JP5854929B2 - Ultrasonic diagnostic apparatus, method for determining reliability of set sound speed, and program - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus that generates a tomographic image of a subject by transmitting and receiving ultrasonic waves.

  2. Description of the Related Art An ultrasonic diagnostic apparatus that transmits ultrasonic waves from an ultrasonic probe to a subject and generates a tomographic image of the subject based on a reflected wave from the inside of the subject is known. In an electronic scanning ultrasonic diagnostic apparatus, in order to improve the azimuth resolution of an ultrasonic image, when transmitting an ultrasonic wave, each electroacoustic transducer is arranged in accordance with the arrangement of each electroacoustic transducer in the ultrasonic probe. Transmission focus for shifting the transmission timing of ultrasonic waves between elements by supplying a drive pulse signal having a difference in delay time is performed. On the other hand, when receiving a reflected wave, a delay time corresponding to the arrangement of each electroacoustic transducer is given to each of the received signals generated in each electroacoustic transducer to align the time phases of the received signals. Receive focus is performed.

  The delay time given to each signal during transmission and reception of ultrasonic waves is set based on the distance from each electroacoustic transducer to the focal point and the sound speed of the propagation medium. The assumed hypothetical sound speed is usually used as the sound speed of the propagation medium. However, the biological tissue that is the propagation medium has different sound speeds depending on the site, so if there is an error between the assumed sound speed used to set the delay time and the actual sound speed, the focus will be appropriately focused on both transmission and reception. The image cannot be formed, resulting in image quality degradation. In response to this problem, the following patent document discloses a technique for improving the image quality of an ultrasonic image by estimating an actual sound speed based on a received signal.

  For example, in Japanese Patent Laid-Open No. 2002-143153, after phasing a received signal with a delay time based on a certain set sound velocity, a phase difference between the received signals of two adjacent channels is detected, and a delay is detected from the detected phase difference. An error ΔD is obtained, an adaptive delay time DA obtained by adding the delay error ΔD and the set delay time D is obtained, and a reference delay time corresponding to a plurality of different medium sound velocities is closest to the adaptive delay time DA. It is described that the medium sound speed corresponding to the selected reference delay time is selected as the biological sound speed. This document also evaluates the accuracy of the estimated values of the medium sound velocities obtained for each measurement area by the dispersion of the adaptive delay time, and the medium sound speed estimated value with the highest evaluation value is common to the multiple areas. Is set as the set sound speed.

JP 2002-143153 A

  In the technique described in Patent Document 1, the delay time error ΔD corresponding to the phase difference between the reception signals of the respective channels phased based on a certain set sound speed is obtained by calculation. However, it is not easy to stably measure the delay time error ΔD between channels. That is, when the intensity of the received signal is reduced or the waveform distortion is caused by the interference of the ultrasonic wave transmitted into the living body, the measurement accuracy of the delay time error ΔD is significantly reduced. As a result, the calculation accuracy of the actual sound speed in the living body is lowered. Further, in the technique described in Patent Document 1, the accuracy of the estimated value of the medium sound speed is evaluated by the dispersion of the adaptive delay time. However, as described above, the delay time error ΔD is stably measured. Since it is not easy, it may be difficult to appropriately determine the probability.

  The present invention has been made in view of the above points, and an ultrasonic diagnostic apparatus, a set sound speed reliability determination method, and a program capable of stably determining the reliability of an estimated sound speed value in a subject The purpose is to provide.

In order to achieve the above object, an ultrasonic diagnostic apparatus according to the present invention acquires a reception signal generated by each of a plurality of electroacoustic transducer elements in accordance with an ultrasonic reflected wave transmitted into a subject. a reception signal obtaining means, a similarity indicating the similarity between the received signal mutual at each of the time domain of said received signal derived on the basis of a plurality of set sound velocities, is derived for each of the plurality of set sound velocities similar to Degree derivation means;
Optimum set sound speed deriving means for deriving an estimated value of sound speed in the subject as the optimum set sound speed based on the similarity for each of the plurality of set sound speeds derived by the similarity degree deriving means;
Reliability deriving means for deriving reliability indicating reliability of the optimum set sound speed derived by the optimum set sound speed deriving means based on the similarity for each of the plurality of set sound speeds derived by the similarity deriving means; including.

Upper Symbol of the ultrasonic diagnostic apparatus, a plurality of received signals generated at each of a plurality of electroacoustic transducer elements of said plurality of electroacoustic transducer elements, further phasing means for phasing for each of the plurality of set sound velocities The similarity calculation unit may derive a similarity between the received signals phased by the phase adjusting unit.

  The similarity deriving unit may derive the similarity by comparing a template signal serving as a reference for comparison with each of the received signals phased by the phase adjusting unit.

  For example, the similarity deriving unit may derive the similarity based on a correlation value between the template signal and each received signal phased by the phase adjusting unit.

  The template signal may be a phasing addition signal obtained by integrating the received signals phased by the phasing means.

  The similarity deriving unit may derive the similarity by comparing adjacent received signals phased by the phase adjusting unit.

  The similarity deriving unit may derive the similarity based on a correlation value between adjacent reception signals phased by the phase adjusting unit.

  The optimum set sound speed deriving unit may derive a set sound speed that maximizes the similarity as the optimum set sound speed.

  The optimum set sound speed deriving means may derive a weighted average value obtained by weighting each of the set sound speeds with the similarity as the optimum set sound speed.

  The reliability deriving means may derive the similarity between the received signals phased based on the optimum set sound speed as the reliability of the optimum set sound speed.

  The reception signal acquisition means may acquire a plurality of lines of reception signals corresponding to each of reflected ultrasonic waves transmitted to a plurality of locations in the subject. In this case, the phasing means gives each delay time calculated based on each of the plurality of set sound velocities to each of the plurality of lines of received signals, and adjusts each of the plurality of lines of received signals for each set sound speed. May be compatible. The similarity deriving means calculates a similarity between the received signals in each of the plurality of lines of received signals phased for each set sound speed by the phasing means, and performs a plurality of calculations along the time axis direction of the received signals. You may derive for every object field. The optimum set sound speed deriving means derives the optimum set sound speed at each of the plurality of parts in the subject based on the similarity between the reception signals in each calculation target region of each of the plurality of lines of reception signals. Also good. The reliability deriving means derives the similarity between the reception signals in each calculation target region of each of the reception signals of the plurality of lines as the reliability of the optimum set sound speed in each of the corresponding parts in the subject. Also good.

