JPH0245043A - Pulse doppler measuring instrument - Google Patents

Abstract

PURPOSE:To measure pulse Doppler with a high signal-to-noise ratio by obtaining the correlation between phase signals respectively having a specific time interval out of phase signals successively sampled at time intervals equal to the wave sending intervals of an ultrasonic wave pulse, obtaining a phase difference vector, and calculating a speed from the angle of the phase difference vector. CONSTITUTION:Out of the phase signals successively sampled at a time interval T equal to the wave sending interval of the ultrasonic wave pulse, the correlation between the phase signals respectively having the time interval of nT (n: an integer >=2) is obtained, the phase difference vector is obtained, and the speed is calculated from the angle of the phase difference vector. The ultrasonic wave pulse sent toward an arbitrary part in a heart at the wave sending interval T is reflected by a blood flow and received. When the received signal is inputted to an input terminal 100, a Doppler signal is detected by a phase comparator 1. The detected signal is made into time series data by an A/D converter 2. An output omegad of a divider 12-1 and a Doppler frequency (the output of a divider 12-2) omegad' obtained by an added part 413 are obtained, either of the outputs is selected by a discriminator 13, and the selected output is outputted.

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) Pp351~
352), ultrasonic pulses (pulsed con
It is known that it is possible to specify the measurement site by repeatedly transmitting a tiny wave (tinious wave) and applying a time gate to the received signal corresponding to the distance to 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 VCO9θ, where θ is the angle with the transmission direction and V is the velocity of blood flow.

[Problem to be solved by the invention]

As mentioned above, by measuring the Doppler frequency, it is possible to know the speed of blood flow, etc. By the way, in order to measure blood flow within a human body, it is necessary to use an MTI (solid object removal) filter in order to separate blood flow from movement of walls such as blood vessel walls and heart walls. For this reason, near the zero point of the MTI filter, the Doppler signal component also has a small amplitude, resulting in a problem that the signal-to-noise ratio deteriorates.

Generally, it is possible to obtain steep filter characteristics in the low frequency range by increasing the number of stages of the MTI filter, devising the feedback loop, etc. however,
For example, in the two-dimensional pulsed Doppler method, the amount of data used is about 10 to 20 samples, so the number of filter stages cannot be increased, and there are limitations such as the inability to use a feedback loop, so countermeasures cannot be taken easily. .

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems with conventional pulsed Doppler measuring devices, and to enable pulsed Doppler measurement in a low frequency range with a high signal-to-noise ratio. The objective is to provide a measuring device.

[Means to solve the problem]

The above object of the present invention is to detect the phase of a reflected signal obtained by repeatedly transmitting ultrasonic pulses to an object at predetermined transmission intervals, and calculate the velocity of the object from the Doppler frequency indicated by the phase signal. In the pulsed Doppler measurement device, n'T (n: an integer of 2 or more) among the phase signals sequentially sampled at time intervals (T) equal to the transmission interval of the ultrasound pulses.
This is achieved by a pulsed Doppler measuring device characterized in that it is configured to obtain a phase difference vector by correlating the time intervals of , and calculate velocity from the angle of the phase difference vector.

The value of n is typically 2. In the pulsed Doppler measuring device according to the present invention, compared to the conventional method of correlating phase signals at time intervals T, noise components in the low frequency region are reduced, and speed measurement accuracy in the low speed region is further improved. On the other hand, the measurement speed limit on the high-speed side is 1/2. In order to compensate for this, in addition to means for correlating phase signals with a time interval of 2T (generally nT) to obtain a phase difference vector, there is also a means of correlating phase signals with a time interval of T to obtain a phase difference vector. The system is also equipped with the following, and is configured so that the speed can be calculated from the results of both.

