JP2003149136A - Optical image measurement method - Google Patents

Abstract

(57) [Summary] To obtain a more accurate component concentration in consideration of the non-linearity between the component concentration of a subject and measurement data. An optical image measurement method for irradiating a living body with light and obtaining an image of light reflected from the living body using a two-dimensional detector, wherein a non-linear relationship between tissue information in the living body and measurement data is obtained. It is obtained in advance, and tissue information in the living body is obtained using this nonlinear relationship. Thus, tissue information in the living body can be obtained in consideration of the nonlinear relationship between the tissue information in the living body and the measurement data.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical image measuring method for measuring the distribution of oxygenated hemoglobin, deoxygenated hemoglobin, and melanin in living tissue, which is displayed on a two-dimensional image to indicate normal tissue or blood flow. It can be applied to biological image diagnosis for diagnosing abnormalities.

[0002]

2. Description of the Related Art An optical measuring method is known in which a subject such as a living body is irradiated with light and the light scattered, reflected and absorbed by the subject is received to optically measure the tissue of the subject. .
As such an optical measurement method, a method of obtaining a two-dimensional image by detecting reflected light or transmitted light from the subject with a two-dimensional detector, or using a plurality of detectors arranged at different distances from the light source A method for obtaining a quantity has been proposed.

However, the method of obtaining a two-dimensional image using a two-dimensional detector has a problem that the measured value is a relative value and an absolute amount cannot be obtained, and the above-mentioned absolute amount measuring method is used. In order to obtain two-dimensional information, it is assumed that the composition of the tissue of the subject is uniform, in addition to the problem that the device configuration and arithmetic processing are complicated. There is a problem that the measured value is not significant and accurate diagnosis is hindered.

Therefore, a method of obtaining significant biological information at the time of measurement by using two-dimensional image information obtained by a two-dimensional detector has been proposed. One method proposed is to obtain a plurality of image data obtained by measuring a two-dimensional change amount of a subject with different measurement wavelengths and measurement times, and calculate the image data of the plurality of wavelengths and a plurality of times. By
This is to obtain significant biological information at the time of measurement. In addition, another method proposed is that two-dimensional measurement image data obtained by detecting a subject with a two-dimensional detector and reference image data obtained independently of the subject are respectively measured at a plurality of measurement wavelengths. The absolute amount is obtained by obtaining and calculating using the measurement image data and the reference image data by the plurality of measurement wavelengths.

[0005]

[Problems to be Solved by the Invention]
The method of obtaining significant biological information at the time of measurement using the two-dimensional image information obtained by the two-dimensional detector is assumed to have a linear proportional relationship between the component concentration in the subject and the measurement data, It is calculated by linear calculation based on this assumption.

However, when the subject is a living body,
Due to strong scattering in the living body, there is no guarantee that a linear proportional relationship is established between the component concentration and the measurement data (absorbance). In particular, hemoglobin concentration (oxygenated hemoglobin, deoxygenated hemoglobin) and melanin concentration When calculating the absolute amount, there is a problem that a large error occurs.

Therefore, the present invention aims to solve the above-mentioned conventional problems and to obtain a more accurate component concentration in consideration of the non-linearity between the component concentration of the object and the measurement data. More specifically, it is an object of the present invention to obtain a more accurate hemoglobin concentration and melanin concentration in consideration of the nonlinearity between the absorbance due to scattering in the living body and the hemoglobin concentration and melanin concentration.

[0008]

The present invention seeks tissue information in a living body in consideration of a non-linear relationship between tissue information in the living body and measurement data. The present invention is an optical image measurement method of irradiating a living body with light and obtaining an image of light reflected from the living body by using a two-dimensional detector, and shows a non-linear relationship between tissue information in the living body and measurement data. Obtained in advance, the tissue information in the living body is obtained using this non-linear relationship. As the tissue information in the living body to be obtained, the component concentration in the living body can be used.

