JP2009201937A - Biological light measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological light measurement apparatus capable of keeping high precision in detection even when the number of channels is increased, while using the modulation of a spectrum diffusion system. <P>SOLUTION: A modulation control part 9 alternately turns on/off a pseudo noise signal for driving the semiconductor laser 2 of the first set and a pseudo noise signal for driving the semiconductor laser 2 of the second set in order to alternately turn on/off the semiconductor laser 2 of the first set and the semiconductor laser 2 of the second set. A detector 6 alternately turns on/off the detecting part of the first set and the detecting part of the second set with referring to a signal from the modulation control part 9. <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 the conventional biological light measurement device, light having different wavelengths is generated by the first and second semiconductor lasers. The first pseudo noise sequence signal is supplied from the first pseudo noise sequence generator to the first laser driver that drives the first semiconductor laser. The second pseudo noise sequence signal is supplied from the second pseudo noise sequence generator to the second laser driver that drives the second semiconductor laser. Thereby, the light intensity amplitudes output from the first and second laser drivers are digitally modulated (ASK) by a spread spectrum method (see, for example, Patent Document 1).

Japanese Patent No. 3623743

  However, in a high-definition type biological light measurement device in which the arrangement density of the irradiation probe and the detection probe is increased in order to increase the spatial resolution, even if the laser beam is modulated by the spread spectrum method, it is not between the irradiation probe and the detection probe. Since strong light from another set of arranged irradiation probes is incident on the detection probe, the detection accuracy of the measurement signal from the original irradiation probe deteriorates.

  The present invention has been made to solve the above-described problems, and provides a biological optical measurement device that can maintain high detection accuracy even when the number of channels is increased while using spread spectrum modulation. For the purpose.

The biological light measurement apparatus according to the present invention includes a plurality of first sets of irradiation probes that irradiate a subject with light, light that is arranged at a predetermined interval with respect to the first set of irradiation probes, and returns light from the subject. A plurality of first detection probes to be detected, a plurality of second sets of irradiation probes for irradiating the subject with light, and light returned from the subject with a predetermined interval with respect to the second set of irradiation probes. A plurality of second sets of detection probes for detecting a light source, a plurality of first sets of light sources corresponding to the first set of irradiation probes, and a plurality of second sets of light sources corresponding to the second set of irradiation probes And the spread spectrum method, the light emitted from the light source unit is subjected to intensity modulation encoded with a pseudo noise signal, and the pseudo noise signal and the second set of light sources for driving the first set of light sources are provided. Alternating with pseudo-noise signal for driving And a modulation control unit for down-off.
In addition, the biological light measurement apparatus according to the present invention includes a plurality of irradiation probes that irradiate a subject with light, and a plurality of detection probes that are disposed at a predetermined interval with respect to the irradiation probe and detect light returning from the subject. A light source unit including a plurality of light sources corresponding to the irradiation probe, and a modulation control unit that applies intensity modulation encoded with a pseudo-noise signal to light emitted from the light source unit by a spread spectrum method, The light emitted from the light source unit is periodically turned on / off by periodically turning on / off the pseudo noise signal, and at least one bit dummy signal is added before the pseudo noise signal for one cycle. .

The biological optical measurement device of the present invention alternately turns on and off the pseudo noise signal for driving the first set of light sources and the pseudo noise signal for driving the second set of light sources. The influence of light from the light source can be removed, and high detection accuracy can be maintained even when the number of channels is increased while using spread spectrum modulation.
In addition, the pseudo-noise signal is periodically turned on and off to periodically turn on and off the light emitted from the light source unit, and at least one bit dummy signal is added before the pseudo-noise signal for one cycle. Therefore, signal fluctuations that occur when switching from off to on can be removed, and high detection accuracy can be maintained even when the number of channels is increased while using spread spectrum modulation.

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 of (only one is shown in the figure) semiconductor lasers 2 that are light sources, and a laser drive circuit 3 that drives each of the semiconductor lasers 2. Each semiconductor laser 2 emits light having a plurality of wavelengths in the visible to infrared wavelength region, for example, light of 780 nm, according to a biological material to be measured.

