JP5901431B2 - Ultrasonic diagnostic apparatus, sound speed derivation method, and program - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, a sound speed derivation method, and a program for generating 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, when transmitting ultrasonic waves, a drive pulse signal having a delay time difference corresponding to their arrangement is supplied to each electroacoustic transducer element of the ultrasonic probe so that an ultrasonic wave is transmitted between the elements. Transmission focus for shifting the transmission timing of sound waves 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 received signal generated by each electroacoustic transducer to align the time phases of the received signals. Receive focus is performed. Thereby, the azimuth | direction resolution of an ultrasonic image can be improved.

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, Japanese Patent Laid-Open No. 2007-7045 discloses , Generate multiple beam profiles with different set sound speeds from the phasing-added echo signals, display the generated multiple beam profiles on the same screen, and select the sound speed corresponding to the one with the smallest beam width. It is described that it is selected as a biological sound speed.

  In Japanese Patent Laid-Open No. 2001-252276, trial injection of ultrasonic waves into a living body is performed with a delay time corresponding to the average sound velocity, and a delay time error is obtained by calculation from the signal of each channel in which the received signal is delay-controlled. It is described that the obtained data is compared with delay time error data of a plurality of sound speeds using a previously stored sound speed as a parameter, and a sound speed corresponding to the matched delay time error is obtained as a sound speed in the living body. ing.

JP 2007-7045 A JP 2001-252276 A

  In the technique described in the above-mentioned patent document, the reception signal is acquired by fixing the depth of transmission focus and the set sound speed. For this reason, there is a difference between the focus depth of the received signal used for obtaining the actual sound speed and the depth of the transmission focus, and it is difficult to calculate the optimum set sound speed with high accuracy. That is, when the reception focal points P1 and P2 are regarded as the focus points for obtaining the optimum set sound speed, the depths of the focus points and the transmission focus T are different. If the point of interest is in the vicinity of the transmission focal point T, the optimum set sound speed can be obtained with high accuracy. However, if the distance between the point of interest and the transmission focal point T is increased, the measurement accuracy of the optimum set sound velocity is lowered. In particular, in the case of speckles, the received signal at a depth different from the depth of the transmission focus is distorted by interference, so that the accuracy of the optimum set sound speed is significantly reduced.

  In order to solve this problem, it is necessary to adjust the depth of transmission focus to the focus depth. At this time, if the set sound speed and the optimum set sound speed are not matched with the depth of the transmission focus, the focus depth and the transmission focus depth will be deviated. Therefore, in order to obtain a high-quality received signal at the depth of interest and obtain the optimum set sound speed with high accuracy, the depth of transmission focus is varied by changing the set sound speed of the transmission focus as well as the reception focus with respect to the depth of interest. It is necessary to adjust the depth to the depth of interest. However, in this case, an enormous number of transmissions is required.

  In order to solve this problem, the present inventor in Japanese Patent Application No. 2010-080595 calculates a transmission delay time based on a preset assumed sound speed and performs transmission focus at a plurality of depth positions. Has been proposed to determine the optimum sound speed using the received signal obtained by performing the transmission focus closest to the target depth. According to this method, it is necessary to perform transmission focus at fine intervals so that a high-quality received signal can be acquired. For example, at a depth of about 2 cm, it is desirable to perform transmission focus at intervals of 4 mm or less with a linear probe and 8 mm or less with a convex probe. In other words, in order to obtain the optimal set sound speed at an arbitrary depth within a certain depth range, it is necessary to perform transmission focus multiple times so as to cover the entire depth range. If the depth range is expanded, the number of transmissions increases.

  However, since there is an upper limit on the time that can be spent for transmission and the capacity of the received signal that can be acquired, it is difficult to increase the number of transmissions indefinitely. Therefore, it is difficult to increase the frequency over a relatively wide depth range. It may be difficult to obtain a quality received signal.

  The present invention has been made in view of the above points, and provides an ultrasonic diagnostic apparatus, a sound speed derivation method, and a program capable of deriving a highly accurate optimum set sound speed while suppressing the number of times of ultrasonic transmission. For the purpose.

In order to achieve the above object, an ultrasonic diagnostic apparatus according to the present invention transmits a plurality of ultrasonic waves into a subject according to a drive signal and generates a reception signal according to a reflected wave of the ultrasonic waves. An electroacoustic transducer, a receiving unit that receives a designation input of a region of interest in the subject, and a plurality of transmission focal points arranged at different depth positions in the region of interest received by the receiving unit, In addition, in the depth region where the transmission F value changes according to the focal length , the depth of each of the plurality of transmission focal points is such that the focal length increases geometrically as the depth position of the transmission focal point becomes deeper. Transmission focus control means for deriving a position; drive signal generation means for generating the drive signal so as to form a transmission focus at each of the depth positions derived by the transmission focus control means; See containing and a sonic velocity derivation means operable to derive an estimate of the sound speed of the region of interest on the basis of the received signal obtained by implementing the transmission focus on each of the depth positions derived by the transmission focus control unit, the transmission The focus control means sets w [i] as a length corresponding to half of an effective area in which a reception signal of a predetermined quality corresponding to an arbitrary transmission focus f [i] is obtained, and a focus of the transmission focus f [i]. When the distance is D [i] and the value corresponding to w [i] / D [i] is k, the value α corresponding to (1 + k) / (1-k) is determined as the common ratio of the geometric series. The depth position of each of the plurality of transmission focal points is derived so that the effective area is continuous between adjacent transmission focal points.

The transmission focus control means is configured to arrange the transmission focal points at equal intervals in a depth region where a transmission F value different from a depth region in which the transmission F value changes according to a focal length is maintained constant. The depth position of each of the plurality of transmission focal points may be derived.

  The transmission focus control unit derives the number n of transmission focal points based on a depth in the depth direction of the region of interest received by the reception unit and a coefficient α corresponding to a predetermined common ratio, and a focal length The depth position of each of the n transmission focal points corresponding to the number n of transmission focal points may be derived so that increases in a geometric series.

  The transmission focus unit derives a coefficient α corresponding to a common ratio based on a width in the depth direction of the region of interest received by the reception unit and a predetermined number n of transmission focal points, and the coefficient α The depth position of each of the n transmission focal points corresponding to the number n of transmission focal points may be derived so that the focal length increases geometrically based on the above.

  Further, the ultrasonic diagnostic apparatus controls the aperture diameter of the electroacoustic transducer according to the depth position of the transmission focal point of the ultrasonic wave transmitted so that the transmission F value becomes a predetermined value, and is transmitted. If the depth position of the transmission focal point of the ultrasonic wave is a depth position where the transmission F value cannot be the predetermined value, an aperture diameter control means for setting the aperture diameter to a maximum value may be further included. .

