JPH01320048A - Pulse dopper measuring device - Google Patents

Abstract

PURPOSE:To detect the velocity of an object from a low velocity up to a high velocity more accurately by providing an angle correcting means to correct the angular difference or a means to shift the angular reference axis to + or -pidirections when the addition of phase difference vectors is carried out. CONSTITUTION:Ultrasound pulses emitted from a wave transmitting circuit 2 are transmitted toward a reflector 11 repeatedly under a constant time interval from an ultrasound transducer 1. Ultrasound pulses reflected from the reflector 11 are received with a wave receiving circuit 3. The outputs of a phase comparator 4 relating to the reflector 11, Vn=Anexp(jthetan), are inputted to a velocity detecting section 7 to obtain the output DELTAthetaA of an angle correcting circuit 720. In a divisional unit 8, the output DELTAthetaA of the velocity detecting section 7 is divided by the transmitting interval T of the ultrasound pulses. The result is the Doppler frequency omegad, that is omegad=DELTAthetaA/T.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pulsed Doppler measurement device, and particularly to a device that detects the velocity of an object using ultrasound, for example, when measuring the blood flow velocity in a living body in real time. This invention relates to a pulsed Doppler measurement device that can perform measurements with a high signal-to-noise ratio.

[Conventional technology]

Various devices have been known for determining the flow velocity of an object using the Doppler effect of sound waves.

In particular, devices using the pulsed Doppler method (for example, "Journal of the Acoustical Society of Japan", Vol. 29, No. 6 (1973), pp. 351--
352), ultrasonic pulses (pulsed co
by repeatedly transmitting a tiny wave) and applying a time gate to the received signal according to the distance to the measurement site.

It is known that it is possible to specify the measurement site.

Examples of conventional ultrasonic Doppler blood flow meter devices include Japanese Patent Application Laid-open Nos. 58-188433 and 60-119929.

As disclosed in Publication No. 61-25527, ultrasonic waves are transmitted toward blood vessels, the Doppler shift frequency of the ultrasonic waves reflected by the blood in the blood vessels is measured, and the direction of blood flow is determined by the ultrasonic waves. An apparatus is known that measures blood flow by measuring vcO5θ, where V is the velocity of O2 blood flow and the angle formed with the transmission direction.

[Problem to be solved by the invention]

As described above, by measuring the Doppler frequency, it is possible to know the velocity of an object, blood flow, or the like. However, in order to measure blood flow in the human body, MTI (solid object removal) is required to separate blood flow from movement of walls such as blood vessel walls and heart S walls.
It is necessary to use a filter. This MTI filter is
When the blood flow velocity is slow, the gain of the Doppler signal decreases, causing an error in the Doppler velocity measuring section, causing a problem in that the velocity is measured as a velocity different from the true blood flow velocity.

This will be explained below based on one drawing.

Figure 7 shows the characteristics of various conventional Doppler measurement devices, where the horizontal axis is the input phase corresponding to the true blood flow velocity;
The vertical axis is the output phase corresponding to the measured speed, which is the result obtained by simulation. At that time, as a model of the output signal of the phase comparator which is a Doppler signal, Xn=A, exp(jωdt)+B(ω,'+jω,"
) is used. However, here the phase noise ω. ′, ω. ″
is white noise, and normal random numbers following a normal distribution N(0,1) are used.

ω. ″ is ω. By generating a random number with a different initial value from ′, an uncorrelated one is used.The cause of this noise is that every time the reflected signal is reflected due to microscopic fluctuations in blood flow. ω1′ is the real part of ω1′. The noise, ω.'' represents the noise in the imaginary part. Note that O6 is the Doppler frequency.

