JP4627221B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that measures a property characteristic of a tissue constituting a subject, particularly an elastic modulus.

  The ultrasonic diagnostic apparatus irradiates a subject with ultrasonic waves and analyzes information included in the echo signal to inspect the subject non-invasively. 2. Description of the Related Art Conventionally, an ultrasonic diagnostic apparatus that has been widely used obtains the structure of a subject as a tomographic image by converting the intensity of an echo signal into the luminance of a corresponding pixel. Thereby, the internal structure of the subject can be known. In addition, an ultrasonic diagnostic apparatus that detects Doppler shift of an echo signal and displays an image of motion information of a subject, for example, blood flow information, has been used.

  On the other hand, in recent years, by analyzing mainly the phase of the echo signal, the movement of the tissue of the subject is accurately measured, and physical (property) characteristics such as tissue distortion, elastic modulus, and viscosity are obtained. Has been tried.

  Patent Document 1 uses the amplitude and phase of the detection output signal of the echo signal to determine the instantaneous position of the subject, thereby tracking the subject tissue with high accuracy and applying it to the beating heart tissue. A method for capturing the minute vibrations that occur is disclosed. According to this method, ultrasonic pulses are transmitted a plurality of times at intervals of ΔT in the same direction with respect to the subject, and the ultrasonic waves reflected by the subject are received. As shown in FIG. 8, the received echo signals are y (t), y (t + ΔT), and y (t + 2ΔT). The reception time t1 of the echo signal obtained from a certain depth x1 is t1 = x1 / (C / 2) where the pulse transmission time is t = 0. Where C is the speed of sound. At this time, if the phase shift between y (t1) and y (t1 + ΔT) is Δθ, and the center frequency of the ultrasonic wave near t1 is f, the movement amount Δx of x1 in this period ΔT is expressed by the following equation ( 1).

  Δx = −C · Δθ / 4πf (1)

  By adding the movement amount Δx to x1, the position x1 ′ of x1 after ΔT seconds can be obtained as shown in the following formula (2). By repeating this calculation, the same part x1 of the subject is obtained. Can be tracked. This method is called a phase difference tracking method.

  x1 '= x1 + Δx (2)

  Patent Document 2 discloses a method of further developing the method of Patent Document 1 and obtaining the elastic modulus of a subject tissue, particularly an arterial wall. According to this method, first, as shown in FIG. 9, ultrasonic waves are transmitted from the probe 101 toward the blood vessel wall 16 and the echo signals from the measurement points A and B set on the blood vessel wall 16 are patented. By analyzing according to the method of Document 1, the movement of the measurement sites A and B is tracked. FIG. 10 shows tracking waveforms TA and TB indicating the positions of the measurement points A and B. An electrocardiographic waveform ECG is also shown.

  As shown in FIG. 10, the tracking waveforms TA and TB have a periodicity that matches the electrocardiogram waveform ECG. This indicates that the artery expands and contracts in line with the heart cycle of the heart. Specifically, when a large peak called an R wave is seen in the electrocardiogram waveform ECG, the contraction of the heart starts, and blood is pushed out into the artery by the contraction of the heart. The blood vessel rapidly expands due to the blood pressure change at this time. Therefore, after the R wave appears in the electrocardiogram waveform ECG, the tracking waveforms TA and TB also rise rapidly, and the artery expands rapidly. Thereafter, as the heart expands slowly, the tracking waveforms TA and TB also gradually fall, and the arterial blood vessels slowly contract. The artery repeats this movement.

  The difference between the tracking waveforms TA and TB is a thickness change waveform W between the measurement points AB. The thickness change waveform W can also be regarded as a distortion waveform between AB. The maximum thickness change amount ΔW can be obtained from the difference between the maximum value Wmax and the minimum value Wmin of the thickness change waveform W.

  ΔW = Wmax−Wmin (3)

  If the reference thickness at the time of initialization between the measurement points AB is Ws, the maximum strain amount ε between the measurement points AB is as follows.

  ε = ΔW / Ws (4)

  Further, the maximum blood pressure Pmax and the minimum blood pressure Pmin of the subject at this time are measured using a blood pressure monitor or the like. The blood pressure difference ΔP is expressed by the following equation.

  ΔP = Pmax−Pmin (5)

  The maximum strain amount ε is considered to have occurred due to the blood pressure difference ΔP. Since the elastic modulus Er is defined as a value obtained by dividing the stress by the strain, the elastic modulus Er between the measurement points AB is expressed by the following equation.

  Er = ΔP / ε = ΔP · Ws / ΔW = ΔP · Ws / (Wmax−Wmin) (6)

  Non-Patent Document 1 discloses a method of calculating the elastic modulus of each part using the maximum strain amount ε and the blood pressure difference ΔP when the blood vessel is a tube having a non-uniform thickness.

By performing these calculations on a plurality of points on the tomographic image, a distribution image of the elastic modulus Er is obtained. As shown in FIG. 9, when the atheroma 11 occurs in the blood vessel wall 16, the elastic modulus is different between the atheroma and the surrounding vascular wall tissue. Therefore, if an elastic modulus distribution image is obtained, it is possible to diagnose the generation and position of atheroma.
Japanese Patent Laid-Open No. 10-5226 JP 2000-229078 A Hasegawa et al., “Measuring method of local wall elastic modulus of pipe with non-uniform wall thickness”, J Med Ultrasonics Vol.28 No.1 (2001)

  However, even if the elastic modulus of the subject is accurately obtained, the elastic modulus itself is a property characteristic and does not necessarily indicate a difference in tissue contained in the subject. For this reason, even if an accurate elastic modulus is required, it may be difficult to make a detailed diagnosis of the state of the subject.

