JP4627220B2 - 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 detecting 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. 9, it is assumed that 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. 10, an ultrasonic wave is transmitted from the probe 101 to the blood vessel wall 16, and 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. 11 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. 11, the tracking waveforms TA and TB have a periodicity that matches the ECG 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 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. 10, 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, the elastic modulus measurement method according to the conventional technique 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. 12 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.

  In making a diagnosis, it is important whether or not a region having a specific elastic modulus is present in the organ to be diagnosed. However, in the B-mode tomographic image, the subject cannot be displayed so that all the organs in the measurement target region can be identified, and the position and range of the target organ may not be specified. Furthermore, since the elastic modulus and the tissue do not necessarily correspond one-to-one, the position and range of the target organ may not be specified using the elastic modulus tomogram.

  The present invention solves such problems of the prior art, reduces the influence of noise, can measure elastic characteristics with high accuracy, and further enables tissue identification. The purpose is to provide.

  An ultrasonic diagnostic apparatus of the present invention includes a transmission unit that generates a drive signal for driving a probe in order to transmit ultrasonic waves to a subject that includes a plurality of different tissues and periodically deforms due to stress. , An echo obtained by reflecting the ultrasonic wave at the subject is received by the probe, and a receiving unit that generates a received echo signal; and any two in the subject based on the received echo signal A calculation unit for calculating a thickness change waveform indicating a distance change between two measurement sites, a reference waveform generation unit for generating a plurality of reference waveforms respectively corresponding to the plurality of tissues, each reference waveform and the thickness change waveform And a thickness change amount estimation unit that calculates an index indicating the degree of coincidence between the thickness change waveform and each reference waveform, and the thickness change waveform is given based on the index 2 Between two measurement sites Organization and a determining tissue determining unit for determining corresponds to any of the plurality of tissue.

  In a preferred embodiment, the thickness change amount estimation unit is configured so that the matching residual between one of the thickness change waveform and each of the reference waveforms and the other multiplied by the coefficient is minimized. A matching residual when using a coefficient is calculated, and the maximum thickness change amount of the thickness change waveform when each reference waveform is used is determined from the coefficient and the amplitude of the reference waveform, and then sent to the tissue determination unit Output.

  In a preferred embodiment, the thickness variation estimation unit outputs each matching residual as the index to the tissue determination unit, and the tissue determination unit generates a reference waveform from which the smallest matching residual is obtained. The corresponding tissue is determined as a tissue between two measurement sites given the thickness change waveform, and the maximum thickness change amount obtained using the reference waveform is output.

  In a preferred embodiment, the ultrasonic diagnostic apparatus obtains an elastic modulus based on information on a stress difference of the stress generated in the deformation cycle of the subject and a maximum thickness change amount output from the tissue determination unit. A calculation unit is further provided.

  In a preferred embodiment, the reference waveform generation unit includes a storage unit that stores data of each reference waveform.

  In a preferred embodiment, the reference waveform is an average of thickness change waveforms acquired in advance from the plurality of tissues of a plurality of subjects.

  In a preferred embodiment, the ultrasonic diagnostic apparatus further includes an image processing unit that generates image data for displaying the elastic modulus based on a result determined by the tissue determination unit.

  In a preferred embodiment, the tissue determination unit, when each of the matching residuals is larger than a predetermined value, the tissue between the two measurement sites given the thickness change waveform is not any of the plurality of tissues Is determined.

  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, and includes a step (A) of driving a probe and transmitting ultrasonic waves, (B) receiving by the probe an echo obtained by reflection of the ultrasonic wave in a subject that includes a different tissue and periodically deformed by stress, and based on the received echo signal A step (C) of calculating a thickness change waveform indicating a change in distance between any two measurement sites in the subject, and a step (D) of generating a plurality of reference waveforms respectively corresponding to the plurality of tissues. A step (E) of calculating an index indicating a degree of coincidence between the thickness change waveform and each reference waveform by comparing each reference waveform with the thickness change waveform; and thickness It encompasses and determining (F) or tissue between two measurement sites gave of waveform corresponds to one of the plurality of tissue.

