Methods and systems are provided for determining the oxygen saturation of a region in a patients body using photoacoustic spectroscopy techniques. One embodiment includes determining an interrogation region, or a region in a patient to be monitored, and using a photoacoustic sensor to emit modulated light in the interrogation region. The modulated light may be absorbed by different absorbers, such as oxygenated hemoglobin and deoxygenated hemoglobin, in the interrogation region. The absorbed light results in an acoustic response which is detected by the photoacoustic sensor. Based on a non-pulsatile component of the acoustic response, the regional oxygen saturation at the interrogation region is calculated.
