Optical characteristic value measuring device and optical characteristic value measuring method

Abstract

The present invention addresses the problem of providing an optical characteristic value measurement device and optical characteristic value measurement method whereby is possible to easily obtain scattering coefficient and absorption coefficient values which are optical characteristic values of a scattering absorber.　In order to solve this problem, provided is an optical characteristic value measurement device 1 comprising: a detection unit 2 including a light emitting unit that emits light from the surface of a target object to the inside thereof, a measurement unit that, at at least two points on said surface at differing distances from the light emitting unit, measures the intensity of light reflected in the inside of the target object and emitted to outside of the target object, and a substrate that is mounted so as to cover said surface between the light emitting unit and the measurement unit, and that increases the reflectance of light emitted to the outside from the inside; and a calculation unit 5 that calculates the absorption coefficient and scattering coefficient of the target object on the basis of the intensity obtained by using the aforementioned measurement.

Description

[Technical Field]

[0001] The present invention relates to a technique for measuring optical property values ​​of a substance. [Background technology]

[0002] Various techniques have been devised so far for measuring internal information of scattering medium such as living organisms. For example, Patent Document 1 discloses a technique in which light is incident on a scattering medium, detection signals are acquired at three or more different incident-detection distances, and the detection signals are processed based on three or more simultaneous relations for the three or more detection signals, thereby deriving internal information of the scattering medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-49304 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 does not mention anything about the reflection (internal reflection) at the surface of the scattering medium when light propagating inside the scattering medium reaches the surface of the scattering medium or the absorption characteristics. Therefore, the technique disclosed in this document has a problem in that it is not possible to separately determine the scattering coefficient and absorption coefficient of the scattering medium.

[0005] The present invention has been made to solve such problems, and aims to provide an optical property value measuring device and an optical property value measuring method that can easily obtain the values ​​of the scattering coefficient and absorption coefficient, which are the optical property values ​​of a scattering medium. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides an optical property value measuring device comprising: a light irradiation means for irradiating light from the surface of an object to the inside; a measurement means for measuring the intensity of light that is reflected inside the object and emitted to the outside at at least two points on the surface that are at different distances from the light irradiation means; a light reflection means that is placed between the light irradiation means and the measurement means so as to cover the surface and increase the reflectance of light that is emitted from the inside to the outside; and a calculation means for calculating the absorption coefficient and scattering coefficient of the object based on the intensity obtained by the measurement.

[0007] In addition, in order to solve the above problem, the present invention provides an optical property measuring device comprising: a measuring means that is disposed on the surface of an object and measures the intensity of light emitted from the inside of the object to the outside; a light irradiating means that selectively irradiates light from the surface to the inside at at least three points on the surface that are each at a different distance from the measuring means; a light reflecting means that is placed between the light irradiating means and the measuring means so as to cover the surface and that increases the reflectance of light emitted from the inside to the outside; and a calculating means that calculates the absorption coefficient and scattering coefficient of the object based on the intensity obtained by the measurement.

