CN1095356C - Mutual correlation-spectrum figure method in supersonic blood current measurement - Google Patents

Abstract

The present invention relates to a mutual correlation-spectrum figure method in supersonic blood current measurement. The method comprises the steps that electrical pulse signals generated by a supersonic transmission circuit for generating pulse signals are applied to a controller and echo signals are amplified by a radio frequency amplifying circuit; the mutual correlation coefficient of the echo signals between two times of transmission is calculated by a mutual correlation arithmetic device; finally, the correlation functions constitute a time-domain complex envelope function and the dynamic power of blood current signals is calculated by a spectrum analyzer. The method of the present invention solves the problem of spectrum aliasing in the high-speed blood current measurement besetting people for a long time, and can be widely applied to medicines and industry.

Description

" cross-correlation-spectrogram " method during supersonic blood is measured

The present invention relates to " cross-correlation-spectrogram " method in a kind of supersonic blood measurement, belong to the physical measurement techniques field.

Measuring human bloodstream with ultrasonic method is widely used in clinical.Traditional supersonic blood measurement is based on the doppler principle design.It has solved the problem of non-invasive measurement human bloodstream to a certain extent.But there is the inherent defective in two aspects in traditional Doppler's method: (1) maximum detection flow velocity and maximum detectable degree of depth mutual restriction; (2) mutual restriction between range resolution ratio and the velocity resolution.Therefore, when tested flow velocity is big, will on the spectrogram of output, aliasing phenomenon occur, bring doubt to clinical diagnosis.How to solve high speed blood flow measurement intermediate frequency spectrum mixed is the problem that people extremely pay close attention to repeatedly always.

During existing ultrasonic doppler blood flow was measured, measurement result was exported (see figure 1) with the mode of dynamic power spectrogram.Abscissa is a time shaft among the figure; Vertical coordinate is a frequency deviation, and it is suitable with flow velocity; The energy that gray scale in the spectrogram represents particular moment, have the echo-signal that the object of certain specific flow velocity produces.Part in the spectrogram above abscissa is represented positive flow (being flow velocity direction directional transducer); The spectrogram of abscissa below is represented reverse flow (being that the flow velocity direction deviates from transducer).When tested blood flow rate than higher the time, the folding phenomenon of spectrogram will take place.For example, higher positive flow part will fold into the zone of reverse flow, as Fig. 2.When the blood flow of more speed occurred, the folding phenomenon that can cause the spectrogram aliasing of serious spectrogram was as Fig. 3.This will bring difficulty to clinical diagnosis.

The spectrogram aliasing is the inherent problem that exists in the Doppler blood flow measurement system.In order to address this problem, the someone has proposed the method for " cross-correlation " blood flow measurement.This method can solve the aliasing in the tachometric survey to a certain extent.But the result that common " cross-correlation " method is measured can only provide mean flow rate, and can not provide spectrogram to show.Such result had not both met doctor's custom, was not easy to use in clinical disease diagnosis yet.

The objective of the invention is to develop " cross-correlation-spectrogram " method in a kind of supersonic blood measurement,, measure human bloodstream (particularly high speed blood flow) more accurately with the aliasing in spectra problem in the high speed blood flow measurement that solves long-term puzzlement people.

" cross-correlation-spectrogram " method during supersonic blood of the present invention is measured comprises following each step:

(1) produce electric impulse signal by the ultrasound emission circuit, be applied on the transducer, the excitation piezoquartz converts ultrasound wave to and injects human body;

(2) amplify faint echo-signal by radio frequency amplifying circuit;

(3) calculate the cross-correlation function of echo-signal between the twice emitting by the computing cross-correlation device, and find the maximum and the time corresponding displacement of cross-correlation function thus;

(4) maximum and the displacement by cross-correlation function constitutes time domain complex-envelope function, and calculates the dynamic power spectrum of blood flow signal by spectralyzer.

" cross-correlation-spectrogram " method during the supersonic blood that the present invention proposes is measured is a kind of anti-blood flow measurement new method repeatedly of mixing.The new method of this being called as " cross-correlation-spectrogram " has solved the aliasing in spectra problem in long-term puzzlement people's the high speed blood flow measurement.Instrument based on this new detection principle design can be used for measuring more accurately human bloodstream (particularly high speed blood flow).This quasi-instrument can also be used for the measurement of commercial production field pipeline inner fluid and the measurement of some velocity to moving target simultaneously.