  The ultrasonic diagnostic apparatus is configured to obtain an optimum set sound speed at a site where the reliability of the optimum set sound speed derived by the optimum set sound speed deriving unit is lower than a predetermined threshold, and an optimum set sound speed having a reliability higher than the threshold. It may further include resetting means for resetting by the interpolation processing used.

  In the above ultrasonic diagnostic apparatus, the delay time calculated by the phasing means based on the optimum set sound speed derived by the optimum set sound speed deriving means and the optimum set sound speed reset by the resetting means Each of the received signals is phased with the received signal, and an adding unit generates a phasing addition signal by integrating each of the received signals phased by the phasing unit, and an image generating unit, The image may be generated according to the phasing addition signal.

In order to achieve the above object, the reliability determination method for the set sound speed according to the present invention is generated by each of the plurality of electroacoustic transducers according to the reflected wave of the ultrasonic wave transmitted into the subject. obtaining a received signal, comprising the steps of phasing the respective delay time calculated for each of the plurality of set sound velocities to each of the received signal given to each of the received signals, for each of the plurality of set sound velocities , a similarity indicating the similarity between the received signal mutual at each of the time domain of the plurality of set sound velocities phasing has been the received signal for each, and deriving for each of the plurality of set sound velocities, the plurality of Deriving an estimated value of sound speed in the subject as an optimal set sound speed based on the similarity for each set sound speed , and reliability of the optimal set sound speed based on the similarity derived for each of the plurality of set sound speeds Show Including the step of deriving the reliability, the.

In order to achieve the above object, a program according to the present invention, computer, each of the delay time calculated for each of the plurality of set sound velocities, the received signals generated by each of the electroacoustic transducer a phasing means for giving to each phasing the received signal for each of the plurality of set sound velocities of the similarity between the received signals mutually in each of the time domain of the phasing has been said received signal by said phase adjusting means the similarity degree indicating the similarity deriving means for deriving for each of the plurality of set sound velocities, the estimate of the sound speed within a subject based on the similarity of each of the plurality of set sound velocities derived by the similarity deriving means and the optimal set sound velocity deriving means for deriving a optimum set sound velocity, the outermost derived by the optimum set sound velocity derivation means based on the plurality of set sound velocities for each of the similarity derived by the similarity deriving means A reliability deriving means for deriving a reliability indicating the reliability of the set sound velocity is a program for functioning as a.

  According to the ultrasonic diagnostic apparatus, the sound speed derivation method, and the program according to the present invention, it is possible to stably determine the reliability of the estimated value of the sound speed in the subject.

1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. It is a flowchart which shows the flow of a process of the optimal setting sound speed derivation processing program performed in the ultrasound diagnosing device which concerns on embodiment of this invention. It is a figure for demonstrating the processing content by the similarity deriving part which concerns on embodiment of this invention, and is a wave form diagram which shows the received signal and template signal which were phased based on setting sound speed. It is a schematic diagram which shows the memory | storage form of the similarity derived | led-out by the similarity deriving part which concerns on embodiment of this invention. It is a figure which shows the memory | storage form of the optimal setting sound speed derived | led-out by the optimal setting sound speed deriving part which concerns on embodiment of this invention, and its reliability. It is a flowchart which shows the flow of a process of the image generation processing program performed in the ultrasound diagnosing device which concerns on embodiment of this invention. It is a figure which shows the interpolation process of the optimal setting sound speed in the ultrasonic diagnosing device which concerns on embodiment of this invention. It is a figure which shows typically the calculation process of a local sound speed value. It is a flowchart which shows the calculation process of a local sound speed value. It is a flowchart which shows the calculation process of a local sound speed value.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, substantially the same or equivalent components or parts are denoted by the same reference numerals.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic diagnostic apparatus 1 according to the first embodiment of the present invention.

  The ultrasonic probe 10 transmits ultrasonic waves toward a diagnosis site of the subject and receives ultrasonic waves reflected inside the subject. The ultrasonic probe 10 includes m piezoelectric elements 10a as electroacoustic transducers arranged in a straight line. One-time transmission / reception of ultrasonic waves is performed using n (m> n) adjacent piezoelectric element groups selected from the m piezoelectric elements 10a. By sequentially shifting n piezoelectric element groups used for transmission / reception of ultrasonic waves, the diagnostic region in the subject is scanned by the ultrasonic beam. The ultrasonic probe 10 may have any scanning method such as a linear type, a convex type, and a sector type. Each of the piezoelectric elements 10a is connected to the multiplexer 11 via an m-channel signal line. Each of the piezoelectric elements 10 a generates an ultrasonic wave according to a drive pulse signal supplied from the transmission control unit 12 via the multiplexer 11. Each of the piezoelectric elements 10 a receives an ultrasonic wave reflected in the subject to generate a reception signal that is an electrical signal, and supplies the reception signal to the reception signal processing unit 16 via the multiplexer 11.

  The multiplexer 11 selects adjacent n piezoelectric element groups to be used for transmission / reception of ultrasonic waves from the m piezoelectric elements 10 a of the ultrasonic probe 10 in accordance with a control signal supplied from the main control unit 30. It is an electronic switch. The multiplexer 11 is connected to the transmission control unit 12 and the reception signal processing unit 16 via an n-channel signal line.

  The transmission control unit 12 generates drive pulse signals for n channels according to the control signal supplied from the main control unit 30. In addition, the transmission control unit 12 gives a delay time to the drive pulse signal for each channel so as to perform transmission focus for converging the ultrasonic beam to the depth position of the region of interest designated by the main control unit 30. The drive pulse signal generated in the transmission control unit 12 is supplied to each of the n piezoelectric elements 10 a selected by the multiplexer 11.

  The reception signal processing unit 16 includes an amplifier and an A / D converter provided for each channel. Each of the received signals generated in the n piezoelectric elements 10a selected by the multiplexer 11 is amplified in an amplifier and converted into a digital signal by an A / D converter.

  The reception signal memory 17 is a storage medium that stores the reception signals of the respective channels converted into digital signals by the reception signal processing unit 16 as reception data.

  The phasing processor 18 calculates a reception delay time based on the set sound speed supplied from the main controller 30. Then, the phasing processing unit 18 gives the calculated reception delay time to the reception signal for each channel supplied from the reception signal processing unit 16 or the reception signal memory 17, thereby aligning the time phases of the reception signals for each channel. Phase processing, that is, reception focus processing is performed. The timing at which the ultrasonic wave reflected at a certain point in the subject enters each piezoelectric element 10a does not match. This is because the propagation distance of the ultrasonic wave from the reflection point to each piezoelectric element 10a is different for each piezoelectric element. The phasing processing unit 18 gives a relatively long delay time to the received signal generated by the piezoelectric element arranged at a position where the distance to the reflection point is relatively short, and a position where the distance to the reflection point is relatively long. By applying a relatively short delay time to the reception signal generated by the piezoelectric element arranged at, reception focus processing is performed to align the time phases of the reception signals of the respective channels.

