JP2009056140A - Ultrasonic diagnostic equipment - Google Patents

Abstract

An ultrasonic diagnostic apparatus capable of correcting a position of a virtual image generated by refraction of ultrasonic waves at an interface between a plurality of regions in a subject to an actual position in an ultrasonic image is provided.
The ultrasonic diagnostic apparatus includes: a transmission / reception unit that processes a plurality of reception signals respectively output from a plurality of ultrasonic transducers that have received ultrasonic echoes reflected by a subject; and a plurality of reception signals Receiving focus processing means for generating a sound ray signal along the receiving direction of the ultrasonic wave by performing reception focus processing, and ultrasonic image generating means for generating an image signal representing an ultrasonic image based on the sound ray signal And a positional deviation correction means for correcting, in the image signal, a positional deviation that occurs in the ultrasonic image due to refraction of the ultrasonic waves at the boundary surfaces of the plurality of areas, using sound velocity distributions in the plurality of areas in the subject. .
[Selection] Figure 1

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 / receiving ultrasonic waves to generate an ultrasonic image used for diagnosis.

  In the medical field, various imaging techniques have been developed in order to observe and diagnose 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 uses 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 areas including gynecological system, circulatory system, digestive system, etc. in addition to 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 point 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).

The acoustic impedance is a constant specific to a substance as represented by the following formula (1). Generally, MRayl (mega-rail) is used as the unit, and 1 MRayl = 1 × 10 ⁶ kg · m ^{−. 2} · s ⁻¹ .
Z = ρ · C (1)
Here, ρ represents the density of the acoustic medium, and C represents the speed of sound in the acoustic medium.

Also, the acoustic impedance of the first medium and Z _1, the acoustic impedance of the second medium adjacent the first medium and Z _2, the ultrasound at the interface between the first medium and the second medium The vertical reflectance R is given by the following equation (2).
R = (Z ₂ −Z ₁ ) / (Z ₂ + Z ₁ ) (2)
In general, an ultrasonic image is generated based on the intensity of the ultrasonic wave reflected at each sample point in the subject. However, since the sound speed varies depending on the tissue in the subject, an artifact (virtual image) is generated. Has occurred.

As shown in FIG. 12, when a region having a slow sound speed value (for example, a fat layer) and a region having a fast sound speed value (for example, a muscle layer) are present in the subject, an ultrasonic probe is used. Since the sound ray of the ultrasonic wave transmitted and received by 10 is refracted at the boundary surface between these regions, the position of the object T in the subject is displayed shifted in the ultrasonic image. In FIG. 12, the broken line indicates the actual sound ray path and the object T, and the solid line indicates the sound ray path and the object F on the ultrasonic image. For example, when the sound velocity value of the fat layer is 1470 m / s, the sound velocity value of the muscle layer is 1550 m / s, and the boundary surface is horizontal and smooth, the incident angle θ _I from the fat layer to the boundary surface is Since the sound ray incident at 45 ° is emitted from the boundary surface to the muscle layer at an emission angle θ _T = 48 °, the ultrasonic image of the object located at a depth of 5 cm from the boundary surface is 0. A shift of 5 cm is expected.

  As a related technique, Patent Document 1 discloses an ultrasonic tissue diagnostic apparatus that can easily distinguish between a lesion site and a normal site and can diagnose a living tissue with high diagnostic efficiency. The ultrasonic tissue diagnostic apparatus includes an ultrasonic transducer array in which a plurality of ultrasonic transducers are arranged, and a plurality of adjacent first transducers connected to each transducer of the ultrasonic transducer array and used for transmission. A switch unit that switches between transmitting and receiving a transducer group and a second transducer group that is used for reception at a predetermined distance from the first transducer group, and a predetermined direction from the first transducer group A transmission unit that supplies a drive pulse having a time difference to each transducer of the first transducer group so that an ultrasonic wave is transmitted, and a propagation that measures a propagation time from this ultrasonic transmission to reception Move the central position of at least one of the time measurement unit, the calculation unit that calculates the sound speed based on the data obtained from the propagation time measurement unit, and the first transducer group and the second transducer group To obtain a one-dimensional or two-dimensional characteristic diagram of sound speed. And means for displaying images. However, Patent Document 1 does not particularly disclose generation of an ultrasonic image using the calculated sound speed.

