JP5371344B2 - Ultrasonic diagnostic method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To judge the properties of a tissue utilizing differences in characteristics of changes in microscopic structures, continued surfaces, linear objects and in the amplitudes and phases of speckles when assumed sound velocities in the generation of images are varied. <P>SOLUTION: An ultrasonic diagnostic apparatus has an ultrasonic wave probe in which a plurality of elements is so arrayed as to transmit ultrasonic waves to a subject while outputting received signals by receiving ultrasonic wave signals reflected from the subject and a property judging means which judges the properties of tissues within the subject from changes in the phase of the signals in the orientation of the elements as focused from the received signals with a delay based on the assumed sound velocities when the assumed sound velocities preset for the actual sound velocities of the ultrasonic waves transmitted to the subject are different from the actual sound velocities. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an ultrasonic diagnostic method and apparatus, and more particularly, to an ultrasonic diagnostic method and apparatus for determining the size, shape, and properties of a reflector based on amplitude / phase characteristics depending on the assumed sound speed at the time of image generation.

  Conventionally, a tomographic image of a subject is obtained using ultrasonic waves and used for medical diagnosis. However, in ultrasonic image processing, microstructures, continuous surfaces, and speckles are detected. There are known techniques for emphasizing or suppressing.

  For example, by extracting a specific signal using the statistical properties of the intensity or amplitude information of an echo signal generated from a subject region, a minute structure is extracted and cirrhosis or a minute abnormal lesion is detected (for example, In addition, the dispersion value for each direction of the echo data is obtained for each of a plurality of reference directions that intersect at the target coordinates and spread three-dimensionally, and further calculate the dispersion value from the plurality of dispersion values for each direction. That extract the surface of the tissue by obtaining the boundary value by using (for example, see Patent Document 2), and an adaptive spatial filter that filters image parameter data to smooth the final ultrasonic image A micro structure, a continuous surface, or speckle is distinguished from the difference in amplitude information value or shape, such as an ultrasound imaging system (see, for example, Patent Document 3). Surgery is known.

  Further, by reading out a plurality of consecutive frames of image data from the memory unit of the ultrasound body of the ultrasound diagnostic apparatus in parallel and statistically processing the plurality of image data, it is determined whether the target image data is speckle noise. Is known (see, for example, Patent Document 4).

Furthermore, in an ultrasound imaging system, a coherent signal that is a phase-matched addition with a time delay that forms a received beam and a non-coherent signal that is a signal that is phase-matched and added with a time delay that does not form a received beam. It is known that the similarity is determined based on whether or not the signal ratio is equal to or greater than a certain threshold, and speckle reduction is performed by suppressing the coherent signal when it is determined that they are similar (see, for example, Patent Document 5) ).
JP 2003-61964 A Japanese Patent Laid-Open No. 7-8487 JP 2000-300561 A JP-A-9-94248 Special Table 2002-534184

  However, for example, in the case of distinguishing from the difference in value and shape of the amplitude information, the echo reflected at the tissue boundary is weak and interferes with the speckle, resulting in discontinuity, or between the microstructure signal and the speckle. There is a problem that they cannot be distinguished when the amplitudes are comparable. In addition, even if focusing on how the amplitude value changes between the frames described above, in the case of a minute structure or a continuous surface that is interrupted, it is not detected continuously between frames, so it is distinguished from the way the speckle changes. There is a problem that is difficult.

Further, the above-mentioned coherent imaging system has a problem that it is difficult to distinguish between a microstructure signal and a continuous surface signal in a coherent signal, although it is possible to distinguish between a coherent signal and a non-coherent signal.

  The present invention has been made in view of such circumstances, and shows differences in amplitude / phase change characteristics of microstructures, continuous surfaces, linear objects, and speckles when the assumed sound speed at the time of image generation is changed. An object of the present invention is to provide an ultrasonic diagnostic method and apparatus that can be used to determine tissue properties.

  In order to achieve the object, the invention according to claim 1 transmits an ultrasonic wave toward the subject and outputs a reception signal by receiving an ultrasonic signal reflected from the subject. When the assumed sound speed set in advance with respect to the actual sound speed of the ultrasonic probe in which a plurality of elements are arranged and the ultrasonic wave transmitted to the subject is different from the actual sound speed, the assumption is made from the received signal. There is provided an ultrasonic diagnostic apparatus comprising: property determining means for determining a tissue property in the subject from a phase change in the arrangement direction of the elements of a signal focused with a delay based on the speed of sound.

  As a result, it is possible to determine the tissue properties by utilizing the phase unevenness characteristic peculiar to the microstructure.

According to a second aspect of the present invention, the property determination means uses a plurality of frames.

According to a third aspect of the present invention, the property determining means uses a signal generated by changing a plurality of the assumed sound speeds from one transmission.

Moreover, as shown in Claim 4, it is an ultrasonic diagnostic apparatus in any one of Claims 1-3 , Comprising: The image in which the determination result by the said property determination means was reflected is displayed individually or in multiple numbers It has the display means to do.

Further, as shown in claim 5 , the ultrasonic diagnostic apparatus according to claim 4 , further comprising means for generating an amplitude image from the ultrasonic signal, wherein the display means displays the determination result. The reflected image and the amplitude image are displayed as they are or in different colors, superimposed or arranged, and displayed alone or in plural.

According to a sixth aspect of the present invention, the display unit modulates the luminance and color of the amplitude image in accordance with an image in which the determination result is reflected, and displays the single or plural images. .

Moreover, as shown in claim 7 , in the ultrasonic diagnostic apparatus according to any one of claims 4 to 6 , the display mode of the display unit is set to a normal display mode and a plurality of images are overlapped or It is characterized by having a mode switching means for switching between display modes that display side by side or display alone or in a plurality.

  As described above, the display unit is provided and various display methods are performed, thereby making it easier to determine the minute structure, the continuous surface, or the speckle.

