JP2012005556A - Optical measurement apparatus for biological function information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire more precise information about deep tissue.SOLUTION: A blood in a living body is roughly classified into a skin bloodstream and a bloodstream in biological tissue. Though a measurement object is the bloodstream in biological tissue, influence of the skin bloodstream due to change in posture affects the measurement since the change in the skin bloodstream around the living body surface is included in a measurement value in a configuration wherein light emitted from a first opening part is received by a second opening part. The bloodstream in biological tissue can be measured more precisely when light receiving intensity around the living body surface in the opening parts and light receiving intensity around the living body surface at an intermediate position between a light emitting point and a light receiving point are subtracted from the overall light receiving amount after assigning weights to them.

Description

  The present invention relates to an apparatus for measuring biological function information using near infrared light.

  Light is effective as a means for easily and non-invasively obtaining information inside a living body, and an apparatus for measuring functional information of a living body using light has been developed. It is generally known that the light absorption characteristics of some kinds of pigments existing in a living body depend on the wavelength. Therefore, for example, if the light absorption characteristics of hemoglobin dyes in blood are measured using two types of light with different wavelengths, the relative amount of oxygenated hemoglobin and deoxygenated hemoglobin, that is, the amount of oxygen consumed is measured. can do.

  As a device for measuring the function of a living body using light having a wavelength from visible to near-infrared, a living body (mainly brain function) optical measuring device called optical topography has been conventionally developed (see, for example, Non-Patent Document 1). .) This is an apparatus for measuring the diffused / reflected light by arranging a light irradiation point and a light receiving point on the surface of a living body (for example, the head), and estimating the oxygen consumption from the light absorption characteristics of the hemoglobin dye.

  A basic conceptual diagram thereof is shown in FIG. When light is irradiated from the opening 1a and received by the opening 1b separated by the distance D, the light received by the light 1b is diffused / reflected light propagated along the propagation path 13. Therefore, it is considered that at the midpoint of the distance D, the propagation path of the deepest c can be measured, that is, the propagation characteristic of the diffuse reflected light due to the blood volume change in the living tissue can be measured. By performing this measurement at a plurality of positions on the surface, the distribution of two-dimensional light propagation characteristics is measured, and the measurement of oxygen consumption in the muscle accompanying exercise and the estimation of the activation state of the brain are performed.

  However, in such a conventional technique, when a set of light irradiation point and light receiving point is considered, a change in the light absorption coefficient occurs in the blood flow in the living tissue in the vicinity of the middle point position. However, most of the light emitted from the air is reflected near the surface of the living body with a high refractive index and diffused and scattered inside. There is a characteristic that light is a part. Furthermore, from the configuration shown in FIG. 8, it is considered that the light actually received includes the light absorption characteristic of skin blood flow due to reflection near the surface. Occurs in the measured value, and there is a problem that the light absorption characteristic of the blood flow in the living tissue cannot be measured accurately.

  In order to solve this problem, a multi-channel topography apparatus has been studied in which a detection probe is arranged at a double density to capture and correct changes in blood volume in the vicinity of the surface layer.

  However, in the above multi-channel topography, since the apparatus becomes large, as a simple correction method that can be applied to a small number of channels, light reception at the same opening as irradiation is used for correction (from the total light reception amount to the vicinity of the opening). A biological light measurement device that is less susceptible to the effects of posture changes has been developed by reducing fluctuations in the measurement values associated with changes in the light absorption coefficient of skin blood flow from the measurement values (Patent Document 1). reference).

  That is, as shown in FIG. 9, the light source has a first light source and a second light source that emit light of the same wavelength, two openings, and two light receiving means, and the light from the first light source is transmitted to the first light source. Irradiate the opening to receive light at the second opening (light reception 1), irradiate the light from the second light source to the second opening and receive light at the first opening (light reception 2), The light source 1 receives light from the first opening (light reception 3), and the light from the second light source receives light from the second opening (light reception 4). The influence of the skin (surface) blood flow is reduced by subtracting the light reception 3 from the light reception 2 by a coefficient corresponding to the light reception intensity.

