JP5879052B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus that displays an ultrasonic tomogram.

  A conventional general ultrasonic diagnostic apparatus includes an ultrasonic transmission / reception unit that transmits / receives an ultrasonic wave to / from a subject, and a subject including a moving tissue using a reflected echo signal from the ultrasonic transmission / reception unit A tomographic scanning unit that repeatedly obtains tomographic image data in a predetermined cycle, and an image display unit that displays time-series tomographic image data obtained by the tomographic scanning unit. And the information which converted the discontinuity degree into the brightness | luminance in the interface where the acoustic impedance along the propagation direction of a sound changes among the structures of the biological tissue inside a subject was displayed as a B-mode image.

  On the other hand, an external force is applied from the body surface of the subject, a curve in which the external force attenuates inside the living body is assumed, pressure and displacement at each point are obtained from the assumed attenuation curve, and distortion is measured. A method for estimating an elastic image based on strain data has been proposed. According to such a distortion image, the hardness and softness of the living tissue can be measured and displayed. In particular, in a tissue having a different feature from the surrounding tissue such as a tumor, the difference in shear wave sound velocity may be large even if the difference in longitudinal wave sound velocity is small from that in the surrounding tissue. In such a case, the change in acoustic impedance does not appear in the image and is indistinguishable on the B-mode image. However, the elastic modulus differs depending on the shear wave sound velocity and reflects the difference in elastic modulus. A distinction may be made on a distorted image.

  Based on the above background technology, the background technology most relevant to the present invention will be described below. This is an imaging method for imaging the boundary between a tumor and a normal tissue shown in Patent Document 1. According to this method, detection is possible even when the acoustic impedance and elastic modulus do not change between the tumor and the normal tissue.

  Specifically, the technique shown in Patent Document 1 is a technique for obtaining a motion vector distribution between frames, detecting a place where the uniformity of the motion vector distribution is disturbed, and determining that there is a boundary of an object at that position. is there. In order to obtain the motion vector, the reference image is divided into a plurality of body motion measurement regions. The reason why the image is divided into a plurality is that if the cross-correlation is taken with a large area, the movement cannot be accurately estimated when the correlation becomes worse due to deformation. For this reason, it is preferable that the body motion measurement region is small so that the movement in the measurement region can be regarded as uniform. However, if it is made too small, the characteristics of the image will be lost, and it will be possible to correlate with every place. Generally, it is preferable to make it as small as possible within a range larger than the speckle size (the size of the ultrasonic beam). In the case of obtaining a correlation between the reference frame N and the adjacent frame N + i, a body motion measurement region is set on each of the image of the frame N and the image of the frame N + i. Cross-correlation (or pattern matching method such as least square method) between the body motion measurement region set on the ultrasonic tomogram of frame N and the body motion measurement region set on the ultrasonic tomogram of frame N + i ), The body motion measurement region on the image of the frame N + i that best matches the body motion measurement region on the image of the frame N is obtained, and the difference between the center coordinates of the two body motion measurement regions is used as the motion vector. The motion vector distribution can be obtained by scanning the body motion measurement region and repeating the same operation.

  Next, a place where the uniformity of the motion vector is disturbed is detected, and it is determined that there is a boundary of the object at that position. As a method for detecting the disturbance of uniformity, it is difficult to determine the vector amount as it is, and an operation for converting a vector into a scalar is necessary. As an example of the operation of converting to a scalar, the vector rotation, dVy / dx-dVx / dy, is obtained for the horizontal component Vx and the vertical component Vy of the motion vector, and this is imaged. Other operations for converting to a scalar include parameters such as the degree of coincidence of pattern matching and the anisotropy of degree of coincidence when obtaining distortion tensors and motion vectors. In this way, the calculated boundary line is displayed superimposed on the B-mode tomographic image, strain image, and ultrasonic blood flow image obtained by the conventional method.

