JP2011036271A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a more accurate, reliable and highly stable ultrasonic diagnostic apparatus capable of estimating an elastic property. <P>SOLUTION: The elastic property value of a vascular wall is estimated based on the shape of the vascular wall, the quantity of distortion of the vascular wall computed from the distribution of the maximum displacement in the depth direction between the bloodstream-intima boundary and the adventitia-body tissue boundary, and the blood pressure value captured from a blood pressure acquisition part 113. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus for measuring tissue properties of a subject.

  A conventional ultrasonic diagnostic apparatus irradiates a subject with ultrasonic waves, converts the intensity of the reflected echo signal into the luminance of a corresponding pixel, and obtains the structure of the subject as a tomographic image. In recent years, there has been an attempt to analyze the amplitude and phase information of the reflected echo signal to measure the movement of the tissue in the subject and grasp the tissue properties such as strain, elastic characteristics, and viscosity characteristics of the tissue. .

  For example, in Patent Document 1 and Non-Patent Document 1, a strain amount is obtained from a displacement amount of a measurement point set on a blood vessel wall caused by a heartbeat, and a local elastic characteristic around the measurement point is calculated from the strain amount and a blood pressure difference. And a method for displaying an image of the spatial distribution of elastic properties. The outline is described below.

  The arterial wall is deformed by a change in blood pressure due to pulsation, and its elastic characteristics are defined from the relationship between the degree of deformation (distortion amount) and the stress in the arterial wall caused by the blood pressure. Here, it is almost impossible to measure the stress distribution in the arterial wall non-invasively or indirectly, so the amount of arterial wall strain ε during one heartbeat can be calculated using ultrasound. In addition to the measurement, the elastic characteristic E of the arterial vessel wall is defined by the following equation based on the relationship between the minimum blood pressure Pd and the maximum blood pressure Ps separately measured by the sphygmomanometer, that is, the pulse pressure ΔP = Ps−Pd.

E = ΔP / ε (1)
Below, the outline | summary of the distortion amount measurement by an ultrasonic wave is demonstrated.
Now, as shown in FIG. 2, it is considered to measure the amount of strain ε of the blood vessel wall between two points, the A point on the intima side and the B point on the adventitia side of the artery wall. If the positions of these two points at time t are XA (t) and XB (t), respectively, and the electrocardiogram R wave trigger time at the end diastole is t = 0, the initial thickness h0 is h0 = XB (0) −XA. (0), the maximum thickness variation is
Since Δh = MAX [| XB (t) −XA (t) |], the strain amount ε is expressed by the following equation.
ε = Δh / h0 = MAX [| XB (t) −XA (t) |] / {XB (0) −XA (0)} (2)
Here, MAX [*] is a function that returns the maximum value of *.

  In general, the displacement of the arterial wall is about several hundreds μm, while the maximum thickness change Δh is about several tens of μm, which is about an order of magnitude smaller than the wavelength of transmitted and received ultrasound (about 300 μm). It is necessary to accurately grasp the change.

In the above description, the calculation of the strain amount ε between two points on the inner membrane side and the outer membrane side has been described. However, in the method shown in Patent Literature 1 and Non-Patent Literature 1, as shown in FIG. Displacement measurement points with an interval of about 80 μm are set on one ultrasonic beam, and the amount of displacement at each measurement point is measured. Next, since the transmission / reception ultrasonic pulse width is about 400 μm, the initial thickness of equation (1) is set between two points separated by h0 = about 400 μm, and the thickness change is assumed to be uniform in the layer. , The maximum thickness change Δh is calculated by the equation (2), and is set as Δh of the center point between the two points. Δh is calculated for each measurement point while moving this layer in the vertical direction from the inner membrane side to the outer membrane side of the blood vessel wall by the interval of the displacement measurement point. Furthermore, by scanning the ultrasonic beam at intervals of about several hundred μm along the long axis direction of the blood vessel, thousands of micro regions are set in the axial direction and the depth direction of the blood vessel wall. Δh is calculated. The strain amount ε of each minute region is calculated from h and Δh obtained in this way, and the elastic characteristic E of each minute region is obtained from the pulse pressure ΔP measured separately by a sphygmomanometer according to the equation (1). .
JP 2000-229078 A Hiroshi Kanai et al. “INNERVISION” August 2005 p. 31-33 Publisher: Inner Vision

However, the above method has the following problems, and the reliability of the obtained elastic characteristics cannot be sufficiently guaranteed.
(1) The amount of strain is defined by the maximum value of the thickness change waveform as shown in equation (2).
(2) The elastic characteristic calculation formula defined by the formula (1) depends on the shape of the blood vessel wall.
Hereinafter, the above (1) and (2) will be specifically described.