Similarly, in order to achieve the object, the invention according to claim 8 transmits an ultrasonic wave from an ultrasonic probe in which a plurality of elements are arranged toward the subject and reflects the ultrasonic wave from the examiner. When the assumed sound speed set in advance with respect to the actual sound speed of the ultrasound transmitted to the subject is different from the actual sound speed, the received signal is based on the assumed sound speed. There is provided an ultrasonic diagnostic method characterized in that a tissue property in the subject is determined from a phase change in an arrangement direction of the elements of a signal focused by delay.

  This makes it possible to determine tissue properties that could not be determined in the past.

  As described above, according to the present invention, it is possible to determine a tissue property using a phase unevenness characteristic peculiar to a microstructure, and it is possible to determine a tissue property that is difficult to determine with a single sound velocity amplitude image. It becomes possible.

  Hereinafter, an ultrasonic diagnostic method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  The present invention determines tissue properties using phase change characteristics when the sound speed of an ultrasonic wave when acquiring an ultrasonic image is changed.

  It should be noted that, in acquiring the ultrasonic image by changing a plurality of ultrasonic sound speeds in increments of a predetermined amount, in the following embodiments, the ultrasonic sound speeds to be changed a plurality are changed with respect to the optimal ultrasonic sound speed (optimal sound speed). This is called the assumed sound speed.

  In the present invention, the tissue properties are determined using the fact that the amplitude / phase change characteristics of the microstructure signal, the continuous surface / line signal, and the speckle signal are different when the assumed sound speed is changed.

  Specifically, the amplitude / phase change characteristics will be described in detail later, but in brief, they are as follows.

  First, in the case of a micro structure, when the assumed sound speed is lower (slower) than the optimum sound speed (actual sound speed), the phase changes upward (convex) in the scanning direction (the direction in which the transducers of the ultrasonic probe are arranged). However, the slope becomes steeper as the assumed sound speed is closer to the optimum sound speed, and if the assumed sound speed is greater (faster) than the optimum sound speed, the phase changes downward in the scan direction (concave), and the slope is optimum. The closer to the speed of sound, the steeper. Further, the amplitude becomes larger and the shape becomes steeper as the assumed sound speed is closer to the optimum sound speed.

  In the case of a continuous surface / line, the phase is uniform regardless of the assumed sound speed, and the amplitude increases as the sound speed approaches the optimum sound speed.

  In the case of speckle, the amplitude and phase change randomly depending on the assumed sound speed.

  In the following embodiment, determination of a microstructure, a continuous surface / line, and speckle is performed based on these facts.

  FIG. 1 is a system configuration diagram showing a schematic configuration of an embodiment of an ultrasonic diagnostic apparatus according to the present invention.

  As shown in FIG. 1, the ultrasound diagnostic apparatus 1 captures and displays an ultrasound image of a diagnosis part of a subject using ultrasound, and includes an ultrasound probe 10, a transmission / reception unit 12, and scanning control. Unit 14, AD conversion unit 16, image generation unit 18, shape / property determination image generation unit 20, display image generation unit 22, monitor 24, and mode switching means 26.

  The ultrasonic probe 10 transmits ultrasonic waves toward a diagnosis site in the body of the subject and receives ultrasonic waves reflected in the body. The ultrasonic probe 10 of the present embodiment includes a plurality of ultrasonic transducers constituting a one-dimensional ultrasonic transducer array, and each ultrasonic transducer is a vibration in which electrodes are formed at both ends of a piezoelectric element such as PZT, for example. Consists of children. This electrode is connected to the transmitting / receiving unit 12 by a signal line. When a voltage is applied to each electrode, the vibrator generates ultrasonic waves. Further, when the transducer receives the reflected ultrasonic wave, it generates an electrical signal, which is output as a received signal.

  The transmission / reception unit 12 applies an ultrasonic transmission signal to the ultrasonic probe 10 to generate an ultrasonic wave from the vibrator, and transmits the ultrasonic wave based on the delay given from the scanning control unit 14. Then, the reflected ultrasonic waves are received and the reception signals of the respective elements output from the ultrasonic probe 10 are amplified as they are (without receiving focus).

  The AD conversion unit 16 receives an ultrasonic reception signal from the transmission / reception unit 12, performs AD conversion, and passes it to the image generation unit 18. The image generation unit 18 stores the reception data received from the AD conversion unit 16. As will be described in detail later, the image generation unit 18 converts the stored reception data of each element into variously set sound speeds (actual sound speeds (actual sound speeds) transmitted to the subject as described above. On the other hand, reception is focused with a delay based on the assumed sound speed, and RF data based on each assumed sound speed is generated.

  The shape / property determination image generation unit 20 generates images for determining microstructures, speckles, and boundaries from images (RF data) generated at various sound speeds (assumed sound speeds).

  The display image generation unit 22 generates a display image to be displayed on the monitor 24 based on the determination result based on the image generated by the image generation unit 18 and the determination image generated by the shape / characteristic determination image generation unit 20. Is. The mode switching means 26 is for switching the display mode of the image on the monitor 24.

  In this embodiment, when an image is reconstructed from received data, a microstructure, a continuous surface / line, and a speckle are determined using phase change characteristics when the assumed sound speed with respect to the actual sound speed is variously changed. However, before describing the operation of the ultrasonic diagnostic apparatus 1, the phase change characteristic when the assumed sound speed is changed will be described.

  2 to 9 are graphs showing the phase change characteristics when the assumed sound speed is changed.

  Each graph shows the phase change characteristic when the assumed sound speed is changed from 1400 [m / s] to 1620 [m / s] in steps of 40 [m / s] or 20 [m / s]. In the scan direction (X position) and the vertical axis as the phase.

  FIG. 2 is a graph showing the phase change characteristic depending on the assumed sound speed of the microstructure signal at the assumed sound speed of 1400 [m / s] to 1500 [m / s], and FIG. 3 is the assumed sound speed of 1500 [m / s]. It is a graph which shows the phase change characteristic depending on the assumed sound speed of the microstructure signal in ˜1620 [m / s].

