Patent ID: 8670810

Claim:
An apparatus comprising: a first amplifier having a first input coupled to a first optical detector and having a first output corresponding to a logarithm of the first input wherein the first input corresponds to light intensity along a first optical path through a tissue, the first optical detector on the first optical path; a second amplifier having a second input coupled to a second optical detector and having a second output corresponding to a logarithm of the second input wherein the second input corresponds to light intensity along a second optical path through the tissue, the second optical detector on the second optical path and wherein the first optical path differs from the second optical path, wherein the light intensity corresponds to concentration of an absorbing species in the tissue; and a differential amplifier having a differential output, the differential amplifier configured to amplify a difference between the first output and the second output and generate an output signal, the output signal provided at the differential output and the output signal corresponding to oxygenation of a region of the tissue.