JP2009000444A - Ultrasonic diagnostic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ultrasonic diagnostic equipment capable of accurately measuring thickness variations and an elasticity modulus of biotissue using a simple arithmetic circuit by taking account of the axial movement of a vascular wall. <P>SOLUTION: This ultrasonic diagnostic equipment includes: a transmission section 13 actuating an ultrasonic probe to transmit first and second transmission waves to a measuring region of a subject including the wall of an artery; a receiving section 12 receiving the reflecting waves acquired respectively when the first and second transmission waves reflect on the subject, using the ultrasonic probe and generating first and second receiving signals respectively; a moving direction determination section 18 for determining the moving direction of the vascular wall of the subject based on the first receiving signal; a delay time control section 14 controlling the transmission section to make the moving direction determined by the moving direction determination section substantially in parallel with the direction of the acoustic line of the second transmission wave; and a computing section 16 for calculating the shape value of the subject based on the second receiving signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a medical ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus for measuring a blood vessel wall.

  In recent years, an increasing number of people suffer from cardiovascular diseases such as myocardial infarction and cerebral infarction, and it has become a major issue to prevent and treat such diseases.

  Arteriosclerosis is closely related to the onset of myocardial infarction and cerebral infarction. Specifically, when an atheroma is formed on the blood vessel wall or new cells of the artery are not made due to various factors such as hypertension, the artery loses its elasticity and becomes hard and brittle. And the blood vessel occludes in the part where the atheroma is formed, the vascular tissue covering the atheroma ruptures, the atheroma flows into the blood vessel, and the artery is occluded in another part, or the artery is hardened These diseases are caused by the rupture of parts. Therefore, early diagnosis of arteriosclerosis is important for the prevention and treatment of these diseases.

  Conventionally, arteriosclerotic lesions have been diagnosed by directly observing the inside of a blood vessel using a vascular catheter. However, this diagnosis has a problem that the load on the subject is large because it is necessary to insert a vascular catheter into the blood vessel. For this reason, observation with a vascular catheter is used to identify the location of a subject who is certain that an arteriosclerotic lesion is present. For example, this method can be used as a test for health care. It was never used.

  Measuring a cholesterol level that is a cause of arteriosclerosis or measuring a blood pressure level is a test that can be easily performed with less burden on the subject. However, these values do not directly indicate the degree of arteriosclerosis.

  Further, if arteriosclerosis is diagnosed at an early stage and a therapeutic drug for arteriosclerosis can be administered to a subject, it will be effective in treating arteriosclerosis. However, when arteriosclerosis progresses, it is said that it is difficult to completely recover the cured artery even though the therapeutic agent can suppress the progress of arteriosclerosis.

  For these reasons, there is a need for a diagnostic method or apparatus for diagnosing the degree of arteriosclerosis at an early stage where arteriosclerosis progresses with less burden on the subject.

  An ultrasonic diagnostic apparatus is widely used as a non-invasive medical diagnostic apparatus that places little burden on the subject. A conventional ultrasonic diagnostic apparatus obtains a tomographic image showing the structure of a subject by converting the intensity of an echo signal into the luminance of a corresponding pixel. The tomographic image is acquired in real time and is used for diagnosing the internal structure of the subject from the tomographic image.

  Advances in electronics technology in recent years have made it possible to dramatically improve the measurement accuracy of ultrasonic diagnostic apparatuses, and accordingly, development of ultrasonic diagnostic apparatuses that measure minute movements of living tissue is progressing. For example, Patent Document 1 discloses a technique for tracking a measurement target with high accuracy by analyzing the amplitude and phase of an ultrasonic echo signal using a constrained least square method. This technique is called a phase difference tracking method. According to this technique, an amplitude due to vascular motion is several microns, and a fast vibration component having a frequency up to several hundred Hz can be measured with high accuracy. For this reason, it has been reported that it is possible to measure the thickness change and distortion of the blood vessel wall with high accuracy on the order of several microns.

Patent Documents 2 and 3 disclose a technique for acquiring a shape value of a blood vessel wall using the technique of Patent Document 1 and calculating an elastic modulus.
Japanese Patent Laid-Open No. 10-5226 International Publication No. 2006/011504 Pamphlet International Publication No. 2006/043528 Pamphlet JP-A-5-115479 JP-A-10-262970 US Pat. No. 6,777,0034 US Pat. No. 6,258,031 S. Golemati, et al., Ultrasound Med. Biol. Vol. 29, pp. 387-399, 2003. J. Bang, et al., Ultrasound Med. Biol., Vol. 29, pp. 967-976, 2003. M. Cinthio, et al., IEEE Trans. Ultrason. Ferroelect. Freq. Contr., Vol. 52, pp. 1300-1311, 2005.

  The artery expands and contracts in the radial direction in accordance with changes in blood flow and blood pressure of blood moving in the artery. The expansion and contraction of the artery is due to the movement only in the direction perpendicular to the axial direction of the artery. Therefore, when the ultrasonic beam is scanned from the direction perpendicular to the axial direction in the cross section passing through the axis of the artery, each ultrasonic beam It is possible to analyze the movement of the blood vessel wall by the echo signal obtained from the above. In other words, the movement of the blood vessel wall tissue on each ultrasonic beam can be obtained without using an echo signal from the adjacent ultrasonic beam. For this reason, in the cross section passing through the axis of the artery, the thickness of the vascular wall tissue can be changed with a relatively small amount of computation by making the ultrasonic beam incident on the artery from the direction perpendicular to the axial direction and receiving the ultrasonic echo. A two-dimensional distribution of quantities can be measured and the elastic modulus can be determined.