  In the case of FIG. 2 where the assumed sound speed is 1400 [m / s] to 1500 [m / s], the graph of the assumed sound speed 1500 [m / s] has a positive slope in the vicinity of the X position 100 to 120. The graphs in which the assumed sound speed is smaller than 1500 [m / s] (that is, the assumed sound speed is slower) are all lower right, and the inclination is steeper as the assumed sound speed is closer to 1500 [m / s]. The inclination becomes gentler as the sound speed becomes slower than 1500 [m / s].

  Further, in the case of FIG. 3 in which the assumed sound speed is 1500 [m / s] to 1620 [m / s], the graphs are all rising to the right in the vicinity of the X positions 100 to 120. The inclination is the largest when the assumed sound speed is 1500 [m / s], and the inclination becomes gentler as the assumed sound speed becomes larger than 1500 [m / s].

  The shape of such a graph of FIG.2 and FIG.3 is considered to show that the micro structure exists in X position 100-120 vicinity.

  FIG. 4 is a graph showing the phase change characteristic depending on the assumed sound speed of the surface signal at the assumed sound speed of 1400 [m / s] to 1480 [m / s], and FIG. 5 is the assumed sound speed of 1540 [m / s] to 1620. It is a graph which shows the phase change characteristic depending on the assumed sound speed of the surface signal in [m / s].

  As can be seen from FIGS. 4 and 5, the phase does not change much even if the assumed sound speed is changed in the vicinity of the X positions 100 to 130 and 150 to 180. This is considered to indicate that a surface (continuous surface) exists in the portion.

  FIG. 6 is a graph showing the phase change characteristic depending on the assumed sound speed of speckle at the assumed sound speed of 1400 [m / s] to 1480 [m / s], and FIG. 7 is the assumed sound speed of 1540 [m / s] to 1620. It is a graph which shows the phase change characteristic depending on the assumed sound speed of the speckle in [m / s]. As shown in FIGS. 6 and 7, in the case of speckle, the phase changes randomly when the assumed sound speed is changed.

  FIG. 8 is a graph showing the amplitude change characteristic depending on the assumed sound speed of the microstructure at an assumed sound speed of 1400 [m / s] to 1500 [m / s], and FIG. 9 is an assumed sound speed of 1500 [m / s]. It is a graph which shows the amplitude change characteristic by the assumed sound speed of the microstructure signal in 1620 [m / s].

  As can be seen from FIGS. 8 and 9, the graphs showing the change in the amplitude of the microstructure are both mountain-shaped (convex upward) graphs having a peak (maximum value) near the X position 110, and an assumed sound speed 1500. The amplitude value is maximum at [m / s], and the maximum amplitude value increases as the assumed sound speed approaches 1500 [m / s], and the shape is steep.

  Next, the reason why the phase change of the microstructure when the assumed sound speed is changed has the characteristics shown in the graphs of FIGS.

In FIG. 10, it is assumed that the ultrasonic wave reflected from the point A (0, z ₀ ) at the sound velocity V ₀ is observed by the element (vibrator) at the position X in the ultrasonic probe 10 at the time t after reflection. Then, this time t is calculated as the following equation (1).

t = sqrt (z ₀ ² + X ² ) / V ₀ (1)
In Equation (1), sqrt () means taking the square root of the value in ().

  Further, in FIG. 10, it is assumed that the ultrasonic wave reflected from the point A ′ (x, z) at the sound velocity V is observed at the time t after reflection by the element (vibrator) at the position X in the ultrasonic probe 10. . Similar to the above, this time t is expressed by the following equation (2).

t = sqrt {z ² + (X−x) ² } / V ... (2)
The trajectory of the point A ′ when the curves given by the equations (1) and (2) touch each other in the (X, t) plane is given by the following equation (3).

z ² = x ² × {V ² / (V ₀ ² −V ² )} + z ₀ ² V ² / V ₀ ² (3)
Point A ′ indicates a position where the signal becomes stronger when the phase is matched and added as the assumed sound speed V with respect to the optimum sound speed (actual sound speed).

From equation (3), the locus of the point A ′ (x, z) is an ellipse centered on the origin when V> V ₀ , and a hyperbola centered on the origin when V <V ₀ . In the B-mode image, since the downward direction of the z-axis is upward, the elliptical locus centered on the origin when V> V ₀ is concave, and the hyperbola centered on the origin when V <V ₀ is used. The locus is convex.

FIG. 11 shows a state where the curves given by the equations (1) and (2) are in contact with each other on the (X, t) plane. FIG. 11A shows the case of V <V ₀ , the solid line J shows the reflected wave from the point A, and the broken line H1 shows the reflected wave from the point A ′ when it is on the right side of the z axis as shown in FIG. Represents. A broken line H2 represents a reflected wave from a point on the left side of the z axis in FIG. Since V <V ₀ at this time, the reflected wave from the point A ′ has a larger time t for the same X position, and therefore the broken line H1 (H2) appears above the solid line J.

FIG. 11B shows a case where V = V ₀ , and FIG. 11C shows a case where V> V ₀ . When V approaches V ₀ , the broken line H approaches the solid line J, and when V = V ₀ , the broken line H coincides with the solid line J. In the case of FIG. 11C, the broken line appears on the lower side of the solid line, contrary to FIG.

  From these figures, it can be intuitively understood that the locus of the point A ′ (x, z) where the broken line touches the solid line has the tendency as described above.

  In the model described here, the observed reflected wave is simply a line. However, in reality, the waveform has a width in the t direction and there is a difference in intensity in the X direction. There is a need to. Moreover, in this model, for the sake of simplicity, reflection from point A and point A ′ is performed simultaneously, but actually, it is necessary to consider the time from when an ultrasonic wave is transmitted to each point to reflection. There is.

  Next, the operation of the image generation unit 18 in the apparatus configuration of FIG. 1 will be described along the flowchart of FIG.

  The image generator 18 generates an image from data obtained at various sound speeds by changing the assumed sound speed.

  First, in step S100 in FIG. 12, the initial value of the assumed sound speed to be changed in various ways is set. This value is not particularly limited and may be determined as appropriate. For example, it may be determined as 1400 [m / s] as in the example of FIG.

