JP5465924B2 - Optical analysis method for heterogeneous materials - Google Patents

Description

  The present invention relates to a heterogeneous substance that can be analyzed quantitatively or qualitatively for a heterogeneous substance that is divided into nonuniform areas inside the substance and that has areas with different component structures. It relates to the analysis method.

  For example, when considering a biological material, it is not an optically uniform material, including complex tissue organs. Conventionally, when analyzing (analyzing) a heterogeneous material in which heterogeneous regions are mixed in this way, the analysis is performed using a formula similar to that for a single material having a uniform composition.

  However, when analyzing a heterogeneous material using a formula similar to that of a single, uniform composition material, if the light exchange between the regions differs due to scattering inside the heterogeneous material, Does not exhibit a simple light distribution that is subject to uniform attenuation or scattering. Therefore, it is necessary to actually consider a special light distribution due to mutual scattering between the internal regions. However, the situation is so complicated that it cannot be handled, and such difficult circumstances have been ignored. As a result, the fact is that we are dissatisfied with the erroneous analysis results. In addition, there is no literature regarding analytical methods for optically analyzing heterogeneous substances.

  The present invention has been made in view of such circumstances, and its purpose is to analyze each region theoretically and accurately even if it is a heterogeneous material in which the inside of the material is divided into non-uniform regions. It is an object of the present invention to provide an optical analysis method for heterogeneous substances.

In order to solve this problem, the invention according to claim 1 of the present invention includes a light source device capable of selecting a wavelength and irradiating measurement light on a test substance body that is a mixture of a plurality of constituent substances, and an incident light A light and a detector capable of measuring the transmitted light and the reflected light, and based on the measured light quantity measured by the detector, t is an effective transmittance when passing through the interface with air , Procedure 1 for obtaining the parameters ρ and λ according to the following equation 1, and measurement at a plurality of wavelengths as necessary, and obtaining ρ and λ from the respective measured values according to the equation 1, and the respective absorption coefficients and scattering of the constituent materials And a step 2 of determining an optical characteristic coefficient composed of a coefficient to identify a component and obtaining a component concentration of each constituent material.

  According to the present invention, since the mediation coefficients ρ and λ are obtained by the equation 1 in the procedure 1, and the component concentrations of each of the plurality of constituent materials are obtained by the optical system coefficient determined by the procedure 2, the inside of the substance is not uniform. Even if a heterogeneous substance is divided into regions, each region can be analyzed theoretically and accurately.

The figure which shows typically the relationship between the 1st area | region x and the 2nd area | region y of a substance.

Hereinafter, the best mode for carrying out the present invention will be described in detail.
An analysis apparatus capable of performing the optical analysis method according to the present invention includes a light source device capable of irradiating a test substance with an appropriate wavelength if necessary, incident light of light emitted from the light source device, and A detector capable of measuring transmitted light and scattered light is provided. In addition, regarding the projection and reception of the reflected light, it is preferable to use a bundle of a plurality of light source device (projector) elements and light receiver (detector) elements adjacent to each other.

  Analyzing the components of a substance using light is a useful inspection method because the inside of the substance can be inspected without damaging the object. Although there are various methods for this optical analysis, the present patent irradiates light from the light source device, measures the reflected light and transmitted light with the detector, and based on these numerical values, is completely new as will be described later. The internal component concentration is qualitatively and quantitatively determined using Equation 1.

  For this purpose, if the characteristic absorption coefficient and scattering coefficient of the substance are known as each spectral data in the wavelength range to be used, the concentration of the substance inside is determined by comparing with the measured value. In addition, identification or quantitative analysis is possible.

  However, general substances are not necessarily composed of a single composition component, and are often composed of a plurality of different components, regions, or parts. In particular, in the medium, light is scattered and enters other inhomogeneous regions, and is governed by different absorption coefficients and scattering coefficients in the respective regions. In other words, in non-uniform materials, light is scattered to other component regions by changing the direction of flow due to scattering, and some of them are scattered back to the original, so the light distribution in the test substance body is It doesn't flow uniformly. Since the light is scattered or absorbed depending on the material characteristics of each component, the light distribution redistributes within the target material, resulting in a non-uniform flow.