  However, as disclosed in Non-Patent Documents 1, 2, 3, and the like, it has been confirmed that the blood vessel wall of the carotid artery may move slightly in the axial direction in synchronization with the cardiac cycle. This movement is considered to be caused by the carotid artery being pulled by the heart as the heart contracts or expands. In such a case, as described above, the elastic modulus obtained on the assumption that the axis does not move in the axial direction is not accurate.

  When the blood vessel wall moves in the axial direction, it is considered that an accurate elastic modulus can be obtained if the two-dimensional motion of the blood vessel wall is accurately measured in a cross section passing through the axis of the artery. For example, it is conceivable to obtain the elastic modulus by two-dimensionally analyzing the motion of the blood vessel wall using the methods disclosed in Patent Documents 4 to 7. However, in order to measure a two-dimensional motion by these methods, a large-scale measurement circuit is required, and the amount of calculation for tracking the measurement target point becomes enormous. In particular, the amount of computation for obtaining the thickness change amount and the elastic modulus of the living tissue is enormous compared to the amount of computation for obtaining the motion speed of the measurement target point. For this reason, it is very difficult to perform such an enormous calculation in the arithmetic circuit used in the conventional ultrasonic diagnostic apparatus. In addition, when a computer having a very high computing capacity is employed in the ultrasonic diagnostic apparatus, the ultrasonic diagnostic apparatus becomes expensive.

  The present invention has been made to solve such a problem of the prior art, and in consideration of the movement of the blood vessel wall in the axial direction, a simple arithmetic circuit for calculating the thickness change amount and the elastic modulus of the living tissue. An object of the present invention is to provide an ultrasonic diagnostic apparatus that can be used and accurately measured.

  The ultrasonic diagnostic apparatus of the present invention includes a transmitter that drives an ultrasonic probe so as to transmit first and second transmission waves to a measurement region of a subject including a blood vessel wall of an artery, and the first Receiving a reflected wave obtained by reflecting the second transmitted wave and the second transmitted wave on the subject using the ultrasonic probe, and generating a first and a second received signal, respectively, A moving direction determining unit that determines a moving direction of a blood vessel wall in the subject based on a first received signal, a moving direction determined by the moving direction determining unit, and a direction of an acoustic line of the second transmission wave; Includes a delay time control unit that controls the transmission unit so as to be substantially parallel, and a calculation unit that calculates the shape value of the subject based on the second received signal.

  In a preferred embodiment, the delay time control unit controls the transmission unit so that an acoustic line of the first transmission wave is substantially perpendicular to an axis of the artery, and the first and second The directions of the acoustic lines of the transmitted waves are different from each other.

  In a preferred embodiment, the ultrasonic diagnostic apparatus further includes a tomographic image generation unit that generates a B-mode image signal based on amplitude information of the first reception signal, wherein the transmission unit and the reception unit are in the measurement region. The first received signal for one frame is repeatedly generated for a plurality of frames by scanning with the first transmission wave, and the tomographic image generation unit generates the B-mode image signal for each frame. The moving direction determination unit determines the moving direction of the blood vessel wall in the subject based on the B-mode image signal.

  In a preferred embodiment, the moving direction determination unit calculates a trajectory of the blood vessel wall using the B-mode image signals for the plurality of frames, and determines the moving direction of the blood vessel wall based on the trajectory. .

  In a preferred embodiment, the moving direction determination unit calculates the trajectory of the blood vessel wall by calculating the correlation of the B-mode image signals for the plurality of frames.

  In a preferred embodiment, the calculation unit calculates a property value of the subject based on the shape value.

  In a preferred embodiment, the calculation unit calculates a property value in each of a plurality of unit regions arranged in two non-orthogonal directions set in the measurement region, and a distribution indicating a two-dimensional distribution image of the property value Generate a signal.

  In a preferred embodiment, the ultrasonic diagnostic apparatus displays a tomographic image generated by the tomographic image generation unit by using a B-mode image signal and a two-dimensional distribution image generated by the calculation unit by the distribution signal. The unit regions in the two-dimensional distribution image are arranged in a direction non-perpendicular to the axial direction of the artery.

  In a preferred embodiment, the property value is an elastic modulus.

  According to the ultrasonic diagnostic apparatus of the present invention, the moving direction of the blood vessel wall is obtained using the first transmission wave, and the acoustic line of the second transmission wave is set parallel to the moving direction of the blood vessel wall. As a result, the blood vessel wall moves on the acoustic line of the second transmission wave. Therefore, when calculating the shape value, the blood vessel wall can be regarded as moving in one dimension along the acoustic line. It is possible to obtain an accurate characteristic value such as elastic modulus without performing the above.

  Embodiments of an ultrasonic diagnostic apparatus according to the present invention will be described below. FIG. 1 is a block diagram showing the structure of an ultrasonic diagnostic apparatus 10 according to the present invention.

  The ultrasonic diagnostic apparatus 10 includes a reception unit 12, a transmission unit 13, a delay time control unit 14, a phase detection unit 15, a calculation unit 16, a tomographic image generation unit 17, a movement direction determination unit 18, and an image synthesis unit 19. In addition, a user interface 24 for an operator to give a command to the ultrasonic diagnostic apparatus 10 and a control unit 23 composed of a microcomputer or the like for controlling each of these components based on the command from the user interface 24 are provided. .