The present invention includes two aspects. According to the first aspect, it is possible to obtain the component concentration in the living body, and according to the second aspect, it is possible to obtain the change in the component concentration in the living body. The first mode is to obtain the concentration of a component in a living body, which can be in two forms. The first form of obtaining the component concentration in the living body is to obtain the non-linear relationship between the component concentration in the living body and the measurement data by a relational expression in advance, and fit the measurement image data at a plurality of measurement wavelengths to this relational expression. Then, the concentration of the component in the living body is obtained. In the second embodiment for obtaining the concentration of components in the living body, the non-linear relationship between the concentration of components in the living body and the measurement data is obtained in advance by a reference table, and the measurement image data at a plurality of measurement wavelengths is collated with this reference table. By doing so, the concentration of the component in the living body is obtained.

The second mode is to obtain the change in the concentration of the component in the living body, and the change in the measurement image data is the change in the concentration of the component in the living body and the distance that light travels in the living body due to diffusion by each component. It is represented by a relational expression including the product of the average optical path length, and the measurement image data at a plurality of measurement wavelengths of at least the same number as the component to be measured is applied to this relational expression to obtain the change in the concentration of the component in the living body.

In the embodiment of the present invention, the absorbance is used as the measurement data, and the oxygenated hemoglobin concentration, the deoxygenated hemoglobin concentration, and the melanin concentration are obtained as the component concentrations in the living body. In addition, the nonlinear relationship between the concentration of components in the living body and the measurement data is that the living body is a layer containing melanin (epidermis), a layer containing oxygenated hemoglobin and deoxygenated hemoglobin (dermis), a layer containing fat (fat layer). ) Is used, and Monte Carlo simulation is applied to the three-layer model to obtain the model. The relational expression of the second aspect is Lambert-
It is obtained by applying the average flight distance of light due to diffusion of each component obtained by Monte Carlo simulation to Beer's law.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. Hereinafter, as the tissue information of the living body measured by the optical image measuring method of the present invention, the component concentration or the change in the component concentration in the living body, particularly the case of oxygenated hemoglobin, deoxygenated hemoglobin, and melanin will be described.

The present invention is to irradiate a living body with light and perform optical image measurement of light reflected from the living body using image data obtained by using a two-dimensional detector. By irradiating light with a plurality of wavelengths, the light reflected from the living body is detected by a two-dimensional detector to obtain measurement data, and by processing the measurement data, oxygenated hemoglobin,
The concentration of components such as deoxygenated hemoglobin and melanin in the living body or the change in the concentration of components is obtained.

In the optical image measuring method of the present invention, in this data processing, by using the non-linear relationship between the concentration of the constituent in the living body and the measurement data, which is obtained in advance,
The component concentration in the living body or the change in the component concentration without the influence of non-linearity is obtained. The optical image measuring method of the present invention includes two aspects. According to the first aspect, it is possible to obtain the component concentration in the living body, and according to the second aspect, it is possible to obtain the change in the component concentration in the living body. . In any of the embodiments, a non-linear relationship between the component concentration in the living body and the measurement data is obtained in advance, and data processing of the measurement data is performed based on this non-linear relationship.

First, an example of obtaining a non-linear relationship between the concentration of a component in the living body and the measurement data will be described. Here, a three-layer model including the epidermis, dermis, and fat layer is assumed for the skin tissue of the living body, and the Monte Carlo simulation method is applied to this model.

FIG. 1 is an example of a model of a skin tissue 1 of a living body, assuming a three-layer model of an epidermis 2, a dermis 2 and a fat layer 3 in order from the surface side, and the epidermis 2 has a thickness of 0.06 mm. It contains melanin, and the dermis 3 has a thickness of 1.0 mm and has oxygenated hemoglobin (oxyHb) and deoxygenated hemoglobin (deoxy).
Hb) is included, and the fat layer has a thickness of 28.94 mm.
And assume that it contains fat.

Here, the absorption coefficient μa in the dermis layer
(Mm ⁻¹ ) is the concentration [oxyHb] of oxygenated hemoglobin (oxyHb), the concentration [deoxyHb] of deoxygenated hemoglobin (deoxyHb), the molar extinction coefficient ε _oxyHb (mM ⁻¹ · cm) of oxygenated hemoglobin (oxyHb). ^{- 1),} the molar extinction coefficient of deoxygenated hemoglobin _(deoxyHb) ε deoxyHb ^{(mM -1}
-Cm <^-1> is used and the coefficient represented by the following formula is used.

