Localised hyperthermia in rodent models using an MRI-compatible high-intensity focused ultrasound system

Purpose: Localised hyperthermia in rodent studies is challenging due to the small target size. This study describes the development and characterisation of an MRI-compatible high-intensity focused ultrasound (HIFU) system to perform localised mild hyperthermia treatments in rodent models. Material and methods: The hyperthermia platform consisted of an MRI-compatible small animal HIFU system, focused transducers with sector-vortex lenses, a custom-made receive coil, and means to maintain systemic temperatures of rodents. The system was integrated into a 3T MR imager. Control software was developed to acquire images, process temperature maps, and adjust output power using a proportional-integral-derivative feedback control algorithm. Hyperthermia exposures were performed in tissue-mimicking phantoms and in a rodent model (n=9). During heating, an ROI was assigned in the heated region for temperature control and the target temperature was 42 degrees C; 30min mild hyperthermia treatment followed by a 10-min cooling procedure was performed on each animal. Results: 3D-printed sector-vortex lenses were successful at creating annular focal regions which enables customisation of the heating volume. Localised mild hyperthermia performed in rats produced a mean ROI temperature of 42.1 +/- 0.3 degrees C. The T10 and T90 percentiles were 43.2 +/- 0.4 degrees C and 41.0 +/- 0.3 degrees C, respectively. For a 30-min treatment, the mean time duration between 41-45 degrees C was 31.1min within the ROI. Conclusions: The MRI-compatible HIFU system was successfully adapted to perform localised mild hyperthermia treatment in rodent models. A target temperature of 42 degrees C was well-maintained in a rat thigh model for 30 min.