JP7302651B2 - Ultrasonic signal processing device, ultrasonic diagnostic device, ultrasonic signal processing method, and program - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to an ultrasonic signal processing method for an ultrasonic diagnostic apparatus, and more particularly to analysis of shear wave propagation in tissue using shear waves and measurement of mechanical properties of tissue.

An ultrasonic diagnostic apparatus transmits ultrasonic waves from a plurality of transducers that make up an ultrasonic probe into the subject, receives ultrasonic reflected waves (echoes) caused by differences in acoustic impedance of the subject's tissue, and obtains This is a medical examination apparatus that generates and displays an ultrasonic tomographic image showing the structure of the internal tissue of a subject based on the electrical signals obtained.

In recent years, evaluation of tissue mechanical properties (SWSM: Shear Wave Speed Measurement, hereinafter referred to as "shear wave speed measurement") applying the mechanical properties of this ultrasonic wave is used in examinations. Because it is possible to noninvasively and easily measure the mechanical properties of tumors found in organs and body tissues, it is possible to examine the hardness of tumors in cancer screening tests, and liver disease tests in liver disease tests. It is expected to be used for evaluation of fibrosis.

In this shear wave velocity measurement, a region of interest (ROI) in the subject is determined, and push waves (focused ultrasound or , ARFI: Acoustic Radiation Force Impulse), the transmission of ultrasonic waves for detection (hereinafter referred to as “detection waves”) and the reception of reflected waves are repeated multiple times, and the acoustic radiation pressure of push waves causes We measure the velocity of shear waves. The mechanical properties of tissue, such as elasticity and viscosity, can then be inferred based on shear wave velocity measurements.

A typical method for measuring shear wave velocity is to detect displacements caused by shear waves at a plurality of positions on the subject, and determine the time at which the displacement peaks as the time at which the shear wave surface passes. As a method for detecting the time at which the displacement peaks, for example, a method of detecting the time at which the value of the displacement is maximized as a function of time (TTP: Time to Peak) is used as a typical method (for example, , Patent Document 1).

U.S. Patent Application Publication No. 2008/0249408 Japanese Patent Application Publication No. 2014-503565

However, if the S/N ratio of the displacement time-series data is not high, such as when the shear wave is attenuated at the observation point where the displacement peak time is to be detected, the TTP method may cause erroneous detection or detection of the peak. Impossibility is likely. Therefore, other methods, such as correlation processing and the technology disclosed in Japanese Patent Application Laid-Open No. 2002-200028, are being studied to detect the time at which the displacement reaches its peak. On the other hand, when the S/N ratio of the displacement time-series data is high, the accuracy of the peak time of the TTP method is high. There is a problem that the time accuracy is not as high as that of the TTP method.

The present disclosure has been made in view of the above problems. The purpose is to improve the reliability of measurement.

An ultrasonic signal processing apparatus according to an aspect of the present disclosure includes a push wave transmission unit that transmits a push wave for generating displacement in a subject to an ultrasonic probe, and following transmission of the push wave, the subject A detection wave transmitting unit that transmits a detection wave passing through a region of interest indicating a measurement target range in the ultrasonic probe, and an ultrasonic wave reflected from the region of interest corresponding to the detection wave using the ultrasonic probe a detection wave receiving unit that receives a sound wave and converts it into a received signal; a phasing addition unit that performs phasing addition for each of a plurality of positions within the region of interest to generate an acoustic line signal; a displacement detection unit that detects displacement at the observation point based on the acoustic line signal corresponding to each of the observation points; an estimating unit, wherein the propagation state estimating unit performs correlation processing between the time-series data of the displacement of the observation point and the reference time-series data in which the time at which the displacement reaches the maximum is known, so that the displacement at the observation point is the maximum. is estimated, and the gate width, which is the time width of the reference time-series data, is reduced as the displacement observation time is earlier with reference to the transmission time of the push wave pulse.

According to the present disclosure, with the above configuration, when the observation time is large, that is, when the shear wave is attenuated and the high S/N ratio of the displacement time-series data is not guaranteed, the gate width is made too small. Since there is no peak, it is possible to detect the time at which the displacement reaches the peak while preventing erroneous detection and impossibility of detection. On the other hand, if the gate width is made small in the correlation processing, high detection accuracy can be obtained as in the TTP method. do. With this configuration, high detection accuracy can be obtained in environments where the TTP method is suitable, and peak times can be detected even in environments where the TTP method is not suitable, so detection sensitivity is increased for all environments. can improve detection accuracy.

FIG. 3 is a schematic diagram showing an outline of an SWS sequence including shear wave velocity measurement in the ultrasonic diagnostic apparatus 100 according to the embodiment; 1 is a functional block diagram of an ultrasonic diagnostic system 1000 including an ultrasonic diagnostic apparatus 100; FIG. (a) is a schematic diagram showing the position of the transmission focal point F of the push wave generated by the push wave pulse generator 104, and (b) is a schematic diagram showing the configuration outline of the detection wave pulse generated by the detection wave pulse generator 105. It is a diagram. 3A is a functional block diagram showing the configuration of a transmission beamformer section 106, and FIG. 3B is a functional block diagram showing the configuration of a reception beamformer section 108. FIG. It is a schematic diagram which shows the outline|summary of a push wave. (a) is a schematic diagram showing an outline of detection wave transmission, and (b) is a schematic diagram showing an outline of reflected wave reception. FIG. 10 is a schematic diagram showing an overview of a method of calculating a propagation path of ultrasonic waves in a delay processing unit 10831. FIG. 3 is a functional block diagram showing configurations of a displacement detection unit 109, a propagation information analysis unit 110, and a mechanical characteristic calculation unit 111; FIG. FIG. 3 is a schematic diagram showing an overview of the integrated SWS sequence process in the ultrasonic diagnostic apparatus 100; 4 is a flowchart showing the operation of SWSM processing in the ultrasonic diagnostic apparatus 100; (a) to (c) are schematic diagrams showing how a shear wave is generated by a push wave pulse pp. FIG. FIG. 4 is a schematic diagram showing the operation of displacement detection and shear wave propagation analysis; 4 is a flowchart showing the operation of shear wave propagation information analysis in the ultrasonic diagnostic apparatus 100. FIG. It is a schematic diagram which shows an example of the relationship between observation time and gate width. (a) to (f) are schematic diagrams showing an overview of peak time detection by correlation processing. (a), (b) is a schematic diagram which shows an example of the time-series change of a displacement. (a), (b) is a schematic diagram which shows an example of the time-series change of a displacement. (a) to (c) are tables showing variations in gate widths, detected peak times, and time differences between peak times.

<<Background to the Form for Working the Invention>>
The inventor conducted various studies to improve the detection accuracy of the time when the displacement peaks in shear wave velocity measurement.

As described above, in shear wave velocity measurement, the displacement in the subject is detected by repeating the transmission and reception of the detection wave following the transmission of the push wave. Estimate location. Then, the moving speed of the wave front is calculated as the moving speed of the shear wave. To estimate the position of the shear wave front, multiple observation points are set in the object, and the time at which the amount of displacement reaches a maximum (peak) at each observation point (hereafter referred to as the "peak time") is detected. , it is common to regard the observation point as having passed through the wave front of the shear wave at the peak time.

As a peak time detection method, for example, as described in Patent Document 1, there is a method (TTP method) of detecting a time when a displacement value becomes maximum with respect to changes in time-series displacement. More specifically, the displacement is regarded as a function of time, and the time at which the displacement value is the largest is searched for. For example, at a position close to the position pressed by the push pulse, the shear wave is hardly degraded, and therefore has a sharp peak when the displacement is regarded as a function of time. Further, for example, when the hardness of the object to be examined is high, the speed of the shear wave is high, so even at a location distant from the location pressed by the push pulse, there is a sharp peak when the displacement is regarded as a function of time. Therefore, in such an environment, the TTP method can detect the peak time of displacement with high accuracy.

On the other hand, when the hardness of the subject tissue is small, that is, when the tissue is soft, the velocity of the shear wave is slow, so the peak is blunted when the displacement is regarded as a function of time. In addition, since the shear wave is degraded by propagation at a location distant from the location pressed by the push pulse, the peak is dull when the displacement is regarded as a function of time. On the other hand, the detection error of the displacement, which is a noise component, depends on the quality of the acoustic line signal, and does not depend on the magnitude of the displacement, which is the signal component. do. In particular, the displacement caused by the shear wave is smaller the further away from the transmission time of the push pulse. This makes it difficult to stably detect peaks. That is, the TTP method may not be able to stably detect the peak time when the peak time exists at a time distant from the transmission time of the push pulse.

As a method for detecting other peaks, for example, a correlation processing method can be considered. The correlation processing method is a method of finding the time lag between the reference sequence data and the target sequence data. It is a method to find by calculating Therefore, for example, even when the peak of displacement is dull, by performing correlation processing using the dull peak as the reference series data, it is possible to eliminate the influence of noise and stably detect the peak.

On the other hand, the correlation processing method has a problem of how to set the gate width. The gate width is the data length of reference sequence data used for correlation calculation. Since the number of calculations in correlation processing is approximately proportional to the gate width, if the gate width is too wide, the calculation load increases. In addition, if the gate width is inappropriately wide, the reference series data includes time-series changes in displacement other than the peak. Therefore, the peak detection accuracy may decrease due to the influence of unnecessary reference series data. On the other hand, when the gate width is very narrow, the absolute value of the series data has a stronger effect on the correlation value than the degree of matching with the reference series data, so it has substantially the same characteristics as the TTP method, There is a problem of having the drawback of the TTP method as it is.

Therefore, the inventor studied a gate width setting method in the correlation processing method, and came up with the ultrasonic signal processing apparatus, the ultrasonic diagnostic apparatus, and the ultrasonic signal processing method according to the present disclosure. .

Hereinafter, an ultrasonic image processing method and an ultrasonic diagnostic apparatus using the same according to embodiments will be described in detail with reference to the drawings.

<<Embodiment>>
The ultrasonic diagnostic apparatus 100 performs processing for evaluating the mechanical properties of a subject by shear wave velocity measurement. FIG. 1 is a schematic diagram showing an outline of an SWS sequence including shear wave velocity measurement in an ultrasonic diagnostic apparatus 100. As shown in FIG. As shown in the frame in the center of FIG. 1, the processing of the ultrasonic diagnostic apparatus 100 includes the steps of “transmission/reception of reference detection wave pulse”, “transmission of push wave pulse”, “transmission/reception of detection wave pulse”, and “calculation of mechanical characteristics”. Configured.

