JP2010207490A - Ultrasonograph and sonic speed estimation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonograph capable of obtaining a sonic speed in a desired region within a subject. <P>SOLUTION: The ultrasonograph includes: signal processing means which generates a sound-ray signal along the receiving direction of ultrasonic waves by subjecting a plurality of reception signals to a reception focus processing and a wave detection processing; image signal generation means which generates an image signal on the basis of the sound-ray signal; focus determination means which determines a beam focusing degree in the reception focus processing when a setting sonic value is changed successively; and sonic speed value calculation means which obtains according to the determination result of the focus determination means a first average sonic speed in a path from an ultrasonic probe to a first area and a second average sonic speed in a path from the ultrasonic probe to a second area and calculates on the basis of the first and second average sonic speeds and the distance from the ultrasonic probe to the first and second areas a average sonic speed in the path from the first area to the second area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus that performs imaging of an organ or the like in a living body by transmitting and receiving ultrasonic waves to generate an ultrasonic image used for diagnosis, and further in such an ultrasonic diagnostic apparatus. The present invention relates to a sound speed estimation method used for estimating sound speed in a living body.

  In the medical field, various imaging techniques have been developed in order to perform diagnosis by observing the inside of a subject. In particular, ultrasonic imaging that acquires internal information of a subject by transmitting and receiving ultrasonic waves enables real-time image observation, and other medical applications such as X-ray photographs and RI (radio isotope) scintillation cameras. Unlike imaging technology, there is no radiation exposure. Therefore, ultrasonic imaging is used as a highly safe imaging technique in a wide range of fields including gynecological, circulatory, and digestive systems as well as fetal diagnosis in the obstetrics field.

  The principle of ultrasonic imaging is as follows. Ultrasound is reflected at the boundary between regions having different acoustic impedances, such as the boundary between structures in the subject. Therefore, by transmitting an ultrasonic beam into a subject such as a human body, receiving an ultrasonic echo generated in the subject, and determining the reflection position and reflection intensity where the ultrasonic echo is generated, It is possible to extract the contour of the structure (eg, internal organs or lesion tissue).

  In general, in an ultrasonic diagnostic apparatus, an ultrasonic probe including a plurality of ultrasonic transducers (vibrators) having an ultrasonic transmission / reception function is used. By scanning a subject using an ultrasonic beam formed by combining a plurality of ultrasonic waves by transmission focus processing, receiving an ultrasonic echo reflected inside the subject, and performing reception focus processing, Based on the intensity of the ultrasonic echo, image information relating to a structure existing in the subject is obtained, and an ultrasonic image is displayed on the display unit.

  Thus, the ultrasonic image displayed in the conventional ultrasonic diagnostic apparatus is a tomographic image obtained by performing luminance modulation according to the intensity of the received signal of the ultrasonic echo reflected from the living body. Here, based on acoustic theory, a tomographic image representing a difference in acoustic impedance unique to each part of tissue in a living body is obtained. However, the clinical meaning of the obtained tomographic image is evaluated empirically, and it cannot be said that it has a physical meaning and is reflected in clinical information.

  On the other hand, it is generally known that the elastic modulus of each part of the tissue gives clinical information as direct physical information, and devices that display a distribution of values corresponding to the elastic modulus as an elastographic image are also commercially available. For example, tumors are generally harder than other tissues and thus have a higher modulus of elasticity. Although the clinical value of elastography has been evaluated, in order to acquire an elastography image, it is necessary to press the living body from the outside, and an extremely advanced examination technique is required.

  By the way, since the sound velocity is given as a function of the elastic modulus, the clinical value indicated by the sound velocity of each part of the tissue in the living body is considered to be equivalent to the elastic modulus. Therefore, it can be inferred that the tomographic image based on the sound velocity has clinical value as well as elastography. The speed of sound is measured by measuring the time for which sound passes a known length, but no method is known for determining the speed of sound in various parts of a living body in a non-invasive manner.

