JPH0972845A - Optical measuring apparatus for light-scattering and -absorbing body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical measuring apparatus by which the absolute measurement of an optical constant can be performed by a stationary light method by a configuration provided with a computing part in which the product of the absorption coefficient of an object, to be inspected, multiplied by its equivalent scattering coefficient is computed on the basis of detected light. SOLUTION: In a probe 20, a light source such as a laser diode or the like and photodetectors D1 , D2 which are at distances a1 , a2 from the light source are installed, and the light source and the photodetectors D1 , D2 are used while they are brought into contact with an object to be inspected. Detection signals of the photodetectors D1 , D2 are designated respectively as S1 , S2 . A μaΝμs computing part 14 for the product of an absorption coefficient μa multiplied by an equivalent scattering coefficient μs is realized by a CPU, and the product μa.μs is computed on the basis of a specific expression. The product μa. μs is computed at every wavelength so as to be displayed on a display part 16. In an oxygenation-degree and blood-amount computing part 18, the ratio of the absorption coefficient μa is computed, and a blood amount is computed on the basis of the product μa.μs in an isosbestic point. In order to constitute an apparatus by which a measurement can be performed at a plurality of wavelength, laser beams at a plurality of wavelengths are changed over so as to be transmitted from a laser device instead of the light source so as to be sent to the object, to be inspected, via a transmission optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measuring device for a light scattering / absorbing body such as a biological oxygen monitor.

[0002]

2. Description of the Related Art In an oxygen monitor, measurement light is made incident on a part of a subject, light emitted from other parts of the subject is detected, and a weighted linear combination of absorbance change amounts measured at a plurality of wavelengths is detected. As the change amount of the target component.

The method will be specifically described. Δ [HbO ₂ ] and Δ [Hb] are the changes in concentration of oxygenated hemoglobin and deoxygenated hemoglobin, respectively, and the parallel shift amount due to scattering components is S. The molecular absorbances of oxygenated hemoglobin for wavelengths λ ₁ , λ ₂ , and λ ₃ are e ₁ , e ₂ , and
Assuming that the molecular absorbances of e ₃ and deoxygenated hemoglobin are b ₁ , b ₂ and b ₃ , respectively, assuming the linearity between the hemoglobin concentration and the absorbance for wavelengths λ ₁ , λ ₂ and λ ₃ , the corresponding absorbance changes ΔA ₁ , ΔA ₂ and ΔA ₃ are ΔA ₁ = e ₁ Δ [HbO ₂ ] + b ₁ Δ [Hb] + S ΔA ₂ = e ₂ Δ [HbO ₂ ] + b ₂ Δ [Hb] + S ΔA ₃ = e ₃ Δ [ HbO ₂ ] + b ₃ Δ [Hb] + S ... (a) If this is solved as a simultaneous equation with Δ [HbO ₂ ], Δ [Hb], and S as unknowns, Δ [HbO ₂ ] = k ₁₁ ΔA ₁ + k ₁₂ ΔA ₂ + k ₁₃ ΔA ₃ Δ [Hb] = k ₂₁ ΔA A solution of the form ₁ + k ₂₂ ΔA ₂ + k ₂₃ ΔA ₃ (b) is obtained. It is also possible to use the method (a) in which the parallel displacement S due to the scattering component is not taken into consideration. In that case, if S = 0 is solved, there are two unknowns and three expressions, so the least squares method is used. You only have to solve it, and the form of the solution is (b)
It becomes an expression.

On the other hand, the characteristics of a uniform light scattering / absorbing material are as follows: absorption coefficient μa and equivalent scattering coefficient μs' (= (1-g) μs; μ
It can be described by two optical constants, s is a scattering coefficient and g is an anisotropic parameter. As shown in FIG. 1, pulsed light of a delta function of unit 1 is made incident on a part of a semi-infinite body at time 0, and 1 at a point ρ mm away from the incident point.
The intensity R (ρ, t) of the light emitted from mm ^{2 at} time t is given by the following equation (1) (APPLIED OPTICS, Vol.28, No.1).
2, pp.2331-2336 (1989)).

(Equation 3) Here, D is a diffusion coefficient, and D = 1/3 (μa + μ
s ′) and c are the speed of light in the medium, Z ₀ = 1 / μs ′. If the light intensity is measured by the time-resolved method at the light receiving point that is separated from the incident point by a certain distance, and is applied to equation (1),
The optical constants μa and μs ′ can be individually calculated, and studies are currently underway in that direction.