  A signal is sent from the transmission / reception unit 12 controlled by the scanning control unit 14 to the ultrasonic probe 10 based on the set initial value, and data based on the assumed initial sound velocity value is acquired and sent to the image generation unit 18.

  Next, in step S110, the assumed sound speed is changed by a predetermined amount by one step, and ultrasonic data based on the changed assumed sound speed is acquired. The predetermined amount of one step is not particularly limited, and may be 40 [m / s], 10 [m / s], 20 [m / s], as in the example of FIG. The assumed sound speed is changed by a fixed amount.

  Next, in step S120, the obtained hypothetical sound speed data are added with their phases matched to generate RF (Radio Frequency) data. This RF data includes both amplitude information and phase information. In this way, RF data is created with images at all assumed sound speeds.

In step S130, it is determined whether or not image generation has been completed. If it has not been completed, the process returns to step S110, and the assumed sound speed is changed by one step and image generation is continued. The end of image generation is determined by whether or not the processing for all assumed sound velocities has been completed. For example, it may be determined in advance by determining in advance how many steps the assumed sound velocity is to be terminated and counting the number of times.

  Next, the operation of the shape / property determination image generation unit 20 will be described.

  FIG. 13 is a flowchart illustrating a process of generating a determination image for determining a minute structure in the shape / characteristic determination image generation unit 20.

  First, in step S200 of FIG. 13, an optimum sound speed value is set. The method for setting the optimum sound speed value is not particularly limited. For example, a known method for determining from the contrast, sharpness, and spatial frequency of the image obtained by the image generation unit 18 (for example, Japanese Patent Laid-Open No. 8-317926). (See the Gazette), or may be specified by the user.

  Next, in step S210, an initial value of the assumed sound speed is set. However, it is only necessary to use data already obtained by the processing in the image generation unit 18. Next, in step S220, the value of each pixel of the determination image is initialized to zero. Next, in step S230, the assumed sound speed is changed by one step, and data at the sound speed is acquired. Data obtained by the processing in the image generation unit 18 may also be used.

Next, in step S240, a secondary differential value in the phase scan direction is calculated from the data at the assumed sound velocity. The scan direction coincides with the arrangement direction of the transducers (elements) of the ultrasonic probe 10.

  Next, in step S250, the secondary differential value is integrated with a kernel of a predetermined size to calculate an integral value. The size of the kernel is not particularly limited, and 9 × 4, 16 × 8, or the like is used depending on the resolution.

  In step S260, the assumed sound speed is compared with the optimum sound speed. If the assumed sound speed is greater than the optimum sound speed, the process proceeds to step S280, and the integrated value is added to the determination image as it is. In step S260, if the assumed sound speed is smaller than the optimum sound speed, the sign of the integral value is reversed in the next step S270, and then the integral value reversed in step S280 is added to the determination image.

  In step S290, it is determined whether or not the processing for all the assumed sound velocities has been completed and the generation of the determination image has been completed. If not yet completed, the process returns to step S230 to return the data for the next assumed sound speed. Perform the process.

  In this way, a determination image is created by adding the value obtained by integrating the secondary differential values for all assumed sound velocities to the determination image initially set to 0. In the case of a minute structure, the second derivative value is positive when the assumed sound speed is faster than the optimum sound speed, and the second derivative value is negative when the assumed sound speed is slower than the optimum sound speed. When the second derivative is integrated with a predetermined kernel, the signal is strong only at the microstructure. Accordingly, the determination image generated by adding these is an image in which a signal is strong only at the minute structure, and it is determined that the image is a minute structure.

  As shown in FIGS. 2 to 9, when the second-order differential value in the scan direction in the kernel is speckle, it is random, 0 for a continuous surface, and the assumed sound speed is optimum for a micro structure. If it is larger, the value is positive, and if the assumed sound speed is smaller than the optimum sound speed, it has a negative value. Therefore, only the fine structure is increased by integration.

  In the above-described example, a plurality of assumed sound velocities are variously changed, but only one type of assumed sound speed may be used.

  In the above example, when the assumed sound speed is smaller (slower) than the optimum sound speed, the sign is inverted because the sign is inverted, but the optimum sound speed and the assumed sound speed are not reversed. You may make it take an absolute value, without comparing.

  Alternatively, an assumed sound speed that is slower than a predetermined value or faster than a predetermined value may be used without setting the optimum sound speed.

  Further, in the vicinity of the optimum sound speed, the region showing the characteristic phase change becomes small, and it may be inaccurate to determine whether the assumed sound speed is faster or slower than the optimum sound speed. Therefore, instead of explicitly setting the optimum sound speed, it is possible to use only an assumed sound speed that is slower than a predetermined speed or only an assumed sound speed that is faster than a predetermined speed. Further, as described above, since the region showing the characteristic phase change becomes small near the optimum sound speed, the size of the kernel used for integration may be made smaller as the sound speed is closer to the optimum sound speed.

  In the flowchart shown in FIG. 13, when the assumed sound speed is faster than the optimum sound speed, the second derivative is positive, the phase change in the scanning direction is concave, and when the assumed sound speed is slower than the optimum sound speed, the second derivative is obtained. In consideration of the fact that the value is negative and the phase change in the scanning direction is convex, the sign is inverted when the secondary differential value is negative, but the phase change characteristic when the assumed sound speed changes In order to make better use of the above, for example, a value obtained by the following method may be added to the determination image.

  FIG. 14 shows a method of adding the difference values of the secondary differential values in the determination of the minute structure.

  In FIG. 14, the upper row shows the case where the assumed sound speed (1) and the assumed sound speeds (2-1) and (2-2) are both faster than the optimum sound speed, and the lower row shows the assumed sound speed (1) and the assumed sound speed (2 -1) and (2-2) are both slower than the optimum sound speed.

  In particular, as shown in the upper part of FIG. 14, when the assumed sound speed is higher than the optimum sound speed, the lower the sound speed in the order of the assumed sound speeds (1), (2-1), and (2-2), The shape of the phase change is convex downward and steep, the slope of the graph of the primary differential value also rises to the right, and the numerical value of the secondary differential value becomes positive and larger.

