JPS61265131A - Ultrasonic doppler blood stream 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 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 at any location within a living body.

BACKGROUND OF THE INVENTION In recent years, ultrasonic Doppler blood flow meters have become popular in medical fields such as the heart and circulatory systems. This ultrasonic Doppler blood flow meter is based on the principle that the ultrasonic waves transmitted into the living body undergo a frequency shift due to the Doppler effect that occurs when reflected from a moving object such as blood flow, and it corresponds to the blood flow velocity. The blood flow velocity distribution in the living body can be easily observed from the body surface by displaying the Doppler shift frequency. The blood flow meter will be explained. In FIG. 5, reference numeral 101 is an ultrasonic transmitting/receiving means (hereinafter referred to as a probe) that transmits ultrasonic pulses into the living body from the ultrasonic transmitting/receiving surface 101a and receives echo signals reflected due to differences in acoustic impedance.
Generally, it is constructed from piezoelectric material. Reference numeral 102 denotes a drive circuit that generates a drive voltage for generating ultrasonic pulses to be transmitted from the probe 101 at the frequency of an external clock and the timing of an external trigger, and drives the probe 101;
3 is a transmission timing circuit that uses the timing when the drive circuit 102 generates a drive voltage as a trigger; 1o4 is a phase detector that detects the phase of the echo signal received by the probe 101; and 105 is a phase detector that detects the phase of the echo signal received by the drive circuit 102. A reference signal generation circuit serves as a standard for the frequency and phase of the reference signal when phase detection is performed by the detector 104, and 106 generates a gate signal at a time corresponding to the propagation time of the ultrasonic wave from the transmitting/receiving surface of the probe 101 to the target site. 107 is an analog switch that allows the phase signal phase-detected by the phase detector 104 to pass through the section of the gate signal generated by the gate signal generation circuit 106; 10B;
110 is an integration circuit that integrates the phase signal that has passed through the analog switch 107, calculates the sum of the phase signals, and obtains a Doppler shift signal by repeating transmission and reception; 110 is an integration circuit 1;
08 is a sample-and-hold circuit that holds the integrated result until the next integration result is obtained in order to perform a reset prior to the integration, and 111 is a sample-and-hold circuit that holds the integrated result until the next integration result is obtained. 112 is a bypass filter 11 that removes signals;
A frequency analyzer 113 analyzes the frequency of the Doppler shift signal that has passed through the frequency analyzer 112. A display unit 113 displays the results of the frequency analyzer 112.

Next, the operation of the transmission timing circuit 103 will be explained with reference to the time chart shown in FIG. 2. The zero transmission timing circuit 103 generates a trigger signal T at constant or arbitrary intervals and supplies it to the drive circuit 102 (a) in FIG. The drive circuit 102 drives the pro 5 ICM with a drive pulse TX using a trigger signal T, and transmits an ultrasonic pulse through the glove 101 into the body.

The ultrasonic pulse propagates inside the living body, is reflected at parts with different acoustic impedances, and reaches the probe 101 again,
The echo signal E is received as an echo signal E (C in the same figure). t. The phase detector 104 generates a reference signal R (d
) is used for orthogonal detection. The orthogonally detected echo signal has a phase difference with the reference signal R and a detection output having the magnitude of the echo signal E, and is obtained in the form of a cloth reception signal C with real and imaginary parts (e in the same figure), which is gated. The analog switch 107 is opened for the section of the gate signal G (f in the figure) generated by the signal generation circuit 106, and the integration circuit 108 performs integration. The gate signal G is an echo signal t1 from the target site in the living body.
~t2, and the voltage of the integration result is adjusted to t1~t2.
The real part signal X and the imaginary part signal Y are obtained as the total 6-page sum of the real part and imaginary part of the orthogonal signal (q in the same figure),
The sample and hold circuit 110 holds the integration results as shown by the broken line (h in the same figure).e Reference signal R used during orthogonal detection and drive pulse TX generated by the drive circuit 102.
is the same phase and frequency for each transmission, and two signals with a phase difference of 900 are generated by the reference signal generation circuit 105. If the echo signal E is from a moving reflecting object, the reference signal R is generated. Since the phase difference between the two changes each time transmission and reception are repeated, this change appears in the real part signal is obtained, and the larger the amplitude of the echo signal, the more orthogonal signal X.

The amplitude of Y also increases. This becomes the Doppler shift signal. In biological tissues where the velocity is slow and the echo signal E is strong,
Because it is a large amplitude, low frequency Doppler shift signal,
By passing the signal through the bypass filter 111, only the Doppler shift signal from the blood flow having a small amplitude and a high frequency can be obtained. Removing the Doppler shift signal from biological tissue is a very important part to expand the dynamic range of the frequency analyzer 112, and is generally
IKl+1. is set to In the frequency analyzer 112,
The real part signal X is a Doppler shift signal.

