JP2015125090A - Scattering absorber measuring device and scattering absorber measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method that enable precise calculation of a conversion scattering coefficient and an absorption coefficient.SOLUTION: A scattering absorber measuring device 1A comprises: a light source part 31 that emits multiple light pulses P(n) mutually differing in wavelength to a scattering absorber B; a light detection part 41 that detects the respective light pulses P(n) propagating through the inside of the scattering absorber B; and an operation part 5 that calculates a conversion scattering coefficient and an absorption coefficient by a time-resolved spectroscopic measurement method. The calculation part 5 preliminarily has data D2 about a conversion scattering coefficient ratio between the wavelengths of the light pulses P(n), and calculates the conversion scattering coefficient and the absorption coefficient by collectively fitting time-resolved measurement profiles of multiple wavelengths to a solution for a light diffusion equation, on the assumption that the conversion scattering coefficient for each wavelength is subjected to the conversion scattering coefficient ratio.

Description

  The present invention relates to a scattering medium measuring apparatus and a scattering medium measuring method.

  Patent Document 1 describes a method and apparatus for measuring internal information of a scattering medium. In the method and apparatus described in this document, light pulses having a plurality of wavelengths are incident on a scattering medium, output light is detected by a photodetector, and internal information of the scattering medium is calculated based on the detection result. The When calculating the internal information, the time-resolved integral measurement method (TIS method) and phase modulation measurement based on the MBL rule are performed by the spectroscopic measurement method (MVS method) using the optical path length average and dispersion, or the physical quantities corresponding to them. The internal information of the scattering medium is calculated by calculating the absorption coefficient difference using the method (PMS method).

  Non-Patent Document 1 describes a method of measuring the concentration of oxygenated hemoglobin and deoxygenated hemoglobin using near infrared time-resolved spectroscopy. In the method described in this document, the Mie scattering approximation is applied, the converted scattering coefficient is used as a function of wavelength, and the concentration is calculated based on each wavelength value.

JP 2000-146828 A

C. D’ Andrea et al., “Time-resolved spectrally constrained method for the quantificationof chromophore concentrations and scattering parameters in diffusing media”, OPTICS EXPRESS, Vol.14, No. 5, pp.1888-1898, 6 March 2006 M.S.Patterson et.al., “Time resolved reflectance and transmittance for non-invasive measurement of tissue”, Optical Properties, Appl Optics 28, pp. 2331-2336, 1989

  When measuring the internal information of the scattering medium non-invasively using light, the internal information may be calculated using reduced scattering coefficients at a plurality of wavelengths. For example, when calculating the concentration information of the light-absorbing substance as the internal information, the absorption coefficient and the converted scattering coefficient at each wavelength are calculated, and the concentration information is calculated based on these values. In such a case, the conventional general method calculates the internal information after calculating the converted scattering coefficient and the absorption coefficient for each wavelength using the light diffusion theory based on the detection result for each wavelength. .

  However, in the above method, when the S / N ratio of the detection signal decreases, for example, when the distance between the light incident position and the detection position is long, or when the concentration of the light-absorbing substance is greatly increased, the converted scattering coefficient is reduced. There is a problem that the accuracy is greatly affected and the calculation accuracy of internal information is lowered. Non-Patent Document 1 proposes a method that considers the wavelength dependence of the converted scattering coefficient, but Mie scattering approximation is used for the wavelength dependence of the converted scattering coefficient. Since Mie scattering is a theory that assumes a uniform sphere (diameter approximately equal to the wavelength) of an arbitrary material in a uniform medium, an error becomes large in an actual scattering absorber such as a biological tissue.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an apparatus and a method that can accurately calculate a reduced scattering coefficient and an absorption coefficient.

  In order to solve the above-described problems, a scattering medium measuring apparatus according to the present invention includes a light incident part that makes a plurality of light pulses having different wavelengths incident on the scattering medium, and each light pulse that has propagated inside the scattering medium. And a calculation unit that calculates a reduced scattering coefficient and an absorption coefficient by a time-resolved spectroscopic measurement method based on a detection result of the light detection unit, and the calculation unit includes a plurality of light pulses. We have data on the ratio of converted scattering coefficients between wavelengths in advance, and assume that the converted scattering coefficient for each wavelength follows the ratio of the converted scattering coefficient. The reduced scattering coefficient and the absorption coefficient are calculated by fitting together to the solution.