As mentioned above, the conventional pulsed Doppler method (autocorrelation method, biaxial component method) has the problem of producing errors for low-velocity blood flow and estimating a velocity that is significantly different from the true velocity. . The reason for this is that it occurs when detecting a phase difference in the autocorrelation method (the same applies to the two-axis component method). That is, in the calculation of adding phase difference vectors, when the noise amplitude B is small (BCl), there is an effect that the noises cancel each other out in the phase terms of the phase difference vectors. Therefore, the phase difference ωdT (T = t n+x
t n) can be determined accurately, but the noise amplitude B is large (
B>1) When the noise is not canceled in the phase term,
Since the addition increases, the phase difference becomes ωdT+ΣΔω, which becomes inaccurate.

On the other hand, in the simple cumulative method in which each phase difference is obtained and then averaged, in that case, noise is canceled and the final phase difference is ωdT+ω. -O1 is found, and the noise is only the initial value and final value. Therefore, more accurate velocity can be measured than the autocorrelation method or the two-axis component method. However, in the case of fast blood flow (velocity where the phase difference is around ±π), the simple cumulative addition method cannot be used because the addition result becomes near zero due to aliasing, resulting in erroneous detection as slow blood flow.

As shown in FIG. 8(a), when the blood flow velocity V is positive, one phase difference ΔO□ to ΔO3 is added eight times.

Since the phase differences Δ0□ and Δ08 exceed +π, they become negative angles, and as a result of averaging, ΔOA becomes a positive angle near zero.

Here, ΔOT is the result of the two-axis component method (or autocorrelation method), and the approximate angle can be displayed. Blood flow velocity V
The same is true when is negative; in the eight additions of 〇1 to Δθ3 to the phase difference, the phase differences Δθ□ and Δ0□ exceed 1π, so the angle becomes erroneously positive, and the average result of addition is ΔOA.
is a negative angle near zero (see FIG. 8(b)).

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems in the conventional pulse Doppler measuring device based on the simple cumulative method, and to enable measurement with a high signal-to-noise ratio. An object of the present invention is to provide a pulsed Doppler measurement device.

[Means to solve the problem]

The above object of the present invention is to receive an ultrasonic pulse reflected by an object, detect the phase difference of the ultrasonic pulse, add one phase difference vector, and then detect the angle of the phase difference vector. In a pulsed Doppler measurement device that calculates the velocity of the object by dividing the angle by the transmission interval of ultrasound pulses to find frequency fluctuations, angle correction means corrects the angular difference when adding the phase difference vectors. ,or,
This is achieved by a pulse Doppler measuring device characterized by providing means for shifting the reference axis of angle in the ±π direction.

[Effect]

The pulsed Doppler measuring device according to the present invention is based on the above-mentioned simple cumulative method, and since the angle is corrected in the vicinity of π above the Doppler deviation angle, it goes without saying that moderately accurate speed measurement is possible.

Furthermore, even for a high-speed object, when the speed V of the object is around ±π, as shown in FIGS. 5(a) and 5(b).

Approximate angle Δ obtained by measuring the coordinates of the origin in advance using a corrector
Since it is set to OT, it is possible to simply add angles in the same way as at low speeds, which has the effect of improving the signal-to-noise ratio. Therefore, the speed of objects ranging from low speeds to high speeds can be detected more accurately.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 is a block diagram of a pulsed Doppler measuring device showing an embodiment of the present invention. In fig.

1 is an ultrasonic transducer, 2 is a transmitter circuit, 3 is a receiver circuit, 4 is a phase comparator, 5 is an A/D converter, 6 is an MTI
filter; 7 is a speed detection section; 8 is a divider; 9 is a control section;
10 indicates a display device. Note that FIG. 1 shows details of the speed detecting section 7. As shown in FIG. This will be detailed later.

The pulse Doppler measuring device shown in this embodiment is based on the simple cumulative method that improves the signal-to-noise ratio, and in the vicinity of the Doppler deviation angle ±π, the simple cumulative method is corrected.
The outline of its operation is as follows.

Ultrasonic pulses sent out by the wave transmitting circuit 2 are directed from the ultrasonic transducer 1 toward the reflecting object 11.

