Device and method for measuring oxyhemoglobin saturation in tissue of subject

Abstract

The present invention relates to an apparatus and a method for non-invasively determining blood oxygen saturation in a tissue of a subject by near infrared spectroscopy using a multi-distance method and taking into account attenuation of a light signal due to light absorbers other than hemoglobin and deoxygenated hemoglobin and scattering properties of the tissue of the subject.

Description

[0001] This invention patent application is a divisional application of the invention patent application with international application number PCT / EP2018 / 053306, international application date of February 9, 2018, application number 201880011276.6 that entered the Chinese national phase, and entitled "Apparatus and method for measuring blood oxygen saturation in tissues of a subject".

[0002] This invention relates to an apparatus for measuring blood oxygen saturation in the tissues of a subject and a method for determining blood oxygen saturation in the tissues of a subject.

[0003] Monitoring tissue oxygen saturation in subjects is clinically important because low oxygen saturation indicates potentially fatal conditions. This is true, for example, in preterm infants who frequently suffer from pregnancy-related gastrointestinal damage, such as necrotizing enterocolitis or constipation, and are constantly at risk of shock. Therefore, in the case of preterm infants, continuous and accurate monitoring of abdominal oxygen saturation is necessary.

[0004] The oxygen saturation in the tissues of the subject was defined as:

[0005]

[0006] in and These are the concentrations of oxyhemoglobin and deoxyhemoglobin, respectively.

[0007] Near-infrared spectroscopy (NIRS) is a non-invasive technique for measuring blood oxygen saturation in a subject's tissues. NIRS depends on oxyhemoglobin (HbA1c). b The unique absorption characteristics of O2 and deoxyhemoglobin (Hb) in the near-infrared spectral range were used to determine H b The relative concentrations of O2 and Hb. NIRS can be performed non-invasively by placing a spectral sensor on the subject's skin and measuring the attenuation of the light signal as it passes through the subject's tissue.

[0008] The measured light attenuation is related to the concentration of the light-absorbing substance (chromophore) as given by Lambert-Beer's law:

[0009]

[0010] in It is the light attenuation at a specific wavelength λ. It refers to the concentration of a specific chromophore. It is the extinction coefficient of a specific chromophore at a specific wavelength, while This is the distance between the light source and the detector. Using the known extinction coefficient, the concentration of the chromophore can be calculated from the measured light attenuation. In the case of a mixture of different chromophores, the relative concentration of the chromophores can be determined by measuring the light attenuation at several different wavelengths, where the extinction coefficients of the chromophores are different. For a mixture containing N different chromophores, this requires measuring the attenuation at at least N different wavelengths.

[0011] In a typical NIRS device, a light signal of known wavelength and intensity is transmitted to the subject's tissue, and the diffusely reflected light from that tissue is detected to calculate the light attenuation. To accurately determine the concentration of chromophores in the tissue that contributes to the measured light attenuation, it is necessary to consider the tissue's optical properties, particularly absorption due to other chromophores present in the tissue and the tissue's scattering properties. In practice, the tissue's scattering characteristics need to be addressed through calibration measurements. To account for H+ scattering... b For chromophores other than O2 and Hb, their absorption spectra must be determined to estimate wavelength-dependent extinction coefficients, and light attenuation must be measured at at least 2 + M wavelengths, where M is the number of additional chromophores to be considered. Several methods for addressing these problems have been developed in the prior art.

[0012] EP 1 259 791 B1 discloses a NIRS method for measuring total intratissue oxygen saturation in a subject by measuring light attenuation at three or more wavelengths and calculating the attenuation difference between wavelengths. This method is also known as the "differential wavelength method." This method requires measurements at N+1 different wavelengths to determine the concentrations of N different chromophores. By determining the differential attenuation, the contributions of tissue light scattering, fixed light absorption components, and measurement device characteristics are relative to the attributable to H... b The attenuation of O2 and Hb is minimized, which improves the accuracy of the measured blood oxygen saturation.

