Acoustic and Thermal Characterization of Tissue-Mimicking Phantoms for Modeling Focused Ultrasound Hyperthermia

Focused ultrasound hyperthermia (HT) uses focused acoustic energy to elevate tissue temperature for therapeutic purposes. Achieving precise thermal dosimetry requires accurate modeling of acoustic heating, which depends on reliable measurements of the material properties of the medium being heated. Tissue-mimicking phantoms (TMPs) are essential tools in therapeutic ultrasound to validate and optimize HT treatment strategies, but their acoustic and thermal properties often vary due to fabrication methods. In this study, TMPs were fabricated using polyvinyl chloride (PVC) plastisol with 0%, 1%, and 4% (w/v) graphite to increase acoustic attenuation. We developed a reproducible workflow to characterize phantom properties and evaluated the optimal phantom in heating experiments (5-min heating followed by 5-min cooling) using a 256-element ring array ultrasound transducer. We then conducted in silico tests replicating these experiments using k-Wave and COMSOL Multiphysics. Acoustic attenuation (1.09-1.48 dB/MHz/cm), sound speed (1407.9-1412.1 m/s), and density (996.7-1036.7 kg/m3) were measured at therapeutic frequencies (1.0-2.2 MHz). Thermal conductivity increased with graphite content (0.152-0.189 W/m/K), while specific heat capacity ranged from 1688.8 to 1771.6 J/kg/K. Using a phantom with 1% graphite, the ring array ultrasound transducer produced a 4.4 °C temperature rise after 5 min of heating at 1.5 MHz. Using the measured properties, both computational studies yielded close agreement with experimental heating and cooling curves within a maximum error of 0.3 °C. This workflow provides a practical, reproducible strategy for phantom characterization, thereby improving the accuracy of HT computational modeling, which serves as a basis for clinical ultrasound treatment planning systems.