Temperature measurement in human fat with T2 imaging.

PURPOSE: To develop a method for noninvasive T2 -based thermometry that enables estimation of the in vivo temperature in adipose tissues at both 1.5T and 3T field strengths. MATERIALS AND METHODS: A total of 27 apparent T2 -temperature measurement sets were performed on 13 human abdominal adipose tissue samples using an inversion prepared dual-echo single-slice sequence for apparent T2 estimation. The measurements were performed on Ingenia 1.5T and 3.0T scanners and Achieva 1.5T and 3.0T scanners. The apparent T2 -values were measured at 4°C temperature intervals during heating from 21 to 45°C and cooling to 21°C. A two-parameter exponential fit was used to estimate the apparent T2 to temperature dependency on a scanner-to-scanner basis. RESULTS: In the temperature range evaluated (21-45°C), the apparent T2 relaxation times increased from an average of ∼100 msec to 190 msec at 1.5T and an average of ∼130 msec to 220 msec at 3T. The measured T2 -relaxation times followed the calibration curve with a median absolute error of 0.37°C and maximum error of 1.7°C in 12 of the 13 samples, with the outlier having a notably different appearance upon visual inspection prior to measurement. CONCLUSION: Changes in apparent T2 relaxation time has the potential to be used for accurately estimating local temperature within in vivo subcutaneous fat.

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 <0.9°C. All in vivo experiments showed temperature-related T2 changes in the near field directly after sonications. As expected, considerable intersubject variations in the cooling times were measured in the in vivo porcine experiments. CONCLUSIONS: The reversibility and linearity of the T2 -temperature dependence of adipose tissue allows for the monitoring of the temperature in the subcutaneous adipose tissue layers.