[0013] US2012 / 0136225A1 discloses a method for determining blood oxygen saturation in the lower gastrointestinal tract of a subject, which involves taking into account the presence of wavelength-dependent absorbing materials absent in the blood. Specifically, US2012 / 0136225A1 suggests considering light attenuation due to the presence of feces in the lower gastrointestinal tract of the subject, particularly meconium present in the gastrointestinal tract of newborn infants. US2012 / 0136225A1 also teaches the use of differential wavelength methods to analyze NIRS data.

[0014] Although the differential wavelength method minimizes the contribution of tissue scattering properties, calibration is still required to account for scattering as well as non-specific background absorption. This calibration is performed by determining the oxygen saturation of the reference tissue, assuming that the oxygen saturation of a given reference tissue is a weighted sum of the oxygen saturations of the subject's venous and arterial blood. However, this requires knowledge of the relative contributions of venous and arterial blood to that tissue. While empirical data on the relative contributions of venous and arterial blood oxygen saturation exist, the reliability of these data is questionable. Therefore, the available calibration methods provide a potential source of error for the differential wavelength method.

[0015] An alternative method for performing NIRS measurements is to measure the light attenuation at several wavelengths and different distances between the light source and the photodetector. A specific wavelength can then be calculated based on the following formula. absorption at the site :

[0016]

[0017] in It is an empirically determined value that takes into account specific wavelengths in the subject's tissues. The attenuation of the light signal caused by light scattering at that location It is a specific wavelength Attenuation at that point, It is the average distance between the light source and the detector, while This is the slope of the attenuation relative to the distance from the light source to the detector. It can be calculated using the Lambert-Beer law based on absorption. The concentration of chromophores is calculated. This method is also known as the "multi-distance method." It has been used to measure blood oxygen saturation in muscle tissue (Tachtsidis, Ilias et al., "A Hybrid Multi-Distance Phase and Broadband Spatially Resolved Spectrometer and Algorithm for Resolving Absolute Concentrations of Chromophores in the Near-Infrared Light Spectrum," published in Advances in Experimental Medicine and Biology, Vol. 662 (2010), pp. 169-175). However, the reported method does not consider the concentration of H+. bOther absorbents besides O2 and Hb, especially light absorbers present in the subject's abdomen.

[0018] Therefore, the object of this invention is to provide an NIRS device and method for more accurately determining blood oxygen saturation in the tissues of a subject. This invention is particularly aimed at more accurately measuring blood oxygen saturation in the abdomen of newborn infants, especially preterm infants.

[0019] To address this problem, the present invention has found that using a multi-distance method, and taking into account absorption caused by light absorbers other than hemoglobin and deoxyhemoglobin in the subject's tissues, as well as absorption caused by light scattering in the subject's tissues, can more accurately determine the blood oxygen saturation within the subject's tissues.

[0020] Therefore, the present invention relates to an apparatus for non-invasively determining intra-tissue oxygen saturation of a subject, comprising: at least one light source for transmitting an optical signal into the subject's tissue; at least one photodetector for detecting the optical signal from the light source after the light source has passed through the subject's tissue, wherein one or more light sources and one or more photodetectors are configured to measure attenuation of the optical signal at two or more light source-to-detector distances; and a processor connected to the light sources and photodetectors, characterized in that the one or more light sources and one or more photodetectors are configured to measure attenuation of the optical signal at three or more different wavelengths in the range of 650 nm to 3 μm, and the processor includes an algorithm for determining the attenuation of the optical signal as a function of wavelength and light source-to-detector distance; calculating the slope of the attenuation of the optical signal as a function of wavelength relative to the light source-to-detector distance; and calculating intra-tissue oxygen saturation of the subject based on said slope of the attenuation of the optical signal and empirically determined data considering attenuation of the optical signal due to light absorbers other than hemoglobin and deoxyhemoglobin in the subject's tissue and due to light scattering in the subject's tissue.

[0021] The relative absorption can be calculated using a multi-distance method by measuring the attenuation as a function of the distance from the light source to the detector. By assuming that the oxygen saturation of a given reference tissue is a weighted sum of the oxygen saturations of the subject's venous and arterial blood, the necessity of performing calibration by determining the oxygen saturation of the reference tissue is eliminated. This invention only needs to consider light scattering from the tissue. This eliminates a source of systematic error because it no longer requires any assumptions about the relative contributions of venous and arterial blood.

