Temperature rise in a tissue-mimicking material generated by unfocused and focused ultrasonic transducers.

The temperature elevation in a homogeneous tissue-mimicking material with tissue-like thermal and acoustic properties, generated by unfocused and focused ultrasonic transducers operating at 1.0 and 3.5 MHz frequencies, was measured. It was found that in the vicinity of a transducer front face, both transducer surface heating and ultrasound absorption are important sources for tissue heating. As for heating due to ultrasound absorption, the experimental results are compared with theoretical predictions for nonperfused tissues resulting from different beam models. The experimental data are in reasonable agreement with the results calculated from a model developed by Nyborg and Steele, a Gaussian beam model and from the model used by the National Council on Radiation Protection and Measurements (NCRP).