JPS63147444A - 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 equipped with a zero shift function, when outputting Doppler sound separately for the left and right sides, the cutoff is set independently for the left and right sides. By providing a low-pass filter that can vary the frequency, Doppler sound noise is reduced.

[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 detects the state of blood flow using the Doppler effect from the received waves, and in particular, the present invention relates to an ultrasonic CW (continuous wave) Doppler blood flow meter that detects the state of blood flow by transmitting ultrasonic waves to a living body and using the Doppler effect from the received waves. This invention relates to an ultrasonic CW Doppler blood flow meter that has the following functions.

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.

In this type of blood flow meter, in addition to the blood flow velocity and distribution based on the frequency axis, Doppler sound of blood flow based on the time axis that can be heard with the ear is also important diagnostic information, and Doppler sound with less noise is important diagnostic information. Sound output is required.

[Conventional technology]

FIG. 3 is a configuration diagram of a conventional ultrasonic CW Doppler blood flow meter.

As shown in FIG. 3, the probe that comes into contact with the living body is composed of a sprint type ultrasonic transducer 5, which is a transmitting transducer 5a and a receiving transducer 5b.
In this case, an oscillation frequency signal of f c (sin) obtained by frequency-dividing the master clock of the master clock source 1 by the frequency divider 2 is applied via the transmission amplifier 3, and the ultrasonic wave is transmitted to the living body. The reflected wave from the blood flow is received by the receiving transducer 5b.
The received signal is input to the quadrature detector 6 via the receiving amplifier 4. The quadrature detector 6 performs so-called hetero gain detection on 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 whose oscillation frequency has been shifted to zero. obtain. Orthogonal detection detects the velocity of blood flowing toward the probe (toward) and the velocity of blood flowing away from the probe (toward).
This is to obtain both of the following ways. The low frequency of this orthogonally detected signal is cut by the bypass filter group 7.

The cutoff frequency of the bypass filter group 7 is specified manually, and the cutoff frequency of the bypass filter group 7 is specified by the manual, and
It is provided to remove (low-frequency) frequency components caused by wall vibrations (chest, surface, etc.).

Generally, a plurality of bypass filters are prepared, and the CPU 9 selects analog switches to select the bypass filters.

The signal that has passed through bypass filter group 7 is input to low-pass filter group 8 . Low-pass filter group 8 is A/D
The cutoff frequency is set according to the Doppler sample frequency Fs of the (analog/digital) converter 11, and signals outside the required band are removed. This low-pass filter group 8
is selected by the CPU 9 according to the Doppler sampling frequency Fs of the A/D converter 11 of the Doppler processor.

The signal A/D converted by the A/D converter 11 is processed by a Doppler processor 0FFT (fast Fourier transformer).
12, the time axis signal is Fourier-transformed into a frequency axis signal, and is displayed as a frequency (Doppler) spectrum in the display circuit 1.
3 on the display unit (CRT) 14, as shown in the explanatory diagram of the prior art in FIG.

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

Generally, the cutoff frequency of such a low-pass filter 8 is determined by the sampling frequency F according to Nyquist's theorem.
For s, determine F s /2.

However, in the case shown in FIG. 4(A), the display area has a center frequency of 0 -Fs/2 and Fs/
2, so in cases where the blood flow rate is fast, etc.
By shifting the center frequency, for example, the display area can be changed to (-Fs
/2+Zr) and (Fs/2+Zr) are provided. This Zr
This is called a zero shift value, and can be performed by the CPU 9 changing the start address for successive analysis spectra of the FFT 12 in accordance with the manually set zero shift value.

For example, if you try to display the blood flow signal bc in addition to ba in FIG. 4(A) using this zero shift function, if the cutoff frequency of the low-pass filter 8 is F s / 2, then -F s / 2 or less , FS/2 or more is not obtained, so the cutoff frequency of the low-pass filter 8 is determined by considering the maximum possible value Fs/2, -FS/2 of the zero shift value Zr, as shown in FIG. 4(B). The sample frequency was set to be the same as F3, and signals from -FS to Fs were allowed to pass.

