JPS6090540A - Ultrasonic blood flow meter - 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 (Technical Field) The present invention relates to a pulsed Doppler type ultrasonic blood flow meter.

(Prior art) In recent years, ultrasonic blood flow meters that apply the principle of the Doppler method in conjunction with ultrasonic tomographic diagnostic devices (B-mode method) and ultrasonic cardiographs (M-mode method) have been provided for the diagnosis of the circulatory system. has been done. Among these, those that adopt the pulsed Doppler method have become mainstream because of their high distance resolution, the ability to share the probe of ultrasound tomographic diagnostic equipment, and the ability to display tomographic images and blood flow patterns simultaneously. ing.

In an ultrasonic blood flow meter that uses the pulsed Doppler method, ultrasonic pulses with carrier frequency fo are emitted from the probe at a predetermined period]/fr as shown in Figure JA, and the ultrasonic pulse generation The reflected waves inside the body are received by the same probe. In this case, the frequency spectrum of the reflected wave received by the probe exists at intervals of frequency fr around the carrier frequency fo, as shown in Figure JB.

FIG. 1C is a partially enlarged view of FIG. 1B, showing the Doppler shift state when blood flow is present at the same time.

Here, if the angle between the ultrasound beam projected into the living body and the blood flow is θ, the blood flow velocity is V, and the sound velocity is C, then the Doppler shift fd at the frequency fs of one spectral component is
is expressed as follows.

The Doppler shift fd at 2 cos θ fd −−□·v −fs becomes indistinguishable from the Doppler shift in the opposite direction of the adjacent spectral component when it exceeds fr/2, so the received reflected wave actually has a frequency f. After mixing the local oscillator outputs of , the cutoff frequency f
f isometrically by passing it through a low-pass filter of r/2. A band/band filter of ±fr/2 is configured to detect only the Doppler shift within this band.

FIG. 2 shows the circuit configuration of a conventional pulsed Doppler type ultrasonic blood flow meter. Transmission pulse generation circuit 1 is MJf
Repetition frequency Wifr of ultrasonic pulse from lIJ circuit 2
A reference signal is input to determine the pulse width, and a transmission pulse is supplied to the probe 3 at a period of ]/fr, and an ultrasonic pulse with a carrier frequency fo and a pulse interval of ]/fr is transmitted from the probe 8 into the living body. Let it project.

The reflected wave of this ultrasonic pulse in the living body is received by the same probe 3, and a high frequency amplifier 4 is used for quadrature phase detection.
are supplied to mixers 5a and 5b, respectively, and the oscillation frequency in these mixers 5a and sb is equal to the carrier frequency f.
. The signals are mixed with the orthogonal phase outputs from the local oscillator 6 and frequency converted. These mixers 5a.

The output of 5b is sampled by a sampling pulse corresponding to a desired diagnosis site in the living body from the control circuit 2 in the range gauges 7a and 7b. In these range gauges 7a and 7b, the sampled reflected wave signals corresponding to the desired diagnosis site are filtered through a low-pass filter s.
a, s b After passing through M, only signals of fr/2 or less are extracted, and passed through low frequency amplifiers 9a and 9b to the sample bold circuit] Oa] sampled and held in Ob, A/D converter] 1a, 11b, it is converted into a digital signal and fed to the real and imaginary input terminals of the fast Fourier transformer 12, where frequency analysis and forward/reverse separation of the blood flow is performed. The output of this fast Fourier transformer]2, that is, the Doppler shift frequency, is converted into an analog signal by the D/A converter J3, and then supplied to an arithmetic circuit (not shown), where the blood flow velocity is calculated and displayed on the monitor. Ru. Note that the control circuit 2 divides the frequency of the local oscillator 6 to determine the repetition frequency fr of the ultrasonic pulse.
A reference signal is created to determine the pulse, and this signal is supplied to the transmission pulse generation circuit as described above, and this reference signal is delayed depending on the desired diagnosis site in the living body, that is, the depth and tissue, and is transmitted to the range gauge). 7a.

qb, sample hold circuit] Oa, ]Ot) and A/D converter] 1a, 1 lb.

However, in the above-mentioned conventional ultrasonic blood flow meter, the oscillation frequency of the local oscillator 6 is fixed to the carrier frequency fo, so as the diagnosis site gets deeper, the Doppler shift detection sensitivity decreases significantly and the measurement accuracy deteriorates. In other words, the frequency spectrum of the reflected wave received by the probe 3 is - If the diagnosis site is shallow, the carrier frequency f of the transmitted ultrasonic pulse is
.

However, if the diagnostic site is deep, the high frequency components will be greatly attenuated, so as shown by the symbol ■, the frequency fp at which the spectrum peaks is the carrier frequency f.

will be considerably lower than Therefore, the oscillation frequency of the four-power oscillator 6 is set to the carrier frequency f. If it is fixed at , when the diagnostic site is deep, the detection sensitivity will drop significantly and the measurement accuracy will deteriorate.

