JP2007111461A - Bio-optical measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bio-optical measurement apparatus which measures functional information of a living body by light and allows measurement to be free from influence by a change in posture because a variation in a measurement value by a change in light absorption coefficient of skin bloodstream is subtracted from the measurement value. <P>SOLUTION: The apparatus comprises a first light source and a second light source which both emit a same wavelength of light, a means for periodically modulating the amplitude of light from the first and second sources, at least two apertures, and at least two light reception means, wherein the first aperture is irradiated with light from the first source, which is received by the second aperture (light reception 1); the second aperture is irradiated with light from the second source, which is received by the first aperture (light reception 2); light from the first source is received by the first aperture (light reception 3); and light from the second source is received by the second aperture (light reception 4). The light reception 4 is subtracted from the light reception 1, and the light reception 3 is subtracted from the light reception 2 in light reception intensity with a coefficient depending on the intensity to reduce the influence by skin bloodstream. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring biological function information with light.

Light is effective as a means for easily and non-invasively obtaining information inside a living body, and an apparatus for measuring biological function information has been developed. It is generally known that the light absorption characteristics of several kinds of pigments existing in a living body depend on the wavelength. Therefore, for example, if the light absorption characteristics of hemoglobin dye in blood is 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 of visible to near-infrared wavelength, a living body light measuring device for living body (mainly brain function) called optical topography has been developed (for example, Non-Patent Document 1). reference.). This is a method of estimating the oxygen consumption from the light absorption characteristics of the hemoglobin dye by measuring the diffused / reflected light by arranging the light irradiation point and the light receiving point on the surface of the living body (for example, the head). As shown in FIG. 11, when light is irradiated from the opening 1a and received by the opening 1b which is a distance D away, the light received by 1b is diffused / reflected light propagated along the light propagation path 13 in FIG. It is considered to be. Therefore, at the midpoint of the distance D in FIG. 11, it is considered that the propagation path of the deepest propagation path can be measured, that is, the propagation characteristic of the diffuse reflected light by the blood flow in the living tissue. 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.
“Spatial and temporal analysis of human motor activity using noninvasive NIR topologies”, Medical Physics vol. 22, pp. 1997-2005, 1995.

  Blood in living tissue is roughly classified into skin blood flow near the surface of the living body and blood flow in living tissue such as muscle and brain. In the prior art, when a set of light irradiation point and light receiving point is considered, it is assumed that a change in the absorption coefficient of light occurs in the blood flow in the living tissue inside the vicinity of the midpoint position. Hemoglobin metabolism is obtained from the measurement result of reflected light. Here, the light has a characteristic that most of the light irradiated from the air is reflected near the surface of the living body having a high refractive index and part of the light diffused and scattered inside. Therefore, from the configuration of FIG. 11, it is considered that the light actually received includes the light absorption characteristic of skin blood flow due to reflection near the surface. Occurred in the measured value, and there was a problem that it was impossible to accurately measure the light absorption characteristics of the blood flow in the living tissue.

  The present invention is intended to solve the problem of such a conventional configuration, and reduces the variation in the measurement value accompanying the change in the light absorption coefficient of the skin blood flow from the measurement value, thereby changing the posture. The objective is to realize a biological light measurement device that is not easily affected by the above.

  In order to achieve the above object, the biological optical measurement apparatus of the present invention temporally transmits light from the first light source and the second light source that generate light of the same wavelength, and the first and second light sources. Amplitude modulating means, at least two openings, means for receiving at least two light, means for converting the received light into electric signals, and amplifying the light converted into electric signals, depending on the modulation frequency Means for phase detection and conversion to received light intensity.

  The effect | action by the said solution means is as follows. The first opening and the second opening for light irradiation / light reception are arranged on the surface of the living body with a distance D apart. Light from the first light source is applied to the first opening and received by the second opening (light received at this time is referred to as light reception 1), and the light from the second light source is the second light. Is received at the first opening (light reception 2), received at the first opening by the first light source (light reception 3), and the second by the second light source. Receives light (received light 4) at the opening. The light receptions 3 and 4 are mainly diffuse reflection lights in the vicinity of the openings, and the light receptions 1 and 2 are diffuse reflection lights in the living tissue between the vicinity of each opening and the first and second openings. Therefore, by subtracting the light receiving 1 to the light receiving 3 and the light receiving 4 from the light receiving 2 to the light receiving 3 and the light receiving 4 with a coefficient corresponding to the received light intensity, the influence of the fluctuation of the skin blood flow is reduced. Can be obtained.