  In a preferred embodiment, the step (E) sets the coefficient and the coefficient so that a matching residual between one of the thickness change waveform and each reference waveform and the other multiplied by the coefficient is minimized. The matching residuals when used are respectively calculated, and the maximum thickness change amount of the thickness change waveform when each reference waveform is used is obtained from the coefficient and the amplitude of the reference waveform.

  In a preferred embodiment, each matching residual is output as the index in the step (E), and the step (F) determines the thickness of the tissue corresponding to the reference waveform from which the smallest matching residual is obtained. A change waveform is determined as a tissue between two measurement sites, and the maximum thickness change amount obtained using the reference waveform is output.

  In a preferred embodiment, the control method includes a step (G) of obtaining an elastic modulus based on information on a stress difference between the stresses generated in the deformation cycle of the subject and the maximum thickness change obtained in the step (F). Is further included.

  In a preferred embodiment, the reference waveform is an average of thickness change waveforms acquired in advance from the plurality of tissues of a plurality of subjects.

  In a preferred embodiment, the control method further includes a step (H) of generating image data for displaying the elastic modulus based on the determination result in the step (F).

  In a preferred embodiment, in the step (F), when each of the matching residuals is larger than a predetermined value, the tissue between the two measurement sites given the thickness change waveform may be any of the plurality of tissues. Judge that there is no.

  According to the present invention, the maximum thickness change amount is estimated by comparing the reference waveform and the thickness change waveform. Even if sudden noise or the like is superimposed on the thickness change waveform by comparing the waveforms, a more accurate maximum thickness change amount and elastic modulus can be obtained. Further, since it is determined from which tissue the obtained elastic modulus is obtained, tissue identification of the site where the elastic modulus is measured is also possible. Therefore, according to the ultrasonic diagnostic apparatus of the present invention, the elastic modulus can be measured with high accuracy, and the tissue of the measured site can be identified with high accuracy.

  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 includes a transmission unit 102, a reception unit 103, a calculation unit 151, a reference waveform generation unit 117, a thickness change amount estimation unit 118, and a tissue determination unit 172. In addition, in order to control each component of the ultrasonic diagnostic apparatus 201, the ultrasonic diagnostic apparatus 201 includes a control unit 100.

  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 this embodiment, the subject includes a blood vessel wall of an arterial blood vessel, and the ultrasonic diagnostic apparatus 201 obtains the elastic modulus of the blood vessel wall. 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. Specifically, the probe 101 converts the echo into an electrical signal, and the receiving unit 103 amplifies the electrical signal to generate 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 include a delay time control unit, and transmits ultrasonic waves so as to scan the subject by controlling the delay time of the drive signal and the reception echo signal. Only ultrasonic waves from the position and direction are detected. 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 the 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 a reference waveform. This reference waveform is a reference for the thickness change waveform calculated by the thickness change waveform calculation unit 116. The reference waveform is prepared for each different tissue included in the measurement target region in the subject. In the present embodiment, the reference waveform is obtained in advance by measurement or the like, and the reference waveform data is stored in a storage unit such as a semiconductor memory provided in the reference waveform generation unit 117.

  As will be described in detail below, the thickness change amount estimation unit 118 compares the thickness change waveform obtained from the thickness change waveform calculation unit 116 with each reference waveform obtained from the reference waveform generation unit 117. The maximum thickness change amount of the thickness change waveform is calculated, and an index indicating how much the two waveforms match is calculated. More specifically, the thickness variation estimation unit 118 uses the coefficient and the coefficient so that the matching residual between one of the thickness variation waveform and the reference waveform and the other multiplied by the coefficient is minimized. The matching residual is calculated. Then, the maximum thickness change amount of the thickness change waveform is calculated from the coefficient and the amplitude of the reference waveform. The maximum thickness change amount and matching residual when each calculated reference waveform is used are output to the tissue determination unit 172.