  Further, the scattering absorber measuring method according to the present invention includes a light detection step of entering a plurality of light pulses having different wavelengths into the scattering absorber and detecting each light pulse propagating through the scattering absorber, and a light detection step. A calculation step of calculating a converted scattering coefficient and an absorption coefficient by a time-resolved spectroscopic measurement method based on a detection result in, and in the calculating step, data relating to a ratio of the converted scattering coefficient between wavelengths of a plurality of light pulses Is prepared in advance, and the converted scattering coefficient for each wavelength is assumed to follow the ratio of the converted scattering coefficient. A coefficient and an absorption coefficient are calculated.

  In the above scattering absorber measuring apparatus and scattering absorber measuring method, data relating to the ratio of the converted scattering coefficient between wavelengths of a plurality of light pulses is prepared in advance. This is because the converted scattering coefficient has a certain correlation with the wavelength, and the ratio of the converted scattering coefficient between a plurality of wavelengths is considered to be substantially constant through a plurality of measurements. Then, in the calculation unit (calculation step), assuming that the converted scattering coefficient for each wavelength follows the ratio of the converted scattering coefficient, fitting the time-resolved measurement profiles of multiple wavelengths based on the detection results to the solution of the light diffusion equation. Thus, the reduced scattering coefficient and the absorption coefficient are calculated. According to such a method, data related to the ratio of the converted scattering coefficient can be measured in advance with good accuracy under favorable conditions, and a plurality of values are simultaneously fitted, so that fitting accuracy is also improved. Therefore, the calculation accuracy of the converted scattering coefficient and the absorption coefficient can be increased as compared with the method of calculating the converted scattering coefficient and the absorption coefficient by applying the light diffusion theory for each wavelength.

  In the scattering medium measuring apparatus, the calculation unit may weight the converted scattering coefficient for each wavelength used for fitting, based on the reliability of the detection result for each wavelength. Similarly, in the above scattering absorber measurement method, in the calculation step, weighting based on the reliability of the detection result for each wavelength may be performed on the converted scattering coefficient for each wavelength used for fitting. When a light pulse is detected in the light detection unit (light detection step), the reliability of the detection result may vary between wavelengths depending on the number of detected photons, the S / N ratio, and the like. Even in such a case, the calculation accuracy of the converted scattering coefficient and the absorption coefficient can be further increased by weighting in consideration of the reliability.

  According to the scattering medium measuring apparatus and the scattering medium measuring method according to the present invention, the reduced scattering coefficient and the absorption coefficient can be calculated with high accuracy.

It is a block diagram which shows roughly the structure of one Embodiment of the measuring apparatus by this invention. It is a graph which shows an example of the time change of each light intensity of the light pulse radiate | emitted from a light source part, and the detection light detected in a light detection part. It is a graph showing the relationship between a conversion scattering coefficient and a wavelength. It is a flowchart which shows operation | movement of a measuring apparatus, and a scattering absorber measuring method. Of the wavelength dependence of the converted scattering coefficient shown in FIG. 3, the converted scattering coefficient ratios R ₁ : R ₂ : R ₃ = 1 confirmed at wavelength λ ₁ = 759 nm, wavelength λ ₂ = 793 nm, and wavelength λ ₃ = 834 nm. .0366: 1.0000: 0.9595), and is a chart showing the converted scattering coefficient obtained by measuring the human forehead part which is a scattering medium. (A) (b) It is a graph which shows the absorption coefficient and conversion scattering coefficient for each wavelength, and the absorption coefficient and conversion scattering coefficient for each wavelength as a comparative example measured by the conventional method. (C) is a chart showing oxygenated hemoglobin concentration, deoxygenated hemoglobin concentration, total hemoglobin concentration, and tissue oxygen saturation. It is a graph which shows the variation coefficient value of the absorption coefficient, conversion scattering coefficient, and hemoglobin amount obtained by changing the measurement time at the time of measuring the forehead part. It is a graph which shows the variation coefficient value of the absorption coefficient, conversion scattering coefficient, and hemoglobin amount obtained by changing the measurement time at the time of measuring the forehead part. It is a graph which shows the result of having measured the absorption coefficient and conversion scattering coefficient for every wavelength using the blood phantom. It is a graph which shows the result of having measured the absorption coefficient and conversion scattering coefficient for every wavelength using the blood phantom. It is a graph which shows the result of having measured the absorption coefficient and conversion scattering coefficient for every wavelength of a human forearm part. It is a graph which shows the result of having measured the absorption coefficient and conversion scattering coefficient for every wavelength of a human forearm part.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a scattering medium measuring apparatus and a scattering medium measuring method according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment)
FIG. 1 is a block diagram schematically showing the configuration of a first embodiment of a measuring apparatus according to the present invention. This measuring apparatus 1A is an apparatus that measures internal information of the scattering medium B by time-resolved spectroscopic measurement using near infrared light. The scattering medium B is, for example, a part of a living body, and the internal information includes, for example, oxygenated hemoglobin concentration, deoxygenated hemoglobin concentration, total hemoglobin concentration, oxygen saturation, and the like. According to this measuring apparatus 1A, hemoglobin dynamics can be quantitatively measured in a non-invasive and simple manner, and therefore can be applied to intracerebral oxygen metabolism monitoring and muscle evaluation during exercise.