  As a related technique, Patent Document 1 discloses that the set sound speed of all the elements of the transmission / reception aperture can be changed to easily check the influence of the change of the set sound speed on the tomographic image, and the set sound speed of each element is always optimal. An ultrasonic diagnostic apparatus intended to converge to a value is disclosed. This ultrasonic diagnostic apparatus transmits ultrasonic waves to a subject and receives a plurality of arranged elements for receiving ultrasonic waves reflected from the subject, and a delay time distribution in each of the transmitted and received signals of the elements A means for forming an ultrasonic beam having directivity in a predetermined direction, a display means for displaying a tomographic image of the subject, and a sound velocity within the subject set for each of the elements to determine a delay time distribution Is changed according to the focal position of the ultrasonic beam and the respective positions of the elements, and the sound speed changing means is arranged at each arrangement position of the elements within the transmission / reception aperture composed of a predetermined number of elements. Corresponding sequential array numbers are regarded as variables, a function that forms an orthogonal function system, and a expansion coefficient that multiplies each function that forms the orthogonal function system, and the speed of sound set for each element is changed. To do. That is, Patent Document 1 discloses that the resolution of the obtained ultrasonic image is determined, and the set sound speed of the medium is changed so that the resolution is optimized.

  As described above, in an ultrasonic diagnostic apparatus that performs transmission / reception beam forming using an array transducer, a technique of focusing an ultrasonic beam on a target region by giving an appropriate delay amount to each element at the time of transmission or reception is used. It is done. When using an array transducer, the transmission / reception path differs depending on the relative geometric position between the transducer and the target region. Therefore, in order to focus the ultrasonic beam on the same target region, it is necessary to delay the transmission signal or the reception signal in order to compensate for the difference between the transmission and reception paths. The amount of delay is given by dividing the path difference between the transducer and the target area by the speed of sound in the medium. That is, in order to focus the ultrasonic beam, a delay amount corresponding to the set medium sound speed is given to each transducer. In particular, at the time of reception, the ultrasonic beam is focused in every region by changing the delay amount according to the change in the depth of the target region.

  When a delay amount is given to each transducer, the sound speed in the medium must be set to a value assumed in advance. However, the actual sound speed in the medium is not always the same as the set sound speed value. In particular, in the living body, since the sound speed is usually unknown, it is generally different from the set sound speed value. is there. Furthermore, in the living body, the sound speed varies depending on the organ and each part, and therefore the actual sound speed may greatly differ from the set sound speed value depending on the location.

  When the set sound speed value is equal to the actual sound speed, the ultrasonic beam is focused as theoretically. The focus state of the ultrasonic beam cannot be improved compared to this state. Further, it can be easily estimated that the image quality of the ultrasonic image is best when the focus state of the ultrasonic beam is the best. Therefore, it is possible to bring the set sound speed value closer to the actual sound speed by determining that the image quality of the ultrasonic image is the best. Patent Document 1 exactly discloses this technique.

  However, even if the ultrasonic image quality is determined and the set sound speed value is brought close to the actual sound speed, the set sound speed value can take only one value. Although it is possible to use different set sound speed values in different regions of interest, the sound speed value set for any region of interest is the same set sound speed value in the entire path until the ultrasonic wave reaches the region of interest. As applied. On the other hand, since the sound speed in the living body is different in each area of the path, the set sound speed value at this time cannot be set as the sound speed in each area of the path. That is, even if the ultrasonic image quality is optimally set for each area and the sound speed value is set for each area, the set sound speed value does not represent the sound speed in that area.

Japanese Patent No. 3174450 (second page, FIG. 1)

  Therefore, in view of the above points, the present invention provides an ultrasonic diagnostic apparatus and a sound speed estimation capable of obtaining a sound speed in a desired region in a subject based on a reception signal of an ultrasonic echo reflected in the subject. It aims to provide a method.

