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Concomitant gradient field effects in balanced steady‐state free precession
Author(s) -
Sica Christopher T.,
Meyer Craig H.
Publication year - 2007
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.21183
Subject(s) - isocenter , imaging phantom , shim (computing) , nuclear magnetic resonance , physics , phase (matter) , magnetic field , signal (programming language) , offset (computer science) , optics , computer science , medicine , quantum mechanics , erectile dysfunction , programming language
Linear magnetic field gradients spatially encode the image information in MRI. Concomitant gradients are undesired magnetic fields that accompany the desired gradients and occur as an unavoidable consequence of Maxwell's equations. These concomitant gradients result in undesired phase accumulation during MRI scans. Balanced steady‐state free precession (bSSFP) is a rapid imaging method that is known to suffer from signal dropout from off‐resonance phase accrual. In this work it is shown that concomitant gradient phase accrual can induce signal dropout in bSSFP. The spatial variation of the concomitant phase is explored and shown to be a function of gradient strength, slice orientation, phase‐encoding (PE) direction, distance from isocenter, and main field strength. The effect on the imaging signal level was simulated and then verified in phantom and in vivo experiments. The nearest signal‐loss artifacts occurred in scans that were offset from isocenter along the z direction with a transverse readout. Methods for eliminating these artifacts, such as applying compensatory frequency or shim offsets, are demonstrated. Concomitant gradient artifacts can occur at 1.5T, particularly in high‐resolution scans or with additional main field inhomogeneity. These artifacts will occur closer to isocenter at field strengths below 1.5T because concomitant gradients are inversely proportional to the main field strength. Magn Reson Med 57:721–730, 2007. © 2007 Wiley‐Liss, Inc.