  Note that each component shown in FIG. 1 is not necessarily configured by independent hardware. For example, the phase detection unit 15, the calculation unit 16, the movement direction determination unit 18, and the like may be configured by a microcomputer and software, and the functions of the respective units may be realized.

  Connected to the ultrasonic diagnostic apparatus 10 are a probe 11 for transmitting and receiving ultrasonic waves and a display unit 20 for displaying measurement results. These may be provided in the ultrasonic diagnostic apparatus 10 or may use the general-purpose probe 11 and the display unit 20. As the probe 11, a one-dimensional array of ultrasonic probes in which a plurality of piezoelectric elements are arranged at least one-dimensionally can be used. For example, a monitor used in a personal computer or the like can be suitably used for the display unit 20.

  The transmission unit 13 receives a command from the control unit 23 and generates a high-voltage transmission signal that drives the probe 11 at a designated timing. The probe 11 converts the transmission signal generated by the transmission unit 13 into an ultrasonic wave and irradiates the subject. As will be described in detail below, the transmission unit 13 drives the probe 11 so that the first transmission wave and the second transmission wave are transmitted from the probe 11. The first transmission wave is used for generating a tomographic image of the subject and for determining the moving direction of the blood vessel wall included in the subject. The second transmission wave is used for calculating the shape value of the blood vessel wall and further calculating the property value.

  The first and second reflected waves by the first and second transmission waves reflected from the inside of the subject are converted into electric signals using the probe 11 and amplified by the receiving unit 12. As a result, first and second received signals are generated.

  The delay time control unit 14 controls the transmission unit 13 and the reception unit 12 to select a piezoelectric element in the probe 11 and adjust timing for applying a voltage to the piezoelectric element. The deflection angle and focus of the acoustic line of the transmitted wave are controlled. In addition, the deflection angle and focus of the ultrasonic wave to be received as the first and second reflected waves are controlled.

  As will be described in detail below, the delay time control unit 14 controls the transmission unit 13 so that the deflection direction of the acoustic line of the first transmission wave is substantially perpendicular to the axis of the artery. On the other hand, the transmission unit 13 is controlled so that the direction of the acoustic line of the second transmission wave is substantially parallel to the movement direction determined by the movement direction determination unit 18. Here, “substantially vertical or parallel” means that the inclination is within a range of several degrees with respect to the vertical or parallel direction.

  By such operations of the transmission unit 13, the reception unit 12, and the delay time control unit 14, the first and second ultrasonic waves irradiated from the probe 11 scan the measurement area of the subject with ultrasonic waves, and one frame Minute first and second received signals are obtained. This scanning is repeated a plurality of times during one cardiac cycle of the subject to obtain first and second received signals for a plurality of frames. For example, received signals for several tens of frames are acquired.

  The phase detector 15 performs quadrature detection on the second received signal. The calculation unit 16 includes a shape value calculation unit 16a and a property value calculation unit 16b. The shape value calculation unit 16a calculates the shape value of the subject based on the second received signal subjected to quadrature detection. Specifically, the movement speed of the measurement target position set two-dimensionally in the region of interest (ROI) set in the measurement area of the subject is calculated from the second received signal, and the position displacement amount is calculated from the movement speed. Ask for. The property value calculation unit 16b obtains a distortion amount between the measurement target positions or between any two measurement target positions from the position displacement amount. In addition, information on the blood pressure of the artery is received from the sphygmomanometer 21, and the elastic modulus is obtained from the strain amount. Since the property values such as the strain amount and the elastic modulus are obtained for each target tissue sandwiched at the measurement target position, a two-dimensional distribution of the property values is obtained in the region of interest. The property value calculation unit 16b further generates a distribution signal suitable for image display. The calculation in the calculation unit 16 is performed for each cardiac cycle using an electrocardiogram waveform received from the electrocardiograph 22 as a trigger.

  The tomographic image generation unit 17 includes, for example, a filter, a logarithmic amplifier, a detector, and the like, and generates a B-mode image signal having luminance information corresponding to the signal intensity (amplitude magnitude) from the first received signal. .

  The movement direction determination unit 18 determines the movement direction of the blood vessel wall based on the first reception signal. As long as the first received signal is used, the moving direction of the blood vessel wall may be determined by any method. For example, the moving direction may be determined using the Doppler effect. In the present embodiment, the movement direction determination unit 18 obtains the correlation of the B-mode image signal generated by the tomographic image generation unit 17 based on the first received signal, calculates the trajectory of the blood vessel wall, and calculates the blood vessel wall from the trajectory. Determine the direction of movement. Information on the determined moving direction is output to the delay time control unit 14.

  The image composition unit 19 superimposes the tomographic image of the measurement region based on the B-mode image signal generated by the tomographic image generation unit 17 and the two-dimensional distribution image of the property value based on the distribution signal generated by the property value calculation unit 16b of the calculation unit 16. The generated image signal is generated and output to the display unit 20. The display unit 20 displays these images based on the image signal.

  Next, the operation of the ultrasonic diagnostic apparatus 10 will be described in detail. First, the reason why the elastic modulus cannot be accurately measured by the conventional method when moving in the direction of the blood vessel wall axis will be described. FIG. 2 schematically shows a procedure for measuring the elastic modulus in a conventional ultrasonic diagnostic apparatus. As shown in FIG. 2, ultrasonic waves are transmitted from the probe 11 in which the piezoelectric elements 11 a are arranged one-dimensionally toward the blood vessel wall 51. The ultrasonic acoustic line L 1 is set perpendicular to the axis of the blood vessel wall 51.