  First, regarding (1), although the above method assumes that the thickness change is uniform between two points separated by the initial thickness h0, the distortion amount between the two points is calculated as the midpoint point. It exists as a distortion amount, and a plurality of existence points of the distortion amount exist between two points, which contradicts the above assumption.

  Further, since the center frequency of the transmission ultrasonic pulse used is about 7 MHz and the transmission / reception ultrasonic pulse width is about 400 μm, the initial thickness of the equation (1) is between two points separated by about h0 = 400 μm. However, the thickness of the blood vessel wall, which is the measurement target area, is about 1 mm at most in cases other than serious patients in the case of the carotid artery. This area is divided into multiple layers, and the distortion amount of each layer In principle, it is almost impossible to calculate accurately by avoiding the transmission / reception ultrasonic pulse width. If the target area length is W and the pulse width is PW, it can only be divided into layers of W / PW.

Further, when calculating the strain amount, the initial thickness h and the maximum thickness change amount Δh are used, and the maximum thickness change amount Δh is defined by the equation (2). When calculating by such a method, the time when XA (t) -XB (t) takes the maximum value is the time when the highest blood pressure is taken, that is, the maximum stress is applied to the blood vessel wall, and the deformation is maximized. It does not necessarily coincide with the time at which the wall displacement is maximized, and what is originally meant by the maximum thickness change in the equation is different.
Regarding (2), in general, the elastic properties of a material are inherent to the material and do not depend on the shape of the material, but the elastic properties of the blood vessel wall expressed by the formula depend on the shape of the blood vessel wall. Therefore, the elastic characteristics of the blood vessel wall itself cannot be expressed. Although it is good to compare the elastic characteristics of the same part of the blood vessel wall of the same subject, it is impossible to compare when the shape of the blood vessel wall is different, for example, the thickness of the blood vessel wall is different.

  In other words, it has been extremely difficult to estimate the elastic characteristics of the blood vessel wall with high reliability with a conventionally used method.

  An object of the present invention is to provide an ultrasonic diagnostic apparatus that can eliminate the above-described problems of the conventional method as much as possible and can estimate the elastic characteristics of the blood vessel wall itself with accuracy and reliability.

  The ultrasonic diagnostic apparatus according to the present invention includes a transmitter that irradiates ultrasonic waves from outside the body through the probe to the inside of the subject, and a reception signal based on the ultrasonic echoes reflected from the inside of the subject irradiated with the ultrasonic waves. A receiving unit that outputs, a displacement measuring unit that measures a displacement amount of an arbitrary region around the arterial blood vessel wall inside the subject based on an output from the receiving unit, an output from the receiving unit, and the displacement measuring unit A boundary detection unit for detecting a blood flow-blood vessel wall boundary and a blood vessel wall-peripheral tissue boundary of a blood vessel wall on the proximal side and the distal side of the probe based on at least one of the outputs from the probe; and A shape determining unit that determines the shape of the arterial blood vessel wall based on the output from the detecting unit, and the output from the boundary detecting unit or the displacement measurement in the blood vessel wall on the proximal side or the distal side of the probe The arterial blood vessel from the output from the section A strain calculation unit that calculates a strain amount of the subject, a blood pressure value acquisition unit that captures the blood pressure value of the subject, an output from the shape determination unit, an output from the strain calculation unit, and an output from the blood pressure value acquisition unit And an elastic characteristic estimation unit that estimates an elastic characteristic value of a blood vessel wall on the proximal side or the distal side of the probe, and the time when the distortion calculation unit calculates the distortion amount is one heartbeat It is a time when the displacement amount of the blood flow-blood vessel wall boundary in the cycle or the blood vessel wall-peripheral body tissue boundary becomes maximum, and at that time, the blood flow-blood vessel between or around the two boundaries The distortion amount is calculated based on a change tendency of the displacement amount in a direction from the wall boundary toward the blood vessel wall-peripheral body tissue boundary. By adopting such a configuration, it becomes possible to eliminate the problems of the conventional method as much as possible and to estimate the elastic characteristics of the blood vessel wall itself with accuracy and reliability.

