JPH0318457B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a correlation detection type ultrasonic blood flow meter,
In particular, it relates to a method for creating data used for correlation, and is designed to accurately remove fixed reflected waves from blood vessel walls and the like.

[Technology background]

A conventional Doppler-type ultrasonic blood flow meter using the pulse method uses only phase information of reflected waves from the object to be measured. Since phase information is proportional only within the range of ±π, the distance at which the movement of the object to be measured can be detected within the repetition time of pulse transmission is ±λ/4 (λ is the wavelength of the ultrasonic wave, and ±λ/4 is (equivalent to ±π), and if the object to be measured moves further than that, data analysis cannot be performed and erroneous analysis results may be output.

Therefore, a correlation detection type that utilizes amplitude information of reflected waves has been developed so that the flow velocity can be detected even if the object to be measured moves by more than ±λ/4 within the repetition time of ultrasonic pulse transmission. .

FIG. 1 is a schematic block diagram of one example of the correlation detection type blood flow meter. In the figure, reference numeral 1 denotes an ultrasonic transmitter, and its output electric pulse (transmission signal) TS is converted into an ultrasonic pulse by a transducer 2. A reflected wave of the ultrasonic pulse from an object to be measured (not shown) is received by the same (or different) transducer 2, and is amplified, orthogonally detected, etc. by the receiver 3. The output signal RS of the receiver 3 is guided to a correlation detection type data generation section 4, and the data generated here is converted into a flow velocity in a correlation data analysis section 5 and further outputted to a display section 6. Note that 7 is a controller that controls each section, and in particular, a sampling position signal S synchronized with the transmission timing is supplied to the correlation detection type data generation section 4.

FIG. 2 shows a specific example of the correlation detection type data generating section 4, and FIG. 3 shows signal waveform diagrams of each section. The received signal RS amplified in the receiver 3 is sent to the amplitude detector 41
After full-wave rectification, high frequencies are cut off.
The waveforms in FIG. 3 indicate the input, intermediate processing, and output of the amplitude detector 41, respectively.

Next, the signal is transferred to the sample and hold circuit 42,
43, samples are taken using two pulses shifted by ΔT shown in the waveform of FIG.

By performing this operation every time an ultrasonic wave is transmitted and received, data shown in the waveform of FIG. 3 can be obtained. Assuming that this data is Y ₁ (n) Y ₂ (n), the cross-correlation detector 45 calculates the cross-correlation Z(τ) of this data as shown in the following equation.

Z(τ)= _o=N 〓 ⁿ⁼⁰ Y ₁ (n) Y ₂ (n+τ) As shown in the waveform of FIG. 3, the maximum of Z(τ) detected by the peak position detector 46 The value τmax indicates the time required to travel the distance corresponding to ΔT. Therefore, from this, the speed of the object to be measured can be known.

Incidentally, since received waves generally include fixed reflected waves from blood vessel walls, etc., the above-mentioned cross-correlation type blood flow meter has a drawback in that its accuracy is inferior to conventional phase information of reflected waves. In Figure 4,
RS0 indicates a fixed reflected wave, and RS1 indicates a reflected wave from blood. The actual received wave is a combination of these RS0 and RS1.

The reflected wave RS1 from the blood moves from the solid line waveform as shown by the dotted line waveform according to the speed of blood flow. Therefore, if the amplitude of the received wave at a certain time t = t ₀ is shown in correspondence with the size of the travel length, it will look like the solid line waveform shown in the bottom row of Figure 4 Ut ₀ , which causes pulsations in the amplitude. It ends up. Note that the dotted line waveform is the one when there is no fixed reflected wave.

In this way, when there is a fixed reflected wave from a blood vessel wall or the like, pure data from only blood, such as the dotted waveform of RS1, cannot be obtained, resulting in a problem of decreased accuracy.

[Object and structure of the invention]

The object of the present invention is to provide a correlation detection type blood flow meter,
The objective is to obtain correlation data that is not affected by fixed reflected waves from blood vessel walls, etc., and for this purpose, a correlation detection type ultrasonic blood flow meter is configured to convert ultrasound reflected wave signals into sine waves and cosine waves, respectively. a quadrature detector that performs detection using a reference wave, two sample-hold circuits that sample and hold quadrature detection output signals on the sine wave side and cosine wave side of the quadrature detector, respectively, and each of the two sample-hold circuits. A device characterized by comprising a connected high-pass filter and a circuit for calculating the sum of squares of the output signals of the two high-pass filters, and performs blood flow measurement by correlation detection based on the sum of squares signal. It is.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to Examples.

FIG. 5 is a configuration diagram of an apparatus according to an embodiment of the present invention. This example device is equipped with two blood flow measurement circuits, one using the correlation detection method shown in Figure 1 and the other using the conventional phase detection method, in parallel, and when the blood flow velocity is low, the measurement circuit using the correlation detection method is used. However, when the blood flow velocity is high, by using a measurement circuit using a correlation detection method, it is possible to measure a wide range of velocities with high precision by taking advantage of the characteristics of each. In particular, according to the present invention, the input stage of the measurement circuit of the correlation detection method includes:
A preprocessing section is provided to remove signal components originating from fixed reflected waves from blood vessel walls and the like.

