When applying ultrasound, which factor has the least impact on the amount of heat absorbed?

The choice of the coupling agent has the least impact on the amount of heat absorbed during ultrasound application. Coupling agents are used to enhance the transmission of ultrasound waves from the transducer to the tissue by minimizing air gaps. While the choice of a coupling agent might affect the effectiveness of ultrasound transmission, it does not significantly influence the amount of heat generated in the tissue.

On the other hand, the intensity of the ultrasound waves plays a critical role in determining the thermal effects, as higher intensities lead to greater absorption and heat generation. Similarly, the duration of exposure is critical, as longer treatment times allow for more heat to accumulate in the tissues. The size of the area being sonated is also important, as larger areas may disperse energy differently, affecting how much heat is produced in that specific area. Therefore, among these factors, the coupling agent has the least impact on heat absorption.