  In addition, since the output light is a mixture of the effects of complex mutual multiple scattering, the light distribution inside the substance takes a special redistribution form. Nonetheless, if we think of it as a single component and apply it only to the simple absorption and scattering formulas of a single substance, it is impossible to know what is being measured and analysis is impossible.

  The heterogeneous state refers to a state in which a plurality of different substances occupy different regions in the test substance body and are mixed. Any substance with a non-uniform composition or structure in a so-called mixture falls into this category. Powders, granules and the like are a mixture of the substance particles and air, and foods are a mixture of various tissue substances and moisture. Since there are various tissue organs in the ecology of plants and animals, they are heterogeneous substances.

  For example, clouds and soot in the atmosphere behave as a mixture with respect to light having a short wavelength, but may be considered as a uniform substance with respect to radio waves having a long wavelength. As can be seen, if the mean free path of light is sufficiently long compared to the size of the region, it can be considered as an averaged uniform material, but if not, the size of each of the regions of multiple materials is It should not be ignored and should be a heterogeneous material. If the size of each region is not small compared to the mean free path of light, it is all within the scope of the present invention, but this size varies depending on the absorption scattering coefficient and is not constant, and is inversely proportional to them. It is different and complicated in some cases.

  Conventionally, there has been no measurement method that can cope with such a case. All previous basic theories for this analysis are based on the assumption that the medium is uniform, and if the medium is non-uniform, it has never been attempted due to the difficulty of the theory. Even though there are studies of the scattering effect, it is difficult to build a theory that can calculate each component separately when a plurality of component regions are mixed unevenly, and there is no precedent in the public literature. However, in terms of numerical calculations, only a numerical solution called the so-called Monte Carlo method, in which specific structures and materials are arranged and simulated one by one, could be achieved. This is something that can only be done if the internal structure of the material region is known. It is self-contradictory and not a general analysis.

  In non-uniform materials, redistribution due to light scattering occurs, and the light distribution inside each component is disturbed, so just measuring the emitted light from the outside only gives the average amount. The amount of light in a component changes substantially, the properties of each component are affected by other parts, and the light behaves differently than in a single substance, so you can determine what the internal substance component is. Disappear. The present invention provides an epoch-making method for quantitatively determining the properties of each individual internal component even in a non-uniform medium.

  Here, a specific example of the optical analysis method according to the present invention will be described. The test substance body (specimen) preferably has a plate shape whose upper and lower sides are surrounded by parallel planes. However, there is no strict requirement for the outer shape as will be described later. In the following, it is considered that the distribution state of each substance in the test substance body in the heterogeneous mixed region is random, and there is no particular unevenness depending on the location, and in that sense, it is “uniformly” nonuniform.

  The irradiation light is assumed to be incoherent at a single wavelength. This is irradiated perpendicularly from above with respect to the plane of the test substance body to receive transmitted light from the back surface. Further, the reflected light is received from the vertical direction on the same upper surface as the test substance body. The scattering in the test substance is assumed to be isotropic scattering for the sake of simplicity. That is, it is assumed that the test substance has no special crystal anisotropy or polarization. This assumption is not necessary if the isotropic scattering is strong because the polarization is suppressed by the scattering.

If the thickness h of the test substance is large and transmitted light cannot be obtained, the reflected light is measured at a point shifted laterally from the light incident point on the same incident surface. It can be regarded as equivalent transmitted light. The incident light generates a component that reverses due to scattering and returns to the original incident surface. At that time, the locus becomes a banana shape (or hairpin shape). What is necessary is just to convert into the locus length. According to Monte Carlo simulation in the human body, which is the most appropriate application example of the present invention, it is understood that this correction coefficient should be regarded as about 1.05 times the linear distance between the incident point and the outgoing point. Yes. In these trajectories, there is almost no component that goes straight from the incident point to the outgoing (reflecting) point due to external loss, and internally, the light amount decreases as the distance travels longer, resulting in an intermediate between them. This is because the banana-like trajectory that is the situation becomes dominant. As long as the mean free path and the size of the tissue region are not significantly different as the present invention is applied, this correction factor will not exceed 1.15 for normal materials.