  In order to solve the above problem, an ultrasonic diagnostic apparatus according to one aspect of the present invention transmits an ultrasonic wave to a subject according to a plurality of drive signals, and receives a plurality of ultrasonic echoes propagated from the subject. An ultrasonic probe including a plurality of ultrasonic transducers that output a reception signal of the same, and a plurality of drive signals are supplied to the plurality of ultrasonic transducers, and a plurality of reception signals output from the plurality of ultrasonic transducers are received. By performing focus processing and detection processing, a signal processing unit that generates a sound ray signal along the reception direction of the ultrasonic wave, and an image signal representing an ultrasonic image based on the sound ray signal generated by the signal processing unit Image signal generating means for generating a signal and a reception focus process when a set sound velocity value is sequentially changed for a plurality of regions in the subject. A focus determination unit that determines a degree of beam convergence, and at least a first average sound velocity in a path from the ultrasonic probe to the first region, and from the ultrasonic probe to the second region according to a determination result of the focus determination unit. The second average sound velocity in the path is obtained, and the first region is changed from the first region to the second region based on the first and second average sound velocities and the distances from the ultrasonic probe to the first and second regions. And a sound speed value calculating means for calculating an average sound speed in the route to reach.

  In addition, the sound velocity estimation method according to one aspect of the present invention supplies a plurality of drive signals to a plurality of ultrasonic transducers in an ultrasonic probe to transmit ultrasonic waves to the subject, and transmits an ultrasonic wave from the subject. Step (a) of generating a sound ray signal along the reception direction of the ultrasonic wave by performing reception focus processing and detection processing on the plurality of reception signals output from the plurality of ultrasonic transducers that have received the acoustic echoes. And (b) generating an image signal representing an ultrasonic image based on the sound ray signal generated in step (a), and the set sound velocity values are sequentially changed for a plurality of regions in the subject. Step (c) for determining the degree of beam convergence in the reception focus processing, and at least the first from the ultrasonic probe according to the determination result in step (c) The first average sound speed in the path to the area and the second average sound speed in the path from the ultrasonic probe to the second area are obtained, and the first and second average sound speeds and the first and second sound speeds from the ultrasonic probe are determined. And (d) calculating an average sound speed in a route from the first area to the second area based on the distance to the second area.

  According to one aspect of the present invention, based on the first average sound velocity in the path from the ultrasonic probe to the first region and the second average sound speed in the route from the ultrasonic probe to the second region. By calculating the average sound velocity in the path from the first region to the second region, the sound velocity in a desired region in the subject can be obtained.

1 is a block diagram illustrating a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. It is a flowchart which shows the sound speed estimation method used in the ultrasound diagnosing device shown in FIG. It is a figure which shows the relative positional relationship between an ultrasonic probe and the region of interest set in the subject.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. The ultrasonic diagnostic apparatus includes an ultrasonic probe 10, a scanning control unit 11, a transmission delay pattern storage unit 12, a transmission control unit 13, a drive signal generation unit 14, a reception signal processing unit 21, and a reception delay pattern. Storage unit 22, reception control unit 23, B-mode image signal generation unit 30, focus determination unit 41, sound speed value calculation unit 42, sound speed map creation unit 43, image display control unit 51, and display unit 52 A console 61, a control unit 62, and a storage unit 63. Here, the transmission delay pattern storage unit 12 to the reception control unit 23 constitute signal processing means.

  The ultrasonic probe 10 includes a plurality of ultrasonic transducers 10a constituting a one-dimensional or two-dimensional transducer array. These ultrasonic transducers 10a transmit ultrasonic waves to the subject based on a plurality of applied drive signals, receive ultrasonic echoes propagating from the subject, and output a plurality of received signals.

  Each ultrasonic transducer 10a includes, for example, a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate), a polymer piezoelectric element represented by PVDF (polyvinylidene difluoride), and the like. It is comprised by the vibrator | oscillator which formed the electrode at the both ends of the material (piezoelectric body) which has the piezoelectricity. When a pulsed or continuous wave voltage is applied to the electrodes of such a vibrator, the piezoelectric body expands and contracts. By this expansion and contraction, pulsed or continuous wave ultrasonic waves are generated from the respective vibrators, and an ultrasonic beam is formed by synthesizing these ultrasonic waves. Each vibrator expands and contracts by receiving propagating ultrasonic waves and generates an electrical signal. These electrical signals are output as ultrasonic reception signals.

