JPS63154164A - Ultrasonic cw doppler blood flowmeter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Field of Application Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems (Fig. 1) Working Example (a) One Example Explanation (Fig. 2) (b) Description of other embodiments Effects of the invention [Summary] In an ultrasonic CW Doppler blood flow meter having a zero shift function, the cutoff frequency of the Doppler signal is for the output of a low-pass filter of Fs. The A/D converter performs A/D conversion at a frequency of 2FS, and the Fourier transform section obtains a Doppler spectrum within the analysis range of 2FS, thereby obtaining a Doppler spectrum with Fourier transform aliasing noise removed. .

[Industrial application field]

The present invention relates to an ultrasonic CW (continuous wave) Doppler blood flow meter that transmits ultrasonic waves to a living body and obtains blood flow velocity and distribution as a Doppler spectrum by utilizing the frequency shift of the received waves due to the Doppler effect, and particularly relates to a zero shift function. The present invention relates to an ultrasonic CW Doppler blood flow needle that can obtain a Doppler spectrum with little aliasing noise.

With the advancement of medical electronics, blood flow meters are widely used to measure blood flow velocity and distribution in various parts of the living body to aid in diagnosis. Ultrasonic CW Doppler blood flow meters that determine the flow velocity and distribution of blood flow from the amount of frequency shift of waves are provided on the market.

Such an ultrasonic CW Doppler blood flow meter is required to reduce aliasing noise caused by having a zero shift function.

[Conventional technology]

FIGS. 3 and 4 are explanatory diagrams of the prior art.

In the ultrasonic CW Doppler blood flow meter, as shown in FIG.
The transmission transducer 5a receives an oscillation frequency signal of fc (sin) obtained by dividing the master clock of the master clock source 1 by the frequency divider 2, and transmits it to the transmission amplifier 3.
It transmits ultrasound waves to the living body. On the other hand, the reflected wave from the living body is received by the receiving transducer 5b, and the received signal is input to the quadrature detector 6 via the receiving amplifier 4. The quadrature detector 6 performs so-called heterodyne detection of the received signal from the reception amplifier 4 using the oscillation frequency signal f c (sin) and the signal f c (cos) orthogonal to this, and detects the signal component in which the oscillation frequency component is shifted to zero. (Doppler detection). The purpose of orthogonal detection is to obtain both the velocity of blood flow toward the probe (towards) and the velocity of blood flow departing from the probe (away). The low frequency of this orthogonally detected signal (Doppler signal) is cut by the bypass filter group 7. The cutoff frequency of the bypass filter group 7 is manually specified and is provided to remove (low frequency) frequency components caused by vibrations of the wall of the region (chest, surface, etc.) to be measured by the probe.

Generally, multiple bypass filters are prepared,
These are performed by selecting an analog switch by selecting the CPU 9.

The signal that has passed through the bypass filter group 7 is input to the low-pass filter group 8 . Low-pass filter group 8 is A/D
The force/throat off frequency is set according to the Doppler sample frequency Fs of the (analog/digital) converter 11,
Remove signals outside the required band. This low-pass filter group 8 has a Doppler sample frequency of 9Fs of the A/D converter 11.
It is selected by the CPU 9 according to the following.

The signal A/D converted by the A/D converter 11 is Fourier-transformed from a time domain signal to a frequency domain signal by an FFT (fast Fourier transformer) 12, and is displayed as a Doppler spectrum via a display circuit 13 on a display unit (CRT) 14. As shown in FIG. 3(C), the horizontal axis represents frequency and the vertical axis represents intensity.

The frequency on the horizontal axis is the amount of frequency shift and therefore corresponds to the blood flow velocity, and the blood flow velocity and distribution are displayed.

The cutoff frequency of such a low-pass filter 8 is generally determined to be F s /2 with respect to the sample frequency Fs (according to Nyquist's theorem).

However, when the blood flow velocity is slow as shown in FIG. 3(C), the display area is 1 F s with the center frequency as
/2 and Fs/2, but in cases such as when the blood flow rate is high, the center frequency may be shifted and the display area may be changed to (-Fs/2+Zr) and (Fs/2+), for example.
A zero shift function is provided that can be changed to ① between Zr).

