Ultrasonic assessment of thermal therapy in rat liver.

One way to assess the efficacy of thermal therapy is to quantify changes in tissue properties through ultrasonic interrogation, which requires knowledge of the acoustic properties of thermally treated tissues. In this study, estimates of ultrasonic attenuation, speed of sound, backscatter coefficient (BSC), and scattering property estimates were generated from rat liver samples submersed for 10 minutes in a saline bath that was heated to one of seven temperature values over a range of 37-70°C. The attenuation coefficient increased monotonically with exposure temperature, with a maximum increase of 90%. Speed of sound changed by <1% for the different treatment conditions. The BSC had close agreement for all thermal doses over the frequency range of 8-15 MHz. Above this frequency range, samples heated ≥55°C demonstrated an increased BSC slope, and the effective scatterer diameter and effective acoustic concentration were able to distinguish treated from nontreated cases. The findings suggest that attenuation and either BSCs or scatterer property estimates above 15 MHz were sensitive to tissue changes in excised liver caused by thermal therapy.