  The addition processing unit 20 integrates the reception signals of the respective channels phased by the phasing processing unit 18 to generate a phasing addition signal.

  The image generation unit 21 performs filtering processing, log compression processing, envelope detection processing, STC (Sensitivity Time Control) processing, interpolation processing, scan conversion processing, and the like on the phasing addition signal supplied from the addition processing unit 20. Then, an image signal for constructing a so-called B-mode image obtained by converting the signal intensity of the phasing addition signal into luminance is generated.

  The monitor 22 is a display device such as a liquid crystal display panel that displays a tomographic image or the like at a diagnostic site based on the image signal generated by the image generation unit 21.

The similarity deriving unit 23 derives an index value (hereinafter referred to as similarity) indicating the similarity between received signals for each channel phased by the phasing processing unit 18 based on the set sound speed. The similarity deriving unit 23, for example, in each of a plurality of calculation target regions divided in the time axis direction of the received signal (that is, the depth direction in the imaging region), a template signal St (t) that serves as a comparison reference described later. And the received signals S ₁ (t) to S _n (t) (both refer to FIG. 3) for each channel, and for each calculation target region (for each depth region) based on the calculated correlation value The similarity between the received signals of each channel is derived. As a template signal serving as a comparison reference, for example, a signal obtained by phasing and adding reception signals of respective channels can be used.

  When the set sound speed used when the phasing processing unit 18 phasing the received signal of each channel is substantially the same as the actual sound speed in the subject, the time phases of the received signals of each channel are similar, and thus similar. The degree of similarity derived by the degree deriving unit 23 increases. As the difference between the set sound speed used when the phasing processing unit 18 phasing the received signal of each channel and the actual sound speed in the subject increases, the time phase shift between the received signals increases. The similarity value derived by the similarity deriving unit 23 is low. On the other hand, the received signal of each channel is distorted due to the influence of ambient scattering on the reflection from the region of interest and aberrations in the propagation process, and the similarity is also low in this case. That is, the similarity derived by the similarity deriving unit 23 is information that can be used to estimate the actual sound speed in the subject, and can be an estimated value or an evaluation value (reliability) indicating the reliability of the received signal. .

  The optimum set sound speed deriving unit 24 calculates the optimum set sound speed that is an estimated value of the actual sound speed in the subject based on the similarity between the received signals derived for each of the plurality of set sound speeds by the similarity degree deriving unit 23. , It is derived for each unit region in the imaging region corresponding to the above-described similarity calculation target region. For example, the optimum set sound speed deriving unit 24 may derive the set sound speed at which the similarity between received signals is the highest as the optimum set sound speed in the unit region. Further, the optimum set sound speed deriving unit 24 calculates the similarity corresponding to the derived optimum set sound speed, that is, the similarity between the received signals when the received signals are phased at the derived optimum set sound speed. Set as a reliability evaluation value (reliability). When there is no distortion of the received signal due to the influence of interference, aberration, etc., the phase of the received signal of each channel phased at the optimum sound speed is completely the same, and as a result, the similarity between the received signals (cross correlation value) Becomes 1. Conversely, when there is distortion in the received signal, even if the received signal of each channel is phased at the optimal sound speed, the time phases do not match completely, and as a result, the similarity between the received signals is less than 1. It becomes. As described above, the similarity corresponding to the optimum set sound speed indicates the degree of distortion of each channel reception signal, and as a result, becomes an evaluation value (reliability) indicating the reliability of each channel reception signal and the estimated optimum set sound speed value. The optimum set sound speed deriving unit 24 stores the evaluation value (reliability) of the reliability of the optimum set sound speed in a memory (not shown) included in the optimum set sound speed in association with the derived optimum set sound speed. The optimum set sound speed deriving unit 24 corresponds to the optimum set sound speed deriving means and the reliability deriving means in the present invention.

  The main control unit 30 comprehensively controls the transmission / reception processing of ultrasonic waves by giving control signals to the multiplexer 11, the transmission control unit 12, and the phasing processing unit 18.

  The operation input unit 40 receives various operation inputs by the user, and is configured by a pointing device such as a mouse or a keyboard, for example.

  The transmission control unit 12, the received signal processing unit 16, the phasing processing unit 18, the addition processing unit 20, the image generation unit 21, the similarity derivation unit 23, the optimum set sound speed derivation unit 24, and the main control unit 30 are shown in FIG. A ROM storing a program describing each process in the optimum set sound speed derivation process routine described later shown in FIG. 2, a CPU for executing the program, a RAM for temporarily storing the processing contents in the CPU, etc. It may be comprised with the computer provided with.

  Next, the ultrasonic diagnostic apparatus 1 according to the present embodiment derives the optimum set sound speed in the subject and derives an evaluation value (reliability) indicating the reliability (probability) of the derived optimum set sound speed. The processing to be performed will be described with reference to the flowchart shown in FIG.

  In step S <b> 1, when the user performs an operation for starting the derivation process of the optimum set sound speed in the subject from the operation input unit 40, the main control unit 30 receives this, and transmits the ultrasonic wave to the transmission control unit 12 and the multiplexer 11. A control signal for starting transmission is supplied.

  In step S <b> 2, the transmission control unit 12 generates a drive pulse signal for each channel according to the control signal supplied from the main control unit 30. The transmission control unit 12 appropriately gives a delay time to the drive pulse signal for each channel so as to perform transmission focus on the region of interest in the subject. Each of the drive pulse signals generated by the transmission controller 12 is supplied to n piezoelectric elements 10 a selected by the multiplexer 11. Thereby, an ultrasonic beam is transmitted from the n piezoelectric elements 10a adjacent to the ultrasonic probe 10 into the subject.

  The echo by reflection of the ultrasonic wave transmitted from each piezoelectric element 10 a of the ultrasonic probe 10 is received by the n piezoelectric elements 10 a selected by the multiplexer 11. Each piezoelectric element 10 a generates a reception signal that is an electrical signal from the reflected echo and outputs the reception signal to the reception signal processing unit 16 via the multiplexer 11. The reception signal processing unit 16 performs signal processing including amplification and A / D conversion on each reception signal, and associates the reception signal subjected to signal processing with one line of reception data in association with the identification number of the line. Store in the received signal memory 17.