[0022] It is possible to account for attenuation due to factors such as feces or other absorbents present in the subject's tissues by measuring light attenuation at three or more different wavelengths and using empirically determined data to account for attenuation caused by light absorbers other than hemoglobin and deoxyhemoglobin. This is particularly important when measuring blood oxygen saturation in the abdomen of newborns, where feces significantly influence absorption characteristics in the near-infrared range. Data can be readily determined using samples with known absorbents, such as samples taken from the feces of many newborns. This significantly improves the accuracy of the measured blood oxygen saturation.

[0023] The light source and photodetector are configured to transmit a light signal into the subject's tissue and detect the light signal after it has passed through the subject's tissue. Preferably, the light source and photodetector are configured such that the detector detects light diffusely reflected from within the subject's tissue. Preferably, the light source and photodetector are configured such that they can be in direct contact with the subject's skin to avoid any interference with ambient light.

[0024] The light source can be a broadband light source that emits light within a certain wavelength range. Alternatively, the light source can be a collection of light sources, each emitting light with a narrow spectral bandwidth, such as a collection of light-emitting diodes (LEDs). In a preferred embodiment, the light source comprises a collection of LEDs, each emitting light at a different wavelength.

[0025] A photodetector can be, for example, a photodiode or any other device that can convert light into an electric current. Each detector can include a collection of individual detectors, each detecting light at a different wavelength.

[0026] The light source and photodetector are configured to measure the attenuation of the optical signal at two or more distances from the light source to the detector. This allows the device to determine the attenuation of the optical signal based on the distance from the light source to the detector and perform analysis according to a multi-distance method.

[0027] In one embodiment, the device includes a single light source and two or more photodetectors located at a fixed distance from the light source. Alternatively, the device includes a single photodetector and two or more light sources located at a fixed distance from the photodetector. In these embodiments, the distance from the light source to the detector does not change during measurement.

[0028] In yet another embodiment, the device includes a single light source and a single photodetector, wherein the light source and / or photodetector is movable to vary the distance between the light source and the detector during measurement. This embodiment has the advantage of allowing sampling of optical signal attenuation as a function of the distance between the light source and the detector over a wide range and a large number of data points.

[0029] The light source and photodetector are configured to measure the attenuation of the optical signal at three or more different wavelengths within a wavelength range of 650 nm to 3 μm, preferably 650 nm to 1 μm, and more preferably 680 nm to 950 nm. For example, each light source may be a collection of individual light sources, each emitting light with a narrow spectral bandwidth. In this case, the detector may be a broadband detector capable of detecting light at least within these spectral ranges. Alternatively, the light source may be a broadband light source, and a diffraction grating or a specific emission filter may be used to detect light in a wavelength-specific manner.

[0030] To improve measurement accuracy, it is preferable to measure attenuation at four or more different wavelengths, more preferably at five or more wavelengths, and most preferably at seven or more wavelengths. In a particularly preferred embodiment, the photodetector is configured to measure the attenuation of the optical signal at seven different wavelengths in the range of 650 nm to 1 μm.

[0031] In measurements performed on the abdomen of subjects, particularly newborns, it has been found that measurements in the 815 to 875 nm range do not increase measurement accuracy. Therefore, the photodetector is configured to measure the attenuation of the light signal at seven different wavelengths in the range of 650 nm to 1 μm, excluding the 815 to 875 nm range.

[0032] In the case of measurements on the subject's abdomen, several wavelength combinations have been identified that provide increased measurement accuracy. These wavelengths can be selected to better distinguish between Hb, HbO2, and other absorbents present in the subject's abdomen, such as feces. These optimized wavelength combinations are described below.

[0033] In one embodiment, the photodetector is configured to measure attenuation at three or more different wavelengths selected from 695±5 nm, 712±5 nm, 733±5 nm, 743±5 nm, 762±5 nm, 783±5 nm, 790±5 nm, 805±5 nm, 880±5 nm, 895±5 nm, and 910±5 nm. Preferably, the wavelengths are selected from 712±5 nm, 733±5 nm, 762±5 nm, 783±5 nm, 805±5 nm, 880±5 nm, 895±5 nm, and 910±5 nm.

