JPH01242042A - Ultrasonic doppler blood flowmeter - Google Patents

Abstract

PURPOSE:To obtain data having good stability, by performing correlational operation between echo signals with respect to transmission timings of at least two times and operating the primary and secondary moments of the correlation coefficient thereof. CONSTITUTION:An ultrasonic probe 1 transmits an ultrasonic wave on the basis of the drive signal applied through a rate pulse generator 2, a delay line 3 and a pulser 4 and the echo signal obtained by the probe 1 is stored in a memory means 10 through a preamplifier 5, a delay wire 6, an adder 7, a gate circuit 8 and an A/D converter 9. The difference of the signals at every rates is calculated by a difference device 11 to be stored in a memory means 12. The data stored in the memory means 12 is sent to an FFT 13 through a switch SW2 and the output thereof is stored in a memory means 14 through switches SW3, SW4. An operation means 15 performs the correlational operation between echo signals with respect to transmission timings of at least two times and the primary and secondary moments relating to the correlation coefficient obtained by said operation are operated.

Description

Detailed Description of the Invention [Objective of the Invention 1 (Industrial Application Field) The present invention relates to an ultrasonic Doppler blood flow meter that measures the velocity of blood flowing in a blood vessel of a subject using an ultrasonic beam. It is.

(Prior Art) A conventional ultrasonic Doppler blood flow meter transmits ultrasonic waves to a subject, obtains blood flow information within the subject, and calculates blood flow velocity from the blood flow information.

In this case, there is a method in the literature [υLTRASONICIHAGING] that obtains a correlation function on the time axis of received echoes obtained at different rates and obtains high-speed blood flow without aliasing.
8.73-85 (1986) P73-P85. An outline of this method will be explained using FIGS. 2 and 3.

As shown in Figure 2, V inside the blood vessel is parallel to its wall.
Consider a system in which the velocity of blood flowing at a certain velocity is measured using an ultrasonic beam as shown in the figure. Here, to simplify the explanation, it is assumed that only one blood cell exists. The received echo at the k-th rate is yk(t), Vk+1(t
), and let the rate period be the king, the blood cells move by ・COSθ・in the time of ■, and normally T=250m, v=
If it is about 1 m/s, vl = 0.25 m, and VT is sufficiently small for the sample volume (3 culms), so the blood cell echo at both the 2nd and +1st rates is yk(t ), yk+1(t), and the echo from the blood cell is delayed by rd=2v-cosθ-T/c (c is the speed of sound) between yk+1(t) and yk(t). In other words, if we measure τd based on this relationship, v
This means that cos θ can be measured (T and C are known). In the prior art, in order to measure τd, the correlation function R(
τ) is determined by the following formula, and R(τ) = f yk(t
)・yk+1(t+τ)dtAs shown in the same figure (C), IR(
The value of τ for which τ)1 is the maximum is taken as the estimated value of τd.

An important advantage of this method is that it is suitable for measuring high velocity blood flow.

(Problem to be Solved by the Invention) However, in the prior art, in order to obtain the average flow velocity in a certain sample volume, as described above, τ at which the absolute value IR(τ)1 of the cross-correlation function is maximum is set as τ , because it is used to calculate the flow velocity V, it is easily affected by speckles, white noise, etc., and there is a problem that the stability of the data is poor.

Furthermore, there was a clinically important problem in that information on dispersion, which is an index of variation in blood flow velocity, could not be obtained.

The present invention was made to solve the above-mentioned problems, and it is an ultrasonic Doppler blood system that can obtain data with good stability and also obtain information on flow velocity variations that could not be obtained with conventional technology. The purpose is to provide a flow meter.

[Structure of the Invention] (Means for Solving the Problems) The structure of the present invention for solving the above-mentioned problems is to transmit and receive ultrasonic waves to and from a subject, obtain information on blood flow inside the subject, and detect blood flow in the subject. In an ultrasonic Doppler blood flow meter that calculates blood flow velocity from flow information, a removal means removes clutter components from received echo signals, and a signal obtained from the removal means is transmitted at least two times at different timings within the subject. The apparatus is provided with a calculation means for performing a correlation calculation between echo signals from the same region, and a means for calculating the first and second moments regarding the correlation function obtained in this calculation.

(Function) Since the first moment (center of gravity) of the correlation function is used to determine the flow velocity, stable data can be obtained, and the second
Information on the dispersion of flow velocity can also be obtained by determining the second moment (dispersion).

(Example) The present invention will be specifically explained below using Examples.

First, in order to explain the present invention in detail, the 81 method of determining the first and second moments of the correlation function used in the embodiments will be explained.

