Quantitative ultrasound assessment of thermal therapy in liver

Quantitative ultrasound (QUS) is a promising technique for non-invasive tissue characterization. In this work, the potential of QUS to assess thermal therapy in liver tissue was examined. Specifically, the QUS parameters of attenuation slope, effective scatterer size (ESD), effective acoustic concentration (EAC), and envelope statistics parameters ?? and k were evaluated with respect to their ability to discriminate between heated and unheated liver tissue. Two sets of experiments were conducted for this purpose. In the first, a series of freshly excised and bisected rat livers was exposed by placing half of a lobe in a saline bath at 60 ??C for 10 minutes and the other half in 37 ??C saline. Each sample was then scanned using single-element ultrasonic transducers with a nominal center frequency of 20 MHz. In the second experiment, a series of fresh rat livers was exposed to high-intensity focused ultrasound (HIFU) to produce a discolored region of permanent damage. These samples were scanned in the area of damage before and after HIFU exposure with a 20 MHz single element transducer. Samples in both experiments were preserved, and histology slides were generated. In the saline bath experiments, statistically significant differences in attenuation slope, ESD, and EAC were observed between heated and unheated samples, while the changes in k and ?? were not statistically significant. Attenuation slope increased on average from 0.65 dB/cm/MHz in untreated liver to 1.1 dB/cm/MHz in treated liver. Statistically significant differences (p