  The scanning control unit 11 sequentially sets the transmission direction of the ultrasonic beam and the reception direction of the ultrasonic echo. The transmission delay pattern storage unit 12 stores a plurality of transmission delay patterns used when forming an ultrasonic beam. The transmission control unit 13 selects one pattern from a plurality of delay patterns stored in the transmission delay pattern storage unit 12 according to the transmission direction set in the scanning control unit 11, and based on the pattern The delay times given to the drive signals of the plurality of ultrasonic transducers 10a are set. Alternatively, the transmission control unit 13 may set the delay time so that ultrasonic waves transmitted at a time from the plurality of ultrasonic transducers 10a reach the entire imaging region of the subject.

  For example, the drive signal generator 14 includes a plurality of pulsars corresponding to the plurality of ultrasonic transducers 10a. The drive signal generation unit 14 sends a plurality of drive signals to the ultrasonic probe 10 so that the ultrasonic waves transmitted from the plurality of ultrasonic transducers 10a form an ultrasonic beam according to the delay time set by the transmission control unit 13. A plurality of drive signals are supplied to the ultrasonic probe 10 so that the ultrasonic waves supplied or transmitted from the plurality of ultrasonic transducers 10a at a time reach the entire imaging region of the subject.

  The reception signal processing unit 21 includes a plurality of amplifiers (preamplifiers) 21a and a plurality of A / D converters 21b corresponding to the plurality of ultrasonic transducers 10a. The reception signal output from the ultrasonic transducer 10a is amplified by the amplifier 21a, and the analog reception signal output from the amplifier 21a is converted into a digital reception signal by the A / D converter 21b. The A / D converter 21 b outputs a digital reception signal to the reception control unit 23.

  The reception delay pattern storage unit 22 stores a plurality of reception delay patterns used when receiving focus processing is performed on a plurality of reception signals output from the plurality of ultrasonic transducers 10a. The reception control unit 23 selects one pattern from the plurality of reception delay patterns stored in the reception delay pattern storage unit 22 based on the reception direction set in the scanning control unit 11, and the reception delay pattern Based on the set sound velocity value, a reception focus process is performed by adding a delay to a plurality of reception signals. By this reception focus processing, a reception signal (sound ray signal) in which the focus of the ultrasonic echo is narrowed is formed. Further, the reception control unit 23 performs envelope detection processing on the formed sound ray signal.

  Here, the delay amount of the reception signal in the reception focus process is determined based on the sound speed in the subject. In general, 1530 m / s or 1540 m / s is set as the in-vivo sound velocity value C0, but actually, the sound velocity value differs depending on the tissue in the living body. Therefore, by setting the average sound velocity Ci in the subject and multiplying the delay amount D0 (j) in the reception delay pattern by (C0 / Ci), a plurality of delay amounts D1 (j) = (C0 / Ci) · D0. (J) is determined (j = 1, 2,..., N). Where N is the number of ultrasonic transducers used.

  The B-mode image signal generation unit 30 generates a B-mode image signal that is tomographic image information related to the tissue in the subject based on the sound ray signal generated by the reception control unit 23. For this purpose, the B-mode image signal generation unit 30 includes an STC (sensitivity time control) unit 31 and a DSC (digital scan converter) 32.

  The STC unit 31 corrects the attenuation due to the distance on the sound ray signal generated by the reception control unit 23 according to the depth of the ultrasonic reflection position. Further, the DSC 32 converts the sound ray signal corrected by the STC unit 31 into an image signal in accordance with a normal television signal scanning method (raster conversion), and performs necessary image processing such as gradation processing to obtain B A mode image signal is generated. An ultrasonic image is displayed on the display unit 52 based on the B-mode image signal generated by the B-mode image signal generation unit 30.