In order to achieve the above object, a sound speed derivation method according to the present invention includes a step of receiving a designation input of a region of interest in a subject, and a plurality of positions at different depth positions in the inputted region of interest. In order to arrange the transmission focal point, and to increase the focal length in a geometric series as the transmission focal point becomes deeper in the depth region where the transmission F value changes according to the focal length , Deriving the depth position of each of the transmission focal points, and deriving an estimated value of the sound speed of the region of interest based on the received signal obtained by performing transmission focus on each of the derived depth positions When, only including, in the step of deriving the depth position of each of the plurality of transmit focal, corresponding to half the predetermined effective area which the received signal is obtained of quality corresponding to any transmit focal f [i] Length (1 + k) / (1-k) where [i] is the focal length of the transmission focal point f [i] is D [i] and k is a value corresponding to w [i] / D [i]. Is defined as a common ratio of the geometric series, and the depth position of each of the plurality of transmission focal points is derived so that the effective region is continuous between adjacent transmission focal points.

In order to achieve the above object, the program according to the present invention is arranged such that a plurality of transmission focal points are arranged at different depth positions in a region of interest inputted by a computer, and the transmission F value is a focal length. The depth position of each of the plurality of transmission focal points is set so that the distance from the adjacent transmission focal point increases geometrically as the depth position of the transmission focal point becomes deeper in the depth region that varies according to A transmission focus control means to derive , wherein w [i] is a length corresponding to half of an effective area in which a reception signal of a predetermined quality corresponding to an arbitrary transmission focus f [i] is obtained, and the transmission focus f When a focal length of [i] is D [i] and a value corresponding to w [i] / D [i] is k, a value α corresponding to (1 + k) / (1-k) is a geometric series. The effective area is defined as a common ratio of Wherein a plurality of transmission focus control means for deriving each of the depth positions of the transmit focal, obtained by implementing the transmission focus on each of the depth positions derived in the transmission focus control means so as to be continuous between the focal And functioning as sound speed deriving means for deriving an estimated value of sound speed of the region of interest based on the received signal.

  According to the ultrasonic diagnostic apparatus of the present invention, it is possible to derive a highly accurate optimum set sound speed while suppressing the number of ultrasonic transmissions.

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 the image generation process by the ultrasonic diagnosing device which concerns on embodiment of this invention. FIG. 3A is a diagram illustrating the shape of an ultrasonic beam having a relatively small transmission F value, and FIG. 3B is a diagram illustrating the shape of an ultrasonic beam having a relatively large transmission F value. It is a figure which shows arrangement | positioning of each transmission focus in the case of implementing a transmission focus in the depth position where the transmission F value derived | led-out by the transmission focus control part which concerns on embodiment of this invention can be maintained constant. It is a figure which shows arrangement | positioning of each transmission focus in the case of implementing a transmission focus in the depth position where the transmission F value derived | led-out by the transmission focus control part which concerns on embodiment of this invention cannot be maintained constant. It is a flowchart which shows the flow of the derivation | leading-out process of the frequency | count of transmission and the transmission focus position by the transmission focus control part which concerns on embodiment of this invention. It is a flowchart which shows the flow of the derivation | leading-out process of the optimal setting sound speed by the ultrasonic diagnosing device which concerns on embodiment of this invention. It is a figure which shows the line which comprises an ultrasonic image. It is a figure which shows the processing method of the acquired ultrasonic image. It is a figure which shows the acquisition method of provisional optimal setting sound speed. It is a figure which shows provisional optimal setting sound speed distribution for every depth position of a transmission focus. It is a figure which shows transition of the standard deviation of provisional optimal setting sound speed distribution with respect to a depth position. It is a figure which shows the range of the effective area | region corresponding to each of an actual transmission focus position. It is a figure which shows the acquisition method of optimal setting sound speed.

  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.

  FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic diagnostic apparatus 1 according to an 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, for example, a plurality of piezoelectric elements 10a as electroacoustic transducers arranged in a straight line. One-time transmission / reception of ultrasonic waves is performed using a piezoelectric element group selected from the plurality of piezoelectric elements 10a. By sequentially shifting the group of piezoelectric elements used for transmission / reception of ultrasonic waves, the diagnostic region in the subject is scanned with the ultrasonic beam. The ultrasonic probe 10 may have any scanning method of linear type, convex type, and sector type.

  Each of the piezoelectric elements 10a is connected to the reception signal processing unit 16 and the transmission control unit 12 through a plurality of channel signal lines. Each of the piezoelectric elements 10 a generates an ultrasonic wave according to the drive pulse signal supplied from the transmission control unit 12. Each of the piezoelectric elements 10 a receives a reflected wave reflected in the subject, generates a reception signal that is an electric signal, and outputs the reception signal to the reception signal processing unit 16.

The transmission control unit 12 generates a drive pulse signal to be supplied to each of the piezoelectric elements 10a. The transmission control unit 12 transmits a drive pulse signal to be supplied to each of the piezoelectric elements 10a used for transmission / reception of ultrasonic waves so as to converge the ultrasonic beam to the depth position of the transmission focus derived by the transmission focus control unit 14. Give each a delay time. The transmission control unit 12 controls the aperture diameter according to the depth position of the transmission focus. More specifically, the transmission control unit 12 controls the aperture diameter so that the aperture diameter increases as the depth position of the transmission focal point increases so that the transmission F value is constant. The aperture diameter corresponds to a value obtained by multiplying the number of piezoelectric elements 10a used for transmitting ultrasonic waves and the interval between the arrangements of the piezoelectric elements 10a. The transmission F value is a value obtained by dividing the focal length D by the aperture diameter A (F value = D / A). Since the aperture diameter is limited by the maximum number of piezoelectric elements 10a used for transmitting ultrasonic waves, the transmission F value cannot be made constant when the ultrasonic transmission focal point exceeds a certain depth. The transmission control unit 12 sets the aperture diameter to the maximum value (maximum aperture diameter A _max ) when the transmission focal point of the transmitted ultrasonic wave is a depth position where the predetermined transmission F value cannot be maintained.

  The transmission focus control unit 14 derives the number n of transmissions of ultrasonic waves (the number of transmission focal points) according to the range of the region of interest in order to perform so-called multistage focusing on the region of interest in the subject designated by the user. The depth position of each transmission focal point is derived. That is, the transmission focus control unit 14 sets the arrangement of each of the plurality of transmission focal points in the region of interest.

  The reception signal processing unit 16 includes a plurality of amplifiers and a plurality of A / D converters provided corresponding to each of the piezoelectric elements 10a used for transmission / reception of ultrasonic waves. Each of the reception signals generated in each piezoelectric element 10a is amplified by 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 signal converted into a digital signal by the reception signal processing unit 16 as reception data.

  The reception control unit 18 calculates the reception delay time based on the set sound speed designated by the main control unit 30 and calculates the reception delay calculated for the reception signal of each channel supplied from the reception signal processing unit 16 or the reception signal memory 17. Give time to phasing. Thereafter, the phasing addition signal is generated by integrating the reception signals of the phasing channels.

