Low-intensity focused ultrasound pulsation device used during magnetic resonance imaging: evaluation of magnetic resonance imaging-related heating at 3 Tesla/128 MHz.

The objective of this study was to determine magnetic resonance imaging (MRI)-related heating for a low-intensity focused ultrasound pulsation (LIFUP) device used during MRI performed at 3 T/128 MHz. A special phantom was constructed to mimic the thermal properties of the human brain, and a piece of human temporal bone (skull) was embedded on top. Four fluoroptic thermometry probes, placed above and below the skull, were used to measure temperature changes during MRI (3 T/128 MHz; scanner-reported head average specific absorption rate 1.1-2 W/kg) with and without concurrent LIFUP sonication. LIFUP sonication was applied using a focused ultrasound device (BXPulsar 1001, Brainsonix, Inc., Los Angeles, CA, USA) at a derated spatial-peak temporal-average intensity of 3870 mW/cm(2) . MRI performed at relatively high specific absorption rate (SAR) caused a slight elevation in temperature (≤0.6°C). Concurrent use of MRI at a medium-strength SAR and LIFUP sonication resulted in maximum temperature rise of 3.1°C after 8 min of continuous use. Under the specific conditions utilized for this investigation, LIFUP sonication does not appear to present significant heating risks when used concurrently with MRI. This information has important implications for the use of the LIFUP sonication in human subjects undergoing MRI at 3 T/128 MHz.