  Thereafter, the multiplexer 11 switches the piezoelectric element to be selected in accordance with the control signal supplied from the main control unit 30, and shifts the piezoelectric element 10a that transmits and receives ultrasonic waves by one piezoelectric element, for example. Thereafter, transmission / reception of ultrasonic waves is performed in the same manner as described above. The multiplexer 11 sequentially shifts the piezoelectric elements 10a that transmit and receive ultrasonic waves, whereby the imaging region in the subject is scanned with the ultrasonic beams that are sequentially transmitted. Thereby, the reception signals of a plurality of lines (L [1], L [2], L [3]...) Corresponding to each transmission are acquired, and the reception signals of each line are associated with the identification numbers of the lines. And stored in the received signal memory 17.

  In step S <b> 3, the main control unit 30 sets the line L [i] (i is a line of the line) that is the target of the similarity derivation process by the similarity derivation unit 23 among the reception signals of each line stored in the reception signal memory 17. A received signal having an identification number and a positive integer) is selected. The main control unit 30 first selects the line L [1]. As a result, the received signal of the first line acquired by the first transmission of the ultrasonic wave is set as a target for similarity calculation.

  In step S4, the main control unit 30 sets the set sound speed C [j] (j is an identification number of the set sound speed and is a positive integer) used for the phasing process of the received signal performed in the phasing process unit 18. One is selected from a plurality of preset sound speeds. That is, the main control unit 30 has, for example, a plurality of set sound speeds C [1], C [2], C [3],... Set at 10 m / s steps in the range of 1400 m / s to 1650 m / s. Is stored in advance in a memory (not shown) provided in the device in association with the identification number of the set sound speed, and one set sound speed is selected from among them. The main control unit 30 first selects the set sound speed C [1]. Thus, 1400 m / s is selected as the set sound speed value used for the phasing process. The set sound speed range and the step width are not limited to those described above, and can be changed as appropriate.

  In step S <b> 5, the phasing processing unit 18 receives the reception signal corresponding to the line L [i] selected by the main control unit 30 in step S <b> 3 based on the control signal supplied from the main control unit 30. Read from. Next, the phasing processing unit 18 calculates the reception delay time for each channel from the set sound speed C [j] selected by the main control unit 30 in step S4 based on the control signal supplied from the main control unit 30. Then, phasing is performed by giving the calculated reception delay time to the reception signal of each channel read from the reception signal memory 17. The phasing processing unit 18 supplies the received signal subjected to the phasing process to the similarity deriving unit 23.

  In step S <b> 6, the similarity derivation unit 23 sets a calculation target region in which similarity derivation is performed for the phased reception signal of each channel. The calculation target area is set by cutting out the received signal in a certain time width (depth range) (see FIG. 3).

  In step S7, the similarity deriving unit 23 derives the similarity that is an index value of the similarity between the received signals for each channel in the calculation target region set in step S6, and includes the derived similarity in its own memory. (Not shown). FIG. 3 is a diagram for explaining the content of the similarity derivation process performed by the similarity derivation unit 23.

In FIG. 3, the received signals S ₁ (t) to S _n (t) of each channel subjected to the phasing process in the phasing processing unit 18 are shown. The similarity deriving unit 23 generates a template signal S _t (t) that serves as a comparison reference for deriving the similarity between the received signals S ₁ (t) to Sn (t). The similarity deriving unit 23 uses the phasing addition signal obtained by integrating the received signals S ₁ (t) to S _n (t) phased at the set sound speed at the same time as the template signal S _t (t ).

The similarity degree deriving unit 23 derives a cross-correlation value R between the template signal S _t (t) and the received signal S ₁ (t) in the calculation target region surrounded by a broken line in FIG. To do. In equation (1), the denominator is the square root of the square sum of the values of the points of the template signal St (t) in the calculation target area and the points of the reception signal S1 (t) in the calculation target area. This is a value obtained by multiplying the square root of the square of the value, and the numerator is the value of each point of the template signal St (t) and the value of each point of the received signal S1 (t) in the calculation target region. This is the integrated value of the multiplied values.

The similarity deriving unit 23 similarly calculates a cross-correlation value R with the template signal St (t) for the received signals S ₂ (t), S ₃ (t),... S _n (t). . Then, the similarity deriving unit 23 calculates the sum of the absolute values of the cross-correlation values R calculated for the reception signals S ₁ (t) to S _n (t) of each channel as the reception signals S ₁ (t) to S _n (t ) It is derived as an index value indicating the similarity between each other, that is, the similarity. The degree of similarity derived in this way becomes higher as the set sound speed is closer to the actual sound speed in the subject.

Note that the above example shows a method for calculating the similarity R by calculating the cross-correlation value R between the template signal S _t (t) and the received signals S ₁ (t) to Sn (t) of each channel. However, cross-correlation values are obtained between received signals adjacent to each other (for example, received signals S ₁ (t) and S ₂ (t), received signals S ₂ (t) and S3 (t), etc.) It is good also as deriving the sum total of the absolute value of as a similarity. In this case, since it is not necessary to generate the template signal S _t (t), it is possible to speed up the arithmetic processing.

  In step S8, the similarity deriving unit 23 determines whether or not similarity derivation has been completed for the entire depth range (all time range) of the received signal. If not, the process returns to step S6. The calculation target area is shifted in the time axis direction (depth direction), a new calculation target area is set, and the similarity is derived for the calculation target area in the same manner as described above. The similarity degree deriving unit 23 repeats the processes of steps S6 to S8 until similarity degree derivation is completed for the entire time range (total depth range) of the received signal.

In step S9, the main control unit 30 increments the identification number j of the set sound speed C [j] by one. In step S10, the main control unit 30 compares the incremented numerical value j with the maximum value j _{max of the} set sound speed identification number j to determine whether or not the derivation of similarities has been completed for all the set sound speeds. judge. If it is determined in step S10 that the derivation of similarities has not been completed for all the set sound speeds, the process returns to step S4, a new set sound speed is set, and the processes in steps S5 to S10 are similarly performed. Is called. The main control unit 30 sequentially increments the identification number j of the set sound speed C [j], so that the received signal phased based on each set sound speed within the range of 1400 m / s to 1650 m / s is as described above. Similarly, the degree of similarity is derived.

