JP2019111104A - Ultrasonic transmission and reception apparatus and ultrasonic transmission and reception method - Google Patents

Abstract

To accurately focus ultrasonic waves at a desired focal point by grasping the shape of a tissue boundary of an inspection target.SOLUTION: Ultrasonic waves are transmitted to an inspection target from a probe in which a plurality of transducers are arranged, and reception signals obtained by receiving ultrasonic waves returning from the inspection target after the transmission respectively by the transducers are used to detect a tissue boundary in the inspection target. At the detected tissue boundary, a path for the ultrasonic waves to be refracted is obtained, and a delay time of the ultrasonic waves to be transmitted for each transducer for focusing the ultrasonic waves at a predetermined focal point on the basis of the path is calculated for each transducer. Ultrasonic waves delayed by the delay time of each transducer are transmitted from each transducer to focus the ultrasonic wave.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic transmitting and receiving apparatus, and relates to a technology for evaluating the property of a living tissue by generating a shear wave in a subject and measuring its propagation speed.

  Medical image display devices typified by ultrasound, MRI (Magnetic Resonance Imaging) and X-ray CT (Computed Tomography) are widely used as devices for presenting invisible information in the living body in the form of numerical values or images. There is. Above all, an ultrasonic imaging apparatus that displays an image using ultrasonic waves has a high time resolution as compared with other apparatuses, and has, for example, the ability to image the heart under pulsation without blurring.

  The waves propagating in the object (living body) are mainly distinguished into longitudinal waves and transverse waves. The technique for visualizing the tissue shape used in the ultrasonic imaging apparatus and the technique for measuring the blood flow velocity mainly use information of a longitudinal wave (sound velocity of about 1540 m / s).

  On the other hand, in recent years, a technique for evaluating the elastic modulus of a tissue using transverse waves (hereinafter, shear waves) propagating in a living body has attracted attention, and clinical use for chronic liver disease and cancer has been advanced. In this technique, a shear wave is generated inside a tissue to be measured, and an evaluation index representing elasticity such as the elastic modulus of the tissue is calculated from the propagation velocity of the shear wave.

  Methods for generating shear waves are roughly classified into mechanical methods and radiation pressure methods. The mechanical method is a method of generating a shear wave by applying vibration of about 1 kHz to a body surface using a vibrator or the like, and a drive device serving as a vibration source is required. On the other hand, in the radiation pressure method, acoustic radiation pressure is applied to the living body using focused ultrasound that focuses ultrasound locally on tissue, and shear waves are generated using instantaneously generated tissue displacement.

  Whichever shear wave generation method is used, tissue displacement caused by the generated shear wave is measured by ultrasonic waves, and the propagation velocity of the shear wave is calculated. From the calculated propagation velocity of shear waves, characteristic values such as elastic modulus representing tissue characteristics are determined by calculation.

  The method of evaluating the elasticity of a tissue using shear waves is extremely important in tumor diagnosis because it can quantitatively measure characteristic values such as elastic modulus, and has high clinical value. However, it is known that ultrasonic waves are affected by reflection, refraction, diffraction, and attenuation depending on the tissue structure, and thus affect measurement accuracy and recall when measuring tissue elasticity using shear waves.

  Patent Document 1 discloses an ultrasonic diagnostic apparatus that transmits an ultrasonic wave into a subject, receives an ultrasonic signal reflected back in the subject, and generates an image of the subject from the received signal. A technique has been disclosed which performs ultrasound focusing during transmission or reception, taking into consideration the refraction of ultrasound at the boundary of the fat layer of a subject. That is, the delay time to be applied to the transmission signal or the reception signal for each transducer is set in consideration of the refraction of ultrasonic waves at the boundary of the fat layer of the subject. Thereby, the influence of the refraction of the ultrasonic wave in the fat layer of the subject can be suppressed, and the degradation of the resolution of the subject image can be prevented. The delay time is set by measuring the thickness of the superficial subcutaneous fat layer, estimating the propagation path from the transducer to the focal point, taking into consideration refraction at the tissue boundary with other living tissues, and propagating the propagation path The propagation time until the sound wave reaches from the sound source to the focal point is calculated from the length of the path and the sound velocity of the tissue on the propagation path, and the delay time for each transducer is set based on this.

Patent No. 4711583

  In the technique of Patent Document 1, it is assumed that a fat layer having a uniform thickness is present, and a propagation path of refraction of ultrasonic waves is calculated. The thickness of the fat layer is measured in one place by calculating the distance between the cursors arranged by the user on the upper and lower surfaces of the fat layer.

  However, depending on the subject, the thickness of the fat layer may not be uniform and may have a complicated shape. In addition, the fat layer and other tissues may be alternately laminated in multiple layers. Furthermore, in the subject, boundaries of various tissues other than the fat layer exist, and form complex shaped tissue boundaries.

  In the method of evaluating the elasticity of tissue using shear waves, in order to measure the elastic modulus of tissue with high accuracy, it is desirable to generate shear waves with a desired strength at a designated position of a desired depth. If the shear wave generation position deviates from the designated position, the shear wave of the strength (amplitude) necessary for the shear wave measurement region does not propagate, and the shear wave measurement becomes difficult. Therefore, when generating a shear wave by focused ultrasound, it is necessary to accurately determine the delay time for focusing the ultrasound at the focal point accurately for each transducer. It is necessary to grasp the position and shape of the tissue boundaries existing up to (the focal point) and to determine the propagation path in consideration of the refraction of ultrasonic waves at those boundaries.

  In the technique of Patent Document 1, since the thickness of the fat layer is measured at one place by the cursor set by the user, when the boundary shape of the tissue is complicated, it is difficult to grasp the shape. Therefore, it is difficult to accurately focus ultrasonic waves having passed through a complex shaped tissue boundary at a desired focal position by applying the technique of Patent Document 1.

  Moreover, when using the technique of patent document 1 for elasticity evaluation using a shear wave, there is no method of knowing the reliability of the obtained elastic modulus.

  An object of the present invention is to grasp the shape of a tissue boundary to be examined and to focus ultrasonic waves precisely on a desired focal point.

  In order to achieve the above object, according to the present invention, a transmission unit that outputs a transmission signal to a probe in which a plurality of transducers are arranged, and transmits ultrasound from the plurality of transducers to an inspection object An ultrasonic transmitting and receiving apparatus is provided that includes a receiving unit that acquires a reception signal output from each transducer that has received an ultrasonic wave that returns from an inspection object after transmission, and a control unit that controls the transmitting unit and the receiving unit. The control unit uses the received signal to obtain a tissue boundary detection unit that detects a tissue boundary in the examination target in a predetermined range, and a path along which ultrasound waves transmitted from a plurality of transducers are refracted at the tissue boundary. And a delay time calculation unit which calculates the delay time of the transmission signal for focusing the ultrasonic wave at a predetermined focal point based on the