Waves are transmitted repeatedly at equal intervals T. The ultrasonic pulse reflected by the reflecting object 11 is received by the wave receiving circuit 3, and the phase comparator 4 outputs the reference signal α=Acosω. t and α””As1nω. A phase comparison is made with t and the respective outputs VR, V.

is obtained.

Now, the output of the phase comparator 4 for the reflector 11 is ■Rn
, vIn (here, n=1.2...), V Rn r V I n can be expressed by the following equation.

V Ro: A ocosθ. ...
・(1) V1o=Aos1nOo ・・
(2) For simplicity, the above equations (1) and (2) are combined into the following equation and written as follows.

Vn'” AneXP(J On)
(3) This is the output of the A/D converter 5.

Next, the output V of the A/D converter 5. ' is input to the MTI6, the output Vn of the MTI6 is obtained. If MT■ is a first-order differential circuit, ■n=Vn'-vn-□...(4)
It is. Hereinafter, the above V. is called the phase vector.

Next, the operation of the speed detection section 7 shown in FIG. 1 will be explained. The speed detection section 7 shown in this embodiment is as follows.

This is the main configuration of the two-axis component method, but in the present invention,
This is used as a correction value detection circuit (719). That is, in the speed detection section 7 shown in this embodiment, TA
When the phase vector vn is input to the "N-" memory 711, the argument On of Vo is obtained.The delay circuit 712 obtains θ.-1 one time ago, and the current θ.

By taking the difference, the phase difference ΔOnΔθ. =On-
On-□ is obtained. This phase difference ΔOn is determined by the cos memory 713
In the °sin memory 714, the phase difference ΔOn is converted into a cosine component and a sine component, respectively. Next, adder 7
At 15.716, the cosine component cosΔ0□ and the sine component sinΔOn are each input to the TAN-1 memory 717 after being averaged an arbitrary number of times. TAN-" memory 717 converts the averaged cosine component to the real part of the complex number and the averaged sine component to the imaginary part of the complex number to the average argument "G.As described above, the present invention In the above, a means for obtaining "I" from the phase difference ΔOn, which is the main configuration of the two-axis component method, is used as the correction value detection circuit 719.

On the other hand, the adder 718 simply cumulatively averages the one phase difference ΔOo. This is a simple addition method. The angle correction circuit 720 determines whether or not the output "G" of the correction value detection circuit 719 exists in the third and fourth quadrants, and if it exists, Sg=-1ifΔθA〉O 5g=+, 1 if ΔOTkuO...(5)S
Give a value to Sg: g=OffΔθ7=7COr-7e.

Next, the new coordinate axis (Re': new real axis) shown in FIG.

I+a': new imaginary axis), count the number of 80n on the positive new imaginary axis 1 side and the number of Δθ on the negative new imaginary axis I++'' side, and call it M. Specifically, M = the number of ΔOn that exists in the new 1st and 2nd quadrant and does not exceed -π in the old coordinates, and the number of 80 that does not exceed +π in the old coordinates forSg = - 1. As a result, the output value Δ of the angle correction circuit 720
OA is ΔOA=τ0. −(NA&, −ΣΔθ.

+5g−M·2π) (However, Sg#O) (7) Corrected as 9, an accurate argument Δθ6 can be obtained. However, Y17 is ±
When it is equal to π (when Sg=O), the correction angle Δ08 is obtained as follows. Namely.

Here, 80 A' ” M 1 πM z K−ΣΔon
..."(9). However, M□=the number of ΔOo existing in the new 1st and 2nd quadrants. This is a special case, and if there is no correction value detection circuit 719 mentioned above, An example of the configuration of the device in this case is shown in FIG. 6. However, the explanation will be given later.

In this way, the declination angle of a high-velocity object can be obtained accurately. Needless to say, this correction is unnecessary when measuring low-velocity objects.

Returning to FIG. 2, the explanation will be continued. The divider 8 divides the output of the speed detector 7 by 0A at the ultrasonic pulse transmission interval T. The result is the Doppler frequency ω6, which is T. The display device 10 displays the above ω6.