(Objective of the Invention) The object of the present invention is to provide an ultrasonic blood flow system configured to eliminate the above-mentioned drawbacks, detect Doppler shift with high sensitivity even if the diagnostic site is deep, and therefore always measure blood flow velocity with high precision. This is an attempt to provide a measurement plan.

(Summary of the Invention) The present invention provides an ultrasonic wave that repeatedly emits ultrasound pulses into a living body, detects Doppler shift by quadrature phase detection of the reflected waves, and measures blood flow velocity based on this Doppler shift. The blood flow meter is characterized in that the reflected wave is subjected to quadrature phase detection at a frequency selected from a plurality of frequencies generated at intervals of the repetition frequency of the ultrasonic pulse.

Furthermore, in the present invention, an ultrasonic wave is repeatedly emitted into a living body, the reflected waves are detected by quadrature phase detection to detect a Doppler shift, and blood flow velocity and degree are measured based on this Doppler shift. In an ultrasonic blood flow meter, a frequency synthesizer capable of generating a plurality of frequencies at intervals of the repetition frequency of the ultrasonic pulse, and means for setting the output frequency of the frequency synthesizer to a preprogrammed value according to the diagnosis site. The apparatus is characterized in that it is configured to perform quadrature phase detection of the reflected wave at the set output frequency of the frequency synthesizer.

(Example) FIG. 4 is a block diagram showing the circuit configuration of an example of the ultrasonic blood flow meter of the present invention. Components having the same functions as those shown in FIG. 2 are given the same reference numerals. The explanation will be omitted. In this example, the clock generator J4 has a frequency equal to the carrier frequency of the ultrasonic pulse. A reference clock is generated, and this is frequency-divided by a frequency divider] 5 to create a reference signal for determining the repetition frequency fr of the ultrasonic pulse. This reference signal is supplied to the transmission pulse generation circuit and transmitted from the probe 3 to the carrier frequency f. , a pulse interval]/fr is emitted, and the ultrasonic pulse is supplied to a delay circuit]6 to generate a sampling pulse with a delay so as to obtain a reflected wave signal strength at a desired diagnostic site. This is a range game) 7a, 7
b, sample hold circuit 10a, ]Ob and A/D
r exchanger]] a.

11b. In this example, a variable resistor]7 is used as a gate device for sampling the reflected wave signal of a desired diagnosis site in range game)7a r7b, and this is converted into an A/D converter. 8 converts it into a digital signal, and according to the information, delays the reference signal from the branching unit 15 in the delay circuit 6, and samples the reflected wave signal of the required diagnosis part by using the range gates 7a and 7bl. Create a sampling pulse to

The output of A/D converter] 8 is also supplied to the address input terminal of 'ROM 1.9, thereby providing 16 diagonal R to the diagnostic site.
Access the data at address 2M17.

In this ROM 19, frequency data that becomes the spectrum deviation of the reflected wave is programmed in advance for each depth G of a standard biological boat, and the A/D converter J8
The frequency data of the accessed address is supplied to the frequency synthesizer 20 according to the gate position.

The frequency synthesizer 20 is a clock generator】4
A reference clock with a frequency fo from the center and a reference signal with a frequency fr from the divider 15 are input, and a plurality of frequencies including the frequency fo:l:nfr(n-
0, 1, 21---), and ROM19
It outputs one frequency whose phase is orthogonal according to the frequency data from , and supplies these to mixers 5a and sb.

According to this embodiment, by providing a gate position for sampling the reflected wave signal of a desired diagnosis site, the reflected wave signal is detected in quadrature phase at a pre-programmed frequency at which the spectrum peaks. , Doppler shift can always be detected with high sensitivity, and therefore blood flow velocity can always be measured with high precision.

FIG. 5 is a block diagram showing the circuit configuration of another example of the ultrasonic blood flow meter of the present invention, and parts having the same functions as those shown in FIGS. 2 and 4 are given the same reference numerals. However, the explanation thereof will be omitted. In this example, the output of the A/D converter ]8 corresponding to the desired diagnosis area given by the variable resistor 17 is
board 21'fi: input to the CPU 22, and in accordance with the information, the CPU 22 controls the delay circuit j6 via the board 21, and the delay circuit 16 converts the frequency divider]5
By delaying the reference signal from
In steps 7a and 7b, a sampling pulse is created to sample the reflected wave signal of a desired diagnostic site.

On the other hand, TGO (Time
The voltage is set by the variable resistance group 23, and the output is converted into a digital signal by the A/D converter 24 and sent to the CPU via the I10 board 2].
22.

Note that (programs for controlling the 3PU 22 and various data are stored in the memory 25 as in a normal system.

In this example, the frequency of the transmitted ultrasonic pulse, the intensity of the spectrum, and its carrier frequency f.

