JP2003254899A - Biological light measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological light measuring apparatus capable of highly accurately measuring very small variations in a flow of blood. <P>SOLUTION: A signal processing part of the biological light measuring apparatus creates a matrix arithmetic expression, on measurement signals acquired at every point of measurement, with measured values and coefficients of variation after correction as variables on the basis of a relational expression between the points of measurement and the coefficients of variation limited to related locations of light irradiation and locations of detection (402) to determine a coefficient (g) of variation with a minimum absolute value of the measured values after correction by the method of least squares (403). The coefficient (g) of variation is used to compute an optimally corrected measured value from the relational expression (404). By this, it is possible to acquire signals from which the effects of the coefficients of variation limited to the locations of light irradiation and the locations of detection are precluded regardless of the types of variations. <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 living body light measuring apparatus for measuring information inside a living body by using light, and particularly, by using detection light from a plurality of measuring positions, measuring an area including these measuring positions. The present invention relates to a biological light measuring device.

[0002]

2. Description of the Related Art A biological light measuring apparatus irradiates a subject with 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 according to the amount of light. It is a device that obtains biological information such as hemodynamics and hemoglobin changes. In recent years, an optical topography device has been proposed, which uses an optical fiber to inspect an area including a plurality of measurement positions and displays biological information about the area, specifically, hemoglobin trends as an image, and put it into practical use. (JP-A-9-98972, JP-A-9-149903, etc.).

Clinical applications of such a biological optical measuring device include, for example, measurement of activation state of hemoglobin change in the brain and measurement of local intracerebral hemorrhage in which the head is measured. It is also possible to measure higher brain functions such as movement, sensation, and thinking in relation to changes in hemoglobin in the brain. These measurements are performed by mounting a probe in which a plurality of optical fiber tips for light irradiation and detection are arranged in a predetermined array on a subject.

[0004]

Brain function measurement using such a biological optical measuring device measures optical changes due to minute blood flow changes associated with brain activity, and therefore minute changes in the measurement system. There is a problem that it is easily affected by optical changes due to changes in probe contact with the skin and the scalp, which reduces the accuracy of measurement signals.

Further, there are various causes of the fluctuation error mixed in the measurement signal, for example, fluctuations in the laser light as the light source, displacement of the probe, changes in the contact state, etc., and it is difficult to reduce these effects as a whole. there were. Therefore, the present invention eliminates the influence of the movement of the subject and the fluctuation of the measuring device,
An object of the present invention is to provide a biological optical measurement device capable of performing highly accurate brain function measurement.

[0006]

In order to achieve the above object, in the biological optical measuring device of the present invention, it is utilized that the measured signal is affected by the fluctuation rate of a specific light irradiation position and a specific light receiving position, Utilizing the relationship between the plurality of measurement signal values and these fluctuation rates, the fluctuation error limited to the light irradiation position and the light receiving position is calculated, and the measurement signal excluding the influence of the fluctuation error is obtained.

That is, the living body light measuring apparatus of the present invention comprises a light source unit for irradiating a plurality of light irradiation positions of a subject with light, and a plurality of light source units arranged at predetermined positions with respect to the plurality of light irradiation positions. At the detection position, the transmitted light from the subject is received and an optical measurement unit that converts the measurement signals from a plurality of measurement positions and a measurement signal from the optical measurement unit is processed, and an area including the plurality of measurement positions. In the biological optical measurement device having a signal processing unit for obtaining biological information, the signal processing unit is included in the plurality of measurement signals, based on the correlation of fluctuation errors limited to the light irradiation position and the detection position, A means for calculating the variation error and correcting the measurement signal is provided.

More specifically, the correcting means creates a matrix operation formula having the corrected signal value and the fluctuation error as variables, and calculates the fluctuation error that minimizes the absolute value of the corrected signal value. As a method of calculating the variation error, for example, the least square method can be used.

According to the living body light measuring apparatus of the present invention as described above, the fluctuation of the light intensity of the light source unit, the displacement of the light irradiation position and the detection position due to the movement of the subject, the slight change of the contact surface, etc. It is possible to eliminate a fluctuation error limited to the light irradiation position and the detection position, and thus it is possible to measure a minute blood flow fluctuation associated with brain function with high accuracy.

Further, since the biological light measuring device of the present invention determines the variation error limited to the light irradiation position and the detection position so as to minimize the absolute value of the corrected signal value, the frequency characteristic of light and Correction can be performed regardless of the type of fluctuation error.

[0011]

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 a biological optical measurement device of the present invention. This biological light measuring device is a light source unit 10 for irradiating the inspection site of the subject 9 with light of a predetermined wavelength.
And a signal from the optical measurement unit 20 having a light receiving element for detecting light transmitted through the inspection region of the subject or light reflected and scattered at the inspection region (hereinafter collectively referred to as transmitted light). And a signal processing unit 30 that creates a biological signal that represents the amount of hemoglobin in blood based on the above, and displays it as an image.