“Spatial and temporal analysis of human motor activity using non-invasive NIR topology”, Medical Physics vol. 22, pp. 1997-2005, 1995.

JP2007-111461A

  Only by subtracting the received light intensity in the vicinity of the living body surface of the opening according to the received light intensity, the influence of the vicinity of the living body surface between the openings remains, and accurate information on the deep tissue is not yet obtained. Therefore, an object of the present invention is to obtain more accurate information on the deep tissue.

  In the present invention, for the purpose of easily deriving a correction coefficient, in addition to the correction of the same opening described above, correction is also made by taking into account information from a point equidistant from both openings. Accurate deep tissue information was obtained.

  In addition, by providing an irradiation point and a light receiving point at the vertex of the regular triangle and setting a supplementary light receiving point at the center of gravity of the regular triangle, simultaneous correction of three triangular vertices is possible.

  In the present invention, in addition to correction of the same opening, correction is also made by taking into account information from a point equidistant from both openings, thereby obtaining more accurate information on the deep tissue of the living body. In addition, by arranging a supplementary light receiving element at the center of gravity of the triangle, it is possible to simultaneously correct the measurement of the light receiving point at each triangular vertex. Thus, by providing correction light receiving points at the midpoint of the opening and the center of gravity of the triangle, more accurate information on the deep tissue can be obtained.

Overall structure of biological light measuring device in case of triangular arrangement according to the present invention Illustration of optical fiber used in the present invention The figure explaining the connection method between the opening part used for this invention, and an irradiation part and a light-receiving part Principle explanatory diagram of biological light measurement according to the present invention Triangular arrangement of measurement points according to the present invention The figure which shows the correction effect of the near surface absorption change by this invention The figure explaining the measuring method using the light of two wavelengths concerning this invention Principle measurement diagram of conventional biological light measurement Explanatory drawing of the improved measurement method of conventional biological light measurement

  Below, the form for implementing this invention is shown. In order to simplify the description, the case where light of one wavelength is used will be mainly described.

  FIG. 1 shows a configuration of a biological light measurement device in a triangular arrangement according to the present invention. In this embodiment, the openings 1a, 1b, 1c, and 1d are disposed on the surface of the living body and used for light irradiation and return light reception. A lens is provided at the opening for condensing as necessary. The openings 1a, 1b, 1c and the light irradiating / light receiving portions 3a, 3b, 3c and the opening 1d and the light receiving portion 3d are connected by optical fibers.

  The light irradiating / light receiving units 3a, 3b, and 3c convert light and electric signals. In the light irradiation section, an electrical signal is converted into an optical signal by a photoelectric conversion element such as a semiconductor laser, and output through a lens as necessary. The light receiving unit receives light through a lens as necessary, and converts it into an electric signal by a light receiving element such as a photodiode. The light irradiation unit 4 adjusts the light to be irradiated to an amplitude necessary for measurement by performing amplitude modulation according to the frequency as necessary. The light receiving circuits 5a, 5b, 5c, and 5d perform amplification and phase detection on the converted signal as necessary to obtain the received light intensity. The signal processing device 6 is connected to the light receiving circuit 5a and the like via a digital / analog converter and an analog / digital converter 7. The signal processing device 6 adjusts the intensity of incident light, performs signal processing of measurement data, and displays a measurement result on the screen.

  When connecting with a single fiber, the optical fiber for irradiation and light reception are fused and input to the opening. When connecting with a plurality of optical fibers, as shown in FIG. 2, irradiation light and light reception are respectively input to an optical fiber bundle 14 composed of a plurality of optical fibers, and these are bundled and connected to an opening. Even if the arrangement of the optical fibers in the opening is random, the optical fiber for irradiation may be arranged in the central portion, the optical fiber for receiving light may be arranged in the peripheral portion, or the fibers for irradiation and light reception may be arranged randomly.

