JPS60203235A - Laser speckle blood flow 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 The present invention utilizes the speckle phenomenon caused by laser light to measure blood flow in living tissues. This invention relates to a laser speckle blood flow meter that measures E.

Generally, when a laser beam is irradiated toward a scattering object, the wavefront is disturbed by diffused reflection, forming a so-called speckle pattern with random spots. When the scattering object moves over time, this speckle pattern changes from moment to moment, and when the speckle pattern is observed at a fixed position on the receiving side, the speckle light intensity I8- changes. It will change over time. The present invention applies this to measurement of blood flow in living tissues.

By the way, conventionally, as a blood flow meter, Japanese Patent Application Laid-Open No. 55-63634
A device described in the above publication is known. This uses a photodetector to receive laser scattered light from moving blood cells,
Among the many beat frequency components included in the frequency sieve of the photodetector's output signal, the high-pass filter removes the DC component, and the remaining AC component is amplified to completely filter the photodetector. The output value is basically correlated with the state of blood flow by dividing it by 'Q.

This conventional device has a laser beam mode of 1' l.
- In order to eliminate the noise caused by the radiation, the two adjacent to the phase crab of the blood cell area irradiated with a single light emitting fiber.
from one area to the IL via two receiving fibers,
This device guides the scattered light to two photodetectors, and performs subtraction using a differential amplifier, and is already commercially available as a laser sampler blood flow meter.

However, in this conventional device, the core diameter is approximately 1 m.
Since a large-diameter fiber of m is used, as the core diameter of the receiving fiber increases, the total amount of received light increases, which is advantageous for detection, but on the other hand, the signal is spatially averaged. As a result, the amplitude of the signal component decreases, and the noise of the laser light source and photodetector, as well as the f8 noise generated by the electronic circuit, cannot be ignored, and this causes unstable measured values in conventional devices. Further, even when a large-diameter fiber is subjected to small vibrations, it generates large modal noise, that is, noise unique to optical fibers, so even slight vibrations of the fiber often make it impossible to read the A11l constant value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser speckle blood flow meter that eliminates the drawbacks of the conventional devices, provides stable measured values, and has a simple configuration.

The object of the present invention to achieve the above-mentioned object is to provide a laser light source, a light emitting fiber for irradiating light from the laser light source to blood cells in a living tissue, A light-receiving fiber that transmits a fluctuating laser speckle signal, a photodetector that detects the speckle light intensity transmitted by the light-receiving fiber, and means for obtaining a frequency gradient of the speckle detected by the photodetector. This is a laser speckle blood flow meter that has a 1 hour signature.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall schematic diagram of an apparatus according to the present invention. He
-N e The coherent laser destination from the laser light source LB is
■If'l is transmitted through the light output fiber F1 of the tree.
! The twinkle light is formed by emitting S, entering the tissue to a depth of about 1 mm, and being scattered by blood cells in the capillaries.
It is detected by a photoelectron finger (i'S tube PM) through a single optical receiving fiber F2.Then, the output of the photomultiplier tube PM changes with time due to the movement of blood cells. The output of the PM is amplified by an amplifier A. The output of the amplifier A is input to a frequency analyzer FA to observe the frequency distribution, or a multi-channel filter, which will be described in detail below.
The signals are input to the MF microcomputer gCOM and signal processing is performed. Note that, at the same time, the output of amplifier A is input to a high-pass filter and a frequency-voltage converter F/V, which is used to perform zero-crossing method processing as required.

That is, the frequency-voltage converter F/V is a high-pass filter H
The DC component is cut through F, and the speckle signal extracted by the exchange is compared with the zero level, and every time the two match, a pulse train is generated that rises and decays with a certain time constant. Averaged through a filter, j [converts to pressure output. Here, a high voltage value is output where the pulse repetition frequency is high, and this output is time-integrated by an integrating circuit. The time-integrated integral value then displays the repetition frequency of the pulse within a predetermined time; if the blood flow is fast, the integral value will be displayed high, and conversely, if the blood flow is slow, the integral value will be displayed low. become.

Note that if the core diameter of the light-emitting fiber F1 is made smaller, the change in the speckle pattern can be made rougher, so it is desirable to make the core diameter of the light-emitting fiber Fl smaller as well as the light-receiving fiber F2. Therefore, in the present invention, optical fibers are used in which the core diameter of the light receiving fiber F2 and the core diameter of the light emitting fiber Fl are 100 gm or less in order to significantly improve the S/N ratio and improve earthquake resistance. According to experiments conducted by the present inventors in 4□5, good results were obtained when the core diameter of the light-emitting fiber F1 was 80 gm and the core diameter of the light-receiving fiber F2 was 10 gm.

The present invention does not require two receiving fibers as in the conventional device, but uses one receiving fiber, which simplifies the device configuration and reduces costs.

