Field drift correction of proton resonance frequency shift temperature mapping with multichannel fast alternating nonselective free induction decay readouts

PURPOSE: To demonstrate that proton resonance frequency shift MR thermometry (PRFS‐MRT) acquisition with nonselective free induction decay (FID), combined with coil sensitivity profiles, allows spatially resolved B (0) drift‐corrected thermometry. METHODS: Phantom experiments were performed at 1.5T and 3T. Acquisition of PRFS‐MRT and FID were performed during MR‐guided high‐intensity focused ultrasound heating. The phase of the FIDs was used to estimate the change in angular frequency δω(drift) per coil element. Two correction methods were investigated: (1) using the average δω(drift) over all coil elements (0th‐order) and (2) using coil sensitivity profiles for spatially resolved correction. Optical probes were used for independent temperature verification. In‐vivo feasibility of the methods was evaluated in the leg of 1 healthy volunteer at 1.5T. RESULTS: In 30 minutes, B (0) drift led to an apparent temperature change of up to –18°C and –98°C at 1.5T and 3T, respectively. In the sonicated area, both corrections had a median error of 0.19°C at 1.5T and –0.54°C at 3T. At 1.5T, the measured median error with respect to the optical probe was –1.28°C with the 0th‐order correction and improved to 0.43°C with the spatially resolved correction. In vivo, without correction the spatiotemporal median of the apparent temperature was at –4.3°C and interquartile range (IQR) of 9.31°C. The 0th‐order correction had a median of 0.75°C and IQR of 0.96°C. The spatially resolved method had the lowest median at 0.33°C and IQR of 0.80°C. CONCLUSION: FID phase information from individual receive coil elements allows spatially resolved B (0) drift correction in PRFS‐based MRT.