Patent ID: 7239901

Claim:
A spectrophotometric instrument; comprising: a source of measurement light signals having measurement light wavelengths; a probe having: a tissue-engaging surface; a send fiber coupled to the measurement light signal source for transmitting the measurement light signals to the tissue-engaging surface; and a receive fiber for receiving light including the measurement light signals after the measurement light has been transmitted through the tissue; reference signal optics coupled to the measurement light signal between the measurement light signal source and the tissue-engaging surface, for transmitting a reference light signal portion of the measurement light signal; a detector for generating electrical signals representative of the measurement light signals and the reference light signals; an optical path for coupling the measurement light signal from the receive fibers and the reference light signal portion from the reference signal optics to the detector; an optical path control for selectively allowing and preventing the reference light signal portion to the detector, whereby the detector can output a reference light sample value when the reference light signal portion is coupled to the detector, and the detector can output a measurement light sample value when the measurement light signal portion is coupled to the detector; and a processor for determining corrected measurement sample signals at each measurement light wavelength as a function of a no light signal, a current measurement signal plus a no light signal and a no light signal plus a current measurement signal plus a current reference signal.