JPH0331049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser speckle blood flow meter that measures the state of blood flow in living tissue using speckle phenomenon caused by laser light.

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

By the way, conventionally, as a blood flow meter, there was a
A device described in Japanese Patent No. 63634 is known.
In this method, a photodetector receives laser scattered light from moving blood cells, and a high-pass filter extracts the DC component among the many beat frequency components included in the frequency range of 0 to 20KHz of the output signal of the photodetector. The basic idea is to create a correlation with the state of blood flow by removing the AC component, amplifying the remaining AC component, and dividing it by the total output signal of the photodetector.

In order to eliminate noise caused by mode interference in the laser beam, this conventional device uses two light-receiving fibers to emit light from two adjacent areas of the blood cell irradiated by one light-emitting fiber. and guide the scattered light to two corresponding photodetectors.
Subtraction is performed using a differential amplifier,
It is already commercially available as a laser Doppler blood flow meter.

However, since this conventional device uses a large-diameter fiber with a core diameter of approximately 1 mm, the speckle signal is is spatially averaged, the amplitude of the signal component decreases, and the noise of the laser light source and photodetector, as well as the thermal noise generated by the electronic circuit, cannot be ignored, and this is the cause of unstable measured values in conventional equipment. I was getting used to it. In addition, large-diameter fibers generate large modal noises, that is, noise unique to optical fibers, even when small vibrations are applied to them, so even slight vibrations of the fibers often made it impossible to read measured values.

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 gist of the present invention to achieve the above objects is as follows:
a laser light source, an irradiation light transmission means for irradiating light from the laser light source to blood cells in a living body, a light reception light transmission means for transmitting a laser speckle signal that changes over time due to the irradiated blood cells;
and a photodetector that detects a speckle signal transmitted by the light-receiving light transmission means, and a device that calculates a blood flow value based on the speckle signal detected by the light-receiving device, wherein the light-receiving light transmission means The laser speckle blood flow meter is characterized in that the means is a single optical fiber with a core diameter of 100 μm or less, and the photodetector is a photomultiplier tube.

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. The coherent laser light from the He-Ne laser light source LB irradiates the skin surface S through one light emitting fiber F1, enters the tissue to a depth of approximately 1 mm, and is scattered by blood cells in the capillaries to form a coherent laser beam. The speckle light is detected by a photomultiplier tube PM via one receiving fiber F2. The output of the photomultiplier tube PM changes with time in accordance with the movement of blood cells, and the output of the photomultiplier tube PM is amplified by the amplifier A. The output of amplifier A can be input to a frequency analyzer FA to observe the frequency distribution, or can be input to a multi-channel filter MF, which will be described in detail below.
The signal is input to the microcomputer μCOM for signal processing. At the same time, the output of amplifier A is input to a high-pass filter and a frequency-to-voltage converter F/V, which is used to perform zero-crossing processing as required.

In other words, the frequency-voltage converter F/V cuts the DC component through the high-pass filter HF, compares the speckle signal from which the AC component is extracted with the zero level, and rises every time the two match, with a constant time constant. It generates a pulse train that is attenuated by a pulse rate, and then passes through a built-in low-pass filter to convert it into an averaged voltage 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 small, the change in the speckle pattern can be made rougher, so it is desirable to make the core diameter of the light-emitting fiber F1 small as well as the light-receiving fiber F2. Therefore, in the present invention, optical fibers having a core diameter of 100 μm or less for the light-receiving fiber F2 and also for the light-emitting fiber F1 are used to significantly improve the S/N ratio and earthquake resistance. In particular, according to experiments conducted by the present inventor, good results were obtained when the core diameter of the light-emitting fiber F1 was 80 μm and the core diameter of the light-receiving fiber F2 was 10 μm.

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

As described above, in the present invention, speckle signal processing is performed using 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 amount of received light. It is directly affected by the time fluctuation of noise generated by the circuit, and is likely to cause drift in measured values. Furthermore, when the fiber diameter is changed, the value of the high frequency component relative to the total amount of light received also changes, so readjustment is 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 log-log graph, and its slope, that is, the frequency slope, is determined, and the ratio of high frequency components to low frequency components is directly calculated. method is adopted. Regarding the latter, specifically, in Figure 2, the low band 40Hz and high band output of the photodetector are
Bandpass filters BPFa and BPFb each selectively pass 640Hz, each amplitude |VL|, |
VH| is obtained, and the analog-to-digital converter A/D and microcomputer μCOM calculate a value based on the intensity ratio of both HLR = |VH| ² / |VL| ²
is calculated and printed out by the printer PT. That is, the ratio of the power spectra at two different frequencies, Hz, will yield the frequency slope.

This frequency gradient differs in each part of the skin surface S,
It was also confirmed that artificially changing the blood flow changes the power spectrum. In other words, Figure 3 a, b, c, and d show the power spectra at the lower lip, fingertips, neck, and foot, respectively. The frequency gradient differs depending on the region. Further, FIG. 4 shows the power spectrum of the palm before and after tightening the upper arm. Here, in FIG. 4, a is a power spectrum in a normal blood flow state, b is a power spectrum in a state where the upper arm is tightened with air pressure to stop blood flow, and c is a power spectrum in a state where the stoppage of blood flow is 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.

Figure 5 shows HLR in each state of Figure 4 a, b, and c.
=|VH ² |/|VL| ² is shown in chronological order.

Note that the above-mentioned frequency gradient is not affected even if the level of noise generated by the measurement system itself changes, so extremely stable measurement is possible.

As described above, according to the laser speckle blood flow meter according to the present invention, the measured values are stable, and the divider
This means that the state of blood flow in living tissue can be measured with a simple configuration without the need for a differential amplifier or the like. The present invention can be used in the medical and surgical fields to diagnose peripheral circulatory insufficiency and evaluate pathological conditions, and in the plastic surgery field, it can be used to measure blood flow conditions after skin and skin flap transplantation to improve transplant surgery. The progress can be easily judged.

[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 Figs. 3 a, b, c, and d are the lower lip, fingertip, Figure 4 is a power spectrum diagram of each part of the neck and legs, Figure 4 is a power spectrum diagram of the palm before and after tightening the upper arm, and Figure 5 is an explanatory diagram showing the frequency gradient in each state in Figure 4 in chronological order. be. 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, MF is a multi-channel filter, BPFa, BPFb are bandpass filters, A/D is an analog-to-digital converter, μCOM is a microcomputer and PT is a printer.

Claims (1)

[Claims] 1. A laser light source, an irradiation light transmission means for irradiating light from the laser light source to blood cells in a living body, and a light reception light transmission means for transmitting a laser speckle signal that changes over time due to the irradiated blood cells; and a photodetector that detects a speckle signal transmitted by the light-receiving light transmission means, and a device that calculates a blood flow value based on the speckle signal detected by the light-receiving device, wherein the light-receiving light transmission means The means is a single optical fiber with a core diameter of 100 μm or less,
A laser speckle blood flow meter characterized in that the photodetector is a photomultiplier tube.