  The image generation unit 20 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 reception control unit 18. Thus, an ultrasonic image signal obtained by converting the signal intensity of the phasing addition signal into luminance is generated.

  The focal position deriving unit 21 analyzes a plurality of ultrasonic images generated from reception signals phased based on a plurality of set sound velocities, so that each transmission focal point of the ultrasonic wave transmitted from the ultrasonic probe 10 is analyzed. The actual depth position is derived.

  The effective area deriving unit 22 derives an effective area corresponding to each of the actual depth positions of the transmission focal points derived by the focal position deriving unit 21. The effective area is an area where a relatively high quality received signal can be obtained centering on the transmission focus.

  The optimum set sound speed deriving unit 24 determines which point in the region of interest each effective point derived by the effective region deriving unit 22 is in, and selects an ultrasound image based on the determination result. Then, by analyzing the selected ultrasonic image, an optimum set sound speed that is an estimated value of the actual sound speed at each point is derived.

  The monitor 28 is a display device such as a liquid crystal display panel, and displays an ultrasonic image corresponding to the ultrasonic image signal generated by the image generation unit 20.

  The main control unit 30 comprehensively controls transmission / reception of ultrasonic waves by giving control signals to the transmission control unit 12, the transmission focus control unit 14, and the reception control unit 18.

  The operation input unit 40 is configured by a pointing device such as a keyboard and a mouse that accepts designation input of a region of interest by the user.

  The transmission control unit 12, the transmission focus control unit 14, the reception signal processing unit 16, the reception control unit 18, the image generation unit 20, the focal position derivation unit 21, the effective area derivation unit 22, the optimum set sound speed derivation unit 24, and the main control The unit 30 temporarily stores a ROM storing an image generation program describing each process in the image generation process routine described later shown in FIG. 2, a CPU for executing the program, and processing contents in the CPU. It can be composed of a computer equipped with a RAM or the like for storing.

  Next, an outline of an image generation process in which the ultrasound diagnostic apparatus 1 according to the present embodiment derives the optimum set sound speed and generates a tomographic image of the subject will be described with reference to the flowchart shown in FIG.

  In step S1, when the user designates the range of the region of interest in the subject from the operation input unit 40, the main control unit 30 receives this and transmits a control signal indicating the range of the designated region of interest. 14.

  In step S2, the transmission focus control unit 14 derives the number of transmission focal points required for obtaining a high-quality reception signal over the entire area of interest indicated by the control signal, that is, the number of transmissions n. Then, the derivation result is supplied to the main control unit 30. A method for deriving the number of transmissions n will be described later.

In step S3, the main control unit 30 determines whether or not the derived number of transmissions n is equal to or less than a predetermined upper limit value n _max . The upper limit value n _{max of the} number of transmissions is a value set in advance in consideration of the processing time and the capacity of the received signal that can be acquired, and may be a value arbitrarily set by the user. If it is determined that the number of transmissions n derived by the transmission focus control unit 14 is not more than the upper limit value n _max , the process proceeds to step S4. On the other hand, when it is determined that the transmission count n derived by the transmission focus control unit 14 is larger than the upper limit value n _max , the process proceeds to step S7.

In step S7, the main control unit 30 displays an error message on the monitor 28, and this routine ends. The display of the error message means that a certain image quality cannot be maintained because the range of the area of interest is too wide for the predetermined number of transmissions n _max . At this time, a message prompting re-designation of the region of interest may be displayed.

In step S4, the main control unit 30 supplies the transmission focus control unit 14 with a control signal indicating that the derived number of transmissions n is less than or equal to the upper limit value n _max . In response to this, the transmission focus control unit 14 derives the depth position of each of the n transmission focal points corresponding to the transmission count n derived in step S2. A method for deriving the depth position of the transmission focus will be described later.

  In step S5, transmission focus is performed at the depth position of each transmission focus derived in step S4. The ultrasonic image obtained in this way is analyzed by the focal position deriving unit 21, the effective area deriving unit 22, and the optimum set sound speed deriving unit 24, and the optimum set sound speed of each point in the region of interest is derived. The optimum set sound speed at each point in the derived region of interest is stored in a memory included in the main control unit 30. Details of the processing contents in this step will be described later.

  In step S <b> 6, the main control unit 30 supplies the reception control unit 18 with a control signal to be subjected to the phasing addition processing of the reception signal based on the optimum set sound speed derived in step S <b> 5. The reception control unit 18 acquires the optimum set sound speed at each point in the region of interest from the main control unit 30 and reads out the received signal already acquired from the reception signal memory 17. The reception control unit 18 adjusts the received signal of each channel by providing the received signal read from the received signal memory 17 with a delay time calculated based on the optimum set sound speed at each point in the region of interest. Accumulate and generate a phasing addition signal. The image generation unit 20 generates an ultrasonic image signal from the phasing addition signal generated by the reception control unit 18 and supplies the ultrasonic image signal to the monitor 28 to display the ultrasonic image. This routine is completed through the above steps.

  Next, an operation in which an ultrasonic beam is transmitted from the ultrasonic probe 10 and the image generation unit 20 generates an ultrasonic image based on the reflected wave will be described.

  When transmitting an ultrasonic beam into the subject, the transmission control unit 12 supplies a drive pulse signal to each of the plurality of piezoelectric elements 10 a of the ultrasonic probe 10. At this time, the transmission control unit 12 applies the drive pulse signal of each channel so that the ultrasonic wave transmitted from each piezoelectric element 10a converges to the depth position of the transmission focus derived by the transmission focus control unit 14. Give the delay time. Each of the piezoelectric elements 10a, when receiving the drive pulse signal, mechanically vibrates to generate an ultrasonic wave, and transmits the ultrasonic wave into the subject.

  The ultrasonic waves transmitted from the respective piezoelectric elements 10a propagate through the subject, are reflected one after another at the discontinuous surface of the acoustic impedance in the middle, and the reflected waves are received by the plurality of piezoelectric elements 10a. Each of the piezoelectric elements 10a generates an electric signal when receiving the reflected wave, and supplies the electric signal to the reception signal processing unit 16 as a reception signal. A high-quality received signal with little distortion can be obtained from the reflected wave reflected in the vicinity of the transmission focal point.

  The reception signal processing unit 16 amplifies the reception signal supplied from each of the plurality of piezoelectric elements 10a and then converts it into a digital signal. The reception signal converted into the digital signal is stored in the reception signal memory 17 as reception data and supplied to the reception control unit 18.

  The reception control unit 18 gives the reception delay time calculated based on the set sound speed value designated by the main control unit 30 to the reception signal of each channel supplied from the reception signal processing unit 16 or the reception signal memory 17. The phasing process is performed by And the reception control part 18 produces | generates a phasing addition signal by integrating | accumulating the receiving signal of each channel phased. The generated phasing addition signal is sequentially supplied to the image generation unit 20.