In the step of "transmitting and receiving a reference detection wave pulse", the reference detection wave pulse pwp0 is transmitted to the ultrasonic probe, and the detection wave pw0 is transmitted to a range corresponding to the region of interest roi in the subject and the reflected wave is transmitted to a plurality of transducers. ec is received to generate an acoustic line signal that serves as a reference for the initial position of the tissue.

In the step of "push wave pulse transmission", a push wave pulse ppp is transmitted to the ultrasonic probe, and a plurality of transducers are caused to transmit the push wave pp by converging ultrasonic waves to a specific site in the subject. A shear wave is excited in the specimen tissue.

After that, in the step of "transmitting and receiving a detection wave pulse", a detection wave pulse pwpl is transmitted to the ultrasonic probe, and a plurality of transducers are caused to transmit the detection wave pwl and receive the reflected wave ec a plurality of times. Measure wave propagation conditions. In the process of "mechanical property calculation", first, the displacement distribution pt1 of the tissue accompanying the propagation of the shear wave is calculated in time series, and then the mechanical property of the tissue is expressed from the time-series change in the displacement distribution pt1. A shear wave propagation analysis is performed to calculate the shear wave propagation velocity, and finally the mechanical properties are imaged and displayed as an image.

A series of processes accompanying one shear wave excitation based on the push wave pp transmission shown above is called an "SWS sequence" (SWS: Shear Wave Speed).

<Ultrasound diagnostic system 1000>
1. Apparatus Overview An ultrasonic diagnostic system 1000 including an ultrasonic diagnostic apparatus 100 according to an embodiment will be described with reference to the drawings. FIG. 2 is a functional block diagram of the ultrasonic diagnostic system 1000 according to the embodiment. As shown in FIG. 2, the ultrasonic diagnostic system 1000 transmits ultrasonic waves toward a subject and receives reflected waves of the ultrasonic waves having a plurality of transducers (array of transducers) 101a arranged on the surface thereof. A probe 101 (hereinafter referred to as "probe 101"), an ultrasonic diagnostic apparatus 100 that causes the probe 101 to transmit and receive ultrasonic waves and generates an ultrasonic signal based on an output signal from the probe 101, and an operator input. It has an operation input unit 102 that accepts and a display unit 113 that displays an ultrasound image on the screen. The probe 101 , the operation input unit 102 and the display unit 113 are each configured to be connectable to the ultrasonic diagnostic apparatus 100 .

Next, each element externally connected to the ultrasonic diagnostic apparatus 100 will be described.

2. probe 101
The probe 101 has, for example, a transducer array (101a) composed of a plurality of transducers 101a arranged in a one-dimensional direction (hereinafter referred to as "transducer array direction"). The probe 101 converts a pulsed electrical signal (hereinafter referred to as a “transmission signal”) supplied from a transmission beamformer 106, which will be described later, into a pulsed ultrasonic wave. The probe 101 measures an ultrasonic beam composed of a plurality of ultrasonic waves emitted from a plurality of transducers in a state in which the transducer-side outer surface of the probe 101 is applied to the skin surface of the subject via ultrasound gel or the like. Send to target. The probe 101 receives a plurality of reflected detection waves (hereinafter referred to as "reflected waves") from the subject, converts these reflected waves into electrical signals by a plurality of transducers 101a, and converts the reflected waves into electrical signals for use in the ultrasonic diagnostic apparatus. 100 supplies.

3. Operation input unit 102
The operation input unit 102 receives various operation inputs such as various settings and operations for the ultrasonic diagnostic apparatus 100 from the examiner, and outputs them to the control unit 115 of the ultrasonic diagnostic apparatus 100 .

The operation input unit 102 may be, for example, a touch panel integrated with the display unit 113 . In this case, various settings and operations of the ultrasonic diagnostic apparatus 100 can be performed by performing a touch operation or a drag operation on the operation keys displayed on the display unit 113, and the ultrasonic diagnostic apparatus 100 can be operated by this touch panel. configured as possible. Further, the operation input unit 102 may be, for example, a keyboard having keys for various operations, an operation panel, a mouse, etc. having buttons and levers for various operations.

4. Display unit 113
The display unit 113 is a display device for so-called image display, and displays an image output from the display control unit 112, which will be described later, on the screen. A liquid crystal display, an organic EL display, a CRT, or the like can be used for the display unit 113 .

<Overview of Configuration of Ultrasound Diagnostic Apparatus 100>
Next, the ultrasonic diagnostic apparatus 100 according to the embodiment will be described.

The ultrasonic diagnostic apparatus 100 selects each of the transducers 101a of the probe 101 to be used for transmission or reception, and secures input/output for the selected transducer. A transmission beamformer unit 106 that controls the timing of applying a high voltage to each transducer 101a of the probe 101 in order to transmit a signal, and a reception beamforming unit 106 based on the reflected wave received by the probe 101 to generate an acoustic line signal. It has a receive beamformer unit 108 .

Further, a region of interest setting unit 103 sets a region of interest roi representing a measurement target range in the subject based on an operation input from the operation input unit 102 with reference to a plurality of transducers 101a, and a push wave pulse is applied to the plurality of transducers 101a. It has a push wave pulse generator 104 for transmitting ppp, and a detection wave pulse generator 105 for transmitting detection wave pulse pwpl multiple times following the push wave pulse ppp.

Further, a displacement detection unit 109 detects the displacement of the tissue within the region of interest roi from the acoustic ray signal, analyzes the propagation information of the shear wave from the detected displacement of the tissue, and detects the wavefront arrival of the shear wave at each observation point within the region of interest roi. It has a propagation information analysis unit 110 that calculates time and a mechanical property calculator 111 that calculates the shear wave propagation velocity and/or mechanical properties at each observation point in the region of interest roi.

Acoustic ray signals output by the reception beam former unit 108, displacement amount data output by the displacement detection unit 109, wavefront arrival time data output by the propagation information analysis unit 110, and mechanical characteristics output by the mechanical characteristics calculation unit 111 A data storage unit 114 for storing data and the like, a display control unit 112 for forming a display image and displaying it on the display unit 113, and a control unit 115 for controlling each component are provided.

Among these, a multiplexer unit 107, a transmission beamformer unit 106, a reception beamformer unit 108, a push wave pulse generation unit 104, a detection wave pulse generation unit 105, a region of interest setting unit 103, a displacement detection unit 109, a propagation information analysis unit 110, The mechanical property calculator 111 and the controller 115 constitute an ultrasonic signal processing circuit 150 . Push wave pulse generating section 104 and transmission beam former section 106 constitute push wave transmitting section 1041, and detection wave pulse generating section 105 and transmission beam former section 106 constitute detection wave transmitting section 1051, respectively.

Each element constituting the ultrasonic signal processing circuit 150, for example, the displacement detection unit 109, the propagation information analysis unit 110, and the mechanical characteristic calculation unit 111, for example, FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated circuit). Alternatively, it may be a configuration realized by a processor such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), a memory, and software that operates the processor. General-Purpose computing on Graphics Processing Unit). These components can be single circuit components or aggregates of multiple circuit components. Also, a plurality of components can be combined to form a single circuit component, or a plurality of circuit components can be aggregated.

The data storage unit 114 is a computer-readable recording medium such as a hard disk, a semiconductor memory, a flexible disk, an MO, a DVD, or a BD. The data storage unit 114 may be a storage device such as a NAS (Network Attached Storage) externally connected to the ultrasonic diagnostic apparatus 100 .

Note that the ultrasonic diagnostic apparatus 100 according to the present embodiment is not limited to the ultrasonic diagnostic apparatus having the configuration shown in FIG. For example, there is a configuration in which the multiplexer section 107 is unnecessary, and a configuration in which the transmission beam former section 106, the reception beam former section 108, or a portion thereof is built in the probe 101 may be employed.

<Configuration of Each Part of Ultrasound Diagnostic Apparatus 100>
Next, the configuration of each block included in the ultrasonic diagnostic apparatus 100 will be described.

1. Region of interest setting unit 103
Generally, in a state in which a B-mode image, which is a tomographic image of the subject acquired by the probe 101 in real time, is displayed on the display unit 113, the operator uses the B-mode image displayed on the display unit 113 as an index. , the measurement target range within the subject is specified and input to the operation input unit 102 . The region-of-interest setting unit 103 sets the information specified by the operator through the operation input unit 102 as an input, and outputs the information to the control unit 115 . At this time, the region-of-interest setting unit 103 may set the region-of-interest roi indicating the measurement target range in the subject based on the position of the transducer array (101a) composed of the plurality of transducers 101a in the probe 101. . For example, the region of interest roi may be all or part of the detection wave irradiation area Ax including the transducer array (101a) made up of a plurality of transducers 101a.

2. Push wave pulse generator 104
The push wave pulse generation unit 104 acquires information indicating the region of interest roi from the control unit 115, and sets a specific point at a predetermined position near or inside the region of interest roi. Then, by causing the plurality of transducers 101a to transmit the push wave pulse ppp from the transmission beamformer 106, the plurality of transducers 101a correspond to a specific point (hereinafter referred to as “transmission focus FP”) in the subject. A push wave pp that focuses an ultrasonic beam on a specific site of is transmitted. This excites a shear wave at a specific site in the subject. Although the number of specific points is assumed to be 1 here, it _is not limited to the above. Push waves pp _k (k=1 to n) that converge on each may be transmitted sequentially.

Specifically, the push wave pulse generating unit 104 determines the position of the transmission focal point FP of the push wave and the transducer array for transmitting the push wave ppp (hereinafter referred to as the “push wave transmission transducer array”) based on the information indicating the region of interest roi. Px”) is determined as follows.

FIG. 3A is a schematic diagram showing the position of the transmission focal point FP of the push wave ppp generated by the push wave pulse generator 104. FIG. the length w in the column direction and the length h in the depth direction of the subject of the region of interest roi are equal to or less than the length a in the column direction and the length b in the depth direction of the subject of the ultrasonic irradiation range of plane waves, respectively; A case where the region of interest roi is set near the center of the irradiation range will be described as an example. In the present embodiment, as shown in FIG. 3A, the column-direction transmission focal position fx of the transmission focal point FP is configured to match the column-direction center position wc of the region of interest roi.

Also, the push wave transmission transducer array Px is set based on the depth direction transmission focal position fz. In this embodiment, the length of the row of push wave pulse transmitting transducers Px is set to the length a of all the plurality of transducers 101a.