In such a Doppler blood flow meter, a Doppler sound output function is provided so that in addition to the Doppler spectrum on the frequency axis that can be seen with the eye, Doppler sound on the time axis can also be used as diagnostic information by the ear.

This includes a Doppler sound separation circuit 15 that receives the output of the low-pass filter 8, and left and right speaker means 16a, 16b.
It is made up of.

The Doppler sound separation circuit 15 includes a pair of phase shifters 150.1
51 and adders 152 and 153, the Doppler signal is divided into the positive frequency component (Doppler signal of the blood flow approaching the transducer 5) ωa and the negative frequency component (from the transducer 5) as follows. Doppler signal of receding blood flow)
It is separated into ωb.

That is, the output Q,1 of the low-pass filter 8 is Q=a
-cos ω at+b ・cos (J) bt
−= ku 1) I=a −5inωa t
-b-sinωb t-(2).

The shift amounts θa and θb of phase shifters 150 and 151 are 90
By adding a degree difference, the phase shifter 150 outputs Q of equation (1).
However, from the phase shifter 151.

I′ shifted by 906 in equation (2) becomes 1′=a((+sωa t −bcosωb t −
(3) is obtained.

Therefore, if the adder 152 calculates the sum of both shifters 150 and 151, Q+ r ′= 2 a − cosωat = −(4
) is obtained, and if the adder 153 takes the difference between both shifters 150 and 151, a negative frequency component of Q −1′ −2b−cosωb t−(5) is obtained.

When these are applied to the left and right speaker means 16a and 16b, the right speaker means 16a outputs Doppler sound with a positive frequency component from the speaker 162 through the amplifier 160, and the left speaker means 16b outputs the Doppler sound from the speaker 162 through the amplifier 161. 163, Doppler sound with negative frequency components can be output.

[Problem that the invention seeks to solve]

In such a conventional ultrasonic CW Doppler blood flow meter capable of outputting Doppler sound, the zero shift function used in displaying the Doppler spectrum allows
Even if the region shown in ■ is displayed as a Doppler spectrum, the cutoff frequency of the low-pass filter 8 is Fs as shown in ■.
Therefore, there is a problem in that noise components in areas other than the displayed area (■) are also output as sound, and the S/N of Doppler sound is degraded.

An object of the present invention is to provide an ultrasonic CW Doppler blood flow needle that can obtain high-quality Doppler sound with little noise even if the band of the low-pass filter is widened due to the zero shift function.

[Means for solving problems]

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

In FIG. 1(A), the same components as those shown in FIG. Pass band control is performed independently for each of the signal Q+1') and the second Doppler signal (Q-1') from the outside, and output to the corresponding speaker means (16a, 16b).

That is, a low-pass filter 17 is provided between the speaker means 16a, 16b and the Doppler sound separation circuit 15.

[Effect]

Since the low-pass filter according to the present invention performs band control independently for a pair of Doppler signals, it is possible to set an optimal pass band according to zero shift.

For example, if a display area by zero shift is set, such as 0 in FIG. 1(B), a band (cutoff frequency) such as O in FIG. 1(B) is set for the first Doppler signal with the set value AS. for the second Doppler signal, with the set value BS, the first
By obtaining a band (cutoff frequency) such as ■ in Figure (B), Doppler sound in a band corresponding to the zero shift can be obtained, and Doppler sound with a good S/N ratio can be output.

〔Example〕

(a) Description of an Embodiment FIG. 2 is a block diagram of a main part of an embodiment of the present invention, showing an externally controlled low-pass filter 17. As shown in FIG.

In the figure, 170 is an oscillator that generates a clock of frequency F0, 171 is a programmable frequency divider,
Frequency division value AS given from CPU9 (see Figure 3),
Those that output frequencies fa and fb that are 50 times (or 100 times) the cutoff frequency fcSfd according to the BS, 17
2 is a switched capacitor filter (Switch
ed Capacitor Fi 1 tar), and the clock frequency fa, fb is 1150 (or 1/10
0) as cutoff frequencies fc and fd.

