JPH0613029B2 - Ultrasonic Doppler blood flow measurement device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an ultrasonic Doppler blood flow measuring device capable of measuring a blood flow velocity in a wide range.

[Technical Background of the Invention and its Problems] Generally, blood pressure measurement is widely used in medical examinations.
If detailed examination is required, more detailed information is required, and blood flow velocity measurement may be required.
In addition, the measurement of the blood flow velocity is an important factor when diagnosing the heart, for example.

As a device for measuring the above blood flow, generally, a Doppler wave that transmits (transmits) an ultrasonic wave to a blood flow portion, and the frequency of the ultrasonic wave that is reflected back from the blood flow portion is shifted according to the blood flow velocity. An ultrasonic Doppler blood flow measurement method, which measures by utilizing the effect, is used.

That is, as shown in FIG. 6, an ultrasonic wave having a frequency _o is emitted from the wave-transmitting probe 2 pressed against the body surface 1 toward the blood vessel 3, and a reflected wave from the blood cells in the blood vessel 3 is generated. When received by the receiving probe 4, the frequency from the reflected signal is Doppler-shifted by the blood flow velocity V, Becomes Here, c is the speed of sound, and α and β are angles formed by the blood flow direction of the blood vessel 3 and the transmitting or receiving directions of the transmitting and receiving probes 2 and 4.

When the above-mentioned transmitting and receiving probes are the same probe, α = β (= θ), and in general, the condition of V << c is entered, and the above equation is expressed as = (1-2Vcosθ / c) _o ... (2) can be approximated. The Doppler shift frequency is _d (= _-o )
Then, the above equation (2) becomes _d = −2cos θV _o / c (3). From this equation, the blood flow velocity V is Becomes

In the ultrasonic Doppler blood flow measurement method, if a continuous wave is used, the reflection signals from the blood vessels near the body surface and the blood vessels on the deep side are mixed because resolution in the distance direction cannot be obtained,
In order to solve this point, there is an M-sequence modulation method in which modulation is continuously performed, but there is the inconvenience that two probes are required to transmit and receive waves.

On the other hand, the pulse-modulated Doppler method (pulse Doppler method) for transmitting in a pulsed manner can be performed by the same probe for transmission and reception, and part of the transmission pulse generation circuit and the reception circuit can be shared with the B-mode ultrasonic diagnostic apparatus. , Currently widely used.

FIG. 7 shows a typical example of a conventional device using the pulse Doppler method.

Ultrasonic probe (ultrasonic transducer) 11 for transmission and reception
Is connected so that the transmission pulse is applied from the transmission pulse generation circuit 12, and the received signal is amplified by the high frequency amplifier 13 and input from one input end of each of the two mixers 14a and 14b.

The two mixers 14a and 14b phase-shift the oscillating wave of the carrier frequency _o output from the oscillator 15 by the phase shift circuit 16 so that they have a phase difference of 90 ° with each other.
Set of quadrature signals (cos2π _o, sin2π _{o t)} is input from the other input terminal, it is to perform the quadrature phase detection by mixing the signals input from the one and the other input terminal described above.

The oscillating wave of the oscillator 15 is divided by the frequency dividing circuit 17, and a pulse having an ultrasonic pulse repetition frequency of _r is output from the frequency dividing circuit 17, and the transmission pulse generating circuit 12 is controlled by this pulse. is doing. The frequency-divided pulse of the frequency-dividing circuit 17 is delayed by the delay circuit 18 by a predetermined time from the transmission timing, that is, after a delay time for separating and extracting only the reception signal from the target blood vessel portion, one pair Sampling pulses are applied to the sample and hold circuits 19a and 19b to sample and hold the detection outputs of the mixers 14a and 14b. Only the Doppler shift frequency component of the sample-held signal is filtered through a pair of low-pass filters 20a and 20b each having a cutoff frequency of _r 2/2. This filtered signal is A
The / D converters 21a and 21b convert it into a digitalized complex signal, and the fast Fourier transform (FFT) circuit 22 performs frequency analysis. Then, the frequency-analyzed signal is displayed on the television monitor 24 through the digital scan converter (DSC) 23. The phase is 90
By using the signals of two different systems, the signals are input to the real axis and the imaginary axis of the FFT circuit 22 so that the forward and reverse of the Doppler shift (that is, the blood flow direction) can be separately detected together with the frequency analysis.