  As shown in FIG. 1, the measuring apparatus 1A includes a light source unit 31, a light irradiation fiber 32, a light detection unit 41, a light detection fiber 42, a calculation unit 5, a display unit 9, and these components. And a control unit 10 that performs control.

  The light source unit 31 and the light irradiation fiber 32 are light incident units in the present embodiment, and a plurality of lights having different wavelengths are incident on the scattering medium B. For example, the light source unit 31 generates N (N is an integer of 2 or more) light pulses P (1) to P (N). The center wavelengths of the N optical pulses P (1) to P (N) are different from each other, and the full width at half maximum of each optical pulse P (n) (where n = 1,..., N) is, for example, 10 ps to A few ns. One end of the light irradiation fiber 32 is connected to the light source unit 31, and the other end (light incident end) of the light irradiation fiber 32 is disposed at a predetermined light incident position S on the surface of the scattering medium B. Each light pulse P (n) output from the light source unit 31 is input to one end of the light irradiation fiber 32 and irradiated to the inside of the scattering medium B from the other end of the light irradiation fiber 32. The light source unit 31 is connected to a signal processing unit 51 (described later) of the calculation unit 5, and a trigger signal S <b> 1 indicating the light emission timing of the light pulses P (1) to P (N) in the light source unit 31 is a signal. The data is output to the processing unit 51. The light emission timing of the light pulses P (1) to P (N) is controlled by the control unit 10.

  As the light source part 31, various things, such as a light emitting diode, a laser diode, various pulse laser apparatuses, are used. The light pulse P (n) generated in the light source unit 31 has a short pulse width to the extent that the amount of change in the absorption coefficient of the scattering medium B can be measured, and the light absorption rate in the light absorption characteristics of the substance to be measured. A near-infrared light pulse having a center wavelength at a low wavelength is used. In one example, n = 3 and the wavelengths of the light pulses P (1) to P (3) are 760 nm, 800 nm, and 830 nm, respectively.

  The light detection unit 41 and the light detection fiber 42 detect each light propagated through the scattering medium B. One end (light detection end) of the light detection fiber 42 is disposed at a predetermined light detection position D on the surface of the scattering medium B, and the other end of the light detection fiber 42 is connected to the light detection unit 41. The light detection unit 41 detects the detection light generated by the light pulse P (n) propagating through the scattering medium B through the light detection fiber 42. The signal output terminal of the light detection unit 41 is connected to a signal processing unit 51 (described later) of the calculation unit 5, and the light detection unit 41 outputs a light detection signal S2 indicating the detection timing of the detected light (photon). The data is output to the processing unit 51.

  As the light detection unit 41, various devices such as a photomultiplier tube (PMT), an avalanche photodiode, a PIN photodiode, and an MPPC (Multi-Pixel Photon Counter) are used. Moreover, as the light detection part 41, what has the spectral sensitivity characteristic which can fully detect each wavelength of the light pulses P (1) -P (N) is desirable. When the detection light is weak, a high sensitivity or high gain photodetector may be used.

  In one example, the light incident end of the light irradiation fiber 32 and the light detection end of the light detection fiber 42 are fixed to the optical fiber holder 2 arranged on the surface of the scattering medium B. The optical fiber holder 2 may be formed of a flexible member that can be deformed along the surface of the scattering medium B, for example.

  The optical fiber holder 2 can be omitted. Further, the light pulse P (n) emitted from the light source unit 31 may be directly input to the scattering medium B by another method without using the light irradiation fiber 32. The detection light emitted from the scattering medium B may be directly input to the light detection unit 41 disposed on the surface of the scattering medium B without passing through the light detection fiber 42.

FIG. 2 is a graph showing an example of the temporal change of each light intensity of the light pulse P (n) emitted from the light source unit 31 and the detection light detected by the light detection unit 41. In FIG. 2, the vertical axis indicates the light amount (logarithmic scale), and the horizontal axis indicates time. Graph G11 is the time waveform of the optical pulse intensity incident from the light source unit 31 into the scattering medium B at time t ₀ (the incident wave). Graph G12 is the time waveform of the detected light intensity corresponding to the incident light pulse at time t ₀ (detection waveform). The time that the light propagated inside the scattering medium B reaches the light detection position D is not uniform depending on the propagation state, and is attenuated by scattering and absorption in the scattering medium B. Therefore, as shown in the graph G12 of FIG. 2, the detected waveform is a certain distribution curve.