The imaginary part signal Y is subjected to frequency analysis, and the direction of blood flow is determined from the phase relationship between the two signals and displayed on the display unit 113 as a blood flow pattern.

Problems to be Solved by the Invention However, in contrast to the trigger signal T shown in FIG. 6a, the echo signal E contains a very strong portion from the living tissue that appears to be almost stationary, as shown in FIG. Therefore, in order to measure the zero blood flow velocity, which is roughly divided into the weak echo signal part a from the blood flow that is constantly moving, it is necessary to amplify the weak echo signal part a from the blood flow with a large gain. If there is only a weak echo signal from the blood flow, the integrating circuit 108 can obtain a real part signal Xa or an imaginary part signal Ya having only an alternating current component with an amplitude at the amplitude limit v-1 of the integrating circuit ( (See figure C)
0 If the measurement point is set to a strong echo signal from the living tissue, the phase of the reference signal R and the echo signal E is always constant or very slow, so the output of the integrating circuit 118 have a real part signal xb with a DC component or a very slow change, and an imaginary part signal Y
The alternating current component of b appears (see d in the same figure). In actual clinical practice, the ultrasound beam transmitted from the glove 101 has a spread of 9, so when a blood vessel smaller than the beam diameter is captured, echo signals from blood flow and living tissue often exist at the same time. Conventionally, a wall filter 111 has been used to remove the influence of living tissue. However, when observing a relatively shallow measurement point, for example, the real part signal Xa and the imaginary part signal Ya are obtained in a form superimposed on the real part signal xb and the imaginary part signal Yb,
Xc.

Yc (see C in the same figure) 0 However, the integrating circuit 1
Due to the amplitude limit V of 0.08, clipping occurs in the shaded portion and the waveform is distorted. If the DC component is small and does not cause saturation, it is possible to remove the DC component with the conventional bypass filter 111.
When measuring blood flow in deep, small blood vessels, the echo signal from the living tissue around the blood vessel is particularly strong due to the spread of the ultrasound beam, and the DC component is particularly increased, so it is necessary to integrate only this DC component. A phenomenon occurs in which the circuit 10g becomes saturated and the Doppler shift signal no longer appears. Therefore, bypass filter 11
1, even if this DC component is removed, a Doppler shift signal cannot be obtained, and unnecessary frequency components are generated in the frequency analysis results, or the analysis results are interrupted. Also, if either the real part signal X or the imaginary part signal Y becomes saturated,
A phenomenon occurs in which information regarding the direction of blood flow cannot be obtained, which poses a diagnostic problem.The present invention therefore solves the above-mentioned problems of the prior art. Ultrasound that removes DC components generated by echo signals of living tissue from the real and imaginary outputs, making it possible to perform frequency analysis of only blood flow and obtain reliable blood flow information. Means for solving the problems of the Doppler blood flow meter and the technical means of the present invention for solving the above problems are to transmit ultrasonic pulses into the living body. , an ultrasonic transmitting/receiving means for receiving echo signals reflected in the living body, a drive circuit for generating ultrasonic pulses to be transmitted by the ultrasonic transmitting/receiving means, and a transmission timing that gives the timing at which the drive circuit generates the ultrasonic pulses. a signal circuit, a phase detector that detects the phase of the echo signal obtained by the ultrasonic transmitting/receiving means, and serves as a standard for the frequency and phase of a reference signal when phase-detecting the transmission signal of the drive circuit and the echo signal. A reference signal generation circuit, a gate signal generation circuit that generates a gate signal at a time corresponding to an echo signal from a target part, and a gate signal that controls opening and closing of the phase signal whose phase is detected by the phase detector. An analog switch and an integration circuit that integrates the phase signal that has passed through the analog switch only in the gate signal section, calculates the sum of the phases within the gate signal section, and obtains a Sidopler shift signal by repeating transmission and reception. The device is equipped with a DC feedback circuit that negatively feeds back the DC component or very low frequency component of the 116-truncated Doppler shift signal obtained by this integration circuit to the integration circuit.

Operation According to the present invention, with the above configuration, an echo signal is orthogonally detected, frequency analyzed, and displayed along the same path as in the conventional example. Here, negative feedback is applied to the integrating circuit by DC components of the real part signal and imaginary part signal after integration, and it functions as a no-pass filter in the extremely low frequency region. Therefore, by selecting a frequency that can remove only the influence of living tissue and that does not adversely affect the detection of Doppler shift from blood flow, only the AC component, which is a Doppler shift signal, can be removed without integrating the DC component. can be output to subsequent circuits. In this way, the direct current or extremely low frequency components of the orthogonal output generated by the echo signals from the living tissue can be removed, and only information on the blood flow direction can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block circuit diagram of an ultrasonic Doppler blood flow meter in one embodiment of the present invention. The ultrasonic Doppler blood flow meter of the present invention uses a direct current and very low frequency components of the orthogonal signal outputted by the sample and hold circuit of the integrating circuit in the conventional ultrasonic Doppler blood flow meter, which is negatively fed back to the input of the integrating circuit. It is equipped with a feedback circuit 9.