  The image generation unit 20 performs a filtering process, a log compression process, an envelope detection process, an STC (Sensitivity Time Control) process, an interpolation process, a scan conversion process, and the like on the phasing addition signal. An ultrasonic image signal in which intensity is converted into luminance is generated. The generated ultrasonic image signal is stored in an image memory included in the ultrasonic image signal and supplied to the monitor 28. The monitor 28 displays a tomographic image of the subject based on the ultrasonic image signal.

  Next, the process of deriving the number n of ultrasonic beam transmissions and the process of deriving the depth position of each transmission focus by the transmission focus control unit 14 corresponding to steps S2 and S4 of the flowchart shown in FIG. 2 will be described.

  In general, in order to obtain a high-quality received signal with small distortion, the beam width of the ultrasonic beam may be reduced, and in order to reduce the beam width, the transmission F value may be reduced. Here, FIG. 3A shows the beam shape of an ultrasonic beam having a relatively small transmission F value, and FIG. 3B shows the beam shape of an ultrasonic beam having a relatively large transmission F value. As shown in FIG. 3A, an ultrasonic beam having a small transmission F value has a small beam width at the transmission focal point f, and a high-quality received signal can be obtained in the vicinity of the focal point. Can be generated. However, the beam width increases rapidly as the distance from the transmission focal point f increases, and the resolution of the obtained ultrasonic image also decreases rapidly as the distance from the transmission focal point f increases. As described above, the ultrasonic beam having a small transmission F value has a relatively narrow range (width in the depth direction) of the effective region centering on the transmission focal point at which a high-quality received signal can be obtained.

  On the other hand, as shown in FIG. 3B, the ultrasonic beam having a large transmission F value has a wide beam width at the transmission focal point f and the resolution near the focal point is not so high, but at a depth position away from the focal position. The beam width is smaller than the ultrasonic beam with a small F value. That is, in an ultrasonic beam having a large transmission F value, a relatively high quality reception signal can be obtained even at a position away from the transmission focal point f. That is, an ultrasonic beam having a large transmission F value has a relatively wide effective area (width in the depth direction) centered on the transmission focal point. Thus, the range of the effective area (width in the depth direction) centering on the transmission focal point at which a high-quality received signal can be obtained becomes wider as the transmission F value increases. The range of the effective area is approximately proportional to the transmission F value.

  The transmission focus control unit 14 uses the property that the range of the effective area centering on the transmission focus at which a high-quality received signal can be obtained is proportional to the transmission F value. The position is derived as follows.

  When the range of the region of interest designated by the user is a region that is relatively close to the body surface (shallow region) and is within a range in which a predetermined transmission F value can be maintained in advance. As shown in FIG. 4, the depths of the transmission focal points f [1] to f [n] are arranged so that the transmission focal points f [1] to f [n] at the time of performing multistage focusing are arranged at equal intervals. Determining the position.

That is, assuming that the predetermined transmission F value is X, the transmission focus control unit 14 divides the focal distance _Dmax when the transmission focus is set at the depth position at the lower end of the region of _interest by the maximum aperture diameter _Amax . The value D _max / A _max is compared with X. If the transmission focus control unit 14 determines that D _max / A _max is equal to or less than X, the transmission focus control unit 14 determines that a predetermined transmission F value can be maintained. In this case, the aperture diameter is controlled by the transmission control unit 12 in accordance with the depth position of the transmission focus so that the transmission F value becomes the predetermined value X.

  The transmission focus control unit 14 derives the number of transmissions (the number of transmission focal points) n and the transmission focal point arrangement interval so that the effective areas r [1] to r [n] of the respective transmission focal points are continuous within the region of interest. . Since the range of the effective area (the width z in the depth direction) is proportional to the transmission F value, it is equal to each other when the transmission F value is kept constant. As shown in FIG. 4, the transmission focus control unit 14 determines that the arrangement intervals of the transmission focal points f [1] to f [n] are the width z in the depth direction of the effective regions r [1] to r [n]. Depth positions of the transmission focal points f [1] to f [n] are derived so as to match. The width z in the depth direction of the effective area can be arbitrarily set according to the required image quality. The number of transmissions n can be derived from L / z, for example, where L is the total length of the region of interest in the depth direction. The depth positions of the transmission focal points f [1] to f [n] can be uniquely determined by, for example, fixing the transmission focal point f [n] arranged at the deepest position to the lower end of the region of interest. It is possible to derive the depth position of each of the transmission focal points f [1] to f [n] by fixing the transmission focal point f [1] arranged at the shallowest position to the upper end of the region of interest. .

  When the transmission focus control unit 14 determines that the range of the region of interest designated by the user includes a relatively deep region from the body surface and cannot maintain a predetermined transmission F value, As shown in FIG. 5, each transmission focal point f [1] to f [n] is increased so that the distance between adjacent transmission focal points increases as the depth of each transmission focal point increases (as the focal length increases). Derived depth position.

That is, assuming that the predetermined transmission F value is X, the transmission focus control unit 14 divides the focal distance _Dmax when the transmission focus is set at the depth position at the lower end of the region of _interest by the maximum aperture diameter _Amax . The value D _max / A _max is compared with X. If the transmission focus control unit 14 determines that D _max / A _max is greater than X, the transmission focus control unit 14 determines that the predetermined transmission F value cannot be maintained. In this case, the opening diameter is fixed to the maximum opening diameter A _max by the transmission control unit 12. When the aperture diameter is constant, the transmission F value is proportional to the focal length D. Further, as described above, the range of the effective area (width in the depth direction) centering on the transmission focal point at which a high-quality received signal can be obtained is proportional to the transmission F value. Therefore, when the aperture diameter is constant, the width of the effective area is proportional to the focal length D. That is, when the aperture diameter is constant and the transmission F value changes according to the focal length, the width of the effective area centering on the transmission focus becomes wider as the depth position of the transmission focus becomes deeper.

  Since the transmission focal points f [1] to f [n] are formed under a condition in which the aperture diameter is fixed, the corresponding transmission F values are respectively set to the focal lengths D [1] to D [n]. The value is in accordance. Accordingly, the widths of the effective areas r [1] to r [n] corresponding to the transmission focal points f [1] to f [n] are different from each other. Here, if the lengths corresponding to half of the widths of the effective areas r [1] to r [n] are w [1] to w [n], respectively, the transmission focus control unit 14 determines the depth of each transmission focus. The position is derived so as to satisfy the following expressions (1) and (2).

w [i] / D [i] = k <1 (1)
D [i] = D [i-1] + w [i-1] + w [i] (2)
(Where i is an integer from 1 to n)

  That is, the transmission focus control unit 14 keeps the ratio of the focal length D [i] corresponding to a certain transmission focal point F [i] and the width of the effective area r [i] centered on the transmission focal point F [i] constant. The depth positions of the transmission focal points are set so that the effective areas between the transmission focal points adjacent to each other are continuous. The following formula (3) is derived from the above formulas (1) and (2).

