JP2704414B2 - Pulse Doppler measurement device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pulse Doppler measuring device, and particularly to a device for detecting the speed of an object by ultrasonic waves, for example, when measuring the blood flow speed in a living body in real time, The present invention relates to a pulse Doppler measurement device capable of measuring with a high signal-to-noise ratio.

[Prior Art] Various devices have been known as devices for knowing the flow velocity of an object by the Doppler effect of sound waves. In particular, an apparatus using the pulsed Doppler method (for example,
In Vol. 29, No. 6, 1973 (pp. 351-352), measurement is performed by repeatedly transmitting an ultrasonic pulse (pulsed continuous wave) and applying a time gate to the received signal corresponding to the distance to the measurement site. It is known that a site can be specified.

Conventional ultrasonic Doppler blood flow meters are disclosed in, for example, JP-A-58-188433, JP-A-60-119929, and JP-A-61-2552.
As disclosed in Japanese Patent Publication No. 7, transmitting ultrasonic waves toward blood vessels, measuring the Doppler shift frequency of ultrasonic waves reflected by blood in the blood vessels, the direction of blood flow and the ultrasonic transmission direction An apparatus is known that measures blood flow by measuring v cos θ when an angle formed by θ and v is a blood flow velocity.

[Problems to be Solved by the Invention] As described above, by measuring the Doppler frequency, it is possible to know the speed of an object or blood flow. However, in order to measure the blood flow in the human body, MTI (fixed object removal) is used to separate the blood flow from the movement of the blood vessel wall and heart wall.
It is necessary to use a filter. If the blood flow velocity is low due to the MTI filter, the gain of the Doppler signal decreases, causing an error in the Doppler velocity measurement unit, and there is a problem in that the velocity is measured as a velocity different from the true blood velocity.

 Hereinafter, this will be described with reference to the drawings.

FIG. 3 shows the characteristics of various conventional Doppler measuring devices, in which the horizontal axis represents the input phase corresponding to the true blood flow velocity, and the vertical axis represents the output phase corresponding to the measured velocity.
It is a result obtained by simulation. At that time, as a model of the output signal of the phase comparator is a Doppler signal, using a _{X n = A n exp (jω} d t) + B n (W n '+ jW n "). However, where the phase noise W _n ′, W _n ″ is white noise, and a normal random number according to a normal distribution N (0, 1) is used.

W _n ″ is different from W _n ′ by generating an initial value of a random number differently, so that it is uncorrelated. This noise is generated by a reflected signal due to a microscopic fluctuation of blood flow. Consideration is given to the acoustic noise caused by the change every time, the non-uniformity of the tissue in the propagation process of the sound wave, the electric noise in the amplifier used for the signal amplification in the measuring device, etc. W _n ′ is The noise in the real part, W _n ″, represents the noise in the imaginary part. Note that ω _d is the Doppler frequency.

For example, in the conventional pulsed Doppler measurement of the type called autocorrelation method shown in U.S. Pat.No. 4,583,409, there was a problem that an error was generated for a low-speed blood flow, and a speed that was significantly different from the true speed was estimated. This is as described above. The reason for this is that the autocorrelation method occurs when detecting the phase difference between Doppler signals. That is,
In the operation of adding the phase difference vector obtained by taking the autocorrelation of the Doppler signals obtained via the MTI at each pulse repetition synchronization, when the noise amplitude B _n is small (B _n ≪1), the phase of the phase difference vector The term has the effect that noise cancels each other out. Therefore, the phase difference ω _d T (T = t _{n + 1}
−t _n ) is accurately obtained, but the noise amplitude B _n is large (B _n ≫
1) Sometimes, the noise is not canceled in the phase term and the addition increases, so that the phase difference is (N is the number of additions), which is inaccurate. Also,
Instead of adding the phase difference vector, the Doppler signal phase (angle) is detected, and the angle difference Δ
θ, and the angle difference is divided into a cos component and a sin component.
After averaging the components, find the phase difference represented by the two components 2
In the method called the axial component method (Japanese Patent Application Laid-Open No. 63-84553), an error exactly the same as that in the autocorrelation method described above occurs. FIG. 3 is a curve in which the output phase corresponding to the measurement speed in the autocorrelation method or the two-axis synthetic grammar is obtained by the above-described simulation with respect to the input phase corresponding to the true blood flow speed. It is clear that there is an error.