  Further, the ultrasonic diagnostic apparatus according to the present invention determines the reliability of at least one feature amount of each boundary detected by the boundary detection unit and the distortion amount calculated by the distortion amount calculation unit, It has the means to alert | report a result, It is characterized by the above-mentioned. With such a configuration, the reliability of the estimated elastic characteristic can be determined.

  Further, the ultrasonic diagnostic apparatus according to the present invention approximates the change tendency of the displacement amount in the direction from the blood flow-blood vessel wall boundary to the blood vessel wall-peripheral body tissue boundary as a function in the strain calculation amount, The spatial differential value in the direction is defined as the distortion amount. With such a configuration, the problems of the conventional method can be avoided, the calculation accuracy of the distortion amount of the blood vessel wall used in estimating the elastic characteristics is improved, and the reliability of the estimated elastic characteristics is improved.

The ultrasonic diagnostic apparatus according to the present invention is characterized in that the function is a linear function.
With such a configuration, the problems of the conventional method can be avoided, the calculation accuracy of the distortion amount of the blood vessel wall used in estimating the elastic characteristics is improved, and the reliability of the estimated elastic characteristics is improved.

  In the ultrasonic diagnostic apparatus according to the present invention, the linear function is a linear function. With such a configuration, the problems of the conventional method can be avoided, the calculation accuracy of the distortion amount of the blood vessel wall used in estimating the elastic characteristics is improved, and the reliability of the estimated elastic characteristics is improved.

  In the ultrasonic diagnostic apparatus according to the present invention, the spatial differential value of the linear function may be calculated using the difference between the maximum displacement amount at two points existing near each of the two boundaries and the distance between the two points. It is characterized by defining by. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that the two points are positions where the echo intensity locally takes a maximum value in the vicinity of the boundary between the two points. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that the maximum displacement amount at each of the two points is an average of the maximum displacement amounts at a plurality of locations around each of the two points. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that the spatial differential value is calculated by a linear least square method. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that the spatial differential value is calculated by a linear least square method weighted by the magnitude of the received signal. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

The ultrasonic diagnostic apparatus according to the present invention is characterized in that the function is a nonlinear function.
With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that the spatial differential value is calculated by a non-linear least square method. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that the spatial differential value is calculated by a non-linear least square method weighted according to the magnitude of a received signal. With this configuration, the problems of the conventional method can be avoided, the calculation accuracy and noise resistance of the vascular wall distortion used for estimating the elastic properties are improved, and the reliability of the estimated elastic properties is improved. Will improve.

  The ultrasonic diagnostic apparatus according to the present invention is characterized in that a feature amount used when determining the reliability of the elastic characteristic value of the artery wall is a sign of the strain amount. With this configuration, the reliability of the estimated elastic characteristic can be easily determined.

  In the ultrasonic diagnostic apparatus according to the present invention, the feature value used when determining the reliability of the elastic characteristic value of the artery wall is a distance between the blood flow-intima boundary and the epicardium-body tissue boundary. It is characterized by being. With this configuration, the reliability of the estimated elastic characteristic can be easily determined.

  In the ultrasonic diagnostic apparatus according to the present invention, the shape of the arterial blood vessel wall is a cylindrical tube, and the shape is expressed by the thickness of the blood vessel wall and the inner diameter of the blood vessel. By adopting such a configuration, the problems of the conventional method can be avoided, and the estimated elastic characteristic does not depend on the shape of the blood vessel, and the elastic characteristic can be estimated accurately and reliably.

  The ultrasonic diagnostic apparatus according to the present invention is characterized by estimating an elastic characteristic of a blood vessel wall on the distal side of the probe. By adopting such a configuration, the displacement measurement accuracy is improved, and accurate and reliable estimation of elastic characteristics becomes possible.

  In the ultrasonic diagnostic apparatus according to the present invention, the transmitting unit transmits a plurality of ultrasonic pulses toward a plurality of points along the long axis direction of the blood vessel, and the elastic characteristic distribution in the long axis direction of the blood vessel is transmitted. It is characterized by obtaining. With such a configuration, an elastic characteristic distribution along the long axis direction of the blood vessel can be obtained, and an abnormal lesion can be easily found.