[0008] In addition, to solve the above problem, the present invention provides an optical property measurement method in which an optical reflection means is placed so as to cover the surface of an object between a position where light is irradiated from the surface to the interior of the object and a measurement position where the intensity of light reflected inside the object and emitted outside the object is measured, the method comprising: a first step of irradiating light from the surface to the interior; a second step of measuring the intensity of light reflected inside the object and emitted outside the object at at least two points on the surface that are different distances from the irradiation position; and a third step of calculating the absorption coefficient and scattering coefficient of the object based on the intensity obtained by the measurement in the second step. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical characteristic value measuring device and an optical characteristic value measuring method that can easily obtain the values ​​of the scattering coefficient and the absorption coefficient, which are the optical characteristic values ​​of a scattering medium. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing the overall configuration of an optical characteristic value measuring device 1 according to a first embodiment of the present invention. [Figure 2] 2A and 2B are diagrams showing the structure of an optical probe constituting the detection unit 3 shown in FIG. 1, with FIG. 2A being a bottom view and FIG. 2B being a side view. [Figure 3] 2 is a flowchart showing the operation of the optical characteristic value measuring apparatus shown in FIG. [Figure 4] FIG. 4 is a first diagram illustrating the principle of the method for calculating the absorption coefficient and the scattering coefficient, which is executed in step S3 of FIG. [Figure 5] FIG. 4 is a second diagram illustrating the principle of the method for calculating the absorption coefficient and the scattering coefficient, which is executed in step S3 of FIG. [Figure 6] 6A and 6B are diagrams showing another embodiment (second embodiment) of the optical probe shown in FIG. 2, where FIG. 6A is a bottom view and FIG. 6B is a side view. [Figure 7] 7A and 7B are diagrams showing a third embodiment of the optical probe shown in FIG. 2, where FIG. 7A is a bottom view and FIG. 7B is a side view. [Figure 8] 8A and 8B are diagrams showing a fourth embodiment of the optical probe shown in FIG. 2, where FIG. 8A is a bottom view and FIG. 8B is a side view. [Figure 9] 9A and 9B are diagrams showing a fifth embodiment of the optical probe shown in FIG. 2, where FIG. 9A is a bottom view and FIG. 9B is a side view. [Figure 10] FIG. 3 is a bottom view showing the sixth embodiment of the optical probe shown in FIG. 2. [Figure 11A] FIG. 10 is a schematic diagram showing a state when a voltage is applied, for explaining the function of the reflectance variable film 20 used in the optical probe constituting the detection unit 2 according to the second embodiment of the present invention. [Figure 11B]FIG. 10 is a schematic diagram illustrating a state when no voltage is applied, for explaining the function of a reflectance variable film 20 used in an optical probe constituting a detecting unit 2 according to a second embodiment of the present invention. [Figure 12] FIG. 10 is a side view showing the structure of the optical probe when measurements are performed at three different SD distances in the second embodiment of the present invention. [Figure 13] FIG. 10 is a side view showing the structure of an optical probe when measurements are performed at two different SD distances in the second embodiment of the present invention. [Figure 14] 14A and 14B are graphs for explaining a modulation method for the internal reflectance of the variable reflectance film 20 shown in FIG. 13, where FIG. 14A shows the change over time in the internal reflectance rd of the variable reflectance film 20, and FIG. 14B shows the change over time in the intensity I1 of the detected light measured by the measurement unit D1 shown in FIG. 13. [Figure 15] FIG. 10 is a side view for explaining the light piping phenomenon in which light propagates through a gap 18. [Figure 16] FIG. 10 is a side view illustrating the light piping phenomenon in which light propagates through the transparent coating layer 17. [Figure 17A] FIG. 10 is a side view showing the structure of an optical probe according to a third embodiment of the present invention. [Figure 17B] 17B is an enlarged view showing the path of light when light is incident on the film 21 shown in FIG. 17A at an incident angle θ1 equal to the critical angle θc in the optical probe according to the third embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Among the optical properties of biological tissue, the absorption coefficient and scattering coefficient (more precisely, the reduced scattering coefficient) are extremely important in biomedical diagnosis using near-infrared light. However, because light is strongly scattered, it is not easy to measure them in a living state, and it was thought that it was impossible to measure their absolute values, especially using simple measurement methods that use continuous light.

[0012] Conventionally, it has been assumed that the contact surface of a measurement probe with a living body is black, and that no light from inside the living body is reflected at the contact surface and all light is absorbed. However, in the following, we will explain a technique for maximizing the reflection of light at the contact surface, or for changing this reflection over time or periodically to increase or decrease it. By applying the theory of light propagation within a living body to such reflection conditions at the contact surface, it becomes possible to determine the absolute values ​​of the absorption coefficient and scattering coefficient separately.

[0013] [Embodiment 1] An optical characteristic value measuring device according to a first embodiment of the present invention will be described in detail below with reference to the drawings, in which the same reference numerals indicate the same or corresponding parts.

[0014] Fig. 1 is a block diagram showing the overall configuration of an optical property measurement device 1 according to a first embodiment of the present invention. As shown in Fig. 1, the optical property measurement device 1 includes a light irradiation unit that irradiates light from the surface of a head of a subject, which is an object to be measured, into the interior of the head, a measurement unit that measures the intensity of light that is reflected inside the head and emitted to the outside of the head at at least three points on the surface that are at different distances from the light irradiation unit, and a detection unit 2 that is mounted on the head and includes a light reflection unit that is placed between the light irradiation unit and the measurement unit so as to cover the surface and increase the reflectance of light that is emitted from the interior to the outside, and a measurement unit 4 that is connected to the detection unit 2 via a bus 3 and calculates an optical property value of the object to be measured based on the light intensity measured by the measurement unit.

[0015] The measurement unit 4 includes a calculation unit 5, a memory unit 6, a display unit 7, and an operation unit 8, all of which are connected to the bus 3. The calculation unit 5 is configured with a central processing unit (CPU) and calculates the absorption coefficient and scattering coefficient of the object to be measured based on the light intensity measured by the measurement unit; this calculation method will be explained in detail later. The memory unit 6 is configured with a semiconductor memory or a hard disk and stores the programs executed by the calculation unit 5, as well as the light intensity measured by the measurement unit and the values ​​calculated by the calculation unit 5. The display unit 7 displays a user interface for the user to operate the device and the calculated values. The operation unit 8 outputs various operating commands to the calculation unit 5 in response to the user's operations.

