JP2009000424A - Biological light measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological light measurement apparatus which achieves high-precision measurement and improves precision of signals by suppressing effects of signals of the other sets. <P>SOLUTION: In the biological light measurement apparatus, a detector 6 converts a detection signal into electric current, an amplifier 13 converts the electric current into voltage, and an analog switch section 14 carries out ON or OFF of the detection signal at a predetermined cycle. The analog switch section 14 attenuates strong signals from the other sets by synchronizing with switching of a light source. A low-pass cut off filter section 15 removes fluctuations due to dark current of the detector 6 or effects of external light due to external illumination or the like. A plurality of sets of capacitors or resistances are used for the low-pass cut off filter section 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a biological light measurement apparatus that measures the optical characteristics of a subject using light.

  In a conventional high-resolution biological light measurement device, a second set (B surface) of the irradiation probe and detection probe is arranged at an intermediate position between the first set (A surface) and the detection probe. And the influence of the light from a different set of irradiation probes is removed by shifting the irradiation timing of the light from the first set of irradiation probes and the irradiation timing of the light from the second set of irradiation probes. In addition, in the biological light measurement, low-accuracy light detection with high accuracy is required. Therefore, in order to eliminate the dark current fluctuation of the detector and the low-frequency fluctuation of the baseline caused by the signal change due to the light from the outside, a low-frequency cut filter ( Capacitors) are connected in series (see, for example, Patent Document 1).

JP 2001-178708 A

  In the conventional biological light measurement device as described above, the measurement set is separated in a time division manner, but the influence of the strong signal from the other set of irradiation probes is influenced by the low-frequency cut filter. Even in the detection time zone, the measurement signal greatly fluctuates, and the signal accuracy is lowered.

  The present invention has been made to solve the above-described problems, and achieves high-definition measurement while reducing the influence of other sets of signals and improving biological accuracy. The object is to obtain a device.

  The biological light measurement device according to the present invention includes a light source unit that generates light modulated at a predetermined modulation frequency, a plurality of irradiation probes that irradiate the subject with light from the light source unit, and a plurality of light that detects light returning from the subject. A detection probe, a detector that photoelectrically converts light incident on the detection probe, a lock-in processing unit that performs a lock-in process on a signal from the detector using a modulation frequency in a light source unit as a reference frequency, and It has a measuring device body that measures the optical characteristics of the subject based on the signal from the lock-in processing unit, and the lock-in processing unit is provided with a capacitor that removes low-frequency components from the signal from the detector. Is provided with a switch unit for turning on / off a signal input to the capacitor in synchronization with on / off of light irradiation from the irradiation probe.

  The living body light measurement apparatus of the present invention is provided with a switch portion that turns on and off a signal input to the capacitor in synchronization with the on / off of light irradiation from the irradiation probe, thereby realizing high-definition measurement. However, the influence of other sets of signals can be reduced and the signal accuracy can be improved.

The best mode for carrying out the present invention will be described below with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a biological light measurement apparatus according to Embodiment 1 of the present invention. In the figure, the light source unit 1 has a plurality (only one is shown in the figure) of semiconductor lasers 2 and a laser drive circuit 3 for driving the semiconductor lasers 2. Each semiconductor laser 2 emits light having a plurality of wavelengths, for example, 780 nm, in a visible to infrared wavelength region.

  The laser drive circuit 3 applies a direct current bias current to the semiconductor laser 2 and applies intensity modulation to the light emitted from the semiconductor laser 2. In this example, digital modulation using a rectangular wave is used as a modulation method, but repetition of an arbitrary waveform such as a sine wave may be used. A modulation frequency is applied to the laser driving circuit 3 by an oscillator 4.

  The light generated by the light source unit 1 is applied to the head of the subject 5. The light transmitted through the subject 5 is detected by a detector 6 that is a photoelectric conversion unit. The light detected by the detector 6 passes through the skin and the skull, and includes information on cerebral blood flow. That is, the amount of light detected by the detector 6 changes according to the hemoglobin concentration at the measurement point. Therefore, the relative change in the hemoglobin concentration can be measured as the optical characteristic of the subject 5 from the change in the detected light amount.

  A detection signal from the detector 6 is input to the lock-in processing unit 7. The lock-in processing unit 7 performs lock-in processing using a signal having the same phase and the same frequency as the modulation frequency as a reference signal. The signal output from the lock-in processing unit 7 is input to a computer 8 serving as a measurement apparatus main body. The computer 8 measures the amount of light detected by the detector 6, measures the amount of change in hemoglobin concentration in the blood at each measurement point from the measurement result, and displays information on the measurement result on the monitor. As the computer 8, for example, a general-purpose personal computer can be used.

