JPS6112690B2 - - Google Patents

Description

[Detailed description of the invention]

Cerebral circulation characteristics (cerebrovascular characteristics), which are effective in predicting cerebrovascular disorders such as cerebral arteriosclerosis, can be determined by clarifying the vascular properties of the carotid artery. That is, the input impedance characteristics of a simulated electric circuit model of the carotid artery system are approximated to the hydrodynamic input impedance characteristics determined from the carotid blood pressure and blood flow velocity, and the cerebral circulation characteristics are measured from the parameter values of this electric circuit model. do. A modified windkessel model is used as the electric circuit model. Therefore, in order to obtain the vascular properties, first, the vascular diameter, carotid artery pressure wave, absolute flow velocity, etc. are given, and the vascular resistance R, vascular inertia value L, and cerebrovascular capacitance C required for the modified windketsu cell model are determined, and then This can be elucidated by determining the input impedance characteristics of blood vessels from these constants. Therefore, in order to investigate cerebral circulation characteristics, it is necessary to measure blood pressure and blood flow in the carotid artery in addition to knowing the above-mentioned blood vessel diameter and carotid artery pressure wave. Blood pressure may be measured using a well-known strain gauge type blood pressure measuring device. On the other hand, there are devices that use ultrasound to measure blood flow in a non-invasive and non-invasive manner. This is an ultrasonic blood flow measurement device. This measuring device applies an ultrasound probe (transducer) 3 to a carotid artery 1 as shown in FIG.
Blood flow velocity is measured by measuring reflected waves of ultrasound (reflected waves subjected to the Doppler effect, hereinafter referred to as Doppler output). here,
The Doppler effect is a phenomenon in which the frequency of ultrasound reflected by blood is shifted depending on the blood flow velocity and the ultrasound irradiation angle. Therefore, the measured values differ significantly depending on the difference in the ultrasonic irradiation angle ξ with respect to the carotid artery. Let's explain this with reference to Table 1.

