Temperature Distribution and Control in Ultrasound-Based Therapy: An Ex Vivo Study with Bioheat Transfer Modeling

In therapeutic applications, ultrasound is widely used in physiotherapy, tissue repair, and cancer treatment. Regarding cancer treatment, as an emerging field for technology, significant research efforts have been devoted to the area of ultrasound therapy. The derived energy from beams can be deposited in tissues not only through heating but also through non-thermal mechanisms, whereby cancer cells are subject to cell death. Ultrasound-induced heating can generate localized temperature elevations within biological tissues, making it a subject of interest for thermal therapeutic applications. Nevertheless, excessive temperature elevations outside the primary exposure region may result in undesirable thermal effects within the surrounding tissue. In this study, we used continuous 3 MHz ultrasound waves at the powers of 0.4 to 1.4 W on ex vivo chicken breast tissue in a water bath to prevent fluctuations in temperature. The process was also numerically modeled with a maximum error of 0.4% from the measured data. Temperature measurements revealed a significant difference between the region of maximum acoustic pressure along the beam axis and deeper tissue locations (in some cases, above 3.5 °C). These findings indicate that temperature gradients can develop within homogeneous tissue during ultrasound exposure, emphasizing the importance of controlling acoustic power and exposure conditions. Moreover, increasing the temperature was significant during the first moments of treatment, which highlights the importance of precise controls for rate and precision in therapy. The numerical simulations also showed that increasing acoustic power elevates tissue temperature while simultaneously producing a less uniform temperature distribution. These observations may be useful for the optimization of future ultrasound-based thermal treatment strategies; however, direct clinical extrapolation requires further investigation using physiologically representative tissue models.