Optoacoustic Monitoring of HIFU Therapy: Feasibility Study

Abstract

The main objective of this study was to evaluate the feasibility of the optoacoustic (OA) technique for the monitoring of HIFU therapy. Optoacoustic phenomenon is the generation of wideband ultrasonic transients through absorption of laser radiation and subsequent expansion of the heated volume. The excited OA transient can be detected by a wideband piezo‐electric transducer and contains information on the distribution of optical properties (absorption and scattering) within the medium. If thermal lesions have different optical properties than the untreated tissue, the lesions will be detectable on the OA waveform. We used boiled and raw porcine liver as phantoms mimicking treated and untreated tissue correspondingly. Optical attenuation, absorption and scattering coefficients of raw and boiled porcine liver were measured by the optoacoustic technique, previously developed by our group [4]. Measured optical absorption in raw liver was at least two times lower than in boiled liver at the laser wavelength of 1064 nm. Then OA technique was employed to detect a lesion produced by a 1.1 MHz focused ultrasound in a liver sample. The lesion was about 2 mm thick located about 1 cm below tissue surface. The feasibility and high promise of the OA approach to lesion detection was demonstrated.