Patent Document 2 discloses an ultrasonic imaging apparatus capable of setting a delay time in consideration of the influence of ultrasonic refraction by the lens layer of an ultrasonic probe and / or a fat layer of a living body. The ultrasonic imaging apparatus includes an ultrasonic probe including an array transducer and each transducer for performing transmission focusing or reception focusing when transmitting and / or receiving ultrasonic waves to a subject. A delay time for performing transmission focusing or reception focusing by incorporating a delay control means for controlling a delay time with respect to an ultrasonic wave and a refraction effect of an ultrasonic wave by an ultrasonic wave propagation medium between the array transducer and a set focal position Is generated and supplied to the delay control means, and a display unit for displaying the ultrasonic image is provided. Patent Document 2 discloses that transmission focusing or receiving focusing is performed by incorporating a refraction effect of ultrasonic waves by controlling a delay time for each transducer, but the signal processing is complicated. The time also becomes longer.
JP 61-290942 A (page 1-2, FIG. 3) WO 01/26555 pamphlet (page 32, Fig. 1)

  Accordingly, in view of the above points, the present invention provides an ultrasonic diagnostic apparatus capable of correcting the position of a virtual image generated by ultrasonic refraction at the boundary surfaces of a plurality of regions in a subject to an actual position in an ultrasonic image. The purpose is to provide.

  In order to solve the above-described problem, an ultrasonic diagnostic apparatus according to one aspect of the present invention supplies a plurality of drive signals to a plurality of ultrasonic transducers to transmit ultrasonic waves to the subject and reflects them by the subject. A transmission / reception unit that processes a plurality of reception signals respectively output from a plurality of ultrasonic transducers that have received the received ultrasonic echo, and a reception focus process on the plurality of reception signals output from the transmission / reception unit A reception focus processing unit that generates a sound ray signal along a sound wave reception direction; and an ultrasonic image generation unit that generates an image signal representing an ultrasonic image based on the sound ray signal generated by the reception focus processing unit. Using the sound velocity distribution in a plurality of regions in the subject, the ultrasonic image is generated by refraction of the ultrasonic waves at the boundary surfaces of the plurality of regions. ; And a positional deviation correcting means for correcting the location shift in the image signal.

  According to the present invention, by using the sound velocity distribution in a plurality of regions in the subject, the positional deviation caused in the ultrasound image due to the refraction of the ultrasound at the boundary surface of the plurality of regions is corrected in the image signal. The position of the virtual image generated by the refraction of the image can be corrected to the actual position in the ultrasonic image.

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, propagation time measurement unit 24, sound speed distribution calculation unit 25, sound speed map generation unit 26, B-mode image generation unit 27, misregistration correction unit 28, image The display control unit 29, the D / A converter 30, the display unit 31, the console 32, the control unit 33, and the storage unit 34 are included.

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

  Each ultrasonic transducer is, for example, a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate) or a polymer piezoelectric element represented by PVDF (polyvinylidene difluoride). It is constituted by a vibrator in which electrodes are formed at both ends of a piezoelectric material (piezoelectric body). When a voltage is applied to the electrodes of such a vibrator by sending a pulsed or continuous wave electric signal, 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 combining the 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 a predetermined 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 transmits the plurality of drive signals to the ultrasonic probe 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. 10 or a plurality of drive signals are supplied to the ultrasound probe 10 so that the ultrasonic waves transmitted from the plurality of ultrasound 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 a predetermined pattern from a 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 based on the pattern. The reception focus process is performed by adding a delay to a plurality of reception signals. By this reception focus processing, a sound ray signal in which the focus of the ultrasonic echo is narrowed is formed.

  The controller 33 controls each unit so as to obtain the ultrasonic velocity distribution in the subject before performing the imaging operation. First, in order to measure the propagation time of the ultrasonic wave in the subject, the ultrasonic beam is sequentially transmitted to a plurality of positions in the subject and the ultrasonic echo is received under the control of the scanning control unit 11. Is done. Based on the delay time set by the transmission control unit 13 and the sound ray signal generated by the reception control unit 23, the propagation time measurement unit 24 transmits the ultrasonic wave at each position in the subject after being transmitted. The propagation time until the reflected ultrasonic echo is received is measured. The propagation time is measured as follows, for example.

  FIG. 2 is a diagram for explaining a method for measuring propagation time according to an embodiment of the present invention. Here, to simplify the description, it is assumed that the ultrasonic probe 10 includes ten ultrasonic transducers 10a at positions A1 to A10. The scanning control unit 11 shown in FIG. 1 sets a point P1 existing in the first region of the subject as a focal point, and accordingly, the transmission control unit 13 drives the ultrasonic transducer 10a at the positions A1 to A3. The delay time given to each signal is set.