  According to the present invention, more accurate and highly reliable and stable elastic characteristics can be obtained.

(First embodiment)
FIG. 1 is a block diagram of the ultrasonic diagnostic apparatus according to the first embodiment of the present invention. 1 includes a probe 101, a transmission unit 102, a reception unit 103, a tomographic image processing unit 104, a memory 105, an image synthesis unit 106, a monitor 107, a displacement measurement unit 108, a distortion calculation unit 109, A boundary detection unit 110, an elastic characteristic estimation unit 111, a memory 112, a blood pressure value acquisition unit 113, a reliability determination unit 114, and a shape determination unit 115 are configured.

  Although not shown, a user interface such as a keyboard, trackball, switch, and button is also connected to the ultrasonic diagnostic apparatus.

  The transmission unit 102 generates a high-voltage transmission signal that drives the probe 101 at a designated timing. The probe 101 converts the transmission signal generated by the transmission unit 102 into ultrasonic waves and irradiates the subject, and converts ultrasonic echoes reflected from the inside of the subject into electric signals. A plurality of piezoelectric transducer elements are arranged in the probe 101, and the deflection angle and focus of the ultrasonic wave to be transmitted are controlled according to the selection of these piezoelectric transducer elements and the timing of applying a voltage to the piezoelectric transducer elements.

  The receiving unit 103 amplifies a reception signal obtained by converting an ultrasonic echo into an electric signal, and adds a different delay for each reception signal received by each piezoelectric transducer, thereby determining a predetermined position (focus). Alternatively, a reception signal based only on ultrasonic waves from the direction (deflection angle) is output.

  The tomographic image processing unit 104 includes a filter, a detector, a logarithmic amplifier, and the like, analyzes at least the amplitude of the reception signal output from the reception unit 103, and images the tissue structure of the subject.

  The boundary detection unit 110 analyzes at least one of the received signal and the displacement amount of the arbitrary part, and the blood flow-intima boundary on the proximal side and the distal side from the probe 101 of the blood vessel wall of the subject, The medial-epicardial boundary and the epicardial-peripheral tissue boundary are detected, and the boundary positions are output to the strain calculation unit 109 and the reliability determination unit 114.

  The displacement measuring unit 108 analyzes at least the phase of the received signal and measures the displacement amount of the measurement point. For example, the amount of displacement may be measured using the method described in Patent Document 1.

  In the strain calculation unit 109, the displacement amount of the blood vessel wall blood-intima boundary, media-outer membrane boundary, outer membrane-peripheral tissue boundary detected by the boundary detection unit 110, or an arbitrary part in the vicinity thereof From this, the distortion amount of the blood vessel wall is calculated.

  The shape determination unit 115 determines the shape of the blood vessel wall from each boundary of the blood vessel wall detected by the boundary detection unit 110.

  The blood pressure value acquisition unit 113 is a means for acquiring a blood pressure value, and may be a keyboard used by the examiner for manual input of the blood pressure value or a connected sphygmomanometer itself.

  In the elastic characteristic estimation unit 111, from the shape of the blood vessel wall determined by the shape determination unit 115, the strain amount of the blood vessel wall calculated by the strain calculation unit 109, and the blood pressure value acquired by the blood pressure value acquisition unit 113, Estimate the elastic properties of the vessel wall. The image synthesizing unit 106 synthesizes the tomographic image and at least one of the numerical value indicating the elastic characteristic and the elastic characteristic distribution image, and displays the synthesized image on the monitor 107.

  The memory 112 stores received signals, and is used to re-estimate the elastic characteristics when the ultrasonic transmission / reception is stopped (hereinafter referred to as the freeze state). The memory 105 stores a tomographic image, and outputs a tomographic image synchronized with the tissue property value in a frozen state.

  A strain amount calculation method and an elastic property estimation method in the ultrasonic diagnostic apparatus configured as described above will be specifically described. In the following, the description is limited to the case where the blood vessel wall distal to the probe 101 is targeted.

