A patient monitoring system may use photoacoustic sensing to determine one or more physiological parameters of a subject. The system may detect an acoustic pressure, response generated by the application and absorption of light, which may include two peaks. The peaks may correspond to surfaces of a feature such as a blood vessel, and the peak information may allow determination of physiological information. For example, the two peaks may be analyzed and an effective attenuation coefficient may be determined, from which hemoglobin concentration, blood oxygen saturation, or other physiological parameters may be derived.