This zero shift function is achieved by setting the cutoff frequency of the low-pass filter 8 to the Doppler sample frequency Fs of the A/D converter 11 of the Doppler processor, and by giving the pass band a characteristic as shown in FIG. 3(B). realizable.

That is, according to Nyquist's theory, the analytical frequency domain is −F
s/2 to +Fs/2, but as shown in Fig. 3 (B
), due to the folding phenomenon of FFT, F s
The signal from /2 to Fs enters the region from -Fs/2 to O, and the signal from -Fs to -Fs/2 enters the region from O to Fs/2.
The blood flow ba between s/2 and Fs is −Fs/
The region from 2 to O is entered and analyzed.

Therefore, FFT12 is 128 in the analysis frequency domain of Fs.
When performing FFT of points, as shown in Figure 4, 128
The results are sequentially stored in the address RAM 120.

If the zero shift value Zr is zero, then Fig. 4(A)
By reading the FFT analysis results from addresses "0" to "127" as shown in FIG.
B) from address “n” to 127” and “
By reading out the FFT analysis results in the order from "0" to "n-1", an area as shown in (2) in FIG. 3(C) is displayed.

[Problem that the invention seeks to solve]

However, in the conventional blood flow meter with zero shift function, since the aliasing phenomenon is used, the white noise is −F s / 2 as shown in FIG. 3(B).
Since the signal is folded back into the region from +F s / 2 to +F s / 2 for analysis, there is a problem in that the Doppler spectrum has a poor S/N ratio. For example, compared to when the cutoff frequency of the low-pass filter 8 was set to F s /'l according to the Nyquist theory, the S/N was reduced by 3 dB.

The present invention provides an ultrasonic CW that has a zero shift function and can prevent S/H deterioration due to aliasing.
The purpose is to provide a Doppler blood flow meter.

[Means for solving problems]

FIG. 1 is a diagram explaining the principle of the present invention.

In FIG. 1(A), the same parts as those shown in FIG. 3 are indicated by the same symbols.

In the present invention, the analysis frequency FS for the quadrature detection output is set to the cutoff frequency, that is, the output of the low-pass filter 8 having the passband -Fs -FS, which is A/D by twice the analysis frequency FS.
By performing A/D conversion in the converter 11, FFT
(Doppler processor) The number of analysis points of 12 is doubled, that is, the analysis frequency range is doubled as shown in Figure 1 (B), and the display means 13.14 displays the Doppler spectrum in the frequency range Fs, which is half of the analysis result. is displayed according to the zero shift value.

C Effect] In the present invention, the cutoff frequency of the low-pass filter 8 is 2 of the CW Doppler sample frequency, which is in accordance with Nyquist's theory. Therefore, aliasing noise can be eliminated.

Furthermore, since half of the analysis range is displayed as shown in FIG. 1(B), the zero shift function can be maintained.

〔Example〕

(a) Description of one embodiment FIG. 2 is a diagram showing the main part of an embodiment of the present invention.

In the figure, the same parts as those shown in FIGS. 1, 3, and 4 are indicated by the same symbols, and 121 is an arithmetic unit of the FFT 12, which inputs the sampling data from the A/D converter 11. Based on high-speed Fourier calculation, 256 points of FF
121a is a register that stores the zero shift value Zr=n from the CPU 9, 121b is a counter, and the data in the register 121a is preset by the brisset pulse PRS. The read address of the RAM 120 is sequentially output in accordance with the generated clock pulse.

Next, the operation of the configuration shown in FIG. 2 will be explained.

When the Doppler analysis frequency Fg is input from the operation panel (not shown), the CPU 9 (see FIG. 3) sets the frequency of the sample clock of the A/D converter 11 to 2Fs from the frequency divider 10, and A clock with a frequency of 2Fs is supplied to the A/D converter 11.

Further, the CPU 9 reads the zero shift value Zr from the operation panel, and stores the corresponding zero shift value Zrwn in the register 121.
Set to a.

As is well known, the output of the A/D converter 11 is sent to the arithmetic unit 12.
1, a fast Fourier operation is performed, time-axis data is converted to frequency-axis data, and the data is stored in the RAM 120 for each frequency.