  Refer to FIG. 1 again. The calculation unit 5 calculates a converted scattering coefficient and an absorption coefficient inside the scattering medium B based on the detection result of the light detection unit 41, and further calculates internal information. The calculation unit 5 includes a signal processing unit 51, an optical characteristic measurement unit 52, a converted scattering coefficient database 53, and a calculation processing unit 54.

  The signal processing unit 51 is connected to the light source unit 31 and receives a trigger signal S1 indicating the light emission timing of the light pulses P (1) to P (N) in the light source unit 31. The signal processing unit 51 is connected to the light detection unit 41 and receives a light detection signal S2 indicating the detection timing of the detected light (photon). Based on the trigger signal S1 and the light detection signal S2, the signal processing unit 51 acquires a plurality (N) of time-resolved measurement waveforms by a time-correlated single photon counting method. . The signal processing unit 51 outputs the data D1 related to the N time-resolved measurement waveforms thus obtained to the optical characteristic measurement unit 52.

The optical characteristic measurement unit 52 uses the data D1 regarding the N time-resolved measurement waveforms provided from the signal processing unit 51, and calculates an absorption coefficient and a converted scattering coefficient based on a light diffusion equation (Photon Diffusion Theory). The optical characteristic measurement unit 52 of the present embodiment reads data D2 stored in advance in a converted scattering coefficient database 53, which is a nonvolatile storage unit, and calculates a converted scattering coefficient using the data D2. The data D2 includes a ratio (R ₁ : R ₂ : ·) of the converted scattering coefficient between the wavelengths (λ ₁ , λ ₂ ,..., Λ _N ) of the plurality of light pulses P (1) to P (N).・ ・: Information on R _N ) is included. This information was obtained by preliminarily measuring the converted scattering coefficient for each wavelength of the reference scattering absorber before use of the measuring apparatus 1A (for example, when manufacturing the measuring apparatus 1A) under suitable conditions. It is a numerical value.

  Here, FIG. 3 is a graph showing the relationship between the converted scattering coefficient and the wavelength obtained by the inventors measuring the converted scattering coefficient for the left and right forehead portions of 50 adult men and women. In the figure, the standard deviation (I mark in the figure) and the average value (black circle in the figure) of the converted scattering coefficient measured at each of the six wavelengths included in the wavelength range from 690 nm to 840 nm are shown. . As shown in the figure, there is a significant correlation between the converted scattering coefficient and the wavelength. In general, the converted scattering coefficient decreases as the wavelength increases. Moreover, it turns out that the conversion scattering coefficient follows a fixed ratio between each wavelength.

The optical characteristic measurement unit 52 reads the data D2 from the converted scattering coefficient database 53, and assumes that the converted scattering coefficient for each wavelength follows a ratio (R ₁ : R ₂ :... R _N ). In other words, the optical characteristic measurement unit 52 calculates the converted scattering coefficient for each wavelength as R ₁ · μ ' _{s, R} , R ₂ · μ' _{s, R} , ..., R _N · μ ' _{s, R} (however, , Μ ′ _{s, R} is assumed to be a basic conversion scattering coefficient). Then, the optical characteristic measurement unit 52 fits the time-resolved measurement profiles at a plurality of wavelengths λ ₁ , λ ₂ ,..., Λ _N based on the data D1 to the solution of the light diffusion equation, thereby performing basic conversion scattering. The coefficient μ ′ _{s, R} and the absorption coefficient μ _{a, λ} (λ = λ ₁ ,..., Λ _N ) for each wavelength are calculated. Note that, when this basic conversion scattering coefficient μ ′ _{s, R} is multiplied by each ratio (R ₁ : R ₂ :... R _N ), a conversion scattering coefficient for each wavelength can be calculated.

  As a more preferred form, the optical characteristic measurement unit 52 may further weight the converted scattering coefficient for each wavelength based on the reliability of the detection result for each wavelength. As an example, the optical characteristic measurement unit 52 has an S / N ratio of N time-resolved measurement waveforms included in the data D1 and / or detection light corresponding to each of the light pulses P (1) to P (N). When determining the measurement reliability of each wavelength from the intensity (number of detected photons) and applying the converted scattering coefficient for each wavelength to the light diffusion equation, a weight distribution calculated from the measurement reliability may be given.