  According to the present invention, since it is possible to grasp the shape of the tissue boundary to be examined, it is possible to focus the ultrasonic waves on a desired focal position with high accuracy. Therefore, a shear wave can be generated and its speed can be measured accurately.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of one structural example of the ultrasonic transmission / reception apparatus of Embodiment 1 of this invention. (A) is an explanatory view showing a path along which the ultrasonic wave is refracted at the tissue boundary of the tissue 1 and the tissue 2 different in sound velocity, (b) a path of the ultrasonic wave when there is no tissue boundary, and a focal point of the ultrasonic wave It is explanatory drawing which shows the appropriate distance with a measurement point. (A) is explanatory drawing which shows transmission / reception of the 1st ultrasound of embodiment, (b) It is description which each shows transmission of a 2nd ultrasound and transmission / reception of a 3rd ultrasound. 5 is a flowchart showing the operation of the ultrasonic transmitting and receiving apparatus of the first embodiment. It is a flowchart which detects a tissue boundary from a B mode image. It is a flowchart which detects a tissue boundary from RF signal. It is the figure which showed the tissue boundary of the structure | tissue 1 and the structure | tissue 2, and the inclination of the tissue boundary. 7 is a flowchart showing an operation (a transducer base point method) of calculating a refraction path of ultrasonic waves according to the first embodiment. It is explanatory drawing which shows the relationship of each point of the ultrasonic refraction | bending path | route used by calculation operation of FIG. FIG. 7 is a diagram showing an estimated ultrasound intensity distribution near the focal point obtained in Embodiment 1. FIG. 13 is a flowchart showing an operation (focusing point method) of calculating a refraction path of ultrasonic waves according to the second embodiment. It is explanatory drawing which shows the relationship of each point of the ultrasonic refraction | bending path | route used by calculation operation | movement of FIG. When using the delay time calculated in Embodiment 2, it is a graph which shows the range which accept | permits the shift | offset | difference of a focus position and an ultrasonic wave arrival point. 7 is a flowchart showing the operation of the ultrasonic transmitting and receiving apparatus of the third embodiment. It is a flow chart which detects a plurality of tissue boundary candidates from a B mode image. It is a flow chart which detects a plurality of tissue boundary candidates from RF signal. 15 is an example of a display mode of the ultrasonic transmitting and receiving apparatus in the third embodiment. 15 is an example of a display mode of the ultrasonic transmitting and receiving apparatus in the third embodiment. (A), (b) is an example of a display type at the time of using presumed intensity distribution of the ultrasonic wave of the focus vicinity in Embodiment 3 as a reliability index. It is an example of a display mode at the time of making presumed intensity distribution of the ultrasonic wave near the focus in Embodiment 3 into a reliability index. (A), (b) shows an example of a display mode at the time of using the tissue displacement of the depth direction by the shear wave in Embodiment 3 as a reliability index. The tissue displacement in the depth direction by the shear wave in Embodiment 3 is shown as an example of a display mode at the time of using as a reliability index. (A), (b) is explanatory drawing which shows propagation to the left-right direction of the wave front of a shear wave, (c) is reliable in the difference of the arrival time of the wave front of the shear wave in Embodiment 3 in the left-right direction. An example of a display mode at the time of using as an index is shown. The example of a display form at the time of using the difference of the arrival time of the right and left direction of the wave face of the shear wave in Embodiment 3 as a reliability index is shown. In (a) and (b), the ultrasonic wave of the third ultrasonic wave is irradiated around the focal point where the shear wave propagates in the third embodiment, and the signal strength of the received signal which received the reflected wave is a reliability index An example of a display form at the time of using as is shown. An example of a display form in the case where the ultrasonic wave of the third ultrasonic wave is irradiated around the focal point where the shear wave propagates in Embodiment 3 and the signal strength of the received signal which received the reflected wave is used as the reliability index is shown. It is

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< First Embodiment >>
The ultrasonic transmitting and receiving apparatus 1 according to the first embodiment will be described with reference to FIG.

  As shown in FIG. 1, the ultrasonic transmitting and receiving apparatus 1 according to the first embodiment includes a transmitting unit (transmission beam former) 21, a receiving unit (reception beam former) 22, and a control unit 30. The transmission unit 20 outputs a transmission signal to the probe 10 in which a plurality of transducers are arranged, and causes the plurality of transducers to transmit an ultrasonic wave to the inspection target 100. After the transmission of the ultrasonic wave by the probe 10, the ultrasonic wave returning from the inspection target 100 is received by each transducer of the probe 10, and each transducer outputs a reception signal. The receiving unit 22 acquires received signals respectively output from the transducers.

  The control unit 30 controls the transmission unit 21 and the reception unit 22. Control unit 30 includes a tissue boundary detection unit 32 and a delay time calculation unit 33. The tissue boundary calculation unit 32 detects the tissue boundary 121 in the examination target 100 in a predetermined range 110, as shown in FIG. 2A, using the reception signal of the reception unit 22. The delay time calculation unit 33 determines a path 411 where the ultrasonic waves transmitted from the plurality of transducers 11 are refracted at the tissue boundary 121, and a transmission signal for focusing the ultrasonic wave on a predetermined focal point 401 based on the path 411. The delay time of each of the transducers 11 is calculated.

  As described above, the ultrasonic transmitting and receiving apparatus according to the first embodiment detects the tissue boundary 121 of the inspection target 100 using the received signal, and calculates the delay time in consideration of the refraction of the ultrasonic wave at the detected tissue boundary 121. As a result, the ultrasound can be focused on the desired focal position with high accuracy.

  Hereinafter, the ultrasonic transmitting and receiving apparatus of the first embodiment will be described in more detail.

  The tissue boundary detection unit 32 controls the transmission unit 21 in order to detect the tissue boundary 121, and the first ultrasonic waves 301 for a predetermined range 110 of the examination object 100, for example, as shown in FIG. 3A. Send it. The ultrasonic waves (echo and the like) 311 returning to the probe 100 from the predetermined range 110 of the test object 100 after the first ultrasonic wave 301 is transmitted are respectively received by the transducers 11 of the probe 100. The tissue boundary detection unit 32 receives the reception signals respectively output from the transducers 11 from the reception unit 22, and detects the tissue boundary 121 of the inspection object 100 present in the predetermined range 110 using the reception signals.

  For example, as illustrated in FIG. 1, the control unit 30 includes the image generation unit 31 that generates an image of the examination target 100 from the reception signal of the vibrator 11. The tissue boundary detection unit 32 is generated by the image generation unit 31. The tissue boundary 121 can be detected by performing image processing on the image of the predetermined range 110. Thereby, the tissue boundary 121 can be detected two-dimensionally in the range of the image.

  In addition, the tissue boundary detection unit 32 may be configured to detect the tissue boundary 121 directly from the received signal. Since the received signal of the transducer is a time series reception of the ultrasonic waves (echo etc.) 311 returned from each depth of the inspection object 100, the time of the time series received signal is reflected etc. Corresponds to the depth of In addition, since the waveform (amplitude, frequency, etc.) of the received signal also changes if the sound speed, scattering characteristics, etc. differ between the tissue 101 and the tissue 102, the tissue boundary detection unit 32 detects the signal waveform of the received signal in time series , The position of the tissue boundary 101 in the depth direction of the inspection object 100 can be detected. That is, the tissue boundary detection unit 32 detects the position of the waveform change in the reception signals of the plurality of transducers 11 so that the position (depth) of the tissue boundary 121 corresponds to at least the number of transducers 11 (reception signals). Can only be detected. The tissue boundary 121 can be extracted as a continuous line by fitting the position of the tissue boundary 121 detected as necessary to a curve or a straight line.

  Further, as shown in FIG. 1, the control unit 30 may further include an elasticity measurement processing unit 34 and a determination processing unit 35.

  The elasticity measurement processing unit 34 controls the transmission unit 21 to cause the transducer 11 of the probe 10 to output the transmission signal delayed by the delay time calculated by the delay time calculation unit 33 for each of the transducers 11. . Thereby, as shown in FIG. 2 (b), a focused ultrasound (second ultrasound) 302 focused on a predetermined position is transmitted from the probe 10 and added by the second ultrasound 302. The acoustic radiation pressure generates a shear wave 304 in the inspection object 100 (FIG. 3 (b)). The elasticity measurement processing unit 34 controls the transmission unit 21 and the reception unit 22 to transmit the third ultrasonic wave 303 to a predetermined measurement region (ROI: Region of Interest) 300 of the inspection target 100. After the transmission of the third ultrasonic wave 303, the ultrasonic wave (echo, etc.) 313 returned from the test object 100 is received by the probe 10. The elasticity measurement processing unit 34 obtains this reception signal from the reception unit 22, measures the displacement of the measurement area generated by the shear wave 304 based on the reception signal, and obtains the elasticity of the inspection object.

  The determination processing unit 35 determines the reliability of the measurement result of elasticity calculated by the elasticity measurement processing unit 34 based on the characteristics of the shear wave 304 at the time of the measurement and the characteristics of the focused ultrasonic waves. For example, the amplitude of the shear wave 304 generated at the focal point 401, the left-right symmetry with respect to the focal point 401 of the propagation of the generated shear wave 304 (for example, the wave front of shear waves to lines A and B disposed equidistant to the left and right of the focal point 401) Index (reliability index) for determining the reliability of the ultrasound intensity in the peripheral area including the focal point 401 estimated from the propagation path obtained by the delay time calculation unit 33). Used as

<Operation of each part>
Hereinafter, the operation of each part of the ultrasonic transmitting and receiving apparatus of the present embodiment will be described with reference to FIG. In the following description, as shown in FIG. 1, the control unit 30 of the ultrasonic transmitting / receiving apparatus includes not only the tissue boundary detection unit 32 and the delay time calculation unit 33 but also the image generation unit 31, the elasticity measurement processing unit 34 and The case where all the determination processing units 35 are provided will be described.

  The image generation processing unit 31, the structure analysis processing unit 32, the delay time calculation unit 33, the elasticity measurement processing unit 34, and the determination processing unit 35 of the control unit 30 can be realized by software, or a part or all of them. Can also be realized by hardware.

