JPH0734801B2 - Ultrasonic CW Doppler blood flow meter - Google Patents

Description

Detailed Description [Table of Contents] Outline Industrial field of application Conventional technology Problems to be solved by the invention Means for solving problems (FIG. 1) Action Example (a) of one embodiment Description (FIG. 2) (b) Description of other embodiments [Outline] When outputting Doppler sounds separately to the left and right in an ultrasonic CW Doppler blood flow meter with a zero shift function, left and right cutoff are performed independently. The noise of the Doppler sound is reduced by providing a low-pass filter that can change the frequency.

[Industrial application field]

The present invention is an ultrasonic wave CW (continuous wave) that transmits ultrasonic waves to a living body and detects the state of blood flow from the received wave by utilizing the Doppler effect.
The present invention relates to a Doppler blood flow meter, and more particularly, to an ultrasonic CW Doppler blood flow meter that has a function of hearing Doppler signals as voice.

With the progress of medical electronics, blood flowmeters that measure blood flow velocity and distribution in various parts of the living body and are useful for diagnosis are widely used. In particular, ultrasonic waves are transmitted to the living body and received from the living body by the Doppler effect. An ultrasonic CW Doppler blood flow meter that obtains the flow velocity and distribution of blood flow from the frequency shift amount of waves is provided on the market.

In such a 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 is heard by the ear is also important diagnostic information, and Doppler noise with low noise is also important. Sound output is needed.

[Conventional technology]

 FIG. 3 is a block 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 split type ultrasonic transducer 5 of a transmitting 5a and a receiving 5b.
An fc (sin) transmission frequency signal obtained by dividing the master clock of the master clock source 1 by the frequency divider 2 is given via the transmission amplifier 3 to transmit ultrasonic waves to a living body. The reflected wave from the bloodstream is received by the receiving transducer 5b, and the received signal is input to the quadrature detector 6 via the receiving amplifier 4. In the quadrature detector 6, the reception signal of the reception amplifier 4 is subjected to so-called heterodyne detection with the transmission frequency signal fc (sin) and the bedding fc (cos) orthogonal thereto, and a signal component in which the transmission frequency is shifted to zero is obtained. The quadrature detection is to obtain both the velocity of blood flowing toward the probe (toward) and the velocity of blood flowing away from the probe (away). The quadrature-detected signal has its low frequency band cut by the high-pass filter group 7. The cutoff frequency of the high-pass filter group 7 is manually specified, and is provided to remove the (low-frequency) frequency component due to the vibration of the wall surface of the site (chest, surface, etc.) to be measured by the probe.

In general, prepare multiple high-pass filters and
This is done by selecting the analog switch in the selection of CPU9.

The signal that has passed through the high pass filter group 7 is input to the low pass filter group 8. The low-pass filter group 8 is set to a cutoff frequency according to the Doppler sample frequency Fs of the A / D (analog / digital) converter 11, and removes signals outside the required band. This low-pass filter group 8 is the Doppler sample frequency F of the A / D converter 11 of the Doppler processor.
Selected by CPU9 according to s.

The signal that has been A / D converted by the A / D converter 11 is subjected to Fourier transform of the time axis signal into the frequency axis signal by the FFT (Fast Fourier Transform) 12 of the Doppler processor, and is passed through the display circuit 13 as a frequency (Doppler) spectrum. The display unit (CRT) 14 displays the horizontal axis as frequency and the vertical axis as strength, as shown in the explanatory view of the prior art of FIG. 4 (A).

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

The cutoff frequency of such a low-pass filter 8 is generally the sampling frequency Fs according to Nyquist's theorem.
On the other hand, Fs / 2 is decided.

However, in the case shown in FIG. 4 (A), the display area is between −Fs / 2 and Fs / 2 where the center frequency is 0, so that when the blood flow velocity is high, the center frequency is For example, shift the display area to (-Fs / 2 + Zr) and (Fs / 2 +
Zr) is provided with a zero shift function. This Zr is called a zero shift value, and it can be performed by the CPU 9 changing the read start address of the analysis spectrum of the FFT 12 according to the zero shift value set manually.