[Effect]

In an MTI filter, when the delay time increases from T to 2T, for example, the frequency characteristics of the filter are compressed to the low frequency range while preserving the shape, and the peak frequency becomes 1/2.
It becomes 1/4T from T. Therefore, the gain increases and contributes to improving the signal-to-noise ratio. In addition, in autocorrelation processing, correlation processing is performed with the Doppler signal delayed by 2T, which improves measurement accuracy by measuring in 2T time and reduces the amount of noise by reducing noise correlation. There is. This is the same even if the delay time is increased to 3T or 4T, and the effect will further increase.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, 1 is a phase comparator, 2 is an A/D converter,
3 and 4 are MTI filters, 7 and 8 are self-phase rJIi devices,
'9.10 is a complex adder, ll-1, 11-2 is an angle detector, 12-1.12-2 is a divider, and 13 is a discriminator.

Ultrasonic pulses transmitted to any location within the heart at a transmission interval T are reflected and received by the blood flow. When the received signal is input to the input terminal 100, the phase comparator 1
The Doppler signal is detected by
The A/D converter 2 converts the data into time series data. This time series data is v′.

(n=1.2...), then vIn is the phase vector (complex number), and V', = Anexp(jθn)・---(1) is A/
It is output by the D converter 2.

Conventionally, this v'1 is expressed as MT (to remove the fixed object)
It is input to the I filter 3, correlation calculation is performed by the autocorrelator 7, and the output of the autocorrelator 7 is input an arbitrary number of times (for example, 8 to 2
0 times), and after addition by the complex adder, the angle detector 11
-1 to obtain the phase difference, and by dividing the phase difference by T in the divider 12-1.

I was getting Doppler frequencies.

On the other hand, in the apparatus shown in this embodiment.

The output ω6 of the divider 12-1 and the Doppler frequency (divider 12-
2) is obtained, and the discriminator 13 selects one of them and outputs it.

Therefore, the additional portion 413 will be explained in detail below.

The MTI filter 4 in the additional section 413 has a delay time of 2T. FIG. 2 shows this MTI filter 4 and the MTI filter 4.
The frequency characteristics of TI filter 3 are shown. MTI (2T)
In filter 4, the gain increases (shaded area) compared to MT I (T) filter 3.

The MTI (2T) filter 4 and the MTI (T) filter 3 can also be configured integrally. A specific example is shown in FIG. In the filter shown in FIG. 3, when the Doppler signal vn'' is input to the input terminal 300,
The output terminal 301 has a differential output vn:V n=v', +1
-V'. ...(2) is the output terminal 30
2 has a differential output Un:U,=V″n,, −v′n
...(3) are output respectively.

This is one of the simplest configurations.

The difference output vn is led to an autocorrelator 7, and finally a Doppler frequency ω6 is obtained. Namely.

In the autocorrelator 7, V n + x is delayed by T time ■.

A complex multiplication with the complex conjugate vector vn is performed.

Let the output of the autocorrelator 7 be yn.

yn=vn+1・vn*...
(4), and yn is input to the complex number adder 9.

FIG. 4(a) is a diagram showing what has been described above. The Doppler signal is subjected to first-order difference by an MTI filter, and M
By using the output of the TI filter and performing normal correlation processing at time T, the output V z V−y V 3 V 2 ” 1・
..., v9V, * is obtained.

In FIG. 1, if the output of the complex adder 9 is set as Yi, then Y=Σy0 =YR+jY1 (5), and if the output of the angle detector 11-1 is set as 80, then Δθ= t
An-"(Yl/YR)" (6) is obtained here, where YR represents the real part and Yl represents the imaginary part.

The divider 12-1 divides the above Δθ by the time parameter T, thereby outputting Doppler frequency ωd: ω4=Δθ/TT YR.

On the other hand, the difference output Un is guided to an autocorrelator 8.

Autocorrelator 8 is the same as autocorrelator 7, but is used slightly differently. That is, in the autocorrelator 8, U
Complex conjugate vector Un of Un delayed by ll+2 and 2T time
A complex multiplication with * is performed.