  The tissue determination unit 172 includes two measurement sites that give the thickness change waveform based on the matching residual calculated using each reference waveform that is an index indicating the degree of coincidence between the thickness change waveform and each reference waveform. It is determined which tissue in the subject is in between. More specifically, the tissue corresponding to the reference waveform from which the smallest matching residual is obtained is determined as the tissue between two measurement sites to which the thickness change waveform is given. Further, the maximum thickness variation obtained using the reference waveform is output.

  The ultrasonic diagnostic apparatus 201 preferably further includes an elastic modulus calculation unit 120 that calculates an elastic modulus from the maximum thickness change amount output from the tissue determination unit 172. The elastic modulus calculation unit 120 receives information related to stress applied to the subject such as the sphygmomanometer 119. For example, the blood pressure difference ΔP between the maximum blood pressure and the minimum blood pressure is received from the sphygmomanometer. 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 is preferably displayed together with the tomographic image of the subject. This is because the position of the measurement site can be easily shown. Therefore, it is preferable that the ultrasonic diagnostic apparatus 201 further includes a tomographic image generation unit 104, an image processing 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 processing unit 105 receives the image signal and the elastic modulus data obtained from the elastic modulus calculating unit 120 and maps the image signal and the elastic modulus so that the obtained elastic modulus is mapped to an appropriate position on the tomographic image. Is combined with the data. At this time, a result of determining which tissue is the measurement site is received from the tissue determination unit 172, and the elastic modulus is displayed based on the determination result. For example, a different color is used for each tissue, and the elastic modulus is displayed with gradation (luminance) corresponding to the elastic modulus value. This makes it possible to obtain the elastic modulus with high accuracy and to easily specify the position of the elastic modulus region indicated by a predetermined color in the subject. Therefore, a highly reliable diagnosis can be performed based on the elastic modulus shown on the image display unit 106.

  Next, operations of the reference waveform generation unit 117, the thickness change amount estimation unit 118, the tissue determination unit 172, and the image processing unit 105, which are the main parts of the present invention, will be described in more detail. First, a subject to be measured in this embodiment will be described. FIG. 2 schematically shows a cross section of an arterial blood vessel included in the subject. As shown in FIG. 2, blood vessel walls 30 ′ and 30 are seen so as to sandwich the blood vessel cavity 40 in a cross section obtained by cutting an arterial blood vessel along a plane including its axis. When distinguishing between the blood vessel walls 30 ′ and 30, the blood vessel wall 30 ′ close to the surface of the subject is called the blood vessel front wall, and the other is called the blood vessel rear wall 30. The blood vessel walls 30 ′ and 30 have a three-layer structure in which different tissues are distributed concentrically. The inner membranes 33 and 33 ′ adjacent to the blood vessel cavity 40 and the outer membranes 32 and 32 ′ located on the outermost side and sandwiched between them. Medium film 34, 34 '. The inner membrane 33 and the inner membrane 34, and the inner membrane 33 'and the inner membrane 34' are collectively referred to as the inner-media complex 31, 31 '. In the present embodiment, in order to measure the elastic modulus of the blood vessel walls 30 ′, 30, reference waveforms corresponding to the inner membranes 33, 33 ′, the inner membranes 34, 34 ′, and the outer membranes 32, 32 ′ are prepared.

3A to 3C show reference waveforms M ₁ (t) to M ₃ (t) stored in the storage unit of the reference waveform generation unit 117, respectively. This waveform is obtained by measuring the thickness change waveforms of the intima 33, 33 ′, the medial films 34, 34 ′ and the adventitia 32, 32 ′ in advance for a plurality of subjects, and averaging the one heart cycle. Is obtained by seeking. Due to the pressure of blood flowing through the blood vessel cavity 40, the inner membranes 33, 33 ′, the medial membranes 34, 34 ′ and the outer membranes 32, 32 ′ of the blood vessel walls 30 ′, 30 are periodically stressed and deformed. However, since the viscous properties and elastic properties of the tissues of the inner membranes 33, 33 ′, the inner membranes 34, 34 ′ and the outer membranes 32, 32 ′ are different from each other, as shown in FIGS. The thickness variation waveform is also different.