Information indicating the position of the transmission focal point FP and the push wave transmission transducer array Px is output to the transmission beam former section 106 as a transmission control signal together with the pulse width PW and application start time PT of the push pulse ppp. Also, the time interval PI between the application start times PT may be included. The pulse width PW, application start time PT, and time interval PI of the push wave pulse ppp will be described later.

Note that the positional relationship between the region of interest roi and the transmission focus FP is not limited to the above, and may be changed as appropriate depending on the form of the site to be inspected of the subject.

For example, the example shown in FIG. 3A is configured such that the column-direction transmission focal position fx among the positions of the transmission focal points FP is offset from the column-direction central position wc of the region of interest roi in the positive or negative direction of the x-axis. You can change it. In this case, the width w of the region of interest and the center of the transducer array in the column direction are different. Further, the column-direction focal position fx of the transmission focal points FP may be offset from the column-direction center wc of the region of interest roi in the positive or negative direction of the x-axis and positioned outside the region of interest roi.

Alternatively, the transmission focal point FP may be set at a predetermined position near the region of interest roi and outside the region of interest roi. At this time, when setting in the vicinity of the region of interest roi, the transmission focal point FP is set to a distance at which the shear wave can reach the region of interest roi with respect to the region of interest roi.

It should be noted that the ultrasonic beam "focused" by the push wave means that the ultrasonic beam is narrowed and focused. It is not limited to the case where the ultrasonic beam is focused on one point. In this case, the “transmission focus FP” refers to the center of the ultrasound beam at the depth at which the ultrasound beam is focused.

Information indicating the position of the transmission focal point F and the push wave transmission transducer array Px is output to the transmission beam former unit 106 as a transmission control signal together with the pulse width of the push wave pulse ppp.

3. Detection wave pulse generator 105
The detection wave pulse generation unit 105 receives information indicating the region of interest roi from the control unit 115, and causes the plurality of transducers 101a to transmit the detection wave pulse pwpl from the transmission beam former unit 106 a plurality of times, thereby generating the ultrasonic beams of interest. The plurality of transducers 101a belonging to the detection wave pulse transmission transducer array Tx are caused to transmit the detection wave pw so as to pass through the region roi. Specifically, the detection wave pulse generating unit 105, based on information indicating the region of interest roi, transmits a transducer train (hereinafter referred to as “detection wave A transmission transducer array Tx”) is determined.

FIG. 3B is a schematic diagram showing an overview of the configuration of the detection wave pulse pwpl generated by the detection wave pulse generator 105. As shown in FIG. As shown in FIG. 3B, the detection wave pulse generation unit 105 generates the detection wave pulse so that the detection wave, which is a so-called plane wave in which the detection wave pulse transmission oscillator is driven in the same phase, passes through the entire region of interest roi. Set the transmission transducer array Tx. The length a of the detection wave pulse transmission transducer array Tx is preferably set larger than the region of interest width w. In this example, the region-of-interest width w is set so as to be positioned inward by a predetermined distance β from the end in the column direction of the array of detection wave pulse transmitting transducers Tx. Since the detection wave pw is a plane wave, it propagates in the Z direction perpendicular to the row direction of the transducers. Therefore, the region of interest roi is included in the ultrasound irradiation region Ax with a margin of distance β at both ends in the X direction. Thus, by transmitting and receiving the detection wave once, the acoustic line signal can be generated for the observation point in the entire region of interest roi, and the detection wave pulse pwpl is transmitted so that the ultrasonic beam reliably passes through the entire region of interest roi. can do.

Note that the traveling direction of the ultrasonic beam, which is the detection wave, is not limited to the Z direction, and may be set so as to travel in a direction forming a predetermined azimuth angle θ with respect to the Z direction.

4. Transmission beamformer section 106
The transmission beamformer unit 106 is connected to the probe 101 via the multiplexer unit 107, and in order to transmit ultrasonic waves from the probe 101, a push wave transmission vibration applied to all or part of the plurality of transducers 101a in the probe 101. This circuit controls the timing of applying a high voltage to each of the plurality of transducers included in the transducer array Px or the detection wave transmitting transducer array Tx.

FIG. 4A is a functional block diagram showing the configuration of the transmission beamformer section 106. As shown in FIG. As shown in FIG. 4( a ), the transmission beamformer section 106 includes a driving signal generating section 1061 , a delay profile generating section 1062 and a driving signal transmitting section 1063 .

(1) Drive signal generator 1061
The drive signal generation unit 1061 generates information indicating the push wave transmission transducer array Px or the detection wave transmission transducer array Tx among the transmission control signals from the push wave pulse generation unit 104 or the detection wave pulse generation unit 105, and the push wave Based on the information indicating the pulse width PW of the pulse ppp and the application start time PT, the pulse width of the detection wave pulse pwpl, and the information indicating the application start time, it corresponds to a part or all of the transducer 101a existing in the probe 101. This is a circuit for generating a pulse signal sp for transmitting an ultrasonic beam from the transmitting transducer.

(2) Delay profile generator 1062
In the delay profile generation unit 1062, among the transmission control signals obtained from the push wave pulse generation unit 104 or the detection wave pulse generation unit 105, the push wave transmission transducer array Px or the detection wave transmission transducer array Tx and the position of the transmission focal point FP Alternatively, a delay time tpk (k is a natural number from 1 to the number kmax of the transducers 101a) from the application start time PT that determines the transmission timing of the ultrasonic beam is set for each transducer based on the information indicating the transmission direction θ. It is a circuit that outputs as As a result, the ultrasonic beams are focused by delaying the transmission of the ultrasonic beams for each transducer by the delay time.

(3) Drive signal transmitter 1063
Based on the pulse signal sp from the drive signal generation unit 1061 and the delay time tpk from the delay profile generation unit 1062, the drive signal transmission unit 1063 selects the push wave transmission transducer array Px among the plurality of transducers 101a in the probe 101. A push wave transmission process is performed to supply a push wave pulse ppp for transmitting a push wave to each transducer included in . The push wave transmission transducer array Px is selected by the multiplexer section 107 .

A push wave that causes a physical displacement in a living body is required to have much higher power than a transmission pulse used for normal B-mode display or the like. In other words, the driving voltage applied to the pulser (ultrasonic generator) may be 30 to 40 V normally for acquisition of a B-mode image, whereas the push wave requires, for example, 50 V or more. Further, in acquiring a B-mode image, the transmission pulse length is about several microseconds, but the push wave requires a transmission pulse length of several hundred microseconds per transmission.

In the present embodiment, the push wave pulse ppp is transmitted from the driving signal transmitting section 1063 to the plurality of transducers 101a at the application start time PT. The push wave pulse ppp is a burst signal having a predetermined pulse width PW (time length), a predetermined voltage amplitude (+V to -V), and a predetermined frequency. Specifically, the pulse width PW may be, for example, 100 to 200 μsec, the frequency may be, for example, 6 MHz, and the voltage amplitude may be, for example, +50 V to −50 V. However, it goes without saying that the application conditions are not limited to the above.

Further, the driving signal transmission unit 1063 supplies a detection wave pulse pwpl for transmitting an ultrasonic beam to each transducer included in the detection wave transmission transducer array Tx among the plurality of transducers 101a in the probe 101. Perform wave transmission processing. The detection wave transmission transducer array Tx is selected by the multiplexer section 107 . However, the configuration related to the supply of the detection wave pulse pwpl is not limited to the above.

After transmitting the push wave pulse ppp, the transmission beamformer 106 transmits the detection wave pulse pwpl multiple times based on the transmission control signal from the detection wave pulse generator 105 . After one transmission of the push wave pulse ppp, each transmission of a series of detection wave pulses pwpl performed multiple times from the same detection wave transmission transducer train Tx is referred to as a "transmission event".

5. Configuration of Reception Beamformer 108 The reception beamformer generates a detection wave based on reflected waves from the subject tissue received in time series by the plurality of transducers 101a corresponding to each of the plurality of detection wave pulses pwpl. Acoustic line signal frame data dsl (l is a natural number from 1 to m; if numbers are not distinguished, acoustic line signal frame data dsl is generated by generating acoustic line signals for a plurality of observation points Pij in the irradiation area Ax). This is the circuit that generates the sequence. That is, after transmitting the detection wave pulse pwpl, the reception beamformer 108 generates an acoustic line signal from the electric signals obtained by the plurality of transducers 101a based on the reflected waves received by the probe 101. FIG. Here, i is a natural number from 1 to n representing the coordinate in the x direction in the detection wave irradiation area Ax, and j is a natural number from 1 to zmax representing the coordinate in the z direction. The "acoustic line signal" is a signal obtained by subjecting the received wave signal (RF signal) to phasing addition processing.

FIG. 4B is a functional block diagram showing the configuration of the reception beamformer section 108. As shown in FIG. The reception beamformer section 108 includes an input section 1081 , a received wave signal holding section 1082 and a phasing addition section 1083 .

(1) Input unit 1081
The input section 1081 is a circuit that is connected to the probe 101 via the multiplexer section 107 and generates a received wave signal (RF signal) based on the wave reflected by the probe 101 . Here, the received wave signal rfk (k is a natural number from 1 to n) is an electric signal A/ The received wave signal rfk is a D-converted so-called RF signal, and the received wave signal rfk is a train of signals (received wave signal train) connected in the transmission direction (depth direction of the subject) of the ultrasonic waves received by each wave receiving transducer rwk. consists of

The input unit 1081 generates a sequence of wave reception signals rfk for each wave receiving transducer rwk for each transmission event based on the reflected waves obtained by each wave receiving transducer rwk. The wave-receiving transducer array is composed of a transducer array corresponding to some or all of the plurality of transducers 101 a present in the probe 101 , and is selected by the multiplexer section 107 based on instructions from the control section 115 . In this example, all of the plurality of transducers 101a are configured to be selected as the wave-receiving transducer row. As a result, all the oscillators are used to receive the reflected waves from the observation points existing in the entire detection wave irradiation area Ax in one reception process, and the receiving wave oscillator train for all the oscillators is generated. can be done. The generated received wave signal rfk is output to the received wave signal holding unit 1082 .

(2) Received wave signal holding unit 1082
The received wave signal holding unit 1082 is a computer-readable recording medium, and can use, for example, a semiconductor memory. The received wave signal holding unit 1082 receives the received wave signal rfk for each receiving transducer rwk from the input unit 1081 in synchronization with the transmission event, and holds it until one acoustic line signal frame data is generated. .