If the output of the autocorrelator 8 is set as Xn, xn=Un+2・UoI (8)
, xn is input to the complex adder 10.

FIG. 4(b) is a graphical representation of what has been mentioned above. Doppler signal VL'lV2'l..., V engineering. ' is subjected to a primary difference by an MTI filter that takes the difference from the value delayed by 2T time, and the MTI outputs U, , U2 . ..., U, is obtained by autocorrelation processing with the 2T-delayed value of the 0th order to obtain the correlation output U, U engineering umbrella, U, U, *, ..., U, UG fist. It is.

The difference from FIG. 4(a) is that values delayed by 2T are used in both the MTI filter and autocorrelation. Conventionally (
Figure 4 (a)), the amount of data required to add the autocorrelation outputs eight times was 9T, which is a new method possible with the same amount of data (Figure 4 (b)). ) is added six times. However, as shown in FIG. 5, the filter characteristics of the MTI (2T) shown in this embodiment are different from those of the conventional MTI.
Compared to the characteristics of TI(T), the gain in the shaded area is improved (up to about 5.7 dB) in the low frequency region.

In FIG. 1, if the output of the complex adder 10 is set as Xi, then X□=ΣXn =XR+jXI (9), and if the output of the angle detector 11-2 is set as ΔO', then Δθ'
=tan-1(X+/xFl) ・---(
io). Here, XP indicates the real part and Xl indicates the imaginary part.

The divider 12-2 divides the above Δθ' by the time parameter 2T to obtain the Doppler frequency ωi': ωi'=Δθ
'72T is output.

As shown in Fig. 6, the phase difference Δθ' is determined by the time parameter 2T.
Therefore, for the same speed, the phase difference rotates by twice the angle compared to 〇. Therefore, it is more accurate than ΔO measured by T. Furthermore, the amount of correlation with respect to noise is reduced, which is advantageous. However, the measurement limits are ±π/T for ω6 and ±π/2T for ω6′.

The discriminator 13 selects one of the above ω6 and ω,′ using a discriminating algorithm.

The discrimination algorithm will be explained below using FIG. 7.

First, it is determined whether the absolute value of the phase difference Δθ is greater than or equal to π12, that is, whether 1Δ01>π/2 (step 51). If true (Yes), Δ0/'r is set to ω6 (step 52). In addition, in the case of false (No), Δ0'
/2TC=ωdl) is set as ω6 (step 53).

From the output terminal 200, the 1 discriminator 13 outputs a Doppler frequency ω6 that is more accurate than the conventional one. On the other hand, output terminal 2
From 01, the conventional Doppler frequency ω6 is output.

In the above embodiment, an example was explained in which the time parameter was 2T as the additional portion 413. The time parameter is not limited to 2T, but also 3T, 4T, etc. - generally mT (
(m: an integer of 3 or more), similar effects can be obtained. In that case, the MTIT filter 4. in FIG. The time parameter 2T in the delay element 6° divider 12-2 of the autocorrelator 8 is changed to mT. In addition, as the discrimination algorithm shown in FIG. 7, first, the phase difference Δθ
Whether the absolute value of is greater than or equal to yc/m, that is, 1Δ01≧
It is determined whether or not π/m (corresponding to step 51).

If true (Yes), set Δ0/T to ω6 (corresponding to step 52); if false (No),
Let Δθ'/m T (=ωi') be ω6 (Step 5
3).

This enables more accurate measurement of low-velocity blood flow than before.

FIG. 8 is a diagram showing the process of obtaining the outputs of the autocorrelators 7 and 8 when the number of filter stages in the MTr filters 3 and 4 of FIG. 1 is set to second order. Specifically, the MT engineered secondary filter includes the delay elements 341 .
This can be realized by changing 342 from T to 2T. The process to obtain the correlation value is the same as that described with reference to FIG.