  Boundary imaging may contain useful information regarding tumor properties. In general, it is known that the adhesive strength between a tumor and surrounding normal tissue may differ depending on the malignancy of the tumor. As a result, when the adhesive force is weak, the two tissues move so as to slide across the boundary, so that the discontinuity of the motion vector distribution increases. When the vector rotation is imaged, the vector rotation has a sharp peak in a direction orthogonal to the boundary. On the other hand, when the adhesive force is strong, the two tissues move together across the boundary, so that the discontinuity of the motion vector distribution becomes small. When a vector rotation is imaged, the vector rotation changes gently in a direction orthogonal to the boundary. By observing the spatial change in the rotation of the vector at this boundary, the degree of adhesion or adhesion between the two tissues across the boundary can be examined.

  As for the movement between the frames, body movement such as breathing and pulsation may be used, or it can be deformed by artificially applying pressure from the outside.

  With respect to the present invention, the above-described technique for detecting the disturbance of the uniformity of the motion vector and imaging the boundary position and properties is improved. However, the related background art in which the features of the present invention become clearer by comparing with the present invention will be described here.

  First, as a related technique of the technique for detecting the disturbance of the uniformity of the motion vector and imaging the position and properties of the boundary, static pressure is applied as shown in Non-Patent Document 1, and the shear strain distribution is imaged. There is an imaging method. The static pressurization is performed at a frequency sufficiently slower than the frame rate, and the object is deformed by pressing the ultrasonic probe against the subject surface. At this time, a shear strain is measured instead of the aforementioned strain. The shear wave distortion is a physical quantity defined by 1/2 (dVy / dx + dVx / dy). Since the slip surface can be detected by measuring the shear wave distortion, the degree of adhesion between the two tissues sandwiching the slip surface can be examined in the same manner as the method of Patent Document 1.

  Further, as a technique related to a technique for detecting the disturbance of uniformity of another motion vector and imaging the position and property of the boundary, there is elastography using radiation pressure shown in Patent Document 2. There is a technique for diagnosing hardness by applying a radiation pressure inside a subject using an ultrasonic focused beam and displacing a target tissue. At this time, the radiation pressure is applied in a pulsed manner to excite a short pulse shear wave. In this technique, the amount of tissue displacement that occurs in the direction in which the focused beam travels is imaged, or shear elasticity is estimated from the estimation of the propagation speed of shear waves that occur in the direction perpendicular to the direction in which the focused beam travels with tissue displacement at the focal point. The elastic modulus such as modulus and Young's modulus is calculated.

JP2008-79792 Special table 2008-534198

J. Ophir et al., Ultrasonic Imag., Vol.13, pp.111-134, 1991.

  In the technique of causing deformation of the object by manually pressing the object through body movement or an ultrasonic probe, and detecting and imaging the boundary, the imaging frame rate and the frequency of deformation Is difficult to synchronize. This is because it is difficult to match the apparatus to the body movement because the body movement has no strict periodicity and it is difficult to predict in advance. The manual compression is the same in that it is difficult to predict in advance because it is difficult to predict in advance because there is no strict periodicity in human freehand movement. As a result, it becomes difficult to display the boundary image stably without depending on the imaging time. This is explained as follows. When the displacement x due to body movement is simplified as x = sin ωt, the time change of the displacement is large when ωt is in the vicinity of an integral multiple of 180 degrees, and it is easy to detect deformation from the comparison of data between frames. On the other hand, in the vicinity of an integral multiple of 180 degrees +90 degrees, the time change of the displacement is small, and it is difficult to detect deformation from a comparison of data between frames. If synchronization is not achieved, it is difficult to select a condition that makes ωt easy to detect deformation, so that stable detection and display becomes difficult.

  A problem in an imaging method shown in Non-Patent Document 1 in which static pressure is applied and a shear strain distribution is imaged will be described. In the case of static pressurization, effective pressurization cannot be performed unless the opposite side of the object is a fixed end when viewed from the probe to be pressed. When the measurement target is the mammary gland, the opposite side of the measurement target is fixed by the ribs, so static pressure works well, but in the case of the pancreas, liver, kidney, etc. Because it is difficult, pressurization is difficult. In particular, it is difficult to apply uniform pressure so as not to cause artifacts. Therefore, it has been desired to realize a method of applying pressure without depending on the mechanical condition of the object opposite to the ultrasonic probe.