In step S11, the main control unit 30 increments the identification number i of the line L [i] of the reception signal corresponding to each transmission of the ultrasonic wave by one. In step S12, the main control unit 30 compares the incremented numerical value i with the numerical value i _max indicating the maximum value of the identification number i to determine whether or not the derivation of similarities has been completed for all lines. To do. If it is determined in step S12 that the derivation of the similarity has not been completed for all the lines, the process returns to step S3, a new line from which the similarity is derived is selected, and steps S4 to S12 are performed. Processing is performed in the same way. As the main control unit 30 sequentially increments the identification number i of the line L [i], the degree of similarity is derived for each set sound speed and each calculation target area in the same manner as described above for the reception signal of each line.

The similarity degree deriving unit 23 stores each degree of similarity between the received signals derived through the above-described processes in a memory (not shown) included in itself in a form as shown in FIG. Α ₁₁₁ , α ₁₁₂ , α ₁₁₃ ,... Shown in FIG. 4 are similarities in each calculation target region (each depth position) of each line derived for each set sound speed. As shown in FIG. 4, the similarity deriving unit 23 calculates the similarity in the unit area obtained by dividing the imaging area by each line and each depth position, to each set sound speed C [1], C [2], C [3 ]... Are derived for each case.

  In step S13, the optimum set sound speed deriving unit 24 reads the similarity between the received signals derived by the similarity deriving unit 23 from the memory in the similarity deriving unit 23, and based on the read similarity, Deriving the optimal sound speed. For example, the optimum set sound speed deriving unit 24 derives the set sound speed that maximizes the similarity between the received signals derived for each depth of each line as the optimum set sound speed at that depth position of that line. Further, the optimum set sound speed deriving unit 24 calculates the similarity corresponding to the optimum set sound speed derived for each depth of each line (that is, the similarity between received signals when phasing at the optimum set sound speed). It is set as the evaluation value (reliability) of the reliability (probability) of the optimum sound speed. As shown in FIG. 5, the optimum set sound speed deriving unit 24 uses the optimum set sound speed derived for each calculation target area (each depth position) of each line in the imaging area as a reliability of the optimum set sound speed. It memorize | stores in the memory (not shown) with which it equips with time.

  The optimum set sound speed deriving unit 24 supplies the optimal set sound speed and the reliability evaluation value (reliability) derived for each part in the imaging region in this way to the main control unit 30, and this routine is completed. To do.

  Hereinafter, an example of image generation processing using the optimally set sound speed derived for each part in the imaging region and the reliability evaluation value (reliability) will be described with reference to the flowchart shown in FIG.

  In step S21, the main control unit 30, for example, in accordance with an operation input from the operation input unit 40 by the user, the optimal set sound speed at each depth position of each line derived by the optimal set sound speed deriving unit 24 and its reliability. The degree is supplied to the phasing processing unit 18, and the phasing processing unit 18 receives this.

  In step S22, the phasing processing unit 18 extracts the optimum set sound speed and the reliability thereof at the depth position D [k] of the line L [i].

  In step S23, the phasing processor 18 determines whether or not the reliability of the optimum set sound speed at the point extracted in step S22 is greater than a predetermined threshold.

  If an affirmative determination is made in step S23, the process proceeds to step S24, and if a negative determination is made, the process proceeds to step S29. When the process proceeds to step S29, the process is suspended until an affirmative determination is made in step S28 described later.

  When the reliability of the optimum set sound speed at the point extracted in step S22 is higher than a predetermined threshold, in step S24, the phasing processing unit 18 adopts the optimum set sound speed at that point as it is. That is, the sound speed value derived by the optimum set sound speed deriving unit 24 is set as the optimum sound speed at that point.

In step S25, the phasing processor 18 increments the identification number k of the depth position D [k] by one. In step S26, the phasing processing unit 18 compares the incremented numerical value k with the numerical value k _max indicating the maximum value of the identification number, thereby determining whether or not the above-described optimum set sound speed can be adopted for all depth positions. Determine if completed. In step S26, when it is determined that the adoption of the optimal set sound speed is not completed for all depth positions, the process returns to step S22, and a point at a new depth position on the same line is extracted. The processes in steps S23 to S26 are performed in the same manner. When the phasing processing unit 18 sequentially increments the identification number k of the depth position D [k], whether or not the optimum set sound speed is adopted at each depth position on the same line is determined in the same manner as described above, and the optimum set sound speed is determined. The optimal set sound speed derived by the optimal set sound speed deriving unit 24 is adopted as it is for each point for which it is determined that the reliability is greater than the threshold.

In step S27, the phasing processor 18 increments the identification number i of the line L [i] by one. In step S <b> 28, the phasing processing unit 18 compares the incremented numerical value i with the numerical value i _max indicating the maximum value of the identification number to determine whether or not the adoption of the optimum set sound speed is completed for all lines. Determine whether. If it is determined in step S28 that the determination of whether or not the optimum set sound speed has been adopted for all lines has not been completed, the process returns to step S22, and points at each depth position in the new line are sequentially extracted. The processes in steps S23 to S26 are performed in the same manner. The phasing processing unit 18 sequentially increments the identification number i of the line L [i], so that whether or not the optimum set sound speed is adopted at each depth position of each line is determined in the same manner as described above, and the optimum set sound speed is trusted. For each point for which the degree is determined to be greater than the threshold, the optimum set sound speed derived by the optimum set sound speed deriving unit 24 is used as it is.

  If it is determined in step S28 that the determination of whether or not the optimum set sound speed can be adopted is completed for all the lines, the process of step S30 is started.

  In step S <b> 30, the phasing processing unit 18 has, for each point where the reliability of the optimum set sound speed is lower than the threshold value, the sound speed at each point where the reliability of the optimum set sound speed is higher than the threshold value. The optimum sound speed is reset by interpolation using the value. For example, as shown in FIG. 7, there are points q <b> 1 to q <b> 8 in which the reliability of the optimum sound speed is determined to be higher than the threshold around the point p where the reliability of the optimal sound speed is determined to be lower than the threshold. Suppose you are. In such a case, the phasing processing unit 18 may derive, for example, the average value of the optimum set sound speeds at the points q1 to q8 as the optimum set sound speed at the point p. Alternatively, a weighted average value obtained by weighting the optimally set sound speed at each of the points q1 to q8 with the respective reliability may be derived as the optimally set sound speed at the point p.

  In step S <b> 31, the phasing processing unit 18 reads the reception signal of each line from the reception signal memory 17.

  In step S <b> 32, the phasing processing unit 18 derives a reception delay time at each point based on the optimum sound speed at each point acquired through the above processing, and converts the reception delay time to the reception signal read from the reception signal memory 17. A phasing process is performed by giving the derived reception delay time. The phasing processing unit 18 supplies the phased received signal to the addition processing unit 20.