[0016] Figure 2 shows the structure of the optical probe that constitutes the detection unit 3 shown in Figure 1, with Figure 2(a) being a bottom view and Figure 2(b) being a side view. The bottom surface shown in Figure 2(a) and the lower surface shown in Figure 2(b) come into contact with the surface of the head.

[0017] Furthermore, the optical probe shown in Figure 2 is the smallest unit that constitutes the detection unit 3, and by forming the detection unit 3 using multiple optical probes, it becomes possible to measure multiple points on the head.

[0018] As shown in Figure 2, this optical probe comprises: a light-emitting unit E1, which consists of a light-emitting diode, a semiconductor laser, or the like, and selectively irradiates light of at least two wavelengths from the surface to the interior; measurement units D1 to D3, which consist of photodetectors such as an avalanche photodiode or a photodiode, and measure the intensity of light reflected inside and emitted to the outside at three points on the surface at distances ρ1, ρ2, and ρ3 from the light-emitting unit E1; a substrate 10, the bottom of which is a highly reflective surface made of a mirror or white surface, and which is placed between the light-emitting unit E1 and the measurement units D1 to D3 so as to cover the surface, thereby increasing the reflectivity of light emitted from the inside to the outside; and a cover material 11, which is arranged to cover the substrate 10 and is made of a material that absorbs light without reflecting it.

[0019] The substrate 10 is made of white plastic, white rubber, white powder molding material, white paper, white cloth, white wood, glossy metal foil, or a combination of these, as well as a reflectance variable film.

[0020] Fig. 3 is a flowchart showing the operation of the optical characteristic value measuring apparatus 1 shown in Fig. 1. The operation of the optical characteristic value measuring apparatus 1 will be described below with reference to Fig. 3.

[0021] In step S1, in the optical property measuring device 1 having the above-described configuration, light is irradiated from the surface to the interior by the light irradiating unit E1. Next, in step S2, the intensity of light reflected inside the surface and emitted to the outside is measured by three measuring units D1 to D3. Then, in step S3, data indicating the light intensity obtained by the measurement in step S2 is stored in memory unit 6 via bus 3, and calculation unit 5 calculates the absorption coefficient and scattering coefficient of the subject's head, which is the measurement object, based on the data stored in memory unit 6. The method of calculating these absorption coefficient and scattering coefficient will be described in detail below.

[0022] First, the principles of spatially resolved spectroscopy (SRS) using near-infrared spectroscopy (NIRS) employed in the above operation will be explained in comparison with the principles employed in conventional such measurements.

[0023] Until now, continuous light has been used in spatially resolved spectroscopy, a technique for estimating brain and muscle activity by measuring changes in the concentration of oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) in living organisms. In this case, the absorption coefficient μ is given by the distance from the light irradiation point to the detection point (hereinafter also referred to as the "SD distance") as ρ and the attenuation of the diffuse reflected light measured at each SD distance from the irradiation light propagating inside the living organism as A. a and the scattering coefficient μ S ‘ It is based on the following relationship between

[0024]

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[0025] In other words, by measuring the attenuation A at multiple distances ρ and finding the slope dA / dρ, the absorption coefficient μ a and the scattering coefficient μ S ´ product μ a μ S At this time, as shown in FIG. 4, in the derivation of Equation (1), the intensity I in It is assumed that when the incident light reaches the surface 12, it is completely absorbed and does not return to the inside, i.e., the zero boundary condition is satisfied. From equation (1), the absorption coefficient μ a and the reduced scattering coefficient μ S In such conventional spatially resolved spectroscopic measurements, the intensities I1 and I2 of the diffusely reflected light are measured at the distances ρ1 and ρ2, respectively. The attenuations A1 and A2 are expressed as A1 = -ln(I1 / I in ), A2=-ln(I2 / I in ) can be calculated using

[0026] In contrast, in the spatially resolved spectroscopic measurement according to the present embodiment, as shown in Fig. 5, light that reaches the surface of biological tissue 9 is strongly reflected by the highly reflective surface of substrate 10 and propagates again within biological tissue 9. Then, intensities I1, I2, and I3 of the diffusely reflected light are measured at measurement points ρ1, ρ2, and ρ3, which are different distances from the irradiation point. The diffuse reflectances R1, R2, and R3 at the three measurement points are expressed by the following equations:

[0027]

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[0028] Then, by increasing the reflectance (internal reflectance) of the surface of the light coming from inside the living body as described above, and by performing numerical calculations using Monte Carlo simulations that simulate the light propagation phenomenon inside the living body and calculating analytical solutions to the equations that represent the light propagation phenomenon, the absorption coefficient μ a and the reduced scattering coefficient μ S The absolute value of ' can be calculated separately, as explained in more detail below.

