JPH1082732A - Optical measuring equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a measurement while distinguishing in the depth direction by employing a transmitting light containing different wavelengths and differentiating the distance between a light transmitting point and a light receiving point on a subject depending on the wavelength. SOLUTION: A light transmitting part S is set at one end of an optical fiber 3 connected with a light source 2. A light of two sets of wavelength is transmitted through a subject 9 from the same transmitting point. A set of wavelengths λL1, λL2 has longer wavelength than a set of wavelengths λS1, λS2. A detecting section DS detects a set of short wavelength and a detecting section DL detects a set of long wavelength. A detector 5-1 is disposed at the end of an optical fiber 4 and a processing circuit 5-3 performs signal processing through a preamplifier 5-2, and the like. The distance dS between the detecting section DS and the transmitting part S is set shorter than the distance dL between the detecting section DL and the transmitting part S. The detecting section DS receives light of short wavelengths λS1, λS2 and measures a shallow part of the subject 9. The detecting section DL receives light of long wavelengths λL1, λL2 and measures a deep part of the subject 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measurement apparatus for irradiating a subject with light, such as an optical CT or a biological oxygen monitor, and detecting transmitted scattered light to measure information in the subject.

[0002]

2. Description of the Related Art A light measuring device that irradiates a subject with light such as visible light or near-infrared light, detects light transmitted and scattered in the subject, and non-destructively measures information in the subject. It has been known.
Optical CT and biological oxygen monitors are examples of measuring devices that apply such an optical measuring device to a living body. The object can be any object that can transmit light such as visible light or near-infrared light, and can be applied to animals, plants, fruits and vegetables, etc. in addition to living organisms.

[0003] In a light measuring device such as an optical CT, a light transmitting means and a light receiving means are arranged at a distance from each other, and a measuring light is irradiated from the light transmitting means into the object and transmitted or scattered in the object. This is a device that receives light with a light receiving unit and obtains measurement data based on the measurement light, and can be applied to a non-invasive quantification method of oxyhemoglobin and deoxyhemoglobin in a living body.

[0004] As an application of this optical measuring device to noninvasive quantitative measurement, a method of determining the amount of change in oxyhemoglobin and deoxyhemoglobin from an initial value using a set of a light transmitting unit and a light receiving unit, a plurality of detection outputs There has been proposed a method of obtaining an absolute value at the time of measurement from the above.

[0005]

In the light measuring device, information on the depth direction of the subject may be required. For example,
In the measurement of oxyhemoglobin and deoxyhemoglobin in a living body, the state of a shallow portion and a deep portion close to the skin may be required. However, the measurement data measured by the conventional optical measurement device is for the entire subject, and there is a problem that it is difficult to measure separately in the depth direction of the subject.

For example, the amount of oxyhemoglobin and deoxyhemoglobin in a tissue measured by a biological oxygen monitor using a conventional light measuring device is determined by the amount of oxyhemoglobin and deoxyhemoglobin in the entire tissue below the light transmitting part and the light receiving part. However, it is difficult to make a distinction between a shallow part of skin or a living body and a deep analysis part for measurement.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the conventional optical measuring device and to enable the measurement to be performed separately in the depth direction.

[0008]

The light measuring device of the present invention comprises:
In an optical measurement device that transmits light to a subject and optically measures the subject by receiving light scattered or transmitted through the subject, the transmitted light is light containing different wavelengths. Thus, the distance between the light transmitting point and the light receiving point on the subject is made different. Thereby, the measurement is performed separately in the depth direction.

A plurality of pairs of a light transmitting point and a light receiving point are formed on an object, and light of one wavelength is incident on the object from one light transmitting point and passed through the object. Is received from one light receiving point, the distance between the light transmitting point and the light receiving point is changed according to the wavelength of the incident light. In general, when a light transmitting point and a light receiving point are set for a subject, the contribution of the light transmitting point and the light receiving point to the amount of light received by each part of the depth of a scatterer such as a biological tissue is represented by the characteristic shown in FIG. It is known that FIG. 1 shows what is called a contribution function for a point-like absorber, and the shading shown in the figure indicates the degree of attenuation of the detected light amount by moving the point-like absorber in the scatterer. The places where the amount of light attenuation is large are displayed darker. The shape of the contribution function depends on the distance between the light transmitting and receiving points, and the greater the distance, the greater the contribution of the deep part of the subject.