[0034] In one embodiment, the photodetector is configured to measure the attenuation of the optical signal at 712±5 nm, 736±5 nm, 762±5 nm, 784±5 nm, and 910±5 nm.

[0035] In one embodiment, the photodetector is configured to measure the attenuation of the optical signal at 712±5 nm, 736±5 nm, 762±5 nm, 784±5 nm, 895±5 nm, and 910±5 nm.

[0036] To measure attenuation at a given number of different wavelengths, it is sufficient to configure the light source and photodetector to measure attenuation over different wavelength ranges, which include at least the specified wavelengths. The spectral bandwidth of each wavelength range can vary, as long as the wavelength ranges can be clearly distinguished. Preferably, attenuation is measured over different wavelength ranges with bandwidths of ±25 nm or less, more preferably ±15 nm or less, and most preferably ±5 nm or less.

[0037] In a preferred embodiment, the device is configured to measure attenuation at two or more light source-to-detector distances to improve the accuracy of the calculated slope of the optical signal attenuation as a function of wavelength relative to the light source-to-detector distance. In a preferred embodiment, the device is configured to measure attenuation at three light source-to-detector distances.

[0038] The minimum and maximum light source distances can be optimized based on the detector's sensitivity and the optical properties of the subject's tissues. In the case of a device for measuring abdominal oxygen saturation in newborn infants, the minimum distance from the light source to the detector is preferably at least 0.8 cm, more preferably at least 0.9 cm, and most preferably at least 1.0 cm. Preferably, the shortest distance between the light source and the detector is in the range of 0.8 to 2 cm, more preferably at least 0.9 to 1.5 cm, and most preferably 0.95 to 1.2 cm. The longest distance from the light source to the detector is preferably in the range of 2 to 10 cm, more preferably in the range of 3 to 8 cm, and most preferably in the range of 4 to 6 cm.

[0039] This algorithm calculates the intratissue oxygen saturation of a subject based on the slope of light signal attenuation as a function of wavelength and the distance from the light source to the detector. Therefore, the algorithm uses a multi-distance method to calculate the oxygen saturation level.

[0040] In a preferred embodiment, the algorithm included in the processor calculates a specific wavelength based on the following equation. Relative absorption at the location :

[0041]

[0042] in It is an empirically determined value that takes into account specific wavelengths in the subject's tissues. The attenuation of the light signal caused by light scattering at that location It is a specific wavelength Attenuation at that point, It is the average distance from the light source to the detector, and It is the slope of the attenuation relative to the distance from the light source to the detector.

[0043] It should be noted that the above formula calculates relative absorption. This is equal to the absolute absorbance multiplied by the factor k. This factor can be determined using calibrated measurements. The relative absorbance is sufficient to calculate the relative concentration of the chromophore. Since blood oxygen saturation, as defined above, is the ratio of HbO2 concentration to total hemoglobin concentration, it is not necessary to determine the absolute concentrations of HbO2 and Hb. Therefore, it is not necessary to determine the factor. And has already been targeted The above formula omits

[0044] Then absorption can be used. We can use Lambert-Beer's law to calculate the concentrations of HbO2, Hb, and other light absorbers.

[0045] Reduced scattering This is an empirically determined value that takes into account the attenuation of the light signal due to light scattering in the subject's tissues. To calculate the relative absorption using the above formula... Knowing the relatively reduced scattering That's enough; it's defined as...

[0046]

[0047] in Scattering parameters of a specific tissue. This can be determined by measuring the scattering properties of a reference tissue. For example, it can be determined by measuring the scattering properties of the abdomens of many newborn infants. In a preferred embodiment, the parameters are assumed to be... In 10 -4 Up to 10 -3 nm -1 Within the range, 2×10 is preferred. -4 Up to 8×10 -4 nm -1 More preferably 5×10 -4 Up to 8×10 -4 nm -1 In a particularly preferred embodiment, it is assumed that... It is 6.4×10 -4 nm -1 These values ​​have been found to accurately explain the scattering from the abdomen of newborn infants.