[0029] absorption coefficient μ a and the reduced scattering coefficient μ S Since the two variables of ´ are unknown, in principle, the absorption coefficient μ can be calculated from the intensities I1 and I2 of the diffuse reflected light measured at two points with distances ρ1 and ρ2. a and the reduced scattering coefficient μ S However, in actual measurements, the intensity of the irradiated light I in Since it is difficult to measure the intensity of the diffuse reflected light I1 and I2, it is not easy to obtain the absolute values ​​of the intensities of the diffuse reflected light I1 and I2. Therefore, the intensities of the diffuse reflected light I1, I2, and I3 are measured at three points, and their ratio J is calculated. 12 (=I1 / I2),J 23 (=I2 / I3),J 13 By solving the simultaneous equations using two of the measured values ​​(=I1 / I3), the absorption coefficient μ a and the reduced scattering coefficient μ S Specifically, we find the ratio J 12 ,J 23 When using the equation, the following simultaneous equations are obtained:

[0030]

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[0031] where R(ρ;μ a ,μ S ´) is the SD distance ρ and the absorption coefficient μ of the medium a , reduced scattering coefficient μ S ´, it is the diffuse reflectance calculated from theoretical calculations of light propagation phenomena, and the right-hand side R(ρ;μ a ,μ SThe absorption coefficient μ when the ratio of a , reduced scattering coefficient μ S ´ is the desired value.

[0032] By transforming equation (3), the absorption coefficient μ a and the reduced scattering coefficient μ S The two functions f1(μ a ,μ S ´),f2(μ a ,μ S The absorption coefficient μ such that ´) becomes zero a and the reduced scattering coefficient μ S ´ is required.

[0033]

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[0034] In the following, the diffuse reflectance R(ρ;μ a ,μ S As examples of theoretical calculations of ´, five methods are explained.

[0035] [1] Monte Carlo simulation method Monte Carlo simulation is known as a method of tracking the propagation of photons after absorption and scattering in a medium, considering light as particles with energy (photons), and has become practical with the development of computers. The direction in which a photon is changed by scattering is given by a random number so that the scattering characteristics are statistically represented, and the distance traveled before the next scattering and the energy loss are also given by a random number so that the absorption characteristics are statistically represented.

[0036] Here, various SD distances ρ and absorption coefficients μ a , reduced scattering coefficient μ S ', perform a simulation to determine the above diffuse reflectance R(ρ;μ a ,μ S ´) table is created, and the absorption coefficient μ that satisfies Eq. (4) is a and the reduced scattering coefficient μ SA lookup table method is used to find combinations of

[0037] [2] Method using the light transport equation The light transport equation is an equation that represents the law of conservation of energy accompanying the propagation of light in a medium where scattering and absorption occur, and is known to be expressed by the following partial differential and integral equation:

[0038]

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[0039] Here, c is the speed of light, t is time, bold s is a direction vector, bold r is a position vector, I is light intensity, μ S is the scattering coefficient, μ a is the absorption coefficient, p(bold s, bold s') is the scattering probability from direction s' to direction s, dΩ' is the infinitesimal solid angle relative to direction s', and q is the light source intensity inside the medium.

[0040] It is also preferable to use the look-up table method by using the equation shown in formula (5) and performing numerical calculations in advance under various conditions, as in the case of using the Monte Carlo simulation.

[0041] [3] Telegraph equation method The telegrapher's equation is an equation obtained by approximating the light transport equation to eliminate the directional dependency of light intensity and the integral term, resulting in a partial differential equation of the integrated light intensity φ(r,t), which includes first and second derivatives with respect to time and second derivatives with respect to space, as shown in the following equation (6).It is known to include the wave nature of light and the diffusive nature within scattering media.

[0042]

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[0043] Here, D = 1 / (3μ s ´) indicates the light diffusion coefficient.

[0044] The analytical solution for the diffuse reflectance obtained by the equation shown in (6) is the reflectance (internal reflectance) when light from inside the body reaches the boundary surface (surface) as r d (0 <r d <1), it can be obtained in the form of an integral as shown in the following equation (7).

[0045]

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[0046] The integrand function shown in Equation (7) rapidly decreases as s increases, so the calculation load is not large. For this reason, it is also preferable to use the lookup table method by performing calculations under various conditions in advance.

[0047] [4] Method using the time-dependent light diffusion equation The light diffusion equation, which is a further approximation of the light transport equation, is a partial differential equation of φ(r, t) that includes a first-order differential with respect to time and a second-order differential with respect to space, as shown in the following equation (9). However, it is assumed that there is no light source inside the medium.

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[0048] The analytical solution for the time-dependent diffuse reflectance in the case of pulsed light irradiation, given by the equation (9), is given by the internal reflectance r d Under the boundary condition, it can be calculated as follows:

[0049]

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[0050] And the diffuse reflectance R(ρ;μ a ,μ S ´) is the diffuse reflectance R(ρ, t; μ a ,μ S ´) with respect to time.