[Table] This measurement example is for human blood with a blood flow velocity of 60 cm/sec. As shown in Figure 1, when blood is flowing in the direction of arrow a, the ultrasound probe 3 is This is the measurement result when it is correct. As is clear from this table, the ultrasound irradiation angle ξ
When is 60 degrees, the output (blood flow velocity) with the least error is obtained, and the error increases beyond this irradiation angle ξ. In this example, the measured value shows a variation of about 25 to 30% due to a ±10 change around the irradiation angle of 60°. This means that the ultrasonic irradiation angle ξ is 60 as shown in Table 1.
This means that correct measurement results will not be obtained unless the setting is always set to °. However, when actually operating this probe, a doctor or the like picks up the probe and applies it to the patient's carotid artery, so the irradiation angle varies. Therefore, the blood flow velocity obtained with this probe differs each time the measurement is performed. Therefore, the measurement accuracy is extremely poor. Taking these points into consideration, the present invention is designed to minimize the measurement error based on the difference in the irradiation angle ξ of the ultrasonic probe 3 as much as possible, so that a measured value (actual value) close to the calculated value can be obtained. It is. The apparatus of the present invention will be explained in detail below with reference to the drawings. In the present invention, when measuring blood flow, a pair of probes is used, and the blood flow is measured using reflected waves obtained by each probe. In this case, as shown in FIG. 2, the irradiation angles of the pair of probes 3A and 3B are selected as follows. That is, let the irradiation angle of one probe 3A be ξ,
When the irradiation angle of the other probe 3B is η, blood flow measurement is performed with the difference ξ−η=θ between these irradiation angles ξ and η always maintained at a predetermined angle. When blood flow is measured while keeping the irradiation angle θ constant, the irradiation angle ξ(η) of the probes 3A and 3B applied to the carotid artery 1, that is, the body surface 2, as described later.
Even if the value changes, a measured value close to the actual blood flow velocity value can be obtained. Next, the above reason will be explained with reference to FIG. Now, as shown in Fig. 1, the velocity of blood flowing in blood vessel 1 (blood flow velocity) is Vb, and the angle between the ultrasound irradiated from probe 3 and blood vessel 1 (ultrasound irradiation angle) is ξ. When, the Doppler output (frequency component) S is S=kVb cosξ...(1) k=2fs/C...(2) where, fs: Irradiation ultrasound frequency (transmission frequency) (Hz) C: In-vivo ultrasound It is well known that the propagation speed of sound waves is approximately 1.5 km/sec. That is, the Doppler output S is proportional to the cos of the ultrasound irradiation angle ξ. Therefore, if the blood flow velocity Vb is now held constant, the relationship between S, Vb, and ξ can be explained using a model as shown in FIG. 3A. In other words, since kVb is constant, if we replace it with the diameter as shown in the figure, the line segment connecting points C and B on the semicircle with the diameter (where ∠ABC=ξ) becomes the Doppler output S. Equivalent to. It can be seen that if the ultrasound irradiation angle ξ changes, the line segment changes and the Doppler output S changes. Next, the blood flow velocity Vb flowing in blood vessel 1 is the same,
Two probes 3A and 3B with different ultrasound irradiation angles
Doppler output obtained from each
Sa and Sb are obtained using equations (3) and (4). Sa＝kVb cosξ ……(3) Sb＝kVb cosη ……(4) However, ξ, η are the ultrasonic irradiation angles shown in Fig. 2,
When the blood flow velocity Vb is constant, the relationship between Sa, Sb, kVb, ξ and η is shown in Figure 3B, as described above.
This can be explained using a model like the one shown below. The diagram is
This is a model of the output relationship when using the configuration shown in FIG. 2, where ξ>η and ξ−η=θ. This invention provides that these pair of probes 3A, 3B
The purpose is to find the blood flow velocity Vb using the Doppler outputs Sa and Sb received at However, DB=Sb AB=kVb holds, and the blood flow velocity Vb can be found from this equation (5). In equation (5), the component is an unknown quantity, so it is found from this and Figure 3B. Since △EBC and △EAD are similar, :=: ...(6) CB, DE and CE are given by the following formulas. =Sa...(8) =- =Sb-Sa/cosθ...(9) =Sa tanθ...(10) From equations (7) to (10), the line segment is Therefore, from equations (11) and (5), the blood flow velocity Vb is becomes. (Table 2) is the blood flow velocity data when changing the ultrasonic irradiation angle ξ, η, and this data is θ
= 15°, the true blood flow velocity V _B to be measured is 60.0 cm/
sec and 100.0 cm/sec, the calculated value Vb using equation (12) is shown.

