JPH06261898A - Ultrasonic device - Google Patents

Abstract

PURPOSE:To improve the measurement accuracy of a propagation time of a pulse wave, and to execute the quantitative determination measurement of a degree of local artery hardening by using together a time measurement by a correlative processing with a measurement executed by a Doppler signal, based on the measurement executed by the Doppler signal. CONSTITUTION:Doppler signals 14, 15 are stored in waveform storage parts 16, 17, and each partial waveform 18 of a temporary storage signal 23 is subjected to Fourier transformation by a Fourier transform 19 and stored in a Fourier storage part 20 as a Doppler time series frequency spectrum. From a result of decision of a signal extracting part 21 for selecting a wide band signal part of a Fourier storage part 20, only a specific part of the temporary storage signal 23 is selected by a signal selecting part 22 and it becomes a reference signal 24. A correlation arithmetic part 26 calculates a mutual correlation coefficient 27 of a reference signal 24 and a temporary storage signal 25, and a moving time from an origin at the time when the maximum value in this waveform appears becomes a pulse wave propagation time between observation points 12 and 13. In this case, a signal converting part 50 corrects the variation direction or the variation width of a frequency of the Doppler signal of Doppler measuring parts 10, 11 and it is stored in waveform storage parts 16, 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic device for measuring arteriosclerosis by measuring the propagation velocity of a pulse wave propagating in a blood vessel by means of ultrasonic waves.

[0002]

2. Description of the Related Art There is a conventional technique for measuring a pulse wave propagation velocity based on a deformation state of a blood vessel wall or a time delay between blood flow Doppler signal waveforms between two points that are distant from each other. For example, Japanese Patent Laid-Open No. 62-
An ultrasonic pulse wave velocimeter is described in Japanese Patent Publication No. 26050, and information representing a temporal change in a tube wall position is generated by utilizing reflection of ultrasonic waves at two points along a conduit, and this information is used to respond. A configuration is shown in which the time difference in which the change occurs at these two points is obtained, and the pulse wave velocity is calculated based on this time difference and the distance between the two points. Also, IEICE Technical Report, MBE 84-17, pp. 9-16 (1984).
Describes a B-mode interlocking type ultrasonic micro-displacement measuring device, which tracks the phase of an ultrasonic echo using a zero-cross tracking mechanism and measures micro-displacement of tissue to obtain not only morphological information but also hard A device aiming to obtain physical property information such as swelling is shown, and non-invasive measurement of local vascular elastic modulus, that is, vascular elasticity distribution, using this device is shown. Furthermore, Proceedings of the Japanese Society of Ultrasonics, 51-PB
-31, pp. 232-232 (November 1987),
There is a description about the measurement of the aortic pulse wave velocity using ultrasonic Doppler blood flow wave, the pulse wave velocity of the common jaw artery and the femoral artery were simultaneously recorded, and the pulse wave velocity calculated using the time difference, By comparing the pulse wave velocities due to the blood flow waves recorded at the same site and then simultaneously recording the blood flow waves in the common jaw artery and femoral artery, it is possible to measure the pulse wave velocity in the more central part of the aorta. It is shown. In the ultrasonic tomography method using a normal reflection signal, a thin blood vessel having a spatial resolution lower than that of the ultrasonic device used cannot be visualized. But,
With the Doppler method, it is possible to distinguish from the surroundings based on blood motion information, and it is possible to detect blood flow in a thin blood vessel. The measurement of the blood flow condition due to the Doppler effect is usually performed by Fourier analysis of the change condition of the reflected signal frequency due to the Doppler effect. In this case, due to the uncertainty principle regarding the resolution of time and frequency in the Fourier transform, the resolution regarding time is limited by the integration time of the Fourier transform, and according to the usual configuration, a time resolution of about 100 msec or more cannot be obtained.

[0003]

DISCLOSURE OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in view of the limitations of the pulse wave propagation time measurement accuracy in the prior art.
The accuracy of measuring the propagation time of a pulse wave propagating in a blood vessel is dramatically improved, and by measuring the propagation time of a pulse wave between two adjacent points, local arteriosclerosis can be measured for thin blood vessels. It is to provide an ultrasonic device that enables measurement.