  In addition, the elastic modulus measurement method according to the prior art has a problem that noise resistance is low because the elastic modulus is measured using the difference between the maximum value Wmax and the minimum value Wmin of the thickness change waveform W. For example, when the thickness change waveform W shown in FIG. 11 is obtained, the elastic modulus is obtained with the values at times t1 and t2 as the maximum value Wmax and the minimum value Wmin, respectively. However, as shown in the figure, the value of the thickness change waveform W at time t2 is not correct because noise is mixed therein.

  The present invention solves at least one of the problems of the prior art, and provides an ultrasonic diagnostic apparatus that can easily identify a tissue contained in a subject and can measure a property characteristic with high accuracy. For the purpose.

  An ultrasonic diagnostic apparatus according to the present invention includes: a transmission unit that generates a drive signal for driving a probe to transmit ultrasonic waves to a subject that is periodically deformed by stress; and the ultrasonic waves in the subject. An echo obtained by reflection is received by the probe, and a change in the distance between any two measurement sites in the subject is shown based on the reception unit that generates a reception echo signal and the reception echo signal By comparing the arithmetic unit for calculating the thickness change waveform, the reference waveform generation unit for generating a plurality of viscosity characteristic reference waveforms, and the plurality of viscosity characteristic reference waveforms and the thickness change waveform, respectively. A comparison unit that calculates a viscosity characteristic index indicating a degree of coincidence between the thickness change waveform and the viscosity characteristic reference waveform; and a viscosity coefficient determination unit that determines a viscosity based on the viscosity characteristic index. Preparation There.

  In a preferred embodiment, the reference waveform for viscosity characteristics is a distortion waveform of the subject obtained based on information indicating a stress change of the subject when a predetermined viscosity is assumed, and the viscosity rate The determination unit outputs a viscosity coefficient assumed in the reference waveform for the viscosity characteristic from which the smallest value among the viscosity characteristic indexes is obtained.

  In a preferred embodiment, the comparison unit includes the coefficient so that a matching residual between one of the thickness change waveform and each of the viscosity characteristic reference waveforms multiplied by a first coefficient and the other is minimized. Is output as the viscosity characteristic index.

  In a preferred embodiment, the information indicating the stress change of the subject is a blood pressure waveform of the subject.

  In a preferred embodiment, the arithmetic unit is based on the movement waveform calculation unit that calculates a movement waveform that indicates a change in position of a plurality of measurement sites in the subject based on the received echo signal, and the movement waveform. And a thickness change waveform calculation unit for calculating a thickness change waveform between the two measurement parts.

  In a preferred embodiment, the ultrasonic diagnostic apparatus further includes a blood vessel diameter calculation unit that calculates a blood vessel diameter change waveform included in the subject based on the movement waveform, and the information indicating the stress change of the subject is: It is a waveform obtained by correcting the blood vessel diameter waveform with the maximum and minimum blood pressure values of the subject.

  In a preferred embodiment, the reference waveform generation unit receives a thickness change waveform at a position close to a blood vessel cavity of a blood vessel wall included in the subject from the arithmetic unit, and a thickness at a position close to the blood vessel cavity. A waveform obtained by correcting the change waveform with the maximum and minimum blood pressure values of the subject is used as information indicating the stress change of the subject.

  In a preferred embodiment, the reference waveform generation unit further generates an elastic characteristic reference waveform, and the comparison unit compares the elastic characteristic reference waveform with the thickness change waveform to thereby calculate the thickness. The maximum thickness change amount of the change waveform is calculated.

  In a preferred embodiment, the comparison unit is configured to minimize the matching residual between one of the thickness change waveform and the elastic characteristic reference waveform multiplied by a second coefficient and the other. A coefficient is determined, and the maximum thickness change amount is calculated from the amplitude of the second coefficient and the elastic characteristic reference waveform.

  In a preferred embodiment, the ultrasonic diagnostic apparatus further includes an elastic modulus calculation unit that receives information on a stress difference of the stress generated in the deformation cycle of the subject and obtains an elastic modulus from the maximum change amount.

  In a preferred embodiment, the reference waveform generation unit generates the elastic characteristic reference waveform based on a blood pressure change waveform of the subject.

The method for controlling an ultrasonic diagnostic apparatus according to the present invention is a method for controlling an ultrasonic diagnostic apparatus by a control unit of the ultrasonic diagnostic apparatus, the step of driving the probe to transmit ultrasonic waves (A),
A step (B) of receiving, by the probe, an echo obtained by reflection of the ultrasonic wave in a subject periodically deformed by a stress, and any two in the subject based on the received echo signal; A step (C) of calculating a thickness change waveform indicating a change in distance between two measurement sites; a step (D) of generating a plurality of viscosity characteristic reference waveforms; and the plurality of viscosity characteristic reference waveforms and the thickness. A step (F) of calculating a viscosity characteristic index indicating a degree of coincidence between the thickness change waveform and the viscosity characteristic reference waveform by comparing each of the change waveforms, and the viscosity characteristic index And determining the viscosity (G).

  In a preferred embodiment, the viscosity characteristic reference waveform is a distortion waveform of the subject obtained based on information indicating a stress change of the subject when a predetermined viscosity is assumed, and the step ( G) outputs the viscosity coefficient assumed in the reference waveform for the viscosity characteristic from which the smallest value among the viscosity characteristic indexes is obtained.

  In a preferred embodiment, the step (F) is performed so that a matching residual between one of the thickness change waveform and each of the viscosity characteristic reference waveforms multiplied by a first coefficient and the other is minimized. The matching residual when the coefficient is determined is output as the viscosity characteristic index.

  In a preferred embodiment, the information indicating the stress change of the subject is a blood pressure waveform of the subject.