  First, as shown in FIG. 3, the strain amount to be calculated by the strain calculation unit 109 is the strain amount of the blood vessel wall distal to the probe 101, and the blood vessel detected by the boundary detection unit 110. It is necessary to calculate the amount of strain between the wall blood flow-intima boundary and the outer membrane-peripheral tissue boundary. Here, it is often difficult to determine the boundary between the outer membrane and the surrounding tissue by analyzing the received signal. In such a case, since the outer membrane-peripheral tissue boundary and the media-exterior membrane boundary are close to each other, the outer membrane-peripheral tissue boundary is the same as or separated from the media-outer membrane boundary by a certain distance. As a matter of fact, there is no practical problem. In the following description, the boundary between the blood vessel wall and the surrounding tissue is described as the outer membrane-peripheral tissue boundary, but this may be replaced with a position that is the same as or separated from the middle membrane-outer membrane boundary. .

  The amount of distortion is defined by the spatial differential of the amount of displacement. Now, in the ultrasonic diagnostic apparatus shown in FIG. 1, since the ultrasonic beam is considered to be transmitted and received one-dimensionally, the traveling direction of the ultrasonic beam, That is, the spatial differential of the displacement amount in the direction from the subject surface toward the blood vessel or body tissue (hereinafter, depth direction) may be considered.

  Here, since the blood vessel wall expands and contracts over one heartbeat cycle due to fluctuations in blood pressure, it is necessary to determine at which time in one heartbeat cycle the amount of distortion, that is, the spatial differential of the displacement amount is taken. In the conventional method, the time when the thickness change between two points separated by about 400 μm takes the maximum value is the time, but in this method, the deformation of the blood vessel wall becomes the maximum and the time when the displacement of the blood vessel wall becomes the maximum This is not necessarily the case, but what is originally meant by the maximum thickness change in equations (1) and (2) is different.

  Usually, the time when the amount of distortion becomes maximum may be considered as the time when the deformation of the blood vessel wall becomes maximum. Therefore, in the present embodiment, the time for defining the distortion amount is limited to the time at which the displacement amount measured for the displacement amount takes the maximum value during one heartbeat period. That is, the distortion amount is defined by the spatial differential in the depth direction of the maximum displacement amount during one heartbeat cycle. In addition, it is assumed that the time to take the maximum displacement at each displacement measurement point in the blood vessel wall is different due to the influence of disturbance noise. In that case, the displacement measurement accuracy of the strong echo site is generally high. Further, the time when the displacement amount of the strong echo portion in the blood vessel wall takes the maximum displacement may be set, or the average time when the maximum displacement of each measurement point in the blood vessel wall is taken.

  In the present embodiment, when the elastic characteristic estimation unit estimates the elastic characteristic of the blood vessel wall, the blood vessel wall is regarded as a thick cylindrical tube, and the elastic characteristic is estimated from the strain amount, blood pressure, and the shape of the blood vessel. If the blood vessel can be regarded as a thick-walled cylindrical tube and is uniformly expanded and contracted by the blood pressure, the degree of deformation, that is, the maximum displacement amount is as shown in FIG. 4 from the blood flow-intima boundary to the outer membrane-body tissue boundary. It decreases monotonously.

  However, the maximum displacement amount of the intima region of the blood vessel wall is usually due to the small received signal strength, interference of the strong echo part existing near the blood flow-intima boundary and the intima-outer membrane boundary, etc. As shown in FIG. 5, the displacement measurement accuracy is poor and does not show a monotonous decreasing trend from the blood flow-intima boundary toward the outer membrane-body tissue boundary. Under such circumstances, even if the amount of strain is calculated at multiple locations from the blood flow-intima boundary to the outer membrane-tissue boundary using the conventional method, the reliability can be guaranteed. It becomes difficult. In addition, as described above, although it is assumed that the thickness change is uniform between the two points separated by the initial thickness, the strain amount between the two points is present as the strain amount at the midpoint. ing. There are a plurality of distortion amount existing points between the two points, which contradicts the above assumption.

  Furthermore, as described above, the center frequency of the transmission / reception ultrasonic wave used in the conventional method is about 7 MHz, and considering the interference of the pulse width, the displacement amount between the two points is independent of the displacement amount between the two points. The distance between the two points can be observed as about 400 μm. The vascular wall of the human carotid artery is about 1 mm at most, except for the case where plaque is present, and even if it is simply considered, the section where the amount of distortion can be calculated is about two sections at most.