ΔW that is the amplitude of the reference waveforms M ₁ (t) to M ₃ (t) is normalized to be a reference value, for example, 1 μm. Since data obtained from a plurality of subjects is averaged, the influence of noise and the like is reduced even with actually measured data.

  In the present embodiment, as described above, in order to obtain the elastic modulus of the blood vessel wall, the thickness change waveform of the intima 33, 33 ′, the medial membranes 34, 34 ′ and the outer membranes 32, 32 ′ constituting the blood vessel wall. Is selected as the reference waveform, but the number of reference waveforms to be prepared depends on the measurement target. In addition, reference waveform data is stored in the storage unit of the reference waveform generation unit 117 for each state of the subject, such as a set of reference waveforms for healthy persons, a set of reference waveforms for diabetic patients, and a set of reference waveforms for arteriosclerosis patients. It is also possible to select a reference waveform set to be used in accordance with an instruction from the operator. This makes it possible to estimate the amount of change in thickness more precisely.

  FIG. 4 shows a thickness change waveform y (t) between two measurement sites in the measurement target region 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 thickness change amount estimation unit 118 receives the reference waveforms M ₁ (t) to M ₃ (t) and the thickness change waveform y (t), and when the amplitude of the thickness change waveform y (t) is multiplied, Whether it is most similar to the reference waveforms M ₁ (t) to M ₃ (t) is calculated by the least square method. a coefficient multiplying the y (t) and k ₁ to k _3, when the square of the difference between M ₁ (t) and k ₁ · y (t) and the R _1, R ₁ is represented by the formula (7) The

Equation (7) the coefficients k ₁ as a variable partial differentiation with k _1, when partially differentiating equation becomes 0, squared difference R ₁ is minimized.

Solving Equation (8) for k ₁ yields Equation (9).

The value of the coefficient k ₁ obtained by the equation (9), when the measured thickness variation waveform y (t) to ₁ × k, becomes the square of the difference between the reference waveform M ₁ amplitude 1 [mu] m (t) is minimized, It means that the two waveforms are the best match. Accordingly, the amplitude A ₁ of the measured thickness change waveform y (t) is obtained by the following equation (10).

A ₁ = 1 / k ₁ (μm) (10)

The thickness change amount estimating unit 118 further substitutes the value of k ₁ obtained by Expression (9) into Expression (7) to obtain R ₁ . Since k ₁ is determined so that the square difference R ₁ is minimized, R ₁ at this time is R _1m . That is, R _1m is obtained by the following equation (11).

R _1m represents a matching residual between the reference waveform M ₁ (t) and the thickness change waveform y (t) multiplied by the coefficient k ₁ .

Similar to the above-described calculation, it may be calculated how many times the amplitude of the reference waveform M ₁ (t) is multiplied to approach the actual thickness change waveform y (t). In this case, if the coefficient multiplied by the reference waveform M ₁ (t) is k ′ ₁ and the residual is R ′ ₁ , the following equation (12) is obtained.

When a value obtained by partial differentiation of R ′ ₁ by k ′ ₁ is set to 0 (Equation (12)) and solving for the coefficient k ′ ₁ , Equation (13) is obtained.

In this case, the coefficient k ′ ₁ is obtained by multiplying the reference waveform having an amplitude of 1 μm by k ′ ₁ and the square of the difference from the actually measured thickness change waveform y (t) is minimized, so that the two waveforms are most consistent. It means that. Therefore, the amplitude A ′ of the thickness change waveform y (t) is obtained by the equation (15).

A ′ ₁ = k ′ ₁ (μm) (15)

The matching residual R ′ _1m is obtained by the following equation (16).

Similarly, for the reference waveforms M ₁ (t) and M ₂ (t), the coefficients k ₂ , k ₃ , amplitudes A ₂ , A _3, and matching residual R _2m are used using the equations (9) to (11). R _3m is obtained. As described above, the coefficients k ′ ₂ and k ′ ₃ , the amplitudes A ′ ₂ and A ′ _3, and the matching residuals R ′ _2m and R ′ _3m may be obtained.