  In step S <b> 33, the addition processing unit 20 integrates the reception signals of the respective channels phased by the phasing processing unit 18 to generate a phasing addition signal, and supplies this to the image generation unit 21.

  In step S34, the image generation unit 21 performs filtering processing, log compression processing, envelope detection processing, STC processing, interpolation processing, scan conversion processing, and the like on the phasing addition signal supplied from the addition processing unit 20. An image signal for constructing a so-called B-mode image obtained by converting the signal intensity of the phasing addition signal into luminance is generated. The image generation unit 21 supplies the generated image signal to the monitor 22.

  In step S <b> 35, the monitor 22 displays an image corresponding to the image signal generated by the image generation unit 21.

  Through the above processes, the image generation process routine ends.

  As is clear from the above description, the ultrasound diagnostic apparatus 1 according to the present embodiment derives the similarity between the received signals of the respective channels phased at each set sound velocity value, and based on the derived similarity To derive the optimal sound speed. In addition, the ultrasound diagnostic apparatus 1 sets the similarity between the received signals phased at the derived optimum set sound speed as the reliability evaluation value (reliability) of the optimum set sound speed. As described above, according to the ultrasonic diagnostic apparatus 1 according to the present embodiment, the optimum set sound speed is derived based on the similarity between the received signals, so that the received signal is caused by ultrasonic interference in the subject. Even when the intensity decreases or the waveform distortion occurs, the similarity itself does not fluctuate greatly, so that the optimum set sound speed can be derived relatively stably, and the accuracy of deriving the optimum set sound speed can be improved. . In addition, since the similarity between the received signals is used as an evaluation value for the reliability of the optimal sound speed, even if there is a decrease in received signal strength or waveform distortion due to ultrasonic interference in the subject, etc. The determination accuracy of the reliability of the set sound speed is not significantly reduced.

  Further, according to the ultrasonic diagnostic apparatus 1 according to the present embodiment, the optimum set sound speed derived by the optimum set sound speed deriving unit 24 is adopted in that the reliability of the optimum set sound speed is high, and the reliability of the lowest set sound speed is adopted. At a low degree, the optimum set sound speed is reset by the interpolation process using the optimum set sound speed with high reliability. As described above, since the optimum sound speed is reset based on the reliability, it is possible to construct a sharp image with little distortion.

  In the above embodiment, the optimum set sound speed deriving unit 24 derives the reliability of the optimal set sound speed derived based on the similarity between the received signals. However, the ultrasonic diagnostic apparatus according to this embodiment According to 1, it is also possible to derive the reliability of the optimum set sound speed derived by other means or other devices. In this case, the phasing processing unit 18 calculates the reception delay time based on the optimum set sound speed derived by some means, and gives the calculated reception delay time to the reception signal read from the reception signal memory 17. Perform phasing. The similarity deriving unit 23 derives the similarity between the reception signals subjected to the phasing process in the same manner as described above. The optimum set sound speed deriving unit 24 derives the similarity derived by the similarity deriving unit 23 as the reliability of the optimum set sound speed. Further, according to the ultrasonic diagnostic apparatus according to the present embodiment, it is possible to derive the reliability of not only the optimal set sound speed obtained by some means but also all set sound speeds based on assumptions and estimations.

In the above embodiment, the optimum set sound speed and the evaluation value of the reliability of the optimum set sound speed are derived for each depth position of each line. However, the present invention is not limited to this. That is, the optimum set sound speed deriving unit 24 calculates a sum α _SUM of similarities of received signals at each depth position of each line in the block in each block composed of a plurality of depth positions of a plurality of lines, and α _SUM May be calculated as the optimum set sound speed in the block, and α _SUM corresponding to the optimum set sound speed may be set as a reliability evaluation value (reliability).

  In the above embodiment, the similarity between the received signals when phasing at the optimal set sound speed is used as the reliability evaluation value of the optimal set sound speed, but the maximum value of the similarity corresponding to each set sound speed is used. A difference between the (similarity corresponding to the optimum set sound speed) and the minimum value may be used as an evaluation value of the reliability of the optimum set sound speed. Alternatively, the range of the set sound speed corresponding to the similarity value that is a predetermined ratio (1 or less) of the similarity (maximum value) corresponding to the optimum set sound speed may be used as the reliability evaluation value. In other words, the similarity is maximized at the optimum set sound speed, and becomes lower at a lower set sound speed and a higher set sound speed. Therefore, the set sound speed at which the degree of similarity is a predetermined ratio (1 or less) of the maximum similarity value is optimally set. Considering that the sound velocity exists on the low and high sound speed sides, the difference between the set sound velocity values may be used as the reliability evaluation value.

In the above-described embodiment, the case where the similarity deriving unit 23 calculates a one-dimensional cross-correlation value between the template signal and the received signal of each channel is exemplified. A two-dimensional cross-correlation value may be calculated by developing the two-dimensional signal in the time axis direction (depth direction). That is, two-dimensional template signals S _t1 (t), S _t2 (t),..., S _tn (t) are generated by arranging the template signals S _t (t) corresponding to the received signals of the respective channels. (Where S _t1 (t) = S _t2 (t) =... = S _tn (t)), and between this and the received signals S ₁ (t) to S _n (t) of each channel, The two-dimensional cross-correlation value R may be calculated according to the equation (2). Here, Σ represents integration with respect to t (time axis direction) and i (direction of the piezoelectric element). When a three-dimensional probe is used, a three-dimensional cross correlation value may be calculated.

Further, in the above embodiment, the similarity of the received signal of each channel is derived based on the cross-correlation value between the template signal S _t (t) and each of the received signals S ₁ (t) to S _n (t). However, the similarity deriving unit 23 performs a cross-correlation operation between the template signal St (t) and each of the received signals S ₁ (t) to S _n (t), and obtains the peak of the obtained cross-correlation function. It obtains a phase shift amount of each of the received signals _{S 1 (t) ~S n (} t) from the present position of the value for the template signal _S t (t), for each received signal _{S 1 (t) ~S n (} t) The absolute value or variance of the obtained phase shift amount may be derived as an index value of similarity between received signals. In this case, the higher the similarity between received signals, the smaller the derived value.

  In the above embodiment, the set sound speed at the part where the degree of similarity is maximized is set as the optimum set sound speed. However, the optimum set sound speed deriving unit 24 weights each set sound speed with the similarity degree at each part. The weighted average value may be derived as the optimum set sound speed in the part.