  Next, the problem of elastography using pulse radiation pressure shown in Patent Document 2 will be described. When using radiation pressure, there is a trade-off between the magnitude of displacement and the temperature rise in the living body. In addition, since shear wave measurement is a transient phenomenon, it is necessary to acquire multiple raster echo signals at once in order to follow this, so the size of the receiving circuit increases by the number of signals to be acquired. The price of the device will be high. Further, as the number of received beams is increased, the transmitted beam is expanded, so that the intensity of the transmitted beam per area is simply decreased, so that the signal-to-noise ratio is decreased. Therefore, it has been desired to realize a method for imaging the displacement distribution without increasing the circuit scale and without causing a decrease in the signal-to-noise ratio.

  In order to achieve the above object, in the present invention, an ultrasonic probe that transmits and receives an echo signal from within an object, a vibration source for generating displacement within the object, and an echo signal from the object A boundary detection unit that detects a boundary between tissues in the target based on the displacement detection result and evaluates the property of the boundary. An ultrasonic diagnostic apparatus having the above-described configuration is provided.

  In order to achieve the above object, the present invention can synchronize the vibration of the vibration source for generating displacement in the object and the imaging rate of tomographic imaging for detecting displacement. An ultrasonic diagnostic apparatus is provided. At this time, the vibration cycle of the vibration source and the imaging cycle are synchronized, and imaging is performed at 0 °, 90 °, 180 °, and 270 ° with respect to the vibration cycle, and the motion is estimated from 0 ° and 180 °, 90 By estimating the motion from ° and 270 °, two motion distributions whose phases are shifted by 90 ° are obtained, so that the motion distribution in the imaging field does not have zero points.

  According to the present invention, by synchronizing the deformation period and the imaging period, the boundary image can be stably displayed without depending on the imaging time.

The block diagram which shows the apparatus structure of this invention Flowchart showing signal processing in the present invention The figure explaining the calculation method of the motion vector in this invention The figure explaining the calculation method of the motion vector in this invention Diagram explaining the relationship between imaging period and vibration period Displacement distribution for each raster Displacement distribution for each raster Displacement distribution for each raster in the sequence

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration example of an ultrasonic diagnostic apparatus according to the present invention. The flow of signal processing for imaging in the ultrasonic diagnostic apparatus will be described with reference to FIG. A transmission electric pulse is transmitted from the transmission beam former 3 to the ultrasonic probe 1 installed on the surface of the subject via the transmission / reception switch 2 under the control of the control unit 4. At this time, the transmission beamformer controls the delay time between the channels of the probe 1 to be in an appropriate state so that the ultrasonic beam travels on a desired scanning line. The electric signal from the transmission beam former 3 is converted into an ultrasonic signal by the ultrasonic probe 1 and an ultrasonic pulse is transmitted into the subject. A part of the ultrasonic pulse scattered in the subject is received again by the ultrasonic probe 1 as an echo signal, and is converted from an ultrasonic signal to an electric signal there. The electric signal converted from the ultrasonic signal is supplied to the receiving beam former 5 via the transmission / reception change-over switch 2, where the echo signal from the desired depth on the desired scanning line is selectively enhanced. The data on the scanning line is stored in the memory 9. The data once stored in the memory is subjected to correlation calculation between frames in the motion vector detection unit 10 to calculate a motion vector. Although details will be described later, in the present invention, imaging is performed by changing some of the vibration phase of the vibration source and the timing of the frame trigger. The plurality of motion vector images are synthesized by the displacement distribution synthesis unit 12. For this reason, the phase of the vibration of the vibration source 15 is also controlled by the trigger control unit 14. Based on the motion vector calculated by the displacement distribution synthesis unit, the boundary between the organs and the tumor and the normal tissue determined from the motion in the image of interest is detected by the boundary detection unit 11. On the other hand, the data from the receiving beamformer 5 is converted from an RF signal into an envelope signal in the B-mode image generator 6, converted into a Log-compressed B-mode image, and sent to the scan converter 7. On the scan converter 7, the imaged boundary information and the B-mode image are superimposed, and scan conversion is performed. The data after the scan conversion is sent to the display unit 8 and displayed on the display unit 8 as an ultrasonic tomographic image.

