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Compensating for magnetic field inhomogeneity in multigradient‐echo‐based MR thermometry
Author(s) -
Simonis Frank F.J.,
Petersen Esben T.,
Bartels Lambertus W.,
Lagendijk Jan J. W.,
Berg Cornelis A.T.
Publication year - 2015
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25207
Subject(s) - imaging phantom , dielectric heating , gradient echo , radio frequency , echo (communications protocol) , nuclear magnetic resonance , materials science , standard deviation , temperature measurement , physics , computer science , biomedical engineering , computational physics , optics , magnetic resonance imaging , mathematics , optoelectronics , statistics , radiology , telecommunications , medicine , computer network , quantum mechanics , dielectric
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 B 0 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. Magn Reson Med 000:000–000, 2014. © 2014 Wiley Periodicals, Inc. Magn Reson Med 73:1184–1189, 2015. © 2014 Wiley Periodicals, Inc.