  The laser drive circuit 3 applies a DC bias current to the semiconductor laser 2 and applies intensity modulation encoded with a pseudo-noise signal to the light emitted from the semiconductor laser 2. In this example, digital modulation (ASK) based on spread spectrum (SS) is used as a modulation method. A pseudo noise signal having a fundamental frequency (chip frequency) f0 is applied to the laser driving circuit 3 by the oscillator 4. The oscillator 4 is controlled by a modulation control unit 9 made of, for example, FPGA.

  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 biological substance concentration at the measurement point, for example, the hemoglobin concentration. Therefore, the relative change in the concentration of the biological material 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 data processing unit 7. The data processing unit 7 extracts a detection signal for each measurement point using the pseudo noise signal from the oscillator 4 as a reference signal. A signal output from the data processing unit 7 is input to the computer 8. The computer 8 measures the detected light amount from the detection signal, measures the amount of change such as 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 points are located between the irradiation probe 11a and the detection probe 11b and between the irradiation probe 12a and the detection probe 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.

  The light source unit 1 includes a plurality (eight in this example) of the first set of semiconductor lasers 2 corresponding to the first set of irradiation probes 11a and a plurality of (6 in this example) corresponding to the second set of irradiation probes 12a. A second set of semiconductor lasers 2 are provided. When the irradiation probes 11a and 12a and the detection probes 11b and 12b are arranged with high definition as shown in FIG. 2, the light irradiation timing is shifted between the first set of semiconductor lasers 2 and the second set of semiconductor lasers 2. . That is, the first set of semiconductor lasers 2 and the second set of semiconductor lasers 2 are turned on and off alternately.

  On the other hand, the detector 6 includes a plurality (eight in this example) of first detection units corresponding to the first set of detection probes 11b and a plurality of (in this example) corresponding to the second set of detection probes 12b. Six) second sets of detection units, and a plurality of analog switches for turning on and off the detection operation by the detection units, respectively. For example, a photodiode is used as each detection unit. The first set of detection units and the second set of detection units are alternately turned on / off in synchronization with the on / off of the corresponding semiconductor laser 2.

  FIG. 4 is a block diagram showing the data processing unit 7 of FIG. The data processing unit 7 includes an amplifier 13, an AD converter 14, and a demodulation calculation unit 15.

  The light intensity signals converted into currents by the detector 6 are converted into voltages by the amplifiers 13 respectively. The light intensity signal output from the amplifier 13 is converted into a digital signal by the AD converter 14 and input to the demodulation arithmetic unit 15.

  Here, the conversion cycle of the AD converter 14 is set to 100 kHz, which is sufficiently larger than the fundamental frequency of the pseudo noise signal 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.

  The demodulation calculation unit 15 is configured by, for example, a DSP (Digital Signal Processor), and performs extraction of a signal synchronized with a reference signal, that is, extraction of a signal for each measurement point, using a pseudo noise signal used for light source modulation as a reference signal.

  Here, the spread spectrum method will be described. The spread spectrum method is a communication method using a pseudo noise signal, and is used as a modulation method of a communication signal such as an audio signal. By using the spread spectrum system, signals from a large number of transmitters can be simultaneously received by one receiver and demodulated as signals from the respective transmitters.

  Further, the pseudo noise signal is a set of signal sequences composed of 0 and 1 and having a finite length. Among such sets, the generation of specific crosstalk and beat signals between different chords can be prevented in a specific set. In addition, a large number of separable signals can be generated in a narrow frequency band.

  Furthermore, the spread spectrum method includes a direct spread method and a hopping method. The direct spreading method is a method of multiplying signal data by a pseudo-random number sequence having a predetermined bandwidth, broadening the frequency band of the data sequence itself, modulating it, and transmitting it. The hopping method is a method of transmitting data while changing the channel at a very short time interval (about 0.1 second) even though the frequency band used per channel is relatively narrow.

  In this embodiment, an example using a direct diffusion method suitable for measurement is shown, but a hopping method can be added to this to further reduce the influence of external noise light.

  There are a plurality of pseudo-noise signal sequences. Among them, the Hadamard sequence has a sum of 0 in the sequence (when digital values of 0 and −1 are used) and is suitable for the measurement modulation method. At the same time, it is easy to create. In addition, an M sequence that is widely used for communication is also applicable.

  The laser modulation waveform is preferably a digital modulation waveform using a rectangular wave, but other waveforms such as a trapezoidal wave can also be used.