  Further, for example, as disclosed in Japanese Patent Application Laid-Open No. 2010-99452, in a technique for obtaining a local sound speed based on optimal sound speeds at a plurality of different points, the optimal sound speed and its reliability are determined by the method according to the present embodiment. And the local sound speed may be obtained by using the optimum set sound speed whose reliability is higher than the threshold, or the local sound speed may be obtained by using the optimum set sound speed weighted and averaged by the reliability.

  In Japanese Patent Application Laid-Open No. 2010-99452, the local sound speed is obtained as follows. FIG. 8 is a diagram schematically showing the content of the local sound speed value calculation process disclosed in Japanese Patent Application Laid-Open No. 2010-99452.

The grid points representing the region of interest ROI in the subject OBJ are X _ROI , and the grid points arranged at equal intervals in the XY direction at positions shallower than the grid point X _ROI are A1, A2 _,. And the lattice points A1, A2,.
Assuming that the elapsed time T and delay time ΔT of the received waves from the lattice points A1, A2,... (WA1, WA2,...) Reach the piezoelectric element are known, the lattice point _XROI and the lattice points A1, A2,. The local sound velocity value at the lattice point X _ROI is obtained from the positional relationship of. Specifically, the fact that the received wave WSUM from the lattice point _XROI and the received wave WSUM virtually combining the received waves from the lattice points A1, A2 _,.

  Specifically, as shown in FIG. 9, optimum sound velocity values at all lattice points set in advance in the subject OBJ are determined (step S40). Here, the optimum sound speed value is a sound speed value at which the contrast and sharpness of the image are the highest, and does not necessarily match the actual local sound speed value in each lattice. As a method for determining the optimum sound speed value in step S10, for example, a method for determining from the contrast of the image, the spatial frequency in the scanning direction, dispersion, and the like (for example, JP-A-8-317926) can be applied. Here, by using the method according to the present embodiment, the optimum set sound speed at each lattice point may be derived to obtain the optimum sound speed value, and the reliability thereof may be derived at the same time.

  Next, based on the optimum sound speed value at each lattice point, the local sound speed value at each lattice is determined (step S42). Here, as the optimum sound speed value at each lattice point, the optimum sound speed value at each lattice point may be replaced with the optimum sound speed value obtained by weighted averaging with the reliability, or only the lattice point having a reliability higher than the threshold value may be used. May be.

The method for determining the local sound speed value based on the optimum sound speed value is as follows. First, as shown in FIG. 10, based on the optimum sound speed value at the lattice point X _ROI, the waveform of the virtual receiving wave WX when the lattice point X _ROI and the reflection point is calculated (step S50).

Next, an initial value of the assumed sound speed at the lattice point X _ROI is set (step S52). Then, the assumed sound speed is changed by one step (step S54), and a virtual combined received wave _WSUM is calculated (step S56). When the local sound speed value at the lattice point _{X ROI} is assumed by V, ultrasound lattice points having propagated from the lattice point _{X ROI} A1, A2, the time to reach ... to _{X ROI A1 / V, X ROI} A2 / V, ... Here, X _ROI A1, X _ROI A2,... _Are the distances between the lattice points A1, A2 _,. Since the optimum sound speed values at the lattice points A1, A2,... Are known at step S40, the received waves from the lattice points A1, A2,. Therefore, the virtual composite received wave _WSUM is obtained by synthesizing the reflected waves (ultrasonic echoes) emitted from the lattice points A1, A2,... With the delays _XROI A1 / V, _XROI A2 / V _,. Can do.

Actually, since the above processing is performed on the element data (RF signal), the time (T1, T2,...) From the lattice point _XROI to the lattice points A1, A2,. It is represented by (2). Here, X _A1 , X _A2 ,... _Are distances in the scanning direction (X direction) between the lattice points A 1, A 2,. Δt is a time interval in the Y direction of the lattice points.

The T1, T2, ..., the lattice point _{X ROI} and same sound ray from the lattice point An Time to reach the grid point _{X ROI (Δt} / 2) each grid point in the delay plus A1, A2, ... from By synthesizing the received wave, a virtual synthesized received wave _WSUM can be obtained.

Here, when the lattice points are set at equal intervals (Δt) on the time axis in the Y direction, the intervals in the space are not necessarily equal. Therefore, when calculating the time until the ultrasonic wave reaches each lattice point, Δt / 2 corrected in Equation (2) instead of Δt / 2 may be used. Here, the corrected Δt / 2 is, for example, a value obtained by dividing the difference in depth (distance in the Y direction) of A1, A2,... Compared with the lattice point X _ROI and the lattice point An of the same sound line by V. A value obtained by adding / subtracting from / 2. The depth of each lattice point A1, A2,... Is obtained because the local sound speed is known at a lattice point shallower than that.

Further, the virtual composite received wave _WSUM is calculated from predetermined pulse waves (WA1, WA2,..., Respectively) actually emitted from the lattice points A1, A2,... With delays _XROI A1 / V, _XROI A2 / V,. ).

Next, an error between the virtual received wave WX and the virtual combined received wave _WSUM is calculated (step S58). Error of the virtual receiving wave WX and the virtual synthesized receiving wave W _SUM is a method of cross-correlating with each other, a method of phase matching addition is multiplied by the delay obtained from the assumed resultant received wave W _SUM to the virtual receiving wave WX, or conversely is calculated by the method of phase matching addition is multiplied by the delay obtained assumed resultant received wave W _SUM from the virtual receiving wave WX. Here, in order to obtain a delay from the virtual received wave WX, the lattice point _XROI is used as a reflection point, and the time at which the ultrasonic wave propagated at the sound velocity V arrives at each element may be set as the delay. Further, in order to obtain a delay from the virtual combined received wave _WSUM , an equiphase line is extracted from the phase difference of the combined received wave between adjacent elements, and the equal phase line is used as a delay, or simply, The phase difference of the maximum (peak) position of the combined received wave may be used as the delay. Further, the cross-correlation peak position of the combined received wave from each element may be set as a delay. The error at the time of phase matching addition is obtained by a method of setting the peak to peak of the waveform after the matching addition or a method of setting the maximum value of the amplitude after the envelope detection.
Next, Steps S54 to S60 are repeated, and when the calculation with all the assumed sound speed values is completed (Yes in Step S60), the local sound speed value at the lattice point _XROI is determined (Step S62). If strictly apply the principle of Huygens, the assumed resultant received wave W _SUM obtained in the step S56 waveforms virtual reception wave when the local sound speed value at the lattice point X _ROI is assumed as V (reflected wave) of WX It becomes equal to the waveform. In step S52, the assumed sound speed value at which the difference between the virtual received wave WX and the virtual synthesized received wave _WSUM is minimized is determined as the local sound speed value at the lattice point _XROI .

