Safety limitations of MR-HIFU treatment near interfaces: a phantom validation

Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) is a noninvasive image-guided technique used to thermally ablate solid tumors. During treatment, ultrasound reflections from distal media interfaces can shift prescribed treatment locations. The purpose of this study was to investigate the effect of normal incidence reflections from air, acrylic (modeling bone), and rubber on treatment location, temperature elevation, and heating patterns by performing ultrasound exposures in a tissue-mimicking phantom and in ex vivo porcine tissue using a clinical MR-HIFU platform. The results demonstrated a shift in treatment location toward the distal interface when targeted closer than 2 cm from the interface, especially for acrylic. Our study demonstrated that the ultrasound wave reflections from a distal air interface had less effect than the acrylic interface (modeling bone) on the heating pattern and focal location. This study provides useful information to better understand the limitations and safety concerns of performing MR-HIFU treatments with commercial clinical equipment.