Patent ID: 8401604

Claim:
A method for measuring a concentration of a substance in a bloodstream of a body, the method comprising the steps of: measuring a first amount of infrared (IR) radiation absorbed or emitted from the body in a first IR wavelength band in which the substance exhibits IR absorption or emission, and generating a first signal having a first radiation measurement value indicative of the first amount; measuring a second amount of IR radiation absorbed or emitted from the body in a second IR wavelength band different from the first IR wavelength band and including wavelengths in which the substance exhibits no more than negligible IR absorption or emission, and generating a second signal having a second radiation measurement value indicative of the second amount; measuring a temperature of a surface on the body and generating a third signal having a third value indicative of the temperature of the surface; measuring an ambient temperature and generating a fourth signal having a fourth value indicative of the ambient temperature; providing a memory device in which is stored an empirically-derived look-up table containing data correlating values for the concentration of the substance in the bloodstream with (a) ambient temperature values, (b) body surface temperature values, and (c) normalized radiation parameter ratio values, each of which is determined by the ratio of (1) a radiation parameter value in the first IR wavelength band normalized against a first blackbody radiation parameter value in the first IR wavelength band to (2) a radiation parameter value in the second IR wavelength band normalized against a second predetermined blackbody radiation parameter value in the second IR wavelength band; providing a processor configured to receive the first, second, third, and fourth signals, the processor being operably associated with the memory device so as to access the lookup table therefrom; and operating the processor to (a) normalize the first radiation measurement value against the first predetermined blackbody radiation value, (b) normalize the second radiation measurement value against the second predetermined blackbody radiation value, (c) calculate a normalized radiation parameter ratio value as the ratio of the normalized first radiation measurement value to the normalized second radiation measurement value, (d) correct the normalized radiation parameter ratio value using the third and fourth values to obtain a corrected normalized radiation parameter ratio value, and (e) determine from the lookup table the concentration of the substance in the bloodstream correlated with the corrected normalized radiation parameter ratio value.