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Effect of head motion on MRI B 0 field distribution
Author(s) -
Liu Jiaen,
Zwart Jacco A.,
Gelderen Peter,
MurphyBoesch Joseph,
Duyn Jeff H.
Publication year - 2018
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.27339
Subject(s) - torso , field (mathematics) , head (geology) , sensitivity (control systems) , nuclear magnetic resonance , computer science , physics , artificial intelligence , mathematics , geology , medicine , anatomy , engineering , geomorphology , electronic engineering , pure mathematics
Purpose To identify and characterize the sources of B 0 field changes due to head motion, to reduce motion sensitivity in human brain MRI. Methods B 0 fields were measured in 5 healthy human volunteers at various head poses. After measurement of the total field, the field originating from the subject was calculated by subtracting the external field generated by the magnet and shims. A subject‐specific susceptibility model was created to quantify the contribution of the head and torso. The spatial complexity of the field changes was analyzed using spherical harmonic expansion. Results Minor head pose changes can cause substantial and spatially complex field changes in the brain. For rotations and translations of approximately 5 º and 5 mm, respectively, at 7 T, the field change that is associated with the subject's magnetization generates a standard deviation (SD) of about 10 Hz over the brain. The stationary torso contributes to this subject‐associated field change significantly with a SD of about 5 Hz. The subject‐associated change leads to image‐corrupting phase errors in multi‐shotT 2 * ‐weighted acquisitions. Conclusion The B 0 field changes arising from head motion are problematic for multishotT 2 * ‐weighted imaging. Characterization of the underlying sources provides new insights into mitigation strategies, which may benefit from individualized predictive field models in addition to real‐time field monitoring and correction strategies.