In FIG. 8(a), the Doppler signal data required to add the autocorrelation values eight times is +v,',v2',...
, Vt □′, and the time length is IOT. The Doppler signal is second-order differentiated by an MTI2T filter that takes the difference from a value delayed by T time, to obtain the MTIT power. MT production output value,
By autocorrelation processing with the value delayed by T time, correlation output V
x V x ” + V x V z ” + ” ”
+ V s V e ” ”.

obtain. This is the same as before.

The processing process in the additional portion 413 is shown in FIG. 8(b). Same Doppler signal data as the conventional part V□″l
It can be seen that the number of autocorrelation values that can be generated using V 2 'l...t V L L' is six. If the number of additions is six, these six correlation outputs may be used. Furthermore, if you want to increase the number of additions to 7, use Figure 8 (b
), in addition to <,Vi,', data of v,' to v,2 are required.

The difference from FIG. 8(a) is that a second-order difference with a value delayed by 2T time is performed using an M T I second-order filter.

Furthermore, in the autocorrelation process, the effect of this embodiment is that the correlation process is performed with a value delayed by 2T time.As explained with reference to FIG. The filter has improved gain (up to about 10.6 dB) compared to the MTI(T) filter,
Figure 9 shows the situation.

In FIG. 1, the Doppler frequency obtained by the time parameter T and the Doppler frequency obtained by the 1-hour parameter 2T are discriminated and selected.

An example of obtaining more accurate Doppler frequency is given. Instead, the phase difference Δθ obtained by the 1-hour parameter T should not be used to calculate the Doppler frequency, but should be used for correction to compensate for the uncertainty in the phase difference Δθ′ obtained by the time parameter 2T that occurs in the high-speed region. You can also do it.

FIG. 10 shows an example of this, and in the figure, symbols 1 to
11-1 and 11-2 indicate the same components as previously shown in FIG. That is, the phase signals of the reflected waves sampled at one time interval T pass through the MTI filter 3 and are sequentially correlated by the autocorrelator 7, and the angle of the phase difference vector obtained thereby, that is, the phase difference Δθ is the angle Obtained by detector 11-1. Further, the correlation between the phase signals having a 1 time interval of 2T is determined by the autocorrelator 8, and the angle of the phase difference vector obtained thereby, that is, the phase difference Δθ' is obtained by the angle detector 11-2. It will be done.

For the same speed, one phase difference Δθ' is twice Δ0, so when Δθ is greater than or equal to π72 or less than -π/2, the true value of Δθ' is greater than or equal to π, or less than -π/2, respectively. , −π or less.

Therefore, in times like this.

Due to R, the above-mentioned angle detector 11-2 that calculates the angle does not output the true value of Δθ'.Therefore, the value of Δθ is input to the quadrant discriminator 15, and this value is changed from 1π/2 to π/ Determine whether the value is between 2 or above.

On the other hand, the angle corrector 16 uses Δθ based on the above-mentioned discrimination output.
′ value is corrected to obtain the value of Δθ′″. Δθ′ and Δθ
The relationship between `` is as follows.

Δ0'-2π (However, Δθ<-1) This value of Δθ''' correctly represents the phase rotation of the reflected signal by 1 time interval 2T as long as Δθ does not exceed the range of 1π to π. The Doppler frequency ω6 is obtained by the device 12 based on the following equation.

ω4 = 80”/2T As a result, just like the example shown in Figure 1, the signal-to-noise ratio in the low-speed region is increased and the speed measurement range is expanded, and by using Δθ, it is possible to increase the signal-to-noise ratio in the high-speed region. The speed measurement limit is within the same range as the conventional one.A Doppler measurement device can be realized.

Furthermore, in the embodiment shown in FIG.

By time parameters T, 2T, 3T,..., nT.

An example of obtaining Doppler frequencies in parallel and at the same time will be shown.

The process of obtaining the Doppler frequency using the time parameters 3T, . . . , nT is similar to the process of obtaining the Doppler frequency using the time parameter 2T. The configuration of each circuit of the additional portion 418 uses a plurality of the same circuits. At this time,
The final Doppler frequency is 2, for example 1. Determination by majority vote is performed by the determiner 130.

