Feasibility and safety assessment of magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU)-mediated mild hyperthermia in pelvic targets evaluated using an in vivo porcine model

Purpose: To evaluate the feasibility and assess safety parameters of magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU)-mediated hyperthermia (HT; heating to 40-45 degrees C) in various pelvic targets in a porcine model in vivo. Methods: Thirteen HT treatments were performed in six pigs with a commercial MRgHIFU system (Sonalleve V2, Profound Medical Inc., Mississauga, Canada) to muscle adjacent to the ventral/dorsal bladder wall and uterus to administer 42 degrees C (+/- 1 degrees) for 30 min (+/- 5%) using an 18-mm target diameter and 100 W power. Feasibility was assessed using accuracy, uniformity, and MR-thermometry performance-based metrics. Safety parameters were assessed for tissues in the targets and beam-path by contrast-enhanced MRI, gross-pathology and histopathology. Results: Across all HT sessions, the mean difference between average temperature (T-avg) and the target temperature within the target region-of-interest (tROI, the cross-section of the heated volume at focal depth) was 0.51 +/- 0.33 degrees C. Within the tROI, the temperature standard deviation averaged 1.55 +/- 0.31 degrees C, the average 30-min T-avg variation was 0.80 +/- 0.17 degrees C, and the maximum difference between T-avg and the 10th- or 90th-percentile temperature averaged 2.01 +/- 0.44 degrees C. The average time to reach >= 41 degrees C and cool to <= 40 degrees C within the tROI at the beginning and end of treatment was 47.25 +/- 27.47 s and 66.37 +/- 62.68 s, respectively. Compared to unheated controls, no abnormally-perfused tissue or permanent damage was evident in the MR images, gross pathology or histological analysis. Conclusions: MRgHIFU-mediated HT is feasible and safety assessment is satisfactory for treating an array of clinically-mimicking pelvic geometries in a porcine model in vivo, implying the technique may have utility in treating pelvic targets in human patients.