That is, reference numeral 1 denotes an ultrasonic transmitting/receiving means (hereinafter referred to as "progue") that transmits ultrasonic pulses into the living body using the ultrasonic transmitting/receiving surface 1a and receives reflected echo signals due to differences in acoustic impedance, and is generally made of piezoelectric material. It is composed of 2 is a drive circuit that generates a drive voltage for generating ultrasonic pulses to be transmitted from the probe 1 at the frequency of an external clock and the timing of an external trigger, and drives the probe 1; 3 is a drive circuit 2 that generates the drive voltage. Transmission timing circuit that gives timing as a trigger, 4 is prog 1
6 is a reference signal that serves as the reference signal frequency and phase standard when the phase detector 4 detects the phase of the transmission signal of the drive circuit 2 and the ECO 13 page 1 signal. A generation circuit 6 is a gate signal generation circuit that generates a gate signal at a time corresponding to the propagation time of the ultrasonic wave from the transmitting/receiving surface 1a of the probe 1 to the target site, and 7 is a phase detected by the phase detector 4. An analog switch that allows the signal to pass through the section of the gate signal generated by the gate signal generation circuit 7; 8 is the analog switch 7;
Integrate the phase signal that has passed through and find the sum of the phase signals,
An integrating circuit that obtains a Doppler shift signal by repeating transmission and reception; 1o is a sample hold circuit that holds the integrated result until the next integration result is obtained in order to perform reset before the integrating circuit 8 performs integration; 9; 11 is a DC feedback circuit that negatively feeds back the DC component and extremely low frequency component of the Doppler shift signal output from the integrating circuit 8 or the sample-and-hold circuit 1o, and 11 is the Doppler shift obtained by the integrating circuit 8. A bypass filter removes signals of several hundred hertz or less from the signal; 12 is a frequency analyzer that analyzes the Doppler shift signal that has passed through the bypass filter 11 into frequency components; 13 displays the results of the frequency analyzer 12; This is a display section that displays

Next, the operation of the above embodiment will be explained. In the above embodiment as well, the echo signal is orthogonally detected, frequency analyzed, and displayed according to the route explained in the conventional example. Negative feedback is applied to the integrating circuit 8 by the direct current components of the real part signal X and imaginary part signal Y after integration, and in the extremely low frequency region, it functions as an e-pass filter. Figure 3 shows the frequency characteristics of the 80 outputs of the integrating circuit. As shown in the figure, by selecting a frequency f that can remove only the influence of living tissue and that does not adversely affect the detection of Doppler deviation from blood flow, Doppler deviation can be detected without integrating the DC component. It becomes possible to output only the AC component, which is a signal, to the subsequent circuit.

In this way, the Doppler shift signals appearing in the orthogonal signals X and Y from which the DC component has been removed will not be affected even if an echo signal from a living tissue is received at the same time. FIG. 4 shows the output waveforms of the integrating circuit 6 according to the embodiment of the present invention and the conventional example. The solid line represents the 15th page in which the present invention was implemented, the broken line represents the conventional example, and the diagonally shaded area represents the image in which the waveform has been removed due to saturation.

As shown in the figure, by carrying out the present invention, the amplitude limit is expanded, and since there is no influence of DC voltage, it is possible to measure even very thin blood vessels, and the integration circuit 8 does not saturate, resulting in Doppler bias. The amplitude of the shifted signal can make maximum use of the amplitude limit (2).