FIG. 3 is a configuration diagram of the speed detection section 7 showing another embodiment of the present invention. First, the phase difference detection unit 701 receives phase signals 1 to 1 V. is input. In order to detect a phase difference in the phase difference detection unit 701, a phase vector V is used. and −vector before time■. V, which is a complex conjugate vector of −0. −
It is sufficient to perform complex multiplication with one umbrella, and this is performed. M
The result of the i-element multiplication is the phase difference vector y. Expressed as 3'
n is expressed by the following formula.

'/n=V.・■o−□Medium=R, +j1. ---・(12) Here, Ro is the real part and I is the imaginary part.

Complex adder 702 is the output of phase difference detector 701 ’I　n　=　Rn　+　J　I.

Add and average an arbitrary number of times. When the result is expressed as R+jl, R+j■ is expressed by the following formula.

R + j = -Σ (Rn + j I n)...
・(13) TAN-' Me(: IJ 703 converts the output R+jr of the complex adder 702 (7) to the argument angle.

The above is the main configuration of the correction value detection circuit 706. The correction value detection circuit 706 outputs the approximate argument "G".

On the other hand, the autocorrelator 701
The complex number output Rn+j■. is used to convert it into an argument angle ΔOo. Adder 705 calculates the argument angle Δθ. It outputs the result of adding .

Furthermore, the angle correction circuit 720 includes the correction value detection circuit 7 described above.
The correction amount is calculated based on the output AQ of 06, and the adder 70
This is to correct the output ΣΔOn of No.5.

This angle correction circuit 720 has already been explained based on FIG. 1, so a description thereof will be omitted here.

FIG. 4 is also a configuration diagram of the speed detection section 7 showing another embodiment of the present invention. In this embodiment, the correction value detection circuit 719 of the embodiment shown in FIG. 1 is slightly modified.

That is, the sine component and cosine component (imaginary axis,
The amplitude component of the phase vector (Doppler signal) that is the output of the MTI 6 is taken into consideration when adding the signals (real axis).

Therefore, an amplitude value detection circuit 735 is used.

In this amplitude value detection circuit 735, the absolute value of the phase vector v7 is determined by the absolute value detection circuit 730.

The absolute value detection circuit 730 is described in (2) above. The square value of the real part and the square value of the imaginary part are added together and then squared.

The multiplier 732-1 outputs the output S of the absolute value detection circuit 730.
Multiplication of n by 5n-i delayed by one time by the delay device 734 is performed. The output of the multiplier 732-1 is sent to the square root detection circuit 7.
31 and the amplitude value A. is detected and output.

In the correction value detection circuit 721, the cos memory 713
The amplitude value A is output. is multiplied by the multiplier 732-2 and inputted to the adder 715, and the output of the sine memory 714 is multiplied by the amplitude value An by the multiplier 732-3 and inputted to the adder 716. This point is different from the embodiment shown in FIG.

Note that A is the square value of the amplitude. When used as a closing method, the square root detection circuit 731 may be removed. The angle correction circuit 720 has already been described.

Any correction value detection circuit in FIG. 1, FIG. 3, or FIG. 4,
Needless to say, this method is effective as a means for correcting the results of the simple addition method. Note that among these circuits, the circuit shown in FIG. 3 shows excellent effects in the low noise level region, the circuit shown in FIG. 1 shows excellent effects in other areas, and the circuit shown in FIG. In either case, there is a characteristic that it shows a moderate effect.

The embodiment shown in FIG. 6 will now be described. In the figure, symbols 701, 704, and 705 are the third
The same components as shown in the figure are shown, and 740
is calculated using the above equations (, 8), (9), and (jO).
An angle correction circuit for calculating Δθ8, 741 is an addition circuit 705
The output of the angle correction circuit 740 and the output of the angle correction circuit 740 are shown. In this embodiment, when the speed is around ±π, the deflection angle can be determined using a simple circuit.

