JPH0217044A - Ultrasonic doppler blood flowmeter - Google Patents

Abstract

PURPOSE:To use a low speed operation type one as an A/D converting means and to reduce cost by applying A/D conversion to the blood flow data on one raster after the orthogonal phase detection of three receiving echoes obtained by performing the transmission and reception of an ultrasonic wave three times at rates different from each other. CONSTITUTION:Transmission driving is performed over three times at different rates in order to obtain three receiving echoes for obtaining the blood flow data on one raster and an ultrasonic receiving system obtains three receiving echoes by said driving. In a B-mode, one raster is obtained by the ultrasonic transmission and reception of one rate. Herein, when a receiving echo in a Doppler mode is set to v(t), v(t) receives the supply of reference signals cos2pif0t, sin2pif0t in mixers 8A, 8B to be subjected to orthogonal phase detection processing. The outputs x(t), y(t) of LPFs 9A, 9B are digitalized by A/D converters 10A, 10B but, since the signals x(t), y(t) subjected to A/D conversion by the A/D converters 10A, 10B are low frequency as compared with the receiving echo v(t), low speed operation type A/D converter (as compared with a conventional one) may be used as each of the A/D converters 10A, 10B.

Description

Detailed Description of the Invention [Purpose of the Invention (Industrial Application Field) The present invention utilizes ultrasonic transmission/reception waves and the Doppler effect to obtain blood flow velocity information as functional information associated with the movement of a moving object within a living body. The present invention relates to an ultrasonic Doppler blood flow meter that is obtained and visualized by a method, and particularly relates to an ultrasonic Doppler blood flow meter that has completely improved imaging techniques.

(Prior art) Ultrasound and diagnostic methods include anatomical information using B-mode images as a representative example, and internal organ movement using M-mode images as a representative example.
Information, such as functional information associated with the movement of a moving object within a living body using the Doppler effect, a typical example of which is blood flow imaging, is used for diagnosis.

Further, typical methods for scanning inside a living body using ultrasound waves include electronic scanning and mechanical scanning. Here, the electronic scanning method will be explained.

In other words, if an array-type ultrasonic probe (7' lobe) consisting of a plurality of ultrasonic transducers arranged in parallel is used for linear amplification scanning, a plurality of ultrasonic transducers is regarded as one unit, and this one This is a method of transmitting an ultrasonic beam by exciting a unit of ultrasonic transducers. For example, the pitch of each unit of ultrasonic transducers is sequentially shifted by one transducer and the position of each unit of element is sequentially changed. This is a scanning in which the transmission point position of the ultrasound beam is electronically shifted by moving the ultrasound beam.

Then, so that the ultrasonic waves are focused as a beam, the excitation timing of the excited ultrasonic transducers is shifted between those located in the center of the beam and those located on the four sides, and the ultrasonic vibrations generated by this are shifted. Ultrasonic total focusing (electronic focus) that is reflected using the phase difference of each sound wave generated by the child.
let Then, the anti-elbow ultrasonic wave e is received by the same vibrator that was excited and converted into an electrical signal, and an echo image of each transmitted and received wave is formed as a tomographic image, for example, and the image is displayed on a cathode ray tube or the like.

In addition, in the case of sector electronic scanning, each transducer is excited so that the transmission direction of the ultrasonic beam changes sequentially into a fan shape for each ultrasonic beam toggle for one unit of excited ultrasonic transducers. The timing is changed according to a desired direction, and the subsequent processing is basically the same as the linear electronic scanning described above.

In addition to the above-mentioned linear and sector electronic scanning, transducer (
There is also mechanical scanning in which ultrasonic scanning is performed by attaching a probe (probe) to a scanning mechanism and moving the scanning mechanism.

On the other hand, in the imaging method, in addition to a B-mode image in which signals accompanying ultrasound transmission and reception are combined to form a tomographic image, an M-mode image based on fixed scanning in the same direction is typical. This M-mode image represents temporal changes in the ultrasonic wave transmitting/receiving site, and is particularly suitable for diagnosing moving organs such as the heart.