As described in detail, according to the ultrasonic Doppler blood flow meter according to the present invention, the DC component or extremely low frequency component of the Doppler shift signal obtained by the integrating circuit is negatively fed back by the DC feedback circuit. This makes it possible to perform frequency analysis of only the blood flow, even if echo signals from living tissues that do not change over time are captured at the same time as echo signals from the blood flow, using a simple circuit configuration. The blood flow pattern above will no longer display anything other than blood flow, making it possible to obtain accurate information regarding the direction of blood flow.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of the ultrasonic Doppler blood flow meter according to the present invention, FIG. 2 is a time chart showing the operation of the Doppler blood flow meter, and FIG. 3 is a block circuit diagram showing an embodiment of the Doppler blood flow meter according to the present invention. Figure 4 is a diagram showing the frequency characteristics of the integrating circuit, Figure 4 is a diagram comparing the integral waveforms of the present invention and the conventional one, Figure 5 is a block circuit diagram of a conventional ultrasonic Doppler blood flow meter, and Figure 6 is a diagram of the conventional ultrasonic FIG. 3 is a diagram showing an integral waveform obtained using a Doppler blood flow meter. 1... Probe (ultrasonic transmitting/receiving means), 2...
...Drive circuit, 4...Phase detector, 5...
...Reference signal generation circuit, 6...Gate signal generation circuit, 7...Analog switch, 8
...Integrator circuit, 9...DC feedback circuit,
10...Sample hold circuit, 11...
... Bypass filter, 12 ... Frequency analyzer, 13 ... Display section. Name of agent: Patent attorney Toshio Nakao and one other person
ゝ-4' □25 Castle Relationship with cases involving persons making three amendments Patent application
Appointment Address: 1006 Kadoma, Kadoma City, Osaka Prefecture
(582) Matsushita Electric Industrial Co., Ltd. Representative Toshihiko Yamashita 4 Agent 571 Address 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Specification 1 Name of the invention Ultrasonic Doppler Blood Flow Meter 2. Claims: Ultrasonic transmitting and receiving means for transmitting ultrasonic pulses into a living body and receiving echo signals reflected within the living body, and a drive circuit that generates ultrasonic pulses to be transmitted by this ultrasound transmitting and receiving means.
A transmission timing signal circuit that provides the timing at which the drive circuit generates an ultrasonic pulse; a phase detector that detects the phase of the echo signal obtained by the ultrasonic transmitting/receiving means; A reference signal generation circuit that serves as a standard for the frequency and phase of a reference signal when performing phase detection, a gate signal generation circuit that generates a gate signal at a time corresponding to an echo signal from a target region, and the phase detector described above. An analog switch that controls the opening and closing of the phase-detected phase signal using the gate signal, and the phase signal that has passed through the analog switch only in the section of the gate signal is integrated, and the sum of the phases within the section of the gate signal is calculated, and the signal is transmitted and received. 2 C. An integrator circuit that obtains a Doppler shift signal by repeating steps 2 and 3, and a DC feedback circuit that negatively feeds back the DC component or very low frequency component of the Doppler shift signal obtained by this integrator circuit to the integrator circuit. An ultrasonic Doppler blood flow meter characterized by: 3. DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an ultrasonic Doppler dosing blood flow meter used in the medical field to measure blood flow velocity at any location within a living body. BACKGROUND OF THE INVENTION In recent years, ultrasonic Doppler blood flow meters have become popular in medical fields such as the heart and circulatory system. This ultrasonic Doppler blood flow meter is based on the principle that ultrasonic waves transmitted into a living body undergo a frequency shift due to the Doppler effect that occurs when reflected from a moving object such as blood flow, and the blood flow velocity is By displaying the corresponding Doppler shift frequency, the blood flow velocity distribution in the living body can be easily observed from the body surface. Hereinafter, with reference to FIG. 6, the conventional ultrasonic Doppler 311
I will explain the blood flow meter. In FIG. 5, 101 is an ultrasonic transmitting/receiving means (hereinafter referred to as a probe) that transmits ultrasonic pulses into the living body from the ultrasonic transmitting/receiving surface 101a and receives reflected echo signals due to differences in acoustic impedance. is made of piezoelectric material. 102
103 is a drive circuit that generates a driving voltage for generating ultrasonic pulses transmitted from the probe 101 at the frequency of an external clock and an external trigger timing, and drives the probe 101; 103 is a timing at which the driving circuit 102 generates the driving voltage. a transmission timing circuit that gives a trigger as 10
4 is a phase detector that phase-detects the echo signal received by the probe 101; 105 is a standard that serves as a reference signal frequency and phase reference signal when the phase detector 104 performs phase detection of the transmission signal of the drive circuit 102 and the echo signal; Signal generation circuit, 1
06 is a signal generation circuit that generates a gate signal at a time corresponding to the propagation time of the ultrasound between the transmitting and receiving surface of the probe 101 and the target region 1; 107 is a phase detector 104;