  The drive signal generation unit 14 generates a plurality of drive signals according to the delay time set by the transmission control unit 13, and supplies these drive signals to the ultrasonic transducer 10a at the positions A1 to A3. Thereby, the ultrasonic wave transmitted from the ultrasonic transducer 10a at the positions A1 to A3 forms an ultrasonic beam (sound ray) whose focus is narrowed down at the point P1 at the transmission angle θ1.

  The ultrasonic beam is partially reflected at the point P1, and the ultrasonic echo is incident on the plural ultrasonic transducers 10a centering on the ultrasonic transducer 10a at the position A6 at the reception angle θ1. The reception control unit 23 performs reception focus processing by adding a delay to a plurality of reception signals based on the reception angle θ <b> 1 set by the scanning control unit 11. By this reception focus processing, a sound ray signal with a focused focus at the point P1 is formed. The propagation time measuring unit 24 measures the propagation time T1 from when the ultrasonic wave is transmitted at the position A2 until the ultrasonic echo reflected at the point P1 is received at the position A6.

Assuming that the distance between the position A2 and the position A6 is Y1, the distance L1 that the ultrasonic wave has propagated is obtained according to the following equation (3).
L1 = Y1 / sin θ1 (3)
The sound speed distribution calculation unit 25 calculates the sound speed C1 in the first region of the subject based on the propagation time T1 measured by the propagation time measurement unit 24 according to the following equation (4).
C1 = L1 / T1 (4)

  In this way, sound speeds at a plurality of positions in the subject are obtained while shifting the focus position. Since the sound speed is almost the same in the region where the density ρ is the same, if the sound speed obtained at the new position changes by more than a predetermined ratio from the sound speed obtained previously, the sound speed is different in the region (organization). You can see that you have overcome the boundary. Thereby, the sound velocity distribution calculation unit 25 can detect the boundary surfaces of a plurality of regions in the subject and obtain the depth D1 of the first region.

  A point P2 shown in FIG. 2 exists in a second region different from the first region. The scanning control unit 11 shown in FIG. 1 sets a point P2 existing in the second region of the subject as a focal point, and accordingly, the transmission control unit 13 drives the ultrasonic transducer 10a at the positions A1 to A3. The delay time given to each signal is set. Thereby, the ultrasonic wave transmitted from the ultrasonic transducer 10a at the positions A1 to A3 forms an ultrasonic beam (sound ray) whose focus is narrowed at the point P2 at the transmission angle θ2.

  The ultrasonic beam is partially reflected at the point P2, and the ultrasonic echo is incident on the plural ultrasonic transducers 10a centering on the ultrasonic transducer 10a at the position A9 at the reception angle θ2. The reception control unit 23 performs reception focus processing by adding a delay to a plurality of reception signals based on the reception angle θ2 set by the scanning control unit 11. By this reception focus processing, a sound ray signal with a focused focus at point P2 is formed. The propagation time measuring unit 24 measures the propagation time T2 from when the ultrasonic wave is transmitted at the position A2 until the ultrasonic echo reflected at the point P2 is received at the position A9.

When the distance between the position A2 and the position A9 is Y2, the distance L2 that the ultrasonic wave has propagated is obtained according to the following equation (5).
L2 = Y2 / sin θ2 (5)
Here, the distance L2 through which the ultrasonic wave has propagated is the sum of the distance 2 · D1 / cos θ2 through which the ultrasonic wave has propagated in the first area and the distance through which the ultrasonic wave has propagated in the second area. (6) is established.
T2 = (2 · D1 / cos θ2) / C1 + (L2-2 · D1 / cos θ2) / C2
... (6)
The sound speed distribution calculating unit 25 calculates the sound speed C2 in the second region based on the propagation time T2 measured by the propagation time measuring unit 24 according to the equation (6).

  However, when the transmission angle θ2 is not zero, since the ultrasonic wave is refracted at the boundary surface between the first region and the second region, an error also occurs in the value of the sound velocity C2 obtained according to the equation (6). . Therefore, when obtaining the value of the sound speed C2 more accurately, the sound ray path may be corrected using the value of the sound speed C2 obtained once, and then the value of the sound speed C2 may be obtained again. The value of the sound speed C2 may be converged by repeating.

