MRI monitoring of the thermal ablation of tissue: Effects of long exposuretimes

MRI-derived thermometry based on the temperature-dependence of the proton r esonant frequency (PRF) is extremely sensitive to changes in tissue unrelat ed to temperature changes, including tissue swelling. This study investigat ed the maximum amount of time that this phase-subtraction-based method can be used to accurately monitor temperature changes in vivo. Long-duration fo cused ultrasound sonications were delivered in rabbit thigh muscle with a p hased-array transducer, and the time that tissue swelling began was monitor ed. Tissue swelling began to occur at about one minute. The temperature cor related well with an implanted thermocouple up to this time. After this tim e, severe artifacts in the phase-difference maps were observed. The thermal dose model predicted the extent of tissue damage wen for subsequent one mi nute sonications. These results will have implications for NM guidance of t hermal therapies with long exposure times. (C) 2001 Wiley-Liss, Inc.