JPH02246949A - Ultrasonic doppler blood flow meter - Google Patents

Abstract

PURPOSE:To suppress the generation of a beat signal and to surely measure even the blood flow speed of a thin blood vessel by providing a band-pass filter and equalizing a frequency difference between the echo signal from an organism and an orthogonal signal to orthogonally detect it. CONSTITUTION:An ultrasonic pulse transmitted into the organism by ac ultrasonic transmitting and receiving means 1 is made into the echo signal, received by the ultrasonic transmitting and receiving means 1, made to pass a band-pass filter 11, orthogonally detected by the orthogonal signal from an orthogonal signal generator 5 by means of orthogonal detectors 6a and 6b and integrated in a period in which a sample gate signal is generated by means of integrators 7a and 7b, and a Doppler signal to an integration result is held in sample holds 8a and 8b. A frequency detecting means 12 outputs the frequency of the echo signal with a corresponding voltage, a filter control means 13 controls the frequency band characteristic of the band-pass filter 11 by the voltage, and the frequencies of the echo signal and orthogonal signal are always made equal. Consequently, a frequency step difference is eliminated, the generation of the beat signal in the integration section is suppressed, and a dynamic range can be widely improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an ultrasonic Doppler blood flow meter used in the medical field to measure blood flow velocity in a living body by transmitting and receiving ultrasonic pulses.

BACKGROUND OF THE INVENTION In recent years, ultrasonic Doppler blood flowmeters have been widely used as a means for non-invasively measuring the blood flow velocity at a specific site within a living body. This type of ultrasonic Doppler blood flow meter measures blood flow velocity by transmitting ultrasonic pulses into a living body, receiving ultrasound echo signals reflected in the living body, and detecting the Doppler shift frequency. .

Echo signals from blood flow are very weak, and on the other hand, echo signals from nearby living tissues are called clutter signals.In order to detect weak echo signals from blood flow, it is necessary to It is necessary to remove the signal as much as possible.

One example of an ultrasonic Doppler blood flow meter that removes the clutter signal is the one previously proposed by the present applicant in JP-A-61
A configuration described in Japanese Patent No. 265131 is known.

The conventional ultrasonic Doppler blood flow meter will be described below with reference to the drawings. FIG. 4 is a block diagram schematically showing the conventional ultrasonic Doppler blood flow meter. In FIG. 4, 1 is an ultrasonic transmitting/receiving means for transmitting ultrasonic pulses into a living body and receiving echo signals from the living body, 2 is a synchronizing signal generator for generating a synchronizing signal for synchronizing transmission and reception, and 3 is a synchronizing signal generator for generating a synchronizing signal for synchronizing transmission and reception. A driving circuit 4 generates ultrasonic pulses in synchronization with a synchronization signal and drives the ultrasonic transmitting/receiving means 1, and 4 is synchronized with the synchronization signal and has a phase relative to 9
An orthogonal signal generator that outputs a set of two orthogonal signals outside the 0 degree section, and 5 a gate that generates a sample gate signal at a desired time from the ultrasonic transmission time according to the depth and range of the part of the living body to be measured. The generators 6a and 66b are first and second orthogonal detectors for orthogonally detecting echo signals from within the living body using orthogonal signals, each of which is composed of two multipliers. 7
First and second quadrature detectors a and 7b integrate the quadrature detection signals from the first and second quadrature detectors 6a and 6b for a period determined by the sample gate signal, and output orthogonal Doppler signals.
The integrators 8a and 8b are the first integrators 8a and 8b. Second integrator 7a, 7b
9a and 9b are first and second sample holds 8a that hold the Doppler signal that is the integration result of
, 8b extracts low-frequency clutter signal components from the Doppler signals output from the first . The second low-pass filters 10a and 10b are the first and second quadrature detectors 6a and 6.
This is an adder that adds the orthogonal detection signal from B and the clutter signals extracted by the first and second low-pass filters 9a and 9b in opposite phases.

The operation of the above configuration will be described below.

