Patent ID: 6882874

Claim:
A method for compensating for subject-specific variability in an apparatus intended for non-invasively determining the amount of at least two light-absorbing substances in the blood of a subject and provided with emitter means for emitting radiation at a minimum of two different wavelengths and with detector means for receiving the radiation emitted, the method comprising the steps of calibrating the apparatus using a nominal calibration, carrying out initial characterization measurements, said measurements to include measuring radiation emitted by said emitter means and received by the detector means without transmission through tissue, based on the characterization measurements, establishing nominal characteristics describing conditions under which the nominal calibration is used, storing reference data indicating the nominal characteristics established, performing in-vivo measurements on living tissue, wherein radiation emitted by the emitter means through the living tissue and received by the detector means is measured, based on the in-vivo measurements and the reference data stored, determining tissue-induced changes in the nominal characteristics, and compensating for subject-specific variation in the in-vivo measurements by correcting the nominal calibration on the basis of the tissue-induced changes.