  The subject 5 is equipped with a probe device (not shown) for irradiating the subject 5 with light from the light source unit 1 and detecting the light returning from the subject 5. The probe device has a holder attached to the head of the subject 5 and a plurality of probes attached to the holder.

  FIG. 2 is an explanatory diagram showing the arrangement state of the probes in the biological light measurement device of FIG. The probe includes a plurality of first sets (surface A) of irradiation probes 11a (shown by hatched squares in FIG. 2) and a plurality of first sets of detection probes 11b (shown by squares without hatching in FIG. 2). A plurality of second sets (surface B) of irradiation probes 12a (indicated by circles with diagonal lines in FIG. 2) and a plurality of second sets of detection probes 12b (indicated by circles without diagonal lines in FIG. 2). It is out.

  That is, in FIG. 2, the first set of probes 11a and 11b is indicated by a square, and the second set of probes 12a and 12b is indicated by a circle. In FIG. 2, the irradiation probes 11a and 12a are hatched, and the detection probes 11b and 12b are not hatched. The irradiation probes 11 a and 12 a irradiate the subject 5 with light from the light source unit 1. The detection probes 11b and 12b receive light transmitted through the subject 5. The lights received by the detection probes 11b and 12b are sent to the detector 6, respectively.

  The first set of probes 11a and 11b are arranged in a matrix. The first set of irradiation probes 11a and detection probes 11b are alternately arranged. The second set of probes 12a and 12b are also arranged in a matrix. The second set of irradiation probes 12a and detection probes 12b are also arranged alternately. Further, the second set of probes 12a and 12b is disposed between the first set of probes 11a and 11b. In each set, the pitch between the irradiation probes 11a and 12a and the detection probes 11b and 12b is 30 mm.

  FIG. 3 is an explanatory diagram showing the distribution of measurement points in the biological light measurement apparatus of FIG. In FIG. 3, the measurement points are indicated by squares. Part of the light emitted from the irradiation probes 11a and 12a passes through the cerebral cortex at the measurement point and enters the detection probes 11b and 12b. Accordingly, the measurement point is located between the irradiation probes 11a and 12a and the detection probes 11b and 12b in FIG. There are 45 measurement points (45 channels) in this example, and the pitch between the measurement points adjacent to each other is 15 mm.

  FIG. 4 is a block diagram showing the lock-in processing unit 7 of FIG. The lock-in processing unit 7 includes an amplifier 13, an analog switch unit 14, a low-frequency cut filter unit 15, an AD converter 16, and a lock-in calculation unit 17.

  The detection signals converted into currents by the detector 6 are converted into voltages by the amplifiers 13 and turned on / off at a predetermined cycle by the analog switch unit 14. The analog switch unit 14 attenuates strong signals from other groups in synchronization with switching of the light sources. The analog switch unit 14 has a plurality of analog switches corresponding to the detection probes 11b and 12b.

  The low-frequency cut filter unit 15 removes the influence of extraneous light due to fluctuations caused by the dark current of the detector 6 and external illumination. As the low-frequency cut filter unit 15, a plurality of sets of capacitors and resistors are used.

  The signals that have passed through the low-frequency cut filter unit 15 are converted into digital signals by the AD converter 16 and input to the lock-in calculation unit 17. The lock-in calculation unit 17 is configured by, for example, a DSP (Digital Signal Processor), and extracts a signal synchronized with the reference signal using a modulation frequency, for example, 10 kHz as a reference signal.

  Here, the conversion cycle of the AD converter 16 is set to 100 kHz which is sufficiently larger than the modulation cycle of the light source unit 1. Thereby, the sample Nyquist frequency of the digital signal becomes 50 kHz, and the modulation signal 10 kHz can be sampled with sufficient accuracy.

  FIG. 5 is a circuit diagram showing a signal modulation circuit and a signal detection circuit related to a pair of irradiation probe 11a and detection probe 11b of the biological light measurement apparatus of FIG. The light generated by the semiconductor laser 2 is sent to the irradiation probe 11a through the irradiation optical fiber 18a. The light incident on the detection probe 11b is sent to the detector 6 through the detection optical fiber 18b.

  The pulse generator 19 turns on and off the light source and generates a pulse for turning on and off the analog switch unit 14. The modulation signal from the oscillator 4 and the pulse signal from the pulse generator 19 are input to the AND gate 20. An output from the AND gate 20 is input to the laser driving circuit 3. As a result, the laser drive circuit 3 turns the semiconductor laser 2 on and off in synchronization with the pulse generated by the pulse generator 19.

  The pulse signal from the pulse generator 19 is also input to the analog switch unit 14. As a result, the analog switch unit 14 turns on / off the signal input to the low-frequency cut filter unit 15 in synchronization with the pulse generated by the pulse generator 19.