The phase signal detected by the gate is sent to the gate signal 41\. An analog switch 1o8 is an analog switch 107 that allows the section of the gate signal generated by the signal generation circuit 106 to pass through.
Integrate the phase signal that has passed through and find the sum of the phase signals,
Integrating circuit that obtains a Doppler shift signal by repeating transmission and reception, 11oll-j: Before the integrating circuit 10 performs integration, it holds the integrated result until the next integration result is obtained in order to reset. 111 is a pull-hold circuit; 111 is a bypass filter that removes signals of several hundred hertz or less from the Doppler shift signal obtained by the integrating circuit 108; 112 is a frequency analyzer that analyzes the frequency of the Doppler shift signal that has passed through the bypass filter 111; 113 is a display section that displays the results of the frequency analyzer 112. Next, the operation will be explained with reference to the time chart shown in FIG. The transmission timing circuit 103 generates a trigger signal T at constant or arbitrary intervals (FIG. 2(a)) and supplies it to the drive circuit 102. Drive circuit 10
2 drives the probe 101 with a driving pulse TX using a trigger signal T (FIG. 2(b)), and transmits an ultrasonic pulse from this probe 101 into the living body. The ultrasonic pulse propagates within the living body, is reflected at parts with different acoustic impedances, reaches the probe 101 again, and is received as an echo signal E ((C) in the same figure). The echo signal E corresponds to the reciprocating propagation time of the ultrasonic wave from the transmitting/receiving surface 101a of the probe 101 to the point where the transmitted ultrasonic pulse is reflected. Since the round trip propagation time of an echo signal from a moving reflector always changes, td also changes. The amount of change in propagation time that changes during the trigger signal T is Δtd
, where the echo signal strength is A, the echo signal E obtained at the n-th transmission/reception is expressed by the following equation. E=Acos(ω(td+n-Δtd)) --
(1) This is detected by the phase detector 104 as a reference signal R(
Orthogonal detection is performed using (d)) in the same figure. Although not shown, the reference signal is the time t of the trigger signal T. There are two constant amplitudes, Vx and Vy, which have a phase difference of 90° from each other, and are expressed by the following equation. vx−CO3ωt d,,, ,,, (2) 6 to −7 Vy = sin (17t d・−(2) In the phase detector 104, E in equation (1) and VX in equation (2). Vy By multiplying each of the following signals...
...(3) The two signals C(
The analog switch 107 is turned on during the interval t1 to t2 of the gate signal G generated by the gate signal generating circuit 106 (FIG. 10(f)), and the integration circuit 108 integrates the signal (e) in the figure. The signal C ((e) in the same figure) shown by equation (3) is (ω
nΔtd) and (2ωt+(υnΔtd)), but the former does not include the time parameter t, so it becomes a DC signal, and the latter is a high-frequency signal with a frequency twice the transmission frequency ω, so it can be integrated. By passing through the circuit 108, the latter component disappears, and the Doppler shift signals X and Y obtained as a result at the integration end time t2 become as follows: K is determined by the circuit constant of the integrating circuit 108. The constant tG is the time width of the gate signal G. The gate signal G is the time t1 when the echo signal from the target site in the living body is received.
~t2, the integration result X received the nth time
, Y includes all the echo signal information between t1 and t2 ((q) in the figure). The voltages of the integration results X and Y are held by the next sample and hold circuits 110 as shown by the broken lines until the next (n+1)th integration result is obtained ((h) in the figure). Integrating circuit 108 is reset when sample hold 110 finishes holding. The integration result obtained in the above manner is a DC voltage as seen from equation (4) when only - times of transmission and reception are performed, but
By repeating transmission and reception every cycle T of the trigger signal T, n increases and X and Y change while maintaining a 90° phase difference. This is a quadrature Doppler signal, and if
Let Y be the real part signal and Y be the imaginary part 88-7' signal. X and Y are each obtained as discrete information for each cycle T, and the difference between the delay time Δtd that changes from the nth transmission/reception to the n111th transmission/reception interval T] and the velocity V of the reflector in the living body. has the following relationship. The deviation frequency fd is expressed by the following equation. fd=(2-v-f-cos θ)/C=-・(6) Here, C is the sound speed in the living body, f is the reference signal frequency (generally equal to the transmitted ultrasound pulse frequency), and θ
is the angle between the moving direction of the reflecting object and the ultrasonic wave propagation direction. In a living body, when an echo signal from the blood flow is captured, the amplitude of the Doppler shift signal is very weak because the reflection intensity of the blood flow is small, and the shift frequency fd is high because the blood flow velocity is high. Become. In biological tissues such as internal organs, the reflection intensity A is large and the movement is slow due to body movements, so the shift frequency fd is very low. By passing this through the bypass filter 111, only Doppler shift signals from the blood flow with small amplitude and high frequency can be obtained. Removing the Doppler shift signal from biological tissue is a very important part to expand the dynamic range of the frequency analyzer 112, which is generally set to 100 to 1 kth. The frequency analyzer 112 performs frequency analysis on the Doppler shift signals X and Y, determines the direction of blood flow from the phase relationship between the two signals, and displays the direction on the display unit 113 as a blood flow pattern. Problems to be Solved by the Invention However, in contrast to the trigger signal T shown in FIG. 6(a), the echo signal E contains signals from living tissues that appear to be almost stationary, as shown in FIG. 6(b). The very strong part is