  As shown in the lower part of FIG. 14, when the assumed sound speed is slower than the optimum sound speed, the phase in the scanning direction increases as the sound speed increases in the order of the assumed sound speeds (1), (2-1), and (2-2). The shape of the change is convex upward and becomes steep, the slope of the graph of the first derivative value becomes steep when it falls to the right, and the numerical value of the second derivative value is negative and smaller (the absolute value is larger).

  Then, when a certain assumed sound speed (1) is faster than the optimum sound speed, the assumed sound speed (2) that is slower than the assumed sound speed (1) and faster than the optimum sound speed (assumed sound speed (2-1) or (2-2) in FIG. 14). The value obtained by subtracting the value of the assumed sound velocity (1) from the second-order differential value in the phase scan direction is positive (see the rightmost diagram in FIG. 14). Therefore, a difference value from the assumed sound speed (1) is calculated for all assumed sound speeds (2) satisfying the above conditions. Next, for each difference value of the assumed sound speed (2), an integral value in a kernel of a predetermined size is calculated.

  When the assumed sound speed (1) is slower than the optimum sound speed, a value obtained by subtracting the second order differential values at all assumed sound speeds (2) faster than the assumed sound speed (1) and later than the optimum sound speed from the value of the assumed sound speed (1). Integrate with the kernel.

  The difference value of the secondary differential value at various hypothetical sound speeds is random in the case of speckle and 0 in the case of a continuous surface, and thus becomes large only in the case of a minute structure, as described above. Thus, a high SN image is obtained from the determination image obtained at the same time. Here, in the vicinity of the optimum sound speed, the scan direction width of the phase unevenness change is small, so that it may not be used or may be used with a limited width.

  Since all the difference values are positive values, SN is improved accordingly. Further, the detection capability is improved by adding the difference values after adding the absolute values. This is because the absolute value is added in consideration of whether the phase change characteristic is convex upward or convex downward, whereas adding the difference value makes each convex This is because information on the shape that the convex shape or the inclination is different is included when the assumed sound speed is different.

  Although the secondary differential value in the case of speckle is random, it can take a large value, and the secondary differential value in the case of a microstructure has a tendency to a small value. This shows that the speckle integral value can be large. Therefore, an integral value of only a sign may be used.

  In the example shown above, the second-order differential value in the scan direction continuously takes positive and negative values as a method for determining the phase change when the scan direction phase unevenness characteristic and the assumed sound speed are changed, which are characteristic of the microstructure. In addition to this, a method of quantifying the uniformity such as dispersion and inclination of the secondary differential value is also possible.

  Alternatively, a method may be used in which a concavo-convex filter corresponding to the difference between the optimum sound speed and the assumed sound speed is prepared in advance, and the correlation is extracted with respect to the phase or waveform image.

  Further, by using the amplitude change characteristics as shown in FIGS. 8 and 9 together, it is possible to obtain a higher SN image. A method similar to the phase can be used as a method of using the amplitude change characteristic in which the convex shape becomes steeper as the optimum sound speed is approached. That is, when a certain assumed sound speed (1) is faster than the optimum sound speed, a value obtained by subtracting from the assumed sound speed (1) the second-order differential value in the amplitude scan direction at the assumed sound speed (2) that is slower than the assumed sound speed (1) and equal to or higher than the optimum sound speed. Therefore, the difference value from the assumed sound speed (1) is calculated for all the assumed sound speeds (2) satisfying this condition, and the integral value is calculated using a kernel of a predetermined size. When the assumed sound speed (1) is slower than the optimum sound speed, a value obtained by subtracting the second order differential values at all assumed sound speeds (2) faster than the assumed sound speed (1) and below the optimum sound speed from the value of the assumed sound speed (1). Integrate with the kernel.

  The amplitude change depending on the assumed sound speed of speckle is random, and since it does not have a convex shape in the case of a continuous surface, only the minute structure has a large value, and the added determination image has a higher SN.

  As a method of using the characteristic of increasing the amplitude value, there is a method of taking the difference between the amplitudes of the assumed sound velocities and integrating. Similarly to the case of using the phase, only the sign may be integrated.

  FIG. 15 shows an example of a result obtained by comparing the ratio between the microstructure and the speckle standard deviation as the SN ratio in the amplitude image and the determination image obtained above.

  In FIG. 15, the horizontal axis represents the number of pixels in the element direction (scan direction), which is the transducer array direction of the ultrasonic probe, and the vertical axis represents the SN ratio. The greater the number of pixels on the horizontal axis, the higher the horizontal resolution. In FIG. 15, D1 and D2 are determination images, and A1 and A2 are amplitude images.

  In the case of an amplitude image, a constant S / N ratio is shown regardless of the resolution in the scan direction, whereas the determination image increases as the resolution in the scan direction increases and becomes about 1.5 times the amplitude image. I understand that. For example, the shape / property determination image generation unit 20 uses high-resolution phase information in the scan direction so that the resolution of the phase information in the scan direction is greater than or equal to the element interval. It shows that the characteristic phase unevenness change and the random phase change of speckle can be more accurately distinguished, and an SN ratio higher than the amplitude value can be obtained.

  In the example described above, the determination image is generated from a single frame. However, a plurality of frames may be used.

  FIG. 16 shows a comparison of the S / N ratio between the amplitude image after averaging of a plurality of frames and the determination image.

  In FIG. 16, D is a determination image, and A is an amplitude image. FIG. 16 shows the result of scanning the average S / N ratio with ± 16 frames used (32 frames in total) to change the frame interval. The wider the frame interval on the horizontal axis, the larger the decimation number. It is shown that.

  It can be seen from the graph of FIG. 16 that if the frame interval is wide, the SN ratio of the determination image and the amplitude image is about the same, but if it is narrow, the difference becomes large and is about 1.3 times. In other words, there is a characteristic that the change in speckle with respect to the microstructure signal is larger than the amplitude change, and by using a plurality of frames having a high frame rate, a determination image having a higher SN than the amplitude image can be obtained. Show.