Utilizing this characteristic, transmission / reception is performed between two different distances, information on a shallow portion is obtained from transmission / reception means arranged at a short distance, and information on a deep portion is obtained from transmission / reception means arranged at a long distance. It is possible to ask for. However, there is one problem here. This is because even if the change in the absorber concentration in the sample is the same, a detector with a longer transmission / reception distance has a larger change in the received signal than a detector with a shorter transmission / reception distance. Sometimes. This is because the average optical path length of light passing through the sample changes depending on the distance between light transmission and reception, and the longer the light transmission and reception distance, the longer the average optical path length. Therefore, if the transmission / reception distance is reduced to measure a shallow portion, the change in the received signal is reduced, and the purpose is not achieved. In other words, if the transmission / reception distance is changed, both the depth information and the information on the measurement sensitivity are combined, which does not lead to the measurement in the depth direction alone.

[0011] In order to solve this problem, the light measuring apparatus of the present invention uses light having different wavelengths as transmitted light, and combines the different wavelengths with the distance between the light transmitting point and the light receiving point. The measurement is performed separately in the depth direction. The magnitude of the extinction coefficient of the light absorber varies depending on the wavelength. For example, in the characteristics of the extinction coefficient with respect to the wavelength of oxyhemoglobin and deoxyhemoglobin shown in FIG. 2, the extinction coefficient at around 800 nm where both cross is 0.2 mM in common logarithm.
Whereas a ^-1 · cm ^-1, the absorption coefficient at 550nm is 10 mM ^-1 · cm ^-1 in common logarithm, a difference of approximately 50 times. In addition, the absorption coefficient based on the absorbance based on the common logarithm used in the field of chemistry according to customs is referred to as “extinction coefficient”, and the one based on the natural logarithm used in the field of physics is referred to as “absorption coefficient μa”. I will. The light measuring device of the present invention combines the difference of the extinction coefficient depending on the wavelength with the contribution characteristic of the absorption depending on the distance between the light transmitting and receiving points.

Here, the 50-fold difference in the absorption coefficient directly appears in the case of a transparent sample containing no scattering substance. In this case, the amount (μa × distance) with respect to the absorption coefficient μa corresponds to the light attenuation.

On the other hand, in the case of a sample containing a strongly scattering substance, such as a living body, the (μa × distance) of the transparent sample does not directly appear but an absorption coefficient μ.
The effective attenuation coefficient μeff determined by both a and the scattering coefficient μs ′ is related to the amount of absorption. The effective attenuation coefficient μeff is given by μeff = (3 μaμs ′) ^1/2 , and (μeff *
The distance) defines the light attenuation for a sample containing a strong scattering material. Since the square root is included in the equation of μeff, if the original absorption coefficient of the absorber has a difference of 50 times as described later, the absorption is reduced to about 7 times in terms of the effective attenuation coefficient. This difference is rather convenient when selecting two light transmission / reception distances, and is advantageous.

Next, the effect of the effective attenuation coefficient μeff will be described using the following equation. Generally, when a point-like (delta function) light having an intensity of unit 1 is incident on a point on the surface of a semi-infinite body,
Intensity R of light received at a point ρmm away from the point of incidence
The logarithm of (a, μeff) is represented by the following equation (1). lnR (a, μeff) = − aμeff + ln (aμeff + 1) -3lna + ln (Z0 / 2π) (1) where a is the distance between the incident point and the light receiving point, ρmm, Z0 =
1 / μs ′ (μs ′ is an equivalent scattering coefficient (= (1-
g) μs; μs is a scattering coefficient, g is an anisotropic parameter)
Is a value represented by a = (ρ ² + Z 0 ² ) ^1/2 . Μeff is an effective attenuation coefficient, and is represented by (3 μa · μs ′) ^1/2 when an absorption coefficient is μa. Further, ln represents a natural logarithm.