In the embodiment shown in FIG. 11, the MTI filter of each circuit of the additional section 418 has a 1-hour parameter of 2 T,
3T,..., nT is used, but as an MTI filter, one with a time parameter T in the basic circuit is used, and its output is transmitted to the delay element 6,...
, 106 via the autocorrelator 8. . . . may be configured to be input to 108.

Further, in the above embodiment, a case was shown in which the decision device 130 executes the decision by majority vote, but the decision device may also be used, for example, as shown in FIG. 12, for each time parameter T, A system in which Doppler frequencies obtained at 2T, 3T, . . . , nT are added and averaged can also be used. In this case, each angle detector 11-3. ...11
1-3 (n pieces) of corrected Doppler phase angles Δθ, , Δθ2. ..., Δθ. A discriminator with an addition function performs arithmetic averaging processing.

Each of the above angle detectors 11-3. . . . Angle correction in 111-3 is performed by angle detectors 11-2. ......, 11
Each output in 1-2 is expressed as Δθ, ′, Δθ, ′,...
, Δθ. ', the correction process is executed as Δ 0□=Δ θ2=. The averaged Doppler phase angle is input to the divider 12-1 to obtain the Doppler frequency.

In the embodiment shown in FIG. 12, the MTI
Filters 3, 4. ..., 104 delay times are all T, and the time parameter only for autocorrelation processing is 2T,
3T, ..., nT. In this example, the same MTI filter as in the conventional configuration can be used, and by only changing the correlation processing part, the effect of improving measurement accuracy and reducing noise similar to that shown in FIG. 11 can be obtained. Also, in the embodiment shown in FIG. 1 or FIG. 10,
Of course, the MTI filter 4 may not be used and the output of the MTI filter with delay time T may be input to the autocorrelator 8.

〔Effect of the invention〕

As described above, according to the present invention, Doppler frequency measurement is possible in the low frequency range with a high signal-to-noise ratio, thereby greatly improving the speed measurement accuracy in the low speed range, and making it possible to measure the speed in the low speed range. This has the remarkable effect of realizing a Doppler measurement device with expanded measurement limits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure shows the frequency characteristics of the MTI filter, Figure 3 shows the configuration example of the MTI filter of the embodiment, and Figure 4 (,)
(b) is a diagram showing the processing process of the embodiment, Figure 5 is a diagram showing the frequency characteristics, Figure 6 is a diagram showing the phase difference, Figure 7 is a diagram showing the discrimination algorithm, Figure 8 (a) (b) is a diagram showing the processing process of another embodiment, FIG. 9 is a diagram showing the same frequency characteristics, and FIGS. 10 to 12 are block diagrams showing still other embodiments. 1: Phase comparator, 2: A/D converter, 3, 4.・・・・・・
, 104: MTI filter, 5, 6. ..., 106
: delay element, 7, 8. ..., 108: Autocorrelator,
9,10. ..., 110: Complex adder, 11-1.
11-2. ..., 111-2: Angle detector, 11-
3. ..., 111-3: Angle corrector, 12-1.1
2-2. ..., 112-2: Divider, 13,130
: Discriminator, 131: Discriminator and averager, 413,
418 and 419: additional parts. Figure 2 Frequency characteristics of MTI (2T) Patent applicant Hitachi Medical Co., Ltd. Σ Σ mouth rapid diagram diagram

Claims (1)