  D [i] = D [i-1] × (1 + k) / (1-k) (3)

Here, if (1 + k) / (1-k) is α,
D [i] = α × D [i−1] = α ⁱ⁻¹ × D [1] (4)

  It can be expressed as. That is, when the range of the region of interest is not within a range in which a predetermined constant transmission F value can be maintained, the transmission focus control unit 14 determines each focal position so that the focal length increases geometrically. Set. The coefficient α (= (1 + k) / (1−k)) is a value larger than 1, and can be arbitrarily set according to the image quality to be obtained. It is a value corresponding to a common ratio.

Further, if the total length in the depth direction of the region of interest is L, and the number of ultrasonic transmissions (the number of transmission focal points) is n,
L = D [n] −D [1] = ( α ⁿ⁻¹ −1) × D [1] (5)
It can be expressed as. From Expression (5), the total length L in the depth direction of the region of interest, the focal length D [1] corresponding to the transmission focal point f [1] arranged at the shallowest depth position, the coefficient α, the number of transmission focal points (super The remaining one variable can be obtained by making three variables of the number of sound wave transmissions) n known variables. The depth positions of the transmission focal points f [1] to f [n] can be uniquely determined by, for example, fixing the transmission focal point f [n] arranged at the deepest position to the lower end of the region of interest. It is also possible to derive the depth positions of the transmission focal points f [1] to f [n] by fixing the transmission focal point f [1] arranged at the shallowest position to the upper end of the region of interest.

  FIG. 6 is a flowchart showing the procedure of the process for deriving the number of transmissions and the depth position of each transmission focus by the transmission focus control unit 14 described above.

In step S <b> 10, the transmission focus control unit 14 receives the control signal indicating the range of the target region from the main control unit 30, thereby obtaining the total length L in the depth direction of the target region and the depth position _Dmax of the lower end of the target region. get.

In step S11, the transmission focus control unit 14 determines whether or not D _max / A _max is equal to or less than X that is a predetermined transmission F value, so that the range of the region of interest is a predetermined transmission F value X. It is determined whether or not it is within a range that can be maintained.

  If the transmission focus control unit 14 determines that the range of the region of interest is within a range in which the predetermined transmission F value X can be maintained, in step S <b> 12, the total length L in the depth direction of the region of interest is set to the predetermined transmission F value X. The number of transmissions n is derived by dividing by the width z of the effective area corresponding to. Next, in step S13, the transmission focus control unit 14 transmits, for example, by fixing the transmission focal point f [n] arranged at the deepest position to the lower end of the region of interest and setting the interval between the transmission focal points to z. The depth position of each of the focal points f [1] to f [n] is derived.

  As described above, when the transmission focus control unit 14 determines that the range of the region of interest is within the range in which the predetermined transmission F value can be maintained, the transmission focal points are arranged at equal intervals. At this time, the aperture diameter is controlled so that the F value is constant in each transmission. Since the transmission F value is constant in each transmission and the transmission focal points are arranged at intervals corresponding to the width z of the effective area, a uniform ultrasonic image can be acquired over the entire area of interest.

On the other hand, if the transmission focus control unit 14 determines in step S11 that the range of the region of interest is not within the range in which the predetermined transmission F value X can be maintained, L = ( α ⁿ⁻¹ −1) × in step S14. The number of transmissions n is derived based on D [1] (the above formula (5)). At this time, the depth position of the upper end of the region of interest may be used as D [1]. It is assumed that the coefficient α is predetermined.

Next, in step S15, the transmission focus control unit 14 derives the depth position of each transmission focus based on D [i] = α ⁱ⁻¹ × D [1] (the above equation (4)). At this time, the depth position of the upper end of the region of interest may be used as D [1]. As described above, when the transmission focus control unit 14 determines that the range of the region of interest is not within the range in which the predetermined transmission F value can be maintained, each transmission focus is controlled so that the focal length increases geometrically. Place. In this case, the aperture diameter is fixed to the maximum aperture diameter _Amax in each transmission.

  As described above, the transmission focus control unit 14 determines the depth of the transmission focus in the depth region where the transmission F value cannot be kept constant, that is, in the depth region where the transmission F value changes according to the focal length. The depth position of each transmission focal point is set so that the distance between the focal points increases as the depth increases (as the focal length increases). As a result, it is possible to obtain a high-quality received signal in each transmission with a smaller number of transmissions compared to the case where a plurality of transmission focal points are arranged at equal intervals. Further, by arranging the transmission focal points so that the focal distance increases geometrically, the arrangement of the transmission focal points can correspond to the range of the effective area, and the arrangement can be made efficient.

  In the present embodiment, the case where the focal length is increased geometrically is illustrated, but it is only necessary that the effective areas corresponding to the transmission focal points are continuous. In other words, the effective areas adjacent to each other may overlap. That is, when the depth position of each transmission focus is set so that the distance between the focal points increases as the transmission focus depth increases, even if D [i] <α × D [i−1]. Good.

  In the present embodiment, the number of transmissions n is derived based on Expression (5) with the coefficient α as a fixed value. Since the coefficient α is a coefficient that affects the image quality of the ultrasonic image to be obtained, the image quality of the ultrasonic image obtained is secured by setting the coefficient α to a fixed value. On the other hand, it is also possible to derive the coefficient α based on the equation (5) with the number of transmissions n as a fixed value. In this case, since α varies according to the range of the region of interest, there is a possibility that the image quality of the obtained ultrasonic image will be deteriorated if the range of the region of interest is too wide. However, by arranging the n transmission focal points based on the equation (4), it is possible to prevent the occurrence of a region having a remarkably low resolution as compared with the case where the transmission focal points are arranged at equal intervals.

  In addition, when the region of interest includes both a range in which the predetermined transmission F value can be maintained and a range in which the predetermined transmission F value cannot be maintained, the transmission F value is controlled to be constant and the transmission focal points are set at equal intervals for the range in which the predetermined transmission F value can be maintained On the other hand, in a range where a predetermined transmission F value cannot be maintained, the transmission diameter may be arranged such that the aperture diameter is fixed to the maximum value and the focal length increases geometrically. Further, without distinguishing between the range in which the predetermined transmission F value can be maintained and the range in which the predetermined transmission F value cannot be maintained, each transmission is performed so that the focal length increases geometrically by fixing the aperture diameter to the maximum value over the entire region of interest. A focal point may be arranged.

  Next, details of the processing contents according to step S5 of the flowchart shown in FIG. 2 will be described with reference to the flowchart shown in FIG.