[0048] Absolutely reduced scattering can be achieved by using the method defined above. Multiply by a factor To determine. However, for the present invention, it is not necessary to determine. .

[0049] parameter and It can be experimentally determined by frequency domain absorption measurements, as described, for example, in "Quantitative determination of the absorption spectra of chromophores in strongly scattering media: a light-emitting-diode based technique" by Sergio Fantini, Maria Angela Franceschini, Joshua B. Fishkin, Beniamino Barbieri, and Enrico Gratton, Applied Optics, Vol. 33, pp. 5204-5213 (1994).

[0050] In one embodiment, the algorithm calculates blood oxygen saturation by determining the relative concentrations of HbO2 and Hb according to the following equation:

[0051]

[0052] in and These are the relative concentrations of oxyhemoglobin and deoxyhemoglobin, respectively. It is based on the equation given above at a specific wavelength. The absorption measured below, It refers to the concentration of light absorbers other than hemoglobin and deoxyhemoglobin present in the subject's tissues, and It is a specific wavelength Light-absorbing substances The extinction coefficient.

[0053] The relative concentration calculated using this formula is equal to the absolute concentration multiplied by the factor. However, in order to calculate blood oxygen saturation Using relative concentration and the following equation is sufficient:

[0054]

[0055] The value represents the data considering the attenuation of the light signal caused by the light absorber. These data can be determined empirically by measuring the absorption spectrum of each light absorber individually.

[0056] To improve the accuracy of measuring neonatal blood oxygen saturation, it is necessary to consider the absorption caused by meconium and transitional stool.

[0057] In one particular embodiment, the determination is made by measuring the absorption spectra of isolated fecal, transitional fecal, meconium, and / or biliverdin samples. In a preferred example, the determination is made by measuring the absorption spectrum of an isolated meconium sample. .

[0058] Meconium is the earliest feces in mammalian infants. It consists of substances ingested by the infant while in the womb: intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. It has been found that the average absorption spectrum of meconium samples taken from a variety of subjects can be used as a source of the extinction data calculated above. In one embodiment, the data on light signal attenuation due to light absorbers therefore includes the wavelength-dependent extinction coefficient of meconium samples taken from newborn infants.

[0059] Transitional feces are produced by newborns on the first day after birth. Transitional feces differ in composition from meconium and contain a significant amount of biliverdin. Therefore, data considering light signal attenuation due to light absorbers preferably include wavelength-dependent extinction coefficients from transitional fecal samples taken from newborns, preferably during the first two weeks after birth, more preferably during the first week after birth, and most preferably during the first five days after birth.

[0060] In another preferred embodiment, the data on light signal attenuation due to the light absorber therefore includes the wavelength-dependent extinction coefficient of biliverdin.

[0061] In another aspect, the present invention also provides a method for non-invasively determining intra-tissue oxygen saturation of a subject, comprising the steps of: transmitting an optical signal from at least one light source into the subject's tissue; and detecting the optical signal after passing through the subject's tissue at one or more detection points and at at least two different light source-to-detector distances; characterized in that the method further comprises the steps of: measuring the attenuation of the optical signal at three or more different wavelengths in the range of 650 nm to 3 μm, determining the attenuation of the optical signal as a function of wavelength and light source-to-detector distance; calculating the slope of the attenuation of the optical signal as a function of wavelength relative to the light source-to-detector distance; and calculating the intra-tissue oxygen saturation of the subject based on the slope of the attenuation of the optical signal and empirically determined data considering the attenuation of the optical signal due to light absorbers other than hemoglobin and deoxyhemoglobin in the subject's tissue and due to light scattering in the subject's tissue.

[0062] This method is particularly suitable for determining blood oxygen saturation in the abdomen of newborn infants because it allows for the consideration of the presence of light-absorbing substances such as meconium and transitional stools, and provides an accurate measurement of blood oxygen saturation. In a preferred embodiment, the method is therefore performed on the abdomen of the subject. The subject is preferably an infant. Preferably, the infant is at most one year old, more preferably at most six months old, and most preferably at most three months old. This method is particularly suitable for non-invasively measuring the blood oxygen saturation of preterm infants.