[0004]

[Means for Solving the Problems] The basic configuration is a combination of the Doppler method and the correlation method, and in order to be able to apply the propagation time of the pulse wave to a thin blood vessel, the measurement based on the Doppler signal is basically used. Focusing on the wide band property of the blood flow Doppler signal, by using the time measurement by the correlation process together with the measurement by the Doppler signal, the measurement accuracy of the pulse wave propagation time is dramatically improved. That is, ultrasonic waves are transmitted, reflection signals are received from a plurality of observation positions, from the temporal change of the Doppler signal of the reflection signals at the plurality of observation positions, the propagation time of the pulse wave between the observation positions is measured, An ultrasonic device that measures the propagation velocity of a pulse group from the propagation time and the distance between observation positions has a correlation calculation unit that calculates the cross-correlation coefficient between Doppler signals, and the pulse wave is calculated using this cross-correlation coefficient. Propagation time is measured. The correlation calculation unit calculates the cross-correlation coefficient by performing the cross-correlation calculation between the complex signals, and at least one of the signals applied to the correlation calculation unit is a signal in which a portion whose frequency significantly changes is selected. The frequency characteristic of at least one signal applied to the can be corrected. The correlation calculation unit once Fourier-transforms the two applied signals, performs the inverse Fourier transform of the product of these Fourier transform results, and performs the correlation calculation to calculate the cross-correlation coefficient. Further, the device of the present invention has a signal conversion unit for correcting the changing direction or the changing width of the frequency of the Doppler signal, in addition to the correlation calculating unit.

[0005]

[Function] According to the ultrasonic tomography method using a normal reflection signal, a thin blood vessel having a spatial resolution or less cannot be visualized. However, according to the Doppler method, it is possible to discriminate from the surroundings based on blood motion information, and blood flow in a thin blood vessel can also be detected.
The measurement of the blood flow condition due to the Doppler effect is usually performed by Fourier analysis of the change condition of the reflected signal frequency due to the Doppler effect. However, in this case, due to the uncertainty principle regarding the resolution of time and frequency in the Fourier transform, the resolution regarding time is limited by the integration time of the Fourier transform, and according to the normal configuration, 100 mse
This means that a time resolution of more than about c cannot be obtained. By the way, the time resolution of the cross-correlation coefficient is approximately 1 / Bsec.
It is known that (B is the frequency bandwidth of the signal: Hz). The band of the Doppler signal in a normal blood vessel is 1 kHz or more. Therefore, in the present invention, by measuring the time difference by the cross-correlation process between the blood flow Doppler signals, the reciprocal of this frequency band, 1/1000.
A time resolution of seconds (1 msec) is realized. On the other hand, since the pulse wave velocity in the living body changes from 4 m / sec to about 10 m / sec, the time required for this pulse wave to pass a distance of 10 cm is 25 msec to 10 msec.
Is. Therefore, the time resolution is 1 by the method of the present invention.
Since it is msec, the pulse wave propagation time can be measured with sufficient accuracy even with a narrow interval of 10 cm, and therefore the local pulse wave velocity can be measured. As described above, the principle of operation of the present invention is that the time measurement accuracy can be improved by the correlation processing of the broadband blood flow Doppler signal.

[0006]

EXAMPLES The basic operation of the ultrasonic apparatus of the present invention will be described in detail with reference to the example shown in FIG. As shown in FIG. 1, a pulse-shaped electric signal is generated from the transmission unit 1 and applied to an array type ultrasonic transducer 2 in which a plurality of transducer elements are arranged. The transducer element groups 4 or 5 are alternately selected by the element selection switch 3 arranged in the array type ultrasonic transmitter / receiver 2, and the reflected signals in the corresponding regions are alternately selected by the ultrasonic beams 6 or 7. It is obtained as a reception signal 8. The received signal 8 is amplified by the amplifier 9 and input to the Doppler measuring units 10 and 11 that extract the Doppler signal. The configuration of the Doppler measurement units 10 and 11 is a configuration based on a normal so-called pulse Doppler method that performs a Doppler signal extraction process for each of the reflected signals from the observation points 12 and 13 on the ultrasonic beams 6 and 7. The Doppler signals 14 and 15 corresponding to the two observation points obtained in this way
Is temporarily stored in the waveform storage units 16 and 17. Each partial waveform 18 of the temporary storage signal 23 stored in the waveform storage unit 17
Is sequentially Fourier transformed by the Fourier transformer 19 and stored in the Fourier storage unit 20 as a Doppler time series frequency spectrum. The configuration for selecting the wideband signal portion in the stored contents of the Fourier storage unit 20 is the signal extraction unit 21. Using the determination result, only a specific portion of the temporary storage signal 23 stored in the waveform storage unit 17 is selected by the signal selection unit 22 and used as the reference signal 24. The correlation calculator 26 calculates a cross-correlation coefficient 27 between the reference signal 24 and the temporary storage signal 25 which is the content of the other waveform storage 16.