  In the following, the mixed state of two types of substances will be handled. If there are three or more types, the first type to be obtained and the other types may be divided into two types and regarded as two types in a pseudo manner, and the unknowns may be separated and handled one after another. However, in this case, since the physical properties of the collected second substance species correspond to unknown substances, the number of unknowns may increase. Therefore, as described later, it is necessary to increase the number of experiments to be measured and increase the number of simultaneous equations.

  As a model of the light flow, a steady light flow inside the test substance body is considered by uniform light irradiating the substance from the z direction as shown in FIG. Let x and y be the names of the two types of substance regions and the amount of light present in each, and the subscripts f and b be the light in the forward and reverse directions, respectively. Further, a and s are the characteristic absorption coefficient and scattering coefficient of each substance, respectively. Let X be the light that is scattered from the x region and terminates in the original region or in another x region. That is, what ends in the y region is 1-X. Y is defined similarly.

  Therefore, the relationship X + Y = 1 is established. The relationship between x, y and X, Y is shown in FIG. Using these definitions, the following equation (Equation 2) is obtained for a steady flow flowing in the z direction.

  Here, the factor of 1/2 is generated by integrating and averaging the portions scattered with a vertical direction component with respect to the dz direction. The above equation is solved and the following equation (Equation 3) is defined.

When some calculations are performed from the above formulas, the following practical formulas are derived.
1. There are three types of measurement light amounts to be used for analysis, where the irradiation light amount is I, the transmitted light amount is T, and the reflected light amount is R. However, since the quantity handled in the calculation is a value inside the substance, the quantity that can be measured outside, that is, the incident light I ₀ , the transmitted light T ₀ , and the reflected light R ₀ is a loss due to a difference in refractive index when passing through the substance interface. Only different. In consideration of this, assuming that the interface transmittance is t, one is air and the average refractive index of the substance is n (where n> 1), and the following equation (Equation 4) is obtained.

  When calculating including this t, the quantity of following Formula (Formula 5) is converted from a measured value.

  Further, when it can be assumed that t = 1, a simplified expression of the following expression (Expression 6) equivalent to the above may be used.

  By solving the above equation, ρ and λ can be determined. An assumed value is substituted for t, and a value sequentially corrected according to the result may be used. Hereinafter, a procedure for obtaining a, x and density c of each component using ρ and λ determined in this way will be described.

  2. As an example when the object to be analyzed is a two-component system, x and y are subscripts representing the respective components, and c is the concentration of each component therein. Further, to obtain a and s or each component concentration by the following method, the following is performed.

In general, A and X are assumed to be the characteristic absorption coefficient and scattering coefficient of component element materials. These are characteristic substance coefficients described in literatures such as data handbooks as characteristic values per unit concentration and as a function of wavelength. That is, the measured absorption coefficient and scattering coefficient are proportional to each other via A and S and the concentration c, and are expressed by the following equations. Since the subsequent calculation is an algebraic calculation, it can be appropriately processed if necessary, and means are known. The following are some examples.
c _x = a _x / A _x = s _x / S _x
c _y = a _y / A _y = s _y / S _y

Further, by substituting ρ and λ obtained by calculation into the following equations, c _x and _cy are obtained.
2ρ ² = c _x ² X _x ² + (c _x ² X) A _x X + _cy ² A _y ² + ( _cy ² Y) A _y S _y
If the unknowns are considered to be c _x , c _y , c _x ² X, and c _y ² Y, measurement can be repeated with four wavelengths selected, and four equations can be determined from the results. . Also,
I / λ = c _x A _x + (c _x X) S _x + _cy A _y + (cy _y ) S _y
Then, there are four unknowns: c _x , c _y , c _x X, and _xy Y.
As the aforementioned measurement wavelength, it is important to select a wavelength at a singular point where the characteristic spectrum of the assumed substance shows a peak.