In this way, the thickness change amount estimation unit 118 receives the reference waveforms M ₁ (t) to M ₃ (t) and the thickness change waveform y (t), and uses the equations (9) to (11). , Amplitudes A _{1 to} A ₃ and matching residuals R _{1m to} R obtained when the matching residuals of the reference waveforms M ₁ (t) to M ₃ (t) and the thickness change waveform y (t) are minimized. _3m is calculated and output to the tissue determination unit 172.

Here, the reason why the maximum thickness change amount is obtained by comparing the reference waveforms M ₁ (t) to M ₃ (t) with the thickness change waveform y (t) will be described. FIG. 5 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. 5, although the amplitudes are different due to the different elastic moduli, 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 the stress change that the subject receives, or the state of the heartbeat is ideally substantially constant. However, since the viscosity characteristic and the elastic characteristic are different depending on the tissue as described above, the change of the thickness change waveform in the time axis direction is different for each tissue. In other words, if the tissue is the same, the thickness change waveform obtained by measurement and the reference waveform have the same change in the time axis direction of the thickness change waveform even if there is a difference in amplitude due to a difference in elastic modulus. .

  As shown in FIG. 5, according to the conventional method, when obtaining the maximum thickness change amount of the thickness change waveform, it is necessary to obtain the maximum value Wmax and the minimum value Wmin of the thickness change waveform. On the other hand, in the present invention, the maximum thickness change amount is estimated by analyzing the consistency between the thickness change waveform and the reference waveform. As described above, when it is assumed that only the thickness change waveform amplitude differs due to the difference in elastic modulus, this means that the maximum thickness change amount is estimated from the thickness change waveform for one cardiac cycle.

As shown in the thickness change waveform y ₀ (t) of FIG. 5, 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 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, information on the maximum value Wmax and the minimum value Wmin is included in each of the inclined portions a1, a2, and a3, so even if a part of one heart cycle of the thickness change waveform is used, 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 (14). 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 (14) can be expressed as follows.

  When the noise n (t) is spike noise or random noise, the second term of the numerator of the formula (9 ′) becomes smaller as compared with the first term as the addition interval becomes longer. Therefore, when the thickness change s (t) is similar to the reference waveform (s (t) = j · M (t)), the addition interval is sufficiently long, and the second term of the equation (14 ′) can be ignored. (14 ′) can be expressed as the following equation (14 ″).

  Therefore, the true coefficient j 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.

  As described above, the change in the time axis direction of the thickness change waveform differs for each tissue. Therefore, when the matching residual is obtained by the above-described calculation using the reference waveform prepared for each tissue, the tissue corresponding to the reference waveform having the smallest matching residual is the tissue from which the thickness change waveform is obtained. It will be. The tissue determination unit 172 performs this determination.

FIG. 6 is a flowchart for explaining the operation of the tissue determination unit 172. The tissue determination unit 172 receives the amplitudes A ₁ , A ₂ , A ₃ and the matching residuals R _1m , R _2m , R _3m after starting the tissue determination operation (step 301) (step 302). The tissue determination unit 172 may receive the amplitudes A ₁ , A ₂ , A ₃ and the matching residuals R _1m , R _2m , R _3m in advance, and the determination operation may be started by a command from the control unit 100. First, the matching residuals R _1m , R _2m and R _3m are respectively compared with a predetermined threshold value R _TH (step 303). When the matching residuals R _1m , R _2m , and R _3m are all greater than the threshold value R _TH , the thickness change waveform y (t) is similar to any of the reference waveforms M ₁ (t) to M ₃ (t). This means that the tissue of the part where the thickness change waveform y (t) is obtained is not any of the tissues corresponding to the reference waveforms M ₁ (t) to M ₃ (t). In this case, the tissue determination unit 172 substitutes 0 for the decision result S and substitutes 0 for the amplitude A (step 304).