  Therefore, in the present embodiment, the amount of distortion of the entire blood vessel wall is calculated instead of dividing the blood vessel wall into minute regions and calculating the amount of distortion for each of them as in the conventional method. With such a configuration, it becomes easy to guarantee the reliability of the resulting elastic characteristics, and noise resistance is improved. Specifically, the displacement measurement accuracy is relatively high at two points (A and B in FIG. 5) of the strong echo portion existing near each of the blood flow-intima boundary and the outer membrane-tissue boundary. The distortion amount is defined as ΔXmax / ΔX by the difference ΔXmax = XBmax−XAmax of the maximum displacement amount and the distance ΔX = A−B between the two points. The two points A and B may be set anywhere as long as they exist in the vicinity of the respective boundaries. However, it is optimal to set the echo intensity locally at the maximum value in the vicinity of each boundary. is there. In addition, two points A and B where the echo intensity is locally maximized are set, and the maximum displacement is obtained by averaging the maximum displacements at several locations around each position to obtain the maximum displacement at each position. It is also good. Further, a depth direction filter may be applied to the maximum displacement amount in advance, so that noise resistance can be increased.

  Next, a method for estimating the elastic characteristic from the strain amount thus obtained, the blood pressure, and the shape of the blood vessel wall will be described.

The elastic characteristic estimated from the strain amount and the blood pressure value according to the equation (1) as in the conventional method changes depending on the shape, and thus does not reflect the elastic characteristic of the blood vessel wall itself. When the blood vessel wall is regarded as a thick cylindrical tube, its elastic characteristic is expressed by the following equation.
E = {(1 + ν) (2νRi / h + 1) / (2 + h / Ri)} · (−ΔP / ε) (3)
Here, Ri is the inner diameter of the blood vessel, h is the thickness of the blood vessel wall at the R-wave trigger time of the electrocardiogram, ΔP is the pulse pressure, and ν is the Poisson's ratio.
Therefore, in the elastic characteristic estimation unit in the present embodiment, the inner diameter R of the blood vessel and the thickness h of the blood vessel wall are calculated from each boundary determined by the boundary detection unit, and these are calculated by the strain calculation unit. The elasticity characteristic of the blood vessel wall is estimated by substituting the strain amount ε and the pulse pressure ΔP, which is the difference between the highest and lowest blood pressures acquired by the blood pressure value acquisition unit, into the equation (3).

  The above is a description of processing on one ultrasonic beam among a plurality of ultrasonic beams, and is an explanation of estimating one elastic characteristic in a blood vessel wall on one ultrasonic beam. Then, as shown in FIG. 7, ultrasonic transmission / reception is sequentially performed in the major axis direction of the blood vessel, and the elastic characteristics are estimated on each ultrasonic beam in the same procedure, thereby distributing the elastic characteristics in the major axis direction of the blood vessel. Will be obtained. In the case of the present embodiment, since the elastic characteristics are defined only in the blood vessel wall region, color coding is performed only on the blood vessel wall region when the image composition unit displays the result on the monitor by combining with the tomographic image. And display. Further, the elastic characteristics estimated on each ultrasonic beam may be displayed numerically, and the average value of the ultrasonic beam scanning range may be displayed numerically.

  Here, as described above, when the blood vessel wall is regarded as a thick cylindrical tube and it expands and contracts due to blood pressure, the depth direction distribution of the maximum displacement shows a monotonous decreasing tendency. Therefore, if the blood vessel wall expands and contracts in a common sense, the sign of the strain amount calculated by the strain amount calculation unit should be negative, and if it is positive, the reliability of the elastic property estimated using the formula The nature will be very low. When the blood flow-intima boundary and the outer membrane-tissue boundary are close to each other, and the distance between the two boundaries is equal to or shorter than the pulse width of the ultrasonic wave, the displacement of each of the two boundary positions is changed. The quantity measurement accuracy is extremely low.

Therefore, in the reliability determination unit, the sign of the strain amount calculated by the strain calculation unit is negative, or between the blood flow-intima boundary and the outer membrane-body tissue boundary detected by the boundary detection unit. If the distance is shorter than a predetermined threshold value, it is determined that the reliability of the estimated elastic property is low, and means for notifying that is provided. When the reliability is low, the image composition unit may be configured not to display the elastic characteristic distribution, or may be configured to notify by visual means such as letters. In the above description, it is assumed that the distortion amount or the boundary position is used. However, any one of the configurations may be used.
(Second Embodiment)
The difference between the present embodiment and the first embodiment is only the part for calculating the strain amount from the displacement amount, and the rest is the same as in the first embodiment, and the description thereof will be omitted.