First moment of correlation function R(τ)! When .tau. is τ and the quadratic 7-men j~ is σ2, these are expressed by the following equation (11, (2+).

fτR(τ)dτ τ−...(1) J R(τ)d°τ f′″′(τ−r)2f?(τ)dτ σ2−□・・・(′2J J R(τ) dτ Here, if the Fourier transform of R(τ) is Vc(f), then V
c(f) is called a cross spectrum and is a complex number, which is divided into an absolute value and a phase and is expressed by the following equation (3).

i f) r(f) VC(f)=! Vc(f) i 6−−−=−,,
, (3) Furthermore, if the Fourier transforms of the two waveforms Vk(t) and yl+t(t), which are input to the calculation of the correlation function, are Vk(f) and Vk÷1(f), then the following equations ( 4) to (6).

vc(r)=Vk(f) ・Vk+1(f)
=(4)Vk(f)=X
k(f)+j Y k(f)...(5)V
k+1(f)-Xk+1(f)+jYk+1m ・
c61Xk(f), Yk(f), Xk+1(f),
If Yk+1(f) is a real number, the above equations (4) to (6)
Therefore, the following equation (7) holds: Vc(f)=Xc(f)+
j Yc(f)X c(f)=X k(f)X k+
1 (f) + Y k (f) Y k ÷ 1 (f) Y c
(f)-X k(f)Y k-1(f)-X k(f)
Y k+1(f)''(7)Xc(f), Yc(f)
is a real number. Also, using the above equations (3) and (7), the following equations (8) and (9
) holds true.

l Vc(f)
...(8) Also, τ and σ2 can be transformed as follows using VC(f).

(margin below) dr2 ter (2π)2. /: τ2 R(r) e-J"dr From these equations, the following equation (g) za2) is obtained.

VC(0)=f”R(r)dr −0
n)... side above (1), (2), (to), (II), (
From equation 12), the following equations (13 and (14)) hold true.

...(14) As mentioned above, using cross spectra, equations (1) and (2) can be expressed as equations (13 and (14)), and (1), (
In the method using equation 2), it is necessary to perform a product-sum wave on the time axis, but in the method using equations (13 and (14)), FFT
(Fast Fourier Transform) is used to find VC(f), which is much faster than the method using equations (1) and (2).
, σ2 can be obtained.

FIG. 1 is a block diagram of an embodiment of the configuration of the present invention for realizing the above principle. The structure and operation will be explained below with reference to the figure.

1 is an ultrasonic probe, rate pulse generator 2. Delay line 3. Ultrasonic waves are transmitted by a drive signal via the pulser 4.

The echo signal obtained by this probe 1 is transmitted to the preamplifier 5. Delay line 6. An output signal Sl is obtained by controlling the phase of the signals of each channel of the array transducer and adding them via an adder 7.
(t). A gate circuit 8 sends the signal QS1(t) to the A/D converter 9 at each rate. The output of the A/D converter 9 is sent to the switch SW1.
The data is sent to the first storage means 10 having a plurality of memories for each rate and stored therein. That is, each memory stores signals ek(t), ek+1(t), and ek+1(t) for each rate.
ek+2(t)-... are stored. The signals stored in each memory in this manner are subjected to an operation to obtain a difference between adjacent rays by a subtractor 11, and the result is stored in a second storage means 12 having a plurality of memories.

That is, each memory has V k(t)−e k
(t)-e k+1(t), v k+1(t)-
e k+1(t)-e k+2(t)-... are stored. The purpose of taking the difference in this way is to cancel the effects of objects other than moving objects such as blood. In this sense, it can be called a clutter removal means.

Next, the information stored in the second storage means 12 is sequentially retrieved via the switch SW2, and the fast Fourier transformer (
FF engineering) Send to 13. In FFT13, the above (5),
J shown in equation (6) is the complex Fourier transform operability, and each frequency spectrum, that is, Xk(f), Y
k(f), stored in multiple memories.

Thereafter, the calculation means 15 performs the following calculation.

That is, first, Vc(f) is obtained by calculating the above equation (7), and then τ is obtained by the above equation (131, (14)).

σ2 is calculated.

τ obtained in this way is 1 of the correlation function R(τ)
This is the second moment, which is the center of gravity of the received signal. Further, σ2 is the second moment and indicates the dispersion of the frequency spectrum of the received signal. Such τ, σ2 (
or σ) is a digital scan converter (DSC>1
6 and processed as a display signal.

Note that the calculation means 15 is not limited to the one that performs the calculations described above, but also directly calculates τ by calculation of the formula (IJ, <2).
, σ2 may be calculated. In addition, the above (13,
(You may perform calculations such as the following equations (15 and (16), which are modified versions of equation 141.

...(16) [Effects of the Invention] In the present invention described in detail above, since the first moment (center of gravity) of the correlation function is used to determine the flow velocity, speckles are instantaneously superimposed on the received signal. If an abnormal peak is observed in the correlation function due to the influence of white noise, etc., stable data with small fluctuations in the value of the center of gravity is selected.

Furthermore, the second moment (dispersion) of the correlation function indicates the dispersion of the arrival time difference between the two received signals, and this is caused by the dispersion of the flow velocity, so the dispersion of this correlation function reflects the dispersion of the flow velocity. Clinically meaningful data can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 and 3 (a) to (C) are diagrams for explaining a conventional example. DESCRIPTION OF SYMBOLS 1... Ultrasonic probe, 11... Clutter removal means, 13... Correlation calculation means, 15... Moment calculation means. Agent Patent Attorney Yudo Chikako
Takeshi Kondo 3rd drawing procedure amendment (voluntary) 63.8. -9 Showa year month day

Claims (1)

[Claims] A removal means for removing clutter components from received echo signals in an ultrasonic Doppler blood flow meter that transmits and receives ultrasound waves to and from a subject to obtain blood flow information within the subject and determine blood flow velocity from the blood flow information. and a calculation means for performing a correlation calculation between echo signals from the same part of the subject at at least two different transmission timings among the signals obtained from the removal means, and a first-order correlation function related to the correlation function obtained by this calculation. and means for calculating a second-order moment.