  When realized by software, the control unit 30 is configured by a processor such as a central processing unit (CPU) or a graphics processing unit (GPU), and an image generation process is performed by reading and executing a program stored in advance in the control unit 30. The functions of the unit 31, the structure analysis processing unit 32, the delay time calculation unit 33, the elasticity measurement processing unit 34, and the determination processing unit 35 are realized. Further, in the case of hardware implementation, an image generation processing unit 31 and a structure analysis processing unit are used using a custom IC such as an application specific integrated circuit (ASIC) or a programmable IC such as a field-programmable gate array (FPGA). The circuit design may be performed to realize at least the operations of the delay time calculation unit 33, the elasticity measurement processing unit 34, and the determination processing unit 35.

  Here, the case where the functions of the respective units of the control unit 30 are realized by software will be described as an example.

  4 to 6 are flowcharts showing the operation of the apparatus.

<Step 200>
First, as shown in FIG. 4, in step 200, the control unit 30 causes the ROI 300 from the user via the external input device 13, the focus 401 of the second ultrasonic wave 302 for generating the shear wave 401, and the inspection target A range 110 to detect 100 tissue boundaries 121 is accepted. The control unit 30 may set the range 110 where the tissue boundary 121 should be detected to include at least the focal point 401. Further, the control unit 30 sets a plurality of measurement points 305 at equal intervals in the direction (for example, the x direction) in which the shear wave 304 in the ROI 300 propagates.

<Step 201>
As illustrated in FIG. 4, in step 201, the tissue boundary detection unit 31 detects the tissue boundary 121 received (or set) in step 200 in the transmission unit (hereinafter, referred to as transmission beam former) 21. It instructs to transmit the first ultrasonic wave 301 toward 110. For example, as shown in FIG. 3A, a plurality of transmission scanning lines 331 are set at predetermined intervals, and it is instructed to sequentially transmit the first ultrasonic waves 301 along them. The transmission beam former 21 outputs a transmission signal to each transducer 11 of the probe 10 based on the instruction. The transducer 11 of the probe 10 converts the transmission signal into an ultrasonic wave, whereby the first ultrasonic wave 301 is transmitted along the transmission scanning line 331. The ultrasonic wave 311 that has been reflected or the like from the inside of the inspection target 100 and returned to the probe 10 is received by the transducer 11 of the probe 10. The reception signals output from the plurality of transducers 11 are acquired by the reception beam former 22 and are received on a predetermined reception scanning line 321 (in the example of FIG. 3A, the reception scanning line 321 is parallel to the transmission scanning line 331). After being phased by delaying for a predetermined reception delay time for each reception focus so as to focus on each of a plurality of reception focal points that have been set, they are added, and are added after the phase adjustment addition (hereinafter referred to as Also referred to as an RF (Radio Frequency) signal.

  The image generation processing unit 31 generates an image (B mode image) by setting the signal intensity of the RF signal or the like to the pixel value of the pixel corresponding to the position of the reception focus.

  Here, although a plurality of transmission scanning lines 331 are set and the first ultrasonic waves 301 are sequentially transmitted to generate RF signals for the reception scanning lines 321 parallel to the transmission scanning lines 331, the first ultrasonic waves 301 are generated. Can be transmitted only once so as to spread widely, and it is also possible to obtain a plurality of RF signals by performing phasing addition on each of a plurality of reception scanning lines 321 according to the reception signal obtained by the transmission.

<Step 202>
Next, in step 202 of FIG. 4, the tissue boundary detection unit 32 generates a B mode image (here, a two-dimensional image in the xz plane) generated by the image generation processing unit 31 from the RF signal acquired in step 201 or the RF signal. Based on the detection of the tissue boundary 121. This detection operation will be described in detail below using FIGS. 5 and 6.

<Detailed Operation Example 1 of Tissue Boundary Detection in Step 202 (Image Processing)>
The detailed operation of the tissue boundary detection unit 32 when detecting the tissue boundary 121 from the B-mode image in step 202 is shown in the flowchart of FIG.

  First, as shown in FIG. 5, in step 3001, the tissue boundary detection unit 32 receives a B-mode image (xz plane) from the image generation processing unit 31.

  Next, in step 3002, the tissue boundary detection unit 32 performs image processing on the B-mode image to extract an image (a straight line or a curve) of the tissue boundary 121 included in the image. As the image processing, for example, processing of binarizing using a predetermined threshold value, edge extraction processing, texture analysis or the like can be used.

  Next, in step 3003, the tissue boundary detection unit 32 obtains information specifying the shape of the extracted tissue boundary 121. For example, on the extracted tissue boundary 121 (straight line or curve), discrete points 71, 72, 73, etc. are set as shown in FIG. 7 and coordinates (Pj showing the positions of these points 71 etc. on the xz plane) And the inclination (angle to the horizontal surface) (αj) of the tissue boundary 121 at the point 71. The coordinates and inclination (Pj, αj) of the point 71 etc. thus obtained are stored in a memory built in the control unit 30.

  In step 3003, information other than the combination of the coordinates and the inclination may be obtained as long as the information can specify the shape of the extracted tissue boundary 121. For example, the shape of the tissue boundary 121 may be fitted to a curve or a straight line, and a function representing that may be obtained. In this case, the obtained function is stored in a memory incorporated in the control unit 30.

<Detailed Operation Example 2 of Tissue Boundary Detection in Step 202 (RF Signal Processing)>
As another operation example of step 202, the detailed operation of the tissue boundary detection unit 32 in the case of detecting the tissue boundary 121 from the received signal is shown in the flowchart of FIG.

  First, in step 4001, the tissue boundary detection unit 32 receives an RF signal (received signal after phasing addition) from the reception beam former 22.

  Next, in step 4002, the tissue boundary detection unit 32 performs signal processing for each RF signal, and detects the time point of a change occurring in the RF signal (time-series signal) due to the existence of the boundary in the tissue. The change occurring in the RF signal is a change occurring in the RF signal due to the change in the reflection characteristic, the scattering characteristic, the propagation characteristic, etc. of the ultrasonic wave due to the two or more tissues being in contact at the boundary. For example, by detecting a change in the amplitude of the RF signal or a change in the frequency component and determining the change time point, the depth 61 (see FIG. 3A) of the inspection object 100 corresponding to the change time point is detected for each RF signal. It can be asked. As a result, the depth of the position 61 of the tissue boundary 121 on the reception scan line 321 can be detected, and the positions 61 indicating the tissue boundary 121 can be discretely determined by the number of reception scan lines 321. Furthermore, if necessary, a straight line or a curve fitted to the position 61 of the tissue boundary 121 for each reception scan line 321 can be determined, and the tissue boundary 121 can be determined as a straight line or a curve.

  Next, in step 4003, as in step 3003, the tissue boundary detection unit 32 obtains information for specifying the shape of the extracted tissue boundary 121. For example, as shown in FIG. 7, coordinates (Pj) indicating the positions of discrete points 71 and the like on the tissue boundary 121 (straight line and curve) on the xz plane and inclinations (αj) of the tissue boundary 121 at the point 71 and the like Ask for At this time, the discrete points 71 and the like may be made to coincide with the position 61 of the tissue boundary of the reception scanning line 321. The coordinates and inclination (Pj, αj) of the point 71 etc. thus obtained are stored in a memory built in the control unit 30.

<Step 203>
Next, in step 203 of FIG. 2, the delay time calculation unit 33 takes into consideration that the ultrasonic wave is refracted at the tissue boundary 121 based on the tissue boundary 121 obtained in the above-mentioned step 202, and the desired transmission focus 401 The delay time of each transducer 11 for transmitting an ultrasonic wave from each transducer 11 is calculated so as to focus on each other.

  The delay time calculation unit 33 performs, for example, the following process in order to calculate a delay time that compensates for refraction at the tissue boundary 121.

  First, from the relationship between the position of the tissue boundary 121 determined by the tissue boundary detection unit 32, the position of each transducer 11 of the probe 10, and the position of the focal point 401, it is transmitted from each transducer 11, and the tissue boundary The propagation path of the ultrasonic wave passing through 121 to the focal point 401 is calculated in consideration of refraction. The refraction angle of the ultrasonic wave propagation path at the tissue boundary 121 is calculated from Snell's law. After calculating the propagation path from each vibrator 11 to the focal point 401, the propagation time from each vibrator 11 to the focal point 401 is calculated.

  The delay time of each transducer 11 is calculated based on the propagation time calculated for each transducer 11. As described above, by calculating the delay time in consideration of the refraction at the tissue boundary 121, the focusing efficiency of the ultrasonic waves to the focal point 401 can be improved.

  The calculation method of the delay time of the delay time calculation unit 33 will be described in more detail later.