  In a preferred embodiment, the step (C) includes a step of calculating a movement waveform indicating a change in position of a plurality of measurement sites in the subject based on the received echo signal, and based on the movement waveform, Calculating a thickness change waveform between the two measurement sites.

  In a preferred embodiment, the control method further includes a step (H) of calculating a blood vessel diameter change waveform included in the subject based on the movement waveform, and the information indicating the stress change of the subject is the It is a waveform obtained by correcting a blood vessel diameter waveform with the maximum and minimum blood pressure values of the subject.

  In a preferred embodiment, the step (C) generates a thickness change waveform at a position close to the lumen of the blood vessel wall included in the subject, and the step (D) is close to the lumen. A waveform obtained by correcting the thickness change waveform at the position with the maximum and minimum blood pressure values of the subject is used as information indicating the stress change of the subject.

  In a preferred embodiment, the step (D) further generates an elastic characteristic reference waveform, and the step (F) compares the elastic characteristic reference waveform with the thickness change waveform, thereby The maximum thickness change amount of the thickness change waveform is calculated.

  In a preferred embodiment, the step (F) is performed so that a matching residual between one of the thickness change waveform and the elastic characteristic reference waveform multiplied by a second coefficient and the other is minimized. A second coefficient is determined, and the maximum thickness change amount is calculated from the amplitude of the second coefficient and the elastic characteristic reference waveform.

  In a preferred embodiment, the control method further includes a step (I) of receiving information on a stress difference of the stress generated in the deformation cycle of the subject and obtaining an elastic modulus from the maximum change amount.

  In a preferred embodiment, the step (D) generates the elastic characteristic reference waveform based on the blood pressure change waveform of the subject.

  According to the present invention, since the viscosity is estimated by comparing the reference waveform and the thickness change waveform, it is possible to identify the difference in the subject tissue from the estimated viscosity. For this reason, it becomes possible to discriminate | determine the structure | tissue whose identification was difficult with the value of the elasticity modulus. Further, the reference waveform and the thickness change waveform are compared to estimate the maximum thickness change amount. For this reason, even if sudden noise or the like is superimposed on the thickness change waveform, it is possible to obtain a more accurate maximum thickness change amount and elastic modulus.

  Hereinafter, embodiments of an ultrasonic diagnostic apparatus according to the present invention will be described. FIG. 1 is a block diagram showing the configuration of the ultrasonic diagnostic apparatus 201. The ultrasonic diagnostic apparatus 201 calculates the elastic modulus of the subject using ultrasonic waves and also estimates the viscosity of the subject. By determining the viscosity, it is possible to determine the difference in the tissue that is difficult to determine only by the elastic modulus. For this purpose, the ultrasonic diagnostic apparatus 201 includes a transmission unit 102, a reception unit 103, a calculation unit 151, a reference waveform generation unit 117, a comparison unit 118, and a viscosity rate determination unit 121. In addition, the ultrasonic diagnostic apparatus 201 includes a control unit 100 in order to control each component of the ultrasonic diagnostic apparatus 201.

  The transmission unit 102 generates a drive signal for driving the probe 101 at a predetermined timing based on a command from the control unit 100. The probe 101 transmits an ultrasonic wave based on the drive signal. The transmitted ultrasonic wave reaches the subject that is periodically deformed by the stress and is reflected inside the subject. In the present embodiment, the subject includes a blood vessel wall of an arterial blood vessel, and the elastic modulus of the blood vessel wall is obtained. Since blood flows in the arterial blood vessel in a cycle that matches the cardiac cycle, the blood vessel wall is periodically deformed by the stress received from the blood.

  The receiving unit 103 receives an echo reflected from the subject by the probe 101, converts the echo into an electric signal, amplifies it, and generates a received echo signal. Also, the received echo signal is converted into a digital signal.

  The transmission unit 102 and the reception unit 103 preferably transmit an ultrasonic wave so as to scan the subject, and set a delay time of the drive signal and the reception echo signal so as to detect only the ultrasonic wave from a predetermined position and direction. It is preferable that a delay time control unit to be controlled is included. The probe 101 preferably includes an array transducer in which a plurality of ultrasonic transducers are arranged.

  The computing unit 151 tracks the movements of a plurality of measurement parts of the subject by analyzing the received echo signal. And the thickness change waveform which is the distance change between the arbitrary two measurement parts in a subject is produced | generated. For this purpose, the calculation unit 151 includes a movement waveform calculation unit 115 and a thickness change waveform calculation unit 116. The movement waveform calculation unit 115 receives the received echo signal, and calculates a movement waveform that is a change in position of a plurality of measurement sites set in the subject according to equations (1) and (2). The thickness change waveform calculation unit 116 calculates a thickness change waveform indicating a change in distance between two selected from a plurality of measurement sites by obtaining a difference between movement waveforms of the two measurement sites.

  A plurality of measurement sites can be set on one ultrasonic beam according to the resolution determined by the frequency of ultrasonic waves to be transmitted. Therefore, by moving the ultrasonic beam, it is possible to acquire each movement waveform of the measurement sites arranged in two dimensions.

  The reference waveform generation unit 117 generates an elastic characteristic reference waveform and a plurality of viscosity characteristic reference waveforms. As will be described in detail below, these reference waveforms serve as a reference for comparison with the thickness change waveform in the comparison unit 118. In the present embodiment, the elastic characteristic reference waveform is generated by obtaining a blood pressure waveform indicating a change in blood pressure of the arterial blood vessel of the subject from the real-time sphygmomanometer 150 and adjusting the amplitude. A plurality of viscosity characteristic reference waveforms are also generated based on the blood pressure waveform. Each viscosity characteristic reference waveform is a distortion waveform of the subject obtained based on the blood pressure waveform when a predetermined viscosity is assumed.