  The blood vessel wall 51 expands in the radial direction as indicated by an arrow E in accordance with the pressure change of the blood flowing through the blood vessel, and becomes a blood vessel wall 51 'in an expanded state. The vessel wall 51 'then contracts and returns. These states are repeated. As shown in FIG. 2, for example, when the measurement target position A1 is set on the blood vessel wall 51 at the time of contraction, the measurement target position A1 moves to An on the expanded blood vessel wall 51 '. As shown in the figure, with the expansion / contraction of the blood vessel wall 51, the measurement target position A1 is located on the same ultrasonic wave line L1. Even if the blood vessel wall 51 expands / contracts, the measurement target position A1 is always on the same ultrasonic acoustic line L1, and therefore the movement of the tissue on the blood vessel wall on each ultrasonic beam is caused by the adjacent ultrasonic beam. It can be obtained without using the received signal.

  However, when the blood vessel wall 51 moves in the axial direction F as shown in FIG. 2, the measurement target position A1 moves in the axial direction on the expanded blood vessel wall 51 '. For example, it has moved to point A1 '. For this reason, even if the ultrasonic waves on the same acoustic line are analyzed, it is not possible to analyze the accurate motion of the tissue.

  In the ultrasonic diagnostic apparatus 10 of the present invention, when the blood vessel wall 51 also moves in the axial direction, in order to obtain a property value such as the elastic modulus of the blood vessel wall 51, first, the moving direction is determined using the first transmission wave. The determination unit 18 obtains a trajectory along which the blood vessel wall of the subject moves in one cardiac cycle. In order to obtain the trajectory, the correlation of the B-mode image can be used as described below. For example, as shown in FIG. 3, the trajectory T of the measurement target position A1 set on the vascular wall 51 in the contracted state is obtained. The trajectory T may be obtained throughout the whole cardiac cycle. In obtaining the maximum strain amount and the elastic modulus, it is only necessary to accurately measure the position of the measurement target position at the time when the blood vessel wall 51 becomes the thickest and the time when the blood vessel wall 51 becomes the thinnest. Therefore, it is only necessary to obtain the trajectory of the blood vessel wall at least between contraction and expansion or between expansion and contraction in one cycle of contraction-expansion-contraction.

  The movement direction determination unit 18 determines the movement direction of the blood vessel wall from the obtained trajectory. For this purpose, the locus is approximated by a straight line, and the inclination of the approximated straight line is determined. Or you may determine the inclination of the straight line which connects the position of the measurement object position in the time when the artery contracted most and the time when it extended most.

  Next, under the control of the delay time control unit 14, the second transmission wave is transmitted so that the obtained movement direction of the blood vessel wall is substantially parallel to the acoustic line, and the second reception signal by the second transmission wave is transmitted. get. The computing unit 16 calculates the shape value of the blood vessel wall from the second received signal, and further calculates the characteristic value.

  As shown in FIG. 3, when the second transmission wave transmitted so as to coincide with the moving direction of the blood vessel wall is used, even if the blood vessel wall moves in the axial direction, Each measurement target position set on the blood vessel wall moves along the acoustic line L2. That is, each measurement target position moves one-dimensionally with respect to the second transmission wave. Therefore, if the measurement target position is set on the acoustic line L2 of the second transmission wave, the movement of the measurement target position can be correctly analyzed using only the second transmission wave, and the property value can be obtained. it can. This makes it possible to obtain an accurate characteristic value of the blood vessel wall without two-dimensionally analyzing the movement of the measurement target position.

  The second transmission wave needs to be scanned in the same direction in the measurement region. This is because when the direction of the acoustic line of the second transmission wave is different within the measurement region, the acoustic lines intersect and the measurement target position cannot be correctly analyzed. Therefore, the movement direction determination unit 18 determines one movement direction of the blood vessel wall that is the direction of the acoustic line of the second transmission wave.

  As shown in FIG. 4, the thickness t ′ of the expanded blood vessel wall 51 ′ is thinner than the thickness t of the contracted blood vessel wall 51. Therefore, when the reference points A1 and A2 are set at different positions in the radial direction of the contracted blood vessel wall 51, the distance between the positions A1 ′ and A2 ′ after the movement of these points in the expanded blood vessel wall 51 ′ is the reference It is narrower than the distance between the points A1 and A2. That is, the trajectory of the measurement target position A1 and the trajectory of the measurement target position A2 are not completely parallel.

  In consideration of these points, the movement direction determination unit 18 may set a reference point for determining a plurality of movement directions on the blood vessel wall in the measurement region, and determine the movement direction by averaging the trajectories. preferable. Alternatively, the reference point A3 may be set near the center in the radial direction of the blood vessel wall, the trajectory of the reference point A3 may be obtained, and the moving direction of the blood vessel wall may be determined.

  FIG. 5 schematically shows the first transmission wave 11 b and the second transmission wave 11 c transmitted from the probe 11. As shown in FIG. 5, the probe 11 includes a plurality of one-dimensionally arranged piezoelectric elements 11a, and an ultrasonic wave is generated by applying a transmission signal from the transmission unit to the piezoelectric elements. The ultrasonic wave transmitted from the probe 11 is generally controlled by the delay time control unit 14 with respect to the phase and timing of transmission signals applied to a plurality of adjacent (several to several tens) piezoelectric elements. To control the direction and spread of the transmitted ultrasonic beam. In the present embodiment, the first transmission wave 11b is an ultrasonic beam having an acoustic line L1 substantially perpendicular to the end face of the probe 11.