Examples of the solution of the light diffusion equation used for fitting include those disclosed in Non-Patent Document 2 described above. As an example, the reduced scattering coefficients R ₁ · μ ' _{s, R} , R ₂ · μ' _{s, R} , ..., R _N · When μ ′ _{s, R} is applied, the following equation (1) is obtained for each wavelength. _{However, F 1 (ρ, t)} , ···, F N (ρ, t) are respectively the wavelength lambda _1, · · ·, the time response function of the reflection type in lambda _N. Ρ is the distance between the optical axes, t is the response time, and c is the speed of light in the scattering medium.

In the present embodiment, the converted scattering coefficient ratio (R ₁ : R ₂ :...: R _N ) is stored in advance in the converted scattering coefficient database 53, but the converted scattering coefficient ratio ( R ₁ : R ₂ :...: R _N ) may be input from outside the measuring apparatus 1A. The converted scattering coefficient ratio (R ₁ : R ₂ :... R _N ) is, for example, the use of MRI or ultrasonic data capable of measuring the structure and water content in the scattering medium B (for example, biological tissue), It is suitably constructed as a database by collecting various measurement sites, interfiber distance, age, and converted scattering coefficient data for each sex by a time-resolved spectroscopic device in a state where sufficient measurement accuracy is realized.

Also, when fitting, the absorption of each wavelength is combined with the nonlinear least square method using the Levenberg-Marquardt method so that the difference between the N time-resolved measurement waveforms and the above equation (1) approaches the minimum. The coefficient and the basic equivalent scattering coefficient μ ′ _{s, R} are determined. Thereafter, the optical characteristic measurement unit 52 determines the determined basic conversion scattering coefficient μ ′ _{s, R} or the converted scattering coefficient R ₁ · μ ′ _{s, R} , R ₂ · μ ′ _{s, R} ,. _N · μ ′ _{s, R} and the absorption coefficient μ _{a, λ} (λ = λ ₁ ,..., Λ _N ) of each wavelength are output to the arithmetic processing unit 54.

更に、演算処理部５４は、算出された酸素化ヘモグロビン濃度Ｃ_HbO2および脱酸素化ヘモグロビン濃度Ｃ_Hbに基づいて、以下の式（３）より組織酸素飽和度ＳＯ₂を算出してもよい。

The arithmetic processing unit 54 calculates internal information inside the scattering medium B, for example, an absorbent concentration. As an example, the arithmetic processing unit 54 of the present embodiment calculates the absorption coefficient μ _{a, λ} (λ = λ ₁ ,..., Λ _N ) of each wavelength provided from the optical characteristic measurement unit 52 by the following formula (2 ) And solve the N simultaneous equations to calculate the oxygenated hemoglobin concentration C _HbO2 and the deoxygenated hemoglobin concentration C _Hb . Ε _{HbO2, λ} is the molar extinction coefficient of oxygenated hemoglobin at wavelength λ, and ε _{Hb, λ} is the molar extinction coefficient of deoxygenated hemoglobin at wavelength λ.

Further, the arithmetic processing unit 54 may calculate the tissue oxygen saturation SO ₂ from the following equation (3) based on the calculated oxygenated hemoglobin concentration C _HbO2 and deoxygenated hemoglobin concentration C _Hb .

The display unit 9 displays arbitrary parameters (for example, oxygenated hemoglobin concentration C _HbO2 , deoxygenated hemoglobin concentration C _Hb ) among the parameters calculated by the optical property measuring unit 52 and the arithmetic processing unit 54. The person who performs the measurement and the subject recognize the parameter value by the display unit 9.

  Operation | movement of 1 A of measuring apparatuses provided with the above structure is demonstrated with the measuring method of the scattering medium by this embodiment. FIG. 4 is a flowchart showing the operation of the measuring apparatus 1A and the scattering medium measuring method.

As shown in FIG. 4, first, a reduced scattering coefficient ratio (R ₁ : R) is measured by measuring a plurality of scattering absorbers B (for example, biological tissues) under stable conditions in which a high S / N ratio is obtained. ₂ :...: R _N ) is determined (step S10). At this time, for example, the converted scattering coefficient ratio may be accurately measured by using MRI or ultrasonic data. In addition, since the converted scattering coefficient greatly depends on the structure and water content in the scattering medium, the age, sex, measurement site, light incident position S and light detection position D of various subjects using time-resolved spectroscopic measurement method. It is preferable to collect converted scattering coefficient data corresponding to the distance to the other and determine a plurality of sets of converted scattering coefficient ratios. The determined converted scattering coefficient ratio (R ₁ : R ₂ :...: R _N ) may be stored in the converted scattering coefficient database 53 or may be manually set during the measurement described later. .

  Next, warm-up operation of the measuring apparatus 1A is performed (step S11), and the optical fiber holder 2 in which the light irradiation fiber 32 and the light detection fiber 42 are attached to the surface of the scattering medium B to be measured. Arrange (step S12).