<Step 204>
Next, in step 204, as shown in FIG. 3B, the elasticity measurement processing unit 34 receives the delay time at the time of transmission for focusing on the transmission focus 401 from the delay time calculation unit 33, and transmits the transmission beam former Set to 21. Thereby, the transmission beam former 21 generates a transmission signal delayed by the delay time for each transducer 11 and outputs the transmission signal to each transducer 11. The transducer converts the received transmission signal into an ultrasonic wave and applies the ultrasonic wave to the inspection object 100. Thus, the emitted second ultrasonic wave 302 can apply an acoustic radiation pressure by the second ultrasonic wave 302 to the position of the focal point 401 in order to focus on the position of the focal point 401. When the irradiation of the second ultrasonic wave 302 is stopped, the pressure load is removed and a restoring force is exerted to generate a shear wave at the position of the focal point 401. The shear wave 304 radially propagates from the position of the focal point 401 where the second ultrasonic wave 30 is irradiated.

<Step 205>
Next, in step 205, the elasticity measurement processing unit 34 irradiates the ROI 300 with the third ultrasonic wave 303 with respect to the transmission beam former 21 and the reception beam former 22, and receives the echo thereof, thereby displacing the tissue. Instruct to measure In the drawing of FIG. 3B, the case of measuring the shear wave 304 propagating from the focal point 401 in the right direction on the drawing is illustrated.

  Specifically, for example, the elasticity measurement processing unit 34 instructs the transmission beam former 21 on the position of a predetermined transmission scanning line, and the third ultrasonic wave 105 is transmitted from the transducer 11 of the probe 10 at a predetermined timing. Each time transmission is performed, the reception signal of the transducer 11 that has received the echo is received via the reception beam former 22. The elasticity measurement processing unit 34 performs reception beam forming on a plurality of reception scanning lines passing through a plurality of measurement points 305 in the ROI 300 to obtain reception signals (RF signals) 313 after phasing addition.

<Step 206>
Next, in step 206, the determination processing unit 35 determines the reliability of the shear wave 304 generated in step 204 in the ROI 300. That is, it is determined whether or not the shear wave 304 has a waveform that can be measured with sufficient accuracy in the ROI 300. For example, the amplitude of the shear wave 304 actually generated or the left-right symmetry of the propagation of the shear wave 304 is determined based on the RF signal determined in step 205, and the determination processing unit 35 determines the reliability as a reliability index. You may judge. Further, the determination processing unit 35 calculates an estimated intensity distribution of ultrasonic waves around the focal point 401 based on the ultrasonic wave propagation path calculated by the delay time calculation unit 33 as described later, and the estimated intensity distribution is used as a reliability. The reliability of the shear wave 304 in the ROI 300 may be determined as an index. A specific example of the reliability index and a calculation method thereof will be described in the third embodiment.

<Step 207>
Next, in step 207, the elasticity measurement processing unit 34 uses the RF signal 313 obtained for each of the plurality of transmissions for the plurality of measurement points 304 in step 205, and the depth direction (z direction) of the plurality of measurement points 305 Measure the displacement for

  Specifically, with respect to the same measurement point 305, displacement in the depth direction (z direction) of the plurality of measurement points 305 is obtained by cross-correlation calculation of RF signals 313 obtained at different timings. Thereby, time change of displacement (amplitude of shear wave) of a plurality of measurement points 305 set in a propagation direction (x direction) of shear wave is obtained. The propagation velocity of the shear wave 304 can be calculated by calculating the phase difference of the time change of the displacement for a plurality of measurement points 305.

<Step 208>
Next, in step 208, the elasticity measurement processing unit 34 calculates the elastic modulus from the obtained velocity of the shear wave using a known mathematical expression.

  Since the processing method for obtaining the shear wave velocity in steps 207 and 208 and the processing method for obtaining the elastic modulus at the measurement point 305 from the shear wave velocity are widely known, the detailed calculation method will not be described.

  The control unit 30 displays the calculated elastic modulus on the display unit 16. The control unit 30 can also generate an elastic modulus map by setting the measurement points 305 in two dimensions and measuring the elastic modulus for each of the measurement points 305. In addition, the control unit 30 may display the reliability index calculated by the determination processing unit 35 on the display unit 16. Thereby, the user can grasp the reliability of the measurement result by the value of the reliability index.

  If the amplitude of the shear wave 304 generated in the above-described step 204 is too small in the ROI 300, the tissue displacement of the measurement point 305 can not be accurately measured due to the transmission and reception of the third ultrasonic wave 303. Speed calculation becomes difficult. In the present embodiment, the tissue boundary 121 is detected in step 202, and the delay time for focusing the ultrasonic wave on the focal point 401 is accurately calculated in step 203 in consideration of the refraction of the ultrasonic wave at the tissue boundary 121. At step 204, a large amplitude shear wave 304 can be generated at the location of the focal point 401. Therefore, the shear wave 304 having a large amplitude can be propagated to the ROI 300, and the tissue displacement by the shear wave 304 can be accurately measured in step 205. Thereby, the accuracy of speed calculation of shear wave 304 can be raised.

<Details of Operation of Delay Time Calculation Unit 33 in Step 203>
Here, an operation in which the delay time calculation unit 33 calculates the delay time in the above-described step 203 will be described using the flow of FIG. In the process of the flow of FIG. 8, an ultrasonic wave path is calculated from the position of the transducer 11 (vibrator starting method).

  In the following description, the focused second ultrasonic wave 302 is irradiated to the examination object 100 to generate a shear wave by acoustic radiation pressure, and the tissue 1 (101) and the tissue 2 (102) are in contact with each other Two layers of tissue (there is only one tissue boundary 121 when propagating from the sound source to the focal point), and the speed of sound (C1, C2) of the tissue 1 (101) and the tissue 2 (102) is known in advance The case of being stored in the memory incorporated in the unit 30 will be described as an example. The positions (S1,..., Si,..., SN) of the respective transducers 11 are also stored in advance in the memory as a table. The positions (S 1,..., Si,..., SN) of the respective transducers 11 are positions such as the center of each of the transducers 11 having a finite width, and N indicates the number of the transducers 11.

  FIG. 9 shows the tissue boundary 121 detected in step 202 of FIG. 2 and the position of the vibrator 11.

  First, in step 801 of FIG. 8, the delay time calculation unit 33 reads the position (F) of the focus 401 received by the control unit 30 in step 200 from the memory incorporated in the control unit 30.

  Next, in step 802, the delay time calculation unit 33 calculates the sound speeds (C1, C2) of the tissue 1 (101) and the tissue 2 (102), and the positions (S1, ..., Si, ..., SN) of the respective transducers 11 , And coordinates (P1,..., Pj,..., PM) and inclinations (α1,... Αj,... ΑM) of the point 71 etc. on the tissue boundary 121 are read from the memory incorporated in the control unit 30.

  Position of focal point (F), position of each transducer 11 (S1, ..., Si, ..., SN), position of tissue boundary (P1, ..., Pj, ..., PM), angle (α1, ... αj, ... αM An example of the positional relationship of) is as shown in FIG. The positions (P 1,..., P j,..., PM) of the tissue boundaries are inherently continuous but are discretized into M points 71, 72, 73,... As described in step 202. ing.

  In step 803, the delay time calculation unit 33 selects one vibrator Si.

  Next, in step 804, the delay time calculation unit 33 selects a point Pj of the tissue boundary 121.

  Next, in step 805, the delay time calculation unit 33 determines the angle of the ultrasonic wave passing through the point Pj of the tissue boundary 121 among the ultrasonic waves transmitted from the transducer Si selected in step 803 with respect to the normal to the tissue boundary 121. Theta is determined by the following equation (1).

  Furthermore, in step 806, the delay time calculation unit 33 performs position F 'when the ultrasonic wave transmitted from the transducer Si passes through the point Pj and refracts at the boundary 121 passes through the depth of the focal point F. The distance FF ′ between the position F ′ and the focal point F is obtained from the equations (2) and (3).

  Next, in step 807, the delay time calculation unit 33 repeats the above steps 804 to 806 for all points Pj on the tissue boundary 121 until j = M, and the position F 'for each point Pj and The distance FF ′ to the focal point F is calculated.

  Next, in step 808, the delay time calculation unit 33 selects a point Pj at which the distance FF 'is the smallest.

  Next, in step 809, the delay time calculation unit 33 determines the propagation time of the ultrasonic wave propagation path SiPjF transmitted from the transducer Si and reaching the focal point F according to equation (4) (Time Of Flight : TOF) is calculated.

Next, in step 810, the delay time calculation unit 33 calculates the delay time t _Di from Expression (5).

