Photoacoustic tomography of foreign bodies in soft biological tissue

Ultrasound imaging suffers from poor sensitivity (~50%) and specificity in detecting small foreign bodies in tissue. Hence, alternative imaging methods are needed. Photoacoustic (PA) imaging takes advantage of strong optical absorption contrast and high ultrasonic resolution. This work employed a PA imaging system to detect foreign bodies in biological tissues. To achieve deep penetration, we used near-infrared light and a 5-MHz spherically focused ultrasonic transducer. PA images were obtained from objects (glass, wood, cloth, plastic, and metal) embedded in chicken tissue. The location and size of the targets from the PA images agreed well with those of the actual samples. Objects were imaged more than 1 cm deep. Spectroscopic PA imaging was also performed on the objects. These results suggest PA imaging can potentially be a useful intraoperative imaging tool to identify foreign bodies and discriminate viable tissues in wounded patients.