Note that the received wave signal holding unit 1082 may be part of the data storage unit 114 .

(3) Delayed addition unit 1083
The phasing addition unit 1083 applies delay processing to the received wave signal rfk received by the receiving transducer Rpk included in the detection wave pulse receiving transducer array Rx from the observation point Pij in the region of interest roi in synchronization with the transmission event. After that, the circuit generates the acoustic line signal ds by adding all the reception transducers Rpk. The detection wave pulse receiving transducer array Rx is composed of receiving transducers Rpk corresponding to some or all of the plurality of transducers 101a in the probe 101, and based on instructions from the control unit 115, the phasing addition unit 1083 and the multiplexer unit 107. In this example, as the reflected wave receiving transducer array Rx, a transducer array including at least all of the transducers constituting the detected wave pulse transmitting transducer array Tx in each transmission event is selected.

The phasing addition section 1083 includes a delay processing section 10831 and an addition section 10832 for processing the received wave signal rfk.

(i) Delay processing unit 10831
The delay processing unit 10831 divides the difference in the distance between the observation point Pij and each of the receiving transducers Rpk by the sound velocity value from the received wave signal rfk for the receiving transducer Rpk in the detection wave pulse receiving transducer array Rx. This circuit compensates for the arrival time difference (delay amount) of the reflected ultrasonic waves to each of the transducers Rpk, and identifies the received signal corresponding to the received transducer Rpk based on the reflected ultrasonic waves from the observation point Pij.

FIG. 7 is a schematic diagram showing an outline of a method of calculating the propagation path of ultrasonic waves in the delay processing unit 10831. As shown in FIG. It shows the propagation path of an ultrasonic wave emitted from the detection wave pulse transmitting transducer array Tx, reflected at an observation point Pij located at an arbitrary position in the region of interest roi, and reaching the receiving transducer Rpk.

a) Calculation of transmission time The detection wave pwl transmitted from the detection wave transmission transducer array Tx (the entire transducer array (101a)) is preferably a plane wave as described above, but is not limited to this. In response to the transmission event, the delay processing unit 10831 delays the transmission path to the observation point Pij until the detection wave pwl emitted perpendicularly to the transducer array from the detection wave transmission transducer array Tx reaches the observation point Pij. , and divided by the speed of sound to calculate the transmission time.

b) Calculation of Reception Time The delay processing unit 10831, in response to the transmission event, receives data from the observation point Pij until it reaches the reception transducer Rpk included in the detection wave reception transducer array Rx after being reflected at the observation point Pij. Calculate route. The length of a path 402 from an arbitrary observation point Pij to each receiving transducer Rpk is geometrically calculated for the receiving path when the reflected wave at the observation point Pij returns to the receiving transducer Rpk. The reception time is calculated by dividing this by the speed of sound.

c) Calculation of Delay Amount Next, the delay processing unit 10831 calculates the total propagation time to each reception transducer Rpk from the transmission time and the reception time, and calculates the total propagation time for each reception transducer Rpk based on the total propagation time. A delay amount to be applied to the received wave signal sequence rfk is calculated.

d) Delay Processing Next, the delay processing section 10831 generates a received wave signal rfk corresponding to the delay amount (a received wave signal corresponding to the time after subtracting the delay amount) from the received wave signal sequence rfk for each receiving transducer Rpk. , is identified as a signal corresponding to the received transducer Rpk based on the reflected wave from the observation point Pij.

The delay processing unit 10831 receives the received wave signal rfk from the received wave signal holding unit 1082 in response to the transmission event, and receives the received wave for each receiving transducer Rpk for all the observation points Pij located within the region of interest roi. Identify the signal rfk.

(ii) adder 10832
The addition unit 10832 receives as input the received wave signal rfk identified corresponding to the receiving transducer Rpk output from the delay processing unit 10831, adds them, and obtains a phased-and-sum acoustic line signal for the observation point Pij. This is the circuit that generates dsij.

Further, the received wave signal rfk identified corresponding to each receiving transducer Rpk may be multiplied by the receiving apodization (weight sequence) and then added to generate the acoustic line signal dsij for the observation point Pij. The receive apodization is a sequence of weighting factors applied to received signals corresponding to receive transducers Rpk in the detected wave receiving transducer sequence Rx. The reception apodization is set so that the weight for the transducer located at the center of the detection wave receiving transducer array Rx in the row direction is maximized, and the central axis of the reception apodization distribution is aligned with the detection wave receiving transducer array central axis Rxo. , and the distribution forms a symmetrical shape with respect to the central axis. The shape of distribution is not particularly limited.

The adder 10832 generates acoustic line signal dsij for all observation points Pij in the region of interest roi to generate acoustic line signal frame data dsl.

Then, the transmission and reception of the detection wave pulse pwpl are repeated in synchronization with the transmission event to generate the acoustic line signal frame data dsl for all transmission events. The generated acoustic line signal frame data dsl is output and stored in the data storage unit 114 for each transmission event.

6. Displacement detector 109
The displacement detection unit 109 is a circuit that detects the displacement of tissue within the detection wave irradiation area Ax from the sequence of the acoustic line signal frame data dsl.

FIG. 8 is a functional block diagram showing configurations of the displacement detector 109, the propagation information analyzer 110, and the mechanical characteristic calculator 111. As shown in FIG.

The displacement detection unit 109 detects one frame of acoustic line signal frame data dsl to be subjected to displacement detection included in a sequence of acoustic line signal frame data dsl and one frame of reference acoustic line signal frame data ds0 (hereinafter referred to as “ (referred to as reference acoustic line signal frame data ds0”) is acquired from the data storage unit 114 via the control unit 115 . The reference acoustic line signal frame data ds0 is a reference signal for extracting the displacement due to the shear wave in the acoustic line signal frame data dsl corresponding to each transmission event. is frame data of an acoustic line signal acquired from the detection wave irradiation area Ax. Then, the displacement detection unit 109 compares the acoustic line signal frame data dsl with the reference acoustic line signal frame data ds0 to determine the displacement (image information) of the observation point Pij within the detection wave irradiation area Ax of the acoustic line signal frame data dsl. movement) Ptij is detected, and the displacement amount frame data ptl is generated by associating the displacement Ptij with the coordinates of the observation point Pij. More specifically, the following processing is performed for each observation point. That is, the reference data sequence corresponding to the observation point and its vicinity is extracted from the reference acoustic line signal frame data ds0, and the data sequence closest to the reference data sequence is searched from the acoustic line signal frame data dsl. Then, when the position (or range) in the subject corresponding to the reference data sequence is used as a reference, the deviation amount of the position (or range) in the subject corresponding to the found data sequence is assigned to the observation point. Calculated as displacement. For the comparison processing, for example, correlation processing, pattern matching, or the like can be used. The displacement detection unit 109 outputs the generated displacement amount frame data ptl to the data storage unit 114 .

7. Propagation information analysis unit 110
The propagation information analysis unit 110 is a circuit that identifies the peak time of displacement at each observation point within the detection wave irradiation area Ax from the sequence of displacement amount frame data ptl and generates wavefront arrival time data ato. In the present embodiment, the displacement peak time is specified by correlation processing using the displacement amount frame data ptl.

As shown in FIG. 8 , propagation information analysis section 110 includes gate width setting section 1101 and correlation processing section 1102 .

(1) Gate width setting unit 1101
Gate width setting section 1101 sets a gate width, which is a data sequence length used in correlation processing in correlation processing section 1102 .

When the time-series displacement amount sequence at the observation point Pij is dij(t), the correlation processing unit 1102 performs correlation processing with the reference displacement amount sequence d0(t). Specifically, correlation processing section 1102 calculates τ that maximizes correlation value c(τ) represented by the following formula.

At this time, the gate width setting unit 1101 sets the gate specified by a and b so that (i) the gate width w _g defined by w _g =ba becomes smaller as t+τ becomes smaller. . That is, the gate is set so that the closer the displacement time related to dij(t+τ) used for calculating the correlation value c(τ) is to the push pulse transmission time, the smaller the gate width. For example, the gate width w _g is set such that w _g is proportional to t+τ when t+τ is 5 ms or less. Alternatively, the gate width w _g may satisfy the following equation.
w _g ={4(t+τ)−2}/3
On the other hand, when t+τ is large, the gate width w _g is set to be constant. For example, the gate width w _g is set so that 6 ms≦w _g ≦8 ms when t+τ is 30 ms or more.
Note that a and b preferably satisfy (ii) that the reference displacement amount sequence d0ij(t) peaks at t=c, which satisfies a<c<b.

Gate width setting section 1101 outputs parameters a and b specifying the set gate to correlation processing section 1102 .

(2) Correlation processing unit 1102
As described above, the correlation processing unit 1102 performs correlation processing between dij(t), which is the time-series displacement amount sequence at the observation point Pij, and the reference displacement amount sequence d0(t). As a result, a data sequence having the highest degree of similarity with the data sequence near the peak time of the reference displacement sequence d0(t) is searched from the displacement sequence dij(t), and the time corresponding to the searched data sequence is detected as the peak time. do. That is, when the peak time of the reference displacement amount sequence d0(t) is t=c, the peak time at the observation point Pij is calculated as t=c+τ.

The reference displacement sequence d0(t) is a displacement sequence whose peak time is known. , the shape of the graph when the amount of displacement is plotted on the vertical axis) are preferably similar. For the reference displacement sequence d0(t), for example, the displacement sequence dkl(t) of an observation point Pkl adjacent to the observation point Pij on the transmission focal point F side of the push wave can be used. At this time, the correlation processing unit 1102 calculates the peak times by correlation processing in order from the observation point closest to the transmission focus F of the push wave. That is, the peak time is specified in order from the observation point at which the wave front of the shear wave passes earlier. As a result, the peak time of the observation point near the transmission focus F with a sharp peak is calculated with high accuracy, and correlation processing is performed between the close observation points, based on the similarity of the displacement amount sequence, Even if the shear wave is attenuated, peak time can be detected while maintaining high peak sensitivity.

When the gate width is extremely small, the displacement peak time detection accuracy is close to that of the TTP method regardless of the degree of similarity between the reference displacement sequence d0(t) and the displacement sequence dij(t). This is because the influence of the features of the reference displacement sequence d0(t) on the correlation value c(τ) is extremely small, and the absolute value of the displacement sequence dij(t) has a strong influence on the correlation value c(τ). because it gives For example, when the gate width is 1 sample, the correlation processing is exactly the same as the TTP method for finding the maximum value of the displacement amount sequence dij(t). Therefore, when the time of displacement related to dij(t) is extremely close to the time of transmission of the push pulse, the gate width is made extremely small, regardless of the contents of the reference displacement amount sequence d0(t), as in the TTP method. In addition, the peak time can be calculated with high accuracy.