Next, at step 811, it is determined whether or not the number i of the oscillator Si is N, and if i is not N, the process returns to step 803 again to repeat steps 803 to 810. In step 811, when i = N, calculation of the delay time t _Di is completed for each of the transducers S 1 to SN.

  In step 808 of FIG. 8 described above, the position (F ′) at which the sound wave transmitted from each transducer Si (i = 1 to N) and having passed through the point Pj (j = 1 to M) on the tissue boundary 121 reaches ) Is calculated. Assuming that the intensities of the ultrasonic waves transmitted from one transducer Si and passing through one point Pj are the same even if the transducers Si are different and the position of the point Pj is different, the above step 801 The intensity of the ultrasonic wave reaching the position F ′ can be estimated by the number of propagation paths reaching the certain position F ′, which has been obtained in the step S-811. Therefore, when graphing the horizontal axis as the position of F ′ and the vertical axis as the number of propagation paths (ultrasonic intensity) reached as shown in FIG. 10, the estimated intensity distribution of ultrasonic waves around the focal point 401 can be determined by calculation. it can.

  Therefore, in step 206 of FIG. 2, the determination processing unit 35 calculates an estimated intensity distribution (FIG. 10) of ultrasonic waves around the focal point 401, and uses this estimated intensity distribution as a reliability index to obtain a predetermined value or more in the ROI 300. It can be determined whether the shear wave 304 of amplitude can be reached.

  Further, as shown in FIG. 2, there is an appropriate range between the wave source (the focal point 401) of the shear wave generated by the second ultrasonic wave 302 and the measurement point 305, and the distance 402 is too short. Even if it is too long, the calculation accuracy of the velocity of the shear wave 304 in the ROI 300 decreases. Therefore, the determination processing unit 305 determines that the peak position of the amplitude of the estimated intensity distribution of the ultrasonic wave around the focal point 401 calculated as described above is the actual wave source, and the distance between the wave source and the measurement point 305 falls within the appropriate range. As described above, the elasticity measurement processing unit 34 may be instructed to shift the measurement point 305. Thereby, since the elasticity measurement processing unit 34 can reset the measurement point 305, it is possible to improve the reliability of measurement of the shear wave 304 in the ROI 300.

  As described above, in the present embodiment, the tissue boundary detection unit 32 two-dimensionally obtains the shape of the tissue boundary 121, and the delay time calculation unit 33 takes into consideration the refraction of ultrasonic waves at the tissue boundary 121, and determines the delay time. It can be calculated. On the other hand, as shown in FIG. 2B, when the second ultrasonic wave 302 is transmitted using the delay time calculated on the assumption that the tissue is homogeneous tissue, the state shown in FIG. As the second ultrasonic wave 302 is refracted at the tissue boundary 121 which actually exists, the second ultrasonic wave 302 is not focused or focused at a position 401 a different from the set focal point 401. As a result, the energy reaching the set focal point 401 decreases, and the tissue displacement generated at the focal point 401 becomes smaller, and it becomes impossible to generate a shear wave of a desired amplitude at the position of the focal point 401. Further, even when the refracted ultrasonic waves converge at the position 401a, the distance 402 with respect to the measurement point 305 may not be kept in an appropriate range because the position 401a is deviated from the set focal point 401. In the present embodiment, since these problems can be solved, the calculation accuracy of the shear wave speed can be improved. That is, in the present embodiment, since the shape of the tissue boundary 121 can be grasped in two dimensions, focal movement and energy dispersion due to refraction of the tissue boundary are suppressed, the amplitude of the generated shear wave is improved, and the shear wave velocity is calculated. It can measure accurately. Thereby, the calculation accuracy of the elastic modulus at the measurement point 305 can be improved.

  In other words, in the present embodiment, the amplitude of the shear wave used in the elasticity measurement processing unit is compensated by compensating for the influence of refraction at the tissue boundary 121 detected by the tissue boundary detection unit 32 and calculating the delay time adaptively. Is improved, and the shear wave velocity can be determined accurately. Then, using the velocity of the shear wave, it is possible to accurately obtain the characteristic value representing the tissue characteristics such as elasticity.

  In the above embodiment, although the examination object 100 in which the tissue boundary 121 is only one has been described, a plurality of tissue boundaries 121 are included in the examination object 100 as in the case where three or more tissues are adjacent to each other. Even in this case, the tissue boundary detection unit 32 can detect each tissue boundary 121 and calculate the delay time by the delay time calculation unit 33 in consideration of the refraction of ultrasonic waves at each tissue boundary 121. . In that case, in place of the above-mentioned equations (1) to (5), an equation for finding a path of an ultrasonic wave which is refracted when passing through a plurality of tissue boundaries 121 is used.

  In the present embodiment, the tissue boundary detection unit 32 extracts the shape of the tissue boundary 121 in the two-dimensional space (x-z plane), but the probe 10 in which the transducers 11 are two-dimensionally arranged is used. In this case, the tissue boundary detection unit 32 can extract the shape of the tissue boundary 121 in three dimensions by using the RF signal in the three-dimensional space acquired by the probe 10.

<< Embodiment 2 >>
The ultrasonic transmitting and receiving apparatus according to the second embodiment will be described with reference to FIGS.

  In the second embodiment, in the calculation process of the delay time in step 203 of FIG. 4, unlike the first embodiment (the transducer base point method), an ultrasonic path is calculated by tracing an ultrasonic path starting from the focal point 401. Yes (Focusing point method). The steps other than step 203 are the same as in the first embodiment, so only step 203 will be described here.

  FIG. 11 is a flowchart showing the operation of delay time estimation in step 203 of FIG. FIG. 12 shows the position of the transducer 11, the tissue boundary 121, and the focal point 401 in step 203 of FIG.

  First, in steps 1101 and 1102 of FIG. 11, the delay time calculation unit 33 calculates the position (F) of the focal point 401, the tissue 1 (101), and the tissue 2 (102) as in steps 801 and 802 of the first embodiment. Sound velocity (C1, C2), the position (S1,..., Si,..., SN) of each transducer 11, and the coordinates (P1,..., Pj,. The inclinations (α 1,..., Α j,..., Α M) are read from the memory incorporated in the control unit 30.

  Next, in the present embodiment, in step 1103, the delay time calculation unit 33 selects one point (Pj, αj) on the tissue boundary 121.

  Next, in step 1104, the delay time calculation unit 33 passes the point (Pj, αj) on the tissue boundary 121 selected in step 1103 to the tissue boundary of the ultrasonic path PjF reaching the position (F) of the focal point 401. The angle φ with respect to the normal of 121 is determined by the following equation (6).

  Next, in step 1105, a certain transducer Si is transmitted to reach a point (Pj, αj) on the tissue boundary 121, and is refracted at the tissue boundary 121 to be refracted at the angle φ calculated in the step 1104. The angle θ of the ultrasound path S′Pj with respect to the normal to the tissue boundary 121 is calculated by equation (7) (see FIG. 12). Furthermore, when the point I (Pj, αj) on the tissue boundary 121 is taken as the intersection point I of the straight line IH in the depth direction and the transducer array, the above-mentioned ultrasonic path S'Pj The distance IS ′ with the intersection point I is obtained from the equation (8).

  Next, at step 1106, the number (i-th) of the transducer Si including the position S ′ from the transducer S1 at the end of the transducer array is determined from the equation (9). In equation (9), pitch is the width per vibrator.

Further, in step 1107, the propagation time t _TOFi of the propagation path SiPjF is _obtained from equation (10).

  Next, in step 1108, the delay time of the transducer Si is obtained from the equation (11).

  Next, in step 1109, steps 1103 to 1109 are repeated for all the points Pj on the tissue boundary 121 until the point j on the tissue boundary 121 is M = M. Thus, the delay time for each transducer can be calculated.

In the method of calculating the delay time t _{Di described in} the first embodiment, the number of iterations of the calculation is N × M (M times from step 804 to step 807 and N times from step 803 to step 811 The result of On the other hand, in the method of calculating the delay time t _{Di according to} the second embodiment described above, the number of iterations of the calculation is M (the number of repetitions is only M times from steps 1103 to 1109). Therefore, in the calculation method of the delay time shown in FIG. 11 of the second embodiment, the number of iterations of calculation is M times, which is smaller than that of the method shown in FIG. 8 (the number of iterations of calculation is N × M times). , There is an advantage that the calculation cost is low.