[Claims] 1. Detecting the phase of a reflected signal obtained by repeatedly transmitting ultrasonic pulses to an object at a predetermined transmission interval, and calculating the velocity of the object from the Doppler frequency indicated by the phase signal. In a pulsed Doppler measuring device that performs A first means for obtaining a phase difference vector, and a second means for calculating a velocity from an angle of the phase difference vector.
A pulse Doppler measurement device characterized by comprising: means. 2. The first means includes an MTI filter with a delay time of nT, and correlates the phase signal from which the solid object signal has been removed by the MTI filter. Pulsed Doppler measurement device. 3. The first means correlates phase signals with a time interval of nT among phase signals from which solid object signals have been removed by an MTI filter with a delay time of T. The pulsed Doppler measuring device according to item 1. 4. A pulsed Doppler measurement device that detects the phase of a reflected signal obtained by repeatedly transmitting ultrasonic pulses to an object at a predetermined transmission interval, and calculates the velocity of the object from the Doppler frequency indicated by the phase signal, a first means for obtaining a first phase difference vector by sequentially correlating phase signals sampled at time intervals (T) equal to the transmission interval of the ultrasonic pulses; a second means for obtaining a second phase difference vector by correlating among the phase signals having a time interval nT;
When the absolute value of the angle of the phase difference vector is π/n, the speed is calculated from the angle, and when the absolute value of the angle is less than π/n, the speed is calculated from the angle of the second phase difference vector. A pulse Doppler measuring device characterized by providing a third means. 5. The first means includes an MTI filter with a delay time of T, and the second means includes an MTI filter with a delay time of nT, and the phase signal from which the solid object signal has been removed by each MTI filter is 5. The pulse Doppler measuring device according to claim 4, which takes a correlation. 6. The first and second means each have a delay time T
5. The pulse Doppler measurement device according to claim 4, wherein the pulse Doppler measurement device includes a MTI filter, and correlates phase signals from which a solid object signal has been removed by each MTI filter. 7. A pulsed Doppler measurement device that detects the phase of a reflected signal obtained by repeatedly transmitting ultrasonic pulses to an object at a predetermined transmission interval, and calculates the velocity of the object from the Doppler frequency indicated by the phase signal, A first phase difference vector is obtained by sequentially correlating the phase signals sampled at time intervals (T) equal to the transmission interval of the ultrasonic pulses, and an angle of the first phase difference vector is calculated. Among the phase signals sampled at the time interval T, the phase signals sampled at the time interval T are correlated with each other at a time interval of 2T to obtain a second phase difference vector, and the angle of the second phase difference vector is determined. and a third means for correcting the angle of the second phase difference vector according to the value of the angle of the first phase difference vector and calculating the speed from the corrected angle. A pulse Doppler measuring device characterized by being provided with means. 8. The first means includes an MTI filter with a delay time of T, and the second means includes an MTI filter with a delay time of 2T, and the phase signal from which the solid object signal is removed by each MTI filter is The pulsed Doppler measuring device according to claim 7, characterized in that a correlation is taken. 9. The first and second means each have a delay time T
8. The pulse Doppler measuring device according to claim 7, wherein the pulse Doppler measurement device includes a MTI filter, and correlates phase signals from which solid object signals are removed by each MTI filter. 10. The correction in the third means is such that when the angle of the first phase difference vector is π/2 or more, the angle obtained by adding 2π to the angle of the second phase difference vector is adjusted to the first phase difference. When the angle of the vector is -π/2 or less, the angle is the angle of the second phase difference vector plus -2π, and the angle of the first phase difference vector is -π/2 and π/
8. The pulse Doppler measuring device according to claim 7, wherein when the value is between 2 and 2, the angle itself of the second phase difference vector is set as a corrected angle. 11. A pulsed Doppler measurement device that detects the phase of a reflected signal obtained by repeatedly transmitting ultrasonic pulses to an object at a predetermined transmission interval, and calculates the velocity of the object from the Doppler frequency indicated by the phase signal, For each phase signal sequentially sampled at a time interval (T) equal to the transmission interval of the ultrasonic pulses, T, 2T, ..., nT, respectively.
A first means for obtaining the respective phase difference vectors by correlating the objects at each time interval, and a second means for calculating the respective velocities from the angles of the respective phase difference vectors are provided. Characteristic pulse Doppler measurement device.