[Table] As is clear from the data in Table 2, no matter how the irradiation angle ξ (or η) is set, the probes 3A and 3B applied to the carotid artery
Even if the irradiation angle ξ (η) changes each time the measurement is performed, it does not have much effect on the blood flow velocity measurement. In addition, when actually measured, the data shown in (Table 2) cannot be obtained. Figure 8 shows the blood flow velocity Vb when θ=15° and ξ is changed around 60°.
It shows the error rate of the measurement data of ξ
When is 60°, true blood flow velocity VB (=60.0cm/sec)
However, when ξ becomes more than or less than 60°, the velocity gradually deviates from the true blood flow velocity as shown by the curve La, and the error rate (Vb/VB×10
0 (%)) becomes higher. However, it is much lower than the error rate (curve Lb) when measuring using one probe. The reason why the actual blood flow velocity value and the measured value differ in this way is that the density of blood cells in the blood and the amount of reflection of the irradiation beam differ each time the measurement is performed. The possible range of the irradiation angle θ is not particularly limited, but in this example, θ=15° is selected. As mentioned above, since the measurement error of a single probe is the smallest when ξ=60°, θ=15° was set in the case of ξ=60°. FIG. 4 is a system diagram showing an example of the ultrasonic blood flow velocity device according to the present invention. In the figure, 7 is an ultrasonic oscillator (ultrasonic signal is about 5 MHz), and the ultrasonic output is supplied to probes 3A and 3B through an amplifier 8. And Doppler output, which is a reflected wave
Sa and Sb are supplied to respective measurement circuits 10A and 10B. These measurement circuits 10A and 10B are for obtaining blood flow waveforms and have substantially the same circuit configuration, so the measurement circuit 10A related to the probe 3A will be explained. The Doppler output Sa is supplied to an amplifier 11A, and then supplied to a detection circuit 13A through a filter 12A composed of a crystal for removing output caused by backflow of blood. Here, the frequency components subjected to the Doppler effect are detected and then supplied to the bandpass filter 14A. The lower limit of the filter is for removing Doppler signals caused by contraction and expansion of the blood vessels themselves, and the upper limit is for S/N.
It is determined from the perspective of In this example 80Hz ~
It is configured to pass 7kHz. The filtered frequency component subjected to the Doppler effect is supplied to a zero-cross counter 16A, where it is frequency-voltage converted, and its output is supplied to a low-pass filter 17A, and then a measurement circuit 10A.
The final output (blood flow velocity wave) is made. In addition,
By supplying this output Sa' to a waveform recorder, the blood flow velocity waveform can be recorded. Probe 3B is also used in the other measurement circuit 10B.
An output Sb′ related to the Doppler output Sb obtained in is formed, and these outputs Sa′ and Sb′ are (12)
The signal is supplied to the first arithmetic processing circuit 20 in order to perform the arithmetic processing as shown in the equation. This arithmetic processing circuit 20 is configured as shown in FIG. 5, and this circuit configuration is for obtaining the blood flow velocity Vb from the formula shown in equation (12).
To explain in sequence, the outputs Sa' and Sb' are supplied to a division circuit 21 to perform Sa/Sb processing, and then supplied to a multiplication circuit 22. This multiplier circuit 22 is supplied with the output of a 1/sin θ constant circuit 23A. Since θ is set to 15° in the above example, 1/sin θ is a constant of 3.867. This multiplication circuit output is supplied to the subtracter 25 at the subsequent stage. The output of the cot θ constant circuit 23B is supplied to this, and the subtracter 25 performs the arithmetic processing of (cot θ−Sa/Sb×1/sin θ). Subsequently, this subtracted output is supplied to a squaring circuit 26 to obtain the square value of the subtracted output, and then supplied to an adder 27. The adder 27 is supplied with the output of the constant circuit 23C, which is 1 in the root (√) shown in equation (12), and performs the calculation of the mathematical expression in the root of equation (6). Subsequently, after being supplied to the square root circuit 28, it is supplied together with the above-mentioned output Sb' to a multiplier 29, and the output thereof is further supplied to a multiplier 30 to which the output of the 1/k constant circuit 23D is supplied.
All operations in equation (12) are performed. Therefore, the output end 30
This means that the blood flow velocity Vb shown by equation (12) is obtained at a. Here, the absolute flow rate of blood is determined by the blood flow velocity Vb per unit cross-sectional area of the carotid artery. Therefore, as shown in FIG. 4, a second arithmetic processing circuit 40 is further provided after the first arithmetic processing circuit 20, and the final absolute flow rate is processed here. Next, regarding this arithmetic processing circuit 40, the fifth
As will be explained with reference to the drawings, it is necessary to determine the blood vessel diameter D for the cross-section of the carotid artery, but this blood vessel diameter can be determined by using the output obtained from a blood vessel diameter measuring device as is well known. This blood vessel diameter measuring device is not directly related to the gist of the present invention and will therefore be omitted. Blood vessel diameter D (diameter) obtained using this measuring device
