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Nuclear paramagnetism‐induced MR frequency shift and its implications for MR‐based magnetic susceptibility measurement
Author(s) -
Park Jinil,
Lee Jeongtaek,
Park JangYeon,
Lee SeungKyun
Publication year - 2017
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.26570
Subject(s) - imaging phantom , nuclear magnetic resonance , paramagnetism , magnetic susceptibility , orientation (vector space) , physics , polarization (electrochemistry) , magnetic field , amplitude , condensed matter physics , optics , chemistry , mathematics , geometry , quantum mechanics
Purpose To investigate the 1 H spin contribution (0.004 parts per million (ppm)) to the water magnetic susceptibility and discuss its implications for high‐precision phase mapping and tissue susceptibility measurement. Methods Free induction decay (FID) signals were acquired at 3 Tesla (T) and 9.4T from thin square phantoms at a range of tip angles. The FID frequency shift was examined at a high resolution ( < 0.01 Hz) for different phantom orientations relative to the main magnetic field (B 0 ). B 0 maps on an axial and a coronal slice of a spherical phantom were obtained at 3T to examine the tip angle and orientation dependence at the 0.001 ppm level. Results A frequency shift of about 0.3 Hz was observed between tip angles of 10 ° and 90 ° when the thin phantom was normal to B 0 at 3T, whereas the shift changed sign and was halved in magnitude when the phantom's face was parallel to B 0 . At 9.4T, the effect size increased proportionately. The orientation‐dependent frequency shift was also observed in the B 0 map experiment. These observations agree with theoretical frequency shift due to longitudinal 1 H spin polarization. Conclusion Magnetic susceptibility contribution from the nuclear paramagnetism should be taken into account in the interpretation of high‐precision phase and susceptibility mapping in MRI. Magn Reson Med 77:848–854, 2017. © 2016 International Society for Magnetic Resonance in Medicine.