  The comparison unit 118 has two functions. One relates to the calculation of the elastic modulus and the other relates to the estimation of the viscosity. Specifically, in order to calculate the elastic modulus, the thickness change waveform obtained from the thickness change waveform calculation unit 116 is compared with the reference waveform for elastic characteristics obtained from the reference waveform generation unit 117 to obtain the thickness. The maximum thickness change amount of the change waveform is calculated. More specifically, the coefficient is determined so that the matching residual between one of the thickness change waveform and the elastic characteristic reference waveform multiplied by the coefficient is minimized, and the determined coefficient and elastic characteristic reference is determined. The maximum thickness change amount is calculated from the waveform amplitude.

  In addition, for estimation of viscosity, each of the plurality of viscosity characteristic reference waveforms is compared with the thickness change waveform, and each viscosity characteristic reference waveform and the thickness change waveform indicate the degree of coincidence. Calculate the indicator. More specifically, the matching residual is calculated when the coefficient is determined so that the matching residual between the thickness change waveform and the reference waveform for each viscosity characteristic multiplied by the coefficient and the other is minimized. These matching residuals are output as an index for viscosity characteristics. The comparison unit 118 performs the calculation of the elastic modulus and the estimation of the viscosity for each period of the thickness change waveform.

  The viscosity determining unit 121 estimates the viscosity based on the viscosity characteristic index. Specifically, the matching residuals obtained using the respective viscosity characteristic reference waveforms are compared with each other, and the viscosity characteristic reference waveform that provides the minimum matching residual is specified. Each viscosity characteristic reference waveform is obtained by assuming a predetermined viscosity, so that the thickness change waveform of the object estimated by the viscosity value assumed in the specified viscosity characteristic reference waveform is estimated. Is the viscosity at the obtained site.

  The ultrasonic diagnostic apparatus 201 preferably further includes an elastic modulus calculation unit 120 that calculates an elastic modulus from the obtained maximum thickness change amount. The elastic modulus calculation unit 120 receives information related to stress applied to the subject such as the real-time sphygmomanometer 150. For example, the blood pressure difference ΔP between the maximum blood pressure and the minimum blood pressure is received from the real-time sphygmomanometer 150. Then, the elastic modulus Er is obtained from the blood pressure difference ΔP and the maximum thickness change amount ΔW according to the equation (6). Here, the reference thickness Ws is a distance (for example, 400 μm) between the two measurement parts for which the thickness change waveform is obtained, and is determined in advance according to the positions of the two measurement parts selected by the thickness change waveform calculation unit 116. Is set. In this way, the elastic modulus of the subject can be obtained.

  The obtained elastic modulus and viscosity are preferably displayed together with the tomographic image of the subject. This is because the position of the measurement site can be easily shown. For this reason, it is preferable that the ultrasonic diagnostic apparatus 201 further includes a tomographic image generation unit 104, an image synthesis unit 105, and an image display unit 106. The tomographic image generation unit 104 includes a filter and an amplitude detector, mainly analyzes the amplitude of the received echo signal received from the reception unit 103, and generates an image signal of a tomographic image obtained by imaging the internal structure of the subject.

  The image construction unit 105 receives the image signal, the elastic modulus data obtained from the elastic modulus calculation unit 120, and the viscosity data obtained from the viscosity determining unit 121, and the obtained viscosity and elastic modulus are tomographic images. The image signal and the elastic modulus data are combined so as to be mapped to an appropriate position above. The image display unit 106 displays the synthesized image. The tomographic image may be displayed on the two image display units 106 so that the viscosity and the elastic modulus are displayed simultaneously, and the viscosity and the elastic modulus may be displayed on the two tomographic images, respectively. Further, one tomographic image may be displayed on the image display unit 106, and the viscosity coefficient and the elastic modulus may be switched and displayed by the operation of the operator.

  Next, the calculation of the elastic modulus and the estimation of the viscosity will be described in detail. First, the elastic modulus calculation method will be described in detail.

  FIG. 2 shows one period of the elastic characteristic reference waveform M (t) generated by the reference waveform generation unit 117. This waveform indicates a blood pressure change in the arterial blood vessel of the subject, and is acquired by the real-time sphygmomanometer 150 or the like. ΔW, which is the amplitude of the elastic characteristic reference waveform M (t), is normalized to be a reference value, for example, 1 μm.

  FIG. 3 shows the thickness change waveform y (t) obtained from the thickness change waveform calculation unit 116. This thickness change waveform is one cardiac cycle of the waveform obtained by actually measuring the subject. t represents the sampling time. When the number of sampling points is N, t is an integer represented by t = 0, 1,... N−1.

  The comparison unit 118 receives the elastic characteristic reference waveform M (t) and the thickness change waveform y (t), and when the amplitude of the thickness change waveform y (t) is multiplied, the elastic characteristic reference waveform M (t) Is calculated by the method of least squares. When the coefficient to be multiplied by y (t) is k, and R is the square of the difference between M (t) and k · y (t), R is expressed by Expression (7).

  The equation (7) is partially differentiated by k using the coefficient k as a variable, and when the partially differentiated equation becomes 0, the square difference R is minimized.

Solving equation (8) for k yields equation (9).

  When the measured thickness change waveform y (t) is multiplied by k, the square of the difference from the elastic characteristic reference waveform M (t) having an amplitude of 1 μm is minimized. It means that the two waveforms are the best match. Therefore, the amplitude A of the measured thickness change waveform y (t) is obtained by the following equation (10).

  A = 1 / k (μm) (10)

  Similar to the above-described calculation, it may be calculated how many times the amplitude of the elastic characteristic reference waveform M (t) is multiplied to approach the actual thickness change waveform y (t). In this case, if the coefficient multiplied by the elastic characteristic reference waveform M (t) is k ′ and the residual is R ′, the following equation (11) is obtained.