It is roughly divided into a weak part a from the constantly moving blood flow. To measure blood flow velocity, it is necessary to amplify the weak echo signal part a from the blood flow with a large gain. A real part signal Xa and an imaginary part signal Ya with
can be obtained with an amplitude up to the amplitude limit V of the integrating circuit (see Figure 1).
0 to 7 (see (C)). Furthermore, when the measurement point is set in a strong echo signal area from living tissue, the phase difference between the reference signal R and the echo signal E is always constant or changes very slowly. In the output, a DC component or an AC component of the real part signal xb1 and the imaginary part signal yb, which change very slowly, appears ((d) in the same figure).
reference). In actual clinical practice, the ultrasound beam transmitted from the probe 101 has a spread, so when a blood vessel smaller than the beam diameter is captured, echo signals from blood flow and living tissue are often present at the same time. , a wall filter 111 was used to remove the influence of living tissue. However, when observing a relatively shallow measurement point, for example, the real part signal Xa and the imaginary part signal Ya are obtained in the form of being superimposed on the real part signal xb and the imaginary part signal Yb, as shown in (
(see e)). However, due to the amplitude limit V of the integrating circuit 108, clipping occurs in the shaded portion, distorting the waveform. If the DC component is small and does not cause saturation, it is possible to remove the DC component with the conventional no-pass filter 111. However, when measuring blood flow in relatively shallow carotid arteries or deep small blood vessels, Due to the spread of the ultrasound beam, the echo signal from the living tissue around the blood vessel is particularly strong, and the DC component is particularly increased.
8 becomes saturated and the Doppler shift signal no longer appears. Therefore, even if the bypass filter 111 removes this DC component, it is not possible to obtain a Doppler shift signal, and an unnecessary frequency component is generated in the frequency analysis result, or the analysis result is interrupted. If either of the distorted Doppler shift signals X or Y becomes saturated, a phenomenon occurs in which information regarding the direction of blood flow cannot be obtained, which poses a diagnostic problem. This method solves the above-mentioned problems, and removes the DC component generated by the echo signal of the living tissue from each of the real part output and imaginary part output from the integrating circuit, and performs frequency analysis of only the blood flow. The present invention aims to provide an ultrasonic Doppler blood flow meter that can obtain as reliable blood flow information as possible. 12'\-7 Means for solving the problem and the technical means of the present invention for solving the above problem is to transmit an ultrasonic pulse into the living body and receive the echo signal reflected inside the living body. an ultrasonic transmitting/receiving means for transmitting an ultrasonic wave, a drive circuit for generating an ultrasonic pulse to be transmitted by the ultrasonic transmitting/receiving means, a transmission timing signal circuit for giving a timing at which the driving circuit generates an ultrasonic pulse; A phase detector for phase-detecting the obtained echo signal, and a reference signal generating circuit serving as a reference signal for the frequency and phase of the reference signal when phase-detecting the transmission signal of the drive circuit and the echo signal. a gate signal generation circuit that generates a gate signal at a time corresponding to an echo signal from the above, an analog switch that uses the gate signal to control opening and closing of the phase signal whose phase is detected by the phase detector, and only the section of the gate signal. An integration circuit that integrates the phase signal that has passed through the analog switch, calculates the sum of the phases within the gate signal section, and obtains a Doppler shift signal by repeating transmission and reception; It is equipped with a DC feedback circuit that negatively feeds back the DC component or very low frequency component of the shifted signal to the integrating circuit. Operation According to the present invention, with the above configuration, an echo signal is orthogonally detected, frequency analyzed, and displayed along the same path as in the conventional example. Here, negative feedback is applied to the integrator circuit by the DC component of the Doppler shift signal resulting from the integration, and the integrator circuit functions as a no-pass filter that blocks extremely low frequency regions. Therefore, by selecting a frequency that can remove only the influence of living tissue and that does not adversely affect the detection of Doppler shift from blood flow, it is possible to integrate only the AC component, which is the Doppler shift signal, instead of integrating the DC component. can be output to subsequent circuits. In this way, the direct current or extremely low frequency components of the orthogonal output generated by the echo signals from the living tissue can be removed, and only information on the blood flow direction can be obtained. Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a bronc circuit diagram of an ultrasonic Doppler blood flow meter in one embodiment of the present invention. The ultrasonic Doppler blood flow meter of the present invention connects the DC and ultra-low frequency components of the orthogonal signal output from the integrating circuit or sample hold circuit in the conventional ultrasonic Doppler blood flow meter to the input of the integrating circuit via an analog switch. It is equipped with a DC feedback circuit 9 that provides negative feedback. That is, reference numeral 1 denotes an ultrasonic transmitting/receiving means (hereinafter referred to as "progue") that transmits ultrasonic pulses into the living body using the ultrasonic transmitting/receiving surface 1a and receives reflected echo signals due to differences in acoustic impedance, and is generally made of piezoelectric material. It is composed of 2 is a drive circuit that generates a drive voltage for generating ultrasonic pulses to be transmitted from the probe 1 at the frequency of an external clock and the timing of an external trigger, and drives the probe 1; 3 is a drive circuit 2 that generates the drive voltage. Transmission timing circuit that gives timing as a trigger, 4 is prog 1