  When the depth position of each transmission focus is derived by the transmission focus control unit 14 as described above, the main control unit 30 determines that the depth position of the transmission focus of the ultrasonic wave transmitted from the ultrasonic probe 10 is the transmission focus No. . A control signal to be set at a depth position corresponding to 1 is supplied to the transmission control unit 12. Thereby, the transmission control unit 12 gives the transmission delay time corresponding to the depth position of the transmission focal point f [1] to the drive pulse signal of each channel, and applies the drive pulse signal of each channel to which the delay time is given to each piezoelectric pulse. It supplies to the element 10a. Note that the transmission delay time here is a value derived based on an assumed set sound speed set in advance assuming the sound speed in the subject. The ultrasonic probe 10 transmits ultrasonic waves into the subject so as to converge at the transmission focal point f [1] (step S20).

  Echoes by reflection of ultrasonic waves transmitted from the piezoelectric elements 10a of the ultrasonic probe 10 are received by the plurality of piezoelectric elements 10a. Each of the piezoelectric elements 10 a that has received the reflection echo generates a reception signal that is an electrical signal and outputs the reception signal to the reception signal processing unit 16. The reception signal processing unit 16 performs signal processing including amplification and A / D conversion on the reception signal of each channel, and stores the reception signal subjected to signal processing in the reception signal memory 17 as reception data (step S22). .

  Based on the control signal supplied from the main control unit 30, the reception control unit 18 receives a line number from the reception signal memory 17. j received signal and a set sound speed No. supplied from the main control unit 30. The reception delay time is calculated based on the set sound speed corresponding to k. The reception control unit 18 then extracts the extracted line No. A received delay time is applied to the received signal of j and reception focus processing is performed to generate a phasing addition signal, which is supplied to the image generation unit 20. The image generation unit 20 generates an ultrasonic image signal from the phasing addition signal generated in the reception control unit 18, and accumulates the generated ultrasonic image signal in an image memory included in the image generation unit 20 (step S24).

  In the present embodiment, a plurality of set sound speeds for the reception control unit 18 to perform the reception focus process are associated with the set sound speed number k (k is an integer from 1 to 251) in the reception control unit 18. It is stored in the provided memory. Set sound speed No. 1-No. 251 corresponds to, for example, set sound speeds of 1400 m / s to 1650 m / s, respectively. Each set sound speed is set at an interval of 1 m / s, for example. The set sound speed range and the set interval are not limited to those described above, and can be changed as appropriate.

  Further, as shown in FIG. 8, line numbers j (j is an integer from 1 to 17), for example, for a line having a width of ± 8 lines centered on the piezoelectric element 10 a at a predetermined opening center C of the ultrasonic probe 10. Is assigned.

  Next, the main control unit 30 increments the set sound speed number (step S26), and then determines whether or not the set sound speed number is greater than the maximum value 251 (step S28). If an affirmative determination is made in step S28, the process proceeds to step S30, and if a negative determination is made, the process returns to step S24.

  When the main control unit 30 sequentially increments the set sound speed number, the reception control unit 18 performs reception focus processing on the reception signal of the line read from the reception signal memory 17 based on each set sound speed, A phasing addition signal is generated for each set sound speed. Then, the generated phasing addition signal for each set sound speed is generated by the image generation unit 20 for each set sound speed, and the generated ultrasonic image signal is stored in the image memory.

  Next, after incrementing the line number (step S30), the main control unit 30 determines whether or not the line number is greater than the maximum value 17 (step S32). If an affirmative determination is made in step S32, the process proceeds to step S34, and if a negative determination is made, the process returns to step S24.

  The main control unit 30 sequentially increments the line number, so that the lines to be processed are sequentially changed, and the processes in steps S24 to S32 are performed on the changed lines. That is, the reception control unit 18 sets the line No. The reception delay process calculated based on each set sound speed is given to the reception signals 1 to 17 and the reception focus process is performed to generate a phasing addition signal for each set sound speed. The generated phasing addition signal for each set sound speed is supplied to the image generation unit 20. The image generation unit 20 generates an ultrasonic image signal for each set sound speed corresponding to each line, and stores these in the image memory.

  In this way, as shown in FIG. 1 to No. 17 are generated for each set sound speed of 1400 m / s to 1650 m / s.

  The image generation unit 20 outputs an ultrasonic image signal for each set sound speed of 1400 m / s to 1650 m / s to the focal position deriving unit 21. The focal position deriving unit 21 transmits the transmission focus No. based on the inputted ultrasonic image signal for each set sound velocity. The depth position of the actual transmission focus corresponding to 1 is derived (step S34).

  Specifically, the focal position deriving unit 21 acquires an image intensity distribution for each line of unit depth surrounded by a broken line in FIG. 9 for the ultrasonic image signal for each set sound speed, and the image for each line. An intensity addition value Σa (k) is derived. In addition, as said unit depth, it is 20 micrometers-50 micrometers, for example. This unit depth is a range narrower than the depth used when obtaining the optimum set sound speed described later. In this way, by using the provisional optimal setting sound speed based on the local narrow range image intensity, the change to the depth can be captured with high accuracy as the optimal setting sound speed not affected by the image intensity at other depths. Can do. In addition, the provisional optimum set sound speed can be obtained in a short time.

  As shown in FIG. 10, the focal position deriving unit 21 acquires the distribution of the added value Σa (k) for each set sound speed from 1400 m / s to 1650 m / s, and the maximum value among the added values Σa (k). And the set sound speed corresponding to the maximum value is acquired as the provisional optimum set sound speed of the subject.

  Then, the focal position deriving unit 21 sequentially changes the unit depth and performs the same processing as described above, thereby obtaining the provisional optimum set sound speed for each unit depth, as shown in the uppermost part of FIG. , Transmission focus No. The distribution of the provisional optimum set sound speed corresponding to 1 (transmission focus f [1]) is acquired.

  Next, the focal position deriving unit 21 obtains the provisional optimum setting sound speed for each unit depth in the distribution of the provisional optimum setting sound speed with respect to the depth as shown in FIG. 11, and varies the provisional optimum setting sound speed with respect to the depth. taking measurement. Specifically, in the distribution of the provisional optimum setting sound speed shown in FIG. 11, for example, a predetermined calculation window is sequentially scanned in the depth direction, and the standard deviation of the provisional optimum setting sound speed in the calculation window is sequentially obtained. In this way, by sequentially obtaining the standard deviation of the provisional optimum set sound speed with respect to the depth direction, the distribution of the standard deviation with respect to the depth direction as shown in FIG. 12 can be obtained. The focal position deriving unit 21 obtains the depth position F1 when the standard deviation of the provisional optimum set sound speed shown in FIG. 1 is acquired as the actual focal position corresponding to 1 (transmission focal point f [1]) (step S34).