On the other hand, if at least one of the matching residuals R _1m , R _2m and R _3m is smaller than the threshold value R _TH , the minimum value is obtained from the matching residuals R _1m , R _2m and R _3m . When the matching residual R _1m is the smallest, the thickness change waveform y (t) is most similar to the reference waveform M ₁ (t), and the tissue of the part where the thickness change waveform y (t) is obtained. Means that the tissue corresponds to the reference waveform M ₁ (t). Therefore, 1 is substituted for the determination result S, and A ₁ is substituted for the amplitude A.

Similarly, when the matching residual R _2m is the smallest, the thickness change waveform y (t) is most similar to the reference waveform M ₂ (t), and the portion where the thickness change waveform y (t) is obtained. Means that the tissue corresponds to the reference waveform M ₂ (t). Therefore, 2 is substituted for the determination result S, and A ₂ is substituted for the amplitude A. When the matching residual R _3m is the smallest, the thickness change waveform y (t) is most similar to the reference waveform M ₃ (t), and the tissue of the part where the thickness change waveform y (t) is obtained. Means that the tissue corresponds to the reference waveform M ₃ (t). Therefore, 3 is substituted for the determination result S, and A ₃ is substituted for the amplitude A. Thereby, the determination in the tissue determination unit 172 is terminated (step 306). When the elastic modulus is measured in two dimensions, determination is made for each point in the two-dimensional matrix.

The tissue determination unit 172 outputs these determination results to the elastic modulus calculation unit 120 and the image processing unit 105. Specifically, the amplitude A into which A ₁ , A ₂ , A ₃ or 0 is substituted is output to the elastic modulus calculation unit 120, and the determination result S into which 0, 1, 2 or 3 is substituted is output to the image processing unit 105. Output to.

In this embodiment, after the matching residuals R _1m , R _2m , R _3m are compared with a predetermined threshold value R _TH , the smallest matching residuals R _1m , R _2m , R _3m are specified. However, the smallest matching residuals R _1m , R _2m , and R _3m may be identified first, and the minimum matching residuals may be compared with the threshold value R _TH .

  The elastic modulus calculation unit 120 obtains the elastic modulus using the received amplitude A as the maximum thickness change amount ΔW as described above. When the value of the amplitude A is 0, it means that the correct maximum thickness change amount has not been obtained, and hence the elastic modulus is not calculated. A numerical value that can be distinguished from the calculation result of the correct elastic modulus, for example, 0 may be substituted as the elastic modulus.

  The image processing unit 105 receives the elastic modulus from the elastic modulus calculating unit 120 and displays the elastic modulus by superimposing it on the tomographic image generated by the tomographic image generating unit 104 based on the determination result S received from the tissue determining unit 172. Generate image data to do. A measurement result for which the elastic modulus is calculated corresponds to a determination result S for determining which tissue the area corresponds to. For this reason, when the elastic modulus is displayed in two-dimensional mapping, it is preferable to display information related to tissue determination and elastic modulus values.

  FIG. 7 shows an example in which image data is generated by the image processing unit 105 so as to display the elastic modulus at a luminance corresponding to the value of the elastic modulus using a different color for each tissue, and the generated data is displayed on the image display unit 106. Is shown. The image display unit 106 shows a tomographic image 50 generated by the tomographic image generation unit 104. In the tomographic image 50, a blood vessel cavity 40, an intima 33, a medial membrane 34, an outer membrane 32, and an extravascular tissue 41 appear. In the figure, the boundaries between the tissues are clear, but these boundaries are often not clear on the actual tomographic image 50. Although the inner film 33 and the inner film 34 are clearly distinguished from each other, the inner film 33 and the inner film 34 are shown with the same level of brightness and may be difficult to distinguish.