  The second transmission wave 11c is an ultrasonic beam having an acoustic line L2 inclined by an angle θ from the vertical direction. As described above, the angle θ is determined so that the direction of the acoustic line of the second transmission wave 11c is substantially parallel to the moving direction of the blood vessel wall obtained by the moving direction determining unit 18.

  The first transmission wave 11b and the second transmission wave 11c are transmitted so that the position of the acoustic line is shifted in the direction indicated by the arrow C while changing the combination of the piezoelectric elements 11a used for generation. The first transmission wave 11b or the second transmission wave 11c is scanned. In FIG. 5, the first transmission wave 11b and the second transmission wave 11c are shown together, but the first transmission wave 11b and the second transmission wave 11c are not transmitted simultaneously.

  FIG. 6A shows the timing of transmitting the first transmission wave 11b and the second transmission wave 11c. Data of n frames is acquired during one cardiac cycle, and each frame includes a period I for transmitting the first transmission wave and a period II for transmitting the second transmission wave. In each period, the first transmission wave or the second transmission wave scans the measurement region.

  As described above, the movement direction of the blood vessel wall is determined using the first transmission wave, and the second transmission wave is controlled so that the determined movement direction is parallel to the acoustic line of the second transmission wave. . In order to determine the moving direction, it is necessary to transmit the first transmission wave and generate the first reception signal at least from the time when the blood vessel of one cardiac cycle contracts most to the time when it expands most. For this reason, the second transmission wave having an acoustic line parallel to the moving direction of the blood vessel wall is transmitted from at least the second cardiac cycle. That is, as shown in FIG. 6B, the moving direction is determined based on the data acquired in the cardiac cycle S1, and a second transmission wave parallel to the determined moving direction is transmitted in the cardiac cycle S2. When it takes time to calculate the moving direction of the blood vessel wall, the moving direction is determined based on the data acquired in the cardiac cycle S1, and a second transmission wave parallel to the determined moving direction is transmitted after the cardiac cycle S3. May be. Since the time of vasoconstriction and the time of expansion during one cardiac cycle are located in the first half of one cardiac cycle, when acquiring data for n frames in the first half of one cardiac cycle, that is, one cardiac cycle, 1 to n Using the first transmission wave for / 2 frames and calculating the direction of movement of the blood vessel wall in the remaining period of one cardiac cycle, the direction of the acoustic line of the second transmission wave is obtained in the immediately preceding cardiac cycle. It is possible to match the moving direction of the blood vessel wall.

  The moving direction of the blood vessel wall may be obtained in each cardiac cycle, and the direction of the acoustic line of the second transmission wave may be sequentially adjusted after the next cardiac cycle. Also, if the moving direction of the blood vessel wall does not change much during measurement, the direction of the acoustic line of the second transmission wave is made constant using the initially determined moving direction of the blood vessel wall. Good. Since the first transmission wave is also used for generating a tomographic image, the first transmission wave is transmitted even when the first transmission wave is not used to determine the moving direction of the blood vessel wall in order to obtain a tomographic image in real time. It is preferable to do.

  Next, a method for determining the moving direction of the blood vessel wall from the first transmission wave will be described in detail with reference to FIGS. 7 (a) to 7 (c) and FIG. As shown in FIG. 7A, assuming that the measurement target positions are arranged in, for example, n rows and m columns in the measurement region 30, for example, in the measurement region 30 in the jth (j = 1 to N−1) frame. One or more reference points (s, t) (s and t are integers of n and m, respectively) are set in the blood vessel wall. Further, a reference area 31 including the set reference point is determined. The accuracy of calculation for obtaining the correlation in the measurement region 30 depends on the size of the reference region 31. In general, the larger the reference area, the higher the calculation accuracy, but the calculation amount increases. For this reason, it is preferable to determine the size of the region of interest 31 in consideration of the calculation amount and the required calculation accuracy. The reference point may be set by moving the cursor or the like by the user interface 24 on the tomographic image displayed on the display unit 20 and designating the position of the cursor, The movement direction determination unit 18 may determine automatically. Further, the operator may designate a reference area instead of the reference point. On the tomographic image displayed on the display unit 20, a reference region is set in the entire region (region of interest) for which the characteristic value of the blood vessel wall is to be obtained or in the region for which the characteristic value is to be obtained. In this case, the movement direction determination unit 18 sets a reference point at the center of the reference region.

  Note that when the reference point is set at the center of the reference region, it is preferable that the reference region does not include a blood flow portion. This is because the blood flow portion moves differently from the blood vessel wall tissue, and therefore, if a reference point is set for the blood flow portion as a reference, the correct movement direction of the blood vessel wall cannot be obtained. Accordingly, when the reference region includes a motion (blood flow portion) different from the blood vessel wall, only the blood vessel wall portion of the tomographic image is extracted and displayed on the display unit 20 or the blood flow portion. It is preferable to display the fact on the display unit 20 so as to be distinguished on the tomographic image, and to assist the operator so that the reference point can be set correctly.