  When a value obtained by partial differentiation of R ′ by k ′ is set to 0 (formula (12)), and solving for the coefficient k ′, formula (13) is obtained.

  In this case, when the elastic characteristic reference waveform having an amplitude of 1 μm is multiplied by k ′, the coefficient k ′ is the smallest square of the difference from the actually measured thickness change waveform y (t), and the two waveforms are the most consistent. Is meant to do. Therefore, the amplitude A ′ of the thickness change waveform y (t) is obtained by the equation (14).

  A ′ = k ′ (μm) (14)

  In this way, the comparison unit 118 receives the elastic characteristic reference waveform M (t) and the thickness change waveform y (t), and uses the equation (9) or equation (13) to determine the elastic property reference waveform M ( The coefficient k or the coefficient k ′ that minimizes the matching residual between t) and the thickness change waveform y (t) is calculated. From the calculated coefficient k or coefficient k ′, a maximum thickness change amount that is an amplitude of the thickness change waveform is further calculated.

FIG. 4 schematically shows one cardiac cycle of thickness change waveforms y ₀ (t) and y ₁ (t) obtained from blood vessel walls having different elastic moduli. As shown in FIG. 4, although the amplitude is different due to the difference in elastic modulus, the changes in the time axis direction of the two thickness change waveforms are the same. This means that the change in blood pressure, which is a change in stress received by the subject, or the state of heart vibration is ideally almost constant.

  As shown in FIG. 4, according to the conventional method, when the maximum thickness change amount of the thickness change waveform is obtained, it is necessary to obtain the maximum value Wmax and the minimum value Wmin of the thickness change waveform. In contrast, in the present invention, the maximum thickness change amount is estimated by analyzing the overall consistency between the thickness change waveform and the elastic characteristic reference waveform. As described above, when it is assumed that only the thickness change waveform amplitude is different due to the difference in elastic modulus, this means that the maximum thickness change amount is estimated from the entire thickness change waveform for one cardiac cycle.

As shown in the thickness change waveform y ₀ (t) in FIG. 4, the maximum value Wmax and the minimum value Wmin of the thickness change waveform are determined at one point of the thickness change waveform y ₀ (t). . However, the inclinations of the inclined portions a1, a2, and a3 between the maximum value Wmax and the minimum value Wmin of the thickness change waveform change according to the maximum value Wmax and the minimum value Wmin. That is, the inclinations of the inclined portions a1, a2, and a3 include information on the maximum value Wmax and the minimum value Wmin. For this reason, even if the maximum value Wmax and the minimum value Wmin cannot be obtained correctly by superimposing noise on the thickness change waveform, as long as the noise is not superposed so that the shape of the thickness change waveform is significantly deformed. The maximum thickness change amount can be estimated from the entire thickness change waveform including the inclined portions a1, a2, and a3.

  Therefore, according to the present invention, the maximum thickness change amount or the elastic modulus can be obtained with high accuracy without being easily influenced by noise such as spike noise that is suddenly mixed.

  As is clear from the above description, since information on the maximum value Wmax and the minimum value Wmin is included in the inclined portions a1, a2, and a3, respectively, even if a part of one heart cycle of the thickness change waveform is used. Thus, it is possible to estimate the maximum thickness change amount in which the influence of noise is reduced as compared with the conventional case. However, since the accuracy of the estimated maximum thickness change amount increases as the section to be selected increases, it is most preferable to obtain the maximum thickness change amount by comparing the reference waveform with the entire one-center cycle of the thickness change waveform. This can be explained as follows using equation (13). When the thickness change waveform y (t) is expressed by the sum of the thickness change s (t) and the noise n (t), the equation (13) can be expressed as follows.

  When the noise n (t) is spike noise or random noise, the second term of the numerator of the equation (13 ′) becomes smaller than the first term as the addition interval becomes longer. Therefore, when the thickness change s (t) is similar to the reference waveform (s (t) = m · M (t)), the addition interval is sufficiently long, and the second term of the equation (13 ′) can be ignored. Can be expressed by the following equation (13 ″).

  Therefore, the true coefficient m can be estimated. On the contrary, it can be understood from this that the thickness change amount in which the influence of noise is reduced can be estimated by comparing the reference waveform with the entire thickness change waveform.

  In the present invention, since the maximum thickness variation and the elastic modulus are obtained using the elastic characteristic reference waveform and the measured value, it is important to prepare an appropriate elastic characteristic reference waveform. In this embodiment, since the elastic characteristic reference waveform is generated based on the blood pressure waveform of the subject, the period of the elastic characteristic reference waveform and the period of the thickness change waveform are in good agreement, and the two waveforms are correct. Can be compared. Further, the blood pressure change of the subject is relatively large, and the measurement of the blood pressure change uses an established technique, so that noise superimposed on the blood pressure waveform is small. For this reason, it is preferable to use the elastic characteristic reference waveform generated based on the blood pressure waveform as the reference of the thickness change waveform affected by noise. In addition, since the elastic characteristic reference waveform is generated based on the blood pressure waveform of the subject, individual differences of the subject can be reflected in the elastic characteristic reference waveform.

