Thermal dose Analysis for High Intensity Focused Ultrasound Applications in Continuous and Pulsed Mode

Thermal ablation is a method used to cause tumor cell death by heating the tissue, and one way to achieve this is to use the heating properties of ultrasound with High Intensity Focused Ultrasound (HIFU). Thermal ablation with HIFU has been shown to be a noninvasive and effective approach to tumor treatment. There are different approaches to the application of HIFU, two of which are continuous and pulsed. To characterize these two modalities, a comparative analysis of the thermal dose (TD) achieved by continuous and pulsed HIFU is performed, keeping all the other parameters constant. The thermal dose is calculated from the temperatures measured using thermocouples inserted in ex vivo skeletal muscle tissue (SMT) samples, exposed to both modalities. A single element HIFU transducer with a f = 1.1 MHz (Sonic Concepts H-104 Transducer Series, Ø64 mm, WA, USA) is used to generate the ultrasound pulses. The continuous mode used consists of a single pulse of 20 s of duration; whereas the pulsed mode consists of two pulses of 10 s of duration separated by 5 s of dead time, during which there is no sonification. Both are excited with an input of 350 mV, resulting in an output power of 31 ± 1 W, this way the same amount of energy is deposited in the sample by both modalities. The TD model CEM43 was used to analyze the response of the sample to the continuous and pulsed HIFU, which is one of the most widely accepted for thermal dosimetry. The results show that the use of continuous HIFU achieves slightly higher temperatures than pulsed HIFU, but the difference becomes more notable in the calculated TD, being the dose of continuous HIFU several times the dose of pulsed HIFU.