  As shown in FIG. 7B, in the kth (k = j + 1) th frame after a predetermined time has elapsed from the jth frame, the blood vessel wall expands to dye in the radial direction and is pulled by the heart in the axial direction. It is assumed that dx is moved to. In this case, the set reference region 31 moves in the axial direction and the radial direction, and moves to a region 31 'centered on the reference point (p, q). As shown in FIG. 7C, in the k-th frame, an area 33 having the same size as the reference area 31 is set at each measurement target position in the measurement area 30, and reception corresponding to the reference area 31 of the j-th frame is performed. The correlation between the amplitude information of the signal and the amplitude information of the received signal corresponding to the region 33 in the kth frame is calculated using a correlation function, and a correlation coefficient is obtained. When the region 33 is set for all the measurement target positions set in the measurement region 30 and the correlation is calculated, as shown in FIG. 7B, the correlation with the region 31 ′ is the highest and the correlation coefficient is also the maximum. It becomes. Therefore, it is estimated that the reference region 31 has moved to the region 31 'in the k-th frame, and the displacement amount in the axial direction at this time is dx and the displacement amount in the radial direction is dy. A method for specifying the position of a region of interest between two frames using the correlation of received signals is disclosed in, for example, Japanese Patent Laid-Open No. 8-164139. When calculating the correlation, if a direction that is impossible as the movement direction of the reference point is known, the calculation when moving in that direction may be omitted. Thereby, the amount of calculation can be reduced.

  The movement direction determination unit 18 performs this calculation between a plurality of frames for all the reference points, and sequentially obtains the locus of the set reference points. The locus of the reference point in each frame may be obtained by performing the above calculation between the frames. Alternatively, the trajectory may be obtained between two frames separated by two or more frames when the movement amount is not large because the time is short between adjacent frames.

  When the movement direction determination unit 18 obtains the trajectories of a plurality of reference points, it calculates one trajectory by averaging these trajectories.

  FIG. 8 schematically shows the trajectory T of the measurement target position thus obtained. The movement direction determination unit 18 obtains an approximate straight line L from the trajectory T by a least square method or the like, and obtains an inclination θ from a direction perpendicular to the axis of the blood vessel wall 51. The inclination θ is the moving direction of the blood vessel wall. The delay time control unit 14 controls the transmission unit 13 so that the movement direction θ of the blood vessel wall obtained by the movement direction determination unit 18 is parallel to the direction of the acoustic line of the second transmission wave. The calculation unit 16 receives the second transmission wave transmitted in parallel with the moving direction of the blood vessel wall and obtains the characteristic value of the blood vessel wall. Hereinafter, the calculation in the calculating part 16 is demonstrated.

As shown in FIG. 9, the second transmission wave 11c transmitted from the probe 11 propagates through the extravascular tissue 52 and the blood vessel wall 51, and is reflected or reflected by the extravascular tissue 52 and the blood vessel wall 51 in the process. Part of the scattered ultrasonic waves returns to the probe 11 and is received as a reflected wave.
The reflected wave is detected as a time series signal r (t), and the time series signal of reflection obtained from the tissue closer to the probe 11 is located closer to the origin on the time axis. The acoustic line L2 of the second transmission wave 11c forms an angle θ with respect to the direction perpendicular to the axis of the blood vessel wall 51.

There are a plurality of measurement target positions P _n (P ₁ , P ₂ , P ₃ , P _k ... P _n , n is a natural number of 3 or more) of the blood vessel wall 51 (front wall) located on the acoustic line L2. P ₁ , P ₂ , P ₃ , P _k ... P _n are arranged in order from the probe 11 at regular intervals. In FIG. 9, coordinate axes with the upper side being positive and the lower side being negative are provided in the depth direction, and the coordinates of the measurement target positions P ₁ , P ₂ , P ₃ , P _k ... P _n are respectively Z ₁ , Z ₂ , Z ₃ , Z _k ,... Z _n , the reflection from the measurement target position P _k is located at t _k = 2Z _k / c on the time axis. Here, c represents the speed of ultrasonic waves in the body tissue. The reflected wave signal r (t) is phase-detected by the phase detector 15, and the detected signal is separated into a real part signal and an imaginary part signal and input to the computing part 16. The measurement target position P _n is set to the vascular wall tissue at a reference time in one cardiac cycle, for example, at the time when the vascular wall contracts most. These measuring points P _n is due to expansion and contraction of the blood vessel wall moves over the acoustic line L2, it returns to the original position to the reference time in the next cardiac cycle.

The calculation unit 16 obtains the position displacement amount in the shape value calculation unit 16a from the phase-detected signal, and obtains the thickness change amount and the maximum value and the minimum value of the thickness change amount in order in the property value calculation unit 16b. Specifically, the shape value calculation unit 16a has a restriction that the amplitude does not change in the reflected wave signal r (t) and the reflected wave signal r (t + Δt) after a minute time Δt, and only the phase and the reflection position change. Originally, the phase difference is obtained by the least square method so that the waveform matching error between the reflected wave signals r (t) and r (t + Δt) is minimized (constrained least square method). From this phase difference, the motion velocity V _n (t) of the measurement target position P _n is obtained, and further integrated to obtain the position displacement d _n (t).

FIG. 10 schematically shows the relationship between the measurement target position P _n and the target tissue T _n for which the elastic modulus is calculated. The target tissue T _k is located with a thickness h in a range between adjacent measurement target positions P _k and P _{k + 1} . In the present embodiment defines of n measuring points P ₁ · · · · P _n the (n-1) pieces of target tissues T _{1 ····} T _n-1.

The property value calculation unit 16b calculates the thickness change amount D _k (t) from the position displacement amounts d _k (t) and d _{k + 1} (t) of the measurement target positions P _k and P _{k + 1} as D _k ( t) = d _k (t) −d _{k + 1} (t).