Further, the ultrasonic Doppler method, of which blood flow imaging is a typical example, is a method of obtaining and visualizing functional information that is present in the movement of a moving object within a living body, and will be described in detail below. That is, the ultrasonic Doppler method utilizes the ultrasonic Doppler effect in which when an ultrasonic wave is reflected by a moving object, the frequency of the reflected wave shifts in proportion to the moving speed of the moving object. Specifically, ultrasonic rate pulse (or continuous wave)
is transmitted into a living body, and the frequency shift due to the Doppler effect is obtained from the phase change of the reflected wave echo.
It is possible to obtain motion information of a moving object at a depth position.

According to this ultrasonic Doppler method, the direction of blood flow, the state of the flow (disturbed or regular), the /4' turn of the flow, the velocity value, etc. of the blood flow at a certain position in the living body can be measured. You can know the status.

Next, the next device (ultrasonic Doppler blood flow meter) to which this ultrasonic Doppler method is applied will be explained. In other words, in order to obtain blood flow information from ultrasound echoes, the ultrasound probe and the transmitter/receiver circuit are driven to repeatedly transmit ultrasound pulses in a certain direction a predetermined number of times, and nine ultrasound echoes are received. is detected by a phase detector to obtain phase information, that is, a signal consisting of a Doppler shift signal due to blood cells and a clutter component. This signal is converted into A/D
The converter converts the signal into a digital signal, removes the cycra component using a filter, and converts the signal into a toggle-91m shift signal (Fi) due to blood cells.For example, in order to obtain a color Doppler image in real time, the frequency is analyzed using a high-speed frequency analyzer such as an autocorrelation method. , the average value of Doppler shift, the variance value of Doppler shift, the average intensity of Doppler shift, etc. are obtained.

Here, by performing the above-described series of processes while scanning the ultrasound beam from one side to the other in correspondence with the sector scan screen, information on two-dimensionally distributed blood flow can be detected.

Then, blood flow information such as a two-dimensional blood flow velocity image showing the direction and speed of blood flow described above, and nine B-mode images and M-mode images obtained using another system are processed using a DSC (digital scan converter). ) and display it on a TV monitor.

As a method for calculating blood flow information in the conventional ultrasonic Doppler blood flow meter described above, an autocorrelation method is adopted. This autocorrelation method calculates the average value of the phase change of the ultrasonic echo and the Sidopler shift frequency, and uses the average frequency to obtain the flow velocity. However, in the case of high-speed blood flow, 'aliasing' occurs. A phenomenon occurred and it was a problem.

As a method to solve the above-mentioned problem, that is, to obtain high-speed blood flow without looping, we can obtain ftf at different rates.
A method of determining the correlation function (cross-correlation function) between the waveforms of r-received echoes on the time axis and determining the blood flow velocity using this cross-correlation function is described in the literature (ULTRASONICrMAGIN).
G 8.73-85 (1986),' TIME Do
KITE IN F'OR LATION OF PULSE-
DOPPLERULTRASOUND AND BLO
OD VELOCITY ESTIMATION BY
CRO8S C0RRELATION”).

In other words, the cross-correlation method uses three different phases for ultrasonic transmission and reception.
By doing this at the rate of
+month+2 is obtained, and based on these, the signal V after clutter removal is
1+ v1+1 lt gain, N'l = al(t) +
a1+1(t)vl+1 ” ' 1+1(t) +
``l+2(t) Obtain the cross-correlation function R(τ) between both signals Ml and vl+1, and from the value of τm and τ that maximizes R(τ), the flow velocity V=τ ・f−!− (however, f is the rate frequency.

max r 2r C is the speed of sound), this flow velocity V is used as the manping data on one ultrasonic raster, and this series of procedures is repeated for each raster to form one frame.