Data on the attenuation characteristics according to the depth, tissue, etc. of the diagnostic site are stored in advance in the memory 25, and these stored data and the desired values set by the variable resistor] 7 and the variable resistance group 23 are stored in advance in the memory 25. Determine the frequency that gives the peak spectrum of the reflected wave signal based on the gate position and TGO voltage data according to the depth and tissue of the diagnostic site, and based on this, (EPU22GC YoIJ l10t knee) 2
], the frequency synthesizer 20 is controlled to output a frequency giving a peak spectrum from the frequency synthesizer 20, and the reflected wave signal is subjected to quadrature phase detection.

Therefore, in this example, first, as shown in FIG. 6, the average gradient dv/dt of the TGOfi pressure shown by the dashed line is calculated from the voltage at each point of the variable resistor group 23 that provides the TGO voltage, or the variable resistor Gate position Δ set by J7
t and the gradient ΔV/Δt from the initial value Vo of TGO [pressure and the difference ΔV of the voltage VG at the gate position Δt, and based on this average gradient dV/at or gradient ΔV/Δt and the stored attenuation characteristic data. carrier frequency f. The damping constant α at . I put it on. Next, find the damping constant α in this way. Using , the attenuation constant α at all frequencies fn except for the frequency fo that can be generated by the frequency synthesizer 2o. For example, α. −α.・The attenuation constant at each frequency (including fo) is multiplied by the spectrum intensity of the corresponding frequency stored in advance in the memory z5 to give the peak of the spectrum intensity. Determine the frequency. By supplying the frequency data thus determined from the 0PU 22 to the frequency synthesizer 20 via the I10 boat 21, the determined frequency is outputted from the frequency synthesizer 2o.

According to this embodiment, T used when displaying a B-mode image
Determine the attenuation constant at the carrier frequency f based on the G (E voltage or this TGO voltage and gate position, determine the frequency that gives the peak spectrum based on this attenuation constant, and output that frequency from the frequency synthesizer 20. Since the reflected wave signals are subjected to quadrature phase detection, the Doppler shift can always be detected with high sensitivity, as in the above embodiment, and therefore the blood flow velocity can always be measured with high precision.

Note that the present invention is not limited to the above-mentioned example, and can be modified or changed in many ways.

For example, the gate position according to the depth of the diagnosis site and group m is
It can also be set by input means other than the variable resistor 17. This also applies to the setting of the TGO voltage in the embodiment shown in FIG. Further, in the embodiment shown in FIG. 4, the entire system can be controlled by software using a microprocessor. Furthermore, the output frequency of the frequency synthesizer 20 may be manually set according to input data, instead of being automatically selected by a program or calculation.

(Effects of the Invention) As described above, according to the present invention, Doppler shift can be detected with high sensitivity even if the diagnostic site is deep, and thus blood flow velocity can always be measured with high precision.

[Brief explanation of the drawing]

] Figure A-0 is a diagram for explaining the principle of a pulsed Doppler type ultrasonic surface M meter, Figure 2 is a block diagram showing the circuit configuration of a conventional ultrasonic blood flow meter, and Figure 8 is a diagram of a conventional ultrasonic blood flow meter. Figure 4 is a block diagram showing the circuit configuration of an example of the ultrasonic blood flow meter of the present invention, Figure 5 is a block diagram showing the circuit configuration of another example, and Figure 6 is a diagram for explaining the drawbacks. FIG. 3 is a diagram for explaining the operation. 1... Transmission pulse generator 3... Probe 4... High frequency amplifier 5a, 5b... Mixer 7a, 7b.
...Range gates 8a, 8b...Low pass filters 9a, gb...Low frequency amplifier]Oa,, ]Ob...Sample and hold circuit 11a
, l1b-A/D converter】2...Fast Fourier transformer・】8...D/A converter 14...Clock generator】5...Frequency divider 16...Delay circuit 17
...Variable resistor]8...A/D converter]9...
ROM 20...Frequency synthesizer 2]...
Ilo boat 22... CPU23...
Variable resistance group 24...A/D converter 25...memory.

Claims (1)

[Claims] L Ultrasonic blood flow in which ultrasonic pulses are repeatedly emitted into a living body, Doppler shift is detected by quadrature phase detection of the reflected waves, and blood flow velocity is measured based on this Doppler shift. 1. An ultrasonic blood flow meter, characterized in that said reflected wave is configured to perform quadrature phase detection at a frequency selected from a plurality of frequencies generated at intervals of a repetition frequency of said ultrasonic pulse. In an ultrasonic blood flow meter that repeatedly emits ultrasonic pulses into a living body, detects Doppler shift by quadrature phase detection of the reflected waves, and measures blood flow velocity based on this Doppler shift, the ultrasonic blood flow meter A frequency synthesizer capable of generating a plurality of frequencies at intervals of a pulse repetition frequency, and a means for setting the output frequency of the frequency synthesizer to a preprogrammed value according to the diagnosis site, An ultrasonic blood flow meter characterized in that the reflected wave is configured to perform quadrature phase detection using the output frequency of a frequency synthesizer.