As mentioned above, in the present invention, speckle signal processing is performed by a method different from that in the conventional apparatus through the signal processing system illustrated in FIGS. 1 and 2. In other words, in conventional equipment, the basic method was to normalize the signal detected by the photodetector by passing it through a high-frequency filter and then dividing it by the total received light jj, but in this method, the laser light source, photodetector, and signal processing It is directly affected by the temporal fluctuations of noise generated by the circuit, and tends to cause drift in measured values. Furthermore, if the fiber diameter is changed, the value of the high frequency component relative to the total amount of light received also changes, so readjustment was required.

In the present invention, unlike this conventional method, the power spectrum obtained by subjecting the speckle signal to the frequency analyzer FA is plotted on a logarithmic graph, and its slope, that is, the frequency gradient, is calculated, and the ratio of high frequency components to low frequency components is calculated. A method of direct calculation is adopted. Regarding the latter, specifically, in Fig. 2, the low band 40Hz of the output of the photodetector is
, high band 640Hz are selectively passed through/hand pass filters BPFa and BPFb, each amplitude IV
LI and IVHI are obtained, and the analog-to-digital converter A/D and the microcomputer pLCOM calculate ip'jHLR= l VHI 2/ according to the intensity ratio of the two.
l VLI 2 are calculated and printed out by printer FT. That is, two different frequencies g9Hz
The frequency slope will be obtained by the ratio of the power spectra at .

This frequency! The slope is skin h'i! It was confirmed that it differs in each part of I'ii S, and that it changes when five blood items are artificially changed. That is, Fig. 3 (a), (b
), (c), and (d) show the power spectra at each site of Th, fingertip, and neck and foot, respectively, and the frequency gradient differs depending on each site. Further, FIG. 4 shows the power spectrum of the palm before and after tightening the upper arm. Here, Po in Fig. 4 is a 4' blood flow shape.
, b is by air pressure" - tighten the arm and stop the blood Z%i: 1
- Shitajii4. , Q is the power spectrum at fnH with blood flow stopped 1- released. In this way, it is understood that a change in the blood flow state at the same site appears as a change in the frequency gradient.

FIG. 5 shows HLR=It/l-121/IVLI2 in each state of FIG. 4(a), (b), and (c) in time series.

Note that the frequency gradient mentioned above is not affected even if the level of noise generated by the measurement system itself changes, so an extremely stable All+ constant can be achieved.

As shown in item 1-, the laser speckle blood flow meter according to the present invention provides stable measurement values, and can measure blood flow in living tissues with a simple configuration that does not require a divider, differential amplifier, etc. It will be possible. The present invention can be used in the fields of internal medicine and surgery to diagnose peripheral circulatory insufficiency and evaluate pathological conditions, and in the field of plastic surgery, it can be used to measure the blood flow status after skin and tributary transplants and the progress of transplant surgery. Judgments, etc. can be easily made.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram of the laser speckle blood flow meter according to the present invention, Fig. 2 is a schematic diagram of the calculation system for calculating the frequency gradient, and Fig. 3 (a), (b), (c), ( d) is a power spectrum diagram of each part of the lower lip, fingertips, neck, and feet, respectively;
FIG. 4 is a power spectrum diagram of the palm before and after tightening the upper arm, and FIG. 5 is an explanatory diagram showing the frequency gradient in the trough 71 of FIG. 4 in time series. Symbol LB is a laser light source, PM is a photomultiplier tube, A is an amplifier, FA is a frequency analyzer, HF is a high-pass filter, F/
V is a frequency-voltage converter, BPFa, BPFb is a band pass filter, A/D is an analog Tenkle converter 1
．． COM is a microcomputer, and PT is a printer. 1~! 111 ” Drawing 1 Figure 2 Figure 3 111&(+z) fA3 Section 4 Figure

Claims (1)

[Scope of Claims] 1. A laser light source, a light emitting fiber that transmits light from the laser light source to blood cells in a living tissue, and a light receiving fiber that transmits a laser speckle signal that changes over time due to the blood cells in the living tissue. and a photodetector for detecting the speckle light intensity transmitted by the optical receiving fiber in 11, and a means for obtaining the frequency gradient of the speckle detected by the photodetector. Laser speckle blood flow meter according to claim 1, in which the power spectrum obtained by the frequency analyzer is plotted on a bi-converting graph, and the gradient of the circumference is calculated based on the slope of the power spectrum. . 3. A filter that extracts frequency components I, l, and 1;
A laser speckle blood flow meter according to claim 1. 4. Among the light emitting fiber and light receiving fiber,
The laser speckle blood flow meter according to claim 1, wherein at least the core diameter of the light-receiving fiber is 100 lm or less. 5. The core diameter of the light output fiber is 11001L.
A laser speckle blood flow meter according to claim 4 below.