Here, if the number of FFT analysis points when the sample clock frequency of the A/D converter 11 is Fs is 128, then since the sample clock frequency is 2Fs, the FFT
The number of analysis points is 256 points, and RAM120 is 0 to 255.
It has up to 256 addresses. That is, the FFT analysis range is from -Fs to FS.

Since the display area of the display unit 14 is Fs in the frequency range,
Of the 256 points of the spectrum in the RAM 120, half of the spectrum may be output to the display circuit 13 according to the zero shift value Zr.

Assuming that the input zero shift value Zr takes a value from -0.5 to 0.5, the value n that the CPU 9 reads the input zero shift value Zr and gives to the register 121a is as follows.

For example, if the spectrum of Fs is stored at the -Fs1 address r255J at the address "0" of the RAM 120, then n=128.Zr+64.

That is, when Z r =-0,5, n=o, and when Zr=O, n=6
4, Z r =0.5 and n=128.

The starting address n is thus obtained from the CPU 9 according to the input zero shift value Zr, and is set in the register 121a.

A preset pulse is sent from a control section (not shown) to counter 1.
21b, thereby presetting the counter 121b with the starting address n of the register 121a, and subsequently 127 clock pulses are applied to the counter 121b.
1b.

Therefore, the counter 121b is n, n+1, -n+12
Since the read addresses up to 7 are given to the RAM 120, R
From the AM 120, spectrum data from address n to n+127 is sequentially output to the display circuit 13. Therefore, on the display section 14, the spectrum of the display area of Fs is displayed centered on the zero shift value, as in FIG. 3(C).

When the 127 clocks are completed, the precent pulse P
R3 is inputted to the counter 121b again, and then the clock is inputted again, address generation is performed again, and R3 is inputted to the counter 121b again.
The contents of AM120 are read.

When the input zero shift value Zr is changed, the CPU 9 sets a corresponding readout start address in the register 121a, so the operator can change the display area (display frequency area) while looking at the Doppler spectrum on the display unit 14. can.

In this way, the cutoff frequency of the low-pass filter 8 is set to Fs, a spectrum corresponding to the zero shift function is secured, and the sample clock frequency of the A/D converter 11 is set to twice Fs, and the Doppler analysis range is set to 2Fs.
Since it satisfies Nyquist's theory, a Doppler spectrum with aliasing noise prevented can be obtained, and half the area of the Doppler analysis result is output for display according to the zero shift value, so the zero shift function is realizable.

(b) Description of other embodiments In the above embodiments, the display means is shown as a soft copy such as a CRT, but it may also be a hard copy such as a printing device. However, other well-known methods may be used.

In addition, the memory and readout circuit for display are FFT12
Although it is provided in the display circuit, it may also be provided in the display circuit.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to eliminate aliasing noise peculiar to an ultrasonic CW Doppler blood flow meter having a zero shift function.

This has the effect of being able to obtain a high-quality Doppler spectrum without S/H deterioration, and contributes to increasing the usefulness of the Doppler spectrum as diagnostic information.

In addition, since it can be realized relatively easily, it also has a practical effect of being inexpensive and easy to achieve.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a configuration diagram of main parts of an embodiment of the present invention, Figs.
The figure is an explanatory diagram of the prior art. In the figure, 5--Ultrasonic transducer, 6--Quadrature detector, 8--Low pass filter, 11--A/D converter, 12--FFT (Fourier transform section), 13-- ...display circuit, 14.-display section.

Claims (1)

[Claims] An ultrasonic transducer that emits and receives ultrasonic waves (
5), a quadrature detector (6) that orthogonally detects the received signal of the ultrasonic transducer (5), a low-pass filter (8) whose cutoff frequency is the analysis frequency Fs for the quadrature detection output, and the low-pass filter An A/D converter (11) that A/D converts the output of the filter (8) at twice the analysis frequency Fs, and a Fourier transform that performs Fourier analysis on the A/D conversion output to obtain a Doppler spectrum in the frequency range of 2Fs. Part (12)
and display means (13, 14) for displaying the Doppler spectrum in a frequency range of Fs, and displaying the Doppler spectrum in a frequency range of ±Fs/2 centered on the zero shift value on the display means (13, 14). An ultrasonic CW Doppler blood flow meter characterized by displaying.