[0005]

The measurement by the conventional oxygen monitor is limited to the measurement of the amount of change from the starting point of measurement being zero, and the measurement of the absolute amount is not performed. At present, only the method of obtaining the absolute amount by the time-resolved method has been studied to measure the absolute amount.However, the time-resolved method requires a large device and is expensive, so it can be realized as a simple measuring device. I can't. for that reason,
Although it has been long sought to obtain the absolute value of the optical constant by the stationary light method, no useful method has been found so far.

A first object of the present invention is to provide a device for making absolute measurement of optical constants by the stationary light method. Here, the absolute amount may be the amount at that time, and it does not matter whether it is in the form of a ratio having no unit or the original absolute amount having a specific unit. Not only the measured amount of change from a specific time, but the measured amount at that time is called an absolute amount.

When a probe having a plurality of distances between the incident point and the light receiving point is used, the deviation of the distance between the incident point and the light receiving point affects the measured value of the product μa · μs'. When the light receiving area is large and the light receiving area is large, the light receiving area also affects the measured value of μa · μs', and the difference in the sensitivity between the light receivers at the plurality of light receiving points also occurs. μa ・ μ
Affects the measured value of s'. When there are a plurality of incident points and a common light receiving point, the difference in the amount of incident light also affects the measured value of μa · μs ′. The amount of incident light, the light receiving area, the sensitivity of the light receiver, etc. are device functions, and each device is calibrated at the factory at the time of shipment, but when the device changes over time and the intensity of the light source changes, If the sensitivity of the changes, the recalibration must be done. Therefore, the second aspect of the present invention
The purpose of is to provide a means for calibrating such a device function.

[0008]

According to the present invention, the product μa of the absorption coefficient μa of the subject and the equivalent scattering coefficient μs ′ from the detected light is used.
-It is a measuring device equipped with a calculation unit that calculates μs' as a collective amount. In the theoretical formula of the intensity of the light incident on one point of the object to be re-emitted from a point distant from the incident point, the product μa · μs' always appears as a unit and the intensity of the re-emitted light If is measured as a function of distance from the point of incidence,
The absolute value of the product μa · μs ′ can be obtained without using the time-resolved method. Furthermore, it was calculated at multiple wavelengths,
By calculating the ratio between multiple (μa · μs') pairs,
The absolute value of the oxygenation degree of the subject in the sense of the ratio of μa of the subject (the value at that time, which is not the change amount) can be calculated. This is because the wavelength dependence of μs' is almost the same for each sample, as will be described later.
This is because the ratio between the sets of s ') erases μs' and leaves only μa.

According to the present invention, the measuring light is made incident on a part of the object which is a light scattering / absorbing body, and the measuring light is received on the object at a light receiving point apart from the incident point of the measuring light. A measuring optical system including a probe provided with a plurality of one of an incident point and a light receiving point so that the distance between the incident point and the light receiving point is different from each other, and one set of the light receiving point and the incident point. The distance between the light receiving point and the incident point at is a ₁ , the light receiving intensity at the light receiving point of the set is I ₁ , and the output signal of the light receiver at that time is S ₁ , and the light receiving at the other set of the light receiving point and the incident point is performed. distance a ₂ between the point and the incident point, the received light intensity I ₂ at the set of the light receiving point, when the output signal of the photodetector at the time and S _2, a plurality light receiving point is the point of incidence probes in common Then S ₁ = k ₁
I ₁ (k ₁ is the constant of the light receiver at the light receiving point at the distance a ₁ from the incident point), S ₂ = k ₂ I ₂ (k ₂ is the light receiver at the light receiving point at the distance a ₂ from the incident point) Constant)

(Equation 4) On the basis seeking .mu.a · .mu.s', when the incident point of the probe light receiving point is common to a plurality, Io ₁ the incident light intensity to the incident point at a distance a ₁ from the receiving point, distance a from the receiving point the incident light intensity to the incident point on the _second and _{Io 2, S 1 = kI 1} , S
₂ = kI ₂ (k is the constant of the receiver at the receiving point),

(Equation 5) And an arithmetic unit for obtaining μa · μs ′ based on In order to calibrate the device constant, by measuring a plurality of optical outputs having different distances between the incident point and the light receiving point using a calibrator whose μa and μs ′ or their product μa · μs ′ is known, A calibration unit for determining the device constant in the equation is further provided.

In general, if (μa · μs') is treated as one constant, it is possible to perform absolute measurement with stationary light. To handle the stationary light, the expression (1) may be integrated over time, and the result is the following expression (2).

