Influence of acoustic power on parietal thermometry during extracorporeal high intensity focused ultrasound treatments

Objectives: Compare the muscular parietal heating during high intensity focused ultrasound (HIFU) at different acoustic power levels. Methods: 3 series of 100 acoustic pulses of same energy but variable power were applied in vivo on the muscular lumbar and abdominal walls in 4 pigs. The target volume was located 47 to 94 mm behind the skin. Two thermocouples were inserted into the muscular wall facing the focal point 10-15 mm and 25-30 mm from the skin. The position of the treatment head was the same for the 3 series of acoustic pulses. The temperatures in the muscular wall were recorded during the HIFU treatment. Results: The lumbar muscular wall heating were: at low acoustic power (53 to 67W) 1.5 to 4.0 degrees C, at medium acoustic power (532 to 654W) 2.3 to 6.5 degrees C and at high acoustic power (1895 to 2372W) 1.2 to 5.0 degrees C. The abdominal muscular wall heating were: at low acoustic power (128 to 163W) 0.5 to 6.5 degrees C, at medium acoustic power (451 to 574W) 2.7 to 8.4 degrees C and at high acoustic power (1213 and 1545W) 3.3 to 8.5 degrees C. Conclusion: During extracorporeal HIFU treatments, the muscular parietal heating is variable among individuals and increases with the acoustic power.