On the other hand, the phase difference of the Doppler signal for each measurement
A method of directly adding the value of the phase difference a plurality of times to obtain an averaged phase difference and converting the averaged speed into a speed is disclosed in the 1978 Ultrasonics Symposium Proceedings (Ultrasonics).
Symposium Proceedings) at pages 348-352. Hereinafter, this is called a phase difference averaging method. In this method, if the phase difference corresponding to the true blood flow velocity is close to π or −π, the detected phase difference may exceed π or −π every time due to the fluctuation of the detected phase difference due to noise. −
A phenomenon occurs in which the summation becomes close to zero due to the folding of the value at π. Therefore, there is a disadvantage that the measurement range in the high-speed region is limited.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pulse Doppler velocimeter having a sufficient measurement range even in a high-speed region and having a small measurement error due to noise in a low-speed region.

[Means for Solving the Problems] To achieve the above object, the pulse Doppler measuring apparatus of the present invention uses a phase difference averaging method for measuring low-speed objects and an autocorrelation method for measuring medium-high-speed objects. Use the output of
That is, a first phase difference detection means based on an autocorrelation method for taking autocorrelation of sequentially obtained phase vector signals, adding the obtained phase difference vectors a plurality of times, and calculating the argument of the added phase difference vector. A phase difference averaging method for adding a plurality of phase differences between sequentially obtained phase vector signals a plurality of times, and a means for selecting one of the outputs of the first and second phase difference detection means. . The selecting means selects the second phase difference detection force as the blood flow velocity when the output of the first phase difference detecting means is smaller than a predetermined threshold. When the threshold value is exceeded, the output of the first phase difference detecting means is used as the blood flow velocity.

According to another feature of the present invention, in addition to the above configuration, further comprising a unit for detecting a variance of the speed indicated by the phase difference vector, and a unit for detecting a reflection intensity of a reflected signal, these speed variances, And the reflection intensity are also used as parameters for determining the blood flow velocity. That is, when both the velocity dispersion and the reflection intensity are larger than a certain threshold value, it is a turbulent state, so that the first
Is selected as the blood flow velocity, and if the velocity variance is larger than the threshold and the reflection intensity is smaller than the threshold, the velocity is set to zero or undefined.

[Operation] In the present invention, for a medium-to-high-speed object, it is possible to measure the speed as in the past by taking advantage of the conventional autocorrelation method. For a low-speed object, the calculated value of the phase difference by the phase difference averaging method is used, so that the noise component is suppressed to 1 / N (N: the number of additions) times, and high-speed measurement with high SN is achieved. In the vicinity of the speed zero, the output value is output as zero or blank, so that there is no erroneous display.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a pulse Doppler measuring apparatus according to an embodiment of the present invention. In the figure, 8 is an ultrasonic transducer, 2 is a transmitting circuit, 3 is a receiving circuit, 4 is a phase comparator, 5 is an A / D converter, 6 is an MTI filter, and 7 is a speed calculation detecting unit. .

The pulse Doppler measuring apparatus shown in the present embodiment is based on the phase difference averaging method in which the signal-to-noise ratio is improved.When the Doppler speed is small, the output of the phase difference averaging method is used. The output is selected.
The outline of the operation is as follows.

The ultrasonic pulse transmitted by the transmission circuit 2 is repeatedly transmitted at equal intervals T from the ultrasonic transducer 1 to the reflecting object 11. The ultrasonic pulse reflected by the reflecting object 11 is received by the receiving circuit 3, and the phase comparator 4 compares the phases of the reference signals α = Acosω ₀ t and α ′ = Asinω ₀ t, The respective outputs V _R and V _I are obtained.

Now, _let the output of the phase comparator 4 for the reflector 11 be V _Rn , V
_In (where n = 1, 2,...), V _Rn and V _In can be represented by the following equations.

V _Rn = A _n cos θ _n (1) V _In = A _n sin θ _n (2) For simplicity, the above equations (1) and (2) are summarized by the following equation.
It shall be described as follows.