From this, the absolute flow rate V is expressed by equation (13). V=Vb・π・(D/2) ² ...(13) Although we will explain the calculation process of equation (13), 41
A is a constant circuit, and 42 is a division circuit. The input 40a is supplied with an output related to the blood vessel diameter D described above. Therefore, the calculation of D/2 is performed in these circuits, and the output thereof is supplied to the squaring circuit 43. The output is then supplied to a multiplier 44 to be multiplied by a constant π. 41B is a constant circuit for determining the constant π. The multiplication output is further calculated by the blood flow velocity Vb obtained by the first arithmetic processing circuit 20.
It is also supplied to the multiplier 45. Since the final absolute flow rate V is determined in this way, it becomes possible to know the absolute flow rate required for the blood vessel properties, as mentioned at the beginning. The measurement error can be minimized by adopting the configuration shown in FIG. FIG. 6 shows an example of the configuration of the probe device. In this example a fixing device 50 is provided. This fixing device 5
As shown in the figure, a pair of half parts 50A and 50B formed at a predetermined inclination to the left and right from the center are integrated, and as shown in Fig. 7, one half part 50A
An insertion hole 51a for inserting and fixing the probe 3A is formed approximately at the center of the hole. Similarly, the other half 5
The insertion hole 51b for the probe 3B is also formed in 0B, and the inclination angle of these insertion holes 51a, 51b is selected to be θ as described above. Note that the through hole 52 formed in the center is connected to a rod 53 for gripping the probe device, as shown in FIG.
This is the hole through which it is inserted. Also, 54a, 54
b is a screw for fixing the probes 3A, 3B inserted through the insertion holes 51a, 51b. When such a fixing device 50 is used, since the angle θ defined by the insertion holes 51a and 51b remains unchanged, the probes 3A and 3B can be simply inserted and fixed into the insertion holes 51a and 51b.
A probe device having an illumination angle θ as shown in FIG. 2 can be constructed. Therefore, an ultrasonic blood flow measuring device with high measurement accuracy can be realized using the probe device integrated in this way. Note that the fixing device 50 is made of a resin material such as ABS resin. As explained above, according to the present invention, by providing a pair of probes and selecting the irradiation angle θ of the ultrasound waves formed by these probes to a predetermined angle, the inclination angle of the probe applied to the carotid artery can be changed. However, unlike conventional methods, the measured values do not fluctuate significantly. Therefore, in the present invention, even if the inclination angle of the probe is different, a measurement value close to the actual blood flow velocity value can be obtained, and the measurement accuracy is extremely high compared to the conventional method. Furthermore, since the structure is extremely simple, it also has the effect that this type of device can be constructed at low cost. In the above example, the illumination angle ξ of the probe 3A is 60
Although the angle has been explained as .degree., it is possible to use other angles. The irradiation angle θ is arbitrary.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a conventional device, FIG. 2 is a diagram showing a configuration example of a probe suitable for use in the ultrasonic blood flow measuring device according to the present invention, and FIG. 3 is a diagram for explaining the same. Fig. 4 is a system diagram of an example of the device of the present invention, Fig. 5 is a system diagram of its main parts, Fig. 6 is a diagram showing an example of a blow device, Fig. 7 is a sectional view of its main parts, and Fig. 8 is an explanatory diagram of measurement data. 1 is a blood vessel, 2 is a body surface, 3, 3A, and 3B are probes, ξ is an irradiation angle of probe 3A, η is an irradiation angle of probe 3B, and θ is an ultrasound irradiation angle determined by probes 3A and 3B.

Claims (1)

[Claims] 1. In an ultrasonic blood flow measuring device that measures blood flow velocity using ultrasonic waves, a pair of ultrasonic blood flow measuring devices are installed so that the ultrasonic waves cross each other in blood vessels, and the irradiation angles of the ultrasonic waves are different from each other. probe and
A fixing means for fixing the pair of probes so as to maintain a difference between the irradiation angles of ultrasonic waves from the pair of probes at a predetermined value, and a Doppler output related to blood flow velocity from the pair of probes. A detection means for detecting the probe, a measurement circuit for obtaining blood flow velocity waveforms from these Doppler outputs, and an arithmetic processing means for calculating the blood flow velocity from the angle of the difference between these blood flow velocity waveforms and the above-mentioned irradiation angle are provided. An ultrasonic blood flow measurement device characterized by measuring blood flow velocity independent of the ultrasonic irradiation angle.