  The control unit 62 controls the sound speed value calculation unit 42 so as to sequentially change the set sound speed value Ci in parallel with the generation of the B mode image signal by the B mode image signal generation unit 30. The focus determination unit 41 determines the beam convergence in the reception focus process when the set sound speed value Ci is sequentially changed for a plurality of regions in the ultrasonic image.

  For example, the focus determination unit 41 performs a fast Fourier transform on the sound ray signal generated by the reception control unit 23 so that the ratio of the high frequency component in the sound ray signal (for example, the ratio of the high frequency component to the mid frequency component) is increased. It may be determined that the beam focusing degree is the maximum when the maximum value is reached, or the B-mode image signal generated by the B-mode image signal generation unit 30 is subjected to fast Fourier transform to obtain a space in the B-mode image signal. It may be determined that the beam focusing degree is maximum when the ratio of the high frequency component of the frequency becomes maximum.

  The sound velocity value calculation unit 42, according to the determination result of the focus determination unit 41, at least the first average sound velocity in the path from the ultrasonic probe 10 to the first area and the path from the ultrasonic probe 10 to the second area. The second average sound speed is obtained, and the first area and the second area are reached based on the first and second average sound speeds and the distances from the ultrasonic probe 10 to the first and second areas. Average sound speed in a path (a third area from the first area to the second area) is calculated. By repeating such calculation for a plurality of regions in the subject, the sound velocity in each region in the subject can be calculated.

  The sound speed map creating unit 43 generates an image signal representing a sound speed map that displays the sound speed distribution in the subject based on the average sound speed calculated for the plurality of regions by the sound speed value calculating unit 42. The image display control unit 51 is a B-mode image signal generated by the B-mode image signal generation unit 30 and an image signal representing a sound speed map generated by the sound speed map generation unit 43 in accordance with an operation of the operator using the console 61. Is selected to generate an image signal for display. The display unit 52 includes, for example, a display device such as a CRT or LCD, and displays an ultrasonic image or a sound velocity map based on a display image signal.

  The control unit 62 controls the scanning control unit 11, the B-mode image signal generation unit 30, the focus determination unit 41, and the like according to an operator's operation using the console 61. In the present embodiment, the scanning control unit 11, the transmission control unit 13, the reception control unit 23 to the image display control unit 51, and the control unit 62 are configured by a CPU and software (program). Or an analog circuit. The software (program) is stored in the storage unit 63. As a recording medium in the storage unit 63, a flexible disk, MO, MT, RAM, CD-ROM, DVD-ROM, or the like can be used in addition to the built-in hard disk.

Next, the sound speed estimation method used in the ultrasonic diagnostic apparatus shown in FIG. 1 will be described in detail.
2 is a flowchart showing a sound speed estimation method used in the ultrasonic diagnostic apparatus shown in FIG. 1, and FIG. 3 shows a relative positional relationship between the ultrasonic probe and a region of interest set in the subject. FIG. In FIG. 3, it is assumed that a region of interest (ROI) is located directly below the ultrasonic probe 10 in order to simplify the description.

  In step S <b> 1 of FIG. 2, the operator sets at least ROI <b> 1 and ROI <b> 2 by operating the console 61. As shown in FIG. 3, ROI1 is set in the subject at a distance (depth) d from the ultrasonic probe 10, and ROI2 is set in the subject at a distance (depth) d + Δd from the ultrasonic probe 10. Is set.

  In step S2 of FIG. 2, the sound speed value calculation unit 42 sequentially changes the set sound speed value, and the reception control unit 23 performs a reception focus process. In step S3, the focus determination unit 41 or the operator determines the beam convergence degree in the reception focus process when the set sound velocity values are sequentially changed for at least ROI1 and ROI2.