V _n ′ = A _n exp (jθ _n ) (3) V _n ′ is the output of the A / D converter. V _n ′ is the MTI filter 6
It is input to obtain an output V _n of the MTI filter 6. Since MIT filter is the primary difference circuit, a _{V n = V n '-V n} -1' (4). Thereafter, the V _n is called a phase vector.

First, a phase vector is input to an autocorrelator (phase difference detector) 701. Autocorrelator 701 V _n-1 is a complex conjugate vector of the phase vector V _n and one unit time before vector V _n-1 in
A complex multiplication with ^* is performed. Output the result of complex multiplication as Y _n
Then, Y _n is represented by the following equation.

_{Y n = V n · V n} -1 * = R n + jI n (5) complex adder 702, R _n + jI which is the output of the autocorrelator 701
_n is averaged an arbitrary number of times. When the resulting output is represented by R + jI, R + jI is represented by the following equation.

The ATAN memory 703 converts the output R + jI of the complex adder into the argument Δθ
Convert to _A. The above is the main configuration of the consecutiveness calculation by the autocorrelation method.

Next, a portion for detecting the velocity dispersion will be described. By inputting the output R _n + jI _n autocorrelator 701 ATAN memory 704, the deflection angle [Delta] [theta] _An is output. Distributed arithmetic unit 705 is ATA
The speed variance σ ² _s is calculated and output from the output of the N memory 703, that is, the average value Δθ _{A of the} speed and the individual deviations Δθ _An .

On the other hand, the power calculator 706 calculates and calculates the sum of squares of the real part V _Rn and the imaginary part V _In of V _n , and further adds them arbitrarily. P _s when the addition result P _s is given by the following equation.

P _s is input to selector 710.

In the speed calculation unit 7, a portion indicated by a dotted line indicates a circuit added this time. They consist of a speed calculator (707, 708, 709, 713, 714) based on the phase difference averaging method and a selector 709. The phase difference averaging method is a method capable of measuring a speed at a high SN. In the phase difference averaging method, first, a phase vector V _n is input to the ATAN memory 707 to obtain a result output of the argument θ _n . By a delay unit 713 and the adder 714, differential output between the deflection angle theta _n-1 before the current argument theta _n and a time instant is obtained. Adder 714
If you put the output of the [Delta] [theta] _n, [Delta] [theta] _n is expressed by the following equation.

Δθ _n = θ _n -θ _n-1 (8) The adder 708 adds Δθ _n arbitrarily. If you put the output of the adder 708 and [Delta] [theta] _T, [Delta] [theta] _T is expressed by the following equation.

Δθ _T is the argument detected by the phase difference averaging method,
Corresponds to the speed of the object. Δθ _T is input to selector 709.

In the selector 709, the declination (average phase difference) Δθ _A and the angular variance σ _S obtained by the autocorrelation method, and the power calculator 70
Blood flow velocity to the reflection intensity P _S obtained by 6 parameters Is performed to determine whether to select Δθ _T or Δθ _A. Figure 2 shows the PAD of the selection algorithm.
A flowchart (hereinafter abbreviated as PAD) is shown, and the description will be made accordingly. σ _C is a threshold value of the angle variance, and it is first determined whether σ _S is smaller than σ _C. True (Y _ES )
If the absolute value of the next [Delta] [theta] _A is determined whether less than a threshold theta _alpha angle. If true, Δθ _T is determined as the blood flow velocity, and if false, Δθ _A is determined as the blood flow velocity. If σ _S is greater than or equal to σ _C , it is determined whether the reflection intensity P _S is greater than the reflection intensity threshold. If true, Δθ _A is the blood flow velocity; if false, the blood flow velocity is determined to be blank (no value) or zero velocity. When determined as Δθ _T , the blood flow is at a low velocity, and when determined as Δθ _A , the blood flow is
If it is judged as medium or high speed, turbulent, blank or zero,
Noise (electrical or acoustic noise of the device) is assumed. The three thresholds σ _C , θ _{α Pn} can be changed from the operation panel. 66 ° to 86 ° is used as the value of σ _C. When the MTI filter is of the first order, approximately 76 ° is appropriate as σ _C and is changed according to the order of the MTI filter. The theta _alpha is appropriate angle in a range of π / 3~π / 2 (60 ° to 90 °). _Pn is a numerical value determined by measuring the electrical noise power of the device.