  Further, in the second embodiment, when the propagation path SiPjF can not be determined for Pj selected in step 1103, a certain tolerance is provided at the position of the focal point 401, and the propagation route reaching within the tolerance is recalculated. Then, a propagation path approximated to the propagation path SiPjF may be determined. For example, as shown in FIG. 13, it is conceivable that the allowable range is defined by a Gaussian half width of ultrasonic intensity centered on the focal point 401 or the like.

<< Third Embodiment >>
<When multiple organization boundary candidates are held>
The ultrasonic transmitting and receiving apparatus of the third embodiment will be described with reference to FIG.

  As in the first embodiment, in the ultrasound transmitting and receiving apparatus according to the third embodiment, the tissue boundary detection unit 32 extracts the tissue boundary 121 by image processing or processing of an RF signal. However, since the tissue structure in the body is complicated, a plurality of tissue boundary 121 candidates may be extracted for the tissue boundary 121 of the two tissues 101 and 102. Therefore, in the third embodiment, the determination processing unit 35 calculates the reliability index for each of the plurality of tissue boundary 121 candidates, and the highest reliability is detected as the tissue boundary detection based on the calculated reliability index. The tissue boundary 121 is determined by the selection of the section 32. This makes it possible to measure shear waves with high robustness and accuracy. The operation of each part of the third embodiment will be described below with reference to FIGS. 14 to 16. In the following description, the description of the same operations as the operations described with reference to FIGS. 4 to 6 of the first embodiment will be omitted.

<Steps 1400 to 1401>
First, as illustrated in FIG. 4, in step 1400, the control unit 30 receives the ROI 300, the focal point 401, and the detection range of the tissue boundary 121 from the user, as in the first embodiment. The control unit 30 sets a plurality of measurement points 305 at equal intervals in the ROI 300.

  At step 1401, the control unit 30 instructs the transmission beam former 21 to transmit the first ultrasonic wave 301. The received signal by the probe 10 of the ultrasonic wave that has been reflected or the like from the inside of the inspection object and returned to the probe 10 is subjected to reception beam forming by the reception beam former 22 and becomes an RF signal.

<Step 1402>
Next, in step 1402 of FIG. 14, boundaries of a plurality of tissues are detected using the B-mode image and RF signal acquired in step 1401.

Boundary detection of tissue from B-mode image
Specifically, when detecting the tissue boundary 121 from the B-mode image, the tissue boundary detection unit 32 performs the steps 3001 to 3001 in FIG. 5 of the first embodiment as in the flow of steps 1502 to 1503 in FIG. As in the case of 3003, the B-mode image is received, the tissue boundary is extracted by image processing, and information (coordinate Pj and inclination angle αj) specifying the shape of the tissue boundary is stored in the memory. At this time, when there are a plurality of candidates for the tissue boundary 121 in step 1502, the tissue boundary detection unit 32 extracts the candidates for the plurality of tissue boundaries 121.

Boundary detection of tissue from RF signal
When the tissue boundary 121 is detected from the RF signal, the tissue boundary detection unit 32 receives the RF signal at steps 1601 to 1603 in FIG. 16 as in steps 4001 to 4003 in FIG. 6 of the first embodiment. By detecting changes in the RF signal, the depth of the tissue boundary 121 is obtained, and information (coordinate Pj and inclination angle αj) specifying the shape of the tissue boundary 121 is stored in the memory. At this time, when there are a plurality of candidates for the tissue boundary 121 in step 1602, the tissue boundary detection unit 32 extracts the plurality of candidates for the plurality of tissue boundaries 121.

  Thus, in the third embodiment, in order to detect a plurality of tissue boundary 121 candidates in step 1402, the tissue boundary detection unit 32 estimates the delay time for each of the candidate tissue boundaries 121 and generates a shear wave. The optimum tissue boundary 32 is selected by measuring and determining the measurement result.

<Step 1403>
In step 1403, the tissue boundary detection unit 32 selects one of the plurality of tissue boundary 121 candidates detected in step 1402.

<Step 1404>
Next, in step 1404, the delay time calculation unit 33 calculates the delay time of each transducer 11 for focusing the ultrasonic wave on the focal point 401 using the one tissue boundary 121 selected in step 1403. The operation of this delay time calculation is performed in the same manner as step 203 of the first embodiment.

<Step 1405>
Next, in step 1405, the elasticity measurement processing unit 304 sets the second ultrasonic wave 302 to the transmission beam former 21 and causes the second ultrasonic wave 302 to be transmitted to the test object 100, with the delay time calculated in step 1404. . As a result, a shear wave is generated in the inspection object 100 at the focal point 401.

<Step 1406>
Next, in step 1406, the elasticity measurement processing unit 34 controls the transmission beam former 21 and the reception beam former 22 to cause the ROI 300 to be irradiated with the third ultrasonic wave 303, and then causes its echo to be received. measure.

<Step 1407>
Next, in step 1407, the determination processing unit 35 determines the reliability of the shear wave 304 in the ROI 300 by calculating the reliability index of the shear wave generated in step 1405. That is, it is determined whether or not the shear wave 304 has a waveform that can be measured with sufficient accuracy in the ROI 300. As the reliability index, the estimated intensity distribution of the ultrasonic wave around the focal point 401 shown in FIG. 10 in the first embodiment, the amplitude of the shear wave measured in step 1406, the both symmetry of the generated shear wave, the shear wave One or more of the luminances of the B-mode image of the focal area at the time of generation and the like are used in combination. The reliability index, its calculation method, and the display method will be described in detail later.

<Step 1408>
Steps 1403 through 1408 are repeated until all tissue boundary candidates have been tried.

<Step 1409>
Next, in step 1409, the tissue boundary detection unit 32 compares the reliability index of shear waves for each candidate tissue boundary 121 calculated in step 1407, and selects the tissue boundary 121 with the largest reliability. Do.

<Steps 1410 to 1411>
Next, in step 1410, as in step 207 of the first embodiment, the elasticity measurement processing unit 34 uses the RF signal 313 obtained multiple times for the plurality of measurement points 304 in step 1406, for the plurality of measurement points 305. The propagation velocity of the shear wave 304 is calculated.

  In step 1411, the elasticity measurement processing unit 34 calculates the elastic modulus from the obtained velocity of the shear wave using a known mathematical expression.

  FIG. 17 is an example of a display mode in which the ultrasonic transmitting and receiving apparatus displays the result of the operation of FIG. 14 on the display unit 16 in the third embodiment. On the display screen of FIG. 17, an area 1701 for displaying the ROI 300 in the examination object 100, an area 1702 for displaying a plurality (n) of candidate images of the tissue boundary 121 obtained in step 1402, and respective tissue boundaries 121 An area 1703 for displaying the reliability (reliability index) obtained in step 1407 for the candidate D.sub.1 and an area 1704 for displaying measurement results such as elastic modulus for each of the measurement points 305 obtained in step 1411 are included. Selection of the candidate of the tissue boundary 121 can be performed automatically or manually using the reliability 1703 for each of the tissue boundary 121 candidates as an index.

  FIG. 18 is an example of a display screen when the tissue boundary detection unit 32 selects an optimum boundary from a plurality of candidates of the tissue boundary 121 in step 1409. The display screen of FIG. 18 includes an area 1701 for displaying the ROI 300, a display area 1704 for measurement results such as elastic modulus of the measurement point, and an area 1703 for displaying the reliability (reliability index). The measurement result displayed in the display area 1704 and the reliability displayed in the display area 1703 are obtained for the tissue boundary 121 after selection in step 1409. Therefore, the user can know the reliability of the measurement result from this display screen, and can make decisions such as re-measurement if the value of the reliability index is low.

  Next, an example of the reliability index, a calculation method thereof, and an example of the display screen will be specifically described with reference to FIGS. 19 to 26.

<Example of using the estimated intensity distribution of ultrasound as a reliability index>
FIGS. 19 and 20 show an example where the estimated intensity distribution of the ultrasonic wave shown in FIG. 10 is used as the reliability index. The method of calculating the ultrasonic intensity distribution is as described in step 206 of the first embodiment. By using the estimated intensity distribution of ultrasonic waves as the reliability index, the reliability index of the candidate of the tissue boundary 121 can be calculated before the second ultrasonic waves 302 are transmitted, so it is optimal before the transmission of the second ultrasonic waves 302. It is possible to select an appropriate tissue boundary 121. That is, step 1405 of transmitting the second ultrasonic wave 302 and step 1406 of transmitting and receiving the third ultrasonic wave 303 in the flow of FIG. 14 can be performed after step 1409 of selecting the optimum tissue boundary 121. Therefore, it is not necessary to repeat the transmission of the second and third ultrasonic waves 302 and 303 by the number of candidates for the tissue boundary 121, and shear waves are accurately generated with a delay time determined based on the optimum tissue boundary 121, The operation of measuring the rate can be performed in a short time.