In this embodiment, the CPU 9, to which the zero shift value Zr and the CW Doppler sample frequency Fs are input, inputs the frequency division value AS,
BS is calculated and the low-pass filter 17 is switched.
The cutoff frequency of the capacitor filter 172 is fc
, fd.

That is, the cutoff frequencies fc and fd of the Doppler sounds (Q+I') and (Q-1) are calculated as shown in FIG. 4 (with Zr as the display area).
As shown in A), it takes a value between -0,5 and 0.5, so f d=Fs (0,5-Zr).

In order to have the cutoff frequency f cs f d related to the switched capacitor filter 172, since the filter 172 has a cutoff frequency of 1150 of the clock frequency, fb=50·fd Therefore, the frequency divider 171 divides The circumference value ASXBS is BS=F
It becomes o/fb.

Therefore, the CPU 9 inputs zero shift values Z and C.
W Doppler sample frequency Fs and (6), (7),
By calculating the equation (8), finding the frequency division values AS and BS, and setting them in the frequency divider 171 of the filter 17,
The cutoff frequency of the switched capacitor filter 172 is set to fc and d, and for the first Doppler signal with a positive frequency, the filter characteristics as shown in For a second Doppler signal with a frequency of
A filter characteristic as shown in (2) in FIG. 1(B) is obtained.

Therefore, only the Doppler sound in the frequency band corresponding to the zero shift value passes through the filter 17, so noise in unnecessary bands is removed, and a Doppler signal with good S/N can be obtained even if the zero shift value is changed.

Further, in this embodiment, the CPU 9 inputs the input zero shift value and C
Filter 17 automatically according to W Doppler sample frequency
The characteristics of the Doppler sound are set so that the Doppler sound with less noise can be changed, so the optimal Doppler sound can be obtained without any special operations.

(b) Description of other embodiments In the embodiments described above, the cutoff frequency of the low-pass filter 8 is set to Fs by the CPU 9, but the cutoff frequency Fm of the low-pass filter 8 is set to a zero shift value (Zr). The CPU 9 may be variable depending on the situation.

The cutoff frequency Fm at this time is Fm=Fs(0,5+1Zrl) -----(9
), and by doing so, the noise on the Doppler spectrum of the Doppler processor 11.12 is reduced.

Furthermore, although the externally controlled low-pass filter 17 has been described as using the switched capacitor filter shown in FIG. 2, it can be constructed from a well-known low-pass filter with a variable cutoff frequency, such as an integrating circuit with variable gain. The output of the Doppler spectrum is not limited to the display section, but may also be output from other well-known devices such as a printing section.

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 output Doppler sound with good S/N to an ultrasonic CW Doppler blood flow meter having a zero shift function. contributes to providing diagnostic information. Furthermore, since this can be achieved by adding a small amount of circuitry such as a filter, it can be realized easily and at low cost.

[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 an embodiment of the present invention, FIG. 3 is a configuration diagram of a prior art, and FIG. 4 is an explanatory diagram of the prior art.・In the figure, 5-ultrasonic transducer, 6-quadrature detector, 8-low-pass filter, 11.12-Doppler processor, 15-Doppler sound separation circuit, 16a516b"-speaker means, 17 -4-part controlled low-pass filter.

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) that cuts the high frequency region of the quadrature detection output, and a low-pass filter (8) that A Doppler processor (11, 12) that performs Fourier analysis on the output and obtains a Doppler spectrum.
), an ultrasonic CW Doppler blood flow meter having a zero-shift function that makes the output frequency region of the Doppler spectrum variable; a pair of speaker means (16a, 16b) for separately outputting the first Doppler signal and the second Doppler signal as audio.
and passband control is performed independently for each of the first Doppler signal and the second Doppler signal, and the corresponding speaker means (1
6a, 16b) is provided with an externally controlled low-pass filter (17).