The selector 709 does not go through the above selection algorithm, but always uses the switch on the operation panel to set the blood flow velocity as Δθ _A
Or Δθ _T is easy to display. Note that Δθ _A or Δθ _T selected as described above is the blood flow velocity itself. It may be input to the display or the like as a signal indicating, but accurately converted into Doppler frequency dividing the value of [Delta] [theta] _A or [Delta] [theta] _T at time intervals T. That is, if the measurement time interval T can be changed in any way, the output of the selector 709 is input to a divider (not shown), the output is divided by T by the divider, and the output is obtained. The blood flow speed It is necessary to

[Effects of the Invention] As described above, according to the present invention, the performance of low-speed blood flow measurement increases due to the SN improvement effect. Specifically, approximately
Measurement of blood flow about 50% slower is possible. Erroneous measurement near the zero speed (erroneous as high speed) is eliminated, and furthermore, zero speed is correctly measured by introducing speed dispersion and reflection intensity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a Doppler speed detection calculation unit according to an embodiment of the present invention, FIG. 2 is a diagram showing a selection algorithm of a speed calculation result, and FIG. 3 is a diagram showing an input phase and a measurement result (output phase) by a simulation experiment. It is. 7: Doppler velocity calculation detector, 701: autocorrelator (phase difference detector), 702: complex adder, 703, 704, 707: ATAN memory, 705:
Distributed arithmetic unit, 706: Power arithmetic unit, 708: Addition averager, 713:
Delay device, 714: adder, 709 selector, 10: additional part, 8: probe, 9: target object.

Continuing from the front page (72) Inventor Satoshi Tamano 2-1 Shinjuyoichi, Kashiwa-shi, Chiba Prefecture Inside the Hitachi Medical Co., Ltd. Osaka Plant (72) Inventor Koji Tanabe 2-1 Shinjuyoichi, Kashiwa-shi, Chiba Prefecture Hitachi Medical Co., Ltd. in the factory

Claims (8)

