Effect of Continuous Application of Heating-Cooling Cycles on Ultrasonic Attenuation of Muscle Tissue

Abstract

In ultrasound therapies with HITU applications, the temperature reached in the tissue depends both on the properties of the tissue to be treated and on the ultrasonic parameters. Ultrasonic attenuation (α) is one such parameters since it plays a fundamental role in the thermal source term of the biothermic equation. The study addresses the behavior of α by subjecting an ex vivo muscle to continuous heating-cooling cycles (15–50 °C). Using the transmission technique of ultrasonic pulse (PU) and a controlled thermal bath, the evolution of the pulses was obtained as a function of temperature. It was observed that, for the first three cycles, the evolution of the attenuation presents a non-reversible behavior. Then, the cycle becomes reversible, but at values very different from the initial value. Disregarding this behavior in the planning of a therapeutic session will result in an over or underestimation of the temperature, and, therefore, compromising the limits of safety and in the effectiveness of the application.