JP2003215032A - Living body optical measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a living body optical measuring device capable of preventing the deterioration of measuring precision caused by wavelength transition of a light source, and performing high-precision measurement. <P>SOLUTION: The living body optical measuring device comprises a semiconductor laser 111 as a light source, a laser activating element 112 for applying a predetermined current to the semiconductor laser 111, and a modulation applying element 113 for superimposing a radio frequency wave of a few megahertz onto the current from the laser activating element 112. This turns on and off the laser at a frequency substantially faster than a sampling interval of a light receiving element, eliminates the discontinuity of the amount of light received occurring in the light receiving element caused by wavelength transition of the laser, and obtains continuous changes capable of being corrected by a temperature compensating circuit or the like. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological optical measurement device, and more particularly to improvement of a light source of a biological optical measurement device using a semiconductor laser as a light source.

[0002]

2. Description of the Related Art A biological light measuring device irradiates a subject with laser light of a specific wavelength from a light source, detects light transmitted through the subject or light reflected by the subject with a light receiving element, and circulates blood based on the amount of light. , A device for obtaining biological information such as hemodynamics and hemoglobin changes. Recently, using an optical fiber, an area including a plurality of measurement points is inspected, and biological information about the area, specifically, hemoglobin movement is displayed as an image, or an active area of the brain is measured. The optical topography device has been proposed and put into practical use.

As a light source of such a living body optical measuring device, for example, an infrared semiconductor laser having an oscillation wavelength of 780 nm or 830 nm is used. In an optical topography device that measures a plurality of measurement points, a modulation signal of several kHz is superimposed and driven on such a semiconductor laser in order to identify a plurality of channels, and the semiconductor laser emits light.

[0004]

Generally, the oscillation wavelength of a semiconductor laser has temperature dependence, and the wavelength shifts as the temperature of the light source itself rises. In order to eliminate the influence of the transition of the wavelength of the semiconductor laser, the warm-up time is usually about 30 minutes, and the measurement is performed with the light source temperature stable. It gradually rises and hinders accurate measurement.

Specifically, as shown in FIG. 8, the wavelength transition due to the temperature fluctuation of the semiconductor laser is a discontinuous change, while the light receiving characteristic of the light receiving element has wavelength dependence. Such a discontinuous change in amount appears as a discontinuous change in the amount of received light. Such discontinuous changes are difficult to distinguish from information from the living body that is the measurement target, and hinder accurate optical measurement of the living body. Further, it is difficult to correct such a discontinuous change by a known correction technique such as a temperature compensation circuit.

Generally in the field of information and communication, a technique is known in which a laser diode (LD) as a light source is driven by being subjected to high frequency modulation of several hundred MHz to cause multimode emission and eliminate the influence of mode hop. In the optical measurement of living body for measuring a minute amount of analog, such high frequency modulation cannot be adopted because it causes measurement noise.

Therefore, it is an object of the present invention to provide a living body optical measurement device capable of preventing a decrease in measurement accuracy due to a wavelength transition of a light source and performing a highly accurate measurement. Another object of the present invention is to provide a living body optical measurement device capable of accurate measurement with a relatively short warm-up time.

[0008]

Means for Solving the Problems A living body optical measurement system according to the present invention that achieves the above-mentioned object transmits light to a living body by emitting light from a light emitting means that emits light of a predetermined wavelength, In a living body optical measuring device comprising a light receiving means for receiving light reflected from a living body and a signal processing means for obtaining living body information from the amount of light detected by the light receiving means, a wavelength transition of light generated by the light emitting means with respect to temperature change Is provided with a means for converting the wavelength into a continuous wavelength change.

According to one aspect of the present invention, the light emitting means includes a semiconductor laser and a laser driving element, and includes a modulation applying element for applying a high frequency of several MHz to the current from the laser driving element. The wavelength transition with respect to the change is converted into a continuous wavelength change.

According to another aspect of the present invention, the light emitting means includes a plurality of semiconductor lasers, and the light from the plurality of semiconductor lasers is combined by the optical coupling means, so that in the combined light, individual temperatures are obtained. The wavelength transition with respect to the change is converted into a continuous wavelength change.

The living body optical measurement system of the present invention preferably comprises means for correcting a continuous wavelength change of light generated by the light emitting means. As the correcting means, for example, a temperature compensating circuit for correcting the light output of the light emitting means can be adopted. Alternatively, the signal processing means may employ software means for performing a calculation for compensating for the change in the amount of received light due to the change in wavelength.

According to the present invention, due to the wavelength transition of the light source,
By changing the discontinuous change in the amount of received light into a continuous change, it is possible to eliminate a measurement error caused by the discontinuous change and perform accurate biological light measurement.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The biological optical measurement device of the present invention will be further described below based on the embodiments shown in the drawings.