  Further, the third light source and the fourth light source having a second wavelength different from those of the first light source and the second light source, and the light from the third light source and the fourth light source are temporally changed. By having means for modulating the amplitude, means for irradiating the first opening with light from the third light source, and means for irradiating the second opening with light from the fourth light source It is possible to measure the relative amounts of oxygenated hemoglobin and deoxygenated hemoglobin using the difference in light absorption characteristics in the living tissue such as blood by the light of the first wavelength and the light of the second wavelength.

  Since the effect of skin blood flow near the surface layer can be reduced using light received from the same opening as the irradiation, it is possible to selectively measure the characteristics of blood flow in living tissue while suppressing the effect . As a result, the living body optical measuring device of the present invention can measure changes due to blood flow in the living tissue more accurately, and measures oxygen consumption and brain function in muscles when accompanied by large posture changes such as exercise. The biological light measurement device can be used in various situations.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. In order to simplify the description, the case where light of one wavelength is used will be mainly described.

(Embodiment 1) FIG. 1 shows the configuration of a first embodiment of a biological light measuring apparatus according to the present invention. In this embodiment, the openings 1a and 1b are arranged on the surface of the living body and are used for light irradiation and light reception. A lens is provided in the opening for condensing as necessary. The optical fiber 12 connects between the openings 1a and 1b and the light emitting / light receiving portions 3a and 3b. When connecting with a single fiber, the optical fiber for irradiation and light reception are fused and input to the opening. In the case of connecting with a plurality of optical fibers, as shown in FIG. 3, 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. 4 shows a configuration example in the case where the spectroscope 11 transmits irradiation 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. The light irradiating / light receiving units 3a and 3b in FIG. 2 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 adjustment circuit 4 performs amplitude modulation on the irradiated light according to the frequency to adjust the light to an amplitude necessary for measurement. The light receiving circuit 5 performs 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 irradiation light adjusting circuit 4 and the light receiving circuit 5 through the digital / analog converter 7 and the analog / digital converter 8. 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.

  The light detection method having the above configuration will be described below with reference to FIG. The openings 1a and 1b are installed at positions separated by a distance D on the surface of the living body. Light P1 is irradiated from the opening 1a and light P2 is irradiated from the opening 1b, and the light intensity is measured. Assuming that the change rate of the light intensity detected when an absorber is present in the living tissue is the light detection sensitivity, the light detection sensitivity S is a perturbation based on the diffusion equation as a function of the distance x, y and the depth direction z. It is given by the formula 1 by theory (Rytov approximation).

Number 1

S (x, y, z) = Φs · Φd / Φd0...
Here, Φs and Φd are the light source, the photon density created by the unit light source at the detector position at the point of interest (x, y, z) where the absorber exists, and Φd0 is the photon density when there is no change in the absorption coefficient. When P1 is received by the same opening 1a as the irradiation, the light intensity is S1A, and when P2 is received by the same opening 1b as the irradiation, the light intensity is S2B, and when P1 is received by the opening 1b different from the irradiation The light intensity when the light is received by the opening 1b different from the irradiation of P1 is S2A. At this time, the detection sensitivity of diffuse reflected light due to blood perfusion in the living tissue to be measured is obtained by Equation 2.

Number 2

S = S1B + S2A−α (S1A + S2B).
Here, α is a correction coefficient, and is determined depending on the optical constant and light intensity of the in vivo tissue to be measured.

  The effects of the embodiment of the present invention will be shown below by computer simulation. FIG. 5 shows light when the light is emitted from the opening 1a and received by the opening 1b (S1B, S2A), and FIG. 6 shows the light when the light is irradiated and received by the same opening of the openings 1a and 1b (S1A + S2B). In this example, the detection sensitivity is calculated at a depth of 1 mm. FIG. 5 shows that the light detection sensitivity is high near the surface layer near the irradiation point and the light receiving point, and low in the propagation path to be measured. In addition, it can be seen from FIG. 6 that when irradiation and light reception are performed through the same opening, the light detection sensitivity is selectively high in the vicinity of the opening and mainly includes a signal due to averaged skin blood flow in the surface layer.

  Further, FIG. 7 shows a correction example according to the embodiment of the present invention. When the distance D between the openings 1a and 1b is 20 mm, the radius rs of the opening is 5 mm, and the absorption coefficient in the living tissue changes as a 1 mm cubic region, the position of the region changes. Distribution. Similar to FIGS. 5 and 6, the calculation was performed by the perturbation theory (Rytov approximation) based on the diffusion equation. Here, optical constants when blood in muscle is a measurement target are used. FIG. 7A shows a calculation result before correction, and B shows a calculation result after correction. It can be seen that by performing the correction based on the present invention, the influence in the shallow region near the opening can be reduced.