  Next, after incrementing the transmission focus number (step S36), the main control unit 30 determines whether or not the transmission focus number is larger than the number of transmissions n derived by the transmission focus control unit 14 ( Step S38). If it is determined that the transmission focus number is smaller than n, the process returns to step S20. By sequentially incrementing the transmission focus number, the transmission focus of the ultrasonic wave transmitted from the ultrasonic probe 10 is the depth position of the transmission focal points f [2] to f [n] set by the transmission focus control unit 14. Are set sequentially. Then, the processes in steps S22 to S34 are performed in the same manner as described above, and the actual focal positions F2 to Fn corresponding to the transmission focal points f [2] to f [n] are acquired in the same manner as described above.

  The effective area deriving unit 22 obtains an effective area corresponding to the actual transmission focal positions F1 to Fn in each transmission focus acquired as described above (step S40). Specifically, the effective range deriving unit 22 calculates the coefficient k from the coefficient α used when deriving the depth position of each of the transmission focal points f [1] to f [n] (k = (α− 1) / (α + 1)). Then, the coefficient k and the focal lengths of the actual transmission focal points F1 to Fn are applied to the above equation (1) to calculate w [i] (i is 1 to n), and double w [i]. Effective regions R1 to Rn corresponding to the actual transmission focal points F1 to Fn are derived (see FIG. 13). The effective area deriving unit 22 supplies information indicating the ranges of the effective areas R1 to Rn determined as described above to the optimum set sound speed deriving unit 24.

  The optimum set sound speed deriving unit 24 derives the optimum set sound speed of the subject at each point in the region of interest designated by the user, based on the input effective areas R1 to Rn (step S42). Specifically, the optimum set sound speed deriving unit 24 determines the transmission focus No. when, for example, a certain point of interest in the region of interest exists at the depth of the effective region R2. 2 is acquired from an image memory provided in the image generation unit 20 for each set sound speed acquired by performing transmission focus corresponding to 2. Then, the optimum set sound speed deriving unit 24 obtains an image intensity distribution having a predetermined line width and depth width around the above-mentioned point of interest for the ultrasonic image signal of each set sound speed, and sets the set sound speed that maximizes the added value. Obtained as the optimum sound speed for that point. In addition, as said predetermined depth width, it is 3 mm-4 mm, for example. The optimum set sound speed deriving unit 24 obtains the optimum set sound speed of each of the plurality of points by performing the above processing at a plurality of points in the region of interest.

  Through the above steps, the optimum set sound speed at each point in the region of interest is derived, and this routine ends.

  The reception control unit 18 calculates the reception delay time at each point based on the optimum sound speed at each point in the region of interest derived as described above, and reads the calculated reception delay time from the reception signal memory 17. A reception focus is performed by giving to the reception signal, and a phasing addition signal is generated. The image generation unit 20 generates an ultrasonic image signal from the phasing addition signal generated based on the optimum set sound speed, and supplies this to the monitor 28. The monitor 28 displays an ultrasonic image corresponding to the ultrasonic image signal supplied from the image generation unit 20.

  As described above, according to the ultrasonic diagnostic apparatus 1 according to the present embodiment, each point for which the optimum set sound speed is to be acquired is extracted from the effective area of the transmission focus, and thus the optimum set sound speed is derived with high accuracy. can do. In addition, since the ultrasonic image is generated using the optimum set sound speed at each point in the region of interest, an ultrasonic image without distortion can be obtained over the entire region of interest.

  In addition, when the transmission focus control unit 14 performs transmission focus at different depth positions in the depth region where the transmission F value changes according to the focal length, Since the depth position of each transmission focal point is set so that the distance between the focal points increases (as the distance increases), the quality of the received signal obtained according to each transmission can be maintained while suppressing the number of ultrasonic transmissions. Is possible.

  In the present embodiment, the optimum set sound speed is acquired using the added value of the image intensity of the ultrasonic image signal for each set sound speed, but the index value for obtaining the optimum set sound speed is the added value. For example, the spatial frequency spectrum of the ultrasonic image signal of the region of interest for each set sound speed may be acquired, and the environmental sound speed may be acquired based on the half width. In order to obtain the optimum set sound speed, a known index value based on the image intensity or the spatial frequency spectrum can be used.

  In this embodiment, every time the transmission focus position is set, the actual focus position with respect to the transmission focus position is acquired. However, the present invention is not limited to this, and all reception signals at each transmission focus position are acquired in advance. After that, the actual focal position for each transmission focal position may be acquired. As described above, the error due to the movement of the subject can be reduced by continuously acquiring the reception signals at the respective transmission focus positions in a short time.

  In addition, it is desirable that the reception signal to be subjected to reception focus is acquired at the time of transmission focus corresponding to the effective range to which the focus belongs, but at the boundary of the effective range, by switching the reception signal to be used Discontinuity occurs. Therefore, for example, for each coordinate, two reception signals acquired at the two transmission focus Nos. That form the transmission focal point sandwiching the coordinates are subjected to reception focus processing with the coordinates as the focal point, and each superordinate is obtained. Sound wave images may be generated and combined by weighting, for example, according to the distance between the reception focal point and two transmission focal points sandwiching it, or the distance between the reception focal point and the effective range.

  As for the method for obtaining the optimum set sound speed, if the actual focus position of each transmission focus is known, the optimum set sound speed can be obtained with high accuracy by other methods as well as the method of the above-described embodiment.

  For example, with respect to the point of interest, two transmission focus numbers forming a transmission focal point sandwiching the point of interest. n, no. As shown in FIG. 14, the reception focus processing based on each set sound velocity is performed on the two reception signals acquired at the time of n + 1 to generate an ultrasound image signal in the range of interest centered on the point of interest. , Index values V1 (n), V2 (n), V3 (n)..., V1 (n + 1), V2 (n + 1), V3 (n + 1). Is calculated. Then, for each set sound speed, as the index value of each depth, the index value of each depth obtained from each of the two ultrasonic images, the distance between that depth and the two transmission focal points, or the depth and its effective range, and .., V1, V2,... Then, an index value obtained by adding the index values of the respective depths within the range of interest may be calculated for each set sound speed and compared to obtain the optimum set sound speed.

  Moreover, you may acquire the optimal setting sound speed with the following method.

  Each transmission focus is performed so as to form a focus at a preset position of the subject under a preset hypothetical sound speed. Therefore, the actual optimum set sound speed of the subject can be acquired from the deviation between the preset position and the actual focal position.

For example, it is assumed that the transmission delay time is set in advance assuming that the assumed sound speed and the focal position are 1540 m / s and 20 mm. When the actual sound speed of the subject is higher than 1540 m / s, the actual focal position formed by the transmission delay time becomes shallower than 20 mm. Also, since the reception time of the reflected wave from the actual focal position is a time obtained by dividing the reciprocating distance to the actual focal position by the actual sound speed, the position converted from this reception time on the assumption of the sound speed of 1540 m / s is It becomes shallower than the actual focal position. Thus, when the actual sound speed of the subject is faster than 1540 m / s, the actual focal position becomes shallower than 20 mm, and the position on the ultrasonic image generated from the received signal becomes even shallower.