If, for example, bc other than the blood flow signal ba in FIG. 4 (A) is to be displayed using this zero shift function, the cutoff frequency of the low-pass filter 8 is −Fs / 2 or less, Fs / 2 or less. Since the above Doppler signals cannot be obtained, FIG. 4 (B)
As shown in, the maximum value of the zero shift value Zr Fs / 2, −
Considering Fs / 2, the cutoff frequency of the low-pass filter 8 is set to be the same as the sampling frequency Fs, and signals from −Fs to Fs are passed.

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

This is composed of a Doppler sound separating circuit 15 which receives the output of the low pass filter 8 and left and right speaker means 16a and 16b.

The Doppler sound separation circuit 15 is composed of a pair of phase shifters 150 and 151 and adders 152 and 153. The Doppler signal is converted into a positive frequency component (a Doppler signal of blood flow approaching the transducer 5) ωa as follows. And a negative frequency component (a Doppler signal of blood flow away from the transducer 5) ωb.

In other words, the outputs Q and I of the low-pass filter 8 are: Q = a · cosωat + b · cosωbt (1) I = a · sinωat−b · sinωbt (2)

When the shift amounts θa and θb of the phase shifters 150 and 151 are different from each other by 90 °, Q of the equation (1) is obtained from the phase shifter 150, and I ′ of the equation (2) which is shifted by 90 ° is obtained from the phase shifter 151. , I ′ = acosωat−bcosωbt (3) is obtained.

Therefore, if the adder 152 sums the quantity shifters 150 and 151, a positive frequency component of Q + I ′ = 2a · cosωat (4) is obtained, and the adder 153 calculates the difference between the quantity shifters 150 and 151. Then, a negative frequency component of Q−I ′ = 2b · cosωat (5) is obtained.

If these are given to the left and right speaker means 16a, 16b,
In the right speaker means 16a, the speaker 16
2 Doppler sound with more positive frequency components, left speaker means 1
In 6b, the Doppler sound having a negative frequency component can be output from 163 via the amplifier 161.

[Problems to be solved by the invention]

In such a conventional ultrasonic CW Doppler blood flow meter capable of outputting Doppler sound, the region shown in (A) and (B) of FIG. 4 is displayed by the zero shift function used in the display of Doppler spectrum. However, since the cutoff frequency of the low-pass filter 8 is set to Fs as shown in, there is a problem that the noise component of the area other than the displayed area is also output as sound, and the S / N of the Doppler sound deteriorates. It was

An object of the present invention is to provide an ultrasonic CW Doppler blood flow meter that can obtain good quality Doppler sound with less 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 an explanatory view of the principle of the present invention.

In FIG. 1 (A), the same components as those shown in FIG. 3 are designated by the same symbols, 17 is an external control type low-pass filter, and the first Doppler signal of the Doppler sound separation circuit 15 ( Q + I ') and the second Doppler signal (Q-I') are independently subjected to pass band control from the outside and output to the corresponding speaker means (16a, 16b).

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

[Action]

Since the low-pass filter according to the present invention performs band control independently for a pair of Doppler signals, an optimum pass band can be set according to zero shift.

For example, if the display area by zero shift is set as shown in FIG. 1B, the band (cutoff frequency) as shown in FIG. 1B is set to the first Doppler signal with the set value AS. If the band (cutoff frequency) as shown in FIG. 1 (B) is obtained with the set value BS for the Doppler signal of 2, the Doppler sound in the band corresponding to the zero shift is obtained, and the S / N Can output good Doppler sound.

〔Example〕

(A) Description of an Embodiment FIG. 2 is a block diagram of the essential parts of an embodiment of the present invention, showing an external control type low-pass filter 17.

In the figure, 170 is an oscillator, which generates a clock of frequency Fo, 171 is a programmable frequency divider, CPU
Cut-off frequencies fc and fd that are 50 times (or 100 times) the frequency division values AS and BS given by 9 (see Fig. 3).
a, fd output, 172 is a switched capacitor
It is a filter (Switched Capacitor Filter) and constitutes a second-order low-pass filter having cut-off frequencies fc and fd at 1/50 (or 1/100) of the clock frequencies fa and fd.