  In the first embodiment, two points (A and B in FIG. 5) of the strong echo portion existing near the boundaries of the blood flow-intima boundary and the epicardium-body tissue boundary with relatively high displacement measurement accuracy. ), And the distortion amount is defined by the difference between the maximum displacement amount and the distance between the two points. In the present embodiment, each boundary between the blood flow-intima boundary and the outer membrane-tissue boundary Assuming that the depth distribution of the maximum displacement between two strong echo parts (A and B in Fig. 5) in the vicinity can be approximated by a function, the spatial differential in the depth direction of the function is the amount of distortion. It is characterized by.

  FIG. 6 shows a distortion amount calculation example when the approximation function is a linear function as a simple example. The depth direction distribution of the maximum displacement amount between the two points C and D of the strong echo portion existing in the vicinity of each of the blood flow-intima boundary and the outer membrane-body tissue boundary in FIG. Suppose that it is approximated by a linear function.

Xmax (d) = α · d + β (4)
Here, Xmax (d) is the maximum displacement at a certain depth d, and α and β are the slope and intercept of the approximated linear function.

  The slope α of the linear function of the equation (4) is estimated by the linear least square method, and is used as the distortion amount. As described above, the intima region of the blood vessel wall has low echo intensity and relatively poor displacement measurement accuracy. Therefore, when estimating the inclination α by the linear least square method, the echo intensity at each measurement point is calculated. Accordingly, the maximum displacement amount may be weighted. Further, a depth direction filter may be applied to the maximum displacement amount in advance, so that noise resistance can be increased.

  In the reliability determination unit, as in the first embodiment, when the sign of the estimated slope α is negative, it is determined that the reliability of the elastic property estimated by the elastic property estimation unit is low. If the value E represented by the following equation representing the degree of fit of the linear function of Equation (4) is higher than the set threshold value, the elastic property estimated by the elastic property estimating unit It may be determined that the reliability is low.

Error = Σ | Xmax_e (d) −Xmax_m (d) | ^ 2 (5)
Here, Xmax_e (d) is the depth direction distribution of the maximum displacement amount calculated by the estimated approximate function, and Xmax_m (d) is the depth direction distribution of the maximum displacement amount actually measured.

  In the above description, the approximate function is described as a linear function, but it may be a linear function such as a polynomial function or another nonlinear function, and the present invention does not limit this. In addition, as a method for estimating the slope of the approximate function, the linear least square method or the linear least square method weighted by the echo intensity is described. However, other estimation methods such as a nonlinear least square method are used. The present invention is not limited to this.

As described above, according to the present invention, it is possible to estimate the elastic characteristics of the blood vessel wall with higher accuracy, reliability, and stability, and it is useful as an ultrasonic diagnostic apparatus for measuring tissue properties of a subject. is there.

1 is a block diagram of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention. Outline explanatory diagram of elastic property estimation of blood vessel wall Illustration of each boundary and region of blood vessel wall Schematic diagram of distribution of maximum displacement around vessel wall Outline | summary explanatory drawing of the distortion calculation method in the 1st Embodiment of this invention Outline explanatory drawing of the distortion calculation method in the 2nd Embodiment of this invention Outline explanatory diagram of elastic property estimation in the conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Probe 102 Transmission part 103 Reception part 104 Tomographic image processing part 105 Memory 106 Image composition part 107 Monitor 108 Displacement measurement part 109 Strain calculation part 110 Boundary detection part 111 Elastic property estimation part 112 Memory 113 Blood pressure value acquisition part 114 Reliability Judgment unit 115 Shape determination unit

Claims (19)