  Then, a converted scattering coefficient ratio suitable for the measurement target is selected from a plurality of sets of converted scattering coefficient ratios. At this time, it is determined whether to use the converted scattering coefficient database 53 for selection of the converted scattering coefficient ratio (step S13). When the converted scattering coefficient database 53 is used (step S13; YES), a converted scattering coefficient ratio suitable for the measurement target is selected from the converted scattering coefficient database 53 (step S14). When the converted scattering coefficient database 53 is not used (step S13; NO), a converted scattering coefficient ratio suitable for the measurement target is manually set (step S15).

  Subsequently, a plurality of light pulses P (n) having different wavelengths from each other are sequentially incident on the light incident position S of the scattering medium B from the light source unit 31 via the light irradiation fiber 32 and the inside of the scattering medium B. Each of the light pulses P (n) propagated through the light is guided to the light detection unit 41 via the light detection fiber 42 and detected (light detection step S16). Next, based on the detection result in the light detection step S13, the signal processing unit 51 generates data D1 related to N time-resolved measurement waveforms. The data D1 is provided to the optical property measurement unit 52.

Subsequently, the optical property measuring unit 52, the wavelengths _{(λ 1, ···, λ N} ) the reduced scattering coefficient for each, a ratio _{(R 1: R 2: ···} : R N) R 1 as conforming to the • μ ′ _{s, R} , R ₂ • μ ′ _{s, R} ,..., R _N · μ ′ _{s, R} (where μ ′ _{s, R} is the basic conversion scattering coefficient). At this time, the optical characteristic measurement unit 52 performs weighting on the converted scattering coefficient for each wavelength based on the reliability of the detection result (N time-resolved measurement waveforms) for each wavelength (step S17). As an example, the optical characteristic measurement unit 52 has an S / N ratio of N time-resolved measurement waveforms included in the data D1 and / or detection light corresponding to each of the light pulses P (1) to P (N). It is preferable to determine the measurement reliability of each wavelength from the intensity (the number of detected photons) and give a weight distribution calculated from the measurement reliability.

Subsequently, the optical characteristic measurement unit 52 calculates the basic conversion scattering coefficient μ ′ _{s, R} and the absorption coefficient μ _{a, λ} (λ = λ ₁ ,..., Λ _N ) for each wavelength by time-resolved spectroscopic measurement. Calculate (calculation step S18). At this time, the optical characteristic measurement unit 52 fits the basic conversion scattering coefficient μ ′ _{s, R} and the absorption for each wavelength by fitting the time-resolved measurement profiles of a plurality of wavelengths based on the data D1 to the solution of the light diffusion equation. The coefficients μ _{a, λ} (λ = λ ₁ ,..., Λ _N ) are calculated.

Subsequently, the arithmetic processing unit 54 calculates internal information inside the scattering medium B, for example, an absorbing substance concentration (step S19). As an example, the arithmetic processing unit 54 of the present embodiment calculates the absorption coefficient μ _{a, λ} (λ = λ ₁ ,..., Λ _N ) of each wavelength provided from the optical characteristic measurement unit 52 from the above equation (2). ) And solve the N simultaneous equations to calculate the oxygenated hemoglobin concentration C _HbO2 and the deoxygenated hemoglobin concentration C _Hb . From these numerical values, the total hemoglobin concentration (C _tHb = C _HbO 2 + C _Hb ), tissue oxygen saturation, etc. can also be calculated.

The effects obtained by the measurement apparatus 1A and the measurement method of the present embodiment described above will be described. As described above, in the present embodiment, data D2 relating to the reduced scattering coefficient ratio (R ₁ : R ₂ :... _RN ) between wavelengths of the plurality of light pulses P (n) is prepared in advance. As shown in FIG. 3, since the converted scattering coefficient has a certain correlation with the wavelength, the converted scattering coefficient ratio (R ₁ : R ₂ :... R _N ) between a plurality of wavelengths is a plurality of times. This is because it is considered almost constant throughout the measurement. Then, the optical characteristic measuring section 52 and the calculation step S18, the reduced scattering coefficient for each wavelength is reduced scattering coefficient ratio _{(R 1: R 2: ···} : R N) as conforming to, a plurality of wavelengths based on the data D1 By fitting the time-resolved measurement profile together with the solution of the light diffusion equation, the basic conversion scattering coefficient μ ' _{s, R} and the absorption coefficient for each wavelength μ _{a, λ} (λ = λ ₁ , ..., λ _N ) Is calculated. According to such a method, it is possible to accurately measure data relating to the reduced scattering coefficient ratio (R ₁ : R ₂ :...: R _N ) in advance under favorable conditions, and to simultaneously calculate a plurality of values. Since fitting is performed, fitting accuracy is also increased. Therefore, the calculation accuracy of the converted scattering coefficient and the absorption coefficient can be increased as compared with the method of calculating the converted scattering coefficient and the absorption coefficient by applying the light diffusion theory for each wavelength.