  Next, the operation will be described. FIG. 6 is an explanatory diagram showing a waveform of a control signal for the light source unit 1 of FIG. In the figure, the modulation frequency of the first set of light sources is f1, and the modulation frequency of the second set of light sources is f2. The light source on / off cycle is 20 milliseconds. That is, the light source is turned on / off at a frequency of 25 Hz. At this time, the first set of light sources and the second set of light sources are alternately turned on and off.

  Here, when the irradiation probes 11a and 12a and the detection probes 11b and 12b are arranged with high definition as shown in FIG. While the distance to the set of detection probes 11b is 30 mm, the distance from the other set of irradiation probes 12a to the set of detection probes 11b is 15 mm. For this reason, even if signal attenuation due to attenuation scattering of the living body is taken into account, the signal strength of another set detected by the detector 6 is about 10 times the signal strength of the own set as shown in FIG. 7, for example. .

  When such a signal is input to the low-frequency cut filter unit 15 without passing through the analog switch unit 14, for example, as shown in FIG. 8, a tail of a strong signal from another group is added to the own signal. The measurement signal of the own set greatly fluctuates and the signal accuracy is lowered.

  In contrast, when a signal as shown in FIG. 7 is input to the low-frequency cut filter unit 15 through the analog switch unit 14 and the on / off state of the analog switch unit 14 is synchronized with the on / off state of the light source, Since other sets of signals are removed upstream of the band cut filter unit 15, for example, as shown in FIG. 9, the influence of the other sets of signals may remain on the signal after passing through the low band cut filter unit 15. Absent. Therefore, while eliminating the baseline fluctuation in the measurement time range of the measurement signal, it is possible to remove the base change due to another set of strong light, and to enable high-precision (high resolution) measurement with high accuracy simply. Can do.

  Such effects of other sets of signals can be removed by digital signal processing, but in order to process signals with high accuracy, an AD converter with a high voltage accuracy and a wide voltage conversion width is required. In many cases, it is difficult to obtain applicable AD converters, and even if available, they are expensive. In addition, since optimal digitization cannot be performed, it is difficult to obtain sufficient signal accuracy.

In the above example, the digital lock-in calculation unit 17 is shown, but an analog lock-in circuit having a similar function may be used.
In the above example, the analog switch unit 14 is provided between the amplifier 13 and the low-frequency cut filter unit 15, but may be provided between the detector 6 and the amplifier 13. Further, the analog switch unit 14 may be provided in the detector 6, and the current signal may be turned on / off by the detector 6. Further, the sensitivity or amplification factor of the detector 6 may be turned on / off by the analog switch unit 14.
Furthermore, in the above example, the irradiation probes 11a and 12a and the detection probes 11b and 12b are divided into two groups, but may be divided into three or more groups.

It is a block diagram which shows the biological light measuring device by Embodiment 1 of this invention. It is explanatory drawing which shows the arrangement | positioning state of the probe in the biological light measuring device of FIG. It is explanatory drawing which shows distribution of the measurement point in the biological light measuring device of FIG. It is a block diagram which shows the lock-in process part of FIG. It is a circuit diagram which shows the signal modulation circuit and signal detection circuit regarding a pair of irradiation probe and detection probe of the biological light measuring device of FIG. It is explanatory drawing which shows the waveform of the control signal with respect to the light source part of FIG. It is explanatory drawing which shows the waveform of the signal detected with the detector of FIG. FIG. 8 is an explanatory diagram illustrating a signal waveform when the signal of FIG. 7 is input to the low-frequency cut filter unit without passing through the analog switch unit of FIG. 5. FIG. 8 is an explanatory diagram illustrating a waveform of a signal when the signal in FIG. 7 is input to the low-frequency cut filter unit through the analog switch unit in FIG. 5.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light source part, 6 Detector, 7 Lock-in process part, 8 Computer (measuring device main body), 11a 1st set irradiation probe, 11b 1st set detection probe, 12a 2nd set irradiation probe, 12b 2nd set Detection probe, 14 analog switch section.

Claims (2)

A light source unit that generates light modulated at a predetermined modulation frequency;
A plurality of irradiation probes that irradiate the subject with light from the light source unit;
A plurality of detection probes for detecting light returning from the subject;
A detector that photoelectrically converts light incident on the detection probe;
A lock-in processing unit that performs lock-in processing on the signal from the detector using the modulation frequency in the light source unit as a reference frequency, and the optical characteristics of the subject based on the signal from the lock-in processing unit In a biological light measurement device equipped with a measurement device main body for measuring
The lock-in processing unit is provided with a capacitor for removing low frequency components from the signal from the detector,
The living body light measurement apparatus according to claim 1, wherein the capacitor is provided with a switch unit for turning on / off a signal input to the capacitor in synchronization with on / off of light irradiation from the irradiation probe.   The biological light measuring device according to claim 1, wherein the switch unit includes a plurality of analog switches provided between the detector and the capacitor.

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