  In the same manner, sound velocity values in the third region and the like are obtained, and as a result, sound velocity distributions in a plurality of regions in the subject are calculated. The sound speed map creating unit 26 shown in FIG. 1 generates an image signal representing a sound speed map for displaying sound speed distributions in a plurality of regions in the subject based on the sound speed distribution calculated by the sound speed distribution calculating unit 25. .

  Alternatively, the sound velocity distribution in the subject may be obtained by a method different from the above. For example, the control unit 33 estimates several sound velocity values in the first region located on the most surface layer in the subject, sets a point existing in the first region as a focal point, and transmits / receives ultrasonic waves. Control each part to do. The reception control unit 23 forms a sound ray signal by performing reception focus processing using each sound velocity value. The control unit 33 determines the focus accuracy in the ultrasonic image generated by the B-mode image generation unit 27 based on the sound ray signal, whereby the optimum sound speed value in the first region can be obtained. By performing such an operation on a plurality of points, the range of the first region having the same sound speed value is recognized.

  When the optimum sound speed value in the first area is obtained, the control unit 33 estimates several sound speed values in the second area located in the deep layer adjacent to the first area, and within the second area. Each part is controlled so as to perform transmission / reception of an ultrasonic wave by setting a point existing in the point as a focus. The reception control unit 23 forms a sound ray signal by performing reception focus processing using the optimum sound speed value in the first region and the sound speed value in the second region. The control unit 33 determines the focus accuracy in the ultrasonic image generated by the B-mode image generation unit 27 based on the sound ray signal, whereby the optimum sound speed value in the second region can be obtained. In the same manner, sound velocity values in the third region and the like are obtained, and as a result, sound velocity distributions in a plurality of regions in the subject are calculated.

  The actually measured sound speed distribution is quite complex, so it is difficult to create a sound speed map with high accuracy. Even if it is possible to create a complex sound speed map with high accuracy, Computation becomes complicated and processing time becomes long. Therefore, it is desirable to create a model that simplifies the sound speed distribution by simplifying the actually measured sound speed distribution. In the following, the case of creating a model in which the sound velocity distribution in the subject is divided into two layers will be described with reference to FIG. 1 and FIG.

  FIG. 3 is a diagram for explaining a process of creating a model in which the sound velocity distribution in the subject is divided into two layers. FIG. 3A shows a sound speed distribution (sound speed map) obtained based on the propagation time measured by the propagation time measuring unit 24. The sound speed distribution calculation unit 25 obtains the sound speed distribution shown in FIG. 3A by performing a smoothing process on the sound speed distribution shown in FIG. The smoothing process is performed, for example, by performing a two-dimensional low-pass filter process on a multi-value signal (for example, 8-bit data) representing the measured sound speed distribution.

  Next, the sound speed distribution calculation unit 25 obtains the sound speed distribution shown in FIG. 3C by performing threshold processing on the sound speed distribution shown in FIG. As the threshold processing, binarization processing using one threshold and multi-value processing using a plurality of thresholds are applicable. Here, binarization processing is performed. Further, the sound velocity distribution calculation unit 25 performs region connection processing on the sound velocity distribution shown in FIG. 3C, thereby integrating the regions in the subject into two regions, and FIG. Is obtained. In the region connection process, the area of each region in the sound velocity distribution is calculated, and the region having a small area is connected to the region having a large area.

  Referring to FIG. 1 again, when the sound velocity distribution in the subject is obtained, the control unit 33 controls each unit to start an imaging operation for generating an ultrasound image. Thereby, transmission / reception of ultrasonic waves is performed, and the B-mode image generation unit 27 generates a B-mode image signal that is tomographic image information related to the tissue in the subject based on the sound ray signal formed by the reception control unit 23. Generate. The B-mode image generation unit 27 includes an STC (sensitivity time control) unit 27a, a comprehensive line detection unit 27b, and a DSC (digital scan converter) 27c.

  The STC unit 27a corrects the attenuation by the distance according to the depth of the reflection position of the ultrasonic wave on the sound ray signal formed by the reception control unit 23. The envelope detector 27b generates an envelope signal by performing an envelope detection process on the sound ray signal corrected in the STC unit 27a. The DSC 27c converts the envelope signal generated by the envelope detector 27b into an image signal according to 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.

  The position shift correction unit 28 uses the sound speed distribution calculated by the sound speed distribution calculation unit 25 to generate a position shift that occurs in an ultrasonic image (B-mode image) due to refraction of ultrasonic waves at the boundary surfaces of a plurality of regions in the subject. Are corrected in the B-mode image signal generated by the B-mode image generation unit 27.