(Problems to be Solved by the Invention) In the above-mentioned cross-correlation type ultrasonic Doppler blood flow meter, the transmitting and receiving system transmits and receives ultrasonic waves three different times.
Three received echoes are obtained, converted into digital signals by an A/D converter, and stored in a memory, and then the data is extracted from the memory and an operation is performed to obtain a correlation function.

However, in the above method, since the received echo, which is a high frequency signal, is directly A/D converted, a high-speed operation type A/D is used.
There was a problem that a converter was required, leading to an increase in cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic Doppler blood flow meter that is capable of calculating blood flow information based on a cross-correlation function using a low-speed operation type A/D converter.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are taken to solve the above problems and achieve the objects.

That is, the present invention transmits ultrasonic waves to the blood flow in the circulatory tissue in a living body, and detects a Doppler shift component shifted by the blood flow from the received echo obtained thereby,
In an ultrasonic Doppler blood flow meter that obtains blood flow information, blood flow information on one raster is generated by three received echoes obtained by transmitting and receiving ultrasound at three different rates. A means to phase detect the received echo and a rono that inputs the phase detection output from this means!
A/D conversion means for converting the output of the filter into a digital signal; means for obtaining a cross spectrum based on the output of this means; and means for obtaining a cross spectrum based on the output of this means; f: Features include means for obtaining a cross-correlation number of echoes, and means for obtaining blood flow velocity information based on the cross-correlation function obtained by this means.

(Function) According to such a configuration, the A/'D conversion means may A/D convert the phase detection output of the received echo,
Here, since the phase detection output has a lower frequency than the received echo, it is possible to use a low-speed operation type A/D conversion means as a result.

(Example) An example of the ultrasonic Doppler blood flow meter according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, an array probe 1 includes a rate pulse generator 2. Delay line 3.・f
Transmission is driven by the ultrasonic transmission system 3 consisting of Luna-4,
Gria pufferfish 5. It is driven for reception by an ultrasonic reception system consisting of a delay line 6° adder 7.

In other words, in Doppler mode, in the ultrasound receiving system, 1
In order to obtain three received echoes for obtaining blood flow information on one raster, transmission is driven three times at different rates, whereby the ultrasonic receiving system obtains three received echoes.

In the B mode, one raster is obtained by transmitting and receiving ultrasonic waves in the route.

Here, if the received echo in Doppler mode is v(t), then v(t) = a(t) 0111(2πfot +φ
) where a(t) is the envelope function, fo is the carrier frequency, and φ is the phase.

At this time, the received wave echo v(1) (actram VCf)
is as follows.

The received echo v(t) expressed by the above equation is sent to the mixer 8 at 8B as a reference signal cm2πf01°[h
The signal is supplied with 12πfot and subjected to quadrature phase detection processing.

This will be explained with reference to FIGS. 1 and 2.

In other words, the signal after mixing is expressed as x'(t), y'(
t) Then, we get the following.

x'(t)" v(t)oos2yrfOt= m(t
) ccs (2πfot+φ) cos 2πfot
y'(t) = v(t)gbs2πfQt=a(t)
2πfot in cm (2Kfot+φ) Here, x'(t)'7X'(f), y'(t)'-yY'
(f) ('7 indicates Fourier transform), it becomes as follows.

Then, when x'(t) and y'(t) are passed through low-noise filters (LPF) 9 A and 9 B, A(
f±2f0) components are removed to obtain x(t) and y(t).

Therefore.

z(t)=-a(t) φ] y(t)=-breath(t)mφ Here, the output x(t) of LPF 9A, 9B,
y(t) is digitized by the A/D converter 101.10f3, and the outputs after this digitization are also written as x(t) and y(t), and the mixer llk
, IIB multiplies cas2πfOt, dn2πfot, x(t).