A phase detector 5 detects the phase of the echo signal received by the drive circuit 2, and 5 is a standard for the frequency and phase of the reference signal when the phase detector 4 detects the transmission signal of the drive circuit 2 and the echo signal 151, near'. 6 is a gate signal generation circuit that generates a gate signal at a time corresponding to the propagation time of the ultrasonic wave from the transmitting/receiving surface 1a of the probe 1 to the target site, and 7 is a phase detector 4 that detects the phase. An analog switch 8 allows the phase signal and DC feedback voltage to pass through the gate signal section generated by the gate signal generation circuit 7. 8 integrates the phase signal that has passed through the analog switch 7, calculates the sum of the phase signals, and repeats transmission and reception. 1o is a sample hold circuit that holds the integrated result until the next integration result is obtained in order to reset the integration circuit 8 before it performs integration; 9 is an integration circuit or a DC feedback circuit that negatively feeds back the DC component or extremely low frequency component of the Doppler shift signal output from the sample and hold circuit 10 to the integrating circuit 8 via the analog switch 7; A bypass filter that removes signals of several hundred hertz or less from the shifted signal, 12 is sent to the bypass filter 16 - 7 A frequency analyzer that analyzes the frequency of the Doppler shift signal that has passed through 11, and 13 is a display that displays the results of the frequency analyzer 12 Department. Next, the operation of the above embodiment will be explained. In the above embodiment as well, the echo signal is orthogonally detected, frequency analyzed, and displayed according to the route explained in the conventional example. Negative feedback is applied to the integrating circuit 8 by DC components of the real part signal X and imaginary part signal Y after integration, respectively, and it functions as a bypass filter in the extremely low frequency region. 3(a) and 3(c) show an example of a specific circuit for the analog switch, the integrating circuit 8, the sample hold circuit 10°, and the DC feedback circuit 9 in the embodiment of FIG. Figures (b) and (d) are similar to Figure 3 (a) and (
It shows the signal waveform of each terminal in each figure of C). The circuit in (C) requires one system each for the real part signal X and the imaginary part signal Y, but one of them is shown in the figure. Both circuits in (C) can achieve exactly the same effect.First, as a first embodiment, the operation of the circuit in FIG. 1(a) will be explained with reference to FIG. 1(b). The integration circuit 8 in the figure has an amplification degree of −A
1, a resistor R1, and a capacitor C0.The input terminals are E, to which the output of the phase detector 4 (see Fig. 1) is applied, and Efo, to which the DC feedback voltage of the DC feedback circuit 9 is applied. The signals at the respective terminals are added just before the analog switch 7, and are integrated when the analog switch 7 is on. The analog switch 7 is turned ON during the period t1 to t2 of the gate signal, and the period tg is integrated, and the input terminal of the DC feedback circuit 9 (
The waveform shown in the figure is obtained at Ef- (output of the integrating circuit). Sample and hold circuit 10id-A (7) Time t from t2 when integration ends with gain. ), and hold this from t3 onwards. After the hold is completed, the integrator circuit resets the analog switch to the interval O from t3 to t4 by using the RESET signal in advance of the next transmission/reception.
C8 is discharged and reset. Output terminal E of sample hold circuit 1o. As shown in the figure, a Doppler signal discretized with a period T appears, and is applied to the next bypass filter 18 and the converter 11 (see FIG. 1). On the other hand, the DC feedback circuit 9
A low-pass filter is constructed with an inverting amplifier OP3, a capacitor Cf, and a resistor Rf. Direct current and extremely low frequency components are extracted from the output signal of the integrating circuit added to the Ef circuit, and negative feedback is provided via the resistor R2. . The inverting amplifier OP2 has a gain of -Af and is used to invert the phase. Therefore, the lower the frequency of the output of the integrating circuit, the more the amount of feedback increases, and the smaller the integration result becomes. The input/output characteristics of the above circuit are
It is calculated as follows. Equation (7) represents the voltage applied to the input terminal Ei within the gate time tg, and Equation (8) represents the integrating circuit output ef applied to the DC feedback circuit 9 and the DC feedback voltage e f o . In equation (8), ω is the output 19 to the integrating circuit.
It is the frequency of the converted Doppler shift signal, (tg/+
t, , )/T is the duty ratio of the Doppler shift signal that exists discretely for each period T, and since the integral interval from t1 to t2 is a transient state leading to .fl, the There are 9 equations less than 1 to correct the duty ratio. From equations (7) and (8), the gain A of the circuit in Fig. 3 (,) is as follows: (9) , (9) - 3 dB low cutoff layer wave number f. The frequency is selected to be able to block