In FIG. 5, 1 is a transmitter, 2 is a transducer, 3 is a receiver, 4 is a correlation detection type data generation section, 5 is a correlation data analysis section, 6 is a display section, 7 is a controller, and 8 is a preprocessing section. 9 indicates a correlation detection type data generation section, and 10 indicates a phase data analysis section. Components indicated by 1 to 7 in the figure correspond to the same numbered elements in FIG. 1, and perform the same operational functions in FIG. 5, so a description thereof will be omitted.

The phase detection type data generation section 9 and the phase data analysis section 10 are measurement circuits based on the conventional method described above, and are used when measuring blood flow of a size that can be detected with phase information in the range of 0 to π. .

FIG. 6 is a detailed configuration diagram of the preprocessing section 8. As shown in FIG. In the figure, 81A and 81B are multipliers, 82A and 82B are low-pass filters, 83A and 83B are sample and hold circuits, 84A and 84B are high-pass filters, and 85
A and 85B are square circuits, 86 is an adder, 87 is an input line, 88 is an output line, 89 and 90 are multiplexed blocks, and 91 is a delay circuit. Here, 81A, 81B, 82A, and 82B constitute orthogonal detectors.

As shown in Fig. 7, the fixed phase reflected wave from the blood wall is defined as A(t)sin(ωt+θ), and the reflected liquid containing the phase change due to the Doppler effect from the blood is defined as B.
(t−an)sin(ωt+bn). Note that n is a transmission repetition number, and b=ωa.

Here, if the above two waves overlap, the input signal C(t) is as follows: C(t)=A(t)sin(ωt+θ)+B(t-an)sin
(ωt+bn), and simply detecting this signal results in B(t
-an) at t=t ₀ (see Figure 4) cannot be sampled. Therefore, multipliers 81A and 81B multiply C(t) by the sin and cos signals to create D ₁ (t) and D ₂ (t).

D ₁ (t)=C(t)・sin ωt=A(t) sin(ωt+θ
)・sin ωt+B(t−an)sin(ωt+bn)・sun ωt=A(t)(−1/2(cos(2ωt+θ)−cos θ)
)+B(t-an)(-1/2(cos(2ωt+bn)-cos b
n)) D ₂ (t)=C(t)・cos ωt=A(t) sin(ωt+θ
)・cos ωt+B(t-an)sin(ωt+bn)・cos ωt=A(t)(1/2(sin(2ωt+θ)+sin θ))
+B(t-an)(1/2(sin(2ωt+bn)+sin bn)
) Here, ω and
By removing the 2ω component and passing only the lower frequency components, E ₁ (t) = 1/2A (t)・cosθ+1
/2B(t-an)cos bn E ₂ (t)=1/2A(t)・sinθ+1
/2B(t-an)sin bn. Here, sample hold circuits 83A, 8
3B, when the time series data sampled at t=t ₀ for each n is passed through the high-pass filters 84A and 84B, the first terms of E ₁ (t) and E ₂ (t) disappear, and n becomes Only the second term, which is increasing, remains.

F ₁ (n) = 1/2B (t ₀ -an) cos bn F ₂ (n) = 1/2B (t ₀ -an) sin bn This is squared by the square circuits 85A and 85B, respectively, and the adder 86 When the sum of squares is obtained by adding them, G(n)=1/4B ² (t ₀ −an), and a value containing only the desired B(t ₀ −an) can be obtained.

The above value of G(n) is sent to the correlation detection type data generation section 4 in FIG. 5, where the correlation is determined as explained in FIG.
The blood flow velocity is calculated.

Blocks 89 and 90 are duplicated to reduce the sampling processing time at t=t ₀ by half, and the input signals E ₁ (t) and E ₂ (t) are used as common inputs, and the sampling positions are as follows. By delaying the sampling signal for block 90 by a certain period of time by a delay circuit 91, a deviation from block 89 is provided. Multiplexing is performed as needed.

〔Effect of the invention〕

As described above, according to the present invention, the influence of fixed reflected waves from the blood vessel wall can be removed, so that the accuracy of blood flow velocity measurement using the correlation detection method can be significantly improved.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the correlation detection type blood flow meter, Figure 2
The figure is a detailed diagram of the correlation detection type data generation section.
The figure is a signal waveform diagram of each part in Figure 2, Figure 4 is an explanatory diagram of the influence of fixed waves, Figure 5 is an overall configuration diagram of one embodiment of the present invention, and Figure 6 is a detailed diagram of its preprocessing section. , FIG. 7 is a signal waveform diagram for explaining the operation. In the figure, 1 is a transmitter, 2 is a transducer, 3
is a receiver, 4 is a correlation detection type data generation section, 6 is a display section, 8 is a preprocessing section, 81A and 81B are multipliers,
82A, 82B are low-pass filters, 83A, 83B
84A and 84B are high-pass filters, 85A and 85B are square circuits, and 86 is an adder.

Claims (1)

[Claims] 1. In a correlation detection type ultrasonic blood flow meter, a quadrature detector detects reflected ultrasound signals using sine wave and cosine wave reference waves, respectively, and a sine wave side and a cosine wave side of the quadrature detector. two sample-and-hold circuits that respectively sample and hold quadrature detection output signals; a high-pass filter connected to each of the two sample-and-hold circuits; and a circuit that calculates the sum of squares of the output signals of the two high-pass filters. 1. A correlation detection type ultrasonic blood flow meter, characterized in that the blood flow measurement is performed by correlation detection based on the sum of squares signal.