Patent ID: 7865223

Claim:
An apparatus for determining blood oxygenation in a tissue, the apparatus comprising: a sensor interface having a first emitter and a second emitter configured to emit light into the tissue and having a first detector and a second detector configured to detect light from the tissue, wherein an emitter-detector distance is selected to provide a light path that travels through the tissue at a depth of penetration that includes a selected region of the tissue; a processor configured to: determine light attenuation LA(A 1 ,wsj) of light emitted by the first emitter and received by the first detector; determine light attenuation LA(A 4 ,wsj) of light emitted by the second emitter and received by the second detector; determine light attenuation LA(A 2 ,wsj) of light emitted by the first emitter and received by the second detector; determine light attenuation LA(A 3 ,wsj) of light emitted by the second emitter and received by the first detector; and determine an optical characteristic of said tissue based on a resulting light attenuation LAwsj at said wavelength wsj, the resulting light attenuation determined by summing the light attenuations of LA(A 2 ,wsj) and LA(A 3 ,wsj) and deducting the light attenuations LA(A 1 ,wsj) and LA(A 4 ,wsj), the optical characteristic representative of oxygenation and corresponding to oxygenation of venous blood in tissue of said selected; and an output device coupled to the processor and configured to receive the optical characteristic.