Compensating for magnetic field inhomogeneity in multigradient-echo-based MR thermometry
Simonis, Frank F J, Petersen, Esben T, Bartels, LW, Lagendijk, JJW, van den Berg, CAT
DOI: https://doi.org/10.1002/mrm.25207
Magnetic Resonance in Medicine 73 (3), p. 1184-9
Abstract
PURPOSE: MR thermometry (MRT) is a noninvasive method for measuring temperature that can potentially be used for radio frequency (RF) safety monitoring. This application requires measuring absolute temperature. In this study, a multigradient-echo (mGE) MRT sequence was used for that purpose. A drawback of this sequence, however, is that its accuracy is affected by background gradients. In this article, we present a method to minimize this effect and to improve absolute temperature measurements using MRI.
THEORY: By determining background gradients using a B0 map or by combining data acquired with two opposing readout directions, the error can be removed in a homogenous phantom, thus improving temperature maps.
METHODS: All scans were performed on a 3T system using ethylene glycol-filled phantoms. Background gradients were varied, and one phantom was uniformly heated to validate both compensation approaches. Independent temperature recordings were made with optical probes.
RESULTS: Errors correlated closely to the background gradients in all experiments. Temperature distributions showed a much smaller standard deviation when the corrections were applied (0.21°C vs. 0.45°C) and correlated well with thermo-optical probes.
CONCLUSION: The corrections offer the possibility to measure RF heating in phantoms more precisely. This allows mGE MRT to become a valuable tool in RF safety assessment.