  Next, the viscosity estimation method will be described in detail. The strain waveform of the subject is determined by the stress change that the subject receives and the viscoelastic characteristics of the subject. Therefore, when the blood pressure waveform p (t) is obtained, the strain waveform εi (t) created on the assumption of various elastic moduli Ei and viscosity ηi has an assumed elastic modulus Ei and viscosity ηi of the subject. When coincident with the true elastic modulus and viscosity, it coincides with the strain waveform ε (t) = y (t) / Ws obtained from the measured thickness change waveform y (t), and ε (t) and εi ( The residual with t) should be zero. Therefore, the residual of ε (t) and εi (t) is evaluated, and the viscosity of the subject is estimated by determining the elastic modulus Ei and the viscosity ηi that minimize the residual. In this embodiment, the vascular wall distortion waveform is selected as the reference waveform. When the viscosity values of the measurement sites are set to η1, η2, and η3 and the blood vessel wall distortion waveform is generated based on the blood pressure waveform, for example, ε1 (t) and ε2 (t) ε3 (t) in FIG. A waveform is obtained. Since the viscosities are different, the changes of these waveforms in the time axis direction are different. Comparing the thickness change waveform y (t) with these distortion waveforms, the thickness change waveform y (t) is the best match with ε2 (t), although the amplitude is different. Therefore, the viscosity assumed in ε2 (t) is estimated as the value of the viscosity of the measurement site.

  Hereinafter, the measurement method will be specifically described. First, the blood pressure waveform of the subject is p (t), and the distorted waveform of the blood vessel wall is ε (t). Assuming that the Laplace transforms of p (t) and ε (t) are p (ω) and ε (ω) and the transfer function of the blood vessel wall is B (ω), the blood pressure waveform p (ω) is expressed by the following equation (15). Indicated by

p (ω) = B (ω) ε (ω) (15)

  When a transfer function B (ω) is expressed using a Voigt model generally used for modeling viscoelasticity, the following equation (16) is obtained.

B (ω) = E ′ + jωη ′ (16)

  Here, E ′ is a static elastic modulus and η ′ is a viscosity. The elastic modulus E0 calculated from the reference waveform for elastic characteristics satisfies the relationship of the following formula (17).

  However, E ′ is E0 · E, and ωη ′ = E0 · ωη. Therefore, the viscosity is estimated with E = E ′ / E0 = 1. Specifically, values η1, η2, η3, η... Ηi..., N that are increased at predetermined intervals so that η includes a value assumed as the viscosity of the subject from 0 are set. By substituting these values into E and η in equation (16), transfer functions B1 (ω), B2 (ω) B3 (ω)... ω)... BN (ω) is calculated. Further, the transfer function Bi (ω) obtained using the assumed viscosity ηi is substituted into the following equation (18).

εi (ω) = p (ω) / Bi (ω) (18)

  Accordingly, εi (ω), i = 1, 2,... N is calculated. By subjecting this to inverse Fourier transform, a distortion waveform εi (t), i = 1, 2,... N is calculated. The reference waveform generation unit 117 generates the distortion waveform εi (t), i = 1, 2,... N as a viscosity characteristic reference waveform. As described above, the viscosity characteristic values are assumed to be η1, η2, η3, η... Ηi.

  Assuming that the relationship between the distortion waveform ε (t) of the blood vessel wall and the blood pressure waveform p (t) is non-linear, equation (19) may be used instead of equation (15).

log (p (ω)) = B (ω) ε (ω) (19)

  Even in this case, the transfer function Bi (ω) when η is assumed to be values η1, η2, η3, η... Ηi. Get.

εi (ω) = log (p (ω)) / Bi (ω) (20)

  Distortion waveform εi (t), i = 1, 2,... N is similarly calculated by inverse Fourier transform of equation (20). In addition, 1 / Bi (ω) is subjected to inverse Fourier transform to obtain an impulse response bi (t), and εi (t is obtained by convolving bi (t) with p (t) or log (p (t)). ) May be requested.

  The comparison unit 118 is obtained by multiplying one of the viscosity characteristic reference waveform εi (t), i = 1, 2,... N and the thickness change waveform y (t) by a coefficient. The matching residuals are calculated when the coefficients are determined so that the matching residual with the other is minimized. Specifically, in the equations (7) and (9), instead of the elastic characteristic reference waveform M (t), the viscosity characteristic reference waveform εi (t), i = 1, 2,... Using N, substitute the value of k obtained in equation (9) into equation (7) to obtain R. Since k is determined so that the square difference R is minimized, R at this time is Rim. That is, the matching residual Rim (i = 1, 2,... N) is obtained by the following equation (21).

  The viscosity determination unit 121 receives the matching residuals R1m, R2m,... RNm from the comparison unit 118, and determines the viscosity ηi assumed in the reference waveform for the viscosity characteristic from which the smallest matching residual is obtained. Then, the determined viscosity is output. Although the determined viscosity is not a value obtained by direct calculation, for the reason described above, it is estimated that the viscosity is a correct viscosity at the measurement site where the thickness change waveform is obtained.

  In this way, the ultrasonic diagnostic apparatus 201 can determine the elastic modulus and viscosity. Therefore, for example, even if it is difficult to determine from the elastic modulus value whether fat is deposited in the intima-media complex or whether the intima-media complex is inflamed due to vasculitis, It is possible to distinguish both from the value of. As a result, according to the present invention, it is possible to discriminate a tissue difference that is difficult to discriminate from only a tomographic image obtained by a conventional ultrasonic diagnostic apparatus or an elastic modulus by obtaining an elastic modulus and a viscosity. This makes it possible to perform more accurate diagnosis.

  In the above-described embodiment, the elastic characteristic reference waveform and the viscosity characteristic reference waveform are generated based on the blood pressure waveform. However, as described above, a stress change applied to the subject or a shape change based on the stress change. Various information can be used to generate the elastic characteristic reference waveform and the viscosity characteristic reference waveform.