[0051]

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[0052] For this reason, it is also preferable to use a look-up table method by performing calculations under various conditions in advance.

[0053] [5] Method using the light diffusion equation for continuous light The light diffusion equation for continuous light that is independent of time is given by the following equation (14):

[0054]

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[0055] The approximate solution of the equation shown in Equation (14) can be easily obtained by using the extrapolated boundary method (mirror method), and the above diffuse reflectance R(ρ;μ a ,μ S ´) is given by the following equation (15):

[0056]

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[0057] If there is no internal reflection, r d =0,A R = 1, and the internal reflectance r d The larger the AR In this case, the diffuse reflectance R(ρ;μ a ,μ S Since the internal reflectance r is given by the simple equation (15), the simultaneous equations in equation (4) can be solved analytically. d When μ is large S z with ´ e Since r becomes large 20 cannot be approximated as ρ. As a result, μ S Since the ´ term appears alone, the absorption coefficient μ a and the reduced scattering coefficient μ S ´ can be separated and found.

[0058] In the above, the optical probe shown in FIG. 2 can obtain the same effects even if various structures such as those described below are adopted.

[0059] Figure 6 is a diagram showing a second embodiment of the optical probe shown in Figure 2, with Figure 6(a) being a bottom view and Figure 6(b) being a side view. As shown in Figure 6, the optical probe according to the second embodiment has a configuration similar to that of the optical probe shown in Figure 2, but differs in that it includes one illumination optical fiber FE1 for irradiating light guided from a light source (not shown), and three detection optical fibers FD1 to FD3 that are disposed at points spaced a distance ρ1, ρ2, and ρ3 from the illumination optical fiber FE1, respectively, and guide detected light to a detector (not shown).

[0060] Figure 7 is a diagram showing a third embodiment of the optical probe shown in Figure 2, with Figure 7(a) being a bottom view and Figure 7(b) being a side view. As shown in Figure 7, the optical probe according to the third embodiment has a configuration similar to that of the optical probe shown in Figure 2, but differs in that it includes one illumination light guide LE1 for irradiating light guided from a light source LS provided in this probe, and three detection light guides LD1 to LD3 that are disposed at points spaced a distance ρ1, ρ2, and ρ3 from the illumination light guide LE1, respectively, and guide detected light to detectors DT1 to DT3 provided in the probe.

[0061] Figure 8 shows a fourth embodiment of the optical probe shown in Figure 2, with Figure 8(a) being a bottom view and Figure 8(b) being a side view. As shown in Figure 8, the optical probe according to the fourth embodiment has a configuration similar to that of the optical probe shown in Figure 2, but differs in that it has one light irradiating unit E1 and three measuring units D1 to D3 that are spaced apart from the light irradiating unit E1 by distances ρ1, ρ2, and ρ3, respectively, and that are not arranged in a straight line.

[0062] Figure 9 shows a fifth embodiment of the optical probe shown in Figure 2, with Figure 9(a) being a bottom view and Figure 9(b) being a side view. As shown in Figure 9, the optical probe according to the fifth embodiment has a configuration similar to that of the optical probe shown in Figure 2, but differs in that it includes one measurement unit D1 and three light irradiating units E1 to E3 disposed at positions spaced a distance ρ1, ρ2, and ρ3 from the measurement unit D1. Note that the three light irradiating units E1 to E3 do not have to be disposed in a straight line as long as they are disposed at positions spaced a distance ρ1, ρ2, and ρ3 from the measurement unit D1, respectively.

[0063] Fig. 10 is a bottom view showing a sixth embodiment of the optical probe shown in Fig. 2. As shown in Fig. 10, the optical probe according to the sixth embodiment has a configuration similar to that of the optical probe shown in Fig. 2, but further includes measurement units D4 to D6, which are arranged at three points at different distances from the light irradiation unit E1 and are made up of photodetectors such as avalanche photodiodes and photodiodes, and the substrate 10, which has high reflectivity, is arranged only between the light irradiation unit E1 and the measurement units D1 to D3.

[0064] With this configuration, the intensity is measured between the light irradiation unit E1 and the measurement units D1 to D3 in a state where the reflectance of the light emitted from the inside to the outside of the object is high, as described above, and the intensity is measured between the light irradiation unit E1 and the measurement units D4 to D6 in a state where the reflectance of the light is low. In this way, the absorption coefficient μ a and the reduced scattering coefficient μ S A method of calculating ' is also preferable, but this method will be explained in the second embodiment below.

[0065] As described above, according to the optical property measuring device 1 according to the first embodiment of the present invention and the method realized by the operation of this device, the absorption coefficient μ a and the reduced scattering coefficient μ S The absolute value of ' can be calculated. S ´) / (4μ a )] 1 / 2 By calculating ρ, it is also possible to calculate an approximation of the optical path length of light propagation within the biological tissue 9, making it possible to more accurately estimate brain activity and muscle activity from the oxygenation state of the blood flowing within the biological tissue 9.

