Single-shot diffusion-weighted RARE sequence: application for temperature monitoring during hyperthermia session

A diffusion-sensitive single-shot RARE (rapid acquisition with relaxation enhancement) sequence was implemented on a 2T whole-body MRI system. The sequence was optimized for diffusion-based MR thermometry, both on a conventional whole-body gradient system and on a high-performance gradient insert. The use of spin-echo versus stimulated-echo diffusion weighting is discussed as a function of gradient performance. Diffusion-based temperature mapping was used to observe the effect of the geometry of the antenna used for radiofrequency (RF) hyperthermia on the temperature distribution. Temperature changes of +/-.5 degrees C in gel and +/-2 degrees C in a muscle sample in vitro could be detected within 16 seconds (gel) or 1 minute (muscle) at a spatial resolution of 2 x 2 x 8 mm. Temperature changes in vivo were also observed on human muscle cooled with ice with comparable sensitivity for the measured apparent diffusion coefficient (ADC) values.