  Recent software-based ultrasonic apparatuses have received signals as digital data. For example, the shape / characteristic determination image generation unit 20 uses received data obtained from the same transmission (one transmission) to perform various types of data. It has become possible to generate images at the assumed sound speed. Also, analog bases have been able to do the same with high-performance circuit configurations.

  The apparatus configuration in this embodiment is useful for the following two reasons. The first point is that RF data at various assumed sound speeds can be obtained without inter-frame shift, and therefore, the use of the subtle features shown in the microstructure signal graph (see FIGS. 2 and 3) is adversely affected. There is nothing. The second point is that a plurality of frames can be used under the high frame rate conditions described above.

  In addition to the method of using multiple frames simply by averaging multiple frames of judgment images or adding the integration value at the same position kernel in multiple frames to the judgment image, the range of variance and change of the integral values in multiple frames Various methods can be considered for evaluating the difference between changes in the microstructure signal and speckle, such as inclination.

  Here, the phase change characteristic of the minute structure is expressed by a change in unevenness in the scanning direction, but it can also be expressed as a phase change depending on the assumed sound speed at the same position, and either characteristic may be used for the determination method.

  FIG. 17 is a flowchart showing a process of generating a determination image for speckle determination in the shape / characteristic determination image generation unit 20.

  First, in step S300, an initial value of the assumed sound speed is set, and a determination image is initialized in the next step S310. In the next step S320, the assumed sound speed is changed by one step. This side is the same as the first step in FIG.

  Next, in step S330, the absolute value of the difference from the phase of the assumed sound velocity one step before in the same pixel is calculated.

  In step S340, the calculated value is added to the determination image. This operation is performed for all assumed sound velocities, and when it is determined in step S350 that the generation of the determination image has been completed, the process ends.

  This is a difference value with the phase at the same pixel of the assumed sound speed adjacent in the same pixel, and when the absolute value is added together, it becomes smaller as the phase change is smaller, but in the case of speckle, Since the phase randomly changes between the same pixels between the assumed sound velocities, the sum of the absolute values becomes a large value, so that speckle can be determined. In the case of a continuous surface, since it continues with the same value all the more uniformly, the difference becomes a small value.

  As can be seen from a comparison between FIGS. 2, 3 and 4, 5 and FIGS. 6 and 7, the phase change when the speculative sound speed of speckle is changed is larger than that of a microstructure or a continuous surface signal. Therefore, in the determination image obtained by the processing of the flowchart of FIG. 17, the center or continuous surface of the minute structure has a small value, and the speckle has a large value. Therefore, if a difference from the determination image obtained by the processing according to the flowchart of FIG. 13 is taken, only the continuous surface can be extracted. Thereby, a continuous surface can be determined.

  Similar results can be obtained by using a differential value in the scanning direction instead of the phase.

  Further, the value is not limited to the absolute difference value, and may be any amount that can evaluate uniformity, such as variance, a difference between the maximum value and the minimum value, and a slope.

  Also, as in the case of microstructure determination, the change in phase uniformity due to speckle assumed sound speed with respect to the signal at the center of the microstructure and the continuous surface signal has characteristics that are larger than the amplitude change, and has a high frame rate. By using such a plurality of frames, it is possible to obtain a determination image having a higher SN than the amplitude image by utilizing this characteristic.

  FIG. 18 is a flowchart showing the processing contents in the display image generation unit 22.

  First, in step S400 of FIG. 18, an amplitude image at the optimum sound speed is acquired. That is, RF data at a plurality of assumed sound speeds generated by the image generation unit 18 is acquired, and an amplitude image is generated therefrom. The method for generating the display image from the RF data is not particularly limited. For example, general envelope detection may be used for each RF data, or the RF data is divided into amplitude information and phase information. If it is, the amplitude may be taken, or if the RF data is divided into IQ forms, the square root of the sum of the square of I and the square of Q may be taken, and a method corresponding to the data format is taken. Use it.

  Next, in step S410, a microstructure, continuous surface, and speckle determination image is acquired from the shape / characteristic determination image generation unit 20. Then, in the next step S420, based on the determination image, the microstructure and the continuous surface of the amplitude image are emphasized or speckle is suppressed.

  Next, in step S430, the result is logarithmically compressed, gain / DR (dynamic range) / STC (depth weighting) / gray map adjustment, and scan-converted to generate a display image.

  In addition, the display mode of the display image includes a mode in which the amplitude image and the determination image are displayed side by side as described above, and other display modes, which are switched by the mode switching unit 26.

  The mode switching unit 26 may display the display image by superimposing the image reflecting the determination result and the amplitude image in different colors, displaying them side by side, or displaying them alone. Or a plurality of them may be displayed. In addition, the mode switching unit 26 may modulate the luminance and color of the amplitude image according to the determination result, and display a single image or plural images.

  As described above, according to the present embodiment, when the amplitude is the same and the shape is similar, it is possible to distinguish between the minute structure and the continuous surface and speckle that cannot be distinguished by the prior art, As a result, it is possible to extract microstructures, extract tissue boundaries and needles, and reduce speckles with a higher SN than in the prior art.

  In the embodiment described above, the case where the transducer array of the ultrasonic probe is one-dimensional has been described, but the present invention is of course applicable to the case where it is two-dimensional. In the two-dimensional case, since the phase-matching addition is performed based on the two-dimensional position of the vibrator, the microstructure signal shows a two-dimensional phase uneven surface with a varying slope depending on the assumed sound velocity, The signal shows a curved surface with a two-dimensional uniform phase, the continuous line signal shows a uniform phase in the direction along the line, a phase unevenness change in the direction perpendicular to the line, and the speckle is two-dimensional. Shows a random phase change.

  For example, by integrating the phase second-order differential values in the two-dimensional scan directions, it is possible to extract a microstructure with better SN than in the case of the one-dimensional case.

  Further, in the above-described embodiment, only the case where one type of RF data is used for the transmission / reception frequency of the ultrasonic wave has been described. However, the present invention is also applicable to the case where RF data having a plurality of different frequencies such as a fundamental wave and a harmonic wave is used. include. For example, the microstructure signal shows the same phase unevenness change in the scan direction even if the frequency is different, but the speckle is a result of interference. A high SN image can be obtained by adding different judgment images.