The correlation processing unit 1102 associates the displacement peak time with the coordinates of the observation point Pij to generate the wavefront arrival time data ato, and outputs the wavefront arrival time data ato to the data storage unit 114 .

8. Mechanical property calculator 111
The mechanical property calculator 111 is a circuit that calculates shear wave propagation velocities or mechanical properties for a plurality of observation points Pij in the region of interest roi, and calculates mechanical property data elf for the region of interest roi.

As shown in FIG. 8, the mechanical property calculator 111 is composed of a propagation velocity converter 1111 and a mechanical property converter 1112 .

(1) Propagation velocity converter 1111
The propagation velocity transforming unit 1111 transforms the wavefront arrival time data ato into the propagation velocity data vij at the observation point Pij in the region of interest roi, generates the propagation velocity data vo for the region of interest roi, and outputs the data to the data storage unit 114. do.

(2) Mechanical property converter 1112
The mechanical property conversion unit 1112 converts the propagation velocity frame data vo into the mechanical property el at the observation point Pij within the region of interest roi, generates the mechanical property data elf for the region of interest roi, and stores the data storage unit 114 output to Examples of mechanical properties include elastic modulus and viscosity, but are not limited to these as long as the properties can be calculated based on shear wave propagation speed.

9. Other configurations The data storage unit 114 stores the generated received wave signal sequence rf, the sequence of acoustic line signal frame data dsl, the sequence of displacement amount frame data ptl, the wavefront arrival time data ato, the propagation velocity data vo, and the mechanical characteristic data. This is a recording medium for sequentially recording elf.

The control unit 115 controls each block in the ultrasonic diagnostic apparatus 100 based on commands from the operation input unit 102 . A processor such as a CPU can be used for the control unit 115 .

Although not shown, the ultrasonic diagnostic apparatus 100 does not transmit the push wave pulse ppp, and the acoustic line signal output based on the transmission and reception of the detected waves in the transmission beam former 106 and the reception beam former 108 is Among these, it has a B-mode image generation unit that generates ultrasonic images (B-mode images) in time series based on reflection components from the tissue of the subject.

<About operation>
The operation of the integrated SWS sequence of the ultrasonic diagnostic apparatus 100 configured as above will be described.

1. Outline of Operation FIG. 9 is a schematic diagram showing an outline of the integrated SWS sequence process in the ultrasonic diagnostic apparatus 100 . The SWS sequence by the ultrasonic diagnostic apparatus 100 performs reference detection wave transmission/reception, acquires reference acoustic line signal frame data ds0 for extracting the displacement due to the shear wave corresponding to each subsequent transmission event (1a); a step (1b) of transmitting a wave pulse ppp to transmit a push wave pp focused on a specific site F in the subject to excite a shear wave in the subject; It consists of a step (1c) of transmitting and receiving a detection wave pulse pwpi that is repeated a plurality of (m) times, and a step (1d) of calculating mechanical characteristics by performing shear wave propagation analysis and calculating the propagation velocity vf of the shear wave and the mechanical characteristics elf. be.

2. Operation of SWS Sequence The operation of SWSM processing after the B-mode image in which the tissue is drawn based on the reflection component from the tissue of the subject is displayed on the display unit 113 based on a known method will be described below.

Note that the frame data of the B-mode image is based on the transmission and reception of ultrasonic waves in the transmission beamformer 106 and the reception beamformer 108 without transmitting the push wave pulse ppp. Based on this, the frame data of the acoustic line signal is formed in time series, the acoustic line signal is subjected to processing such as envelope detection and logarithmic compression, and after being converted into a luminance signal, the luminance signal is coordinate-transformed into an orthogonal coordinate system. to generate. The display control unit 112 causes the display unit 113 to display a B-mode image in which the tissue of the subject is drawn.

FIG. 10 is a flow chart showing the operation of SWSM processing in the ultrasonic diagnostic apparatus 100 .

[Steps S100 to 130]
In step S100, the ultrasonic diagnostic apparatus 100 displays on the display unit 113 a B-mode image, which is a tomographic image of the subject acquired by the probe 101 in real time. The information specified by the operator is input, and the region of interest roi representing the measurement target range within the subject is set with reference to the position of the probe 101 and output to the control unit 115 .

The operator designates the region of interest roi by, for example, displaying the latest B-mode image recorded in the data storage unit 114 on the display unit 113 and specifying the region of interest roi through an input unit (not shown) such as a touch panel or mouse. by specifying Note that the region of interest roi may be, for example, the entire area of the B-mode image, or may be a certain range including the central portion of the B-mode image.

Next, in step S110, the ultrasonic diagnostic apparatus 100 determines a detection wave pulse transmission transducer train so that the detection waves pass through the entire region of interest roi. In this example, as shown in FIG. 6(a), the propagation direction of the detection wave is the z-axis direction, and the detection wave pulse transmission transducer array Tx is set to include the range w of the region of interest roi in the x direction. . Note that the detection wave pulse transmission transducer array Tx may be all the elements of the probe 101 .

Information indicating the propagation direction of the detected wave and the detected wave pulse transmission transducer train Tx is output to the transmission beam former section 106 as a transmission control signal.

Next, in step S120, the push wave pulse generating unit 104 receives information indicating the region of interest roi from the control unit 115, and sets the position of the transmission focal point F of the push wave pulse ppp and the push wave transmission transducer array Px. . In this example, as shown in FIG. 3B, the column direction transmission focal position fx coincides with the column direction central position wc of the detection wave irradiation area Ax, and the depth direction transmission focal position fz is the center of the detection wave irradiation area Ax. It was configured to match the depth d up to. Also, the push wave transmitting transducer array Px is all of the plurality of transducers 101a. However, the positional relationship between the detection wave irradiation area Ax and the transmission focus F is not limited to the above, and may be changed as appropriate depending on the form of the site to be inspected of the subject.

Information indicating the position of the transmission focal point F and the push wave transmission transducer array Px is output to the transmission beam former unit 106 as a transmission control signal together with the pulse width of the push wave pulse ppp.

Next, in step S130, the transmission beam former unit 106 causes the transducers included in the push wave transmission transducer array Px to transmit the push wave pulse ppp, thereby causing the transducers to transmit within the subject corresponding to the transmission focus F. A push wave pp that focuses an ultrasonic beam on a specific site of is transmitted.

Specifically, the transmission beamformer 106 generates a transmission control signal including information indicating the position of the transmission focal point F and the push wave transmission transducer array Px acquired from the push wave pulse generation unit 104, and the pulse width of the push wave pulse ppp. Generate a transmission profile based on The transmission profile consists of a pulse signal sp and a delay time tpk for each transmission transducer included in the push wave transmission transducer array Px. Then, a push wave pulse ppp is supplied to each transmission transducer based on the transmission profile. Each transmitting transducer transmits a pulsed push wave pp focused on a specific site within the subject.

Here, the generation of the shear wave by the push wave pp will be described with reference to the schematic diagrams of FIGS. 11(a) to (c). FIGS. 11(a) to 11(c) are spring models showing the mechanism of shear wave excitation by push waves pp. FIG. In FIGS. 11( a ) to 11 ( c ), the elastic tissue within the subject is shown as a plurality of spheres connected by springs, one sphere corresponding to each position of the tissue within the subject. are doing.

First, a push wave pp is applied to a focal point in the subject corresponding to the transmission focal point F while the probe 101 is brought into close contact with the skin surface. As a result, the sphere 603 corresponding to the focal point is moved in the Z direction by the push pulse. Then, as shown in FIG. 11B, the ball 604 connected to the ball 603 is pulled in the Z direction, and the balls 613 and 614 are pushed in the Z direction by the balls 603 and 604, respectively. As a result, as shown in FIG. 11(c), the balls 612 and 623 pushed by the balls 602 and 603 directly pushed by the push pulse move in the Z direction and push the other balls, and the ball 604 The sphere 614 pushed in the Z direction and pulled in the Z direction by the sphere 613 moves in the Z direction. This action propagates vibration in the Z direction to the positions of the spheres 604 and 614 that are not directly pressed by the push pulse. That is, when the focal region is pressed in the Z direction, the focal region vibrates in the Z direction, and the tissue adjacent in the X direction is pulled in the Z direction, and the tissue also vibrates in the Z direction. Furthermore, a chain motion occurs in which tissue adjacent to the tissue vibrating in the Z direction is pulled in the Z direction and vibrates in the Z direction. Furthermore, by repeating such an operation, a phenomenon occurs in which the vibration in the Z direction propagates in the X direction, that is, the shear wave propagates in the X direction.

[Step S140]
Returning to FIG. 10, the description continues.

In step S140, the detection wave pulse pwpl is transmitted/received to/from the region of interest roi a plurality of times, and the acquired sequence of acoustic line signal frame data dsl is stored. Specifically, the transmission beam former unit 106 causes the transducers included in the detection wave transmission transducer array Tx to transmit the detection wave pulse pwpl toward the subject, and the reception beam former unit 108 causes the detection wave pulse reception oscillation. Acoustic line signal frame data dsl is generated based on the reflected waves ec received by the transducers included in the element array Rx. Immediately after the end of transmission of the push wave pp, the above processing is repeated, for example, 5000 times per second. As a result, the acoustic line signal frame data dsl within the detection wave irradiation area Ax of the object is repeatedly generated from immediately after the generation of the shear wave until the end of propagation.

More specifically, the transmission time required for the transmitted detection wave to reach the observation point Pij is calculated for each observation point Pij. The transmission time can be calculated by dividing the distance between the observation point Pij and the surface of the probe 101 on a straight line parallel to the propagation direction of the detected wave and passing through the observation point Pij by the speed of sound. In this example, since the propagation direction of the detected wave is the Z direction, it can be calculated by dividing the difference in Z coordinate between the surface of the probe 101 and the observation point Pij by the speed of sound. Next, for each combination of the observation point Pij and the wave-receiving transducer, the reception time required for the reflected detection wave reflected at the observation point Pij to reach the wave-receiving transducer is calculated. The reception time can be calculated by dividing the geometric distance between the observation point Pij and the receiving transducer by the speed of sound. Then, by calculating the delay time for each wave receiving transducer, identifying the wave receiving signal rfk corresponding to the observation point Pij, and performing weighted addition, the acoustic line signal dsl corresponding to the observation point Pij is generated.