Μ _a = ln10 · (ε _oxyHb · [oxyHb] + ε _deoxyHb · [deoxyHb]) / 10 (1) The Monte Carlo simulation method is applied to this model for each wavelength, and The reference light of the light quantity I ₀ is generated pseudo in the model, and the light quantity I of the reflected light emitted from the living body by scattering this light in the model is obtained. By using the light amount I ₀ and the light amount I obtained by applying the Monte Carlo simulation, the value (abs = −log (I / I ₀ )) corresponding to the absorbance can be obtained. Since the value obtained by applying the Monte Carlo simulation to this model includes the nonlinear relationship between the concentration of the constituent in the living body and the measured data, the nonlinearity between the concentration of the constituent in the living body and the measured data is reversed from this value. You can know the relationship.

Using the light quantity I ₀ and the light quantity I obtained by applying Monte Carlo simulation to the above model, the absorbance (Z = −log (I /
By obtaining a plurality of I ₀ )) and plotting the relationship between the plurality of absorbances and the concentration of each component, a non-linear relationship between the component concentration and the measurement data can be expressed. This non-linear relationship can be represented by, for example, a graph or a relational expression.

FIG. 2 is a graph display example showing a non-linear relationship between component concentrations and measured data. Note that FIG. 2 shows an example in which the measurement wavelength is 581 nm. In this graph display, the absorbance obtained by Monte Carlo simulation is Z
Along the axis, the hemoglobin absorption coefficient μ _a (mm ⁻¹ ) in the dermis at each wavelength represented by the formula (1) is represented by X.
It is shown on the axis, and the epidermal melanin concentration (mg / ml) is shown on the Y axis. The nonlinear relationship between the component concentration and the measurement data is obtained for each wavelength.

The non-linear relationship between the component concentration and the measured data can be expressed by the following expression.

Z = AZ ³ + BX ² Y + CXY ² + DY ³ + EX ² + FXY + GY ² + HX + IY + J (2) Here, X is the hemoglobin absorption coefficient μ _a (mm) in the dermis.
^-1 ), and Y is the epidermal melanin concentration (mg / ml)
Is. Further, the coefficients A to J are constants that differ for each wavelength, and the coefficient J is an offset value common to all wavelengths. Table 1 shows the measurement wavelengths of 512 nm, 557 nm and 5 nm, respectively.
The respective coefficients A to J of the equation (2) obtained in the case of 68 nm, 581 nm, 619 nm, and 700 nm are shown.

[0023]

[Table 1]

According to the optical image measuring method of the present invention, the component concentration in the living body or the component concentration change is obtained based on the non-linear relationship between the component concentration and the measurement data. First, the first mode for obtaining the component concentration in the living body by using the non-linear relationship between the component concentration and the measurement data will be described.

In the first aspect, the measurement image data at a plurality of measurement wavelengths is fitted to the above relational expression (2), or the non-linear relationship between the concentration of components in the living body and the measurement data is obtained in advance by a look-up table. Then, the concentration of the component in the living body is obtained by collating the measurement image data of a plurality of measurement wavelengths with this reference table.
The lookup table can be in the form of the graph shown in FIG. 1, for example. Hereinafter, a case will be described where the measured image data is fitted to the relational expression (2) to obtain the component concentration in the living body.

In the case of this fitting, the absorbance abs actually measured from the measurement data of at least two wavelengths of the living body is obtained, the absorbance Z is obtained from the simulation result of the same two wavelengths, and the actually measured absorbance abs and the absorbance Z by the simulation are obtained. The hemoglobin absorption coefficient X (= μ _a ) (m
m ^{- 1} ) and the melanin concentration Y (mg / ml) are determined, and the melanin concentration and hemoglobin concentration are calculated from this. The measured absorbance abs and the simulated absorbance Z
The difference S between and is expressed by the following equation (3), and the number of wavelengths to be used n
X, Y that minimizes the difference S is obtained.

