In Vivo Evaluation of Multi-Echo Hybrid PRF/T1 Approach for Temperature Monitoring During Breast MR-Guided Focused Ultrasound Surgery Treatments

Purpose: To evaluate the precision of in vivo temperature measurements in adipose and glandular breast tissue using a multi-echo hybrid PRF/T1 pulse sequence. Methods: A high-bandwidth, multi-echo hybrid PRF/T1 sequence was developed for monitoring temperature changes simultaneously in fat-and water-based tissues. The multiple echoes were combined with the optimal weightings for magnitude and phase images, allowing for precise measurement of both T1 and the proton resonance frequency (PRF) shift. The sequence was tested during in vivo imaging of 10 healthy volunteers in a breast-specific MR-guided focused ultrasound system and also during focused ultrasound heating of excised breast adipose tissue. Results: The in vivo results indicated that the sequence can measure PRF temperatures with 1.25 x 1.25 x 3.5 mm resolution, 1.9 s temporal resolution, and 1.0 degrees C temperature precision, and can measure T1 values with 3.75 x 3.75 x 3.5 mm resolution, 3.8 s temporal resolution, and 2.5%-4.8% precision. The excised tissue heating experiments demonstrate the sequence's ability to monitor temperature changes simultaneously in water- and fat-based tissues. Conclusion: The addition of a high-bandwidth, multi-echo readout to the hybrid PRF/T1 sequence improves the precision of each measurement, providing a sequence that will be beneficial to several MR-guided thermal therapies. (C) 2013 Wiley Periodicals, Inc.