The moving time τ from the origin at the time when the maximum value in the waveform of the cross-correlation coefficient 27 appears (see FIG. 2).
(F)) is the pulse wave propagation time between the observation points 12 and 13. The velocity calculation unit 28 is a unit that measures the propagation time and divides it by the distance between the observation points 12 and 13 determined by the distance determination unit 29 to calculate the velocity. Control unit 30
Is a part for setting the spatial position of the ultrasonic beam and the distance from the transceiver to the observation points 12 and 13, and by providing these setting information to the distance determination part 29, The distance between can be calculated. The pulse wave velocity thus determined is displayed on the display unit 31. In this display, the flow path 32 of the target blood vessel or the like and the flow direction 33 are displayed. The angle formed by the flow direction and the ultrasonic beam direction is θ. The operation of each unit having such a configuration will be described in more detail based on the signal waveforms in each unit. The output signals of the Doppler measurement units 10 and 11 correspond to the observation points 12 and 13, respectively.
4 and 15 are shown in FIGS. 2 (a) and 2 (b). Both of them show the same change in the instantaneous frequency corresponding to the change of the flow velocity, and this frequency fluctuation in the downstream Doppler signal 15 is different from that of the upstream Doppler signal 14 at the observation point 13.
1 to 12 are delayed by the pulse wave propagation time τ. Here, the pulse wave propagation time τ is τ = L / C, where L is the distance between the observation points and C is the pulse wave propagation velocity. Such Doppler signals 14 and 15 are stored in the waveform storage units 16 and 17, respectively. When these waveforms are respectively Fourier-transformed, the conversion results are shown in FIGS. 2 (c) and 2 (d). Here, as shown in FIGS. 2A and 2B, the integration time of the Fourier transform is T, and the waveform within the integration time T is sequentially Fourier-transformed. The actual frequency change of the Doppler signal is shown in FIG.
As shown by the solid line in (b), since frequency resolution is generally 1 / T and time resolution is T when a frequency analysis with an integration time T is performed, the dotted line in FIGS. The output signal is distributed within the range. Therefore, it is difficult to determine the mutual time difference τ with high accuracy from these Fourier transform results. Therefore, in the present invention, the partial waveform signal 18 which is the content of the waveform storage unit 17 is Fourier transformed by the Fourier transformer 19 to obtain the frequency spectrum information 34 already shown in FIG.

The frequency spectrum information 34 is stored in the Fourier storage section 20. The area selection unit 21 detects a portion 35 having a large frequency change in the spectrum information stored in the Fourier storage unit 20. The detecting means can have various configurations such as automation or determination by visual recognition. The change width of the frequency here is V (m / se
c) and the ultrasonic frequency to be used is f (Hz), the relation is B = f × 2 cos θ × V / c (Hz). Here, c is the propagation velocity of ultrasonic waves, which is about 1500 m / sec in water. If the amount of change in flow velocity is 1.5 m / sec, the ultrasonic frequency used is 1 MHz, and θ is 0 degrees, the frequency change width B is 2000 Hz. The signal selecting unit 2 outputs the time domain selection signal 36 for selecting the portion 35 having such a large frequency change.
2 is applied. The signal selection unit 22 extracts only the time component corresponding to the portion 35 of the temporary storage signal 23 where the frequency change is large by the time domain selection signal 36, and the reference signal
Output as 4. The reference signal 24 is shown in FIG.
Up to this point, it was explained as a real signal for simplicity, but
Since the normal Doppler measurement is performed as a complex signal, the Doppler signals 14 and 15 are actually complex signals, and therefore the reference signal 24 is also a complex signal having the orthogonal component shown by the dotted line in FIG. Therefore, all the processes after the actual Doppler measurement are executed as a complex signal. The correlation calculation unit 26 calculates the cross-correlation coefficient 27 between the reference signal 24 that is such a complex signal and the temporary storage waveform 25 that has the same shape as the Doppler signal 14. The output of the correlation calculator 26 is the cross-correlation coefficient R (σ) 27 shown in FIG.
From the maximum position in the cross-correlation coefficient R (σ), the time difference between the Doppler signals 14 and 15 can be obtained as τ. Here, the maximum width is 1 / B (sec), where B is 2000 Hz.
Therefore, the time measurement accuracy is as high as 1/2000 = 0.5 msec. This time τ is calculated by the speed calculation unit 28.
Then, the pulse wave velocity C is calculated as C = L / τ from the distance L between the observation points, and the result is displayed on the display unit 31.