In this embodiment, the CPU 9 to which the zero shift value Zr and the CW Doppler sample frequency Fs are input, calculates the dividing values AS and BS, and the cutoff frequency of the switched capacitor filter 172 of the low pass filter 17 is fc, It is set to fd.

That is, the cutoff frequencies fc and fd of the Doppler sounds (Q + I ') and (Q-I) take a value between -0.5 and 0.5 as shown in FIG. fc = Fs (0.5 + Zr) fc = Fs (0.5 + Zr) ... 6).

In order to have the cutoff frequencies fc and fd related to the switched capacitor filter 172, the filter 172 uses the clock frequency 1/50 as the cutoff frequency, so fa = 50 · fc fb = 50 · fd …… ( 7) Therefore, the frequency division values AS and BS of the frequency divider 171 are AS = Fo / fa Bs = Fo / fb (8).

Therefore, the CPU 9 calculates equations (6), (7) and (8) from the input zero shift value Zr and the CW Doppler sampling frequency Fs to obtain frequency division values AS and BS, and the frequency divider of the filter 17 is calculated. 171
By setting this to, the switched-capacitor filter 172 sets the cutoff frequencies to fc and fd, and for the first Doppler signal of positive frequency, the first
The filter characteristic as shown in FIG. 1B is obtained for the second Doppler signal having a negative frequency as shown in FIG. 1B.

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

Further, in this embodiment, since the CPU 9 automatically sets the characteristics of the filter 17 according to the input zero shift value and the CW Doppler sample frequency so that a Doppler sound with less noise can be obtained, it is optimal without special operation. Doppler sound is obtained.

(B) Description of Other Embodiments In the above-described embodiments, the low-pass filter 8 is shown as the CPU 9 setting the cutoff frequency to Fs.
The CPU 9 may change the cutoff frequency Fm of the low-pass filter 8 according to the zero shift value (Zr).

At this time, the cutoff frequency Fm may be Fm = Fs (0.5+ | Zr |) (9), and by doing so, noise on the Doppler spectrum of the Doppler processors 11 and 12 is reduced.

Also, the external control type low pass filter 17 has been described using the switched capacitor filter of FIG.
It can be configured by a well-known low-pass filter with a variable cutoff frequency such as a gain variable integrator circuit, and the output of the Doppler spectrum is not limited to the display unit but may be another well-known one such as a printing unit.

Although the present invention has been described with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention, and these modifications are not excluded from the present invention.

〔The invention's effect〕

As described above, according to the present invention, for the ultrasonic CW Doppler blood flow meter having a zero shift function, there is an effect that it is possible to output a Doppler sound with a good S / N, and on a more accurate time axis Contribute to providing diagnostic information. Further, since it is possible to add a small number of circuits called filters, there is an effect that it can be realized easily and inexpensively.

[Brief description of drawings]

FIG. 1 is a diagram illustrating 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 conventional technique, and FIG. 4 is an explanatory diagram of the conventional technique. In the figure, 5 ... Ultrasonic transducer, 6 ... Quadrature detector, 8 ... Lopal filter, 11, 12 ... Doppler processor, 15 ... Doppler sound separation circuit, 16a, 16b ... Speaker means, 17 ... … Externally controlled low-pass filter.

Claims (1)

[Claims] 1. An ultrasonic transducer (5) for transmitting and receiving a continuous wave ultrasonic wave, a quadrature detector (6) for quadrature detecting a reception signal of the ultrasonic transducer (5), and the quadrature detection output. A low-pass filter (8) that cuts the high-frequency region and a Doppler processor (11, 12) that obtains a Doppler spectrum by Fourier-analyzing the output of the low-pass filter (8), and the output frequency region of the Doppler spectrum is variable. In the ultrasonic CW Doppler blood flowmeter having a zero shift function, the first Doppler signal of the blood flow from the output of the low-pass filter (8) toward the ultrasonic transducer (5) and the second Doppler signal away from the ultrasonic wave are separated. Means (15), a pair of speaker means (16a, 16b) for separately outputting the first Doppler signal and the second Doppler signal as audio, The Doppler signal and the passband controlled independently for each of the second Doppler signals, corresponding said speaker means (16
Externally controlled low-pass filter for output to a, 16b) (17)
An ultrasonic CW Doppler blood flow meter characterized by being provided with.