Modeling of the spatiotemporal distribution of temperature fields in skin and subcutaneous adipose tissue after exposure to ultrasound waves of different frequencies

Temperature fields produced in the skin and adjacent subcutaneous white adipose tissue (sWAT) during and after exposure to ultrasound (US) waves are significantly dependent on the US frequency. In this study, we present theoretical descriptions of temperature fields appearing in composite skin/sWAT after exposure to US at frequencies of 3 MHz, 10 MHz, and 19 MHz. While the temperature increased by approximately 1.5°C in skin during US exposure at intensities up to 10.0 W/cm2 and a frequency of 3 MHz, this increase reached 9.0°C and 16.0°C at US frequencies of 10 MHz and 19 MHz, respectively. Because of the large difference in heat capacitances and US attenuation coefficients in the skin and adjacent sWAT, the interface between these two layers was subjected to a temperature gradient that increased with US frequency. This gradient was low after applications of US at 3 MHz but was as high as 7.5°C/mm at 10 MHz and 14.0°C/mm at 19 MHz for US intensities of 10.0 W/cm2. High temperature gradients produced by US at the dermis/sWAT interface can significantly affect the adherence between these two layers and thus modulate effective mechanical properties of the skin.