  For example, the ultrasonic diagnostic apparatus 202 shown in FIG. 6 includes a blood vessel diameter calculation unit 142, and generates an elastic characteristic reference waveform and a viscosity characteristic reference waveform based on a blood vessel diameter change waveform. Specifically, the blood vessel diameter calculation unit 142 may generate two movement change waveforms in the vicinity of the vascular lumen of the intima from the movement waveform calculation unit 115 or two points of movement change in the vicinity of the epicardial extravascular tissue. A waveform is received, and a blood vessel diameter change waveform is generated from these two points. The reference waveform generation unit 117 ′ receives the blood vessel diameter change waveform, normalizes the amplitude to be 1 μm, for example, and generates an elastic characteristic reference waveform. Further, the blood vessel diameter change waveform is corrected by the maximum blood pressure value and the minimum blood pressure value received from the sphygmomanometer 119 to generate a blood pressure waveform p ′ (t). Further, based on the blood pressure waveform p ′ (t), the viscosity characteristic reference waveform εi (t), i = 1, 2,... N is generated as described above. In this case, it is preferable to use a blood vessel inner diameter change waveform as the viscosity characteristic reference waveform in order to avoid the influence of the viscosity of the blood vessel wall.

  In the ultrasonic diagnostic apparatus 203 shown in FIG. 7, the reference waveform generation unit 117 ″ receives two thickness change waveforms close to the vascular cavity of the intima from the thickness change waveform calculation unit 116, and the amplitude Is standardized to be 1 μm, for example, and a reference waveform for elastic characteristics is generated. Further, the two thickness change waveforms close to the blood vessel cavity are corrected by the maximum blood pressure value and the minimum blood pressure value received from the sphygmomanometer 119 to generate the blood pressure waveform p ′ (t). Further, based on the blood pressure waveform p ′ (t), the viscosity characteristic reference waveform εi (t), i = 1, 2,... N is generated as described above.

  Such a blood vessel diameter change waveform and two thickness change waveforms in the vicinity of the blood vessel cavity of the intima are very similar to a waveform indicating a change in stress that the subject undergoes as blood pressure change. Therefore, even if the elastic characteristic reference waveform and the viscosity characteristic reference waveform are generated using these waveforms, the elastic modulus and viscosity can be obtained as described above.

  Further, the same effect can be obtained by using the velocity difference waveform between the two points obtained from the vascular diameter change waveform and the two points close to the vascular cavity of the intima. In this case, the velocity difference waveform between the two measurement sites may be obtained in advance, or the velocity difference waveform may be obtained by time differentiation of the blood vessel diameter change waveform. Further, the speed difference waveform may be obtained by time differentiation of the blood pressure waveform.

  In the above-described embodiment, the ultrasonic diagnostic apparatus calculates both the elastic modulus and the viscosity, but the elastic modulus may not be obtained when it is intended to discriminate the difference between tissues.

  The ultrasonic diagnostic apparatus of the present invention is suitable for discriminating tissues constituting a subject and measuring physical properties such as tissue thickness change amount, strain amount, and elastic properties.

1 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention. The reference waveform produced | generated in the reference | standard waveform production | generation part of the ultrasonic diagnosing device of FIG. 1 is shown. The thickness change waveform output from the thickness change waveform calculation part of the ultrasonic diagnostic apparatus of FIG. 1 is shown. It is a figure explaining the information contained in a thickness change waveform. It is a figure explaining the method of calculating | requiring a viscosity. It is a block diagram which shows the other structure of the ultrasonic diagnosing device by this invention. It is a block diagram which shows the other structure of the ultrasonic diagnosing device by this invention. It is a figure explaining the method of tracking a structure | tissue from the phase difference of an ultrasonic echo signal. A cross section of a subject measured by a probe is schematically shown. It is a figure explaining the method of calculating | requiring a distortion amount from the tracking waveform of a subject tissue. It is a figure explaining an error arising in the maximum thickness change amount when noise is superimposed on the thickness change waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Species 12 Subject 16 Blood vessel wall 100 Control part 101 Probe 102 Transmission part 103 Reception part 104 Tomographic image generation part 105 Image composition part 106 Image display part 115 Moving waveform calculation part 116 Thickness change waveform calculation part 117, 117 ', 117' Reference waveform generation unit 118 Comparison unit 119 Sphygmomanometer 120 Elastic modulus calculation unit 121 Viscosity determination unit 142 Blood vessel diameter calculation unit 150 Calculation unit 201, 202, 203 Ultrasonic diagnostic apparatus

Claims (22)