[0027]

[Equation 1]

Further, the hemoglobin absorption coefficient μa, the melanin concentration and the absorbance Z shown in the graph shown in FIG. 1 are prepared as a table, and between the measured absorbances abs of a plurality of wavelengths and the absorbance value Z of the simulation result provided in the table. The melanin concentration and the hemoglobin concentration can be obtained by determining X and Y that minimize the difference S. Table 2 shows
It is an example of the result of fitting with respect to the measured data actually measured.

[0029]

[Table 2]

In Table 2, Examples 1 to 4 show the respective states of the same person at rest, during heating, under pressure, and during release, and Example 5 shows the state of another person, each of which has a relational expression. Oxygenated hemoglobin concentration [oxyH] which is a variable of (1)
b] (μM), deoxygenated hemoglobin concentration [deoxyHb]
(ΜM), melanin concentration [melanin] (mg / ml),
In addition to offset value, oxygenated hemoglobin concentration [oxyHb]
And deoxygenated hemoglobin concentration [deoxyHb], the total hemoglobin concentration [totalHb], oxygen saturation SO ₂ (100 [o
xyHb] / [totalHb]) and the maximum residual absorbance after fitting.

Next, a second mode for obtaining the component concentration change in the living body by using the non-linear relationship between the component concentration change and the measurement data change will be described. In the second aspect, by a relational expression including a product of a change in the concentration of a component in a living body and an average optical path length in which light flies in the living body due to diffusion by each component,
The change in the measurement image data is expressed in advance, and the change in the concentration of the component in the living body is obtained by applying to this relational expression the measurement image data at a plurality of measurement wavelengths at least as many as the components to be measured.

The relational expression of the second aspect can be obtained by applying the average optical path length of light due to diffusion of each component obtained by Monte Carlo simulation to the Lambert-Beer law.

When the average optical path length d of light due to diffusion is applied to the Lambert-Beer law, it is expressed by the following equation (4). ΔZ = d _oxyHb · ε _oxyHb · Δ [oxyHb] + d _deoxyHb · ε _deoxyHb · Δ [deoxyHb] + d _melanin · ε _melanin · Δ [melanin] + ΔJ (4) where ΔZ is the change in oxygenated hemoglobin concentration Δ [ oxyH
b], change in deoxygenated hemoglobin concentration Δ [deoxyHb],
And the change in absorbance due to changes delta [melanin] melanin _{concentration, d oxyHb, d deoxyHb, d} melanin is the mean path length of light by the diffusion of the respective oxygenated hemoglobin, deoxygenated hemoglobin, and melanin.

In formula (2), the absorbance Z is a function of oxygenated hemoglobin concentration [oxyHb], deoxygenated hemoglobin concentration [deoxyHb], melanin concentration [melanin], and constant J, so ΔZ is The first-order approximation can be performed by the equation (5).

ΔZ = (∂Z / ∂ [oxyHb]) ・ Δ [oxyHb] + (∂Z / ∂ [deoxyHb]) ・ Δ [deoxyHb] + (∂Z / ∂ [melanin]) ・ Δ [melanin] + ΔJ (5) By comparing the equation (5) with the equation (1), the relationships represented by the following equations (6), (7), and (8) are obtained.

(∂Z / ∂ [oxyHb]) = (∂Z / ∂X) ・ (∂X / ∂ [oxyHb]) = (∂Z / ∂X) ・ (ln10 / 10) ・ d _oxyHb (6) ) (∂Z / ∂ [deoxyHb]) = (∂Z / ∂X) ・ (∂X / ∂ [deoxyHb]) = (∂Z / ∂X) ・ (ln10 / 10) ・ d _deoxyHb … (7) (7) ∂Z / ∂ [melanin]) = (∂Z / ∂Y) (8) Using formulas (6), (7), and (8), comparing formula (4) and formula (5), The average optical path length can be expressed by the following equation (9).

D _oxyHb = (∂Z / ∂X) · (ln10 / 10), d _deoxyHb = (∂Z / ∂X) · (ln10 / 10), d _melanin = (∂Z / ∂Y) · (1 / Ε _melanin ) (9) (∂Z / ∂X) and (∂Z / ∂Y) in the formula (9) are expressed by the following formulas (10) and (1) from the formula (2). .