Hereinafter, using the above equation (1), the effective attenuation coefficient μeff (= (3 μa · μs ′) ^1/2 ) represents the distance between transmission and reception and the degree of absorption in the depth direction. To indicate that Here, two different effective attenuation coefficients μeff1 and μeff2 (= α · μeff1) whose absorption coefficients differ by α times.
If the following equation (2) holds true for the absorption of light, the light intensity R at the light receiving point becomes the same.

0 = (a1 μeff1−α · a2 μeff1) + ln {(α · a2 μeff1 + 1) / (a1 μeff1 + 1)} − 3ln (a2 / a1) (2) The above equation (2) always holds. This is when Expression (3) below holds. a1 = α · a2 (3) Accordingly, a is a value represented by (ρ ² + Z 0 ² ) ^1/2 , and is a value mainly determined by the distance ρ between the transmitting and receiving points. 3) indicates that the difference in the effective attenuation coefficient μeff corresponds to the difference in the distance between the transmitting and receiving points.
Further, from the correlation between the distance between the light transmitting and receiving points and the depth of the subject, which is shown by the contribution function of FIG. 1, the degree of difference in the effective attenuation coefficient μeff corresponds to the degree of difference in the depth direction of the subject. You can see that

Here, when the value of the absorption coefficient of hemoglobin (unit: mM ⁻¹ · cm ⁻¹ ) shown in FIG. 2 is converted from a common logarithm to a natural logarithm and per mm to obtain an absorption coefficient per mm, At 800 nm, 0.046 mM ^-1 · mm ^-1
At 550 nm, it is 2.3 mM ^-1 · mm ^-1 .
If the absorption coefficient per mM is multiplied by 0.3 mM of the concentration of hemoglobin in the living body, the absorption coefficient μa becomes 0.014 at 800 nm per mm, and becomes 0.14 at 550 nm.
69. Using this value, 800 nm and 550 nm
Are calculated as 0.2 (= (3 × 0.014 × 1) ^1/2 ) and 1.4, respectively.
3 (= (3 × 0.69 × 1) ^1/2 ). The scattering coefficient μs ′ is 1 mm ⁻¹ .

Therefore, the effective attenuation coefficient μef of hemoglobin
f differs about 7 times between 800 nm and 550 nm. The fact that the effective attenuation coefficient μeff is seven times different is that, assuming that the light receiving sensitivity at the light receiving point is the same, the absorption intensity of 550 nm light is about 7 times larger than that of 800 nm light, and the depth direction is Indicates that information about 1/7 of the depth is output. Therefore, when measuring at the same level of light receiving sensitivity, by combining the distance between the sending and receiving light and the wavelength, it is possible to separately measure in the depth direction while reducing the decrease in light receiving sensitivity.

In the first embodiment of the present invention, a plurality of transmitting / receiving sections having different distances between transmitting and receiving light are used, and light having a shorter wavelength is used for a shorter distance, and light having a shorter wavelength is used for a longer distance between transmitting and receiving. Uses light of a long wavelength, thereby measuring a shallow part of the subject by measurement at a short wavelength and measuring a deep part of the subject by measurement at a long wavelength. As an example of a typical wavelength, the wavelength range for measuring the shallow portion of the subject is 500 nm to 650 nm, and the wavelength range for measuring the deep portion of the subject is 650 nm to 1000 nm. The measurement of hemoglobin and deoxyhemoglobin in a living body is performed while being distinguished in the depth direction.

Here, when it is originally intended to separate and measure the two components of oxyhemoglobin and deoxyhemoglobin, the measurement of a shallow portion should be performed in a short wavelength region such as 560 n.
A set of two wavelengths of m and 580 nm and a set of two wavelengths of 760 nm and 830 nm in a long wavelength range are used for measuring a deep block portion. By solving a system of two unknowns for each of the shallow and deep sets, the wavelength at which the absorption coefficients of oxyhemoglobin and deoxyhemoglobin become equal can be selected from the short wavelength range and the long wavelength range. For example, the short wavelength range is set to 560 nm, and the long wavelength range is set to 800 nm. In addition, a modification in which the long wavelength region is set to two wavelengths and the short wavelength region is set to one wavelength is also possible in the middle.