The light source unit 10 is composed of a plurality of (four in the figure) optical modules 11, and each optical module 11 has a predetermined wavelength within a wavelength range from visible light to infrared, for example, two wavelengths of 780 nm and 830 nm. It is equipped with two semiconductor lasers that emit light.
The light source unit 10 also includes an oscillating unit 12 including a plurality of oscillators having different oscillating frequencies. This gives different modulations to the semiconductor lasers. A light emitting diode may be used as the light source instead of the semiconductor laser. The wavelengths used are not limited to the above two wavelengths, and the wavelengths may be changed according to the object to be measured (usually oxygenated hemoglobin and deoxygenated hemoglobin, but other chemical species are also targeted). Is also good.

FIG. 2 shows the configuration of an optical module 11 using a two-wavelength semiconductor laser. As shown in the figure, the optical module 11 includes two semiconductor lasers 13a and 13b (a and b correspond to light of two wavelengths), their drive circuits 14a and 14b, and a condenser lens.
15, an optical fiber 16, an optical coupler 17, and an optical fiber 18. The semiconductor lasers 13a and 13b include drive circuits 14a and 1b.
DC bias current is applied by 4b and oscillator
When the different frequencies are applied by 12, the lights modulated at the different frequencies are emitted.
In the present embodiment, analog modulation is performed using a sine wave, but digital modulation using rectangular waves with different time intervals may be used.

Lights from the semiconductor lasers 13a and 13b are introduced into an optical fiber 16 by a condenser lens 15, respectively, and lights of two wavelengths are mixed by an optical coupler 17 and introduced into one irradiation optical fiber 18. To be done. That is, the two wavelengths of light modulated at different frequencies are introduced into the irradiation optical fiber 18 for each optical module 11.

Irradiating optical fiber 18 and receiving optical fiber 19
The tip of is fixed to a mounting tool (probe) made of, for example, plastic for mounting on the subject 9. The probe is formed with a socket with which these optical fiber tips are engaged, and by engaging the tip with the socket, the optical fiber tips can be arranged in a predetermined arrangement.

An example of the arrangement of the tips is shown in FIG. In this example, the tips of the four irradiation optical fibers 18 indicated by white circles and the tips of the five light receiving optical fibers 19 indicated by black circles are alternately arranged at the intersections of the square lattice. From the tip of the irradiation optical fiber 18, two wavelengths of light having different frequencies depending on the irradiation position are irradiated, and the light reflected or transmitted by the head surface of the subject 9 is the light for reception adjacent to the irradiation optical fiber 18. fiber
It will be detected at 19. Therefore, in the optical measurement, the points between the irradiation optical fiber 18 and the light receiving optical fiber 19 which are adjacent to each other are measured, and the points between these points are the measurement points. In the illustrated example, there are 12 measurement points as indicated by the numbers 1 to 12 in FIG. Although FIG. 3 shows an example in which the optical fiber tip is arranged at the intersection of a 3 × 3 square lattice, the matrix size is not limited to this, and 4 × 4, 5 × 5 or the like may be adopted.

As shown in FIG. 1, the optical measuring section 20 is connected to each light receiving optical fiber 19 and is a photoelectric device such as a photodiode for converting the light guided by the light receiving optical fiber 19 into an electric signal corresponding to the amount of light. A conversion element 21, a modulation signal detection circuit 22 such as a lock-in amplifier for inputting an electric signal from the photoelectric conversion element 21, and selectively detecting a modulation signal corresponding to an irradiation position and a wavelength, and a modulation signal detection circuit. A / D signal from 22
And an A / D converter 23 for conversion.

A photomultiplier tube may be used as the photoelectric conversion element 21. When the photodiode 21 is used, an avalanche photodiode that can realize highly sensitive optical measurement is suitable. The modulation signal detection circuit 22 selectively detects the modulation signal corresponding to the irradiation position and the wavelength, and uses the lock-in amplifier 22 in the case of analog modulation as in the illustrated embodiment. In the case of digital modulation, a digital filter or digital signal processor is used. Further, in this embodiment, since light of two wavelengths is used as irradiation light and there are 12 measurement points, the number of signals to be measured (the number of channels) is 24, and a total of 24 lock-in amplifiers are used as lock-in amplifier modules. Prepare The signal detected for each measurement channel is converted into a digital signal by the A / D converter 23 and sent to the signal processing unit 30.

The signal processing unit 30 processes the signal from the optical measuring unit 20, and performs a calculation for correcting the change amount of blood hemoglobin and various errors included in the change amount, and a calculation unit 31.
A storage unit 32 for storing the calculation result of 31 and data necessary for the calculation, and a display unit 33 for displaying the time course of the measurement signal and the topography image as the calculation result are provided.