The operation of the correlation calculator 26 will be described below.
Let the signal shown in FIG. 2 (e) be a (t),

[0010]

## EQU00001 ## Let a (t) = u (t) exp {j.theta.a (t)} (Equation 1). Further, the temporary storage signal 25 is set to b (t),

[0011]

## EQU00002 ## Let b (t) = v (t) exp {j.theta.b (t)} (Equation 2). At this time, the output R (σ) of the correlation calculation unit 26 is

[0012]

## EQU3 ## R (σ) = | ∫ <a (t)> b (t + σ) dt | (Equation 3) is calculated. Here, <a (t)> represents the conjugate relation of a (t), and the lower and upper limits of integration are 0 and T ₀ , respectively. Moreover, from the well-known relationship of Fourier transform, FIG.
As shown in, both signals of the reference signal 24 and the temporary storage signal 25 are Fourier transformed by the Fourier transformers 39 and 38,
One of them is converted into a conjugate complex number by a conjugate complex number converter 40, a product of them is made by a complex multiplier 41, and a Fourier inverse transform is performed by a Fourier inverse transformer 42 to calculate a complex correlation coefficient. Absolute value calculator 4
The output R (σ) is obtained by setting the complex absolute value by 3. In such a configuration in which the Fourier transform is once performed, it is possible to perform a process of selectively suppressing an unnecessary frequency component such as a DC component before the inverse Fourier transform. Furthermore, as a simplified configuration of the correlation calculation unit, a configuration in which one of the input signals is a real number can be used in some cases. In this case, for example, a (t) of (Equation 1) is used and the temporary storage signal 25 is set to b.
Only the real part of (t),

[0013]

## EQU00004 ## Let c (t) = Real {b (t)} = v (t) cos {.theta.b (t)} (Equation 4). At this time, the output R (σ) of the correlation calculation unit 26 is

[0014]

[Equation 5] R (σ) = | ∫ <a (t)> c (t + σ) dt | (Equation 5) This is obtained by calculating and the calculation process is simplified. In (Equation 5), <a (t)> represents the conjugate relation of a (t), and the lower and upper limits of integration are 0 and T ₀ , respectively. The time resolution in cross-correlation improves in proportion to the frequency bandwidth of the signal. Therefore, the resolution can be further improved by performing the correction processing of the frequency characteristic for the frequency band in which the signal exists, for example, by emphasizing the high band and the low band. In the present embodiment, the complex signal configuration is mainly described as a strict configuration, but the configuration is not limited to this.
It is also possible to arbitrarily configure only the real part or the imaginary part. As a method of measuring the distance between observation points, a curved path can be correctly measured by using a cursor, a marker, a pointer 37, or the like as in the screen of the distance determination unit 29 shown in FIG. Here, when the changing direction of the frequency of the Doppler signal is inverted as shown in FIG. 5, the Doppler frequency increases at the observation point 12, and therefore the Fourier transform A of the Doppler signal a (t) at this point is obtained. (T) becomes the frequency rising signal 44 shown in FIG. On the other hand, since the Doppler frequency drops at the observation point 13, the Fourier transform B (t) of the Doppler signal b (t) at this point becomes the frequency drop signal 45 shown in FIG. Since the waveforms of the two are different, it is difficult to measure the time even if the correlation processing is performed as it is. Therefore, one signal, for example, the conjugate complex number of b (t) is taken and <b (t)> is c
By setting (t),

[0015]

[Mathematical formula-see original document] c (t) = <b (t)> = v (t) exp {-j [theta] b (t)} (Equation 6), and this Fourier transform has the shape shown in the corrected signal 46, and the frequency rising signal 44 is obtained. And a high degree of correlation. Further, in a situation where the frequency change width of the frequency of the Doppler signal is different as shown in FIG.
4 and the frequency falling signal 45 respectively become the large change width signal 47 and the small change width signal 48 in FIG. 8, and the degree of correlation is lowered because the change width of the frequency is different. In this case, one of the signals, for example b (t),

[0016]

B (t) = v (t) exp {jθb (t)} = v (t) exp {j∫Δθb (t) dt} (Equation 7) (the lower and upper limits of integration are respectively , 0, t), and the phase difference Δθb (t) between adjacent times, which is the measured value here, is multiplied by a constant α to obtain c (t). here,

[0017]