  In the present invention, other than the motion vector detection unit 10 and the boundary detection unit 11, the displacement distribution synthesis unit 12, the vibration source 15, the vibration source trigger control unit 14, and the process of superimposing the result on the B-mode image on the scan converter 7 Is executed by a normal ultrasonic diagnostic apparatus, and detailed description thereof is omitted here. Hereinafter, the detection of the motion vector and the detection of the boundary will be described.

  A processing flow in this embodiment will be described with reference to FIG. First, in order to obtain a motion vector, the frame image is divided into a plurality of body motion measurement regions (S11). The reason why the image is divided into a plurality is that if the cross-correlation is taken with a large area, the movement cannot be accurately estimated when the correlation becomes worse due to deformation. For this reason, it is preferable that the body motion measurement region is small so that the movement in the measurement region can be regarded as uniform. However, if it is made too small, the characteristics of the image will be lost, and it will be possible to correlate with every place. Generally, it is preferable to make it as small as possible within a range larger than the speckle size (the size of the ultrasonic beam). In the case of obtaining a correlation between the frame N and the frame N + i, a body motion measurement region is set on each of the image of the frame N and the image of the frame N + i as schematically shown in FIG. FIG. 3A is a diagram showing one body motion measurement region (region indicated by a dotted line) set on the ultrasonic tomographic image of frame N, and FIG. 3B is an ultrasonic tomographic image of frame N + i. It is a figure which shows the body movement measurement area | region set up above. Here, i is set according to the speed of movement of the object, i is reduced when the movement is fast, and a large integer is selected as i when examining a region where the movement is slow.

Next, a cross-correlation (or least square method or the like) between the body motion measurement region set on the ultrasonic tomogram of frame N and the body motion measurement region set on the ultrasonic tomogram of frame N + i Any other method may be used as long as it is a method widely used for pattern matching (step S12 in FIG. 2). The motion vector is defined as follows. As shown in FIG. 3, the center point of the motion vector measurement region set in the frame N is (x _N , y _N ), and the center point of the region that best matches the body motion measurement region of the frame N in the frame N + i is Assuming that (x _{N + i} , y _{N + i} ), the motion vector V is expressed as V (x _{N + i} −x _N , y _{N + i} −y _N ). In order to examine the motion distribution, a plurality of body motion measurement areas 21 to 26 may be set in the frame N as shown in FIG. For each corresponding body motion measurement region on the frame N + i, a motion vector is obtained by the same method, and a motion distribution is obtained.

Since it is preferable to detect the motion vector finely in the image, the schematic diagram of FIG. 4 only shows the body motion measurement region sparsely, but in practice, a large number of body motion measurement regions are set to overlap each other. It is preferable to do this. When the i-th body motion measurement region from the upper left to the right and the j-th body motion measurement region from the lower left is expressed as (i, j), the motion vector corresponding to this body motion measurement region is V _ij ^N = (Vx _ij ^N , Vy _ij ^N ). Can be expressed as

  Next, a place where the uniformity of the motion vector is disturbed is detected, and it is determined that there is a boundary of the object at that position (S13 in FIG. 2). As a method for detecting the disturbance of uniformity, it is difficult to determine the vector amount as it is, and an operation for converting a vector into a scalar is necessary. In the present embodiment, a scalar quantity is extracted from the horizontal component Vx and the vertical component Vy of the motion vector by vector rotation dVy / dx−dVx / dy, and this is imaged.

  Thus, the calculated boundary line is superimposed and displayed on the B-mode tomographic image, elastic modulus image, and ultrasonic blood flow image obtained by the conventional method (S14 in FIG. 2).