  FIG. 4 is a diagram for explaining a method for correcting misalignment occurring in an ultrasonic image. As an example, it is assumed that the subject includes a fat layer having a sound velocity value C1 and a biological layer having a sound velocity value C2 (C2> C1). In FIG. 4, the actual sound ray path and the object T are indicated by broken lines, and the sound ray path and the object F on the ultrasonic image are indicated by solid lines.

First, the positional deviation correction unit 28 extracts a boundary line between the fat layer and the biological layer based on the sound speed distribution calculated by the sound speed distribution calculation unit 25, and the boundary with respect to the transmission / reception surface of the ultrasound probe 10. The angle θ _S of the line is obtained, and the sound incident on the boundary line from the fat layer according to the following equation (7) from the angle θ _{P of the} ultrasonic beam (sound ray) transmitted from the ultrasonic probe 10 determining the incident angle theta _I lines.
θ _I = θ _P + θ _S (7)

Next, the positional deviation correcting unit 28, according to Snell's law represented by the following formula (8), determine the emission angle theta _T sound ray emitted to the living body layer from the boundary line.
(Sin θ _I ) / C1 = (sin θ _T ) / C2 (8)

When the intersection of the boundary line and the sound ray is Q, the positional deviation correction unit 28 determines the position of the object F (vector QF) on the ultrasonic image according to the following equation (9) as the actual position of the object T ( Vector QT). Here, R (θ _T −θ _I ) represents a tensor used for vector conversion.

  Thereby, in FIG. 4, in the fat layer positioned above the boundary line, the B-mode image signal generated by the B-mode image generation unit 27 is used as it is, and the biological layer positioned below the boundary line In the B-mode image signal generated by the B-mode image generation unit 27, a positional shift caused by ultrasonic refraction is corrected.

  Referring again to FIG. 1, the image display control unit 29 includes an ultrasonic image based on the B mode image signal generated by the B mode image generation unit 27 and a sound speed map based on the image signal generated by the sound speed map generation unit 26. And at least one of the ultrasonic images based on the image signal corrected by the misalignment correction unit 28, a display image signal is generated.

  The D / A converter 30 converts the digital image signal output from the image display control unit 29 into an analog image signal. The display unit 31 includes, for example, a display device such as a CRT or LCD, and displays a diagnostic image based on an analog image signal.

  The control unit 33 controls the scanning control unit 11, the propagation time measurement unit 24 to the image display control unit 29, and the like according to the operation of the operator using the console 32. In the embodiment, the scanning control unit 11, the transmission control unit 13, the reception control unit 23 to the image display control unit 29, and the control unit 33 are configured by a CPU and software (program). You may comprise with an analog circuit. Software (program) is stored in the storage unit 34. As a recording medium in the storage unit 34, a flexible disk, MO, MT, RAM, CD-ROM, or DVD-ROM can be used in addition to the built-in hard disk.

  In the above description, the case where the sound speed in the subject is obtained by measurement has been described. However, the operator (diagnostic) may use the console 32 to set boundaries and sound speed values of regions having different sound speeds. good.

  FIG. 5 is a diagram illustrating an example of an ultrasonic image displayed on the display unit. The operator operates a mouse or the like while viewing an ultrasonic image based on the B-mode image signal generated by the B-mode image generation unit 27 shown in FIG. In addition, the sound speed of region 1 and the sound speed of region 2 can be set. The misregistration correction unit 28 uses the sound velocity distribution set by the operator to correct the misregistration in the ultrasonic image due to the refraction of the ultrasonic waves at the boundary surfaces of the plurality of regions in the subject in the B-mode image signal.

  FIG. 6 is a diagram illustrating another example of the ultrasonic image displayed on the display unit. The sound speed distribution calculated by the sound speed distribution calculating unit 25 shown in FIG. 1 is not limited to the layer structure as shown in FIG. 4, and may have various shapes. In FIG. 6, a layer having a slow sound velocity value (for example, a fat layer), a layer having a fast sound velocity value (for example, a biological layer), and a portion having a fast sound velocity value in the fat layer (for example, a rectus abdominis muscle) are shown. Has been. Even in such a case, the positional deviation correction unit 28 uses the sound speed distribution calculated by the sound speed distribution calculation unit 25 or the sound speed distribution set by the operator on the boundary surfaces of a plurality of regions in the subject. It is possible to correct a positional shift that occurs in an ultrasonic image due to refraction of ultrasonic waves.

