JPH0843295A - Optical measuring apparatus for biological organism - Google Patents

Abstract

PURPOSE:To optically measure a biological organism dealing with the light quantity over a wide range, to relatively shorten the measuring time, and to realize a small size and a low cost. CONSTITUTION:Pulses of light from a light source 22 are emitted toward a specimen 28 to be detected, and a diffused transmitted reflected light to be emitted from the position separated from a light emitting point is received by a photomultiplier 32. The photomultiplier 32 is driven by a gate signal synchronized with the irradiation light, and the signal is set to shorter than the interval T of the irradiation light pulse train, delayed, and the delay is sequentially varied. The signal of the photomultiplier 32 is integrated by an integrator 44 via a preamplifier 40, and fetched, and the integrated signal is sequentially changed between 0 to T to the light propagating waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical biometric apparatus for irradiating a subject of a living body with near-infrared light and detecting the diffuse transmitted / reflected light to noninvasively obtain information in the subject. Is. Such an optical biometric device is used, for example, as a biological oxygen monitor or optical CT.

[0002]

2. Description of the Related Art Near-infrared rays in the range of 600 to 1200 nm have relatively good permeability in a living body and maintain sufficient intensity for measurement even after passing through the living body for several cm. Conveniently, since the absorption spectra of hemoglobin and cytochrome oxidase, which are important substances that reflect biological functions, exist in this wavelength range, this property of near-infrared light is utilized to eliminate biological functions. Invasive measurements are performed.

A two-dimensional detector such as a CCD camera that irradiates a living body with near-infrared light, scatters the near-infrared light at various parts of the living body, and passes through the living body (called diffuse transmitted / reflected light). It is known that light is received by and the distribution of absorption inside the living body is imaged by calculation.

When an ultrashort light pulse is input to a part of the subject, the time response curve R of the light emitted from the other part of the subject
The analytical solution for (t) can be found in the article by Patterson et al. (APPLIED OPTICS,
It is given by the equation (7) in Vol.28, No.12, pp.2331-2336 (1989). In that document, the absorption coefficient μa and the equivalent scattering coefficient μs ′ (= (1-g) μ included in the time response waveform are described.
s; μs is the scattering coefficient, g is the anisotropic parameter of scattering)
One way to find is shown. (9) in that document
As shown in the formula, the value of the slope (time portion) of the time response waveform when the time is made infinite, that is, the slope of the tail of the time response waveform becomes −μa · c, The coefficient μa is obtained. The equivalent scattering coefficient μs ′ is given as a function of μa in the equation (10) of that document, and if μa is found, μs ′ can also be found by calculation.

An example of a time-resolved measurement method used for obtaining a time response curve of light emitted from a subject is shown in FIG.
It shows in (A). This method is "single photon time correlation counting method"
The excitation pulsed light is emitted from the light source 3 driven by the pulse driving unit 1 to the subject 2 of the living body, and the diffuse transmitted reflected light from the subject 2 in the single photon state is photoelectron multiplied. Detect with tube 4. TAC (Time to Ampl
The output signal of the photomultiplier tube 4 and the excitation pulse optical signal are input to the amplitude converter 10 via the preamplifier 6 and the discriminator 8, and the time difference (arrival time ti) between the two pulse signals is converted as a voltage. It The multi-channel analyzer (MCA) 12 digitally converts this voltage and counts it at each arrival time, and a time response waveform can be obtained by accumulating the arrival times ti for many pulses. In addition to the above methods, streak cameras and optical oscilloscopes are also used as detection methods. A streak camera or an optical oscilloscope converts light into electrons on the photocathode and then changes the time axis to the space axis by electric field sweeping for measurement.

[0006]

In optical biomedical measurement including optical CT, the amount of received light greatly differs depending on the distance between the light irradiation point on the living body subject and the detection point. In addition, since it is necessary to measure at many irradiation points, there is a demand for shortening one measurement time as much as possible.