Furthermore, according to the measurement apparatus 1A and the measurement method of the present embodiment, even when the exact distance between the light incident position S and the light detection position D is unknown, the converted scattering coefficient ratio (R ₁ : R _2: ···: by using R _N), the absorption coefficient than the conventional _{μ a, λ (λ = λ} 1, ···, λ N) can be accurately measured, further oxygenation Hemoglobin concentration, deoxygenated hemoglobin concentration, total hemoglobin concentration, and tissue oxygen saturation can be accurately measured.

  Further, as in the present embodiment, weighting based on the reliability of N time-resolved measurement waveforms may be performed on the converted scattering coefficient for each wavelength used for fitting. When light is detected by the light detection unit 41 (light detection step S16), the reliability of the N time-resolved measurement waveforms may vary depending on the number of detected photons, the S / N ratio, and the like. . Even in such a case, weighting in consideration of reliability can suppress the influence of a wavelength having a low S / N ratio, and can further increase the calculation accuracy of the converted scattering coefficient and the absorption coefficient.

  Here, the results of measuring the conversion scattering coefficient, oxygenated hemoglobin concentration, deoxygenated hemoglobin concentration, tissue oxygen saturation, etc. of a plurality of subjects using the measurement apparatus 1A and the measurement method of the present embodiment will be described.

FIG. 5 shows the converted scattering coefficient ratios R ₁ : R ₂ confirmed at the wavelength λ ₁ = 759 nm, the wavelength λ ₂ = 793 nm, and the wavelength λ ₃ = 834 nm among the wavelength dependence of the converted scattering coefficient shown in FIG. R ₃ = 1.0366: 1.0000: 0.9595), and is a graph showing the converted scattering coefficient obtained by measuring the human forehead part which is a scattering medium. In addition, in FIG. 5, the numerical value obtained by the conventional measuring method (The conversion scattering coefficient is determined for every wavelength) is also shown as a comparative example. Referring to FIG. 5, it can be seen that the ratio of the converted scattering coefficient obtained by the present embodiment follows the above-described converted scattering coefficient ratio (R ₁ : R ₂ : R ₃ ).

6A and 6B show an absorption coefficient and a converted scattering coefficient for each wavelength measured by the measuring apparatus 1A and the measuring method of the present embodiment, and a comparative example measured by a conventional method. It is a graph which shows the absorption coefficient and conversion scattering coefficient for each wavelength as. Further, FIG. 6C shows oxygenated hemoglobin concentration C _HbO2 , deoxygenated hemoglobin concentration C _Hb , total hemoglobin concentration C _tHb , and tissue calculated from the results of FIGS. _6A and 6B. is a table showing the oxygen saturation SO _2. In addition, each numerical value described in FIG. 6 represents (average value) ± (standard deviation).

  Referring to FIG. 6, it can be seen that the standard deviation of the numerical values obtained by the measuring apparatus 1A and the measuring method of this embodiment is much smaller than the standard deviation of the numerical values of the comparative example. From this, it can be seen that according to the measurement apparatus 1A and the measurement method of the present embodiment, the calculation accuracy of the converted scattering coefficient and the absorption coefficient can be improved.

7 and 8 show the absorption coefficient, the converted scattering coefficient, and the amount of hemoglobin (total hemoglobin concentration C _tHb and tissue oxygen saturation SO ₂₎ obtained by changing the measurement time during the measurement of the forehead from 100 ms to 5000 ms. It is a graph which shows the variation coefficient value of). FIG. 7 shows variation coefficient values obtained by the conventional method, and FIG. 8 shows variation coefficient values obtained by the measuring apparatus 1A and the measurement method of the present embodiment. Note that the reduced scattering coefficient ratio R ₁ : R ₂ : R ₃ is the same as described above. Normally, the coefficient of variation value decreases as the measurement time increases (that is, the measurement accuracy increases). As is apparent from a comparison between FIG. 7 and FIG. 8, the measurement apparatus 1A and measurement method of the present embodiment are the same. When compared by measurement time, the coefficient of variation value is smaller than that of the conventional method. In other words, the measurement time for obtaining a certain measurement accuracy can be shortened by the measurement apparatus 1A and the measurement method of the present embodiment.