[0063] The distance from the light source to the detector is preferably set as discussed above for the apparatus of the present invention.

[0064] Preferably, the attenuation of the optical signal is measured at three or more different wavelengths selected from 695±5 nm, 712±5 nm, 733±5 nm, 743±5 nm, 762±5 nm, 783±5 nm, 790±5 nm, 805±5 nm, 880±5 nm, 895±5 nm, and 910±5 nm. Preferably, the wavelengths are selected from 712±5 nm, 733±5 nm, 762±5 nm, 783±5 nm, 805±5 nm, 880±5 nm, 895±5 nm, and 910±5 nm.

[0065] In one embodiment, the attenuation of the optical signal is measured at 712±5 nm, 736±5 nm, 762±5 nm, 784±5 nm, and 910±5 nm.

[0066] In one embodiment, the attenuation of the optical signal is measured at 712±5 nm, 736±5 nm, 762±5 nm, 784±5 nm, 895±5 nm, and 910±5 nm.

[0067] The step of calculating blood oxygen saturation preferably includes the same steps as those discussed above for the algorithm of the device of the present invention.

[0068] Preferably, the step of calculating the intratissue oxygen saturation of the subject includes calculating a specific wavelength based on the following equation. Relative absorption below :

[0069]

[0070] in It is an empirically determined value that takes into account specific wavelengths in the subject's tissues. The attenuation of the light signal caused by light scattering at that location It is a specific wavelength Attenuation at that point, It is the average distance between the light source and the detector, while It is the slope of the attenuation relative to the distance from the light source to the detector.

[0071] Preferably, yes

[0072]

[0073] in Assumed to be in 10 -4 Up to 10 -3 nm -1 Within the range.

[0074] Preferably, the step of calculating blood oxygen saturation includes calculating the relative concentrations of oxyhemoglobin and deoxyhemoglobin in the subject's tissues according to the following equation.

[0075] in and These are the relative concentrations of oxyhemoglobin and deoxyhemoglobin, respectively. It is based on the equation given above at a specific wavelength. The absorption measured at the site, It refers to the concentration of light absorbers other than hemoglobin and deoxyhemoglobin present in the subject's tissues, and It is a specific wavelength Extinction coefficient of light-absorbing material .

[0076] Preferably, blood oxygen saturation is calculated from the relative concentrations of HbO2 and Hb according to the following equation. :

[0077]

[0078] Preferably, the data taking into account the attenuation of the optical signal due to the light absorber includes data taking into account the attenuation of the optical signal due to the light absorber, including the wavelength-dependent extinction coefficient of one or more of the following: meconium samples taken from newborn infants, transitional fecal samples taken from newborn infants, and biliverdin.

Claims

1. A device for non-invasively determining intra-tissue blood oxygen saturation in a subject, comprising: At least one light source is used to transmit light signals to the tissues of the subject; At least one photodetector is used to detect the light signal from the light source after the light source has passed through the tissue of the subject, wherein the one or more light sources and the one or more photodetectors are configured to measure the attenuation of the light signal at two or more distances from the light source to the detector; as well as The processor connected to the light source and the photodetector Its features are, The one or more light sources and the one or more photodetectors are configured to measure the attenuation of the optical signal at three or more different wavelengths, including 762±5 nm and 910±5 nm, and selected from at least one of 712±5 nm, 733±5 nm, and 743±5 nm. The processor includes an algorithm for determining the attenuation of the optical signal as a function of the wavelength and the distance from the light source to the detector; Calculate the slope of the attenuation of the optical signal as a function of the wavelength relative to the distance from the light source to the detector; and The oxygen saturation in the subject's tissues is calculated based on the slope of the attenuation of the light signal and empirically determined data considering light absorbers other than hemoglobin and deoxyhemoglobin in the subject's tissues, as well as the attenuation of the light signal due to light scattering in the subject's tissues. The data that takes into account the attenuation of the light signal due to light absorbers include wavelength-dependent extinction coefficients of one or more of the following: meconium samples taken from newborn infants, transitional fecal samples taken from newborn infants, and biliverdin.

