Proton Resonance Frequency MRI Shows Focal Spot Shifts Due to Interfaces During MR-HIFU Treatment

Elizabeth Hipp¹, Xiaobing Fan¹, Ari Partanen², Gregory S. Karczmar¹

MR-HIFU is emerging as a treatment modality for a variety of pathologies. Treatments near tissue interfaces can result in unwanted heating caused by an impedance mismatch. This research uses the proton resonance frequency measured by MRI to explore the changes in heating pattern and shift in sonication focus as a result of proximity to an interface in a thermal phantom. Air, acrylic, rubber and a tissue-equivalent gel pad were tested with treatment cells focused at 1, 2 and 4 cm from the interface material revealing 0.7 to 3 mm shifts depending on focal position and interface material.