Next, the signal correction processing in the arithmetic unit 31 of the signal processing unit 30 will be described with reference to FIG. These correction processing procedures are incorporated in the signal processing unit 30 in advance as programs. In the following description, one wavelength signal of the measurement signals will be described, but correction processing is performed for signals of other wavelengths in the same procedure.

First, a matrix arithmetic expression is calculated from a relational expression including the signal values of the measurement signals S1 to S12 input from the optical measuring unit 20 to the signal processing unit 30 and the variation rate due to external factors (step 401, 402). External factors include variations in the light intensity of the light source unit 10 and variations in the contact position and angle of the tip of the measurement probe (optical fiber). The rate of variation due to these external factors is limited to the measurement probe. Rate is g1
~ G9. When one measurement signal is considered, the signal is affected by each one of the light irradiation position and the detection position. It can be represented by 1).

[0023]

[Equation 1] In the formula, i is the measurement channel number from 1 to 12, and n and m are S
i is the number of the associated grid point. Taking the logarithm of this equation (1),

[Equation 2] And this

[Equation 3] Substituting into, the matrix operation formula (4) using these variables is created.

[0024]

[Equation 4] In Expression (4), A is a matrix derived from the relationship between the grid points and the measurement points, and has 1 and 0 as elements. In particular,
As shown in FIG. 5, it is a matrix of size 12 × 9 (the number of measurement points × the number of grid points) for connecting the measurement signal of one measurement point to the variation rate of the two grid points associated therewith. X in the equation (4) indicates the logarithm of the measured value after correction.

Next, the logarithm z (log (g)) of the fluctuation rate g when the correction is optimized is calculated based on this matrix calculation formula. That is, when the correction is optimized, X indicates the minimum absolute value when z is a variable. Therefore, the square value of X is calculated, and the optimum Z is obtained by the least square method. The variation rate g is obtained from z thus obtained (step 40
3) By using this, the equation (2) is calculated to obtain the optimum corrected measured value Sti (step 404).

As described above, according to the present embodiment, the correlation of the fluctuation rates limited to the respective light irradiation positions and detection positions is utilized,
Since the variation rate that can be optimally corrected is found, the optimally corrected measured value can be obtained regardless of the frequency characteristic of the measured value and the type of variation.

In the above embodiment, the case where the optimum correction term is obtained by the least square method has been described. However, the mathematical method for obtaining the optimum correction term is the least square method as long as it is a method for obtaining independent displacement of each probe. It can be adopted without limitation.

Based on the measurement signals thus corrected, for example, changes in oxygenated hemoglobin concentration, changes in deoxygenated hemoglobin concentration, and changes in total hemoglobin concentration are calculated (FIG. 4, FIG.
Step 405), as in the case of signal processing in normal biological light measurement, for example, it is displayed as a time-course graph displaying time-series changes, or the hemoglobin change amount at each measurement point is contour-lined or colored. It can be displayed as an image (topography image). It is also possible to make various determinations on brain function from the numerical value of the change in concentration.

[0029]

According to the present invention, there is provided a living body optical measurement system capable of measuring minute changes in blood flow associated with brain function with high accuracy. Further, according to the present invention, it is possible to perform the measurement with the influence of the variation error minimized regardless of the type of the variation error.

[Brief description of drawings]

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

FIG. 2 is a diagram showing details of an optical module.

FIG. 3 is a diagram showing an example of an array of light irradiation positions and detection positions.

FIG. 4 is a diagram showing an example of a correction processing procedure performed by a signal processing unit.

FIG. 5 is a diagram showing an example of a matrix arithmetic expression used in a correction process performed by a signal processing unit.

[Explanation of symbols]

10 ... Light source part, 18 ... Irradiation optical fiber, 19 ...
Optical fiber for receiving light, 20 ... Optical measuring unit, 30 ... Signal processing unit, 31 ... Calculation unit

Claims (3)

[Claims] 1. A light source unit for irradiating light to a plurality of light irradiation positions of a subject, and a plurality of detection positions arranged at predetermined positions with respect to the plurality of light irradiation positions. An optical measurement unit that receives transmitted light and converts it into a measurement signal at a plurality of measurement positions, and a signal processing unit that processes the measurement signal from the light measurement unit and obtains biological information of a region including the plurality of measurement positions. In the biological optical measurement device comprising, the signal processing unit is included in the plurality of measurement signals, based on the correlation of the fluctuation error limited to the light irradiation position and the detection position, calculates the fluctuation error, the measurement A living body optical measurement device comprising means for correcting a signal. 2. The correcting means creates a matrix arithmetic expression having the corrected signal value and the fluctuation error as variables, and calculates the fluctuation error that minimizes the absolute value of the corrected signal value. The biological optical measurement device according to claim 1. 3. The biological optical measurement device according to claim 2, wherein the variation error is calculated by a least square method.