FIG. 1 is a diagram showing an overall outline of an optical topography apparatus to which the present invention is applied. This optical topography device is a light source unit 1 for irradiating a test region of a subject with light of a predetermined wavelength, and light transmitted through the test region of the subject or light reflected and scattered at the test region (hereinafter, collectively The optical measurement unit 2 having a light receiving element for detecting (transmitted light), the irradiation optical fiber 6 for guiding the light from the light source unit 1 to the inspection site of the subject and the transmitted light from the inspection site to the optical measurement unit. In order to bring each tip of the guiding detection optical fiber 7 into contact with the test site of the subject, a probe 3 that detachably fixes each tip, and blood hemoglobin based on the signal measured by the optical measurement unit 2. A signal processing unit (4) for creating a biometric signal representing a quantity or the like and imaging it.

The light source unit 1 modulates the light from the semiconductor laser 11 that emits light having a predetermined wavelength in the visible to infrared wavelength range, for example, 780 nm or 830 nm, and the light from the semiconductor laser 11 at a plurality of different frequencies. And a plurality of optical modules 12 each having a modulator for As a method of modulation, there are a method of modulating a drive signal of the semiconductor laser 11 and a method of modulating light from the semiconductor laser 11 using an optical element, but either method may be used. Also, as the semiconductor laser 11, 2
When light of wavelengths is used, the light of these two wavelengths is mixed, then modulated to a different frequency for each optical module, and irradiated to the inspection site of the subject through the optical fiber 6.

The optical measuring unit 2 is connected to the detecting optical fiber 7, and a photoelectric conversion element such as a photodiode 21 for converting the light guided by the detecting optical fiber 7 into an electric signal corresponding to the amount of light, and the photodiode 21. Lock-in amplifier 22 for selectively detecting a modulation signal corresponding to an irradiation position and a wavelength, and an A / D converter 23 for A / D converting the signal from the lock-in amplifier 22. Consists of. A / D
The output of the converter 23 is sent to the signal processing unit 4, where it is subjected to signal processing, and then an image showing changes and distribution of the hemoglobin amount and the like is created and displayed. The signal processing unit 4 is a control unit that controls the entire device, a storage unit 41 that stores conditions and the like necessary for control and signal processing, a signal processing unit 42, and a display device that displays an image.
It has 5.

The details of the light source unit 1 are shown in FIG. The semiconductor laser 111 is connected to a drive element 112 connected to a power supply circuit (not shown), and a current required to obtain an optical output of a predetermined wavelength is supplied via the drive element 112. Here, when the light of the semiconductor laser 111 is modulated by modulating the drive signal, the current supplied to the plurality of semiconductor lasers 111 is several kHz to 10 kHz in order to identify each channel.
It is modulated by the frequency of. The semiconductor laser 111 is
It is connected to a modulation applying element 113 that superimposes a frequency of several MHz on the current from the drive element 112. This modulation applying element 1
As shown in FIG. 3, 13 turns on / off the semiconductor laser 111 at a frequency of several MHz.

In the light source section 1 having such a structure, when the temperature rises with the start of driving the semiconductor laser 11, the oscillation wavelength also changes as shown in FIG. 8, but a high frequency of several MHz is superimposed on the driving current. By doing so, lighting and extinguishing are repeated at this frequency. This is the same state as shown in FIG. 4 in which oscillation is caused at two wavelengths, the wavelength λ1 before the transition and the wavelength λ2 after the transition, and the transition of the wavelength λ2 appears as the temperature rises. It becomes more frequent.
And the frequency (several MHz) of repeated turning on and off is
Since it is sufficiently faster than the sampling interval (usually about 0.1 seconds) by the light receiving element, the measured light quantity is 401 in FIG.
It becomes a continuous change as shown in. That is, in the light receiving element, as the time elapses (that is, the temperature rises), the wavelength λ1
The light continuously changing from the low value at the time to the value at the wavelength λ2 is detected.

As described above, according to this embodiment, the light from the light source laser is turned on and off at a frequency sufficiently faster than the sampling interval of the light receiving element, so that the wavelength which is a discontinuous change due to the temperature change is changed. The transition can be converted so that the light-receiving side has a continuous change in the amount of received light. As a result, it is possible to easily perform temperature correction using hardware such as a temperature compensation circuit or software such as fitting treatment during measurement signal analysis processing. If the wavelength changes continuously with the temperature change, it is possible to perform optical measurement without temperature correction, but it can be corrected by a temperature compensation circuit or signal processing as described below. desirable.

FIG. 5 shows an example of a light source section provided with a temperature compensation circuit.
Shown in. Here, the same elements as those in FIG. 2 are indicated by the same numbers. In the illustrated example, the change in light quantity shown in FIG. 4 is regarded as a primary change, and the temperature compensating circuit inputs the output of the thermistor 114 having a primary output characteristic opposite to the change in light quantity to the drive element 112 of the semiconductor laser 111. I have to. This makes it possible to obtain a measurement result that does not depend on temperature.