  In addition, in order to increase the light receiving efficiency, it is possible to make the light receiving fiber thicker than the irradiation fiber or increase the number of fibers. It is also possible to connect a spectroscope between the irradiation unit and the light receiving unit.

  FIG. 3 shows a configuration example in the case where the spectroscope 11 transmits the radiation and inputs it to the opening, and reflects and receives the return light. In order to increase the light receiving efficiency, the spectral ratio of the spectroscope 11 may be designed so that the reflectance is higher than the transmittance. Further, the surface of the housing 15 is processed so as to be able to absorb light so that light unnecessary for measurement is not reflected.

FIG. 4 is a diagram for explaining a measurement method of biological light measurement according to the present invention. Light P1 and P2 are irradiated from the opening A and the opening B, and the light from the opening A is received by the opening B (the intensity is S _AB . The same applies hereinafter). The light from B is received (S _BA ). In the openings A and B, light emitted from the same opening, that is, light in the opening A (S _AA ) and light in the opening B (S _BB ) (same opening correction) is received. In addition, at the position D equidistant from the irradiation point and the light receiving point, light (S _AD and S _BD ) (equal distance point correction) by irradiation from the points A and B is detected.

If the change in the light intensity detected when the absorber is present is the light detection sensitivity when the absorber is not present in the living tissue, the light detection sensitivity S is the perturbation theory (Rytov) based on the diffusion equation. (Approximation) is given by the following equation (1).
S (x, y, z) = Φs · Φd / Φd0 (1)
Here, Φs and Φd are photon densities formed by the light source and the unit light source at the detector position at the point of interest (x, y, z) where the absorber exists, and Φd0 is a photon density when there is no change in the absorption coefficient. . At this time, the detection sensitivity of the diffuse reflected light due to blood circulation in the living tissue to be measured is the corrected light detection sensitivity if the correction coefficients by the same aperture correction and the equidistant point correction are α and β, respectively. S_correct is expressed by the following equation (2).
S_correct = (S _AB + S _BA ) / 2
-Α (S _AA + S _BB ) / 2-β (S _AD + S _BD ) / 2 (2)

  The same aperture correction (correction coefficient α) is the correction of the influence of the surface layer near the irradiation and light receiving points, which has the highest influence, and the equidistant point correction (correction coefficient β) is information on the size and position of the absorber. There are benefits to be gained. By selectively using two types of correction signals, it is possible to easily perform highly accurate measurement.

As specific correction means, two types of correction are selected depending on conditions. In equidistant point correction, paying attention to the point that overcorrection occurs when the change region of the absorber is directly below point D, the ratio of deep light reception to equidistant point light reception (S _AD + S _BD ) / (S _AB + S Selection conditions are determined using _BA ) as an index. The same aperture correction is applied when this value is remarkably small (local change is directly under points A and B) and large (local change is directly under point D), and equidistant point correction is applied otherwise.

  In this embodiment, instead of placing the light receiving element at the midpoint of the two points, as shown in FIG. 5, the irradiation device and the light receiving device are arranged at the three vertices of the equilateral triangle, Place only the light receiving device. At the vertices A, B, and C, the light of the depth signal and the same aperture correction is received along with the irradiation, and at the center of gravity position D that is equidistant from the points A, B, and C, the light of the equidistant point correction is received. At each point, three types of light are received as shown in the figure. In each of the sides A-B, B-C, and C-A of the equilateral triangle, a signal to which two types of corrections are applied can be obtained in the same manner as the side A-B shown in the equation (1).

  By arranging equilateral triangles and light-receiving points for equidistant point correction at the center of gravity, overcorrection can be easily detected and correction detection points can be reduced. Furthermore, the arrangement of equilateral triangles makes it easier to arrange on a spherical surface such as the head than in the case of arranging in a square, and since the measurement points can be densely provided, an improvement in position resolution can be expected.

In FIG. 5, the distance between A, B and C is 30 mm, the position of the surface absorber is 2 mm deep, the size is 8 × 8 × 1 mm, the radius of the opening is 3 mm, and the absorption coefficient μa = 0.01 mm ^−1. The simulation was performed by approximating the diffusion equation with the reduced scattering coefficient μs = 1.0 mm ⁻¹ .