  Conversely, when the actual sound speed of the subject is slower than 1540 m / s, the actual focal position becomes deeper than 20 mm, and the position on the ultrasonic image generated from the received signal becomes deeper. By utilizing this fact, the actual sound speed can be acquired from the deviation between the preset focal position and the actual focal position. For example, the actual focal position on the ultrasonic image generated from the reception signal of the reflected wave from the focal point formed by driving each element with the transmission delay time set to 1540 m / s and 30 mm as the assumed sound velocity and the focal position is 27 mm. If this is the case, the actual sound speed can be obtained as follows.

  First, the depth of focus is converted into ultrasonic propagation time. Specifically, since the focal position is 27 mm on the ultrasonic image generated at the assumed sound velocity of 1540 m / s, it is converted into the propagation time [s] at 27 [mm] / 1540000 [mm / s].

Next, the transmission delay of each element is obtained. The transmission delay for forming the transmission focus at a position of 30 mm at 1540 m / s is uniquely determined.

  Then, the ultrasonic propagation time from the focal point to each element is obtained. Specifically, the ultrasonic propagation time from the focal point to each element is acquired based on the ultrasonic propagation time obtained above and the transmission delay of each element.

  Then, the assumed sound speed is set, and the provisional ultrasonic propagation time from the focal point to each element is acquired based on the assumed sound speed. The provisional ultrasonic propagation time and the ultrasonic wave from the focal point obtained above to each element are obtained. The assumed sound speed that minimizes the error from the propagation time is acquired as the actual sound speed.

  By the above-described procedure, about 1620 m / s can be acquired as the actual sound speed (optimum set sound speed). In this method, only the optimum set sound speed at the actual focal position can be acquired. However, the optimum set sound speed at a nearby actual focus position can be assigned to any target point, or can be obtained by interpolation.

DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic apparatus 10 Ultrasonic probe 10a Piezoelectric element 12 Transmission control part 14 Transmission focus control part 16 Reception signal processing part 17 Reception signal memory 18 Reception control part 20 Image generation part 21 Focus position deriving part 22 Effective area deriving part 24 Optimal Set sound speed deriving unit 30 Main control unit 40 Scan input unit

Claims (7)

A plurality of electroacoustic transducers that transmit ultrasonic waves into the subject according to the drive signals and generate reception signals according to the reflected waves of the ultrasonic waves;
Accepting means for accepting designation input of a region of interest in the subject;
The depth position of the transmission focal point in the depth region where the transmission F value changes according to the focal length so that the plurality of transmission focal points are arranged at different depth positions in the region of interest received by the reception unit. Transmission focus control means for deriving the depth position of each of the plurality of transmission focal points so that the focal length increases geometrically as the depth increases.
Drive signal generation means for generating the drive signal so as to form a transmission focus at each of the depth positions derived by the transmission focus control means;
A sound speed deriving means for deriving an estimated value of the sound speed of the region of interest based on a reception signal obtained by performing transmission focus at each of the depth positions derived by the transmission focus control means;
Only including,
The transmission focus control means sets w [i] as a length corresponding to half of an effective area in which a reception signal of a predetermined quality corresponding to an arbitrary transmission focus f [i] is obtained, and the transmission focus f [i]. Where D [i] is the focal length of k, and k is the value corresponding to w [i] / D [i], the value α corresponding to (1 + k) / (1-k) is the common ratio of the geometric series And an ultrasonic diagnostic apparatus that derives the depth position of each of the plurality of transmission focal points so that the effective region is continuous between transmission focal points adjacent to each other . The transmission focus control means is configured to arrange the transmission focal points at equal intervals in a depth region where a transmission F value different from a depth region in which the transmission F value changes according to a focal length is maintained constant. The ultrasonic diagnostic apparatus according to claim 1, wherein a depth position of each of the plurality of transmission focal points is derived. The transmission focus control unit derives the number n of transmission focal points based on a depth in the depth direction of the region of interest received by the reception unit and a coefficient α corresponding to a predetermined common ratio, and a focal length There ultrasonic diagnostic apparatus according to claim 1 or claim 2 derives the respective depth positions of the n number of transmitting focal points corresponding to the number n of transmit focal to increase geometrically. The transmission focus control unit derives a coefficient α corresponding to a common ratio based on a width in the depth direction of the region of interest received by the reception unit and a predetermined number n of transmission focal points, and the coefficient The superposition according to claim 1 or 2, wherein a depth position of each of the n transmission focal points corresponding to the number n of the transmission focal points is derived so that a focal length increases geometrically based on α. Ultrasonic diagnostic equipment. The opening diameter of the electroacoustic transducer is controlled according to the depth position of the transmission focal point of the ultrasonic wave transmitted so that the transmission F value becomes a predetermined value, and the depth position of the transmission focal point of the transmitted ultrasonic wave If There comprising a depth position can not this be the sending F value and the predetermined value, super according to any one of claims 1 to 4 having the further opening diameter control means for setting the maximum value of the opening diameter Ultrasonic diagnostic equipment. Receiving a designated input of a region of interest in the subject;
As the plurality of transmission focal points are arranged at different depth positions in the input region of interest, and the depth position of the transmission focal point becomes deeper in the depth region where the transmission F value changes according to the focal length. Deriving the depth position of each of the plurality of transmit focal points such that the focal length increases geometrically;
Deriving an estimated value of sound speed of the region of interest based on a received signal obtained by performing transmission focus on each of the derived depth positions;
Including
In the step of deriving the depth position of each of the plurality of transmission focal points, a length corresponding to half of an effective region in which a reception signal of a predetermined quality corresponding to an arbitrary transmission focal point f [i] is obtained is represented by w [i ], The focal length of the transmission focal point f [i] is D [i], and the value corresponding to w [i] / D [i] is k, which corresponds to (1 + k) / (1-k). And a sound speed derivation method for deriving the depth position of each of the plurality of transmission focal points so that the effective region is continuous between transmission focal points adjacent to each other . The depth position of the transmission focal point becomes deep in a depth region where the transmission F value changes according to the focal length so that a plurality of transmission focal points are arranged at different depth positions in the region of interest inputted by the computer. Transmission focus control means for deriving the depth position of each of the plurality of transmission focal points so that the focal length increases geometrically according to the predetermined distance corresponding to an arbitrary transmission focal point f [i]. The length corresponding to half of the effective area from which a quality received signal can be obtained is w [i], the focal length of the transmission focal point f [i] is D [i], and w [i] / D [i]. When the corresponding value is k, the value α corresponding to (1 + k) / (1−k) is defined as the common ratio of the geometric series, and the effective area is continuous between the transmission focal points adjacent to each other. A transmitter for deriving the depth position of each of the plurality of transmitter focal points. And the residue control means,
Sound speed deriving means for deriving an estimated value of the sound speed of the region of interest based on a reception signal obtained by performing transmission focus at each of the depth positions derived in the transmission focus control means;
Program to function as.