It can be seen from FIG. 3 and the following equation that v(t) can be completely reconstructed using y(t). FIG. 3 is a diagram showing the corresponding part in FIG. 1 and a processing system for x(t), y(t), and v(1), including a Dei Zotal mixer 21 for explanation.

v(t)=a(t)cllm(2πfot+φ)=
t(t)((cm2πf, t, 1lcosφ−[out2π
fot〕mφ)=x(t)co+2πfot+y(t)
From gm2πfot or more, A/D converter 101.10f
No. 46 x(t) and y(t) to be A/D converted by No. 3 are as follows:
Since the frequency is lower than that of the received echo v(t), the A/D converter 10A.

The JOB may be of a low-speed operation type (compared to conventional ones). In this case, it is sufficient for the A/D converter 10 that the sampling frequency of the IOH is twice or more the maximum frequency component in the spectrum of the envelope function a(t).

Here, as shown in FIG. 4, V(f) and X(f)
.

Considering the band Y<f), xcf), y(f) is A
It is the same as that of (f), and V(f) is A(f) with its center frequency shifted to f=±f0.

And v(t) (x(t)cog2πfot, y
(t)・th2πfOt) is the fixed canceller 121
．． 12B, data X, Cf), Xk+1Cf),
7. (f), +1 to 7 (first memory 13 consisting of four memories holding n, and F'F'T analysis section 24A, 1
4B, data Xk(f), Xk+1(f).

A second memory 15 consisting of four memories holding Y, (f), Yk-□, (f) and an operation 1 for calculating blood flow velocity, its average value, 2 variance, etc. from the cross-correlation function R(τ). '1-
a1e is input to the cross-correlation method analysis unit CCA.

In this cross-correlation method analysis unit CCA, the above-mentioned digital signal x (t) ・as 2πfOt, y
(t) Cross spectrum Ve(f
) = V);”(f)' Vk, H(7) is obtained and the cross-correlation function R(τ) is obtained by inverse Fourier transform.
This cross-correlation interval t! 1. From R(τ), this R
(τ) is the value of τ at which it peaks, and the first moment of τ is taken to obtain a blood flow velocity report.

The blood flow velocity information obtained as described above is allocated to each raster in the DSC 77, a frame is formed together with the gutter from the B-mode image generation section 18, and after being converted into an analog signal by the D/A converter 19, A display is made on the monitor 20.

In the above, the A/D converter 10A.

The output of 10B may be directly input to the cross-correlation method analysis unit CCA, that is, the mixers 17A and 11Bf may be omitted. In this case, v(t) will not be completely reproduced.

The present invention is not limited to the above embodiments, and can be implemented with various modifications without departing from the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, since the received echo is A/D converted after quadrature phase detection, a low-speed operation type can be used as the A/D conversion means. is possible,
It is effective in reducing costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the ultrasonic Doppler blood flow meter according to the present invention, FIGS. 2 and 3 are diagrams showing the main parts in FIG. 1, and FIG. It is a figure showing the circumferential e11 band. 1...Array probe, 2...Rate noculus occurs! , 3...Delay line, 4...Noyalcer 5...Preamplifier, 6...Delay line, 7...Adder, 1? A,
JB...mixer, 9, 9B...low, noise, filter (LPF), 10A, JOB...A/D converter, llk, 111 (...mixer, CCA...mutual Correlation method analysis section, 17.
converter (osc), ts...B mode image generation unit,
19...D/A converter, 20...monitor.

Claims (1)

[Claims] Ultrasonic Doppler transmits ultrasonic waves to the blood flow in the circulatory tissue of a living body, and detects Doppler shift components shifted by the blood flow from the received echoes obtained thereby to obtain blood flow information. In a blood flow meter, blood flow information on one raster is
It is generated by three received echoes obtained by transmitting and receiving ultrasonic waves at three different rates, and includes means for phase detecting the received echoes, and a low pass filter to which the phase detection output from this means is input. and A which converts the output of this low pass filter into a digital signal.
/D conversion means; means for obtaining a cross spectrum based on the output of this means; means for obtaining a cross-correlation number of the three received echoes based on the output of this means; An ultrasonic Doppler blood flow meter comprising means for obtaining flow velocity information.