Since the above simultaneous equations are linear, they can be easily solved, and in the same manner, solutions can be obtained by combining necessary amounts. As a simple example, if all S are equal and S _x = S _y = S, then three measurement wavelengths are required, which is simplified as follows. In this case, there are three unknowns (c _x , c _y , X), and simultaneous equations can be obtained by measuring three wavelengths. For example, the concentration is expressed by the following equation (Equation 7). Subscripts are the respective wavelengths, and subscripts 1, 2, and 3 indicate the three wavelengths.

  Similarly, other quantities can be obtained by algebraic calculation. As in this example, an appropriate formula may be established and solved depending on the characteristics and cases of each substance. If these simple methods are not found, it is obvious that these simultaneous equations can always be solved within the range of linear algebra if data are collected by repeating measurement by changing the wavelength by the number of unknowns.

  Of course, if the information of X and Y is known, it may be used, and it is not limited to the above-described proportional relationship, and an arbitrary unknown can be obtained if the number of necessary simultaneous equations is sufficient. In addition, when there is background noise or mixed light, the background amount is determined in advance by experimentally measured values, theoretically predicted amounts, or amounts according to known laws, and subtracting from the measured signal Can be treated as equivalent to increasing unknowns.

  In addition, a surface layer such as skin tissue may exist in a biological material. In such a case, since the characteristic coefficient of the epithelial layer is generally known, it is better to exclude them by calculation in advance and handle only the inside. Otherwise, simultaneous equations may be connected at the interface between the epithelial layer and the determined interior. Use the least squares method if necessary.

  As described above, the optical analysis method according to the present invention has an excellent feature that even an inhomogeneous substance can be analyzed by algebraic calculation. Specifically, it is a heterogeneous substance in which the inside of the substance is divided into non-uniform areas by the procedure for obtaining the mediation coefficients ρ and λ by Equation 1 and the procedure for determining the optical system coefficient and the component concentration of each substance. However, each region can be extracted and analyzed in a theoretically accurate manner. As a result, it is possible to provide for the first time an optical analysis method for non-invasive analysis of heterogeneous complex mixed materials, for example, biological materials, for which there has been no means in the past, and it is an extremely useful invention for industrial technical applications. It is.

  It is obvious that the mathematical formula that can be derived by the formula 1 (that is, mathematically equivalent to the formula 1) is directly derived by the formula 2 and is naturally equal to the formula 1. This is the same for all the mathematical formulas from the mathematical formula 6 to the mathematical formula 7, and the mathematical formulas derived mathematically from them are all equivalent to the results directly calculated from the mathematical formulas 1 and 3. Therefore, each is mathematically equivalent to the original expression. A method of using such an expression is also included in the present invention. In addition, since the algebra calculation described above can be calculated sufficiently quickly, once the spectrum indicating the target component is determined, the amount of light can be traced over time. For example, it is possible to monitor and track how a specific biological material changes over time. Such temporal analysis is naturally included in the present invention.

  The present invention is not limited to biological materials and can be used for optical analysis of all heterogeneous materials.

    x... the substance region, X... probability that the scattered light from the x region terminates in x, y... the substance region, Y... the probability that the scattered light from the y region terminates in y.

Claims (1)

A light source device that can irradiate measurement light by selecting a wavelength to a test substance body that is a mixture of a plurality of constituent substances, and a detector that can measure incident light and transmitted and reflected light thereof
Procedure 1 for determining parameters ρ and λ according to Equation 1, where t is the effective transmittance when passing through the interface with air , based on the amount of light measured by the detector,
If necessary, measure at a plurality of wavelengths and obtain ρ and λ from the respective measured values according to the above formula 1, determine the optical characteristic coefficient consisting of the absorption coefficient and the scattering coefficient of each constituent material, and identify the component, Procedure 2 for determining the component concentration of each constituent material,
A method for optical analysis of heterogeneous material, comprising:

Images