  In FIG. 6, the simulation result of the photodetection sensitivity at the time of moving the change area | region of a surface layer absorber from the A point (0 mm) to the gravity center D direction is shown. The horizontal axis in the figure indicates the distance in the AB direction, and the position of 15 mm corresponds to the center of gravity D. The correction α is the same aperture correction, the correction β is the equidistant point correction, and the correction α · β is the result of correction by selecting α and β according to the conditions. When correction is not performed, the light detection sensitivity of the surface layer absorber is high in the vicinity of the opening A, and decreases as the distance increases. When correcting, α is applied in the vicinity of the opening, β in the vicinity of 5 to 10 mm, and α is applied in the vicinity of the center of gravity so as not to be overcorrected. It is.

  In the above-described embodiment, the case where light of one wavelength is used has been described. In order to examine changes due to oxygenation and deoxygenation of hemoglobin, measurement is performed by combining at least two light sources having different light absorption characteristics. It is common.

  FIG. 7 shows a measurement method when light of two wavelengths is used. Lights P11 and P21 having the first wavelength and P12 and P22 having the second wavelength are input to the openings 1a and 1b that perform light irradiation and light reception, respectively. At this time, the light intensity by the diffuse reflected light of the first and second wavelengths due to blood circulation in the living tissue to be measured is obtained. However, the correction coefficient due to the diffusely reflected light of the first and second wavelengths varies depending on the wavelength of the light. An optical fiber bundle for inputting light of the second wavelength is added to the optical fiber bundle of FIG. 2 for the connection between the openings 1a, 1b, 1c and the light emitting / receiving sections 3a, 3b, 3c. If a three-branch type optical fiber bundle is used, it is possible to easily realize that two irradiation lights are fused and input to the openings 1a and 1b and received from one fiber.

  According to the present invention, a biological function such as a brain associated with a change in oxygenation state of blood flow in a biological tissue can be measured in a biological optical measurement device while suppressing the influence of skin blood flow. For this reason, it is possible to provide a biological optical measurement device that can accurately measure the influence of skin blood flow even when posture changes such as exercise are large, under a wide range of conditions in the fields of medicine and psychology. Can be measured.

DESCRIPTION OF SYMBOLS 1, 1a, 1b, 1c, 1d Opening part 3a, 3b, 3c, 3d Light irradiation / light-receiving part 4 Incident light adjustment circuit 5a, 5b, 5c, 5d Light-receiving circuit 6 Signal processing device 7 A / D converter 11 Spectroscopy Device 12 Optical fiber 13 Light propagation path 14 Optical fiber bundle 15 Case

Claims (3)

A biological light measurement device, comprising: a first light source that generates light of a first wavelength; a second light source that generates light of the same wavelength as the first light source; three openings and three light receiving means Have
Irradiating the first opening with light from the first light source and receiving the light through the second opening (light reception 1);
Irradiating the second opening with light from the second light source and receiving the light through the first opening (light reception 2);
The light from the first light source is received by the first opening (light reception 3),
The light from the second light source is received by the second opening (light reception 4),
Irradiating the first opening with light from the first light source and receiving the light through the third opening (light reception 5);
The second light source is irradiated with light from the second light source, and is configured to receive light (light reception 6) at the third opening,
A living body light measuring device comprising means for converting the light received by the light receiving 1 to the light receiving 6 into an electric signal and means for converting the light converted into the electric signal into a light receiving intensity.   Means for subtracting the light reception 3 from the light reception 1 and the light reception 5 with a coefficient corresponding to the light reception intensity, and subtracting the light reception 4 and the light reception 6 from the light reception 2 with a coefficient according to the light reception intensity, respectively. The living body light measuring apparatus according to claim 1, further comprising: means. The living body light measurement apparatus according to claim 1, wherein the first and second light sources include a switch that switches to light having a second wavelength different from the light having the first wavelength.

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