[0038] ^{∂Z / ∂X = 3AX 2 + 2BXY} + CY 2 + 2EX + FY + H ... (10) ∂Z / ∂Y = BX 2 + 2CXY + 3DY 2 + FX + 2GY + I ... (11) (10), of (11) (∂Z / ∂X) , (∂Z / ∂
To determine Y), it is necessary to specify X and Y values in each measurement example. Then, when the average optical path lengths are obtained for the examples 1 and 5 of the above Table 2, the values shown in Tables 3 and 4 are obtained. Table 3 shows the values according to Example 1, and Table 4 shows the values according to Example 2.

[0039]

[Table 3]

[0040]

[Table 4]

When the average optical path length shown in Table 3 is applied to the equation (4), the absorbance change ΔZ at each wavelength is represented by the equation (12).

[0042]

[Equation 2]

From this equation (12), the oxygenated hemoglobin concentration change Δ [oxyHb], the deoxygenated hemoglobin concentration change Δ [deoxyHb], the melanin concentration change Δ [melanin], and the constant change ΔJ are expressed by the respective equations (13). Can be solved.

[0044]

[Equation 3]

Similarly, by solving for Example 5 as well, the equation (1) corresponding to the equations (12) and (13) is obtained.
4) and (15) are obtained.

[0046]

[Equation 4]

[0047]

[Equation 5]

The optical image measuring method of the present invention comprises the above-mentioned first method.
The image data can be obtained by, for example, obtaining the component concentration in the living body obtained in the above aspect and the change in the component concentration in the living body obtained in the second aspect for each pixel, and the image data can be displayed as a two-dimensional image. .

[0049]

As described above, according to the optical image measuring method of the present invention, a more accurate component concentration can be obtained in consideration of the non-linearity between the component concentration of the subject and the measurement data. You can Also, considering the non-linearity of the absorbance due to scattering in the living body and the hemoglobin concentration and melanin concentration,
More accurate hemoglobin concentration and melanin concentration can be obtained.

[Brief description of drawings]

FIG. 1 is an example of a model of skin tissue of a living body.

FIG. 2 is a graph display example showing a non-linear relationship between a component concentration of optical image measurement of the present invention and measurement data.

[Explanation of symbols]

1 ... Living tissue, 2 ... Epidermis, 3 ... Dermis, 4 ... Fat layer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naofumi Sakauchi             1 Nishinokyo Kuwabaracho, Nakagyo Ward, Kyoto City, Kyoto Prefecture             Shimadzu Corporation F term (reference) 2G059 AA01 BB12 CC18 EE01 HH02                       HH06 KK04 MM01 MM05 MM09                       MM10                 4C038 KK01 KL07 KX01

Claims (5)

[Claims] 1. An optical image measuring method of irradiating a living body with light and obtaining an image of the light reflected from the living body by using a two-dimensional detector. The optical image measuring method is characterized in that the concentration of a component in a living body is obtained by fitting a relational expression representing a non-linear relation between the measurement data and the measurement data. 2. An optical image measuring method of irradiating a living body with light and obtaining an image of the light reflected from the living body by using a two-dimensional detector, wherein measured image data at a plurality of measuring wavelengths is used as a component concentration in the living body. A method for measuring an optical image, characterized in that the concentration of a component in a living body is obtained by comparing a reference table showing a non-linear relationship between the measurement data and the measurement data. 3. An optical image measuring method for irradiating a living body with light and obtaining an image of the light reflected from the living body by using a two-dimensional detector. Expressed by a relational expression including a product with an average optical path length that is a distance that light travels in a living body due to diffusion by components, at least measurement image data with a plurality of measurement wavelengths of the same number as the component to be measured is applied to the relational expression. The optical image measuring method is characterized in that the change in the component concentration in the living body is obtained by the above. 4. The measurement data is absorbance, and the component concentrations in the living body are oxygenated hemoglobin concentration, deoxygenated hemoglobin concentration, and melanin concentration, according to any one of claims 1 to 3. The optical image measuring method described in one. 5. The non-linear relationship is obtained by applying a Monte Carlo simulation to a three-layer model of a layer containing melanin, a layer containing oxygenated hemoglobin and deoxygenated hemoglobin, and a fat layer in the living body. The optical image measuring method according to any one of claims 1 to 3.