  In the above embodiment, the case where light of one wavelength is used has been described. In order to examine the change due to oxygenation and deoxygenation of hemoglobin, measurement is performed by combining light sources of at least two wavelengths having different light absorption characteristics. Is common. In this case, as shown in FIG. 8, light P11 and P21 of the first wavelength and light P12 and P22 of the second wavelength are input to the openings 1a and 1b that perform light irradiation and light reception, respectively. At this time, the photodetection sensitivity by the diffuse reflected light of the first and second wavelengths due to blood perfusion in the living tissue to be measured is obtained in the same manner as Equation 2. However, the correction coefficient due to the diffusely reflected light of the first and second wavelengths varies depending on the wavelength of the light. The connection between the openings 1a and 1b and the light irradiators / light receivers 3a and 3b is a three-branch type in which an optical fiber bundle for inputting light of the second wavelength is added to the optical fiber bundle in FIG. If an optical fiber bundle is used, it can be easily realized that two irradiation lights are fused and input to the openings 1a and 1b and received from one fiber.

  Next, the arrangement of the opening on the surface of the living body and the measurement position will be described. The value measured from the principle of measurement is considered to be located at approximately the midpoint of each opening. FIG. 9 shows an example in which nine openings 1c to 1j are arranged. The crosses in the figure indicate estimated measurement positions. In the configuration of FIG. 9, measurement can be performed at 12 points that are substantially the same interval as the aperture interval. FIG. 10 shows an example in which seven openings 1c to 1j are arranged based on a triangle. Measurements can be made at 12 points alternately in the vertical direction at intervals equal to and half the interval between the openings. If the openings are basically arranged in a triangle, it is possible to measure at many points in the same area, so that the resolution of the position is improved and it is easy to arrange in a circle, so it is suitable for placement on a spherical biological surface such as the head. .

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.

The block diagram of the optical measuring device which shows embodiment of this invention. The figure explaining the measuring method by the optical measuring device of this invention. The figure explaining the connection method between the opening part of the optical measuring device of this invention, and the light irradiation part and light-receiving part. The figure explaining the connection method between the opening part of the optical measuring device of this invention, and the light irradiation part and light-receiving part. The figure which shows the example of calculation of the photodetection sensitivity at the time of performing light irradiation and light reception in a different opening part. The figure which shows the example of calculation of the photodetection sensitivity at the time of performing light irradiation and light reception in the same opening part. The figure which shows the example of a calculation regarding the effect of the optical measurement by this invention. The figure explaining the measuring method using the light of two wavelengths of this invention. The figure explaining arrangement | positioning and the presumed measurement position of the opening part of this invention. The figure explaining arrangement | positioning and the presumed measurement position of the opening part of this invention. The figure explaining the measuring method by the conventional optical measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a, 1b, 1c Opening part 3a, 3b Light irradiation and light-receiving part 4 Incident light adjustment circuit 5 Light receiving circuit 6 Signal processing device 7 Analog / digital converter 8 Digital / analog converter 11 Spectrometer 12 Optical fiber 13 Light Propagation path 14 Optical fiber bundle 15 Housing

Claims (3)

  At least one first light source and second light source for generating light of the same wavelength, means for generating light from the first light source and the second light source, at least two openings, and at least two Means for receiving one light, irradiating the first opening with the light from the first light source and receiving the light through the second opening (light reception 1), and receiving the light from the second light source. The second opening is irradiated to receive light at the first opening (light reception 2), light from the first light source is received at the first opening (light reception 3), and the second opening is received. Means for receiving light from the light source through the second opening (light reception 4), means for converting the light received by the light reception 1 to light reception 4 into electric signals, and receiving the light converted into electric signals; A biological light measuring device comprising means for converting the intensity.   2. The means according to claim 1, further comprising means for subtracting the light reception 3 from the light reception 1 and the light reception 4 and subtracting the light reception 3 and the light reception 4 from the light reception 2 with a coefficient corresponding to the light reception intensity. Biological light measuring device.   A third light source and a fourth light source having a second wavelength different from those of the first light source and the second light source, means for generating light from the third light source and the fourth light source, The above-mentioned claim 1, characterized in that the first opening is irradiated with light from the third light source and the second opening is irradiated with light from the fourth light source. 2. The biological light measurement device according to claim 3.

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