[0066] [Embodiment 2] The reflectance of the substrate 10 according to the first embodiment is constant. However, by performing similar measurements using a film with a variable reflectance instead of the substrate 10, the absorption coefficient μ a and the reduced scattering coefficient μ S The absolute value of ' can be calculated. In the following, an embodiment using a variable reflectance film will be described.

[0067] 11A and 11B are schematic diagrams for explaining the function of the reflectance variable film 20 used in the optical probe constituting the detection unit 2 according to embodiment 2 of the present invention, with Fig. 11A showing the state when a voltage is applied and Fig. 11B showing the state when no voltage is applied. As shown in Fig. 11A and 11B, the reflectance variable film 20 includes a liquid crystal layer 15, two electrodes 16 that sandwich the liquid crystal layer 15, and two transparent cover layers 17 that are respectively disposed on the outside of the two electrodes 16.

[0068] By using the reflectance variable film 20 having such a configuration, it is possible to actively change the internal reflectance of the biological tissue 9. That is, since the reflectance variable film 20 is a liquid crystal film having the above-mentioned configuration, as shown in FIG. 11A, by applying a voltage in the film thickness direction of the liquid crystal film to align the liquid crystal molecules in one direction, it is possible to transmit light and achieve a non-reflective state. On the other hand, as shown in FIG. 11B, by turning off the voltage and disordering the orientation of the liquid crystal molecules, light is diffusely reflected, and therefore it is possible to variably control the reflectance within the liquid crystal layer by changing the voltage. Below, it will be described how to actively change the internal reflectance in this way and change the absorption coefficient μ of the biological tissue 9. a and the reduced scattering coefficient μ S An example of a method for measuring ' will be described.

[0069] [1] Measurements are taken at three different SD distances. 12 is a side view showing the structure of the optical probe when performing measurements at three different SD distances in the second embodiment of the present invention. As shown in FIG. 12, in this case, the internal reflectance r d1 or internal reflectance r d2 Using the variable reflectance film 20, the intensities I1, I2, and I3 of the diffuse reflected light are measured at three measurement points D1 to D3. 12 (=I1 / I2) and J 23 (=I2 / I3) is the two internal reflectances r d1 ,r d2 Since the four simultaneous equations shown in the following equation (17) hold true,

[0070]

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[0071] In equation (17), the function R is the SD distance ρ and the internal reflectance r d , absorption coefficient μ a , scattering coefficient μ s Since this is an analytical solution for the diffuse reflectance when s ´,μ a), or four unknowns (μ s ´,μ a ,r d1 ,r d2 ) can be solved.

[0072] [2] When measuring at two different SD distances 13 is a side view showing the structure of the optical probe when measurements are performed at two different SD distances in the second embodiment of the present invention. As shown in FIG. 13, in this case, the internal reflectance r d1 or internal reflectance r d2 Using the variable reflectance film 20, the intensities I1 and I2 of the diffusely reflected light are measured at two measuring sections D1 and D2.

[0073] In this measurement, the same internal reflectance r d The ratio J of the intensities I1 and I2 at different SD distances ρ 12 (=I1 / I2) but with different internal reflectance r d The ratio of the intensities I1 and I2 at the same SD distance ρ is J(ρ1)(=I1(ρ1,r d1 ) / I2(ρ1,r d2 ) ) and J(ρ2)(=I1(ρ2,r d1 ) / I2(ρ2,r d2 ) ) is obtained, the following simultaneous equations with two unknowns are established. Note that with the same internal reflectance r d The ratio J of the intensities I1 and I2 at different SD distances ρ 12 (=I1 / I2) and different internal reflectances r d The ratio of the intensities at the same SD distance ρ to J(ρ1)(=I1(ρ1,r d1 ) / I2(ρ1,r d2 ) ) may be used.

[0074]

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[0075]

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[0076] The simultaneous equations shown in equation (18) or equation (19) are solved in two unknowns (μ s ´,μ a ) can be solved. This method is advantageous in that it requires fewer measuring units and fewer measurements than when measurements are taken at three different SD distances, making it easier to find the solution.

[0077] [3] When the internal reflectance of the variable reflectance film 20 is modulated with frequency ω FIG. 14 is a graph for explaining a method for modulating the internal reflectance of the variable reflectance film 20 shown in FIG. 13. FIG. 14(a) shows the internal reflectance r d 14(b) shows the time change in the intensity I1 of the detected light measured by the measuring unit D1 shown in FIG.