(Equation 6)

Here, the diffusion coefficient D = 1/3 (μa + μ
In s'), .mu.a is about 1/100 of .mu.s', so .mu.a can be ignored, and D = 1/3 .mu.s' is completely acceptable. Substituting this into equation (2),
Further, if a = (ρ ² + Z ₀ ² ) 1/2, then the following equation (3) is obtained.

(Equation 7)

It is noted that in equation (3), (μa · μs') appear together in the form of one product. This means that μa and μs ′ cannot be distinguished in the stationary light system and must always be handled collectively. But,
Considering (μa · μs') as one optical constant, (3)
Since there is only one optical constant in the equation, it becomes easy to obtain by calculation. If the measurement is performed at multiple wavelengths, (μa
Since .mu.s ') is obtained for each wavelength, it can be connected to an operation for obtaining the ratio of (.mu.a.mu.s') at each wavelength as described later.

By modifying the equation (3), the following equation (4) is obtained.

(Equation 8)

In the actual measurement, a is several tens of millimeters and can be considered to be sufficiently large, so 1 / a of the final term of the equation (4) can be approximated to 0 or a small constant. As a result, if ln (2πa ² R) in the equation (4) is represented by f (a), the equation (4) becomes a linear equation of a, as shown in FIG. Therefore, if the emission rate R is measured at two types of distances a ₁ and a ₂ and f (a ₁ ) and f (a ₂ ) are obtained from it, then (4)
The slope of the straight line of the formula is

[Equation 9] Therefore, μa · μs ′ can be obtained from the equation (5).

In the actual measurement, the emission rate R is R = I / Io (I:
Emission light intensity, Io: incident light intensity), and the emission light is given by an output signal S (= kI, k: constant) at the light receiver.
The distance between the light receiving point and the incident point in one set of the light receiving point and the incident point is a ₁ , the received light intensity at the light receiving point of the set is I ₁ , the output signal of the light receiver at that time is S ₁ , and the light receiving point is Let a ₂ be the distance between the light receiving point and the incident point in the other set of the light receiving point and the light receiving intensity at the light receiving point of the set be I ₂ , and the output signal of the light receiver at that time be S ₂ . When the incident point of the probe is common and there are multiple light receiving points, if S ₁ = k ₁ I ₁ and S ₂ = k ₂ I ₂ , then (5)
The formula is the following formula (6a).

(Equation 10) That is,

[Equation 11]

On the other hand, when there are a plurality of incident points of the probe and the light receiving point is common, the incident light intensity at the incident point at the distance a ₁ from the light receiving point is Io ₁ , and the incident point at the distance a ₂ from the light receiving point is Suppose that the incident light intensity on the beam is Io ₂ , S ₁ = kI ₁ , S ₂ = kI ₂ (k
Is the constant of the light receiver at the light receiving point), the equation (5) becomes the following equation (6b).

(Equation 12) That is,

(Equation 13)

(Usage and Usefulness of μa · μs ′) Next, the use and usefulness of μa · μs ′ will be described.
μa · μs ′ is expressed as μas ′. μas ′ = μa · μs ′ (7) It is assumed that this is obtained at each wavelength, for example, λ ₁ , λ ₂ , λ ₃ , and at each time t. That is, μas' (λi, t) (i = 1,2,3).

The advantage that the optical constant μas ′ is in the form of a product is that μs ′ is slightly larger on the short wavelength side,
It is considered that the wavelength dependence is small, and the wavelength dependence f (λ) and the sample dependence can be separated. Therefore, it is expressed as μas ′ = f (λi) · s (t) (8). f (λi) is a wavelength-dependent term, s (t) is a term depending on the individual specimen and time t, and is a term not depending on the wavelength.

When the value of the equation (8) is obtained for, for example, three wavelengths and their ratio is taken, s (t) disappears and the following is obtained. m ₁ = μas '(λ ₁ ) / μas' (λ ₃ ) = (f (λ ₁ ) / f (λ ₃ )) (μa (λ ₁ ) / μa (λ ₃ )) = f ₁₃ · (μa ( λ ₁ ) / μa (λ ₃ )) m ₂ = μas '(λ ₂ ) / μas' (λ ₃ ) = (f (λ ₂ ) / f (λ ₃ )) (μa (λ ₂ ) / μa (λ ₃ )) = f ₂₃ · (μa (λ ₂ ) / μa (λ ₃ )) Therefore, μa (λ ₁ ) = μa (λ ₃ ) × (m ₁ / f ₁₃ ) μa (λ ₂ ) = μa (λ ₃ ) × (m ₂ / f ₂₃ ) ... (9) is obtained. From this, the ratio of absorption coefficients can be obtained. That is, μa (λ ₁ ): μa (λ ₂ ): μa (λ ₃ ) (m ₁ / f ₁₃ ) :( m ₂ / f ₂₃ ): 1 (10)