The operation of the conventional example thus configured will be described below.

A transmission pulse is applied from the transmission pulse generation circuit 12 to the probe 11 every cycle 1 / _r , and an ultrasonic pulse having a carrier frequency _o shown in FIG. 8 is emitted.

As shown in FIGS. 9 (a) and 9 (b), the frequency spectrum in this case has a center frequency at the carrier frequency _o and a component having a repetition frequency _r on both sides thereof, that is, _o ± n _r ( n = 1, 2, ...). When this transmission pulse is reflected by a moving object, that is, a blood cell having a velocity V in a blood vessel, the frequency spectrum of the reflection signal shows the spectrum component of an arbitrary transmission pulse as _η (= _o + n _r , n = 0,
1, 2 ... Here, η is a symbol in which n is made small and both are symbolically equal), and is represented by the above-mentioned equation (2) (however, _o is replaced by _η ). Therefore, the Doppler shift frequency _ηd for that frequency component _eta (= -
_η ) is _ηd = -2COSθ _η / c corresponding to the above-mentioned equation (3), and is obtained by shifting each transmission pulse spectrum shown by the broken line to the frequency position shown by the solid line as shown in FIG. 9 (c). Becomes Therefore, the spectral components in the Doppler-shifted reflected signal have a Doppler shift with respect to _o .
_{If you say do} , It is represented by. Note that n = 0, 1, 2, ...

The reflected signal having the Doppler shift component is received by the ultrasonic probe 11 and converted into an electric signal, and the high frequency amplifier 1
After being amplified by 3, it is input to the mixers 14a and 14b,
The oscillating wave of the frequency of the oscillator 15 is mixed with the phase-shifted local output, and is converted into the sum frequency component and the difference frequency component. The difference signal of this signal is taken out, and the delay circuit 1
Only the reflection signal of the target blood vessel portion is captured by the sample hold circuits 19a and 19b to which the sampling pulse having passed 8 is applied. This captured signal is a low-pass filter 20 with a cutoff frequency of _r / 2.
Filtered at a, 20b. As shown in FIG. 9 (c), this is equivalent to passing through a bandpass filter having a band of ± _r / 2 centered on the original spectrum frequency _o , and the Doppler shift with respect to the spectrum frequency _o . Only the frequency _do is detected.

Actually, the Doppler shift detected in relation to performing the sample hold includes not only _do as shown in FIG. 10 but also other Doppler components _dη , and the spread of the spectrum occurs, resulting in the notation of FIG. 9 (c). The method lacks rigor, but in the following description, focusing on only the spectrum component _do does not cause any inconvenience, and therefore the schematic notation as shown in FIG. 9C is used to simplify the description. To use.

In the above conventional device, the low-pass filters 20a and 20b having a cutoff frequency of _r / 2 are used to prevent mixing of Doppler shift of adjacent spectrum components.
Therefore, a blood flow velocity V _max causing a Doppler shift of _r / 2, that is, _d = ± _r / 2 in the equation (4).
Substituting, that is, Is the maximum blood flow velocity that can be measured by the conventional apparatus using the pulse Doppler method, and there is a drawback that a blood flow velocity higher than this cannot be measured.

[Object of the Invention] The present invention has been made in view of the above points, and a maximum blood flow velocity that can be detected is not limited by the repetition frequency _{r of the} ultrasonic pulse, and a large blood flow velocity can be detected. An object is to provide an ultrasonic Doppler blood flow measuring device.