  FIGS. 19 (a) and 19 (b) show examples of the results of calculation of the estimated intensity distribution of ultrasound for each of the tissue boundary 121 candidates, as in FIG. The horizontal axis is the distance from the focal point, and the vertical axis is the estimated intensity of ultrasonic waves. The larger the estimated ultrasound intensity at the focal point 401, the larger the amplitude of the shear wave excited by the second ultrasound 302. Therefore, the peak value and the half value width of the estimated intensity distribution of ultrasonic waves can be used as a reliability index at the time of selecting an optimal tissue boundary 121 candidate. Further, the positional shift amount between the peak position of the estimated intensity distribution of the ultrasonic wave and the desired focal point 401 (ideal focal point) can also be used as a reliability index when selecting an optimal tissue boundary candidate. That is, it is desirable that the peak value is large, the half width is narrow, or the peak position is close to the focal point 401. For example, in the example of FIGS. 19A and 19B, the estimated intensity distribution of the ultrasonic wave of FIG. 19A has a larger peak value and a narrower half width than the distribution of FIG. 19B. And, since the peak position is close to the focal point 401, it is desirable. Therefore, in the determination process of step 1407 of FIG. 14, the tissue boundary 121 for which the estimated intensity distribution of FIG. 19A is calculated is selected as the optimum tissue boundary.

  FIG. 20 is an example of a display screen displayed on the display unit 16 in steps 1402, 1407, 1409 and the like in the operation flow of FIG. 14 when the estimated intensity distribution of ultrasonic waves is used as the reliability index. On this display screen, there are shown an area 2001 respectively showing an image showing the shapes of the plurality of tissue boundary 121 candidates detected in step 1402 of FIG. 14 and the estimated intensity distribution of ultrasonic waves calculated in step 1407 for each candidate. An area 2002 to be displayed and an area 2003 to display numerical values such as the peak value and half width of the estimated ultrasound intensity distribution are included. Among these candidate tissue boundaries 121, a display 2004 (here, boxed) indicating that the tissue boundary 121 selected in step 1409 of FIG. 14 is the optimum tissue boundary is displayed as the determination result. .

Example of using the value of tissue displacement due to shear waves as a reliability index
21 (a), (b) and FIG. 22 show examples of display screens when tissue displacement in the depth direction due to the shear wave 304 generated in step 1405 is used as a reliability index. The tissue displacement value in the depth direction uses the value calculated for each measurement point 305 in step 1406 of FIG. In each of FIGS. 21A and 21B, the tissue displacement obtained for each of a plurality of measurement points 305 arranged two-dimensionally in the ROI 300 set so as to include the focal point 401 is a position corresponding to the measurement point 305 It is an example of a distribution image (tissue displacement map) of tissue displacements generated as pixel values (colors) of certain pixels. In addition, a color bar 2102 indicating the relationship between the size of the displacement and the color is displayed next to the tissue displacement map.

  FIG. 22 corresponds the area 2202 showing the tissue displacement map shown in FIGS. 21A and 21B to the area 2001 showing an image showing the shape of the candidate of the tissue boundary 121 from which the tissue displacement map was obtained. It is an example of a screen shown. Further, in the vicinity of the tissue displacement map, an area 2203 indicating numerical values such as the maximum value of the tissue displacement and the position of the maximum displacement is also displayed.

  When tissue displacement is used as a reliability index, in order to increase the measurement accuracy of shear wave velocity, it is preferable that the tissue displacement be large, and it is more desirable that the position of the maximum displacement is closer to the ideal focal point 401 position. For example, comparing the tissue displacement maps of FIG. 21 (a) and FIG. 21 (b), the position of the maximum displacement of the tissue displacement map of FIG. 21 (a) is higher than that of FIG. 21 (b). Is desirable because it is close to the position of the ideal focal point 401 and the maximum displacement is also large. Therefore, in the determination process of step 1407 of FIG. 14, the tissue boundary 121 corresponding to the tissue displacement map of FIG. 21 (a) is selected as the optimum tissue boundary. In the display screen of FIG. 22, a display 2204 (here, framed) indicating that it is optimal is displayed at the selected optimal tissue boundary 121.

<Example of using the left-right symmetry of shear waves as a reliability index>
FIGS. 23C and 24 show examples of display screens in the case where the left-right symmetry with respect to the focal point 401 of the propagation of the shear wave excited by the second ultrasonic wave 302 transmitted in step 1405 of FIG. Is shown. The wavefront 2303 of the shear wave is detected as shown in FIGS. 23A and 23B by transmission and reception of the third ultrasonic wave in step 1406 of FIG. The shear wave is excited at a position 2304 near the set ideal focal point 401 and spreads radially, so it propagates also in the left and right directions 2301 and 2302 around the focal point 401, respectively. At this time, when the lines A and B are set equidistantly in the left and right direction from the focal point 401 and the time for the shear wave to reach the lines A and B is determined, the position 2304 at which the shear wave is actually excited is set. The closer to the focal point 401, the smaller the difference in time for the shear wave to reach the lines A and B, and the higher the symmetry of the shear wave propagation with respect to the focal point 401. Therefore, by calculating the difference between the shear wave arrival times to the lines A and B in the step 1407, the determination processing unit 35 can obtain the left-right symmetry of the shear wave propagation with respect to the focal point 401 as the reliability index. .

  For example, when the difference in the arrival time of the shear wave (lines of reliability) to the lines A and B in the example of the shear wave shown in FIGS. 23 (a) and 23 (b) is graphed, the result is shown in FIG. It looks like the example image of.

  FIG. 24 shows a region 2402 shown as a difference (reliability index) of arrival time of the shear wave to the left and right lines A and B shown in FIG. 23 (c) and a tissue boundary 121 at which the reliability index is obtained. It is an example of a screen which makes an area 2001 showing an image showing a shape of a candidate correspond to each other. Further, in the vicinity of the area 2402 indicating the reliability index, an area 2403 indicating the numerical value or the like of the difference in arrival time of the shear wave to the lines A and B is also displayed.

  When the difference in arrival time of the shear wave to the left and right lines A and B is used as the reliability index, the shear wave shown in FIG. The difference is smaller than that in (b), which is a shear wave generated at a position closer to the focal point 401, which is desirable. Therefore, in the determination processing of step 1407 of FIG. 14, when the reliability indexes of FIG. 23A and FIG. 23B are compared, the tissue boundary 121 corresponding to the reliability index of FIG. Selected as being an organizational boundary. In the display screen of FIG. 24, a display 2404 (here, a frame) is displayed on the selected optimum tissue boundary 121.

<Example of using the reception intensity of the reflected wave of the third ultrasonic wave as the reliability index>
25 (a), (b), and FIG. 26, in step 1406, the ultrasonic wave of the third ultrasonic wave is applied to the focal point 401 where the shear wave propagates and the ROI 300 around it, and the reflected wave is probed It is an example of a display screen at the time of using the signal strength (reception strength of a reflected wave) of the received signal received by child 10 as a reliability index. The signal strength of the received signal is the signal strength of a predetermined depth (for example, the depth of the focal point 401) of the RF signal after phasing addition obtained by the reception beam former 22 for the reception scanning line at the position of the measurement point 305. Or the average of the signal strengths of the RF signals obtained for a predetermined depth range. Moreover, as a timing which obtains a received signal about each measurement point 305, the same time after transmission of a 3rd ultrasonic wave may be sufficient, and the time average of the received signal repeatedly acquired in the predetermined time range may be sufficient.

  25 (a) and 25 (b) respectively correspond to the measurement points 305 for the signal strengths of the reception signals obtained for the plurality of measurement points 305 arranged two-dimensionally in the ROI 300 set so as to include the focal point 401. Is an example of an image (luminance distribution) generated as the luminance of the pixel at the position where the Further, next to the intensity distribution of the reflected wave, a luminance bar 2503 indicating the relationship between the intensity of the reflected wave and the luminance is displayed.

  FIG. 26 shows an area 2602 showing the intensity distribution of the reflected wave shown in FIGS. 25 (a) and 25 (b) and an area showing an image showing candidate shapes of the tissue boundary 121 for which the intensity distribution of the reflected wave was obtained. It is an example of a screen which makes 2601 correspond and shows. In the vicinity of the intensity distribution of the reflected wave, numerical values such as the maximum value of the reflected wave intensity, the position where the reflected wave intensity is the maximum value, and the deviation between the position where the reflected person intensity is the maximum value and the focal point 401 An area 2603 indicating the is also displayed.