Description of drawings:

Fig. 1 is normal blood flow spectrogram.

Fig. 2 is the folding phenomenon of spectrogram.

Fig. 3 is the spectrogram aliasing.

Fig. 4 is the theory diagram of the inventive method.

Fig. 5 is the computing cross-correlation schematic diagram.

Fig. 6 and Fig. 7 are the anti-repeatedly principles of sound spectrogram of mixing of utilizing the inventive method to obtain.

Fig. 8 is an embodiment of the inventive method.

Fig. 9 is radiating circuit figure.

Figure 10 is radio frequency amplifying circuit figure.

Figure 11 is a computing cross-correlation device circuit diagram.

Below in conjunction with accompanying drawing, introduce content of the present invention in detail.

Among Fig. 4-Figure 10, the 1st, transducer, the 2nd, skin, the 3rd, ultrasonic beam, the 4th, blood vessel, the 5th, tissue scattering object.

Figure 4 shows that the theory diagram of the inventive method, the operation principle of each key step is as follows:

(1) radiating circuit:

In pulsed wave ultrasound blood flow measurement system, ultrasonic transducer is single piezoquartz.Produce electric pulse by radiating circuit, the excitation piezoquartz converts ultrasound wave to and injects human body.The echo that internal organs of the body causes converts the signal of telecommunication to by piezoquartz more conversely and enters receiving circuit.

(2) radio frequency amplifying circuit:

Because echo-signal is very faint, therefore need just can do further information retrieval through amplifying.Radio frequency amplifier among the figure must have certain gain and bandwidth.

(3) computing cross-correlation device:

The computing cross-correlation device is used for detecting the echo-signal displacement in time that same moving target produces during the twice emitting, and its principle is referring to Fig. 5.

As can be seen from Figure 5, suppose that distance, delta d has been moved in moving object in the interval T of twice emitting, in echo-signal, will occur corresponding time difference Δ t so.Simple derivation can get: $\mathrm{\Δt}=\frac{2\mathrm{\Δd}}{c}----\left(1\right)$

C is the spread speed of ultrasound wave in human body in the formula.

If the echo-signal after the twice emitting is done computing cross-correlation, maximum will appear in cross-correlation function when τ=Δ t.In other words, by detecting the moment that the cross-correlation function maximum occurs, just can obtain Δ t.Can obtain Δ d by Δ t.Again displacement d has just been obtained the axial velocity V of moving object divided by time T. $v=\frac{\mathrm{\Δd}}{T}----\left(2\right)$

Obtain the average speed of moving object under a certain designated depth with the time domain cross-correlation method, but the spectrogram that such result and doctor use is different in clinical.

(4) spectralyzer:

The result of cross-correlator output is the time difference that target occurs in echo-signal during the twice emitting, and this time difference has reflected the speed of object of which movement.

For this movable information is shown with the sound spectrogram form, can construct a time domain complex-envelope signal with the following method, obtain sound spectrogram by spectralyzer then.

The time domain complex-envelope signal of being constructed is:

x(n)＝A(n)e ^j(n) (3)

Amplitude function A in the formula (n) and phase function (n) are respectively $A\left(n\right)=\sqrt{R_{\max }^{\left(n\right)}\left({\mathrm{\τ}}_{\max }^{\left(n\right)}\right)}----\left(4\right)$

In the formula

It is the displacement time of the n time emission when maximum occurring with the cross-correlation function of (n+1) inferior emission back echo signal; Be to be at displacement The time auto-correlation function value.

Can prove that the time-domain signal of (3) formula formation is done Fourier transform and asked its power spectrum is exactly that traditional Doppler's method obtains the blood flow signal sound spectrogram.

(5) spectrogram shows:

Can on monitor, show by traditional method for the sound spectrogram that in (4) step, obtains.The form that shows is the same with the example that Fig. 1 provides, and promptly abscissa is a time shaft; Vertical coordinate is a frequency deviation, and it is suitable with flow velocity; The energy that gray scale in the spectrogram represents particular moment, have the echo-signal that the object of certain specific flow velocity produces.