Further, 3 in each of a short wavelength region and a long wavelength region.
Variations that select more than the wavelength are also possible. In the case of three or more wavelengths, this is the case of so-called over-determination, which is a simultaneous equation of the least squares method, but is the same as the method performed when the distance between these light sources and the detector is one. It is.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 3 is a schematic block diagram for explaining one embodiment of the light measuring device of the present invention. FIG. 3 shows a configuration example in which two light receiving units are provided for one light transmitting unit. In FIG. 3, the light measuring device 1 includes a light transmitting section S, detecting sections Ds and DL, and is mounted in contact with the subject 9. The light transmitting unit S can be one end of the optical fiber 3, and the other end of the optical fiber 3 is connected to the light source 3, and a pair of two wavelengths (λL1, λL2) and (λ
S1, λS2) is transmitted, and the subject 9 is transmitted from the same transmitting point.
It is incident inside. Here, the set of wavelengths λL1, λL2 is longer than the set of wavelengths λS1, λS2.

The detecting section DS detects the short-wavelength pairs λS1 and λS2, and the detecting section DL detects the long-wavelength pairs λL1 and λL2. One end of the optical fiber 4 or a light-to-electric converter such as a silicon diode. It can be an element. When the detection units DS and DL are formed at one end of the optical fiber 4, a detector 5-1 such as a silicon diode is provided at the other end. The output of the detector 5-1 is subjected to signal processing in a processing circuit 5-3 via a preamplifier 5-2 or the like, and an operation for obtaining, for example, the degree of oxygenation or blood volume is performed.

The distance dS between the detecting section Ds for detecting the short wavelength and the light transmitting section S is determined by the detecting section DL and the transmitting section S for detecting the long wavelength.
The distance is set shorter than the distance dL. This distance dS, dL
Can be set according to the depth in the subject to be measured. The detector DS receives the light having the short wavelength λs,
The detector DL receives light of the short wavelength λL and measures the deep part of the subject 9.

FIG. 4 is a schematic block diagram for explaining another embodiment of the light measuring device of the present invention, and is an example of a configuration in which one light receiving unit is provided for two light transmitting units. FIG.
1, the light measuring device 1 includes a light transmitting section SS, a light transmitting section SL, and a detecting section D, and is mounted in contact with the subject 9. The light transmitting sections SS and SL can be ends of an optical fiber each having a light source connected to one end. Two different sets of wavelengths λS1, λS2, λL1, λL2 are transmitted, and the subject is transmitted from different transmitting points. 9 is incident.

The detection section D is a section for detecting two short wavelengths λS1 and λS2 and two long wavelengths λL1 and λL2, and can be an optical fiber or a detector as in FIG. The distance dS between the light transmitting section SS for the short wavelength incidence and the detecting section D is set shorter than the distance dL between the light transmitting section SL and the detecting section D for the long wavelength incident. The distances dS and dL are
It can be set according to the depth in the subject to be measured. The detector D receives the light of the short wavelengths λS1 and λS2 to measure four shallow portions of the subject 9 and receives the light of the long wavelengths λL1 and λL2 to measure the deep portion of the subject 9. The wavelength λ to be received is distinguished from each wavelength (two wavelengths on the long wavelength side and two wavelengths on the short wavelength side).
Wavelength) are sequentially turned on in time, so that they can be easily distinguished after being received by a common detector. Note that the hatched portions in the subject 9 in FIGS. 3 and 4 schematically show the portions where the measurement is performed by absorbing the light having the short wavelengths λS1, λS2 and the long wavelengths λL1, λL2.

In the embodiment shown in FIGS. 3 and 4, the change from the initial stage is measured by one set of light transmitting and receiving means for each set of wavelengths. On the other hand, another embodiment of the optical measurement device of the present invention shown in FIG. 5 is configured with two sets of light transmitting and receiving means having different installation distances for each set of wavelengths, thereby providing an absolute value. The measurement is performed.