Furthermore, the property value calculation unit 16b obtains the maximum value and the minimum value of the thickness change amount. The change in the thickness of the tissue T _{k on} the anterior wall of the blood vessel is caused by a change in blood flowing through the blood vessel formed by the anterior wall of the blood vessel due to heartbeat. Therefore, the maximum value H _k (value at the minimum blood pressure) of the thickness of the target tissue T _k, the difference Delta] h _k and the diastolic blood pressure value between the maximum value and the minimum value of the thickness change amount D _k of the target tissue (t) Using the pulse pressure Δp, which is the difference from the maximum blood pressure value, the elastic modulus E _k in the radial direction of the blood vessel, which is the distortion rate of the target tissue T _k , can be obtained by the following equation. The minimum blood pressure value and the maximum blood pressure value are received from the sphygmomanometer 21.

However, while the pulse pressure Δp, which is blood pressure information, is a value obtained in the direction perpendicular to the axis of the blood vessel, the change in the thickness of the tissue T _{k on} the anterior wall of the blood vessel changes in the axial direction of the blood vessel wall. Based on exercise information including exercise. Therefore, the elastic modulus is calculated by obtaining the component of the thickness change in the direction perpendicular to the axial direction of the blood vessel wall.

Ek = (Δp × H _k ) / (Δh _k · cos θ)

In the above description, the elastic modulus of the target tissue T _n between adjacent measurement target positions is obtained, but any two points of the measurement target positions having a plurality of elastic moduli can be selected. In this case, the same calculation can be performed using the maximum value of the thickness between the two selected points and the difference between the maximum value and the minimum value of the thickness change amount between the two selected points.

In this way, a plurality of target tissues T _n are set on the acoustic line of the second transmission wave, and the elastic modulus is calculated. Since a plurality of second transmission waves are transmitted along the axial direction of the blood vessel wall 51 so as to scan the measurement region, the elastic modulus is obtained two-dimensionally in the measurement region.

  FIG. 11 shows an example of a screen 40 displayed on the display unit 20. The screen 40 of the display unit 20 shows a tomographic image 41 including the blood vessel wall 51 generated by the tomographic image generating unit 17. The tomographic image 41 shows a region of interest 42 that specifies a region for which the elastic modulus is to be obtained. The region of interest 42 can be designated at an arbitrary position by the operator through the user interface 24.

  The obtained secondary distribution image 44 of the elastic modulus is superimposed on the tomographic image 43 and displayed on the screen 40. The secondary distribution image 44 is shown in tone or color tone according to the value of the elastic modulus, and a bar 45 indicating the correspondence between the elastic modulus and tone or color tone is shown on the screen 40 together.

  As shown in FIG. 11, in the secondary distribution image 44, the unit areas 44a indicating the target tissue are arranged along the direction of the acoustic lines of the second transmission wave. That is, they are arranged in a direction that is not perpendicular to the axial direction of the blood vessel wall 51. For this reason, the shape of each unit region 44a is also a parallelogram. This is because the acoustic lines of the second transmission wave are inclined by an angle θ from the direction perpendicular to the axial direction of the blood vessel wall 51 and the measurement target positions are also arranged obliquely as shown in FIG. . By arranging the unit regions 44a in this way, the positions of the target tissue indicated by the tomographic image 43 and the target tissue for which the elastic modulus is obtained correspond correctly. The arrangement direction of the unit regions 44a is preferably parallel to the acoustic line of the second transmission wave. Therefore, it is preferable that the property value calculation unit 16b generates a distribution signal indicating a two-dimensional distribution image of the property characteristic values so that the unit area is parallel to the acoustic line of the second transmission wave.

  However, the unit regions 44a only need to be arranged along the direction of the acoustic line of the second transmission wave. For example, as shown in FIG. 12, the shape of each unit region 44a is square or rectangular, The direction can also be a non-vertical direction along the direction of the acoustic line of the second transmission wave.

  As described above, according to the ultrasonic diagnostic apparatus of the present invention, the moving direction of the blood vessel wall is obtained using the first transmission wave, and the acoustic line of the second transmission wave is set in parallel with the moving direction of the blood vessel wall. As a result, the blood vessel wall moves on the acoustic line of the second transmission wave. Therefore, when calculating the shape value, the blood vessel wall can be regarded as moving in one dimension along the acoustic line. It is possible to obtain an accurate characteristic value such as elastic modulus without performing the above.

  In this embodiment, an example in which the elastic characteristic of a cross section parallel to the axis of the blood vessel is measured has been described. However, the present invention can also measure the elastic modulus of the blood vessel in a cross section perpendicular to the axis of the blood vessel. is there. In a cross section perpendicular to the axis of the artery, when extravascular tissue around the blood vessel is uneven, for example, when muscle and fat are unevenly distributed around the blood vessel, the blood May move in a cross section perpendicular to the axis. Even in such a case, the elastic modulus of the blood vessel wall in a cross section perpendicular to the axis of the blood vessel can be obtained by using the ultrasonic diagnostic apparatus of the present invention.

  In the cross section perpendicular to the axis of the blood vessel, the blood vessel wall expands and contracts in the radial direction. Therefore, even when the blood vessel does not move in the cross section, the moving direction varies depending on the position of the blood vessel wall. For this reason, when measuring the elastic modulus in a cross section perpendicular to the axis of the blood vessel, according to the prior art, an accurate elastic modulus can be obtained only on the acoustic line passing through the axis of the blood vessel, and there is an acoustic line passing through the axis. Only after the ultrasonic wave was determined, the correct elastic modulus could not be obtained.