A two-dimensional mapping image 56 of elastic modulus is superimposed on the tomographic image 50. Each region of the two-dimensional mapping image 56 is displayed with a gradation corresponding to a color and a modulus of elasticity different for each tissue. Specifically, the tissue determination unit 172 substitutes 1 for the determination result S of the region 52 from the thickness change waveform used to calculate the elastic modulus of the region 52. That is, it is determined that the intima corresponds to the reference waveform M ₁ (t). Similarly, the region 53 and the region 54 are determined to be the media and outer membrane, respectively. On the other hand, the thickness change waveforms obtained from the region 51 and the region 55 are not similar to any of the reference waveforms M ₁ (t) to M ₃ (t), and 0 is substituted for the determination result S. . That is, the region 51 and the region 55 are determined not to be any tissue of the intima, the media, and the adventitia. For this reason, for example, in order to show the difference in structure in the regions 52, 53, and 54, yellow, red, and brown are used, and the elastic modulus obtained with the luminance corresponding to the elastic modulus value is displayed. As shown in FIG. 7, a region 57 having a high elastic modulus exists in the region 53 determined to be the media. Since the regions 51 and 55 are neither tissue of the intima, media, or outer membrane, they are displayed in gray, for example. In the region 51 and the region 55, the elastic modulus is not obtained.

  In addition, based on the determination result of the tissue determination unit 172, only the elastic modulus of the region determined to be a specific tissue may be displayed. For example, as shown in FIG. 8, in the two-dimensional mapping image 56 of the elastic modulus superimposed on the tomographic image 50, the determination result S is 2, and only the region 53 determined to be the media is the elastic modulus value. It is displayed with the corresponding brightness.

  As shown in FIG. 7, since the elastic modulus is color-coded for each tissue type, it can be easily determined that the region 57 having a high elastic modulus is in the media. Therefore, on the tomographic image 50, it is easy to correctly specify a diseased site even if the tissue boundary is not clear. In particular, as shown in FIG. 8, by displaying only the elastic modulus of a specific tissue, it is possible to more easily identify a disease site from the elastic modulus. In addition, in the conventional tomographic image, it is possible to specify the boundary between the intima and the media, or the boundary between the media and the adventitia in the blood vessel wall, which is difficult to discriminate.

  Thus, according to the present invention, the maximum thickness change amount is estimated by comparing the reference waveform with the thickness change waveform. 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. In addition, since it is determined from which tissue the calculated elastic modulus is obtained, it is easy to specify which tissue in the subject the specific part of the elastic modulus is. In particular, even in a tissue that is difficult to discriminate in a B-mode image, it is possible to specify which tissue of the subject has a portion with a unique elastic modulus.

  In each of the above embodiments, the distance (thickness) change waveform between any two measurement sites in the subject is used as the reference waveform. However, the velocity between any two measurement sites in the subject is used. Even if the difference waveform is used as the reference waveform, the same effect can be obtained. In this case, a velocity difference waveform between two measurement sites may be obtained in advance from a plurality of subjects, or a velocity difference waveform may be obtained by time-differentiating a blood vessel diameter change waveform. Further, the speed difference waveform may be obtained by time differentiation of the blood pressure waveform.

  The ultrasonic diagnostic apparatus of the present invention is suitable for measuring property characteristics such as a thickness change amount, a strain amount, and an elastic property of a tissue constituting a subject.

1 is a block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention. It is a figure which shows typically the cross-sectional structure of the blood vessel wall which is a subject. (A), (b) and (c) show reference waveforms of the intima, media and adventitia of the blood vessel wall, respectively. 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 flowchart explaining operation | movement of a structure | tissue determination part. An example of the elastic modulus two-dimensional mapping image displayed on the image display unit is shown. The other example of the two-dimensional mapping image of the elasticity modulus displayed on an image display part is shown. 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 12 Subject 31 Blood vessel front wall 32 Blood vessel cavity 33 Blood vessel rear wall 100 Control part 101 Probe 102 Transmission part 103 Receiving part 104 Tomographic image generation part 105 Image processing part 106 Image display part 115 Moving waveform calculation part 116 Thickness change waveform Calculation unit 117 Reference waveform generation unit 118 Thickness change estimation unit 119 Sphygmomanometer 120 Elastic modulus calculation unit 150 Calculation unit 172 Tissue determination unit 201 Ultrasonic diagnostic apparatus

Claims (15)