It is known that the product of the absorption coefficient μa, which is the optical constant of the subject, and the equivalent scattering coefficient μS is obtained as an absolute value by using the measured values obtained by two sets of light transmitting and receiving means having different installation distances. ing. It is also known to obtain an absolute value such as a degree of oxygenation by calculating the ratio of a plurality of sets of the optical constants.

Therefore, in the embodiment shown in FIG. 5, the light measuring device 1 includes a light transmitting unit SS, a light transmitting unit SL, a detecting unit D1, and a detecting unit D, and is mounted in contact with the subject 9. The light transmitting sections SS and SL can be ends of optical fibers each having a light source connected to one end. From the light transmitting section SS,
The two wavelengths .lambda.S1 and .lambda.S2 in the short wavelength range are transmitted, and the two wavelengths .lambda.L1 and .lambda.L2 in the long wavelength range are transmitted from the light transmitting section SL. These four total wavelengths are sequentially switched in time and transmitted.
On the other hand, two detectors are also provided, which are for measuring the absolute value, and receive both short wavelengths and long wavelengths. That is, the two detectors D1 and D2 receive all of the light having the four wavelengths of the short wavelength region and the long wavelength region. As shown in the arrangement of FIG. 5, D1 and D2 are far away from the long-wavelength light source SL, and thus contribute to the measurement of deep parts. However, the point is that the light transmitting unit SS is disposed between the detecting units D1 and D2, and therefore, the common detecting units D1 and D2
2 has a clever structure that is provided at a short distance from the light transmitting section SS for a shallow portion. In this way, it is practically important that the structure shown in FIG. 5 can be formed by simply adding the light transmitting section SS on the short wavelength side to the conventional absolute value measuring type measuring section. The detection unit D1 and the detection unit D2 are the same as those in FIG.
Similarly to 4, it can be an optical fiber or a detector.

A light transmitting section Ss and a detecting section D1 for receiving short wavelength light.
Is the distance dL1 between the light transmitting unit SL and the detecting unit D1.
The detection unit D1 is set to be shorter than the short wavelength λ.
The light of S1 is received to measure the shallow portion of the subject 9, and the light of long wavelength λL1 is received to measure the deep portion of the subject 9. In addition, the distance dS2 between the light transmitting unit SS and the detecting unit D2 for entering the short wavelength is set shorter than the distance dL2 between the light transmitting unit SL and the detecting unit D2 for entering the long wavelength. The light of the short wavelength λS2 is received to measure a shallow portion of the subject 9, and the light of the long wavelength λL2 is received to measure the deep portion of the subject 9.

Further, the absolute value can be measured by using the two sets of outputs. Further, at each of the long and short wavelengths, different wavelengths λS1, λS2, and λL1, λL1 are incident, and a plurality of sets of the optical constants are obtained.
By determining the ratio between these sets, for example, the absolute value of the degree of oxygenation of the subject can be determined.

Next, an example of the configuration of the light measuring device of the present invention will be described. FIG. 6 is a diagram illustrating an example of the configuration of the light measurement device according to the present invention. The configuration example shown in FIG. 6 corresponds to the embodiment of FIG. 5 described above, and includes a light transmitting unit SS for transmitting light of a short wavelength and a light transmitting unit S for transmitting light of a long wavelength in the probe 6.
L, a detection unit D1, and a detection unit D2 are provided, and their ends are set to face the subject 9 side. The light transmitting unit SL and the light transmitting unit SS are connected to the light source unit 2 through optical fibers 3-1 and 3-2, and transmit the wavelengths λL1 and λL2 and the wavelengths λS1 and λS2 from the LD or LED light sources 2-1 to 2-4, respectively. Then, the light enters the subject 9. The detectors D1 and D2 output detection outputs D1out and D2out from the probe 6 to the outside.