  When the intensity of the reflected wave is used as the reliability index, it is desirable that the intensity of the reflected wave is high in order to increase the measurement accuracy of the shear wave velocity, and the position where the intensity of the reflected wave is the maximum is ideal. It is desirable to be closer to the focal point 401 position. For example, comparing the intensity distributions of the reflected waves in FIGS. 25 (a) and 25 (b), the maximum value of the reflection intensity in FIG. 25 (b) is larger than that in FIG. 25 (a). Therefore, in the determination process of step 1407 of FIG. 14, the tissue boundary 121 corresponding to the tissue displacement map of FIG. 25 (b) is selected as the optimal tissue boundary. On the display screen of FIG. 26, a display 2604 (here, framed) indicating that it is optimal is displayed at the selected optimal tissue boundary 121.

  As described above, in the third embodiment, an optimal tissue boundary 121 can be determined by extracting a plurality of tissue boundary 121 candidates and calculating a reliability index for each candidate. Therefore, a shear wave of desired intensity can be generated in the ROI 300 using the delay time calculated based on the selected tissue boundary 121. In addition, since the user can visually check the reliability index on the display screen, it is possible to visually and visually confirm the correction effect of the delay time by the selected tissue boundary 121.

10: Probe 13: External input device 16: Display unit 20: Transmission / reception control unit 21: Transmission unit (transmission beam former)
22: Receiver (Receiver beam former)
30: control unit 31: image generation processing unit 32: structure analysis processing unit 33: delay time calculation unit 34: elasticity measurement processing unit 35: determination processing unit 100: inspection object 300: ROI
301: first ultrasonic wave 302: second ultrasonic wave 303: third ultrasonic wave 304: shear wave 305: measurement point 101: tissue 1
102: Organization 2
121: tissue boundary 401: focal point 402: appropriate distance 1701: ROI display area 1702: tissue boundary candidate display area 1703: reliability index display area 1704: measurement result display area 2001: tissue boundary candidate display area 2002: Display area of reliability index (estimated intensity distribution of ultrasonic waves) 2003: Display area of numerical value of reliability index 2004: Display 2102 indicating optimum tissue boundary: Color bar 2202 representing displacement magnitude: Display area 2203 of reliability index (tissue displacement map): display area 2204 of reliability index: display 2301 or 2302 indicating an optimum tissue boundary: propagation direction of shear wave (horizontal direction)
2303: Wave front 2304 of shear wave: Location 2402 at which shear wave is excited: Display area of reliability index (difference in arrival time of shear wave) 2403: Display area of numerical value of reliability index 2404: Optimal tissue boundary Indication 2503: Intensity bar 2603 representing the magnitude of the intensity of the reflected wave: Display area of the numerical value of the reliability index 2604: Indication showing the optimum tissue boundary

Claims (15)

A transmission unit for outputting a transmission signal to a probe in which a plurality of transducers are arranged, and transmitting ultrasonic waves from the plurality of transducers to an inspection object, and receiving an ultrasonic wave returning from the inspection object after transmission A receiving unit for obtaining received signals respectively output from the vibrators, and a control unit for controlling the transmitting unit and the receiving unit,
The control unit uses the received signal to detect a tissue boundary in the examination target in a predetermined range, and a ultrasonic wave transmitted from a plurality of transducers is refracted at the tissue boundary. And a delay time calculator configured to calculate a delay time of the transmission signal for finding a path and focusing an ultrasonic wave at a predetermined focal point based on the path. apparatus. The ultrasonic transmitting and receiving apparatus according to claim 1,
The tissue boundary detection unit controls the transmission unit to transmit the first ultrasonic wave to the predetermined range to be inspected, and receives the ultrasonic wave returned from the predetermined range after the transmission. An ultrasonic transmitting and receiving apparatus comprising: receiving from the receiving unit a received signal output from each transducer, and detecting the tissue boundary of the examination object present in the predetermined range using the received signal. The ultrasonic transmitting and receiving apparatus according to claim 1, wherein the control unit further includes an image generation unit that generates an image of the inspection target from the reception signal.
The ultrasound transmitting / receiving apparatus, wherein the tissue boundary detection unit detects the tissue boundary by processing the image in the predetermined range generated by the image generation unit.   The ultrasound transmission / reception device according to claim 1, wherein the tissue boundary detection unit detects the time point of change in the signal waveform of the received signal in time series of a plurality of the transducers, thereby detecting the depth of the examination target. An ultrasonic transmitting and receiving apparatus characterized in that the position of the tissue boundary in the longitudinal direction is detected. The ultrasonic transmitting and receiving apparatus according to claim 1, wherein the control unit further includes an elasticity measurement processing unit,
The elasticity measurement processing unit controls the transmission unit to output the transmission signal delayed by the delay time calculated by the delay time calculation unit for each vibrator to the vibrator, respectively. After transmitting a focused ultrasonic wave focused on a predetermined focal point to generate a shear wave, the transmitter and the receiver are controlled to transmit the ultrasonic wave to a predetermined measurement area of the inspection object, and the inspection is performed. Ultrasonic wave transmission / reception characterized in that a received signal receiving ultrasonic waves returning from an object is obtained, displacement of the measurement area caused by the shear wave is measured based on the received signal, and elasticity of the inspection object is determined. apparatus.   The ultrasonic wave transmitting and receiving apparatus according to claim 5, wherein the control unit further includes a determination processing unit, and the determination processing unit is configured to determine the reliability of elasticity obtained by the elasticity measurement processing unit as the shear wave. An ultrasonic transmitting and receiving apparatus characterized in that it is determined based on the characteristics of or the characteristics of the focused ultrasonic waves.   The ultrasonic wave transmitting and receiving apparatus according to claim 6, wherein the characteristic of the shear wave used for the judgment by the judgment processing unit is an amplitude of the shear wave, and a wave front of the shear wave to a point disposed on the left and right with respect to the focal point. An ultrasonic transmission / reception device characterized in that it is a difference in arrival time of the displacement, and a displacement of the measurement area due to shearing.   The ultrasound transmitting and receiving apparatus according to claim 6, wherein the characteristic of the focused ultrasound used by the determination processing unit for the determination is an estimated intensity distribution of the ultrasound around the focal point. apparatus.   The ultrasonic transmitting and receiving apparatus according to claim 6, wherein the characteristic of the focused ultrasonic wave used for the judgment by the judgment processing unit is that the ultrasonic wave is irradiated around the focal point and the reception intensity of the reflected wave is An ultrasonic transmitter-receiver characterized by the above.   The ultrasonic transmitting and receiving apparatus according to claim 1, wherein the delay time calculation unit calculates the refracting path that reaches the focal point with the transducer as a base point.   The ultrasonic transmitting and receiving apparatus according to claim 1, wherein the delay time calculation unit calculates the refracting path that reaches the transducer with the focal point as a base point. The ultrasonic transmitting and receiving apparatus according to claim 5, further comprising: a determination processing unit configured to calculate a value of a predetermined reliability index indicating the characteristic of the shear wave or the characteristic of the focused ultrasonic wave. And
The tissue boundary detection unit detects a plurality of candidates for the tissue boundary,
The determination processing unit calculates the value of the reliability index based on the ultrasonic wave transmitted using the delay time calculated by the delay time calculation unit for each of the plurality of candidates for the tissue boundary, and the calculated reliability An ultrasonic transmitting and receiving apparatus characterized in that the tissue boundary candidate indicating that the value of the index is the most reliable is selected.   The ultrasonic transmitting and receiving apparatus according to claim 12, wherein the control unit displays reliability indexes of the plurality of tissue boundary candidates in correspondence with the tissue boundary candidates. Sound wave transmitter and receiver. Ultrasonic waves are transmitted from the probe in which a plurality of transducers are arrayed to the examination subject, and ultrasonic waves returning from the examination subject after transmission are transmitted using the received signals respectively received by the transducers, and tissue in the examination subject Detecting the boundary;
In the detected tissue boundary, a path along which the ultrasonic wave is refracted is determined, and the delay time of the ultrasonic wave to be transmitted for each transducer for focusing the ultrasonic wave at a predetermined focal point based on the path is determined for each transducer Step to calculate
Transmitting ultrasonic waves delayed by the delay time of each of the transducers from the transducers to focus the ultrasonic waves on the focal point. 15. The ultrasonic transmitting and receiving method according to claim 14, wherein the step of detecting the tissue boundary performs image processing on an image generated from the received signal, or a point in time when a signal waveform of the received signal changes in time series. And detecting a position of the tissue boundary in a predetermined range by detecting

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