High-intensity Focused Ultrasound Thermal Mapping by using a Thermocouple embedded in a Tissue-Mimicking Material

High-intensity focused ultrasound is a non invasive technique for tumor ablation. Focused ultrasound concentrates energy at a small spot called "focus". Temperature elevation at the focus can reach over 56 degrees C rapidly. This causes irreversible damages to cells and provokes coagulative necrosis. Common acoustic characterization is performed by scanning with a hydrophone across and along the beam path. The disadvantage of this technique is that it has to be done at low power in order to avoid hydrophone damage. Thermocouple displacement across and along the beam path allows the temperature measurement at high acoustic power or at similar clinical conditions. In this paper, it is presented the temperature measurement as a complementary technique to characterize acoustic fields and to explore the thermal distribution at focus. HIFU thermal mapping is performed by recording the temperature sensed by a hypodermic thermocouple embedded in a tissue mimicking material. The thermal distribution of a HIFU transducer with focal distance of 17 mm is reported. Temperature maps 2 mm ahead and 2 mm behind the focal distance with a 1 mm z-displacement are presented. HIFU transducer was excited with a 1.9 MHz continuous wave at 20 W. Thermal maps showed a different temperature distribution for each transversal plane reconstructed.