[0078] As shown in Fig. 14(a), the internal reflectance of the reflectance variable film 20 is modulated at a frequency ω, and the intensity of the modulated component of the diffusely reflected light is measured using a lock-in amplifier with frequency ω. The intensity I1 at this time and the measured value J(ρ) measured by the measuring units D1 and D2 shown in Fig. 13 are measured as follows:

[0079] The intensity I1 detected at the SD distance ρ1 is the steady-state intensity I 10 Using [I 10 +δI1(ωt)]. Therefore, the following equation (20) holds.

[0080]

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[0081] In addition, in equation (20), the absolute value of ΔI1(ωt) indicates the output value of the lock-in amplifier at frequency ω.

[0082] Incidentally, since there is a functional relationship between the control voltage and the internal reflectance of the variable reflectance film 20, the control voltage waveform to the variable reflectance film 20 can be shaped so that the periodic average of the fluctuation term ΔI1(ωt) becomes zero. This makes it easy to establish the above equation (20).

[0083] Similarly, the following equation (21) holds for the intensity I2.

[0084]

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[0085] The values ​​J(ρ1) and J(ρ2) obtained in this way from equations (20) and (21) are advantageous in that they are more resistant to noise and have higher measurement accuracy than when only the DC component is measured at the two different SD distances mentioned above. In this case, the simultaneous equations are as follows:

[0086]

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[0087] [Embodiment 3] In the optical probe described above, if the contact surface with the biological surface is a non-reflective or fully absorbing surface but a highly reflective surface, the contact may be insufficient and a gap may form between the optical probe and the biological surface. As shown in Figure 15, this can cause a phenomenon known as optical piping or optical channeling, in which light propagates along the gap 18, and light that does not propagate through the biological tissue 9 may be detected. Note that in the case of a non-reflective surface, even if there is a small gap, this is not a problem because the light is absorbed by the optical probe surface.

[0088] Also, a concern that arises when using the variable reflectivity film 20 as described above is that in a liquid crystal film having a structure as shown in FIG. 16, the transparent coating layer 17 contacts the living tissue 9. Through this transparent coating layer 17, optical pipelining as indicated by the arrow in FIG. 16 occurs. In such optical pipelining, since light is reflected at the interface between the transparent film layer 17 and the liquid crystal layer 15, a problem occurs in that the contrast when the voltage applied to the variable reflectivity film 20 is turned on and off decreases.

[0089] Therefore, in order to avoid such a problem, it is preferable to insert a film 21 having a louver structure having a shielding effect against obliquely incident light as shown in FIG. 17A between the substrate 10, the variable reflectivity film 20, and the living tissue 9.

[0090] As shown in FIG. 17B, let the refractive indices of the living tissue 9, the film 21, the transparent coating layer 17 of the variable reflectivity film 20, or the substrate 10 be n1, n2, and n3, respectively, and let the magnitude relationship between them be n1 < n2, n3. At this time, if the incident angle of light from the living tissue 9 to the film 21 is θ1, when the incident angle θ1 is smaller than the critical angle θ c (= sin ―1 (n1 / n3)), the light passes through the film 21 and enters the substrate 10 or the variable reflectivity film 20, and when it is greater than or equal to the critical angle θ c In the above case, the light is totally reflected by the transparent coating surface 17. Thus, the above optical pipelining can be avoided.

Explanation of Reference Numerals

[0091] 1 Optical characteristic value measuring device, 2 Detection unit, 5 Calculation unit, 10 Substrate, 20 Variable reflectivity film, 21 Film, E1 to E3 Light irradiation unit, D1 to D6 Measurement unit, FE1 Irradiation optical fiber, FD1 to FD3 Detection optical fiber, LE1 Irradiation light guide, LD1 to LD3 Detection light guide, LS Light source, DT1 to DT3 Detector.

Claims

1. a light irradiation means for irradiating light from the surface of the object to the inside; a measuring means for measuring the intensity of the light reflected inside the object and emitted to the outside of the object at at least two points on the surface that are at different distances from the light irradiating means; a light reflecting means placed between the light irradiating means and the measuring means so as to cover the surface, and which increases the reflectance of light emitted from the inside to the outside; a calculation means for calculating an absorption coefficient and a scattering coefficient of the object based on the intensity obtained by the measurement, the internal reflectivity of the light reflecting means is periodically modulated; Optical property measurement device.

2. a light irradiation means for irradiating light from the surface of the object to the inside; a measuring means for measuring the intensity of the light reflected inside the object and emitted to the outside of the object at at least two points on the surface that are at different distances from the light irradiating means; a light reflecting means placed between the light irradiating means and the measuring means so as to cover the surface, and which increases the reflectance of light emitted from the inside to the outside; a calculation means for calculating an absorption coefficient and a scattering coefficient of the object based on the intensity obtained by the measurement, Further, a light shielding means is provided between the object and the light reflecting means to prevent light piping from occurring at a boundary between the object and the light reflecting means. Optical property measurement device.