Next, processing such as interpolation of the B-mode image signal performed by the misalignment correction unit 28 will be described.
FIG. 7 is a diagram illustrating an example in which a region in which the density of sound rays decreases due to refraction of ultrasonic waves at a boundary surface between a plurality of regions in a subject is generated. As shown in FIG. 7, when there is a slow sound velocity value layer (for example, a fat layer) and a fast sound velocity value layer (for example, a biological layer) in the subject, the sound rays are refracted by refraction of ultrasonic waves. A region where the density decreases is generated.

In such a case, the misregistration correction unit 28 uses, for example, the following formula ( _B) using the luminance value D _A of the pixel A on the first sound ray and the luminance value D _B of the pixel B on the second sound ray. The luminance value D _X of the pixel X between the first sound ray and the second sound ray is interpolated by performing weighted addition according to 10).
D _X = (L _B D _A + L _A D _B ) / (L _A + L _B ) (10)
Here, L _A represents the distance between the pixel A and the pixel X, and L _B represents the distance between the pixel B and the pixel X. Furthermore, in order to simplify the calculation, one of the luminance values of the pixel A and the pixel B may be used as the luminance value D _X of the pixel X. For example, the luminance value of the pixel closer to the pixel X out of the pixels A and B is used as the luminance value D _X of the pixel X.

Alternatively, by setting the density ρ1 of the fat layer having the slow sound velocity value C1 and the density ρ2 of the biological layer having the fast sound velocity value C2, the acoustic impedance of these layers can be obtained according to the equations (11) and (12). .
Z1 = ρ1 · C1 (11)
Z2 = ρ2 · C2 (12)
Furthermore, the incident angles of the first and second sound rays that enter the boundary surface from the fat layer are θ1 _I and θ2 _I , respectively, and the emission angles of the first and second sound rays that are emitted from the boundary surface to the biological layer are Assuming that θ1 _T and θ2 _T respectively, the transmittance T1 of the first sound ray and the transmittance T2 of the second sound ray are obtained according to the equations (13) and (14).
The positional deviation correction unit 28 uses these transmittances to perform weighted addition according to the following equation (15), whereby the luminance value D _X of the pixel X between the first sound ray and the second sound ray is obtained. Is interpolated.
D _X = (T1 · D _A + T2 · D _B ) / (T1 + T2) (15)

  FIG. 8 is a diagram illustrating an example in which a plurality of sound rays intersect due to refraction of ultrasonic waves at the boundary surfaces of a plurality of regions in the subject. As shown in FIG. 8, when there are a layer having a slow sound velocity value (for example, a fat layer) and a portion having a fast sound velocity value (for example, a rectus abdominis muscle) in the subject, a plurality of refractions are caused by ultrasonic refraction. There are cases where sound rays intersect.

In such a case, the positional deviation correction unit 28 uses, for example, the following formula (16) by using the luminance value D _A of the pixel on the first sound ray and the luminance value D _B of the pixel on the second sound ray. The luminance value D _X of the pixel X at which a plurality of sound rays intersect is obtained by performing weighted addition according to.
D _X = (mD _A + nD _B ) / (m + n) (16)
Here, the values of m and n are determined based on, for example, the average value of the luminance values of the plurality of pixels on the first sound ray and the average value of the luminance values of the plurality of pixels on the second sound ray. The Further calculations To simplify, one of the luminance values of the pixels on the pixel and the second sound ray on the first sound ray may be used as a luminance value D _X of the pixel X. For example, among the first sound line and the second sound rays, the luminance value of the sound rays of the pixels of the smaller incidence angle at the time of entering the rectus abdominis muscle, used as a luminance value D _X of the pixel X It is done.

  Alternatively, the misregistration correction unit 28 sets the density ρ1 of the fat layer having the slow sound velocity value C1 and the density ρ2 of the living body layer having the fast sound velocity value C2, so that a plurality of sounds are obtained according to the equations (11) to (15). A luminance value of a pixel at a position where a plurality of sound rays intersect in the subject may be obtained by weighted addition of luminance values of a plurality of pixels corresponding to the line.