  Since signals from the plurality of irradiation probes 11a and 12a are simultaneously input to the detection probes 11b and 12b, it is necessary to separate the signals input to the detection probes 11b and 12b according to the irradiation probes 11a and 12a. For this reason, in this embodiment, a Hadamard sequence pseudo-noise signal is used.

  Further, the modulation control unit 9 turns on and off the first set of semiconductor lasers 2 and the second set of semiconductor lasers 2 alternately, so that a pseudo noise signal for driving the first set of semiconductor lasers 2 The pseudo noise signals for driving the second set of semiconductor lasers 2 are alternately turned on / off. Further, the detector 6 refers to the signal from the modulation control unit 9 and alternately turns on and off the first set of detection units and the second set of detection units.

  FIG. 5 is a block diagram showing the demodulation calculation unit 15 of FIG. The demodulation calculation unit 15 includes a multiplication unit 16 and an addition calculation unit 17. The multiplication unit 16 performs a multiplication process with the reference signal sequence of 1, −1 corresponding to 1, 0 of the Hadamard sequence pseudo-noise sequence used for modulation and the measurement data. The addition operation unit 17 obtains an addition average over the entire period of the pseudo-noise signal in the ON period for the numerical values after multiplication of the respective sample points obtained by the multiplication unit 16.

  Thereby, signals from the desired irradiation probes 11a and 12a can be selectively extracted, and random fluctuations due to other pseudo noise signals and external light can be removed.

  Furthermore, in this embodiment, as shown in FIG. 6, the semiconductor laser 2 is turned on / off at a cycle that is a multiple of one cycle of the pseudo-noise signal. That is, while the semiconductor laser 2 is on, laser light is generated in the form of pulses encoded by the pseudo noise signal. In addition, during the period when the semiconductor laser 2 is off, a signal string in which only 0s are arranged is supplied from the oscillator 4 to the laser driving circuit 3.

  However, in this embodiment, a dummy signal (dummy pulse) of one pulse or more (at least one bit) is added before the pseudo-noise signal for one cycle. At the time of demodulation, one period of the pseudo noise signal excluding the dummy signal is calculated and demodulated by the above method. As a result, signal fluctuations that occur when switching from off to on can be eliminated.

  That is, when the laser beam is turned on after the 25 ms off period has elapsed, overshoot occurs due to a rapid temperature change in the laser light. On the other hand, a stable signal can be measured by adding a dummy signal.

  At this time, if a pulse signal having a chip width of spread spectrum modulation is used as the dummy signal to be added, the circuit configuration can be simplified. In addition, by controlling the number of pulses of the dummy signal to be added according to the time width in which the occurrence of overshoot is assumed, it becomes possible to easily cope with the laser characteristics.

In such a biological light measurement device, the pseudo noise signal for driving the first set of semiconductor lasers 2 and the pseudo noise signal for driving the second set of semiconductor lasers 2 are alternately turned on / off. The influence of light from another set of semiconductor lasers 2 can be removed, and high detection accuracy can be maintained even when the number of channels is increased while using spread spectrum modulation.
Also, the pseudo noise signal for the first set of semiconductor lasers 2 and the pseudo noise signal for the second set of semiconductor lasers 2 can be overlapped. In this case, the configuration of the modulation control unit 9 can be facilitated. it can.

  Furthermore, since a dummy signal of at least 1 bit is added before the pseudo-noise signal for one cycle, it is possible to remove the fluctuation of the signal that occurs when switching from off to on, and using spread spectrum modulation, Even if the number of channels is increased, high detection accuracy can be maintained.

  Here, when the lock-in method is used as the signal separation method, the modulation frequency of a certain semiconductor laser 2 is 10 kHz, and in order to avoid interference, on / off of the signal is performed every 20 milliseconds, that is, 25 Hz, modulation is performed at 10 kHz. What has been received will be further modulated at 25 Hz. For this reason, the measurement signal has sideband signal components at intervals of 25 Hz of 10025 Hz, 10050 Hz,... In addition to the modulation frequency of 10 kHz of the measurement signal, for example.

  Therefore, in the lock-in method, a high frequency component of 20050 Hz and a low frequency component of 25 Hz are generated after the multiplication processing unit. As a result, the frequency position of the signal in the low-pass filter is as shown in FIG. 7, and a signal deviated from the original center frequency is generated. Therefore, it is impossible to capture all signals with the narrow-band low-frequency filter. Yes, the accuracy of the measurement signal will deteriorate.

