Normalization method for a chronically implanted optical sensor
First Claim
1. A method for accurately estimating a saturation metric for a metabolite of interest in a volume of fluid by an optical sensor measurement substantially independent of the presence of encapsulating tissue over all or a portion of a lens of the optical sensor, comprising:
- determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in a dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to an amount of a metabolite of interest present in a volume of fluid and said second wavelength of radiation is substantially independent to the amount of the metabolite present in the volume of fluid;
determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to a volume of fluid containing a material having known optical properties;
determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation;
placing the dual wavelength optical sensor in a volume of fluid may contain an amount of the metabolite;
measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to the volume of fluid; and
calculating a saturation metric for the metabolite of interest based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval.
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Accused Products
Abstract
A system and method are provided for accurately estimating blood oxygen saturation independent of tissue encapsulation of the optical sensor. The method includes determining a tissue overgrowth correction factor that accounts for the optical properties of the tissue that cause scattering of the emitted light to a light detector and the relative amplitudes of the emitted light wavelengths. A corrected time interval measured for infrared light is based on an infrared signal returned from fluid with no tissue overgrowth. A corrected time interval for red light is determined by subtracting a red light signal attributed to the presence of tissue overgrowth. The amount of red light signal attributed to the presence of tissue overgrowth is proportional to the total infrared signal less the nominal infrared signal. Oxygen saturation is estimated based on standard calibration factors and the ratio of the corrected infrared time interval and the corrected red time interval.
75 Citations
26 Claims
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1. A method for accurately estimating a saturation metric for a metabolite of interest in a volume of fluid by an optical sensor measurement substantially independent of the presence of encapsulating tissue over all or a portion of a lens of the optical sensor, comprising:
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determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in a dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to an amount of a metabolite of interest present in a volume of fluid and said second wavelength of radiation is substantially independent to the amount of the metabolite present in the volume of fluid;
determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to a volume of fluid containing a material having known optical properties;
determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation;
placing the dual wavelength optical sensor in a volume of fluid may contain an amount of the metabolite;
measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to the volume of fluid; and
calculating a saturation metric for the metabolite of interest based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for accurately estimating blood oxygen saturation in a volume of fluid by optical sensor measurement independent of the presence of encapsulating tissue over all or a portion of a lens of an optical sensor, comprising:
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means for determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in a dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to an amount of a metabolite of interest present in a volume of fluid and said second wavelength of radiation is substantially independent to the amount of the metabolite present in the volume of fluid;
means for determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to a volume of fluid containing a material having known optical properties;
means for determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation;
means for placing the dual wavelength optical sensor in a volume of fluid that may contain an amount of the metabolite;
means for measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to the volume of fluid; and
means for calculating a saturation metric for the metabolite of interest based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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19. A computer readable medium for storing instructions to cause a programmable processor to perform a method for accurately estimating blood oxygen saturation in a volume of fluid by optical sensor measurement independent of the presence of encapsulating tissue over all or a portion of a lens of an optical sensor, comprising:
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instructions for determining a tissue overgrowth correction factor (K) for a first and a second wavelength of optical radiation in a dual wavelength optical sensor, wherein said first wavelength of optical radiation is substantially proportional to an amount of a metabolite of interest present in a volume of fluid and said second wavelength of radiation is substantially independent to the amount of the metabolite present in the volume of fluid;
instructions for determining a nominal time interval for detecting the second wavelength of optical radiation (T2) after it is directed to a volume of fluid containing a material having known optical properties;
instructions for determining a pair of calibration constants (A,B) for said first and said second wavelength of optical radiation;
instructions for measuring a first time interval for the first wavelength of radiation and a second time interval for the second wavelength of radiation when said first and second wavelengths of radiation are directed to a volume of fluid that may contain an amount of analyte; and
instructions for calculating a saturation metric for the metabolite of interest based upon the tissue overgrowth correction factor (K), the pair of calibration constants (A,B), the nominal time interval, the first time interval and the second time interval. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26)
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Specification