Photoacoustic Detection and Optical Spectroscopy of High-Intensity Focused Ultrasound-Induced Thermal Lesions in Biologic Tissue

In this study, the capability of a photoacoustic (PA) method in detecting high-intensity focused ultrasound (HIFU) thermal lesions was investigated in chicken breast tissue in vitro and the optical properties of the HIFU-treated and native tissues were determined. Created with a 1-MHz HIFU transducer, the detectability of the induced thermal lesions was assessed photoacoustically at 720 and 845 nm and their optical properties were characterized in the wavelength range 500-900 nm. The results show that the averaged ratio of the peak-to-peak PA signal amplitude of HIFU-treated tissue to that of native tissue is more than 3 fold. The optical spectroscopy investigation revealed that the absorption and reduced scattering coefficients are higher for HIFU-treated tissues than native tissues. This work demonstrates the capability of the PA method in detecting HIFU-induced thermal lesions due, in part, to the increase in their optical absorption coefficient, reduced scattering coefficient, and deposited laser energy fluence.