If the absorption coefficients μa (λ ₁ ), μa (λ ₂ ), and μa (λ ₃ ) μa are the oxygenated hemoglobin amount [Hb,
O ₂ ], the amount of hemoglobin [Hb] and the amount of cytochrome oxidase [Cyt],
The amount ratio of these components can be obtained from the ratio of the above three wavelengths, and conventionally the change amounts Δ [HbO ₂ ], Δ [Hb] and Δ
This means that progress has been made from the state where only the ratio of [Cyt] was required to the place where the ratio of absolute values was required. That is, not the amount of change but the amount at that point in time as a ratio is obtained.

The quantity representing the ratio of μa to each wavelength is information on the degree of oxygenation. On the other hand, the blood volume information is included in the absolute value of μa and s (t) in the equation (8), and therefore cannot be evaluated by the ratio in the equation (10). However, at the isosbestic point (λ = 805 nm) μas ′ = μa (80
5) × μs ′ (805) gives information on blood volume.

[0022]

EXAMPLE FIG. 3 shows an example. The probe 20 is provided with one light source L such as a laser diode, and light receivers D ₁ and D ₂ at positions a ₁ and a ₂ from the light source L, respectively, and the light source L and the light receivers D ₁ and D ₂ are provided. ₂ is used in contact with the subject 2. The detection signals of the photo detectors D ₁ and D ₂ are S ₁ and S ₂ , respectively. The μa · μs ′ calculation unit 14 is realized by a CPU and calculates μa · μs ′ based on the equation (6a). μa · μs ′ is calculated for each wavelength and displayed on the display unit 16. Oxygenation and blood volume calculator 18
Then, the ratio of absorption coefficients as given by the equation (10) is calculated, or the blood volume is calculated from μa · μs ′ at the isosbestic point. In order to make an apparatus capable of measuring at a plurality of wavelengths, laser light of a plurality of wavelengths λ ₁ , λ ₂ , λ ₃ is switched and emitted from the laser device instead of the light source L, and is transmitted via a light transmitting fiber. It may be sent to the sample.

Calibration of device constants will be described. In FIG. 4, the light source L at the incident point is common, and a plurality of light receivers at the light receiving point (D
₁ , D ₂ ) is an example of the provided probe 20. In the probe 20, the pitch between the light transmitting and receiving portions is fixed, and when the light receiving area is so small that it does not affect the distance a, the device constant as an unknown in Equation (6a) is
Since there is only ln (k ₁ / k ₂ ), only one calibrator for calibration in which μa and μs ′ or their product μa · μs ′ is known is sufficient.

When the probe 20 is attached to the calibrator 22 as shown in FIG. 4 (B) and measurement is performed, the device constant ln (k
₁ / k ₂ ) is ln (k ₁ / k ₂ ) = (a ₁ -a ₂ ) (3 μa · μs') 1/ _2- ln (S ₂ / S ₁ )-
It can be obtained as ln (a ₂ / a ₁ ) ² .

When the light receiving area is large enough to affect the distance a or when the distance a is deviated, the device constant as an unknown in the equation (6a) is 1 / (a ₂ -a ₁ ) and { Since 1 / (a ₂ -a ₁ )} ln (k ₁ a ₂ ² / k ₂ a ₁ ² ), two types of calibration calibrators are used for measurement, and simultaneous equations are solved to solve the device. Determine the constant.

When a plurality of light sources at the incident point are provided and the light receiver at the light receiving point is common, the calibration can be similarly performed. However, in this case, if the light receiving area is so small that it does not affect the distance a, the device constant as an unknown in Equation (6b) is only ln (Io ₁ / Io ₂ ).
Using various kinds of calibrators, ln (Io ₁ / Io ₂ ) = (a ₁ −a ₂ ) (3 μa · μs ′) 1/2 − ln (S ₂ /
It can be obtained as S ₁ )-ln (a ₂ / a ₁ ) ² .