Next, the relationship between the vibration period Tv and the imaging period Tf, which is a feature of the present invention, will be described. One case is when the same phase displacement is used in the frame when Tv> Tf as shown in FIG. The displacement distribution in the frame at this time is as shown in FIG. By setting Tv> 4Tf, it is possible to select two frames in which the phases of the displacements in the frame are the same and the phases are reversed. (For example, the tissue displacement in each raster (R ₁ , R ₂ ,, R _M ) of frame N in FIG. 5 (a) is substantially in phase. Similarly, in frame N + 3, the displacement is almost in phase. As a typical condition, let us consider a case where the shear wave velocity is 1 m / s, the imaging period is 1/50 s, and the imaging visual field width is 10 cm. In order to make the phase of displacement uniform within the imaging field of view, the wavelength of the shear wave needs to be 40 cm (4 times the imaging field width), so Tv = 0.4 s (2.5 Hz in terms of frequency). In this case, in addition to the displacement caused by the vibration of the excitation source, the movement caused by the body movement cannot be ignored, and it becomes difficult to synchronize the vibration and the imaging. The motion detection follows the motion along the frame, but cannot respond to the motion in the direction orthogonal to the frame. This is because the movement along the frame is less deformed because the deformation can be basically represented as a parallel movement. On the other hand, since the motion orthogonal to the frame always causes deformation, the motion cannot be examined by a method such as pattern matching in principle. If the time between frames becomes long, the motion of the orthogonal method cannot be ignored in the frames, so that it becomes difficult to detect the motion in principle.

  In the second case, there is a case where Tv <Tf as shown in FIG. In this case, as shown in FIG. 7, when the distribution of displacement is examined for each raster, there is a raster in which the displacement is periodically zero, and therefore the displacement distribution becomes striped. (In the example of FIG. 7, the raster numbers are 2, 4, 6, and 8) Therefore, as shown in FIG. 8, when the vibration is expressed as cos (ωt + φ), φ = 0 °, 90 °, Four images with phases corresponding to 180 ° and 270 ° are taken. Specifically, imaging at the above four phases is performed by adjusting the timing of the frame trigger and the time difference between the triggers that apply vibration to the vibration source. Then, by taking a correlation between 0 ° and 180 ° and 90 ° and 270 °, two displacement distributions having a phase relationship between cos and sin can be obtained. This is because cos (ωt + 90 °) is sin (ωt). If two sets of displacement distribution of sin and cos are obtained, the sum of the square of sin and the square of cos is always 1, that is, constant regardless of the phase of sin and cos, so measure the displacement distribution independent of phase. Is possible. This process can be explained in another way as follows. The signal obtained from the 0 ° and 180 ° frames and the signal obtained from the 90 ° and 270 ° frames are shifted by 90 ° as shown in FIG. This corresponds to the real part and the imaginary part of the complex signal. Therefore, the square sum process described above corresponds to a process for obtaining an absolute value from the real part and the imaginary part. In this method, since Tf is the same as the normal imaging rate, the total imaging time is about 4/50 s, that is, 0.08 s, and the influence of body movement can be reduced. Even if there is a non-uniform sound speed, only the wavelength changes, and two sets of data, sin and cos, can be obtained, and the displacement distribution in the entire frame can be imaged. When the body movement is small and there is a margin for improving the signal-to-noise ratio, it is also effective to set the phase interval to be finer than 90 °, 60 ° or 45 °.

  Next, the vibration source will be described. For example, an eccentric motor can be used as the vibration source. This is a motor in which a weight is fixed to the shaft of a small motor while being shifted from axial symmetry. By attaching the weight in such a state shifted from the shaft, that is, in an eccentric state, vibration of the rotation period of the motor can be caused. It is also easy to control the amplitude of vibration with the maximum rotation radius of the weight. By using an eccentric motor, a shear wave can be caused in a direction perpendicular to the normal direction to the subject surface, that is, along the subject surface. If the eccentric motor is placed inside the ultrasonic probe (for example, the back side of the transducer), the operator can pick up an image by grasping only the ultrasonic probe with his / her hand. In addition, when it is desired to change the place where the shear wave is generated freely, it is also an effective method to make the eccentric motor a component separated from the ultrasonic probe.

  When the motion vector distribution is obtained by the method described so far, the rotation vector of the motion vector field is calculated. A boundary surface with small adhesion, adhesion, or infiltration is imaged as a sharp boundary with a large rotation vector, and a boundary surface with large adhesion, adhesion, or infiltration is imaged as a gentle boundary with a small rotation vector. It becomes possible to distinguish the boundary properties.

