Photoacoustic monitoring technique

A photoacoustic monitoring system, comprising:

• a monitor configured to:
• receive a signal representative of an indicator concentration in an artery and a vein;
• and
• determine a physiological parameter based at least in part on the signal;
• and
• a sensor coupled to the monitor, comprising:
• a light source configured to emit light into a tissue, wherein the tissue includes an artery and a vein;
• and
• a flat or fixed focus ultrasound receiver configured to detect a photoacoustic effect from the light emitted into the tissue to generate the signal, wherein a focal length of the flat or fixed focus ultrasound receiver encompasses the artery and the vein.

A method, comprising:

• using a processor:
• receiving a signal from a fixed focus or flat acoustic detector configured to detect a photoacoustic effect from light emitted into a patient's tissue, wherein the signal is representative of an indicator concentration in an artery and a vein;
• and
• determining a physiological parameter based at least in part on the signal.