  For example, when the focus determination unit 41 performs fast Fourier transform on the sound ray signal generated by the reception control unit 23, the ratio of the high frequency component in the sound ray signal (for example, the ratio of the high frequency component to the mid frequency component). It may be determined that the beam focusing degree is the maximum when the maximum value is reached, or the B-mode image signal generated by the B-mode image signal generation unit 30 is subjected to fast Fourier transform to obtain a space in the B-mode image signal. It may be determined that the beam focusing degree is maximum when the ratio of the high frequency component of the frequency becomes maximum. Alternatively, the operator may determine the beam focusing degree in the reception focus process based on the image quality of the ultrasonic image displayed on the display unit 52.

Here, it is reasonable to consider that the set sound speed value when the image quality in ROI 1 is optimal is the average sound speed C ₁ in the path from the ultrasonic probe 10 to ROI 1 (depth d). This is because the image quality is optimal in ROI1, and it is considered that the ultrasonic beam is most focused in ROI1. The amount of delay given to the vibrator at this time is equal to the delay time calculated based on the set sound speed value for the entire path regardless of the sound speed distribution of the path. Similarly, the set sound speed value when the image quality in ROI 2 is optimum is considered to be the average sound speed C ₂ in the path from the ultrasonic probe 10 to ROI 2 (depth d + Δd).

Thereby, in step S4, the sound speed calculation unit 42 calculates the average sound speed C in the path from the ultrasonic probe 10 to the ROI 1 based on the set sound speed value that maximizes the beam convergence degree (image quality of the ultrasonic image) in the ROI 1. ₁ determined in step S5, based on the set sound velocity for beam focusing degree (quality of ultrasound images) to the maximum in ROI2, obtaining an average acoustic velocity C ₂ in the path leading to the ultrasonic probe 10 ROI2.

In step S6, sound velocity calculation unit 42, an average acoustic velocity _{C 1} and _{C 2,} based on the distance from the ultrasonic probe 10 to the ROI1 and ROI2, calculates the average speed of sound Cx in leading path ROI2 from ROI1 .

Here, if the sound velocity according to the distance (depth) from the ultrasonic probe 10 is g (x), the average sound velocity C ₁ in the path from the ultrasonic probe 10 to the ROI ₁ is expressed by the following equation (1). Is done.

ただし、ＲＯＩ１からＲＯＩ２に至る経路における平均音速Ｃｘは、次式（３）によって表されるものである。

Similarly, the average acoustic velocity _{C 2} in the path leading to the ultrasonic probe 10 ROI2 is expressed by the following equation (2).

However, the average sound velocity Cx in the route from ROI1 to ROI2 is expressed by the following equation (3).

式（４）は、ＲＯＩ１からＲＯＩ２に至る領域における平均音速を与える。２つのＲＯＩの間隔を短くすれば、任意の場所における音速を求めることが可能となる。即ち、目的とする領域の上下にＲＯＩ１及びＲＯＩ２を設定すれば、その領域における音速を求めることができる。また、ＲＯＩの設定を順次切り換えて、超音波画像全体について各部の音速を算出すれば、音速マップを作成することも可能となる。 Based on the equation (2), to represent the average acoustic velocity Cx using an average acoustic velocity _{C 1} and _{C 2,} so that the following formula (4).

Equation (4) gives the average sound velocity in the region from ROI1 to ROI2. If the interval between the two ROIs is shortened, the sound speed at an arbitrary location can be obtained. That is, if ROI1 and ROI2 are set above and below the target area, the sound speed in that area can be obtained. Further, if the setting of the ROI is sequentially switched and the sound speed of each part is calculated for the entire ultrasound image, a sound speed map can be created.

  INDUSTRIAL APPLICABILITY The present invention can be used in an ultrasonic diagnostic apparatus that performs imaging of an organ or the like in a living body by transmitting and receiving ultrasonic waves and generates an ultrasonic image used for diagnosis.