The generated sequence of acoustic line signal frame data dsl is output to and stored in the data storage unit 114 .

[Steps S151 to S152]
In step S151, the displacement detection unit 109 detects the displacement of the observation point Pij within the region of interest roi in each transmission event.

FIG. 12 is a schematic diagram showing the operation of displacement detection and shear wave propagation analysis.

First, the displacement detection unit 109 acquires the reference acoustic line signal frame data ds0 stored in the data storage unit 114 in step S130. As described above, the reference acoustic line signal frame data ds0 is acoustic line signal frame data acquired before the push wave pp is transmitted, that is, before the shear wave is generated.

Next, the displacement detection unit 109 detects the difference between each acoustic line signal frame data dsl stored in the data storage unit 114 in step S150 and the reference acoustic line signal frame data ds0. Detect the displacement of each pixel at the acquired time.

Column A in FIG. 12 indicates the reference acoustic line signal frame data ds0 and acoustic line signal frame data dsl generated in each transmission event, and column B indicates the displacement amount frame calculated for each transmission event in step S150. Data ptl is shown. As shown in columns A and B of FIG. 12, the displacement amount frame data ptl compares the acoustic line signal frame data dsl and the reference acoustic line signal frame data ds0, and obtains the observation point Pij in the reference acoustic line signal frame data ds0. is similar to the acoustic line signal dsij of which observation point P'ij in the acoustic line signal frame data dsl, and to calculate the position change amount of the observation point P'ij with respect to the observation point Pij. Detected by

Specifically, for example, the acoustic line signal frame data dsl and the reference acoustic line signal frame data ds0 are correlated with the observation point Pij and its vicinity as gates, and the reference acoustic line signal frame data ds0 corresponding to the observation point Pij is calculated. The data most similar to the data in dsl are extracted from the acoustic line signal frame data dsl. Then, the position in the subject corresponding to the extracted data is set as the movement destination of the observation point Pij, and the displacement of the observation point Pij is detected.

The displacement detection method is not limited to correlation processing. The acoustic line signal frame data dsl is divided into regions of a predetermined size such as 8 pixels×8 pixels, and each region and the reference acoustic line signal frame data ds0 are divided. The displacement of each pixel of the acoustic line signal frame data dsl may be detected by pattern matching. Any technique other than pattern matching that detects the amount of motion between two pieces of acoustic line signal frame data dsl may be used.

The displacement detection unit 109 generates displacement amount data ptij of the observation points in the region of interest roi by associating the displacement of each observation point Pij related to the acoustic line signal frame data dsl of one frame with the coordinates ij of the observation point, The displacement amount frame data ptl for the generated region of interest roi is output to the data storage unit 114 . The displacement detection unit 109 performs this process for all transmission events to generate and store displacement amount data ptij for all transmission events (step S152).

[Steps S160 to S180]
In step S160, the propagation information analysis unit 110 receives the sequence of the displacement amount frame data ptl as input, identifies the peak time from the time-series change of the displacement amount data ptij for each of the observation points Pij in the region of interest roi, and identifies the peak time. The wavefront arrival time data at is generated by considering the arrival time of the wavefront of the shear wave and is output to the data storage unit 114 . The operation of step S160 will be described later.

In step S170, the mechanical property calculation unit 111 receives the wavefront arrival time data at as input, estimates the shear wave velocity for each observation point Pij in the region of interest roi, and calculates the mechanical property based on the shear wave velocity. presume.

First, the mechanical characteristic calculation unit 111 acquires the wavefront arrival time data at stored in the data storage unit 114 in step S160. Next, the mechanical property calculator 111 assumes that the shear wave propagates substantially in the x direction, and divides the distance between two observation points close to each other in the x direction by the difference in wave front arrival time to obtain the shear wave Estimate wave speed. Column D in FIG. 12 shows the state in which shear wave velocities are associated with coordinates ij of observation points. The mechanical property calculator 111 stores the propagation velocity data vf generated by associating the velocity of the shear wave with the coordinate ij of the observation point in the data storage 114 .

Note that the mechanical property calculator 111 may calculate the mechanical property of the subject based on the velocity of the shear wave. Examples of mechanical properties include elastic modulus and viscosity (viscosity coefficient). As shown in column E of FIG. 12, the mechanical property calculation unit 111 associates the mechanical properties with the coordinates ij of the observation point, and stores them in the data storage unit 114 as mechanical property data elf.

In step S180, the mechanical property calculation unit 111 generates a mechanical property image in which color information is mapped based on the property value indicated by the generated mechanical property data elf or propagation velocity data vf, and the display control unit 112 , the mechanical characteristic image is subjected to coordinate transformation and output to the display unit 113 .

Thus, the SWSM processing shown in FIG. 10 is completed.

3. Details of the processing in step S160 In step S160, the propagation information analysis unit 110 receives the sequence of the displacement amount frame data ptl as input, and calculates the peak time from the time series change of the displacement amount data ptij for each observation point Pij within the region of interest roi. is identified, the peak time is regarded as the arrival time of the wavefront of the shear wave, and wavefront arrival time data at is generated and output to the data storage unit 114 . A more detailed description will be given below with reference to the flow chart of FIG. 13 .

First, in step S1601, the coordinate ij of the observation point Pij is initialized so that the distance from the transmission focal point F of the push wave becomes small. Specifically, when the transmission focal point F of the push pulse exists within the region of interest roi, the position of the transmission focal point F is set as the position of the observation point Pij. On the other hand, if the transmission focus F of the push pulse does not exist within the region of interest roi, among the observation points having the same depth (z coordinate) as the transmission focus F, the observation point closest to the transmission focus F is the observation point Pij position.

Next, in step S1602, a reference displacement amount sequence d0ij is set. The reference displacement sequence d0ij is displacement sequence data having a tendency of time-series change similar to the time-series change of displacement at the observation point Pij, and is displacement sequence data with a known peak time. As the reference displacement amount sequence d0ij, for example, a reference displacement amount sequence d0ij of an observation point closer to the transmission focus F than the observation point Pij can be used. Note that the reference displacement amount sequence d0ij stored in advance in the data storage unit 114 may be used.

Next, in step S1603, a gate range for correlation processing is set. Specifically, first, the acquisition time of data used for correlation processing in the displacement amount sequence dij of the observation point Pij is specified, and converted into an observation time, which is a relative time with the push pulse transmission time set to 0. Next, the gate width is set according to the observation time value. Specifically, when the observation time is in the range of 2 ms to 5 ms, the gate width is set in the range of 2 ms to 6 ms, and the gate width increases as the observation time increases. For example, when the observation time is t, the gate width w _g may be w _g =(2t+2)/3. Alternatively, w _g =t may be set. On the other hand, when the observation time is 30 ms or more, the gate width is set within the range of 6 ms to 8 ms. As an example of setting the gate width, for example, the relationship shown in FIG. 14 may be used. Finally, the peak range a to b is set so that the data extracted from the reference displacement amount sequence d0ij includes data corresponding to the peak time. It is preferable that the center (a+b)/2 of the peak range be the peak time of the reference displacement amount sequence d0ij.

Next, in step S1604, the time difference τ is initialized to 0.

Next, in step S1605, the correlation value c(τ) is calculated for the time difference τ. Next, in step S1606, step S1605 is repeated while varying τ until correlation values c(τ) are calculated for all time differences τ. The process advances to step S1607.

Next, in step S1607, the peak time is specified based on the time difference τ with respect to the maximum value of the correlation value c(τ). Specifically, the maximum value is obtained from all the calculated correlation values c(τ), and the time difference τ corresponding to the maximum value is specified. Then, with respect to the peak time c in the reference displacement amount sequence, the time c+τ is specified as the peak time of the displacement of the observation point Pij.

Next, in step S1608, it is determined whether or not the peak time has been calculated for all the observation points Pij. If there is an observation point Pij for which the peak time has not been calculated, in step S1609, a push wave is transmitted. The next observation point Pij is determined so as to move away from the focal point F, and the processing from steps S1602 to S1607 is performed. Thereby, the peak time is calculated for all the observation points Pij.

Finally, in step S1610, propagation information analysis section 110 generates wavefront arrival time data at within region of interest roi by associating the peak time of displacement at observation point Pij with coordinates ij of the observation point, 114.

<Relationship between gate width and peak time detection accuracy>
Experimental results will be evaluated below regarding the relationship between the displacement peak time detection accuracy and the gate width.

Four types of phantoms having uniform hardness were used for evaluation. In the evaluation experiment, as shown in FIG. 15(a), a first position P1, a second position P2, a third position P3, a fourth position P1, a second position P2, a third position P3, and a fourth position are placed on a straight line passing through the transmission focal point F of the push pulse and parallel to the x-axis. P4 were provided at equal intervals, and these four points were used as observation points to detect the time-series change in displacement and the peak time of displacement.

FIG. 16(a) shows time series changes in displacement in a phantom with an elastic modulus of 44 kPa. It shows a time-series change in the displacement of the fourth position. FIG. 16(b) shows time-series changes in displacement in a phantom with an elastic modulus of 25 kPa. It shows a time-series change in the displacement of the fourth position. FIG. 17(a) shows time-series changes in displacement in a phantom with an elastic modulus of 12 kPa. It shows a time-series change in the displacement of the fourth position. FIG. 17(b) shows time series changes in displacement in a phantom with an elastic modulus of 3.7 kPa. Position, the time-series change of the displacement of the 4th position is shown.

16A to 17B, the higher the elastic modulus of the subject, the sharper the peak, and the lower the elastic modulus, the duller the peak. Also, the higher the elastic modulus of the subject, the earlier the peak time, and the lower the elastic modulus, the later the peak time. This tendency is because the higher the elastic modulus of the subject, the stronger the restoring force against the displacement caused by the push pulse, so the peak tends to be sharper and the propagation speed is faster. On the other hand, focusing on the time-series changes in the displacement near the peak, if the elastic moduli are the same, the change tendencies are similar. That is, in the phantom with an elastic modulus of 44 kPa, the waveforms near the peaks of the displacements 711 and 712 at different positions are similar. The waveforms near the peak of displacement 742 are similar. That is, when the hardness is uniform, the waveforms are similar at two adjacent observation points, and it can be assumed that the peak time of displacement can be easily detected by correlation processing.