TAC is a single photon condition (for example, one photon is detected at the probability of 1/20 or less of irradiation cycle).
Is satisfied, that is, no two or more pulses should come in the measurement time width T as shown in (C). If two pulses come, the arrival time ti for the first pulse is measured and the subsequent pulses are not measured, which is an error. Therefore, even in the measurement with a relatively large amount of light, a dimming mechanism for weakening the intensity of the incident light on the photomultiplier tube 4 is required to such an extent that the pulses do not enter the photomultiplier tube 4 in this way, and the amount of light is forced. Will be dropped and measured.

Moreover, due to the limitation of the maximum count rate, in order to obtain a sufficient S / N ratio, the measurement time must be lengthened to increase the number of integrated pulses. That is, the measurement using the TAC has a drawback that the measurement time is long in order to increase the S / N ratio, regardless of the amount of light. A typical measurement time is 10-30 minutes. The streak camera and the optical oscilloscope do not have such a restriction, but the device becomes large and expensive, and it is not practically suitable for the optical CT that simultaneously measures a plurality of channels.

An object of the present invention is to realize photobiological measurement over a wide range of light quantities, relatively short measuring time, and small size and low cost.

[0010]

An optical biological measurement apparatus of the present invention comprises an irradiation optical system for irradiating a subject with irradiation light of high-speed repetitive optical pulse trains or high-speed modulated light, and diffuse transmission scattered light from the subject. The photodetector that receives the light and the photodetector that operates with a delay gate signal that has a shorter cycle than the irradiation light and that is synchronized with the irradiation light, and that sequentially changes the delay time of the delay gate signal. Drive circuit.

This detection method is known as a boxcar integral measurement method, but it is generally used for the purpose of sampling a waveform ("Spectral Technique Handbook", pages 456-457, published by Asakura Shoten, 1990. Reference), the invention is not considered to be used for high-speed photobiological measurement such as about 10 nanoseconds.
In biometrics, the light propagation waveform detected is relatively gentle, so high resolution is not required, and if the gate signal is treated as a convolution function, it does not need to be an extremely short width gate signal. Therefore, the boxcar integration method can be applied.

[0012]

In the present invention, the photodetector is gated so as to be integrated so that only a part of the light propagation waveform can be integrated by the photodetector.
The convolution waveform of the optical propagation waveform and the gate signal is measured by sequentially detecting the gate delay time while shifting. Since the gate signal waveform can be known separately, the original light propagation waveform itself or a parameter characterizing it can be obtained by subjecting the obtained convolution waveform to data processing such as deconvolution.

[0013]

EXAMPLE FIG. 2 schematically shows the configuration of one example. The light source 22 is driven by the oscillator 24 as a repetitive train of very short pulsed lights. Pulsed light I from the light source 22
₀ (t) is applied to the living body subject 2 by the irradiation optical fiber 26.
Irradiate 8. Diffuse transmitted / reflected light emitted from a position away from the light irradiation point on the subject 28 is guided to the photomultiplier tube 32 by the detection optical fiber 30. The light source is driven so that the light pulse train of the irradiation light is generated so that the adjacent light propagation waveforms detected by the photomultiplier tube 32 are spaced so as not to overlap each other. In the case of a streak camera, the drive of the light source requires a return of sweep, so a longer interval is needed than the interval at which adjacent light propagation waveforms do not overlap, and in TAC, due to the limitation of the conversion speed of the MCA. In addition, there is a time zone that is not detected even when irradiated, and the time zone extends from several times to several ten times the length of the waveform.
Therefore, the driving of the light source in the present invention can be performed at a higher speed than that of the streak camera or TAC. Such light irradiation to the subject 28 and detection of the light propagation waveform from the subject 28 are the same as the time-resolved measurement method conventionally proposed as a photobiological measurement device.