  In the above embodiment, the similarity is derived using the received signal after the phasing process. However, the present invention is not limited to this, and the received signal of each channel is determined based on the set sound speed. On the other hand, a calculation target region centered on the reception delay time calculated for the received signal of each channel may be obtained, and the similarity between the reception signals in each calculation target region may be derived.

DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic apparatus 10 Ultrasonic probe 10a Piezoelectric element 12 Transmission control part 16 Reception signal processing part 17 Reception signal memory 18 Phase adjustment process part 20 Addition processing part 21 Image generation part 23 Similarity deriving part 24 Optimal setting sound speed deriving part 30 Main control unit 40 Operation input unit

Claims (15)

A reception signal acquisition means for acquiring a reception signal generated by each of the plurality of electroacoustic transducers according to the reflected wave of the ultrasonic wave transmitted into the subject;
A similarity indicating the similarity between the received signal mutual at each of the time domain of said received signal derived on the basis of a plurality of set sound velocities, and similarity deriving means for deriving for each of the plurality of set sound velocities,
Optimum set sound speed deriving means for deriving an estimated value of sound speed in the subject as the optimum set sound speed based on the similarity for each of the plurality of set sound speeds derived by the similarity degree deriving means;
Reliability deriving means for deriving reliability indicating reliability of the optimum set sound speed derived by the optimum set sound speed deriving means based on the similarity for each of the plurality of set sound speeds derived by the similarity deriving means;
An ultrasonic diagnostic apparatus including: A plurality of reception signals generated at each of a plurality of electroacoustic transducer elements of said plurality of electroacoustic transducer elements further comprises a phasing unit for phasing for each of the plurality of set sound velocities,
The ultrasonic diagnostic apparatus according to claim 1 , wherein the similarity deriving unit derives a similarity between reception signals phased by the phase adjusting unit. The ultrasonic diagnostic apparatus according to claim 2 , wherein the similarity deriving unit derives the similarity by comparing a template signal serving as a comparison reference with each of the reception signals phased by the phase adjusting unit. The ultrasonic diagnostic apparatus according to claim 3 , wherein the similarity deriving unit derives the similarity based on a correlation value between the template signal and each of the reception signals phased by the phase adjusting unit. The ultrasonic diagnostic apparatus according to claim 3 or 4 , wherein the template signal is a phasing addition signal obtained by integrating the reception signals phased by the phasing means. The ultrasonic diagnostic apparatus according to claim 2 , wherein the similarity deriving unit derives the similarity by comparing adjacent reception signals phased by the phase adjusting unit. The ultrasonic diagnostic apparatus according to claim 6 , wherein the similarity deriving unit derives the similarity based on a correlation value between adjacent reception signals phased by the phase adjusting unit. The ultrasonic diagnostic apparatus according to claim 1 , wherein the optimum set sound speed deriving unit derives a set sound speed that maximizes the similarity as the optimum set sound speed. The ultrasonic diagnostic apparatus according to claim 1 , wherein the optimum set sound speed deriving unit derives a weighted average value obtained by weighting each of the set sound speeds with the similarity as the optimum set sound speed. The ultrasonic diagnostic apparatus according to claim 2 , wherein the reliability deriving unit derives a similarity between received signals phased based on the optimum set sound speed as a reliability of the optimum set sound speed. The reception signal acquisition means acquires a plurality of lines of reception signals corresponding to each of reflected ultrasonic waves transmitted to a plurality of locations in the subject,
The phasing means gives each delay time calculated based on each of a plurality of set sound speeds to each of the plurality of lines of received signals to phase each of the plurality of lines of received signals for each set sound speed,
The similarity deriving means calculates a similarity between the received signals in each of the plurality of lines of received signals phased for each set sound speed by the phasing means, and performs a plurality of calculations along the time axis direction of the received signals. Derived for each target area,
The optimum set sound speed deriving means derives the optimum set sound speed in each of the plurality of parts in the subject based on the similarity between the received signals in each calculation target region of each of the plurality of lines of received signals,
The reliability deriving unit derives the similarity between the reception signals in each calculation target region of each of the reception signals of the plurality of lines as the reliability of the optimum set sound speed in each of the corresponding parts in the subject. Item 3. The ultrasonic diagnostic apparatus according to Item 2 . The optimum set sound speed in a region where the reliability of the optimum set sound speed derived by the optimum set sound speed deriving means is lower than a predetermined threshold is reset by interpolation processing using the optimum set sound speed having a reliability higher than the threshold. The ultrasonic diagnostic apparatus according to claim 11 , further comprising resetting means. The phasing means gives each of the received signals each delay time calculated based on the optimum set sound speed derived by the optimum set sound speed deriving means and the optimum set sound speed reset by the resetting means. Phase the received signal,
An adding means integrates each of the received signals phased by the phasing means to generate a phasing addition signal,
The ultrasonic diagnostic apparatus according to claim 12 , wherein an image generation unit generates an image according to the phasing addition signal. Obtaining a reception signal generated by each of a plurality of electroacoustic transducers according to the reflected wave of the ultrasonic wave transmitted into the subject;
A step of phasing each of the delay time calculated for each of the plurality of set sound velocities to each of the received signal given to each of the received signals, for each of the plurality of set sound velocities,
A step of similarity indicating the similarity between the received signal mutual at each of the time domain of the phasing has been the received signal for each of the plurality of set sound velocities, is derived for each of the plurality of set sound velocities,
Deriving an estimated value of sound speed in the subject as an optimal set sound speed based on the similarity for each of the plurality of set sound speeds;
Deriving a reliability indicating the reliability of the optimum set sound speed based on the similarity derived for each of the plurality of set sound speeds ;
Reliability determination method for set sound speed including Computer
Phasing for phasing each of the plurality of set sound velocities each delay time calculated for the, the received signal is given to each of the received signals generated by each of the electro-acoustic transducer for each of the plurality of set sound velocities Means,
A similarity deriving means for similarity is derived for each of the plurality of set sound velocities indicating the similarity between the received signals mutually in each of the time domain of the phasing has been said received signal by said phase adjusting means,
Optimal setting sound speed deriving means for deriving an estimated value of sound speed in the subject as the optimal setting sound speed based on the similarity for each of the plurality of set sound speeds derived by the similarity deriving means;
Reliability deriving means for deriving reliability indicating reliability of the optimum set sound speed derived by the optimum set sound speed deriving means based on the similarity for each of the plurality of set sound speeds derived by the similarity deriving means; Program to function as.

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