SUMMARY OF THE INVENTION The present invention follows a Doppler shift of a received ultrasonic signal and provides a feedback loop that forms a tracking filter whose virtual center frequency changes, and detects and displays the frequency shift of the signal through this tracking filter. With such a configuration, it is possible to detect a large blood flow velocity without being restricted by the Doppler shift amount (width).

Embodiments of the Invention Hereinafter, the present invention will be specifically described with reference to the drawings.

1 and 2 relate to a first embodiment of the present invention, FIG. 1 shows a main part of the configuration of the first embodiment, and FIG. 2 shows a tracking filter as a main part in the first embodiment. It is a figure for demonstrating operation.

A high frequency wave having a center frequency of _o is applied to the ultrasonic probe from a transmission pulse generating circuit (not shown) with a pulse of a cycle 1 / _r having a repetition frequency of _r , and the ultrasonic wave transmission pulse shown in FIG. Is fired to the side. Then, it was received by the probe and converted into an electric signal (ultrasonic wave).
The reflected signal is amplified by the high frequency amplifier circuit and is input to one input end of the first pair of mixers 34a and 34b forming the tracking filter. These mixers 34a, 34
In b, the frequency _out is added to the output signal of the voltage controlled oscillator (VCO) 35 by the phase shift circuit 36, and each set of quadrature signals having a phase difference of 90 ° is inputted from the other input end, These input signals are mixed (first detection) and output. The difference signals in the first detected signals are paired with sample-hold circuits 39a and 39a, respectively.
Input to b. Then, similarly to the above-described conventional device, the signals input to the sample hold circuits 39a and 39b are divided by the frequency dividing circuit into oscillating waves of frequency _o , and further, through the delay circuit, at every cycle 1 / _r . The sample and hold circuits 39a and 39b are sampled and held by the sampling pulse applied thereto. This sample-and-hold signal is filtered by the low-pass filters 40a and 40b,
Is applied to one input end of each of the pair of mixers 41a and 41b.

The cutoff frequencies of the low-pass filters 40a and 40b may be _r / 2 or a narrower band. 1
The pair of mixers 41a and 41b have a relatively low frequency ₁ (for example, several times _r to several 1) output from the local oscillator 42.
0 times) oscillation waves pass through the phase circuit 43 and
The quadrature signals that have a phase difference of 0 ° are applied to the other input ends. These mixers 41a, 41
The mixed output of b is added by the adder 44, and then the frequency /
When a signal of frequency _x is input to the voltage (F / V) converter 45, a voltage output of E = g ( _x - ₁ ) is output from the F / V converter 45 with the conversion coefficient as g. It is getting done.

The output of the F / V converter 45 is sent to a display device and is passed through a low-pass filter 46 to output the VCO 35.
Is applied to the frequency control input terminal, and the output frequency _out is variably controlled according to the voltage level applied to this input terminal. In the first embodiment configured as described above,
The characteristic is that the frequency of the VCO 35 is varied in accordance with the deviation of the Doppler signal, and a feedback loop is formed which functions as a tracking filter in which the center frequency of the filter follows the Doppler deviation. There is.

The operation of the first embodiment thus configured will be described below.

Now, assuming that the component of the received high frequency signal is _o + _do ± n _r {1+ ( _do / _o )} as shown in the above equation (5) and the output frequency of the VCO 35 is _o + Δ, 1
The difference component of the signals mixed by the pair of mixers 34a and 34b becomes _do −Δ ± n _r {1+ ( _do / _o )}. (Although not shown, it is assumed that a low-pass filter for removing high frequencies is incorporated on the output side of the mixers 34a, 34b, and the sum component is not considered.) The sample hold circuits 39a, 39b and the low-pass filters 40a, 40b After passing, the frequency component is (
_do- Δ) only. (As described above, the spread of the spectrum caused by the sample hole is omitted.) This signal and the orthogonal signal of frequency ₁ are mixed by the second pair of mixers 41a and 41b, and the adder 44 is added.
When added with, the frequency component becomes ₁ + ( _do- Δ). This signal is an F / V that exhibits an input / output characteristic in which the output voltage E is g ( _x - ₁ ) with respect to the input signal of frequency _x.
By the converter 45, g { ₁ + ( _do −Δ) −
₁ } = g ( _do −Δ) level signal. This signal has a V level that converts the input voltage level to E and the output frequency to a frequency at which _out is _o + hE.
The CO 35 converts the signal into a signal having a frequency of _o + h {g ( _do- Δ)}. By the way, the first VCO3
Since the frequency of 5 was _o + Δ, the output frequency _o + Δ or Δ of the VCO 35 is locked so as to satisfy _o + h {g ( _do− Δ)} = _o + Δ by forming a feedback loop. That is To lock in.