Next, with respect to a method for smoothly connecting ultrasonic images at the boundary between the regions when correcting a positional shift generated in the ultrasonic image due to refraction of the ultrasonic waves at the boundary surfaces of the plurality of regions in the subject, FIG. A description will be given with reference to FIG.
FIG. 9 is a diagram for explaining a method for smoothly connecting ultrasonic images at boundaries between a plurality of regions. As an example, it is assumed that the subject includes a layer having a slow sound velocity value (for example, a fat layer) and a layer having a fast sound velocity value (for example, a biological layer). In FIG. 9, the actual sound ray path and the objects T1 and T2 are indicated by broken lines, and the sound ray path and the objects F1 and F2 on the ultrasonic image are indicated by solid lines.

  The position shift correction unit 28 rotates the image in a predetermined region (region of several wavelengths to several tens of wavelengths) in the vicinity of the refraction point of the emission side portion where the sound ray is refracted from the boundary surface to the living body layer. The closer the angle θ is to the refraction point, the closer to zero. For example, the rotation angle θ is reduced to θ, 3θ / 4, θ / 2, θ / 4, and 0 as it is closer to the refraction point. In FIG. 9, if the rotation angles calculated for the objects T1 and T2 are θ1 and θ2, the rotation angle θ2 is used as it is for the object T2, and the rotation angle θ1 is used instead of the rotation angle θ1 for the object T1. / 2 is used. As a result, even if the accuracy of the sound velocity map is low and an error occurs in the correction of the ultrasonic image, the ultrasonic image can appear naturally at the boundaries between the plurality of regions.

  Further, the positional deviation correction unit 28 may correct the positional deviation generated in the ultrasonic image due to the difference in the acoustic velocity in the plurality of regions in the B-mode image signal using the sound velocity distribution in the plurality of regions in the subject. good. This will be described with reference to FIG.

  In FIG. 4, it is assumed that the subject includes a fat layer having a sound velocity value of C1 and a biological layer having a sound velocity value of C2 (C2> C1), and the actual sound ray path and the object T are broken lines. The sound ray path on the ultrasonic image and the object F are indicated by solid lines.

On the upper side of the boundary line between the fat layer and the living body layer, the positional deviation generated in the ultrasonic image due to the difference in sound speed is corrected according to the following equation (17).

Further, on the lower side of the boundary line between the fat layer and the living body layer, the positional deviation generated in the ultrasonic image due to the difference in sound speed is corrected according to the following equation (18).
In the above, as C0, generally used sound speed in the living body (1530 m / s or 1540 m / s) is used.

  Further, the sound speed map creating unit 26 shown in FIG. 1 uses the sound speed distribution in a plurality of areas in the subject to detect a positional shift that occurs in the sound speed map due to the difference in sound speed in the plurality of areas in the image signal representing the sound speed map. You may make it correct | amend.

Next, an example of an image displayed on the display unit 31 illustrated in FIG. 1 will be described.
FIG. 10 is a diagram illustrating a first example of an image displayed on the display unit. In FIG. 10, the display unit 31 includes a B mode image (refractive index correction off) 31 a based on the B mode image signal generated by the B mode image generation unit 27 and the image signal generated by the sound velocity map generation unit 26. A sound speed map 31b based on the image and a B-mode image (refractive index correction on) 31c based on the image signal corrected by the positional deviation correction unit 28 are displayed.

  FIG. 11 is a diagram illustrating a second example of an image displayed on the display unit. The positional deviation correction unit 28 may generate an image signal in which the ultrasonic refraction direction is displayed in the B-mode image generated by the B-mode image generation unit 27. Further, the sound speed map creating unit 26 may generate an image signal in which the refraction direction of the ultrasonic wave is displayed in the sound speed map. In FIG. 11, the B-mode image (refractive index correction off) 31d and the sound velocity map 31e generated in this way are displayed together with the B-mode image (refractive index correction on) 31c.

  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.

1 is a block diagram illustrating a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. It is a figure for demonstrating the measuring method of the propagation time in one Embodiment of this invention. It is a figure for demonstrating the process of producing the model which made the sound velocity distribution in a subject into 2 layers. It is a figure for demonstrating the correction method of the position shift which arises in an ultrasonic image. It is a figure which shows an example of the ultrasonic image displayed on a display part. It is a figure which shows another example of the ultrasonic image displayed on a display part. It is a figure which shows the example which the area | region where the density of a sound ray falls by the refraction | bending of the ultrasonic wave in the interface of the several area | region in a subject generate | occur | produces. It is a figure which shows the example which a some sound ray cross | intersects by the refraction | bending of the ultrasonic wave in the interface of the some area | region in a subject. It is a figure for demonstrating the method of connecting an ultrasonic image smoothly in the boundary of a some area | region. It is a figure which shows the 1st example of the image displayed on a display part. It is a figure which shows the 2nd example of the image displayed on a display part. It is a figure for demonstrating the refraction | bending of the ultrasonic wave in the interface of the several area | region in a subject.