3. 3. The optical property measuring device according to claim 1, wherein the measuring means measures the intensity of the light reflected inside the object and emitted to the outside at three points on the surface that are at different distances from the light irradiating means.

4. 3. The optical characteristic value measuring device according to claim 1, wherein the internal reflectance of said light reflecting means is variable.

5. 3. The optical characteristic measuring device according to claim 1, wherein the calculation means calculates the absorption coefficient and the scattering coefficient by calculating a diffuse reflectance of the light on the object by Monte Carlo simulation.

6. 3. The optical characteristic value measuring device according to claim 1, wherein the calculation means calculates the absorption coefficient and the scattering coefficient by calculating the diffuse reflectance of the light on the object as a solution of a telegrapher's equation.

7. 3. The optical characteristic measuring device according to claim 1, wherein the calculation means calculates the absorption coefficient and the scattering coefficient by calculating the diffuse reflectance of the light on the object as a solution of a light diffusion equation.

8. 3. The optical characteristic value measuring device according to claim 1, wherein the calculation means calculates the absorption coefficient and the scattering coefficient by calculating a diffuse reflectance of the light on the object as a solution of a light transport equation.

9. a measuring means disposed on the surface of the object and configured to measure the intensity of light emitted from the inside of the object to the outside; a light irradiation means for selectively irradiating light from the surface to the interior at at least three points on the surface that are at different distances from the measurement means; a light reflecting means disposed between the light irradiating means and the measuring means so as to cover the surface, and which increases the reflectance of the light emitted from the inside to the outside; a calculation means for calculating an absorption coefficient and a scattering coefficient of the object based on the intensity obtained by the measurement, the internal reflectivity of the light reflecting means is periodically modulated; Optical property measurement device.

10. a measuring means disposed on the surface of the object and configured to measure the intensity of light emitted from the inside of the object to the outside; a light irradiation means for selectively irradiating light from the surface to the interior at at least three points on the surface that are at different distances from the measurement means; a light reflecting means disposed between the light irradiating means and the measuring means so as to cover the surface, and which increases the reflectance of the light emitted from the inside to the outside; a calculation means for calculating an absorption coefficient and a scattering coefficient of the object based on the intensity obtained by the measurement, Further, a light shielding means is provided between the object and the light reflecting means to prevent light piping from occurring at a boundary between the object and the light reflecting means. Optical property measurement device.

11. In an optical characteristic value measuring device, a light reflecting means for increasing the reflectance of light emitted from the inside to the outside of an object is placed so as to cover the surface between a position where light is irradiated from the surface of the object to the inside and a measurement position where the intensity of the light reflected inside the object and emitted to the outside of the object is measured, a first step of irradiating light from the surface to the interior; a second step of measuring the intensity of the light reflected inside the object and emitted to the outside of the object at at least two points on the surface that are at different distances from the irradiation position; a third step of calculating an absorption coefficient and a scattering coefficient of the object based on the intensity obtained by the measurement in the second step; the internal reflectivity of the light reflecting means is periodically modulated; Optical property measurement method.

12. In an optical characteristic value measuring device, a light reflecting means for increasing the reflectance of light emitted from the inside to the outside of an object is placed so as to cover the surface between a position where light is irradiated from the surface of the object to the inside and a measurement position where the intensity of the light reflected inside the object and emitted to the outside of the object is measured, a first step of irradiating light from the surface to the interior; a second step of measuring the intensity of the light reflected inside the object and emitted to the outside of the object at at least two points on the surface that are at different distances from the irradiation position; a third step of calculating an absorption coefficient and a scattering coefficient of the object based on the intensity obtained by the measurement in the second step; the optical characteristic value measuring device further includes a light shielding means disposed between the object and the light reflecting means, for preventing light piping from occurring at a boundary between the object and the light reflecting means; Optical property measurement method.

13. 13. The optical characteristic value measuring method according to claim 11, wherein in the third step, the absorption coefficient and the scattering coefficient are calculated by calculating the diffuse reflectance of the light on the object by Monte Carlo simulation.

14. 13. The optical characteristic value measuring method according to claim 11, wherein in the third step, the absorption coefficient and the scattering coefficient are calculated by calculating the diffuse reflectance of the light on the object as a solution to a telegrapher's equation.

15. 13. The optical characteristic value measuring method according to claim 11, wherein in the third step, the absorption coefficient and the scattering coefficient are calculated by calculating the diffuse reflectance of the light on the object as a solution of a light diffusion equation.

16. 13. The optical characteristic value measuring method according to claim 11, wherein in the third step, the absorption coefficient and the scattering coefficient are calculated by calculating the diffuse reflectance of the light on the object as a solution of a light transport equation.

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