DESCRIPTION OF SYMBOLS 10 Ultrasonic probe 10a Ultrasonic transducer 11 Scan control part 12 Transmission delay pattern memory | storage part 13 Transmission control part 14 Drive signal generation part 21 Reception signal processing part 21a Amplifier 21b A / D converter 22 Reception delay pattern memory | storage part 23 Reception control part 30 B-mode image signal generator 31 STC unit 32 DSC
DESCRIPTION OF SYMBOLS 41 Focus determination part 42 Sound speed value calculation part 43 Sound speed map preparation part 51 Image display control part 52 Display part 61 Console 62 Control part 63 Storage part

Claims (6)

An ultrasonic probe including a plurality of ultrasonic transducers that transmit ultrasonic waves to a subject according to a plurality of drive signals and output a plurality of received signals by receiving ultrasonic echoes propagating from the subject;
A plurality of drive signals are supplied to the plurality of ultrasonic transducers, and a reception focus process and a detection process are performed on the plurality of reception signals output from the plurality of ultrasonic transducers, so that the ultrasonic reception direction can be obtained. Signal processing means for generating a sound ray signal along;
Image signal generating means for generating an image signal representing an ultrasonic image based on the sound ray signal generated by the signal processing means;
Focus determination means for determining the beam convergence in the reception focus processing when the set sound velocity value is sequentially changed for a plurality of regions in the subject;
According to the determination result of the focus determination means, at least a first average sound speed in a path from the ultrasonic probe to the first area and a second average sound speed in the path from the ultrasonic probe to the second area. The average sound speed in the path from the first area to the second area is calculated based on the first and second average sound speeds and the distance from the ultrasonic probe to the first and second areas. Sound velocity value calculation means to
An ultrasonic diagnostic apparatus comprising: The first average sound velocity and C _1, the second average sound velocity and C _2, wherein the distance from the ultrasonic probe to the first region is d, the distance from the first region to the second region Δd When the sound speed value calculation means calculates the average sound speed Cx in the path from the first area to the second area, Cx = {(d + Δd) / Δd} C ₂ − (d / Δd) C ₁ The ultrasonic diagnostic apparatus according to claim 1, which is calculated as follows.   The focus determination means determines that the beam convergence is maximum when the ratio of the high frequency component in the sound ray signal generated by the signal processing means is maximum, and the sound speed value calculation means is the first The first average sound speed is obtained based on the set sound speed value that maximizes the beam focusing degree in the region, and the second average sound speed is obtained based on the set sound speed value that maximizes the beam focus degree in the second area. The ultrasonic diagnostic apparatus according to claim 1 or 2.   The focus determination unit determines that the beam focusing degree is maximum when the ratio of the high frequency component of the spatial frequency in the image signal generated by the image signal generation unit is maximized, and the sound velocity value calculation unit is The first average sound speed is obtained based on the set sound speed value that maximizes the beam focusing degree in the first region, and the second average is calculated based on the set sound speed value that maximizes the beam focusing degree in the second region. The ultrasonic diagnostic apparatus according to claim 1, wherein a speed of sound is obtained.   The sound velocity map creation means which produces | generates the image signal showing the sound speed map which displays the sound speed distribution in a subject based on the average sound speed calculated about a some area | region by the said sound speed value calculation means, The 1st aspect further comprises. The ultrasonic diagnostic apparatus according to any one of 4. A plurality of drive signals are supplied to a plurality of ultrasonic transducers in the ultrasonic probe to transmit ultrasonic waves to the subject, and are output from the plurality of ultrasonic transducers that have received ultrasonic echoes propagating from the subject. (A) generating a sound ray signal along the reception direction of ultrasonic waves by performing reception focus processing and detection processing on a plurality of reception signals;
A step (b) of generating an image signal representing an ultrasonic image based on the sound ray signal generated in step (a);
A step (c) of determining a beam convergence degree in the reception focus process when the set sound velocity value is sequentially changed for a plurality of regions in the subject; and
According to the determination result in step (c), at least a first average sound speed in a path from the ultrasonic probe to the first area and a second average sound speed in the path from the ultrasonic probe to the second area are calculated. The average sound speed in the path from the first area to the second area is calculated based on the first and second average sound speeds and the distance from the ultrasonic probe to the first and second areas. Performing step (d);
A sound speed estimation method comprising:

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