Explanation of symbols

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 unit 24 Propagation time measurement unit 25 Sound velocity distribution calculation unit 26 Sound velocity map creation unit 27 B-mode image generation unit 27a STC unit 27b Envelope detection unit 27c DSC
28 Position shift correction unit 29 Image display control unit 30 D / A converter 31 Display unit 32 Console 33 Control unit 34 Storage unit

Claims (11)

A plurality of drive signals are respectively supplied to the plurality of ultrasonic transducers to transmit ultrasonic waves to the subject, and a plurality of output signals are output from the plurality of ultrasonic transducers that have received the ultrasonic echoes reflected by the subject. A transceiver for processing the received signal;
Reception focus processing means for generating a sound ray signal along the reception direction of the ultrasonic wave by performing reception focus processing on a plurality of reception signals output from the transmission / reception unit;
Ultrasonic image generating means for generating an image signal representing an ultrasonic image based on the sound ray signal generated by the reception focus processing means;
A positional deviation correction unit that corrects a positional deviation generated in an ultrasonic image due to refraction of ultrasonic waves at a boundary surface of the plurality of areas in an image signal using sound velocity distributions in a plurality of areas in the subject;
An ultrasonic diagnostic apparatus comprising: Based on the sound ray signal generated by the reception focus processing means, a propagation time measuring means for measuring a propagation time from when an ultrasonic wave is transmitted until an ultrasonic echo is received;
A sound speed distribution calculating means for calculating a sound speed distribution in a plurality of regions in the subject based on the propagation time measured by the propagation time measuring means;
The ultrasonic diagnostic apparatus according to claim 1, further comprising:   The sound speed distribution calculating means obtains a second sound speed distribution by performing a smoothing process on the first sound speed distribution obtained based on the propagation time measured by the propagation time measuring means, thereby obtaining a second sound speed. 3. The sound velocity distribution in the plurality of regions is calculated by obtaining a third sound velocity distribution by performing threshold processing on the distribution, and performing region connection processing on the third sound velocity distribution. Ultrasonic diagnostic equipment.   The ultrasonic diagnostic apparatus according to claim 3, wherein the sound velocity distribution calculating unit integrates the region in the subject into two regions.   The said position shift correction | amendment means interpolates an image signal in the area | region where the density of a sound ray falls by the refraction of an ultrasonic wave in the boundary surface of the some area | region in a subject. Ultrasonic diagnostic equipment.   The position shift correction means obtains the value of an image signal related to a position where a plurality of sound rays intersect in a subject by weighting and adding the value of a plurality of image signals corresponding to the plurality of sound rays. The ultrasonic diagnostic apparatus according to any one of 1 to 5.   The position shift correction unit corrects a position shift generated in an ultrasonic image due to a difference in sound speed in the plurality of regions in an image signal using sound velocity distribution in the plurality of regions in the subject. The ultrasonic diagnostic apparatus of any one of Claims.   The sound speed map creating means for generating an image signal representing a sound speed map for displaying the sound speed distribution in a plurality of regions in the subject based on the sound speed distribution calculated by the sound speed distribution calculating means. The ultrasonic diagnostic apparatus according to any one of 2 to 4.   Based on the sound speed distribution calculated by the sound speed distribution calculating means, the sound speed map creating means corrects a positional shift that occurs in the sound speed map due to differences in sound speed in a plurality of regions in the subject in an image signal representing the sound speed map. The ultrasonic diagnostic apparatus according to claim 8.   The misregistration correction unit generates an image signal in which an ultrasonic refraction direction is displayed in the ultrasonic image generated by the ultrasonic image generation unit, and / or the sound speed map generation unit includes a sound speed map. The ultrasonic diagnostic apparatus according to claim 8 or 9, which generates an image signal displaying a refraction direction of ultrasonic waves.   An ultrasonic image based on the image signal generated by the ultrasonic image generation means, a sound speed map based on the image signal generated by the sound speed map generation means, and an ultrasonic wave based on the image signal corrected by the positional deviation correction means. The ultrasonic diagnostic apparatus according to claim 8, further comprising image display control means for selectively displaying at least one of the sound wave images on the display unit.