In vivo T2 -based MR thermometry in adipose tissue layers for high-intensity focused ultrasound near-field monitoring

Purpose During MR-guided high-intensity focused ultrasound (HIFU) therapy, ultrasound absorption in the near field represents a safety risk and limits efficient energy deposition at the target. In this study, we investigated the feasibility of using T2 mapping to monitor the temperature change in subcutaneous adipose tissue layers. Methods The T2 temperature dependence and reversibility was determined for fresh adipose porcine samples. The accuracy was evaluated by comparing T2-based temperature measurements with probe readings in an ex vivo HIFU experiment. The in vivo feasibility of T2-based thermometry was studied during HIFU ablations in the liver in pigs and of uterine fibroids in human patients. Results T2 changed linearly and reversibly with temperature with an average coefficient of 5.2 ± 0.1 ms/°C. For the ex vivo HIFU experiment, the difference between the T2-based temperature change and the probe temperature was