9 and 10 are graphs showing the results of measuring the absorption coefficient and the reduced scattering coefficient for each wavelength (689 nm, 732 nm, and 759 nm) using a blood phantom. 9 and 10, the horizontal axis represents time, and the vertical axis represents the absorption coefficient (unit: cm ⁻¹ ) and the reduced scattering coefficient (unit: cm ⁻¹ ). FIG. 9 shows the result of the conventional method, and FIG. 10 shows the result of the measuring apparatus 1A and the measuring method of the present embodiment. Time t ₁ in the figure shows the timing when dry yeast was added to consume oxygen in the blood phantom, time t ₂ shows the timing when the attenuator was changed, and time t ₃ shows the timing when the attenuator was further changed. .

11 and 12 are graphs showing the results of measuring the absorption coefficient and the converted scattering coefficient for each wavelength (689 nm, 732 nm, and 759 nm) of the human forearm. 11 and 12, the horizontal axis represents time, and the vertical axis represents the absorption coefficient (unit: cm ⁻¹ ) and the reduced scattering coefficient (unit: cm ⁻¹ ). FIG. 11 shows the result of the conventional method, and FIG. 12 shows the result of the measuring apparatus 1A and the measuring method of the present embodiment. Time t ₄ in the figure indicates the timing when the cuff is attached to the forearm, and time t ₅ indicates the timing when the cuff is removed.

In the measurement using the blood phantom shown in FIGS. 9 and 10, the tissue oxygen saturation SO ₂ is in a wide range of 0% to 100%, unlike a living body. Therefore, the S / N ratio tends to be lower than that of a living body. In the measurement of the forearm shown in FIG. 11 and FIG. 12, the absorption coefficient at 689 nm is increased abruptly by attaching a cuff and giving a rapid change (deoxygenation) in the amount of hemoglobin. The ratio is lowered. Referring to FIGS. 9 to 12, even in the state where the S / N ratio is low as described above, the measurement apparatus 1A and the measurement method (FIG. 9) of this embodiment are compared with the conventional methods (FIGS. 9 and 11). 10 and FIG. 12), it can be seen that the amplitude of the graph is small and the measurement can be stably performed with high accuracy. This also makes it possible to shorten the measurement time.

  DESCRIPTION OF SYMBOLS 1A ... Scattering absorber measuring apparatus, 2 ... Optical fiber holder, 5 ... Calculation part, 9 ... Display part, 10 ... Control part, 31 ... Light source part, 32 ... Light irradiation fiber, 41 ... Light detection part, 42 ... Optical detection fiber, 51... Signal processing unit, 52... Optical characteristic measurement unit, 53... Converted scattering coefficient database, 54 .. arithmetic processing unit, B .. scattering absorber, D ... light detection position, P (n). , S: Light incident position.

Claims (4)

A light incident part that impinges on the scattering medium a plurality of light pulses having different wavelengths from each other;
A light detection unit for detecting each light pulse propagated inside the scattering medium;
Based on the detection result in the light detection unit, a calculation unit that calculates a reduced scattering coefficient and an absorption coefficient by a time-resolved spectroscopic measurement method,
With
The calculation unit has data related to the ratio of the converted scattering coefficient between wavelengths of the plurality of light pulses in advance, and the detection result is assumed that the converted scattering coefficient for each wavelength follows the ratio of the converted scattering coefficient. A scattering absorber measuring apparatus, wherein the converted scattering coefficient and the absorption coefficient are calculated by fitting together time-resolved measurement profiles of a plurality of wavelengths based on the above to a solution of a light diffusion equation.   2. The scattering according to claim 1, wherein the calculation unit performs weighting based on reliability of the detection result for each wavelength with respect to the converted scattering coefficient for each wavelength used for the fitting. Absorber measuring device. A light detection step of entering a plurality of light pulses having different wavelengths from each other into the scattering medium and detecting each light pulse propagating through the scattering medium; and
Based on the detection result in the light detection step, a calculation step of calculating a reduced scattering coefficient and an absorption coefficient by a time-resolved spectroscopic method,
With
In the calculation step, data on the ratio of the converted scattering coefficient between the wavelengths of the plurality of light pulses is prepared in advance, and the detection result is assumed that the converted scattering coefficient for each wavelength follows the ratio of the converted scattering coefficient. A method for measuring a scattering medium, wherein the reduced scattering coefficient and the absorption coefficient are calculated by fitting together time-resolved measurement profiles of a plurality of wavelengths based on the above to a solution of a light diffusion equation.   The weighting based on the reliability of the detection result for each wavelength is performed on the converted scattering coefficient for each wavelength used for the fitting in the calculation step. Scattering absorber measurement method.

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