According to each of the above embodiments, in the simple addition of angular differences, N
The signal-to-cone ratio is improved by a factor of N/v/''T (4v'T times for 8 times), compared to the conventional v
/''It is possible to estimate the Doppler frequency more accurately than with T times.

〔Effect of the invention〕

As described above, according to the present invention, ultrasonic pulses reflected by an object are received, the phase difference of the ultrasonic pulses is detected, the phase difference vectors are added, and then the phase difference vector l- In a pulse Doppler measuring device that calculates the velocity of the object by detecting an angle and dividing the angle by the transmission interval of ultrasound pulses to find the frequency fluctuation, the angle is Since an angle correction means for correcting the difference or a means for shifting the angle reference axis in the ±π direction is provided, it is possible to realize a pulsed Doppler measuring device that can perform measurements with a high signal-to-noise ratio. .

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a speed detection unit which is a main part of a pulsed Doppler measurement device according to an embodiment of the present invention, FIG. 2 is a block configuration diagram of the entire pulsed Doppler measurement device of the embodiment, and FIGS. The figure is a configuration diagram showing another embodiment of the speed detection section,
FIG. 5 is a diagram explaining the present invention in detail, FIG. 6 is a block diagram showing still another embodiment of the present invention, FIG. 7 is a diagram showing the characteristics of various conventional Doppler measuring devices, and FIG. FIG. 2 is a diagram illustrating problems of the prior art. 2: Transmitting circuit, 3: Receiving circuit, 4: Phase comparator, 5: A
/D converter, 6: MTI filter, 7: Speed detection section, 8
: divider, 9: control unit, lO: display device, 701: autocorrelator, 702: complex number adder, 703°704.71
1 and 717: TAN-” memory, 70'5,
715, 716 and 718: adder, 712, 734
: Delay device, 713 : COS memory, 714 :
sin memory, 706, 7] 9 and 721: correction value detection circuit, 720, 7407 angle correction circuit, 741: selector. Figure 5 (Part 1) 0 Figure 7 Input phase

Claims (1)

[Claims] 1. Receiving an ultrasonic pulse reflected by an object, detecting the phase difference of the ultrasonic pulse, adding the phase difference vectors, and then detecting the angle of the phase difference vector, In a pulsed Doppler measurement device that calculates the velocity of the object by dividing the angle by the transmission interval of ultrasound pulses to find the frequency fluctuation, the angle at which the angular difference is corrected when adding the phase difference vectors. A pulse Doppler measuring device characterized by being provided with a correction means. 2. The angle correction means includes means for detecting an approximate angle from means for detecting a phase difference, means for using the angle as a base axis of the angle, means for converting and adding angles based on the base axis, and the approximate angle. 2. The pulse Doppler measuring device according to claim 1, further comprising means for adding the angle added by the adding means. 3. The pulsed Doppler measuring device according to claim 2, characterized in that average angle detection means based on an autocorrelation method is used as the means for detecting the phase difference. 4. The pulsed Doppler measuring device according to claim 2, characterized in that angle detection means based on a two-axis component method is used as the means for detecting the phase difference. 5. The pulsed Doppler measuring device according to claim 4, wherein the angle detection means using the two-axis component method is means for multiplying a phase difference vector by an amplitude value and adding the result. 6. Receive the ultrasonic pulse reflected by the object, detect the phase difference of the ultrasonic pulse, add the phase difference vectors, detect the angle of the phase difference vector, and use the angle as the ultrasonic pulse. In the pulsed Doppler measurement device that calculates the velocity of the object by dividing by the transmission interval of the wave to find the frequency fluctuation, means is provided for moving the angular reference axis in the ±π direction when adding the phase difference vectors. A pulse Doppler measurement device characterized by: 7. A pulse Doppler measuring device characterized by being provided with means for selecting between a standard angular reference axis and the reference axis set forth in claim 6.