FIG. 18 shows a comparison of variation (standard deviation) in peak time difference between an example in which the gate width of correlation processing is set as in the embodiment and a comparative example in which the gate width of correlation processing is fixed. be. FIG. 18A shows peak times of displacement at the first, second, third, and fourth positions in the phantom with an elastic modulus of 12 kPa in the example and the comparative example with a fixed gate width. , the difference in peak time between two adjacent observation points, and its standard deviation. As described above, the phantom has a uniform hardness, and the first, second, third, and fourth positions are set on a straight line at equal intervals. The difference in peak time between two adjacent stations, which corresponds to the travel time of , should be equal for all three. Therefore, it can be estimated that the smaller the standard deviation value, the more accurate the detection accuracy of the peak time. In this experiment, detection waves were transmitted and received every 200 μs, and peak times are indicated by sample numbers. For example, the first position peak time 24 indicates that the peak time is 4.8 ms.

In the embodiment, the gate width is 1 ms for the first position, the gate width is 2 ms for the second position, and the gate width is 4 ms for the third and fourth positions. Since the peaks are sharp at the first position and the second position, the peak time can be detected with high accuracy even if the gate width is narrow. In particular, when the gate width is extremely narrowed, even the correlation processing method has characteristics similar to those of the TTP method. Therefore, it is effective to narrow the gate width in the time period when the S/N ratio is high. On the other hand, if the gate width is set wide, the data other than the peak will be included in the gate because the peak is sharp, so the data other than the peak will affect the correlation processing, and the detection accuracy will decrease. It is conceivable that At the third and fourth positions, as shown by displacements 733 and 734 in FIG. 17(a), the shear wave is attenuated in the process of propagating, resulting in dull peaks and a low S/N ratio. Therefore, if the gate width is too narrow, erroneous detection of noise is likely to occur as in the TTP method. On the other hand, even if the gate width is increased more than necessary, the detection accuracy does not improve, and only the amount of calculation increases. Therefore, when the gate width is fixed, if the gate width is narrow, the peak detection accuracy at the 3rd position and the 4th position decreases, so the error between the 2nd-3rd time difference and the 3rd-4th time difference tends to increase. If the gate is wide, the peak detection accuracy at the first position and the second position is lowered, so it can be inferred that the errors in the first-second time difference and the second-third time difference tend to increase. On the other hand, in the embodiment, since the gate width for correlation processing is changed for each observation point, it can be assumed that an appropriate gate width can always be used and the standard deviation value is reduced.

FIG. 18(b) shows the same evaluation for a phantom with an elastic modulus of 25 kPa. In the embodiment, the gate width is 1 ms for the first and second positions, 2 ms for the third position, and 4 ms for the fourth position. In the phantom with an elastic modulus of 25 kPa, the speed of the shear wave is faster than in the phantom with an elastic modulus of 12 kPa, as is clear from the comparison between FIG. 16(b) and FIG. 17(a). Therefore, not only the first position and the second position, but also the third position has a sharp peak similarly to the first position, and even if the gate width is narrow, the peak time can be detected with high accuracy. Regarding the fourth position, similarly to the third position in the phantom with an elastic modulus of 12 kPa, if the gate width is too narrow, false detection of noise is likely to occur as in the TP method. It is considered that only the amount of calculation increases without improving the accuracy. Therefore, when the gate width is fixed, if the gate width is narrow, the peak detection accuracy at the 4th position decreases, and the error between the 3rd and 4th time differences tends to increase. It can be inferred that the errors in the first-second time difference and the second-third time difference tend to increase because the peak detection accuracy of the position decreases. On the other hand, in the embodiment, since the gate width for correlation processing is changed for each observation point, it can be assumed that an appropriate gate width can always be used and the standard deviation value is reduced.

Moreover, FIG. 18(c) shows the same evaluation for a phantom with an elastic modulus of 44 kPa. In the embodiment, the gate width is calculated to be 1 ms for all of the first, second, third and fourth positions. As is clear from FIG. 16A, the phantom with an elastic modulus of 44 kPa has a faster shear wave velocity than the phantom with an elastic modulus of 25 kPa. Therefore, not only the first, second, and third positions, but also the fourth position has a sharp peak like the first position, and even if the gate width is narrow, the peak time can be detected with high accuracy. Therefore, if the gate width is fixed, it can be inferred that a wide gate width reduces the peak detection accuracy, and thus the time difference error tends to increase. On the other hand, in the embodiment, since the gate width for correlation processing is changed for each observation point, it can be assumed that an appropriate gate width can always be used and the standard deviation value is reduced.

As described above, if the gate width of correlation processing is too small, erroneous detection of noise is likely to occur for dull peaks and the like, and erroneous detection may occur at a time greatly deviated from the peak time. On the other hand, if the gate width of the correlation processing is too large, the amount of calculation increases, and the error in the peak time may increase due to the use of data of the time off the peak. In contrast, in the embodiment, the gate width is reduced when the observation time based on the transmission time of the push pulse is early. With this configuration, when deterioration due to shear wave propagation is small and the absolute amount of displacement and the degree of change are large, it is possible to increase the detection accuracy of the peak time similarly to the TTP method. On the other hand, if the observation time based on the transmission time of the push pulse is late, the gate width is increased. With this configuration, erroneous detection of noise and the like can be suppressed when deterioration due to shear wave propagation is large and the absolute amount of displacement and the degree of change are small. As shown in FIG. 18(a), even if the gate width is increased more than necessary, the amount of calculation increases and the peak time detection accuracy does not change. detection accuracy is reduced. In the embodiment, by adaptively changing the gate width based on the observation time, it is possible to apply a suitable gate width for each observation point, and detect peak time while suppressing false detection of noise. It is possible to improve the accuracy.

<Other Modifications>
Although the description has been made based on the above embodiment, the embodiment according to the present disclosure is not limited to the above embodiment, and may have the following configuration.

(1) When the ultrasonic diagnostic apparatus 100 according to the embodiment detects the peak time of displacement at the observation point Pij, the time series of the displacement of the observation point Pkl adjacent to the observation point Pij on the transmission focus F side is The reference time-series data is used as the data, but the reference time-series data only needs to have a known peak time and a certain degree of similarity to the time-series data of the displacement of the observation point Pij. For example, for a plurality of observation points arranged in the x-direction, time-series data of the displacement of the 2n-th observation point (n is an integer of 1 or more) may be used as the reference time-series data, or the 3n-th or 4n-th observation point may be used as the reference time-series data. The time-series data of the displacement of the eye observation point may be used as the reference time-series data. Alternatively, reference time-series data stored in advance may be used. For example, when the same region of interest is measured a plurality of times, the time-series data of the displacement related to the previous push pulse transmission may be used as the reference time-series data. data.

(2) Although the ultrasonic diagnostic apparatus 100 according to the embodiment transmits a push pulse focused on the transmission focus F, the push pulse wave may be any device that excites a shear wave in the subject. It may be a push pulse that is focused on a region with a sharpness.

In addition, although the ultrasonic diagnostic apparatus 100 transmits a plane wave as a detection wave, the detection wave can be transmitted a sufficient number of times to detect the speed of the shear wave, and displacement can be detected based on the acoustic line signal generated by reception. As long as the accuracy is sufficiently high, it may be, for example, a focused wave, a spherical wave, or the like.

(3) The ultrasonic diagnostic apparatus according to the embodiments and modifications may be implemented by a single-chip integrated circuit or multiple-chip integrated circuit, or may be implemented by a computer program. or any other form. For example, the propagation analysis unit and the evaluation unit may be implemented on one chip, or only the ultrasonic signal acquisition unit may be implemented on one chip, and the displacement detection unit and the like may be implemented on another chip.

When implemented as an integrated circuit, it is typically implemented as an LSI (Large Scale Integration). Although LSI is used here, it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

Also, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after the LSI is manufactured, or a reconfigurable processor that can reconfigure the connections and settings of the circuit cells inside the LSI may be used.

Furthermore, if a technology for integrating circuits to replace LSI appears due to advances in semiconductor technology or another technology derived from it, the technology may naturally be used to integrate the functional blocks.

Also, the ultrasonic diagnostic apparatus according to each embodiment and each modification may be realized by a program written in a storage medium and a computer that reads and executes the program. The storage medium may be any storage medium such as a memory card, CD-ROM, or the like. Also, the ultrasonic diagnostic apparatus according to the present invention may be realized by a program downloaded via a network and a computer that downloads the program from the network and executes it.

(3) All of the embodiments described above are preferred specific examples of the present invention. Numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of constituent elements, steps, order of steps, and the like shown in the embodiments are examples, and are not intended to limit the present invention. In addition, among the constituent elements of the embodiments, steps not described in the independent claims representing the top concept of the present invention will be described as arbitrary constituent elements constituting more preferred embodiments.

In order to facilitate understanding of the invention, the scales of the constituent elements in the respective drawings described in the above embodiments may differ from the actual ones. Moreover, the present invention is not limited by the description of each of the above embodiments, and can be modified as appropriate without departing from the scope of the present invention.

Furthermore, in the ultrasonic diagnostic apparatus, there are circuit parts, lead wires and other members on the board, but various aspects can be implemented based on common knowledge in the relevant technical field regarding electrical wiring and electrical circuits, Description is omitted because it is not directly related to the description of the present invention. Each figure shown above is a schematic diagram, and is not necessarily strictly illustrated.

≪Supplement≫
(1) An ultrasonic signal processing apparatus according to an embodiment includes a push wave transmission unit for transmitting a push wave for generating a displacement in a subject to an ultrasonic probe; a detection wave transmitting unit that transmits a detection wave passing through a region of interest indicating a measurement target range in a subject to the ultrasonic probe; a detection wave receiving unit that receives ultrasonic waves and converts them into received signals; a phasing addition unit that performs phasing addition for each of a plurality of positions in the region of interest to generate an acoustic line signal; A displacement detection unit for detecting displacement at each of a plurality of observation points based on acoustic line signals corresponding to each of the observation points; and a state estimator, wherein the propagation state estimator performs correlation processing between the time-series data of the displacement of the observation point and the reference time-series data in which the time at which the displacement reaches the maximum is known, and the displacement at the observation point is calculated. It is characterized by estimating the maximum time and reducing the gate width, which is the time width of the reference time-series data, as the observation time, which is the time of displacement based on the transmission time of the push wave pulse, is earlier.