In the above equation, the conversion coefficient g of the F / V converter 45 and the VCO
If 35 product gh of transform coefficients h of sufficiently large delta ≒ _do next, the oscillation frequency of the VCO35 it can be seen that substantially follow the Doppler shift of one spectral component of the original received signal.

Since the oscillation frequency of the VCO 35 also shifts with the shift amount of the Doppler shift frequency _do in the ultrasonic signal received as described above, the output frequency _min of the first pair of mixers 34a and 34b is Therefore, it can be seen that the low-pass filters 40a and 40b may have a very narrow band. In practice, the blood flow velocity itself has a distribution, and the spectrum is widened by performing sample hold as described above. Therefore, the cutoff frequencies of the low-pass filters 40a and 40b are _r 2/2.
The appropriate value may be selected below. It should be noted that, when the filter characteristics that constitute the feedback loop through the low-pass filter after being mixed with the VCO output following the Doppler shift in this way are considered by returning to the original high frequency region, they are equivalently shown in FIG. Thus, it is the same as applying a bandpass filter centering the VCO frequency.

That is, when the reflected signal is Doppler-shifted by _{do and} becomes the spectrum shown by the solid line with respect to the spectrum of the transmission pulse shown by the broken line as shown in FIG. 2 (a), the VCO output is generated by the feedback loop in the first embodiment. The frequency changes following the Doppler shift amount _do . Even if the Doppler shift amount _do is small as shown in FIG. 9A or becomes large as shown in FIG. 7B, it changes in accordance with the change amount. In other words, the center frequency of the filter is (following) the spectrum position that is almost Doppler-shifted.
Since it is locked, the Doppler shift amount is _r /
Even if the number exceeds 2, the adjacent spectrum components (in the conventional example) do not mix, and it is possible to solve the limitation of the pulse repetition frequency (PRF) in the pulse Doppler device in the conventional example, which is not affected by this PRF. Blood flow velocity can be detected with. A filter that functions in this way is generally called a tracking filter.

Since the output of the F / V converter 45 directly corresponds to the average frequency of the Doppler shift in the first embodiment configured and operated in this manner, the time change of this voltage may be displayed on the CRT or the like. The voltage passed through the second low pass filter 46 may be displayed on a CRT or the like.

3 and 4 relate to a second embodiment of the present invention, FIG. 3 shows a main part of the second embodiment, and FIG. 4 is for explaining the operation thereof.

The same elements as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The output signals of the pair of low-pass filters 40a, 40b are further applied to one input end of each of the third pair of mixers 51a, 51b, and the VCO 35 is applied to each of the other input ends of these mixers 51a, 51b. Is applied to the output signal of the phase shifter circuit 36 with a phase difference of 90 ° with respect to each other.
It outputs to 2. The addition output of the adder 52 is further applied to one input end of each of the fourth pair of mixers 53a and 53b. Then, these mixers 53
The signals a and 53b, to which the quadrature signal obtained by converting the signal of the frequency _o oscillated by the local oscillator 54 into the signal of the phase difference of 90 ° by the phase shift circuit 55 is applied to the other input ends of both a and 53b, are applied to both of these input ends. The applied signals are mixed and output as signals of the sum and difference frequencies. Each mixer 53a, 53b
Each of the signals output from is passed through the low-pass filters 57a and 57b (however, the cutoff frequency is sufficiently larger than _r / 2) for removing high frequency components,
The quadrature signal _do is converted into a complex digital signal by a pair of A / D converters 58a and 58b and input to the FFT circuit 59.