In order to control the operation of the photomultiplier tube 32, a gate signal generator 34 for generating a gate signal in synchronization with a signal for driving the light source 22 by the oscillator 24, and a delay for delaying the generated gate signal. The switch 36 generates a delayed gate signal to the high voltage power supply 38 which generates a high voltage to be applied to the dynode of the photomultiplier tube 32. The width of this gate signal is the irradiation interval T of the irradiation light pulse train.
Set shorter than. The delay time of the delay gate signal generated by the delay switching unit 36 is controlled by the control and data collecting unit 42 so as to sequentially change. The delay time is switched by the delay switch 36 by, for example, switching the length of a cable for transmitting a signal,
It can be realized easily and inexpensively.

Since the high voltage applied from the high voltage power source 38 to the photomultiplier tube 32 is a delayed gate signal, the detection signal of the photomultiplier tube 32 is integrated by the integrator 44 via the preamplifier 42 and taken in. Further, by sequentially switching the delay times, the integrated signal sequentially changes from 0 to T with respect to the optical propagation waveform.

The operation of this embodiment will be described with reference to FIG.
For one pulse of the irradiation light to the subject 28, the light propagation waveform s (t) incident on the photomultiplier tube 32 is a waveform having a peak at a position delayed from the irradiation time 0 as shown in (A). Become. The convolution value of the light propagation waveform s (t) and the gate signal g (tz) is the observed value. Here, z is the delay time. If the gate signal g (tz) is a rectangular wave as shown in FIG. 3, it means that a part of the waveform s (t) is integrated. The observed waveform m (z) collected while changing the delay time between 0 and T is a convolution waveform of the optical propagation waveform s (t) and the gate signal g (tz). Therefore, if the gate signal g (t) is obtained in advance by another method, the original optical propagation waveform s (t) can be obtained from the relationships of the equations (1) to (3) shown in FIG. it can.

Here, of the components included in the gate signal, the solution for ω = 0 is indefinite in solution, and therefore the required resolution component ω (≠ 0) must be included in the gate signal. There is. When the gate signal is a sin wave, the observed waveform obtained is the modulation method (SPIE Vol.1204, 4
81-491 (1990)).

Even when the detected light is very weak and the photon count level is reached, it can be dealt with by switching the integrator to a combination of a discriminator and a counter. Further, the photon condition at this time is only required to be a level at which the two photons can be separated by the discriminator and can be counted by the counter, and there is no limitation of 1/20 or less of the irradiation cycle as in TAC.

[0019]

In the present invention, since the boxcar integration method is applied to optical biometrics, a wide range of light quantities can be accommodated, so a complicated dimming mechanism is not required, and biometrics can be performed with a compact and inexpensive device. become able to. In addition, it is necessary to switch the delay of the gate signal,
Since a long dead time as in the case of the streak camera or the TAC method is not required, it is possible to realize measurement in a short measurement time as a whole.

[Brief description of drawings]

1A and 1B are diagrams showing a conventional measuring device by a single photon counting method by a TAC method, in which FIG. 1A is a block diagram showing a configuration, and FIG. 1B is a diagram showing a time response waveform;
(C) is a diagram showing a detection pulse in a measurement time width T.

FIG. 2 is a schematic configuration diagram showing an embodiment.

FIG. 3 is a waveform diagram showing the operation of the same embodiment.

[Explanation of symbols]

 22 light source 24 oscillator 28 subject 32 photomultiplier tube 34 gate signal generator 36 delay changer 38 high-voltage power supply 40 control and data acquisition unit 42 integrator

Claims (1)

[Claims] 1. An irradiation optical system for irradiating a living body object with irradiation light of high-speed repeating light pulse trains or high-speed modulated light, a photodetector for receiving diffuse transmitted scattered light from the object, and a photodetector. Has a cycle shorter than that of the irradiation light, and is operated with a delay gate signal synchronized with the irradiation light, and is provided with a photodetector drive circuit that sequentially changes the delay time of the delay gate signal. Optical biometric device.