A transmitter that generates a drive signal for driving the probe in order to transmit ultrasonic waves to a subject that is periodically deformed by stress;
A reception unit that receives an echo obtained by the reflection of the ultrasonic wave at the subject by the probe and generates a reception echo signal;
A calculation unit that calculates a thickness change waveform indicating a change in distance between any two measurement sites in the subject based on the received echo signal;
A reference waveform generator for generating a plurality of reference waveforms for viscosity characteristics;
Comparison for calculating a viscosity characteristic index indicating a degree of matching between the thickness change waveform and the viscosity characteristic reference waveform by comparing the plurality of viscosity characteristic reference waveforms and the thickness change waveform, respectively. And
A viscosity determining unit that determines the viscosity based on the viscosity characteristic index;
An ultrasonic diagnostic apparatus comprising: The viscosity characteristic reference waveform is a distortion waveform of the subject obtained based on information indicating a stress change of the subject when a predetermined viscosity is assumed,
The ultrasonic diagnostic apparatus according to claim 1, wherein the viscosity determining unit outputs a viscosity assumed in the reference waveform for the viscosity characteristic that provides the smallest value among the indices for the viscosity characteristic.   The comparison unit performs matching when the coefficient is determined so that one of the thickness change waveform and the reference waveform for each viscosity characteristic is multiplied by the first coefficient and the matching residual between the other is minimized. The ultrasonic diagnostic apparatus according to claim 2, wherein a residual is output as the viscosity characteristic index.   The ultrasonic diagnostic apparatus according to claim 3, wherein the information indicating the stress change of the subject is a blood pressure waveform of the subject.   The calculation unit includes a movement waveform calculation unit that calculates a movement waveform that indicates a change in position of a plurality of measurement parts in the subject based on the received echo signal, and the two measurement parts based on the movement waveform The ultrasonic diagnostic apparatus according to claim 3, further comprising a thickness change waveform calculation unit that calculates a thickness change waveform therebetween.   The blood vessel diameter calculating unit further calculates a blood vessel diameter change waveform included in the subject based on the movement waveform, and the information indicating the stress change of the subject includes the blood vessel diameter waveform as the highest and lowest of the subject. The ultrasonic diagnostic apparatus according to claim 5, wherein the waveform is a waveform corrected with a blood pressure value.   The reference waveform generation unit receives a thickness change waveform at a position close to a blood vessel cavity of a blood vessel wall included in the subject from the calculation unit, and receives the thickness change waveform at a position close to the blood vessel cavity. The ultrasonic diagnostic apparatus according to claim 3, wherein a waveform corrected with the highest and lowest blood pressure values is used as information indicating a stress change of the subject. The reference waveform generation unit further generates a reference waveform for elastic characteristics,
8. The super-compact according to claim 1, wherein the comparison unit calculates a maximum thickness change amount of the thickness change waveform by comparing the reference waveform for elastic characteristics with the thickness change waveform. 9. Ultrasonic diagnostic equipment.   The comparison unit determines the second coefficient so that a matching residual between one of the thickness change waveform and the elastic characteristic reference waveform multiplied by a second coefficient and the other is minimized, The ultrasonic diagnostic apparatus according to claim 8, wherein the maximum thickness change amount is calculated from a second coefficient and an amplitude of the elastic characteristic reference waveform.   The ultrasonic diagnostic apparatus according to claim 9, further comprising: an elastic modulus calculation unit that receives information on a stress difference of the stress generated in the deformation cycle of the subject and obtains an elastic modulus from the maximum change amount.   The ultrasonic diagnostic apparatus according to claim 8, wherein the reference waveform generation unit generates the elastic characteristic reference waveform based on a blood pressure change waveform of the subject. A method of controlling an ultrasonic diagnostic apparatus by a control unit of the ultrasonic diagnostic apparatus,
(A) transmitting the ultrasonic wave by driving the probe;
A step (B) of receiving an echo obtained by the reflection of the ultrasonic wave by the probe periodically deformed by stress by the probe;
Calculating a thickness change waveform indicating a change in distance between any two measurement sites in the subject based on the received echo signal (C);
Generating a plurality of viscosity characteristic reference waveforms (D);
Calculating a viscosity characteristic index indicating a degree of coincidence of the thickness change waveform and the viscosity characteristic reference waveform by comparing the plurality of viscosity characteristic reference waveforms and the thickness change waveform, respectively; (F) and
Determining a viscosity based on the viscosity characteristic index (G);
A method for controlling an ultrasonic diagnostic apparatus including: The viscosity characteristic reference waveform is a distortion waveform of the subject obtained based on information indicating a stress change of the subject when a predetermined viscosity is assumed,
13. The method of controlling an ultrasonic diagnostic apparatus according to claim 12, wherein the step (G) outputs a viscosity coefficient assumed in the reference waveform for the viscosity characteristic that gives the smallest value among the viscosity characteristic indicators. .   In the step (F), when the coefficient is determined so that the matching residual between the one obtained by multiplying one of the thickness change waveform and the reference waveform for each viscosity characteristic by the first coefficient and the other is minimized. The method of controlling an ultrasonic diagnostic apparatus according to claim 13, wherein the matching residual is output as the viscosity characteristic index.   The method for controlling an ultrasonic diagnostic apparatus according to claim 14, wherein the information indicating the stress change of the subject is a blood pressure waveform of the subject. The step (C)
Calculating a movement waveform respectively indicating a change in position of a plurality of measurement sites in the subject based on the received echo signal;
The method of controlling an ultrasonic diagnostic apparatus according to claim 14, further comprising: calculating a thickness change waveform between the two measurement sites based on the movement waveform. A step (H) of calculating a blood vessel diameter change waveform included in the subject based on the movement waveform;
The method of controlling an ultrasonic diagnostic apparatus according to claim 14, wherein the information indicating the stress change of the subject is a waveform obtained by correcting the blood vessel diameter waveform with the highest and lowest blood pressure values of the subject. The step (C) generates a thickness change waveform at a position close to the lumen of the blood vessel wall included in the subject,
The step (D) uses the waveform obtained by correcting the thickness change waveform at a position close to the lumen with the maximum and minimum blood pressure values of the subject as information indicating the stress change of the subject. Method for ultrasonic diagnostic apparatus. The step (D) further generates a reference waveform for elastic properties,
19. The step (F) calculates the maximum thickness change amount of the thickness change waveform by comparing the elastic characteristic reference waveform and the thickness change waveform. Method for ultrasonic diagnostic apparatus.   The step (F) determines the second coefficient so that a matching residual between one of the thickness change waveform and the elastic characteristic reference waveform multiplied by the second coefficient and the other is minimized. The method of controlling an ultrasonic diagnostic apparatus according to claim 19, wherein the maximum thickness change amount is calculated from the second coefficient and the amplitude of the elastic characteristic reference waveform.   21. The method of controlling an ultrasonic diagnostic apparatus according to claim 20, further comprising a step (I) of receiving information on a stress difference of the stress generated in the deformation cycle of the subject and obtaining an elastic modulus from the maximum change amount. 20. The method of controlling an ultrasonic diagnostic apparatus according to claim 19, wherein the step (D) generates the elastic characteristic reference waveform based on a blood pressure change waveform of the subject.

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