  In this case, the S / N ratio can be improved by creating and adding a low-frequency filter at a position shifted by 25 Hz with a sufficiently narrow bandwidth. Can not.

  Further, when the irradiation probes 11a and 12a and the detection probes 11b and 12b are arranged with high definition as in this embodiment, the sideband is repeatedly generated at 25 Hz when the modulation is turned on / off. Further, when signals from a large number of semiconductor lasers 2 are detected at the same time, even if the modulation frequency is shifted, there is a high possibility that sidebands of signals from other sets of semiconductor lasers 2 are mixed into the original measurement signal.

  On the other hand, for example, if high-density modulation is performed with an ideal sine wave without using an on / off modulation waveform, the sidebands are only two near the fundamental frequency, so that mixing of signals can be prevented. . However, since the laser has nonlinearity, it is difficult to synthesize the light source waveform into a sine wave. Also, mutual interference cannot be reduced sufficiently.

  For this reason, in an apparatus such as a biological light measurement apparatus that needs to emit light at a plurality of wavelengths or a plurality of semiconductor lasers 2 at the same time, it is difficult to select a modulation frequency for signal separation. is there. In this embodiment, since the spread spectrum method using the pseudo noise signal is used, such a problem can be solved.

In the case where the semiconductor laser 2 is not periodically turned on / off, for example, when measuring only one of the measurement points of the first set and the second set, for example, at a frequency of an appropriate interval of about 100 kHz, for example. If the signal is modulated and demodulated by a lock-in circuit, the SN ratio can be improved. In other words, it is possible to provide an apparatus configuration that has both functions of the spread spectrum method and the lock-in method and can select either one of the methods.

In the above example, a dummy signal is added before the pseudo-noise signal for one period. However, a dummy pulse is included in the head part of the pseudo-noise signal, and the dummy pulse part is canceled (invalidated) by demodulation calculation. You may do it.
Furthermore, in the above example, the measurement points are divided into two groups of the first group and the second group, but may be divided into three groups or more.

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 data processing part of FIG. It is a block diagram which shows the demodulation calculating part of FIG. It is explanatory drawing which shows an example of the signal supplied to a laser drive circuit from the transmitter of FIG. It is explanatory drawing which shows the frequency distribution of the signal in a lock-in system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light source part, 2 Semiconductor laser (light source), 6 Detector, 7 Data processing part, 9 Modulation control part, 11a 1st set irradiation probe, 11b 1st set detection probe, 12a 2nd set irradiation probe, 12b Second set of detection probes.

Claims (4)

A plurality of first set of irradiation probes for irradiating the subject with light;
A plurality of first detection probes arranged at a predetermined interval with respect to the first set of irradiation probes and detecting light returning from the subject;
A plurality of second set of irradiation probes for irradiating the subject with light;
A plurality of second sets of detection probes arranged at a predetermined interval with respect to the second set of irradiation probes and detecting light returning from the subject;
A light source unit including a plurality of first sets of light sources corresponding to the first set of irradiation probes and a plurality of second sets of light sources corresponding to the second set of irradiation probes; And a pseudo noise signal for driving the first set of light sources and a pseudo noise signal for driving the second set of light sources. A biological light measurement device comprising a modulation control unit that alternately turns on and off.   2. The biological light measurement apparatus according to claim 1, wherein the modulation control unit turns on and off the first set of light sources and the second set of light sources in a cycle that is a multiple of one cycle of the pseudo-noise signal. .   The biological light measurement device according to claim 1, wherein the modulation control unit adds a dummy signal of at least 1 bit before a pseudo-noise signal for one period. A plurality of irradiation probes for irradiating the subject with light;
A plurality of detection probes which are arranged at a predetermined interval with respect to the irradiation probe and detect light returning from the subject;
A light source unit including a plurality of light sources corresponding to the irradiation probe, and a modulation control unit that applies intensity modulation encoded with a pseudo-noise signal to light emitted from the light source unit by a spread spectrum method,
The modulation control unit periodically turns on and off the pseudo noise signal to periodically turn on and off the light emitted from the light source unit, and at least 1 before the pseudo noise signal for one cycle. A biological light measurement device, characterized by adding a bit dummy signal.

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