Compare with traditional Doppler blood flow measurement, " cross-correlation-sound spectrogram " method that patent of the present invention proposes not only can provide same sound spectrogram to show to the user, the more important thing is that the peak flow rate (PFR) that this method can survey is unfettered.

Peak flow rate (PFR) during sound spectrogram shows is relevant with the sample rate of analyzed time domain data.In traditional method, sample rate equals exomonental repetition rate PRF.In case the frequency deviation that higher flow velocity produces surpasses the half of PRF, aliasing will take place in frequency spectrum.During " cross-correlation-sound spectrogram " method of employing,, can will once record with the method for interpolation if velocity ratio is higher

Be divided into the arrival of two steps, so just be equivalent to sample rate PRF is doubled.If will

Get carefullyyer, just be equivalent to obtain higher sample rate.Naturally just can avoid in frequency spectrum, occurring aliasing with such method.Even under the velocity ratio condition with higher, no exception (referring to Fig. 6 and Fig. 7).

Introduce one embodiment of the present of invention below, as shown in Figure 8.

Present embodiment leads to microcomputer as basic hardware platform with a Daepori.The emission of signal, detection and analysis are all realized by homemade hardware.Corresponding above 5 steps provide the method that adopts in the present embodiment.

(1) radiating circuit (referring to Fig. 9)

Radiating circuit is made up of two audions, two VMOS pipes and a transformator.Give two audions respectively by two complementary transmitted pulse signals that system, control circuit produces, through the switch of control VMOS pipe after the level conversion.Two VMOS pipe alternate conduction, formed transmitted pulse is through transformer coupled to the transducer wafer.

(2) radio frequency amplifying circuit (referring to Figure 10)

Radio frequency amplifier is selected AD600 for use, and this is a broadband, low noise radio frequency amplifier.

The input stage of amplifier connected a L, C resonance circuit are so that select the signal relevant with tranmitting frequency targetedly.

The preamplifier output signal is delivered to the related operation device.

(3) computing cross-correlation device (referring to Figure 11)

Computing cross-correlation device in the present embodiment is selected the TMC2023 Digita Correlator (JP) for use.It is the digital correlation computing special chip of 64 of a slices.The input of this chip is that output is exactly the auto-correlation function R (N) of twice emitting back echo signal through the ultrasound echo signal f (n) that amplifies.

The output of computing cross-correlation device obtains maximum cross-correlation value through the testing circuit of maximum related value With corresponding time delay

(4) spectralyzer:

Spectralyzer is a commercial TMS320C25 high speed signal transaction card.This is one is the signal processing card at center with TMS320C25.Program with the TMS320C25 assembler language and can in 5ms, realize 256 plural FFT.

Whole system is based upon on the platform of a general purpose PC.By the necessary various control parameters of the mutual interface of people's one machine in can control system work.Sound spectrogram is presented on the display of PC.

Claims (1)

1, " cross-correlation-spectrogram " method during a kind of supersonic blood is measured is characterized in that this method comprises following each step:

(1) produce electric impulse signal by the ultrasound emission circuit, be applied on the transducer, the excitation piezoquartz converts ultrasound wave to and injects human body;

(2) amplify faint echo-signal by radio frequency amplifying circuit;

(3) calculate the cross-correlation function of echo-signal between the twice emitting by the computing cross-correlation device, and find the maximum and the time corresponding displacement of cross-correlation function thus;

(4) constitute time domain complex-envelope function by spectralyzer by the maximum and the displacement of cross-correlation function, the time domain complex-envelope signal of being constructed is:

x(n)＝A(n)e ^j(n) (1)

Amplitude function A in the formula (n) and phase function (n) are respectively $A\left(n\right)=\sqrt{R_{\max }^{\left(n\right)}\left({\mathrm{\τ}}_{\max }^{\left(n\right)}\right)}----\left(2\right)$

In the formula

It is the displacement time of the n time emission when maximum occurring with the cross-correlation function of (n+1) inferior emission back echo signal;

Be to be at displacement

The time auto-correlation function value,

The time-domain signal that above-mentioned (1) formula constitutes is done Fourier transform and is asked its power spectrum, promptly obtains the blood flow signal sound spectrogram, and calculates the dynamic power spectrum of blood flow signal thus.

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