2. The apparatus as claimed in claim 1, characterized in that, The minimum distance from the light source to the detector is 0.8 cm.

3. The apparatus as described in claim 1, characterized in that, The algorithm includes calculating a specific wavelength based on the following equation. Relative absorption at the location Steps: in It is an empirically determined value that takes into account specific wavelengths in the subject's tissues. The attenuation of the light signal caused by light scattering at that location It is a specific wavelength Attenuation at that point, It is the average distance from the light source to the detector, and It is the slope of the attenuation relative to the distance from the light source to the detector.

4. The apparatus as described in claim 3, characterized in that, yes in Assumed to be in 10 -4 Up to 10 -3 nm -1 Within the range.

5. The apparatus as described in claim 3, Its features are, The algorithm includes the step of calculating the relative concentrations of oxyhemoglobin and deoxyhemoglobin in the subject's tissues according to the following equation. in and These are the relative concentrations of oxyhemoglobin and deoxyhemoglobin, respectively. It is based on the equation given above at a specific wavelength. The absorption measured at the site, It refers to the concentration of light absorbers other than hemoglobin and deoxyhemoglobin present in the subject's tissues, and It is a specific wavelength Extinction coefficient of light-absorbing material .

6. A method for non-invasively determining intra-tissue oxygen saturation in a subject, comprising the following steps: Light signals from at least one light source are transmitted to the tissues of the subject; as well as The light signal after passing through the subject's tissue is detected at one or more detection points and at least two different light sources at the detector distance; The method is characterized by further comprising the step of measuring the attenuation of the optical signal at three or more different wavelengths, including 762±5 nm and 910±5 nm, and selected from at least one of 712±5 nm, 733±5 nm, and 743±5 nm. Determine the attenuation of the optical signal as a function of the wavelength and the distance from the light source to the detector; Calculate the slope of the attenuation of the optical signal as a function of the wavelength relative to the distance from the light source to the detector; and The oxygen saturation in the subject's tissues is calculated based on the slope of the attenuation of the light signal and empirically determined data considering light absorbers other than hemoglobin and deoxyhemoglobin in the subject's tissues, as well as the attenuation of the light signal due to light scattering in the subject's tissues. The data that takes into account the attenuation of the light signal due to light absorbers include wavelength-dependent extinction coefficients of one or more of the following: meconium samples taken from newborn infants, transitional fecal samples taken from newborn infants, and biliverdin.

7. The method as described in claim 6, characterized in that, The tissue in question is the subject's abdomen.

8. The method as described in claim 6, characterized in that, The subjects were infants up to one year old.

9. The method as described in claim 6, characterized in that, The minimum distance from the light source to the detector is set to at least 0.8 cm.

10. The method as described in claim 6, characterized in that, The step of calculating the tissue oxygen saturation of the subject includes calculating a specific wavelength based on the following equation. Relative absorption at the location : in It is an empirically determined value that takes into account specific wavelengths in the subject's tissues. The attenuation of the optical signal caused by light scattering at that location. It is the specific wavelength Attenuation at that point, It is the average distance between the light source and the detector, while It is the slope of the attenuation relative to the distance from the light source to the detector.

11. The method as described in claim 10, characterized in that, yes in Assumed to be in 10 -4 Up to 10 -3 nm -1 Within the range.

12. The method as described in claim 10, Its features are, The step of calculating the blood oxygen saturation in the subject's tissues includes calculating the relative concentrations of oxyhemoglobin and deoxyhemoglobin in the subject's tissues according to the following equation. in and These are the relative concentrations of oxyhemoglobin and deoxyhemoglobin, respectively. It is based on the equation given above at a specific wavelength. The absorption measured at the site, This refers to the concentration of light absorbers other than hemoglobin and deoxyhemoglobin present in the tissues of the subject. It is the specific wavelength Extinction coefficient of light-absorbing material .

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