The signal frequency-analyzed by the FFT circuit 59 is DS
It is displayed on the television monitor 61 via C60. When the blood flow is not measured in the DSC 60, a B-mode signal is input so that an ultrasonic tomographic image can be displayed on the television monitor 61.

The second embodiment is such that the blood flow measurement range is not restricted by the tracking filter function of the first embodiment and the frequency analysis and the forward / reverse separation of the Doppler shift can be displayed as in the conventional example. Yes, the operation will be described below. (The description of the operation of the same parts as in the first embodiment is omitted.) As described in the first embodiment, the reflected wave signal (received RF).
Frequency component of the signal) _o + _do ± n _r (1+
_do / _o ) and the output frequency of the VCO 35 is _o + Δ, the frequency component passing through the pair of low-pass filters 40a and 40b is _do −Δ. This signal is the third one
The pair of mixers 51a and 51b mixes with the frequency component of the VCO 35 and performs quadrature phase modulation, and the second adder 5
It is added by 2. This addition output is mixed with a quadrature signal of frequency _o having a phase difference of 90 °, and then the low-pass filters 57a and 57b use the Doppler shift frequency as a difference signal.
_{The Do} signal is passed, and the Doppler shift component is converted into a complex digital signal by the A / D converters 58a and 58b, and F
The ET circuit 59 performs frequency analysis and forward / backward separation of the Doppler shift, and the result is displayed on the television monitor 61 via the DSC 60.

Since a feedback loop functioning as a tracking filter is formed, admixture of adjacent spectrum components does not occur even when the Doppler shift amount _do exceeds 1/2 of the pulse repetition frequency _r .

The above operation can be mathematically described as follows. still,
In order to simplify the notation, the angular frequency ω (= 2π) is used.

As shown in FIG. 4 (a), the angular frequency spectrum of the transmission pulse before undergoing the Doppler shift is ωη (η = 0,
. +-.. +-.. ±.), Which results in Doppler shift due to blood flow, resulting in ω _η 'as shown in FIG.
However, ω _η = ω _o + nω _r , and ω _η ′ = (ω _o + ω
_do ) {1 + n (ω _r / ω _o )}. Also, VCO
The angular frequency of 35 is ω _v . Now the received signal is S (t)
And Is represented.

If the outputs of the first pair of mixers 34a and 34b are M ₁ (t) and M ₂ (t), respectively. Becomes When these M ₁ (t) and M ₂ (t) are passed through the low-pass filters 40a and 40b, respectively, as shown in FIG. 4 (c), only the term of (ω _o ′ −ω _v ) remains, and M ₁ (t) ，
M ₂ (t) is M ₁ (t) = (1/2) a _o sin (ω _o ′ −)
ω _v ) t M ₂ (t) = (1/2) a _o cos (ω _o ′ −
ω _v ) t. The result of performing quadrature modulation with ω _v again by the third pair of mixers 51a and 51b is D ₁ (t), D
_{If 2} (t), D ₁ (t) = M ₁ (t) · cosω _v t = (1/4) a _o {sinω _o ′ t−
sin (2ω _v −ω _o ′) t} D ₂ (t) = M ₂ (t) · sin ω _v t = (1/4) a _o {sinω _o ′ t +
sin (2ω _v −ω _o ′) t}, and when added by the second adder 52, D ₁ (t) + D ₂ (t) = (1/2) a _o sin
ω _o ′ t, and finally only the term ω _o ′ remains as shown by the solid line in FIG. 4 (d), and the other adjacent spectrum contained in the original signal S (t) disappears.

