 Thermoacoustic waves are induced within the anatomy wherever absorption takes place, and the strength of these thermoacoustic waves is proportional to the energy absorbed within the tissue.Some of these waves propagate through the anatomy over some time interval ("time-of-flight") before being detected by one or more of the acoustic transducers.The exact time-of-flight is proportional to the distance between an absorption site and a transducer, assuming for the moment that each transducer is a "point" detector.