It is appropriate to choose -1z. Next, as a second embodiment, the operation of the circuit shown in FIG. 3(c) will be explained with reference to FIG. 2(d). The main configuration and operation are the same as the first embodiment shown in FIG. Figure 3 (c
) is different in that the output of the sample hold circuit 1o is applied to the integrating circuit. Additionally, the inverting amplifier ○P2 used in the first embodiment is not needed in this embodiment because the sample and hold circuit 10 also serves this function. The input/output characteristics of this circuit are determined as follows. ... (11) Equations (11) and (12) correspond to Equations (1) and (8), respectively. From the above equations, the gain AV of the circuit in Figure 3 (C) is calculated by the following equation: It is shown in The key is the -3 dB low cutoff wave number f in equation (13). is expressed by the following equation. The determination of fo is the same as in the third figure), and the figure (e) is
The frequency characteristics of the circuits of FIGS. 3(a) and 3(c) are shown. As shown in the figure, the frequency f is capable of removing only the influence of living tissue and does not adversely affect the detection of Doppler shift from blood flow. By selecting , it is possible to output only the AC component, which is a Doppler shift signal, to the subsequent circuit without integrating the DC component. In this way, the Doppler shift signals appearing in the orthogonal signals X and Y from which the DC component has been removed will not be affected even if an echo signal from a living tissue is received at the same time. FIG. 4 shows output waveforms of the integrating circuit 6 of the embodiment of the present invention and the conventional example. The solid line is the one in which the present invention is implemented, 22 b,
The broken line is the conventional one, and the diagonal line is the one whose waveform has been shaved off due to saturation. As shown in the figure, by carrying out the present invention, the amplitude limit is expanded, and since there is no influence of DC voltage, it is possible to measure even very thin blood vessels, and the integration circuit 8 does not saturate, resulting in Doppler bias. The amplitude of the shifted signal can make maximum use of the amplitude limit V. As described in detail, according to the ultrasonic Doppler blood flow meter according to the present invention, the DC component or extremely low frequency component of the Doppler shift signal obtained by the integrating circuit is negatively fed back by the DC feedback circuit. This makes it possible to perform frequency analysis of only the blood flow, even if echo signals from living tissues that do not change over time are captured at the same time as echo signals from blood flow, using a simple circuit configuration. The flow pattern does not display anything other than blood flow, and accurate information regarding the direction of blood flow can be obtained. 4. Brief description of the drawings Fig. 1 is a block circuit diagram showing the ultrasonic doso 23 Bagepla blood flow meter in one embodiment of the present invention, Fig. 2 is a time chart showing the operation of the blood flow meter, and Fig. 3 3(b) is a time chart showing the operation of the circuit in FIG. 3(a).
Figure (C) is a specific circuit diagram of another embodiment of the main parts of the same blood flow meter, Figure 3 (d) is a time chart showing the operation of the circuit in Figure 3 (c), Figure 3 (,) is shown in Figure 3(a),
A diagram showing the frequency characteristics of the circuit in (C), FIG. 4 is a diagram comparing the integral waveforms of the present invention and a conventional one, FIG. 5 is a block circuit diagram of a conventional ultrasonic Doppler blood flow meter, and FIG. 6 is a conventional one. FIG. 2 is a diagram showing an integral waveform obtained using an ultrasonic Doppler blood flow meter. 1... Probe (ultrasonic transmitting/receiving means), 2...
...Drive circuit, 4...Phase detector, 5...
・Reference signal generation circuit, 6...Gate signal generation circuit, 7...Analog switch, 8...Integrator circuit, 9...DC feedback circuit, 10... ... Sample hold circuit, 11 ... Bypass filter, 12 ... Frequency analyzer, 13 ... Display unit. Name of agent: Patent attorney Toshio Nakao and one other person
Q 0

Claims (1)

[Claims] an ultrasonic transmitting/receiving means for transmitting ultrasonic pulses into the living body and receiving echo signals reflected within the living body; a drive circuit for generating the ultrasonic pulses to be transmitted by the ultrasonic transmitting/receiving means;
A transmission timing signal circuit that provides the timing at which the drive circuit generates an ultrasonic pulse; a phase detector that detects the phase of the echo signal obtained by the ultrasonic transmitting/receiving means; A reference signal generation circuit that serves as a standard for the frequency and phase of a reference signal when performing phase detection, a gate signal generation circuit that generates a gate signal at a time corresponding to an echo signal from a target region, and the phase detector described above. An analog switch that controls the opening and closing of the phase-detected phase signal using the gate signal, and the phase signal that has passed through the analog switch only in the section of the gate signal is integrated, and the sum of the phases within the section of the gate signal is calculated, and the signal is transmitted and received. The present invention is equipped with an integrator circuit that obtains a Doppler shift signal by repeating the above steps, and a DC feedback circuit that negatively feeds back the DC component or extremely low frequency component of the Doppler shift signal obtained by this integrator circuit to the integrator circuit. Features: Ultrasonic Doppler blood flow meter.