist.sup.tr1(t) and
hist.sup.tr2(t) corresponding to the respective measurement points
are calculated. The intervals between bins of a histogram 133 in
FIG. 13 are adjusted in accordance with time intervals of
measurement of displacement. In the embodiment, a histogram of the
PT is calculated as an example of information representing a
frequency distribution of the PT. Further, another feature value to
show the wave distribution is available to calculate the frequency
distribution.
[0071] Thereafter, noise is removed in Step 123. The removal method
is performed according to a method that is generally used in the
field of signal processing. For example, an outlier is removed with
a significance level of 0.3% or a significance level of 5%.
Thereafter, a smoothing filter is applied on the assumption that
the histogram 133 is a polynomial function (Step 124). The type of
smoothing filter is not particularly limited. However, it is
necessary to determine the size in consideration of the wavelength
of the shear waves. Basically, the size is set in a range not
exceeding one fourth of the wavelength. FIG. 13 shows the histogram
133 calculated at the respective measurement points and a graph 134
of the results obtained by applying the smoothing filter. In this
case, the results obtained by using a Gaussian filter are shown as
an example.
[0072] In Step 125, a cross-correlation operation is performed
using the histogram in which the smoothing filter is applied
(Equation 6). The horizontal axis of the histogram represents a
time axis, and identification of positions that are highly
correlated with each other means calculation of the propagation
time of the shear waves between the measurement points. Thus, the
velocity of the shear waves is calculated using the result of the
correlation operation and the distances between the measurement
points. At the same time, a correlation value indicating the
consistency of the histogram is calculated (Step 126).
[0073] The histogram of the respective measurement points
represents the wavefront shapes at the positions. For example, in
the case where the wavefront is largely disordered with the
propagation, the shape of each histogram is largely changed. Thus,
the calculated correlation value becomes small. Namely, the
correlation value calculated using the cross-correlation operation
between the histograms can be obtained by directly evaluating the
reliability of the result of measurement of the velocity in the
viewpoint of the wavefront disorder. Accordingly, in the ultrasonic
diagnostic apparatus of the embodiment, the signal processing unit
23 displays the correlation value calculated using the correlation
operation of the histogram on the display unit 20 as the elastic
evaluation value of the reliability index of the shear wave
velocity, as will be described later.
[0074] FIG. 14 shows an example of a display configuration in the
case where the correlation values are used as the elastic
evaluation values, namely, the reliability indexes at the time of
the elastic evaluation by the ultrasonic diagnostic apparatus of
the second embodiment. As similar to FIG. 10, the values of the
correlation values are expressed using different colors, and are
reflected on the measurement results at the ROI1, ROI2, ROI3, and
ROI4. According to the display configuration, an operator can
visually determine a highly-reliable elastic evaluation value to be
used as accurate diagnostic information.
[0075] Further, as similar to the case of FIG. 10, the value
indexes indicating statistical interpretation such as the average
value, the dispersion, and the standard deviation of the elastic
evaluation values of the all ROIs are displayed together while
limiting to the ROI where a highly-reliable elastic evaluation
value can be obtained, so that new diagnostic information can be
offered to an operator. Specifically, in the ultrasonic diagnostic
apparatus of the embodiment, the signal processing unit 23 displays
the dispersion or the standard deviation of the elastic evaluation
values calculated in the ROIs that are plural measurement regions
on the display unit 20 as an index, namely, "all ROIs" to determine
unevenness of elasticity of the measurement target.
[0076] In general, the standard deviation of the measurement
results represents affects of statistical errors and systematic
errors. However, the value indexes in the all ROIs are calculated
on the basis of the result in which the reliability of the
measurement itself has been already evaluated, and represent the
difference between the elastic evaluation values in the same tissue
rather than the measurement errors. Specifically, the statistical
value indexes of the elastic evaluation values in the all ROIs
shown in FIG. 14 are presented as diagnostic information
representing unevenness of the progression rates and the sites of
onset of disease
[0077] The effect of the embodiment can be enhanced by being
combined with the ROI detection method described in the first
embodiment in detail in which an index indicating a region proper
for the elastic evaluation is calculated on the basis of the
brightness distribution, and the measurement region is detected on
the basis of the calculated index. The elastic evaluation with a
high degree of accuracy is realized by the results of all processes
in which the shear waves are allowed to be generated at proper
regions, the shear wave velocity is detected at a high degree of
accuracy, and the adequacy of the result is determined.
Specifically, the ultrasonic diagnostic apparatus having the
highly-reliable tissue elastic evaluation unit can be realized by
using the ROI detection method using the index indicating a region
proper for the elastic evaluation on the basis of the brightness
information and the elastic evaluation method in which velocity
detection by the cross-correlation operation on the basis of the
histogram and calculation of the elastic evaluation value as the
reliability index are performed.
[0078] Various embodiments of the present invention have been
described above. However, the present invention is not limited to
the above-described embodiments, but includes various modified
examples. For example, the above-described embodiments have been
described in detail for a better understanding of the present
invention, and are not necessarily limited to those having the all
configurations described above. Further, a part of the
configuration in one embodiment can be replaced by a configuration
of another embodiment, and the configuration in one embodiment can
be added to another embodiment. For example, a signal processing
unit having the configurations of FIG. 1 and FIG. 2 can be used. In
addition, a part of the configuration in each embodiment can be
added to or replaced by another, or deleted.
[0079] Further, the above-described configurations, functions,
processing units, and the like have been described mainly using
examples of creating programs realizing a part or all thereof.
However, it is obvious that, for example, the scan converter, and
the like may be realized using hardware by designing a part or all
thereof using, for example, integrated circuits.
* * * * *