A transmitter that includes a plurality of different tissues and generates a drive signal for driving the probe 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 respectively corresponding to the plurality of tissues;
A thickness change amount estimation unit that calculates an index indicating a degree of coincidence between the thickness change waveform and each reference waveform by comparing each reference waveform with the thickness change waveform;
Based on the index, a tissue determination unit that determines which of the plurality of tissues corresponds to the tissue between two measurement sites that gave the thickness change waveform;
An ultrasonic diagnostic apparatus comprising:   The thickness variation estimation unit uses the coefficient and the coefficient so that a matching residual between one of the thickness variation waveform and each of the reference waveforms and the other multiplied by the coefficient is minimized. The matching residual is calculated, and the maximum thickness change amount of the thickness change waveform when each reference waveform is used is calculated from the coefficient and the amplitude of the reference waveform, and is output to the tissue determination unit. The ultrasonic diagnostic apparatus as described. The thickness change amount estimation unit outputs each matching residual as the index to the tissue determination unit,
The tissue determination unit determines the tissue corresponding to the reference waveform from which the smallest matching residual is obtained as the tissue between the two measurement sites given the thickness change waveform, and is obtained using the reference waveform The ultrasonic diagnostic apparatus according to claim 2, which outputs a maximum thickness change amount.   4. The hypermodulation unit according to claim 3, further comprising an elastic modulus calculation unit that obtains an elastic modulus based on information on a stress difference of the stress generated in the deformation cycle of the subject and a maximum thickness change amount output from the tissue determination unit. Ultrasonic diagnostic equipment.   The ultrasonic diagnostic apparatus according to claim 1, wherein the reference waveform generation unit includes a storage unit that stores data of each reference waveform.   The ultrasonic diagnostic apparatus according to claim 5, wherein the reference waveform is an average of thickness change waveforms acquired in advance from the plurality of tissues of a plurality of subjects.   The ultrasonic diagnostic apparatus according to claim 4, further comprising an image processing unit that generates image data for displaying the elastic modulus based on a result determined by the tissue determination unit.   The tissue determination unit determines that the tissue between the two measurement sites to which the thickness change waveform is given is not any of the plurality of tissues when each matching residual is larger than a predetermined value. An ultrasonic diagnostic apparatus according to 1. 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 reflection of the ultrasonic wave in a subject including a plurality of different tissues and 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 reference waveforms respectively corresponding to the plurality of tissues;
A step (E) of calculating an index indicating a degree of coincidence between the thickness change waveform and each reference waveform by comparing each reference waveform with the thickness change waveform;
A step (F) of determining, based on the index, which of the plurality of tissues corresponds to the tissue between the two measurement sites to which the thickness change waveform is given;
A method for controlling an ultrasonic diagnostic apparatus including:   The step (E) includes a matching residual when the coefficient and the coefficient are used so that a matching residual between one of the thickness change waveform and each reference waveform and the other multiplied by the coefficient is minimized. The method of controlling an ultrasonic diagnostic apparatus according to claim 9, wherein the difference is calculated, and the maximum thickness change amount of the thickness change waveform when each reference waveform is used is obtained from the coefficient and the amplitude of the reference waveform. Outputting each matching residual as the index in step (E);
The step (F) is obtained by determining the tissue corresponding to the reference waveform having the smallest matching residual as the tissue between the two measurement sites to which the thickness change waveform is given, and using the reference waveform. The method for controlling an ultrasonic diagnostic apparatus according to claim 10, wherein the maximum thickness change amount is output.   The step (G) of obtaining an elastic modulus based on the information of the stress difference of the stress generated in the deformation cycle of the subject and the maximum thickness change obtained in the step (F). Control method of ultrasonic diagnostic apparatus.   The method of controlling an ultrasonic diagnostic apparatus according to claim 9, wherein the reference waveform is an average of thickness change waveforms acquired in advance from the plurality of tissues of a plurality of subjects.   The method of controlling an ultrasonic diagnostic apparatus according to claim 12, further comprising a step (H) of generating image data for displaying the elastic modulus based on the determination result in the step (F). The step (F) determines that the tissue between the two measurement sites to which the thickness change waveform is given is not any of the plurality of tissues when each matching residual is larger than a predetermined value. The control method of the ultrasonic diagnostic apparatus of Claim 11.

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