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Abstract #3485

Impact of eddy currents and mechanical oscillations on B0 mapping at 7T

David Leitão1, Daniel West1, Sarah McElroy2, Barbara Dymerska3, Oliver Josephs3, Martina F. Callaghan3, Sharon L Giles1,4, Philippa Bridgen4,5, Jo Hajnal1,6, Tomoki Arichi6, Tobias C Wood7, and Shaihan Malik1,6
1Imaging Physics & Engineering Research Department, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, 2Siemens Healthcare Limited, Frimley, United Kingdom, 3Functional Imaging Laboratory, Department of Imaging Neuroscience, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom, 4Guy's and St. Thomas' NHS Foundation Trust, London, United Kingdom, 5London Collaborative Ultra high field System (LoCUS), King's College London, London, United Kingdom, 6Early Life Imaging Research Department, School of Biomedical Engineering & Imaging Sciences, King's College London, London, United Kingdom, 7Department of Neuroimaging, King's College London, London, United Kingdom

Synopsis

Keywords: System Imperfections, System Imperfections: Measurement & Correction, Eddy currents, B0 mapping, Ultra-high field

Motivation: Eddy currents and field oscillations due to mechanical resonances are known to adversely impact image quality at ultra-high field. These have already been shown to distort applied field gradients.

Goal(s): To investigate spatially-constant zero-order field oscillations and their impact on phase-based measurements including B0 mapping.

Approach: Measure phase oscillations on two different 7T MR systems and perform B0 mapping using different gradient orientations and echo spacings to assess bias.

Results: Similar oscillatory phase behaviour was observed at both 7T sites. Biases in B0 mapping are introduced that depend on sequence parameter choice, most notably readout direction.

Impact: Phase oscillations relating to a mechanical resonance lead to variable phase measured in gradient echo scans consistently at two sites. This leads to biases in B0 mapping that depend on the choice of echo spacing and readout axis.

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Keywords