(57) [Claims] 1. A pulse Doppler measuring apparatus for transmitting an ultrasonic pulse to a test object at a predetermined time interval and obtaining a reflected signal from the test object as a received signal to obtain a speed of the test object. Means for detecting the phase of the wave signal, obtaining a phase vector for each of the predetermined time intervals, and adding a phase difference vector obtained from a correlation between the sequentially obtained phase vectors, and calculating an argument of the added phase difference vector. First phase difference detection means for obtaining, second phase difference detection means for obtaining a phase difference vector by averaging the phase differences between the sequentially obtained phase vectors, and the value of the speed of the inspection object Based on the first phase difference detection means, the second phase difference detection means
Selecting means for selecting any output of the phase difference detecting means as a signal indicating the speed of the inspection target. 2. A pulse Doppler measuring apparatus for transmitting an ultrasonic pulse to a test object at a predetermined time interval and obtaining a reflected signal from the test object as a received signal to determine a speed of the test object. Means for detecting the phase of the wave signal, obtaining a phase vector for each of the predetermined time intervals, and adding a phase difference vector obtained from a correlation between the sequentially obtained phase vectors, and calculating an argument of the added phase difference vector. First phase difference detection means for obtaining, second phase difference detection means for obtaining a phase difference vector by averaging the phase differences between the sequentially obtained phase vectors, and the first phase difference detection means Selecting means for selecting any one of the outputs of the second phase difference detecting means as a signal indicating the speed of the inspection target, wherein the selecting means includes an output of the first phase difference detecting means. Absolute value of Selecting an output of the second phase difference detecting means when the angle is smaller than a predetermined angle, and selecting an output of the first phase difference detecting means when the absolute value is equal to or larger than the predetermined angle; A pulse Doppler measurement device characterized by the above-mentioned. 3. The pulse Doppler measuring apparatus according to claim 2, wherein the predetermined angle is in a range of π / 3 to π / 2. 4. A pulse Doppler measuring apparatus for transmitting an ultrasonic pulse to a test object at a predetermined time interval and obtaining a reflected signal from the test object as a received signal to obtain a speed of the test object. Means for detecting the phase of the wave signal, obtaining a phase vector for each of the predetermined time intervals, and adding a phase difference vector obtained from a correlation between the sequentially obtained phase vectors, and calculating an argument of the added phase difference vector. First phase difference detection means for obtaining, means for obtaining the variance of the argument of the phase difference vector obtained from the correlation between the sequentially obtained phase vectors, means for obtaining the intensity of the reflected signal, A second phase difference detecting means for obtaining a phase difference vector by averaging the phase differences between the sequentially obtained phase vectors, an output of the first phase difference detecting means, the variance value, and Selecting means for selecting one of the outputs of the first phase difference detecting means and the second phase difference detecting means as a signal indicating the speed of the inspection target based on the intensity of the emission signal A pulse Doppler measurement device characterized by the above-mentioned. 5. The pulse Doppler measuring apparatus according to claim 4, wherein the intensity of the reflected signal is obtained from a sum of squares of a real part and an imaginary part of the phase vector. 6. A pulse Doppler measuring apparatus for transmitting an ultrasonic pulse to a test object at a predetermined time interval and obtaining a reflected signal from the test object as a received signal to obtain a speed of the test object. Means for detecting the phase of the wave signal, obtaining a phase vector for each of the predetermined time intervals, and adding a phase difference vector obtained from a correlation between the sequentially obtained phase vectors, and calculating an argument of the added phase difference vector. First phase difference detection means for obtaining, means for obtaining the variance of the argument of the phase difference vector obtained from the correlation between the sequentially obtained phase vectors, means for obtaining the intensity of the reflected signal, Second phase difference detection means for calculating a phase difference vector by averaging the phase differences between sequentially obtained phase vectors, wherein the variance value is smaller than a predetermined variance value,
When the absolute value of the output of the first phase difference detecting means is smaller than the predetermined angle, the output of the second phase difference detecting means is selected as a signal indicating the speed of the inspection object, and the variance is selected. The value is smaller than a predetermined variance value,
When the absolute value of the output of the phase difference detecting means is equal to or greater than the predetermined angle, the output of the first phase difference detecting means is selected as a signal indicating the speed of the inspection target, and the variance value is When the intensity is equal to or larger than the predetermined dispersion value and the intensity of the reflection signal is higher than a predetermined intensity, an output of the first phase difference detection unit is selected as a signal indicating the speed of the inspection target. A pulse Doppler measuring device, comprising: selecting means. 7. The pulse Doppler measuring apparatus according to claim 6, wherein when the variance value is equal to or more than a predetermined variance value and the intensity of the reflected signal is equal to or less than the predetermined intensity value, the speed of the inspection object is adjusted. Pulse Doppler measurement device characterized by zero or anxiety. 8. A transmitting circuit for transmitting an ultrasonic pulse from an ultrasonic transducer to an object to be inspected at a predetermined time interval;
A receiving circuit that obtains a reflected signal from the inspection target as a received signal, a phase comparing unit that performs a phase comparison between the received signal and a reference signal, and an A / D that converts an output of the phase comparing unit into a digital signal A converter, an MTI filter connected to the A / D converter, and outputting a phase vector for each of the predetermined time intervals of the received signal, and a correlation for obtaining a phase difference vector from a correlation between the sequentially obtained phase vectors. An adder for adding the outputs of the correlators obtained sequentially, means for determining the argument of the phase difference vector added by the adder, storage means for storing the output of the correlator, and the correlator Means for obtaining the variance of the argument of the phase difference vector obtained in the above, and means for obtaining the intensity of the reflected signal from the sum of squares of the real part and the imaginary part of the phase vector, the speed of the inspection object Pulse dop The measuring device, means for determining the polarization angle difference between said sequential obtaining phasor comrades,
Means for calculating an average argument difference by averaging the outputs of the means for acquiring the argument difference, and the argument of the added phase difference vector, any one of the argument differences, the speed of the inspection object; Selecting means for selecting a signal indicating the phase difference vector, wherein the variance value is smaller than a predetermined variance value, and the absolute value of the argument of the added phase difference vector is the predetermined angle. When smaller, the argument difference is selected, and when the variance value is smaller than a predetermined variance value and the absolute value of the argument of the added phase difference vector is equal to or greater than the predetermined angle. Selecting the argument of the added phase difference vector, and when the variance value is equal to or greater than the predetermined variance value and the intensity of the reflected signal is greater than a predetermined intensity, Selecting the argument of the phase difference vector, That pulsed Doppler measuring device.