A transmitter that emits ultrasonic waves from outside the body through the probe to the inside of the subject; and
A receiving unit that outputs a reception signal based on an ultrasonic echo reflected from the inside of the subject irradiated with ultrasonic waves;
A displacement measuring unit for measuring a displacement amount of an arbitrary part around the arterial blood vessel wall inside the subject based on an output from the receiving unit;
Based on at least one of the output from the receiving unit and the output from the displacement measuring unit,
A boundary detector for detecting blood flow-blood vessel wall boundary and blood vessel wall-peripheral tissue boundary of the blood vessel wall on the proximal side and the distal side of the probe;
A shape determining unit that determines the shape of the arterial blood vessel wall based on the output from the boundary detecting unit;
A strain calculation unit that calculates the amount of distortion of the arterial blood vessel wall from the output from the boundary detection unit or the output from the displacement measurement unit in the blood vessel wall on the proximal side or the distal side of the probe;
A blood pressure value acquisition unit that captures the blood pressure value of the subject;
Based on the output from the shape determination unit, the output from the distortion calculation unit, and the output from the blood pressure value acquisition unit,
An elastic property estimation unit for estimating an elastic property value of a blood vessel wall on the proximal side or the distal side of the probe;
The time when the distortion calculation unit calculates the distortion amount is a time when the displacement amount of the blood flow-blood vessel wall boundary in one heartbeat cycle or the blood vessel wall-peripheral body tissue boundary becomes maximum.
At that time, a distortion amount is calculated based on a change tendency of the displacement amount in a direction from the blood flow-blood vessel wall boundary to the blood vessel wall-peripheral body tissue boundary between or around the two boundaries. Ultrasonic diagnostic equipment. It has means for determining the reliability of at least one feature amount of each boundary detected by the boundary detection unit and the distortion amount calculated by the distortion amount calculation unit, and notifying the result. The ultrasonic diagnostic apparatus according to claim 1. In the strain calculation amount, the change tendency of the displacement amount in the direction from the blood flow-blood vessel wall boundary to the blood vessel wall-peripheral body tissue boundary is approximated by a function, and the spatial differential value in the direction is the strain amount. The ultrasonic diagnostic apparatus according to any one of claims 1 and 2. The ultrasonic diagnostic apparatus according to claim 3, wherein the function is a linear function. The ultrasonic diagnostic apparatus according to claim 4, wherein the linear function is a linear function. 6. The spatial differential value of the linear function is defined by a difference between maximum displacement amounts at two points existing in the vicinity of each of the two boundaries and a distance between the two points. The ultrasonic diagnostic apparatus as described. The ultrasonic diagnostic apparatus according to claim 6, wherein the two points are positions where the echo intensity locally takes a maximum value near each of the two boundaries. The ultrasonic diagnostic apparatus according to claim 6, wherein the maximum displacement amount at each of the two points is an average of the maximum displacement amounts at a plurality of locations around each of the two points. The ultrasonic diagnostic apparatus according to claim 3, wherein the spatial differential value is calculated by a linear least square method. The ultrasonic diagnostic apparatus according to claim 3, wherein the spatial differential value is calculated by a linear least square method weighted according to a magnitude of a received signal. The ultrasonic diagnostic apparatus according to claim 3, wherein the function is a nonlinear function. The ultrasonic diagnostic apparatus according to claim 3, wherein the spatial differential value is calculated by a non-linear least square method. The ultrasonic diagnostic apparatus according to claim 3, wherein the spatial differential value is calculated by a non-linear least square method weighted according to a magnitude of a received signal. The ultrasonic diagnostic apparatus according to claim 1, wherein a feature amount used when determining the reliability of the elastic characteristic value of the artery wall is a sign of the strain amount. 14. The feature amount used when determining the reliability of the elastic characteristic value of the arterial wall is a distance between the blood flow-intima boundary and the epicardium-body tissue boundary. The ultrasonic diagnostic apparatus in any one of. 14. The feature amount used when determining the reliability of the elastic characteristic value of the arterial wall is a distance between the blood flow-intima boundary and the epicardium-body tissue boundary. The ultrasonic diagnostic apparatus in any one of. The ultrasonic diagnostic apparatus according to claim 1, wherein the arterial blood vessel wall has a cylindrical tubular shape, and the shape is expressed by the thickness of the blood vessel wall and the inner diameter of the blood vessel. The ultrasonic diagnostic apparatus according to claim 1, wherein an elastic characteristic of a blood vessel wall on a distal side of the probe is estimated. The transmission unit transmits a plurality of ultrasonic pulses toward a plurality of points along the long axis direction of the blood vessel to obtain an elastic characteristic distribution in the long axis direction of the blood vessel. The ultrasonic diagnostic apparatus in any one of.

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