FIG. 7 is a view for explaining another example of the configuration of the light measuring device of the present invention. In the configuration example shown in FIG. 7, the detection unit is configured by the CCD camera 7, and the light transmission unit SS that transmits short wavelength light and the light transmission unit SL that transmits long wavelength light into the dark room 8. The CCD camera 7 detects light from the subject 9. The light transmitting unit SL and the light transmitting unit SS are connected to the light source unit 2 through an optical fiber, and each has a wavelength λ.
Receiving L1, λL2 and wavelengths λS1, λS2, the light is incident on the subject 9, and the CCD camera 7 receives and detects light within the measurable range 12 of the light from the subject. In the light transmitting unit, a light shielding plate 10 or a light reducing filter 11 is provided around the light transmitting unit SL, and the light transmitting unit SS is disposed outside the light transmitting unit SL.
With this configuration, a combination of the wavelength and the distance between the transmission and reception is configured.

The light receiving state of the configuration shown in FIG. 7 will be described with reference to FIG. In FIG. 8, since the light incident from the light transmitting section SL has a long wavelength, the degree of attenuation near the light transmitting point is small, and as shown in FIG. The broken line in the figure) becomes larger. Therefore, the light transmission section SL
This light is shielded or dimmed by a light shielding plate or a dimming filter provided around, and the light intensity is balanced so that the intensity range can be measured by the CCD. Further, since the light incident from the light transmitting section SL has a short wavelength, the light absorption near the light transmitting point is strong as shown in FIG. Emits relatively weak light. Therefore, it is possible to perform a measurement using a light shielding plate or a dimming filter. In this way, the planar light intensity is measured around the light transmitting unit, and the measurement of the concentration of the subject is performed in the same manner as described above.

FIG. 9 shows a light transmitting unit S applied to the configuration example of FIG.
This is an example of the configuration. In this configuration example, a coaxial optical fiber is used, and a central portion is a light transmitting portion SL for transmitting long wavelength light, and a peripheral portion is a light transmitting portion SS for transmitting short wavelength light. In this configuration, the light transmitting section SS can be configured as a dimmer.

According to the optical measurement device of the present invention, the wavelength range in which absorption is large is selected while the optical path length is reduced, and the product of the optical path length and the effective attenuation coefficient is made equal. On the other hand, the measurement can be performed without lowering the detection sensitivity. When hemoglobin is to be measured, a near-infrared region can be used for a long wavelength region for a deep portion, and a visible region can be used for a short wavelength region for a shallow portion. In addition, by using the visible region, it is possible to correct the absorption of melanin, a pigment in skin having an absorption region in the visible region.

[0037]

As described above, according to the optical measurement device of the present invention, it is possible to perform measurement separately in the depth direction.

[Brief description of the drawings]

FIG. 1 is a diagram showing a contribution function for a point-like absorber.

FIG. 2 is a characteristic diagram of absorption coefficients of oxyhemoglobin and deoxyhemoglobin with respect to wavelength.

FIG. 3 is a schematic block diagram for explaining an embodiment of the optical measurement device of the present invention.

FIG. 4 is a schematic block diagram for explaining another embodiment of the light measuring device of the present invention.

FIG. 5 is a schematic block diagram for explaining another embodiment of the light measuring device of the present invention.

FIG. 6 is a diagram illustrating a configuration example of a light measuring device according to the present invention.

FIG. 7 is a diagram illustrating another configuration example of the optical measurement device of the present invention.

FIG. 8 is a diagram illustrating a light receiving state of another configuration example of the light measuring device according to the present invention.

FIG. 9 is an example of a light transmitting unit of another configuration example of the light measuring device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical measuring device, 2 ... Light source, 3, 4 ... Optical fiber, 5
... Measurement device, 6 ... Probe, 7 ... CCD camera, 8 ... Dark room, 9 ... Subject, 10 ... Light shield plate, 11 ... Dark filter, 12 ... Measurable range, S ... Light transmission unit, D ... Detection unit.

Claims (1)

[Claims] 1. An optical measuring device for transmitting light to a subject and optically measuring the subject by receiving light scattered or transmitted through the subject, wherein the transmitted light includes different wavelengths, An optical measurement device, wherein a distance between a light transmitting point and a light receiving point on a specimen is varied according to the wavelength.