When the correction is performed by software,
For example, as shown in FIG. 6, a temperature sensor 115 is attached to the light source unit 11, and the temperature of the light source unit 1 detected by the temperature sensor 115 is sent to the signal processing unit 4. On the other hand, the storage unit 41 of the signal processing unit 4 stores a correction amount according to the temperature in advance. Alternatively, when the amount of received light is a linear function of temperature, the parameter is stored. Then, the measured light amount is corrected using the temperature detected by the temperature sensor 115 during the light measurement and the correction amount at that temperature.

Next, a second embodiment of the present invention will be described.
In this embodiment, the temperature at which the wavelength transition of the laser occurs is
Taking advantage of the fact that different laser elements of the same type differ from one solid to another, by combining the light from multiple laser elements into a single light source, the effects of wavelength transitions of individual laser elements are smoothed, and as a whole, it is continuous. The changes are made.

An outline of the light source laser according to the second embodiment is shown in FIG. As shown, the irradiation optical fiber 6
Are connected to a plurality of semiconductor lasers LD1 to LDi via an optical coupler 71. The semiconductor lasers LD1 to LDi generate light of the same type and the same wavelength.

The light generated by the semiconductor lasers LD1 to LDi is
The light is mixed by the optical coupler 71, and the living body is irradiated from the tip of the optical fiber 6. At this time, as the temperature of the light source unit 1 changes, the respective semiconductor lasers LD1 to LDi independently cause wavelength transitions according to their individual temperature-dependent characteristics. Is reduced and can be regarded as a continuous change. In order to smooth the wavelength transition, the larger the number of semiconductor lasers (i), the better. However, the number is practically several to ten or more.

When a light source laser having a plurality of wavelengths is used as the light source 1, as shown in FIG. 7B, a plurality of laser elements LD11 to LD1i and LD21 to LD2i are provided for each wavelength.
The optical couplers 72 and 73 may be mixed together, and the optical coupler 74 may be further mixed. Alternatively, as shown in FIG. Can be irradiated. By thus mixing and irradiating from one optical fiber tip, it is possible to perform measurement without lowering the position resolution even when measuring at a plurality of measurement points.

Also in the present embodiment, as shown in FIG. 5 or 6, by providing a temperature compensating circuit or performing correction processing in the signal processing section, it is possible to obtain a measurement result having no temperature dependence.

[0027]

According to the present invention, since the discontinuous change in the amount of light received due to the wavelength transition of the laser can be smoothed, the fluctuation of the optical output due to the temperature change can be easily corrected, and a highly accurate living body can be obtained. Optical measurement is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall outline of a biological optical measurement device to which the present invention is applied.

FIG. 2 is a diagram showing an embodiment of the light source unit of FIG.

FIG. 3 is a diagram showing an output of a modulation applying element.

FIG. 4 is a diagram showing a relationship between a laser after modulation and a light amount measured by a light receiving element.

FIG. 5 is a diagram showing an example of a light source section provided with a temperature compensation circuit.

FIG. 6 is a diagram showing another embodiment of the biological optical measurement device according to the present invention.

FIG. 7 is a diagram showing another embodiment of the biological optical measurement device according to the present invention.

FIG. 8 is a diagram showing temperature dependence of a semiconductor laser.

[Explanation of symbols]

1 ... Light source part (light emitting means), 2 ... light measuring part, 4 ...
Signal processing unit, 11 (111) ... Semiconductor laser, 113 ...
Modulation applying element, 114 ... Temperature compensation circuit, 115 ... Temperature sensor

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Claims (6)

[Claims] 1. A light emitting means for generating light of a predetermined wavelength,
In a living body optical measurement device comprising a light receiving means for receiving light transmitted through or reflected by a living body by irradiating light from the light emitting means, and a signal processing means for obtaining living body information from the amount of light detected by the light receiving means. A living body optical measurement device comprising means for converting a wavelength transition of light generated by the light emitting means with respect to a temperature change into a continuous wavelength change. 2. The light emitting means comprises a semiconductor laser and a laser driving element, and the converting means is a modulation applying element for applying a high frequency of several MHz to the current from the laser driving element. Biological light measurement device. 3. The living body according to claim 1, wherein the light emitting means includes a plurality of semiconductor lasers, and the converting means is an optical coupling means for combining lights from the plurality of light source lasers. Optical measuring device. 4. The living body optical measurement apparatus according to claim 1, further comprising means for correcting a continuous wavelength change of light generated by the light emitting means. Optical measuring device. 5. The biological optical measurement device according to claim 4, wherein the correcting unit is a temperature compensating circuit that corrects the light output of the light emitting unit. 6. The biological optical measurement device according to claim 4, wherein the correction means is software means provided in the signal processing means and performing a calculation for compensating a change in the amount of received light due to a wavelength change. .