The drive circuit 3Fi pulse signal is given to the ultrasonic transmitting/receiving means 1 in synchronization with the synchronization signal generated by the synchronization signal generator 2, and the orthogonal signal generator 4 generates a set of two orthogonal signals having a relatively 90 degree phase difference. The gate generator 5 generates a sample gate signal at an ultrasonic round trip propagation time corresponding to the distance to the target site to be measured and its range. The ultrasonic pulse generated by the ultrasonic transmitting/receiving means 1 and transmitted into the living body by driving the driving circuit 3 becomes an echo signal by living tissue and blood flow during propagation, and is received by the ultrasonic transmitting/receiving means 1. . This echo signal is transmitted to the first and second quadrature detectors 6a,
6b performs orthogonal detection using the orthogonal signal from the orthogonal signal generator 4, and then integrates the sample gate signal from the gate generator 5 in the first and second integrators 7a and 7b for the period in which the sample gate signal is generated, and the orthogonal Doppler signal is generated. A signal is output. Regarding the Doppler signal which is the integration result at the time when the sample gate signal ends, the first and second sample holds 8a and 8
b holds. 1st. Second sample hold 8a, 8
The value held by b corresponds to the phase relationship between the echo signal received by the ultrasonic transmitting/receiving means 1 and the orthogonal signal from the orthogonal signal generator 4 shown on the orthogonal target; one is the real part, and the other is the real part. Ten thousand represents the imaginary part. Therefore, when transmission and reception are repeated at regular intervals, the values of sample holds 8a and 8b change quickly for echo signals from fast-moving reflectors, and the values of sample holds 8a and 8b change quickly for echo signals from slow-moving reflectors. , 8b change slowly. This is a Doppler signal, which is generally frequency-analyzed by a frequency analyzer (not shown), converted to blood flow velocity, and then used as diagnostic data. The degree of this change, that is, the frequency, is proportional to the speed of the reflector, and since the speed of living tissue is relatively slow, the frequency of the obtained Doppler signal is also low. 1st. The second low-pass filters 9a and 9b extract the low-frequency Doppler signal, which is the clutter signal component, and combine this with the first and second low-pass filters.
The orthogonal detection signals from the second orthogonal detectors 6a and 6b are
, the clutter signal components applied to the inputs of the first and second integrators 7a and 7b can be canceled out and removed by adding them in opposite phases in the second adders 10a and 10b.

Therefore, the outputs of the first and second integrators 7a and 7b are
Even if the integration range is made large, the integration result can be focused to zero for low Doppler shift frequencies, and the first
．． The dynamic range of the second integrators 7a, 7b can be equivalently expanded.

Problems to be Solved by the Invention However, in the configuration of the conventional example described above, the influence of frequency-dependent attenuation when the ultrasound pulse propagates in the living body, and the frequency of the probe used in the ultrasound transmitting/receiving means 1. Due to the influence of band characteristics, etc., the frequency of the received echo signal and the frequency of the orthogonal signal used for orthogonal detection of this echo signal by the orthogonal detectors 6a and 6b do not match, and the beat of the echo signal and the orthogonal signal is detected by the orthogonal detector. Appears in the output. In particular, in the case of small blood vessels, the above-mentioned tendency becomes more pronounced when there is a large amount of echo signals mixed in from surrounding tissues.

Figure 3 shows the quadrature detectors 6a, 6b and the integrator 7a at that time.
, 7b shows the output waveform of the same figure (at is an explanatory diagram of the output waveform when the frequencies of the echo signal and the orthogonal signal are different, the same figure (
bl is an explanatory diagram of an output waveform when the image frequencies match. When the frequencies are the same, no beat occurs, as shown in (bl) of the same figure, but if the frequencies are different, saturation occurs during the integration due to the influence of the beat, as shown in (a) of the same figure.

The shaded portion is the portion lost due to saturation, resulting in an error in the integration result. This appears as a distortion of the Doppler signal waveform, resulting in the output of blood flow information that should not exist, or in the case of even stronger saturation, no results are output. As described above, there was a problem in that it was not possible to measure blood flow velocity particularly in small blood vessels.

The present invention solves the above-mentioned problems of the prior art, and uses a beat signal generated by the frequency difference between an echo signal received by an ultrasonic transmitting/receiving means and an orthogonal signal detected by orthogonally detecting this echo signal by a quadrature detector. The ultrasonic Doppler blood flow meter can prevent the occurrence of circuit saturation caused by the oscillation, and therefore can increase the circuit gain, making it possible to reliably measure the blood flow velocity even in particularly small blood vessels. The technical solution of the present invention to achieve the above object is as follows:
repetitive pulse generating means for generating periodic repetitive pulses; orthogonal signal generating means for outputting orthogonal signals whose phases are orthogonal to each other in synchronization with the repetitive pulse; and in synchronization with the repetitive pulses from the repetitive pulse generating means. an ultrasonic transmitting/receiving means for transmitting and receiving ultrasonic pulses; a bandpass filter whose center frequency is externally controllable and for passing the echo signal received by the ultrasonic transmitting/receiving means; and an echo signal passed through the bandpass filter. The apparatus is equipped with orthogonal detection means for performing orthogonal detection using the orthogonal signal.

The apparatus also includes a frequency detection means for detecting the center frequency of the echo signal, and a filter control means for controlling the frequency characteristics of the bandpass filter based on the center frequency detected by the frequency detection means.

An FM detector or a frequency-to-voltage converter is used as the frequency detection means.

Therefore, according to the present invention, the bandpass filter is adjusted so that the frequency of the echo signal from the living body received by the ultrasonic transmitting/receiving means matches the frequency of the orthogonal signal which orthogonally detects this echo signal by the orthogonal detection means. By controlling the frequency characteristics, generation of beat signals can be suppressed and saturation of the circuit can be prevented.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to one drawing.

First, a first embodiment of the present invention will be described.

FIG. 1 is a block diagram schematically showing an ultrasonic Doppler blood flow meter according to a first embodiment of the present invention.