After this, the same processing as in FIG. 7 is performed. That is, the fourth pair of mixers 53a and 53b are used for quadrature phase detection at the frequency _o , and the low pass filters 57a and 57b are input to the FFT circuit 59 through the Doppler shift component for frequency analysis and forward / backward separation of the Doppler shift. Then, it is displayed on the television monitor 61.

Although the above explanation has been given for the case where the spectrum subjected to the Doppler shift does not have a spread, the spectrum included in the band of the tracking filter is shown in FIG. 4 even when each spectrum has a spread due to the blood flow velocity distribution. Obviously, it is restored to the exact same shape as shown by the broken line in (d).

Further, since the Doppler signal from the inside of the living body generally contains a clutter component (reflection component from an unmoving body), the tracking property of the tracking filter is improved by using the clutter removal filter 71 as shown in FIG. 5 (a). be able to. Here, reference numeral 72 is a delay line with a delay time τ of 1 / _r . By subtracting from a signal which does not pass the signal passing through the delay line 72 by a subtractor 73, the difference signal is outputted. As shown in FIG. 7B, a comb filter having a NULL point for each frequency _r can be constructed. Clutter removal filter 7 shown in FIG.
1 is a first embodiment shown in FIG. 1 or a second embodiment shown in FIG.
Used in the preceding stage of the circuit of the embodiment (first pair of mixers 3
Immediately before 4a, 34b or in the preceding stage of the high-frequency amplifier circuit in the preceding stage. In this case, it is generally better to have the SN ratio after the amplification by the high frequency amplification circuit. Note that, in FIGS. 1 and 3, a two-dimensional Doppler tomographic image is extracted by configuring without using the sample and hold circuits 39a and 39b, and tracking the tracking signal to the received signal in real time. It is also possible to apply it.

As the detection circuit system or display circuitry of the second adder 52 after the Doppler shift frequency in Figure 3 but limited to the illustrated example the center frequency _o
The FM detection circuit set to can be used.

[Effect of the Invention] As described above, according to the present invention, the feedback loop functioning as a tracking filter is formed which follows the frequency shift due to the Doppler effect and the center frequency of the filter changes. It is possible to eliminate the limitation of the maximum blood flow velocity that is possible and to deal with high blood flow velocity.

Further, by using the tracking filter, the blood flow distribution can be always locked and displayed at the center of the filter.

Further, it is possible to display a two-dimensional Doppler tomographic image.

[Brief description of drawings]

1 and 2 relate to a first embodiment of the present invention, FIG. 1 is a block diagram showing a configuration of a main part of the first embodiment, and FIG. 2 is an explanatory view of operation of the first embodiment. 3 and 4 relate to the second embodiment of the present invention, FIG. 3 is a block diagram showing the configuration of the main part of the second embodiment, and FIG. 4 is an operation explanatory diagram of the second embodiment. 5 (a) is a configuration diagram showing a crack removing filter in the third embodiment of the present invention, FIG. 5 (b) is a characteristic diagram showing transmission characteristics with respect to frequencies in FIG. 5 (a), and FIG. 6 is Doppler. FIG. 7 is a block diagram showing a configuration of a conventional example, FIG. 8 is a waveform diagram showing a waveform of a transmission pulse, FIG. 9 is an operation explanatory diagram of the conventional example, and FIG. It is a distribution diagram which shows the spread of the spectrum of the Doppler shift in an example. 34a, 34b ... Mixer 35 ... Voltage controlled oscillator (VCO) 36 ... Phase shift circuit 39a, 39b ... Sample hold circuit 40a, 40b ... Low-pass filter 41a, 41b ... Mixer 42 ... Local oscillator, 43 ... Phase shift circuit 44 ... Adder, 45 ... Frequency / voltage converter 46 ... Low-pass filter 59 ... Fast Fourier transform circuit 60 ... Digital scan converter 61 ... TV monitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-51-145375 (JP, A) JP-A-58-63861 (JP, A) JP-A-61-98244 (JP, A) JP-A-60- 90541 (JP, A) JP 60-90540 (JP, A) JP 61-92657 (JP, A) Actual development JP 56-176706 (JP, U)