On the other hand, according to the ultrasonic diagnostic apparatus 10, even if the whole blood vessel is moved by the above-described method using the first transmission wave, unless the reference region for obtaining the correlation is set large, the whole blood vessel is moved. In addition to the direction, it is possible to accurately determine in which direction the measurement region is moving in the radial direction. For example, as shown in FIG. 13, 'in the center from C ₀ C _0' contracted dilated vessel wall 51 and vessel wall 51 when moving into, the respective parts move of the vessel wall indicated by the arrow, the entire vessel And a component due to the expansion of the blood vessel wall. However, according to the ultrasonic diagnostic apparatus 10, the reference region 42 is set, and the moving direction determination unit 18 determines the moving direction of the set reference region 42. Regardless, the correct moving direction can be obtained. As a result, by performing measurement using the second transmission wave having an acoustic line parallel to the obtained moving direction, the blood vessel wall in the cross section perpendicular to the blood vessel axis can be easily and accurately compared to the conventional case. The elastic modulus can also be obtained.

  The ultrasonic diagnostic apparatus of the present invention is suitably used for measuring the property characteristics of a living tissue, and particularly suitable for accurately measuring the elastic modulus.

1 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus of the present invention. It is a schematic diagram explaining the ultrasonic beam in the case of measuring an arterial wall using the conventional ultrasonic diagnostic apparatus. It is a schematic diagram explaining an ultrasonic beam in the case of measuring an arterial wall using the ultrasonic diagnostic apparatus of the present invention. It is a schematic diagram explaining the moving direction of a blood vessel wall. It is a figure explaining the ultrasonic beam transmitted from a probe in the ultrasonic diagnosing device of the present invention. (A) is a figure explaining the timing which transmits the 1st and 2nd transmission wave in one cardiac cycle, (b) is a figure explaining the timing which sets the acoustic line of a 2nd transmission wave. is there. (A)-(c) is a figure explaining the procedure which calculates | requires the moving direction of a blood vessel wall in a moving direction determination part. It is a figure explaining the procedure which determines the moving direction of a blood vessel wall from the locus | trajectory of a blood vessel wall. It is a figure explaining the measuring object position set on the acoustic line of the 2nd transmission wave. It is a figure which shows the relationship between a measurement object position, object structure | tissue, and an elasticity modulus. It is a figure which shows an example of the image displayed on the display part of the ultrasonic diagnosing device of this invention. It is a figure which shows the other pattern of the two-dimensional distribution image of a property value. FIG. 4 shows vessel contraction and expansion in a cross section perpendicular to the axis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ultrasonic diagnostic apparatus 11 Probe 12 Reception part 13 Transmission part 14 Delay time control part 15 Phase detection part 16 Calculation part 16a Shape value calculation part 16b Property value calculation part 17 Tomographic image generation part 18 Moving direction determination part 19 Image composition 20 Display unit 21 Sphygmomanometer 22 ECG

Claims (9)

A transmitter that drives the ultrasound probe to transmit the first and second transmission waves to the measurement region of the subject including the blood vessel wall of the artery;
Receiving units that receive reflected waves obtained by reflecting the first and second transmission waves on the subject using the ultrasonic probe and generate first and second received signals, respectively. When,
A moving direction determining unit that determines a moving direction of a blood vessel wall in the subject based on the first received signal;
A delay time control unit that controls the transmission unit such that the movement direction determined by the movement direction determination unit and the direction of the acoustic line of the second transmission wave are substantially parallel;
A computing unit that calculates a shape value of the subject based on the second received signal;
An ultrasonic diagnostic apparatus comprising:   The delay time control unit controls the transmission unit so that the acoustic line of the first transmission wave is substantially perpendicular to the axis of the artery, and the acoustic line of the first and second transmission waves The ultrasonic diagnostic apparatus according to claim 1, wherein directions are different from each other. A tomographic image generator that generates a B-mode image signal based on the amplitude information of the first received signal;
The transmission unit and the reception unit repeatedly generate the first reception signal for one frame by scanning the measurement region with the first transmission wave for a plurality of frames,
The tomographic image generation unit generates the B-mode image signal for each frame,
The ultrasonic diagnostic apparatus according to claim 2, wherein the moving direction determination unit determines a moving direction of a blood vessel wall in the subject based on the B-mode image signal.   The said moving direction determination part calculates the locus | trajectory of the said blood vessel wall using the signal for B mode images for the said some flame | frame, and determines the moving direction of the said blood vessel wall based on the said locus | trajectory. Ultrasonic diagnostic equipment.   The ultrasonic diagnostic apparatus according to claim 4, wherein the moving direction determination unit calculates a trajectory of the blood vessel wall by calculating a correlation of the B-mode image signals for the plurality of frames.   The ultrasonic diagnostic apparatus according to claim 5, wherein the calculation unit calculates a property value of the subject based on the shape value.   The calculation unit calculates property values in a plurality of unit regions arranged in two non-orthogonal directions set in the measurement region, and generates a distribution signal indicating a two-dimensional distribution image of the property values. 6. The ultrasonic diagnostic apparatus according to 6. A display unit that superimposes and displays a tomographic image generated by the B-mode image signal generated by the tomographic image generation unit and a two-dimensional distribution image generated by the distribution signal generated by the calculation unit;
The ultrasonic diagnostic apparatus according to claim 7, wherein the unit areas in the two-dimensional distribution image are arranged in a direction that is not perpendicular to the axial direction of the artery.   The ultrasonic diagnostic apparatus according to claim 8, wherein the property value is an elastic modulus.

Images