(8) c (t) = v (t) exp {j∫αΔθb (t) dt} (Equation 8) (the lower and upper limits of integration are 0 and t, respectively). The integration here is usually executed by cumulative addition of measured values at discrete times. By transforming (increasing in this case) the frequency and setting it as c (t), this Fourier transform becomes the shape shown in the correction signal 49, and by the process shown in FIG. It shows a high degree of correlation with the width signal 47. FIG. 9 shows a configuration for performing such a waveform conversion process.
Here, the signal conversion unit 50 is a waveform conversion unit that performs a process of changing the direction or the frequency change width. This device is naturally constructed by being combined with a display device for displaying a tomographic image of an ultrasonic wave or a stereoscopic image, but as the structure, all known structures such as an electronic sector, an electronic linear, and a convex can be applied. In addition, coupling with a color Doppler device is also very effective in detecting microvessels.

[0018]

EFFECT OF THE INVENTION In an ultrasonic device for measuring the propagation velocity of a pulse wave propagating in a blood vessel by ultrasonic waves and diagnosing arteriosclerosis, the accuracy of measuring the propagation time of the pulse wave is dramatically improved and the two are close to each other. The pulse wave propagation time between points can be measured, and the local arteriosclerosis degree can be measured even in microvessels.
As described above, according to the present invention, it is possible to measure the pulse wave velocity of the local microvessels, which enables the quantitative measurement of the local arteriosclerosis degree.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an ultrasonic device which is an embodiment of the present invention.

FIG. 2 is a diagram for explaining signal waveforms of respective parts constituting the ultrasonic device of the present invention.

FIG. 3 is a diagram showing a configuration example of a correlation calculation unit of the ultrasonic apparatus of the present invention.

FIG. 4 is a diagram for explaining an example of a method for measuring an observation point interval of the ultrasonic device of the present invention.

FIG. 5 is a diagram showing a Doppler signal when the changing direction of the frequency of the Doppler signal is inverted.

FIG. 6 is a diagram showing a frequency change when the change direction of the frequency of the Doppler signal is reversed.

FIG. 7 is a diagram showing a Doppler signal when the variation width of the frequency of the Doppler signal is different.

FIG. 8 is a diagram showing a frequency change when the frequency change width of the Doppler signal is also different.

FIG. 9 is a diagram showing a configuration example of a waveform conversion unit of the ultrasonic device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transmission part, 2 ... Array type ultrasonic wave transmitter / receiver, 3 ... Element selection switch, 4, 5 ... Transducer element group, 6, 7 ... Ultrasonic beam, 8 ... Received signal, 9 ... Amplifier, 10, 11 ... Doppler measurement unit, 12, 13 ... Observation point, 14, 15 ... Doppler signal,
16, 17 ... Waveform storage section, 18 ... Partial waveform, 19 ... Fourier transformer, 20 ... Fourier storage section, 21 ... Signal extraction section, 22 ... Signal selection section, 23, 25 ... Temporary storage signal, 2
4 ... Reference signal, 26 ... Correlation calculation part, 27 ... Cross correlation coefficient, 28 ... Velocity calculation part, 29 ... Distance determination part, 30 ... Control part, 31 ... Display part, 32 ... Flow path, 33 ... Flow direction Three
4 ... Frequency spectrum information, 35 ... Large frequency change portion, 36 ... Time domain selection signal, 37 ... Marker, 38,
39 ... Fourier transformer, 40 ... Conjugate complex number converter, 41
... Complex multiplier, 42 ... Fourier inverse transformer, 43 ... Complex absolute value calculation unit, 44 ... Frequency rising signal, 45 ... Frequency falling signal, 46,49 ... Correction signal, 47 ... Large change width signal, 4
8 ... Small change width signal, 50 ... Signal conversion unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shoichi Senda 3738-36 8 wards, Kita-cho, Takamatsu City, Kagawa Prefecture (72) Inventor Hirohide Matsuo 5319-70, Anji-cho, Kida District, Kagawa Prefecture

Claims (1)

[Claims] 1. An ultrasonic wave is transmitted, a reflection signal is received from a plurality of observation positions, and a propagation time of a pulse wave between the observation positions is measured from a temporal change of a Doppler signal of the reflection signal at the plurality of observation positions. However, in the ultrasonic device that measures the propagation velocity of the pulse group from the propagation time and the distance between the observation positions, the cross-correlation coefficient has a correlation calculation unit that calculates the cross-correlation coefficient between the Doppler signals. An ultrasonic device, comprising: a signal converter that measures the propagation time of a pulse wave using the signal wave and corrects the changing direction or the changing width of the frequency of the Doppler signal.