If the light receiving area is large enough to affect the distance a or if there is a deviation in the distance a, (6
In equation (b), there are two unknown device constants, 1 / (a ₂ -a ₁ ) and {1 / (a ₂ -a ₁ )} ln (Io ₁ a ₂ ² / Io ₂ a ₁ ² ). Therefore, measurement is performed using two types of calibration calibrators, and simultaneous equations are solved to determine the device constant. The obtained device constant is held in the CPU that realizes the calibration unit, and is used when the probe 20 is attached to the unknown sample 24 to perform the measurement as shown in FIG. More calibrators may be used to increase the accuracy of the calibration.

[0028]

According to the present invention, the absorption light μa and the equivalent scattering coefficient μs ′ are obtained by receiving the measurement light at a plurality of light receiving points which are separated from the incident point of the measurement light on the subject by different distances by the stationary light method. The absolute value of the product μa · μs' can be obtained, and the absolute measurement of the optical constant by the stationary light method, which has been impossible in the past, becomes possible. Conventionally, there is a possibility of absolute measurement of optical constants if the time-resolved method is used, but there is no method that performs absolute measurement by the stationary light method. As a result, according to the present invention, absolute measurement of optical constants can be realized with an inexpensive stationary light type apparatus. Furthermore, in the present invention, the absolute value of the concentration, which has been a concern in the past, can be obtained by a simple method except for the proportional coefficient. By calibrating the instrument constants using a calibrator,
Irrespective of the gains and the light receiving areas of the plurality of light receivers, the entire apparatus can be calibrated in a lump including the drift of the sensitivity of the plurality of light receivers, and μa · μs ′ can be accurately measured. Therefore, for example, in the absolute measurement of the amount of hemoglobin, the accuracy can be improved. By equipping the device with a calibrator as an accessory,
Calibration can be easily performed when necessary, and the limit of calibration at the time of shipment can be exceeded.

[Brief description of drawings]

FIG. 1 is a diagram showing pulsed light incidence and emission in a light scattering / absorbing body.

FIG. 2 is a diagram showing a method for obtaining μa · μs ′ in the present invention.

FIG. 3 is a schematic sectional view showing an optical system according to an embodiment,
It is a figure which shows a calculating part with a block diagram.

FIG. 4 is a diagram showing an operation in one embodiment, (A)
Is a cross-sectional view of the probe, (B) is a cross-sectional view showing the calibration operation,
(C) is a sectional view showing a measurement operation of an unknown sample.

[Explanation of symbols]

 2 subject 4 light transmitting fiber 8-1, 8-2 light receiving fiber 10-1, 10-2 detector 14 μa · μs ′ calculator 18 oxygenation / blood volume calculator 20 probe 22 calibrator 24 unknown sample

Claims (2)

[Claims] 1. A measurement light is made incident on a part of a subject which is a light scattering / absorbing body, and the measurement light is received on the subject at a light receiving point distant from the incident point of the measurement light, and the incident point is And a light receiving point, a measuring optical system equipped with a probe provided with a plurality of one of an incident point and a light receiving point so that the distance between the light receiving point and the light receiving point is different, The distance between the point and the incident point is a ₁ , the received light intensity at the light receiving point of the set is I ₁ , the output signal of the light receiver at that time is S ₁ , and the light receiving point in another set of the light receiving point and the incident point is When the distance from the incident point is a ₂ , the received light intensity at the light receiving point of the set is I ₂ , and the output signal of the photodetector at that time is S ₂ , the incident point of the probe is common and the light receiving points are plural. When S
₁ = k ₁ I ₁ (k ₁ is the constant of the light receiving point at the distance a ₁ from the incident point), S ₂ = k ₂ I ₂ (k ₂ is the light receiving point at the distance a ₂ from the incident point) Constant of the light receiver of On the basis seeking .mu.a · .mu.s', when said light receiving point of incidence point in a plurality of probes is common, the incident light intensity to the incident point at a distance a ₁ from the receiving point I
o _1, the incident light intensity to the incident point at a distance a ₂ from the light receiving point and Io _2, as _{S 1 = kI 1, S 2} = kI 2 (k is a constant of the light receiver of the light receiving point), Equation 2] An optical measuring device comprising: a calculating unit that calculates μa · μs ′ based on However, μa; absorption coefficient μs ′ = (1-g) μs; μs; scattering coefficient g; anisotropic parameter of scattering 2. Each of μa and μs ′ or their product μa
. Further comprising a calibrator for determining a device constant in the above formula by measuring a plurality of light outputs having different distances between an incident point and a light receiving point using a calibrator having a known μs ′. The optical measuring device described.