Claims (5)

[Claims] 1. An ultrasonic Doppler blood flow measuring device for transmitting an ultrasonic pulse into a living body at a constant repetition frequency and detecting the blood flow velocity in the living body from the frequency shift amount of a received reflected ultrasonic signal, A voltage-controlled oscillator that generates a set of quadrature signals having phases different from each other by 90 °, a first mixer pair that mixes an output signal of the voltage-controlled oscillator and a received high-frequency signal, and an output of the mixer pair. A pair of sample and hold circuits that sample and hold in synchronization with the repetition period of the transmitted ultrasonic pulse;
A first for filtering the output of the pair of sample and hold circuits
Low-pass filter pair, a fixed-frequency local oscillator that generates a set of quadrature signals whose phases differ from each other by 90 °, and a second output that mixes the output of the local oscillator and the output of the first low-pass filter pair. , A mixer for adding the outputs of the second mixer pair, a frequency / voltage converter for converting the average frequency of the output of the adder to a voltage, and an output of the frequency / voltage converter And a second low-pass filter for controlling the output frequency of the voltage-controlled oscillator by applying the filtered signal to the voltage-controlled oscillator and tracking the change in the Doppler shift of the received ultrasonic signal to generate a virtual An ultrasonic Doppler blood flow measuring apparatus, characterized in that a detection filter for detecting the frequency shift amount of a reflected ultrasonic signal is formed through the tracking filter by providing a tracking filter whose central frequency changes. 2. The ultrasonic Doppler blood according to claim 1, wherein the output voltage of the frequency / voltage converter changes with time as a blood flow rate change. Flow measuring device. 3. An ultrasonic Doppler blood flow measuring device for transmitting an ultrasonic pulse into a living body at a constant repetition frequency and detecting a blood flow velocity in the living body from the frequency shift amount of a received reflected ultrasonic signal, A voltage-controlled oscillator that generates a set of quadrature signals having phases different from each other by 90 °, a first mixer pair that mixes an output signal of the voltage-controlled oscillator and a received high-frequency signal, and an output of the mixer pair. A pair of sample and hold circuits that sample and hold in synchronization with the repetition period of the transmitted ultrasonic pulse;
A first for filtering the output of the pair of sample and hold circuits
Low-pass filter pair, a fixed-frequency local oscillator that generates a set of quadrature signals whose phases differ from each other by 90 °, and a second output that mixes the output of the local oscillator and the output of the first low-pass filter pair. , A first adder for adding the outputs of the second mixer pair, a frequency / voltage converter for converting the average frequency of the output of the adder to a voltage, and
A tracking filter comprising a second low pass filter for filtering the output of the voltage converter and applying a filtered voltage to the voltage controlled oscillator; and an output of the first low pass filter pair for the voltage controlled oscillator. A third mixer pair for remixing with the output, a second adder for adding the outputs of the third mixer pair, and a frequency detector for detecting a frequency change of the output of the second adder. An ultrasonic Doppler blood flow measuring apparatus comprising: a means for detecting a frequency shift amount. 4. The frequency detecting means have phases of 90 degrees relative to each other.
A second local oscillator that produces a different set of quadrature signals;
A fourth mixer pair for mixing the output of the local oscillator and the output of the second adder, a third low pass filter pair for filtering the output of the fourth mixer pair, and the low pass filter. The ultrasonic Doppler blood flow measuring device according to claim 3, wherein the ultrasonic Doppler blood flow measuring device is constituted by a fast Fourier transformer (FET) that calculates a frequency spectrum by using a pair of outputs as a complex signal input. 5. The ultrasonic Doppler blood flow measuring apparatus according to claim 1 or 3, wherein the tracking filter is provided with a comb filter for removing clutter signals in the preceding stage.