  At the end of the embodiment, the difference between the two techniques described in the background art and the present invention will be described. First, the difference from the imaging method shown in Non-Patent Document 1 in which static pressure is applied and the distribution of shear strain is imaged will be described. In the case of static pressurization, effective pressurization cannot be performed unless the opposite side of the object is a fixed end when viewed from the probe to be pressed. When the measurement target is the mammary gland, the opposite side of the measurement target is fixed by the ribs, so static pressure works well, but in the case of the pancreas, liver, kidney, etc. Because it is difficult, pressurization is difficult. In particular, it is difficult to apply uniform pressure so as not to cause artifacts. On the other hand, when a vibration source is used as in the present invention, it is easy to generate a shear wave regardless of whether the opposite side is a fixed end or a free end. Thus, the feature of the present invention is that the range that can be selected as an object is expanded. The problem of using the vibration source, which is to solve the phase non-uniformity in the image, is to synchronize the vibration body with the imaging and use the displacement image at two phases different by 90 degrees. It is.

  Next, differences from elastography using radiation pressure shown in Patent Document 2 will be described. Further, in measuring shear waves, it is necessary to acquire echo signals of a plurality of rasters at a time in order to capture a transient phenomenon of propagation of pulsed shear waves. To do this, the size of the receiving circuit is increased by the number to be acquired, and the price of the device is increased. Further, as the number of received beams is increased, the transmitted beam is expanded, so that the intensity of the transmitted beam per area is simply decreased, so that the signal-to-noise ratio is decreased. On the other hand, in the present invention, the deformation caused by the vibration source propagates as a continuous wave shear wave, which is a repetitive phenomenon. Therefore, since it is possible to take an image with a certain amount of time, unlike the conventional method of measuring as a transient phenomenon, the conventional method of receiving one raster with a single transmission is sufficient in time, which increases the circuit scale and signal noise. The reduction in the ratio is not a problem. In addition, when using radiation pressure, there is a trade-off between the magnitude of displacement and the temperature rise in the living body, but in the present invention, irradiation with strong ultrasonic waves for generating radiation pressure is not necessary. There is no need to worry about the rise.

  INDUSTRIAL APPLICABILITY The present invention is useful as an ultrasonic diagnostic apparatus that detects a boundary inside a subject by ultrasonic transmission / reception and diagnoses the state of adhesion or infiltration between two tissues sandwiching the boundary.

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic probe, 2 ... Transmission / reception changeover switch, 4 ... Control system, 5 ... Received beam former, 6 ... B mode image generation part, 7 ... Digital scan converter, 9 ... Memory, 10 ... Motion vector detection part , 11 ... boundary detection unit 12 ... displacement distribution synthesis unit, 13 ... vibration source, 14 ... trigger control unit,

Claims (4)

A vibration source that gives displacement to living tissue, an ultrasonic transducer, a beam former that transmits and receives ultrasonic waves into a subject, and a displacement of a region of interest in the living body is detected by the ultrasonic transducer and beam former. And a signal processing unit
The vibration source vibrates at a vibration period in which the signal processing unit detects the displacement at a plurality of phases having a shift of 90 ° ,
The signal processing unit detects the displacement generated by the vibration source with a phase detection period of 0 °, 90 °, 180 °, and 270 °, and measures a spatial distribution of the detected displacement. . The signal processing unit obtains the spatial distribution of the displacement from the two odd-numbered detections , obtains the spatial distribution of the displacement from the two even-numbered detections, and obtains one displacement space from the sum of squares of the two spatial distributions. The ultrasonic measurement apparatus according to claim 1, wherein a distribution image is obtained.   The ultrasonic measurement apparatus according to claim 1, wherein a rotation vector of the vector is imaged from the spatial distribution of the displacement.   The spatial distribution of the displacement is obtained by pattern matching between a plurality of body movement measurement regions set in two frames for examining motion, and the anisotropic spatial distribution of the matching degree of the pattern matching is imaged. The ultrasonic measurement apparatus according to claim 2.