  In the embodiment described above, the microstructure, continuous surface / line, and speckle are determined using the phase change characteristic when the sound speed of the ultrasonic wave when acquiring the ultrasonic image is changed. However, an example in which the tissue property is determined using the phase unevenness change will be described below.

  19 to 21 are conceptual diagrams illustrating the principle of determining tissue properties.

  FIG. 19A shows the phase of an ultrasonic signal from the parenchyma of a normal liver as a waveform, and the right direction in the figure is the scanning direction. As described above, the change in the scan direction phase of the normal speckle in the normal liver is random, and the speckle is very uniform. FIG. 19B is a histogram of phase unevenness values corresponding to this. Here, the phase unevenness value is a value obtained by quantifying the phase unevenness shape, and is obtained by adding the second derivative values of the phase unevenness (accurately, obtained by integration). In the case of normal liver, speckles change randomly, so that the histogram has a substantially normal distribution as shown in FIG.

  FIG. 20A shows the phase of the ultrasonic signal from the isolated point as a waveform, and the scan direction phase change has a minute convex shape (in this case convex downward). On the other hand, when a histogram is taken, the phase unevenness value corresponding to this is isolated and displayed as shown in FIG.

  FIG. 21A shows the phase of the ultrasonic signal from the lesioned liver parenchyma mixed with the fiber as a waveform. As shown in FIG. 21 (a), in this case, a convex shape 30 is locally seen therein. FIG. 21B is a histogram of phase unevenness values corresponding to this. In this case, since the convex shape 30 (isolated point) is included locally, the phase unevenness value corresponding to this isolated point appears, so that it does not become a normal distribution, and is shown surrounded by a broken line in the figure. The histogram is biased to one side.

  Accordingly, it is possible to determine the tissue property of whether the liver is normal or lesioned by seeing the uneven distribution of the phase unevenness value.

  Therefore, in the example described below, tissue properties are determined using the difference in amplitude / phase change characteristics of microstructures, continuous surfaces / lines, and speckles when the assumed sound speed at the time of image generation is changed. More specifically, a locally strong echo due to fiber or calcification in speckles of a homogeneous medium such as liver parenchyma or breast is analyzed.

  Hereinafter, an example in which the tissue property is determined based on the amplitude / phase characteristics depending on the assumed sound speed at the time of image generation will be described.

  FIG. 22 is a flowchart illustrating a first example of determining tissue properties.

  First, in step S500 of FIG. 22, the user sets an ROI (Region Of Interest, target area). Next, in step S510, the phase unevenness change in the scan direction is quantified in the ROI. This is obtained by integrating the secondary differential values of the phase irregularities. Next, in step S520, the histogram is taken and the mixing ratio of the minute structure in the speckle is determined from the distribution bias.

  Here, as a method for quantifying the phase unevenness, an example in which the secondary differential value of the phase unevenness is integrated is given as an example, but the numerical expression of the phase unevenness is not limited to this. For example, a predetermined uneven pattern for extracting phase unevenness may be prepared in advance, a correlation with the uneven pattern may be obtained, and the correlation value may be used. Alternatively, waveform addition along an unevenness obtained by adding waveforms of RF data including phase and amplitude at different timings may be used.

  In addition, as a method for evaluating the distribution bias for determining the mixing ratio of the microstructure in the speckle, for example, the average of the maximum value and the minimum value of the phase unevenness may be taken, or the difference between the absolute values may be taken. May be. Alternatively, for example, a method of evaluating with the difference between the average of the lowest 10 and the average of the highest 10 or the average or the difference between the absolute values can be considered.

  By evaluating the distribution deviation in this way, the mixing ratio of the microstructures and the like in the speckle is determined from the distribution deviation.

  Next, a second example of determining tissue properties will be described using the flowchart of FIG.

  The method shown in FIG. 23 is based on whether or not the phase changes when the assumed sound speed is changed, not by looking at the phase unevenness.

  First, in step S600 of FIG. 23, the ROI is set similarly to the example of FIG. Next, in step S610, the sum of the absolute values of the phase differences of the assumed sound velocities is calculated for each pixel in the ROI. In this method, the phase values at the same pixel in an ultrasonic image at each assumed sound speed are calculated for each assumed sound speed, and the absolute values are added.

  At this time, the sum is small if the phase is constant regardless of the assumed sound speed, and conversely, if the phase changes greatly, the sum of absolute values becomes large.

  Therefore, in the next step S620, the mixing ratio of other signals in the speckle is determined from the bias of the sum of the phase differences. Here, the other signal means that not only the minute structure but also a signal other than speckle such as a continuous surface signal is included.

  If the signal is an intrinsic signal other than speckle, the phase is constant and the phase change is small even if the assumed sound speed is changed, even if it is a micro structure or a continuous surface. Whether it is included or not can be determined. That is, in this example, the tissue property is determined by utilizing the difference in phase change characteristics based on the assumed sound speed of the microstructure or continuous surface signal and the speckle signal.

  Here, the sum of the absolute values of the phase differences is taken as a numerical value for determining whether or not the phase has changed, but the numerical value is not limited to this.

  For example, any amount can be used as long as the phase uniformity can be evaluated, such as dispersion, a difference between maximum and minimum values, or a slope. In addition to taking the sum of the absolute values of the changing phase differences, it is possible to evaluate by changing the variance, the maximum change, the difference between the maximum and minimum values, and the changing slope. Also, stability is better when the phase difference in the scan direction or the phase difference in the distance direction is used instead of simply using the phase.

  In addition, the evaluation of the deviation of the phase difference can be performed using the minimum value of the distribution, the average of a predetermined number, the ratio or difference between the minimum value and the average value, and the like.