Further, the ultrasonic signal processing method according to the embodiment causes the ultrasonic probe to transmit a push wave for generating a displacement in the subject, and following the transmission of the push wave, the measurement target range in the subject Sending a detection wave passing through a region of interest showing to the ultrasonic probe, receiving and converting an ultrasonic wave reflected from the region of interest corresponding to the detection wave using the ultrasonic probe into a received signal, performing phasing addition for each of the plurality of positions within the region of interest to generate an acoustic line signal, and based on the acoustic line signal corresponding to each of the plurality of observation points within the region of interest, the displacement at the observation point; and estimating the propagation state of the shear wave based on the time change of the displacement of each of the observation points, wherein when estimating the propagation state of the shear wave, the displacement of the observation point By correlating the time-series data with reference time-series data for which the time of maximum displacement is known, the time of maximum displacement at the observation point is estimated. By correlation processing with reference time-series data whose time is known, the time at which the displacement at the observation point becomes maximum is estimated, and the earlier the observation time of the displacement based on the transmission time of the push wave pulse, the earlier the reference time It is characterized by reducing the gate width, which is the time width of series data.

Further, a program according to an embodiment is a program for causing an ultrasonic signal processing apparatus to which an ultrasonic probe is connected to perform shear wave propagation analysis processing, wherein the shear wave propagation analysis processing is performed by causing the ultrasonic probe to transmit a push wave for generating; following the transmission of the push wave, causing the ultrasonic probe to transmit a detection wave passing through a region of interest indicating a measurement target range within the subject; Using an ultrasonic probe, ultrasonic waves reflected from the region of interest corresponding to the detected waves are received and converted into received signals, and phasing addition is performed for each of a plurality of positions within the region of interest to obtain an acoustic line. generating a signal, detecting a displacement at the observation point based on the acoustic line signal corresponding to each of the plurality of observation points in the region of interest, and detecting a shear wave based on the time change of the displacement at each of the observation points; This is a process for estimating the propagation state, and when estimating the propagation state of the shear wave, by correlation processing between the time-series data of the displacement of the observation point and the reference time-series data in which the time when the displacement reaches the maximum is known , estimating the time at which the displacement at the observation point becomes maximum, and reducing the gate width, which is the time width of the reference time series data, as the displacement observation time is earlier with reference to the transmission time of the push wave pulse. Characterized by

According to the present disclosure, with the above configuration, when the observation time is large, that is, when the shear wave is attenuated and the high S/N ratio of the displacement time-series data is not guaranteed, the gate width is made too small. Since there is no peak, erroneous detection of the peak and failure to detect the peak can be prevented, and the time at which the displacement peaks can be detected with a high probability. On the other hand, if the gate width is made small in the correlation processing, high detection accuracy can be obtained as in the TTP method. do. With this configuration, high detection accuracy can be obtained in environments where the TTP method is suitable, and peak times can be detected even in environments where the TTP method is not suitable, so detection sensitivity is increased for all environments. can improve detection accuracy.

(2) Further, in the ultrasonic signal processing apparatus of (1) above, the propagation state estimating unit linearly increases the gate width with respect to the observation time when the observation time is within a predetermined range. may be set to

With the above configuration, peak time detection accuracy can be improved by reducing the gate width especially when the observation time is early and the displacement is large.

(3) Further, in the ultrasonic processing apparatus of (2) above, the predetermined range may be in the range of 2 ms to 5 ms, and the gate width in the predetermined range may be in the range of 2 ms to 6 ms. .

With the above configuration, peak time detection accuracy can be improved by reducing the gate width for observation points with early observation times and large displacements.

(4) Further, in the ultrasonic signal processing apparatus of (1) to (3), the propagation state estimating unit sets the gate width to a constant length when the observation time exceeds a predetermined threshold. You can do it.

With the above configuration, it is possible to suppress an increase in the amount of calculation by not excessively widening the gate width for an observation point with a late observation time and a small displacement.

(5) Further, in the ultrasonic signal processing apparatus of (4) above, the predetermined threshold may be 30 ms, and the constant length may be a value of 6 ms or more and 8 ms or less.

With the above configuration, an increase in the amount of computation can be suppressed by preventing the gate width from being excessively widened.

(6) Further, in the ultrasonic signal processing apparatus of the above (1) to (5), the propagation state estimating unit is configured such that the displacement is maximized in order from the observation point closest to the position in the subject where the push wave causes the displacement. A part of the time-series data of the displacement of the observation point, which estimated the time when the displacement becomes maximum, is used as a reference time series when estimating the time when the displacement of other observation points reaches the maximum It may be used as data.

With the above configuration, the degree of similarity between the displacement time-series data and the reference time-series data related to correlation processing is improved, so that peak time detection accuracy can be improved particularly when the observation time is late.

The ultrasonic diagnostic apparatus and ultrasonic signal processing method according to the present disclosure are useful for measuring mechanical properties of a subject using ultrasonic waves. Therefore, it is possible to improve the measurement accuracy of the mechanical properties of tissues and substances, and it has high applicability in medical diagnostic equipment, non-destructive inspection equipment, and the like.

100 ultrasonic diagnostic apparatus 101 ultrasonic probe (probe)
101a transducer 102 operation input unit 103 region of interest setting unit 104 push wave pulse generation unit 1041 push wave transmission unit 105 detection wave pulse generation unit 1051 detection wave transmission unit 106 transmission beam former unit 1061 drive signal generation unit 1062 delay profile generation unit 1063 Drive signal transmission unit 107 Multiplexer unit 108 Receiving beamformer unit 1081 Input unit 1082 Received wave signal holding unit 1083 Phasing addition unit 10831 Delay processing unit 10832 Addition unit 109 Displacement detection unit 110 Propagation information analysis unit 1101 Gate width setting unit 1102 Correlation processing Section 111 Mechanical Property Calculator 1111 Propagation Velocity Conversion Section 1112 Mechanical Property Conversion Section 112 Display Control Section 113 Display Section 114 Data Storage Section 115 Control Section 150 Ultrasonic Signal Processing Circuit 1000 Ultrasonic Diagnostic System

Claims (9)

a push wave transmitter that causes the ultrasonic probe to transmit a push wave for generating displacement in the subject;
a detection wave transmitting unit that causes the ultrasonic probe to transmit, following the transmission of the push wave, a detection wave that passes through a region of interest indicating a measurement target range within the subject;
a detection wave receiving unit that receives ultrasonic waves reflected from the region of interest corresponding to the detection waves using the ultrasonic probe and converts them into received signals;
a phasing addition unit that performs phasing addition for each of a plurality of positions in the region of interest to generate an acoustic line signal;
a displacement detection unit that detects displacement at the observation point based on acoustic line signals corresponding to each of the plurality of observation points in the region of interest;
a propagation state estimating unit that estimates the propagation state of the shear wave based on the time change of the displacement of each of the observation points,
The propagation state estimating unit estimates the time at which the displacement at the observation point reaches its maximum by correlation processing between the time-series data of the displacement at the observation point and the reference time-series data in which the time at which the displacement reaches its maximum is known. ,
An ultrasonic signal processing apparatus, wherein a gate width, which is a time width of the reference time-series data, is reduced as a displacement observation time is earlier with reference to a transmission time of a push wave pulse. The ultrasonic signal according to claim 1, wherein the propagation state estimator sets the gate width so as to linearly increase with respect to the observation time when the observation time is within a predetermined range. processing equipment. The ultrasonic signal processing apparatus according to claim 2, wherein the predetermined range is from 2 ms to 5 ms, and the gate width in the predetermined range is from 2 ms to 6 ms. The ultrasound according to any one of claims 1 to 3, wherein the propagation state estimator sets the gate width to a constant length when the observation time exceeds a predetermined threshold. Signal processor. The ultrasonic signal processing apparatus according to claim 4, wherein the predetermined threshold value is 30 ms, and the constant length is a value of 6 ms or more and 8 ms or less. The propagation state estimating unit estimates the time at which the displacement is maximized in order from the observation point closest to the position in the subject where the push wave causes the displacement,
A part of the time-series data of the displacement of the observation point for which the time of maximum displacement is estimated is used as reference time-series data when estimating the time of maximum displacement of another observation point. The ultrasonic signal processing apparatus according to any one of claims 1 to 5. an ultrasound probe;
An ultrasonic signal processing apparatus according to any one of claims 1 to 6;
An ultrasonic diagnostic apparatus, comprising: a mechanical property estimating unit for estimating mechanical properties of a subject based on the shear wave propagation state estimated by the propagation state estimating unit. causing the ultrasonic probe to transmit a push wave for generating displacement within the object;
Following the transmission of the push wave, causing the ultrasonic probe to transmit a detection wave passing through a region of interest indicating a measurement target range within the subject;
receiving ultrasonic waves reflected from the region of interest corresponding to the detected waves using the ultrasonic probe and converting them into received signals;
performing a delayed summation for each of a plurality of positions within the region of interest to generate an acoustic line signal;
detecting a displacement at the observation point based on acoustic line signals corresponding to each of the plurality of observation points in the region of interest;
An ultrasonic signal processing method for estimating a propagation state of a shear wave based on a time change in displacement of each of the observation points,
When estimating the propagation state of the shear wave, the displacement at the observation point is maximized by correlation processing between the time-series data of the displacement at the observation point and the reference time-series data in which the time at which the displacement reaches its maximum is known. Estimate the time when
An ultrasonic signal processing method, wherein a gate width, which is a time width of the reference time-series data, is reduced as a displacement observation time is earlier with reference to a push wave pulse transmission time. A program for causing an ultrasonic signal processing device to which an ultrasonic probe is connected to perform shear wave propagation analysis processing,
The shear wave propagation analysis process includes
causing the ultrasonic probe to transmit a push wave for generating displacement within the subject;
Following the transmission of the push wave, causing the ultrasonic probe to transmit a detection wave passing through a region of interest indicating a measurement target range within the subject;
receiving ultrasonic waves reflected from the region of interest corresponding to the detected waves using the ultrasonic probe and converting them into received signals;
performing a delayed summation for each of a plurality of positions within the region of interest to generate an acoustic line signal;
detecting a displacement at the observation point based on acoustic line signals corresponding to each of the plurality of observation points in the region of interest;
A process of estimating the propagation state of the shear wave based on the time change of the displacement of each of the observation points,
When estimating the propagation state of the shear wave, the displacement at the observation point is maximized by correlation processing between the time-series data of the displacement at the observation point and the reference time-series data in which the time at which the displacement reaches its maximum is known. Estimate the time when
A program characterized in that a gate width, which is the time width of the reference time-series data, is reduced as the observation time of the displacement based on the transmission time of the push wave pulse is earlier.

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