In this embodiment, the same parts as those of the conventional example shown in FIG. 4 are given the same reference numerals, and the explanation thereof will be omitted, and the different configuration will be explained. In FIG. 1, reference numeral 11 denotes a bandpass filter (B, P, F) that changes the frequency of the echo signal from the living body received by the ultrasound transmitting/receiving means 1.
), and a variable capacitance diode, a PIN diode, etc. are used as constituent elements so that the center frequency is controlled by a voltage applied from the outside to a control terminal.

12 is a frequency detection means for detecting the frequency of the echo signal, and a frequency-to-voltage converter such as an FM detector or an F-V converter is used. 13 is frequency detection means 1
This is a filter control means that controls the bandpass filter 11 based on the detection result of step 2.

The operation of the above configuration will be described below.

Similar to the conventional example, the ultrasonic pulse transmitted into the living body by the ultrasonic transmitting/receiving means 1 becomes an echo signal by living tissue or blood flow during propagation, and
received at The echo signal is passed through a bandpass filter 11
, and the 1st. After being orthogonally detected by the orthogonal signal from the orthogonal signal generator 5 in the second orthogonal detectors 6a and 6b, it is integrated by the first and second integrators 7a and 7b for the period in which the sample gate signal is generated. Doppler signals, which are the integration results, are held in first and second sample holds 8a and 8b. The frequency detection means 12 outputs the frequency of the echo signal with a corresponding voltage. The filter control means 13 controls the frequency band characteristics of the bandpass filter 11 using the voltage from the frequency detection means 12, and always makes the frequencies of the echo signal and the orthogonal signal equal. Therefore, the frequency step is eliminated or reduced.

It is possible to suppress the generation of heat signals within the integral interval as shown in FIG. 3 (al) and to significantly improve the dynamic range.

Note that the frequency of the echo signal is detected by quadrature detectors 6a and 6b.
It can also be realized by a detection signal that has passed through the echo signal, in which case the frequency of the echo signal appears as the difference frequency of the orthogonal signals.

Next, a second embodiment of the present invention will be described.

FIG. 2 is a block diagram schematically showing an ultrasonic Doppler blood flow meter according to a second embodiment of the present invention.

In the first embodiment, the first and second low-pass filters 9a, 9b and the adder 10a, ! By providing the low-pass filter 9, the measurement dynamic range for the clutter signal becomes very large.In this embodiment, as shown in FIG.
a, 9b and adders 10a, 10b are removed, and even with such a configuration, generation of beat signals due to frequency differences can be suppressed and the dynamic range can be improved.

Effects of the Invention As described above, according to the present invention, the frequency difference between the echo signal from the living body received by the ultrasonic transmitting/receiving means and the orthogonal signal which orthogonally detects this echo signal by the orthogonal detection means is reduced by the bandpass filter. can be made equal, so
It is possible to suppress the generation of beat signals and prevent saturation of the circuit. Therefore, the circuit gain can be increased, and the blood flow velocity in even small blood vessels can be reliably measured, which has great clinical effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing an ultrasonic dragura blood flow meter according to a first embodiment of the present invention, and FIG.
A block diagram schematically showing the ultrasonic Doppler blood flow meter in the embodiment, FIG. 3 is an explanatory diagram of the signal waveform in the integrator,
FIG. 4 is a block diagram schematically showing a conventional ultrasonic draglar blood flow meter. 1... Ultrasonic transmitting/receiving means, 2... Synchronization signal generator. 3... Drive circuit, 4... Quadrature signal generator, 5, Gate generator, 6a, 6b... Quadrature detector, 7a, 7b.
...Integrator, 8a, 8b, sample hold, 9a. 9b...Low pass filter, 10a, 10b...Adder, 11...Band pass filter, 12...Frequency detection means, 13...Filter control means. Name of agent: Patent attorney Shigetaka Awano and 1 other person
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Claims (4)

[Claims] (1) A repetitive pulse generating means for generating a periodic repetitive pulse, an orthogonal signal generating means for outputting orthogonal signals whose phases are orthogonal to each other in synchronization with the repetitive pulse, and a repetitive pulse from the repetitive pulse generating means. an ultrasonic transmitting/receiving means for transmitting and receiving ultrasonic pulses in synchronization; a bandpass filter whose center frequency is externally controllable; and a bandpass filter for passing the echo signal received by the ultrasonic transmitting/receiving means; An ultrasonic Doppler blood flow meter comprising orthogonal detection means for orthogonally detecting an echo signal using the orthogonal signal. (2) The filter according to claim 1, further comprising a frequency detection means for detecting the center frequency of the echo signal, and a filter control means for controlling the frequency characteristics of the bandpass filter based on the center frequency detected by the frequency detection means. Ultrasonic Doppler blood flow meter. (3) The ultrasonic Doppler blood flow meter according to claim 1 or 2, wherein the frequency detection means is an FM detector. (4) The ultrasonic Doppler blood flow meter according to claim 1 or 2, wherein the frequency detection means is a frequency-to-voltage converter.