  In the above, we have explained the method of structural property analysis using the phase unevenness change of microstructures or using the difference in phase change characteristics due to the assumed sound speed of microstructures / continuous surfaces and speckles. The tissue property analysis used can be considered similarly. In other words, when the assumed sound speed is changed, the characteristics of microstructures and continuous surfaces that increase in amplitude and the characteristics of microstructures that become steep are digitized, and the tissue properties can be judged from the distribution bias. good.

  According to the example described above, it is possible to determine tissue properties that are difficult to determine with a single sound velocity amplitude image. The tissue property determination process described above is performed in the shape / characteristic determination image generation unit 20 (see FIG. 1).

  The ultrasonic diagnostic method and apparatus of the present invention have been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications can be made without departing from the spirit of the present invention. Of course it is good.

1 is a system configuration diagram showing a schematic configuration of an embodiment of an ultrasonic diagnostic apparatus according to the present invention. It is a graph which shows the phase change characteristic depending on the assumed sound speed of the microstructure signal in the assumed sound speed of 1400 [m / s] to 1500 [m / s]. It is a graph which shows the phase change characteristic by the assumption sound speed of the microstructure signal in assumption sound speed 1500 [m / s]-1640 [m / s]. It is a graph which shows the phase change characteristic by the assumption sound speed of the surface signal in assumption sound speed 1400 [m / s]-1480 [m / s]. It is a graph which shows the phase change characteristic by the assumption sound speed of the surface signal in assumption sound speed 1520 [m / s]-1640 [m / s]. It is a graph which shows the phase change characteristic according to the assumed sound speed of speckle in assumption sound speed 1400 [m / s]-1480 [m / s]. It is a graph which shows the phase change characteristic depending on the assumed sound speed of the speckle in the assumed sound speed of 1520 [m / s] to 1640 [m / s]. It is a graph which shows the amplitude change characteristic depending on the assumed sound speed of the microstructure in the assumed sound speed of 1400 [m / s] to 1500 [m / s]. It is a graph which shows the amplitude change characteristic by the assumption sound speed of the microstructure signal in assumption sound speed 1500 [m / s]-1640 [m / s]. It is explanatory drawing which shows an ultrasonic signal reception state. It is explanatory drawing which shows a mode that the curve given by Formula (1) and Formula (2) touches in the (X, t) plane, (a) is a case where V <V ₀ , (b) This is a case where V = V ₀ , and (c) is a case where V> V ₀ . It is a flowchart which shows the effect | action of an image generation part. It is a flowchart which shows the process which produces | generates the determination image for determination of the micro structure in a shape and property determination image generation part. It is explanatory drawing which shows the method of adding the difference value of a secondary differential value in determination of a microstructure. It is explanatory drawing which shows the example of the result of having compared the ratio of a microstructure and a speckle standard deviation as SN ratio in an amplitude image and a determination image. It is explanatory drawing which shows what compared the SN ratio of the amplitude image after several frame average, and the determination image. It is a flowchart which shows the process which produces | generates the determination image for the determination of a speckle in a shape and property determination image generation part. It is a flowchart which shows the processing content in a display image generation part. (A) is an ultrasonic image which shows a normal liver, (b) is a graph showing the histogram of the phase unevenness value. (A) is an ultrasonic image which shows an isolated point, (b) is a graph showing the histogram of the phase unevenness value. (A) is an ultrasonic image showing a liver including a lesion, and (b) is a graph showing a histogram of phase unevenness values. It is a flowchart which shows the example which performs structure | tissue property determination using the phase unevenness | corrugation change of a microstructure. It is a flowchart which shows the example which performs the structure | tissue property determination using the difference in the phase change characteristic by the assumed sound speed of a microstructure / continuous surface and speckle.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasound diagnostic apparatus, 10 ... Ultrasonic probe, 12 ... Transmission / reception part, 14 ... Scan control part, 16 ... AD conversion part, 18 ... Image generation part, 20 ... Shape and property determination image generation part, 22 ... Display image Generation unit, 24 ... monitor, 26 ... mode switching means, 30 ... (local) convex shape

Claims (8)

An ultrasonic probe in which a plurality of elements that transmit an ultrasonic wave toward the subject and output a reception signal by receiving an ultrasonic signal reflected from the subject are arranged;
When the assumed sound speed preset with respect to the actual sound speed of the ultrasonic wave transmitted to the subject is different from the actual sound speed, the element of the signal focused by the delay based on the assumed sound speed from the received signal An ultrasonic diagnostic apparatus comprising: property determining means for determining tissue properties in the subject from a phase change in the arrangement direction. The ultrasonic diagnostic apparatus according to claim 1, wherein the property determination unit uses a plurality of frames. The property determination means, ultrasonic diagnostic apparatus according to claim 1 or 2, characterized by the use of one signal generated by changing a plurality of the assumed sound speed from transmission. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3 , further comprising display means for displaying an image in which the determination result by the property determination means is reflected alone or in plurality. Ultrasonic diagnostic equipment. 5. The ultrasonic diagnostic apparatus according to claim 4 , further comprising means for generating an amplitude image from the ultrasonic signal, wherein the display means displays the image reflecting the determination result and the amplitude image. An ultrasonic diagnostic apparatus characterized in that it is displayed as it is or in a different color, overlapped or aligned, and displayed alone or in a plurality. The ultrasonic diagnostic apparatus according to claim 5 , wherein the display unit modulates luminance and color of the amplitude image according to an image in which the determination result is reflected, and displays the single or a plurality of the amplitude images. . The ultrasonic diagnostic apparatus according to any one of claims 4 to 6 , further comprising: a normal display mode as a display mode of the display means and a plurality of images superimposed or side by side, or a single or a plurality of displays. An ultrasonic diagnostic apparatus comprising mode switching means for switching between display modes. While transmitting an ultrasonic wave from the ultrasonic probe in which a plurality of elements are arranged toward the subject, receiving an ultrasonic signal reflected from the subject,
The element of the signal focused with a delay based on the assumed sound speed from the received signal when the assumed sound speed preset with respect to the actual sound speed of the ultrasonic wave transmitted to the subject is different from the actual sound speed An ultrasonic diagnostic method comprising: determining a tissue property in the subject from a phase change in the arrangement direction of the subject.

Images