Premium
B 0 concomitant field compensation for MRI systems employing asymmetric transverse gradient coils
Author(s) -
Weavers Paul T.,
Tao Shengzhen,
Trzasko Joshua D.,
Frigo Louis M.,
Shu Yunhong,
Frick Matthew A.,
Lee SeungKyun,
Foo Thomas KF,
Bernstein Matt A.
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.26790
Subject(s) - ghosting , physics , amplitude , optics , offset (computer science) , nuclear magnetic resonance , phase (matter) , magnetic field , concomitant , computer science , mathematics , statistics , quantum mechanics , programming language
Purpose Imaging gradients result in the generation of concomitant fields, or Maxwell fields, which are of increasing importance at higher gradient amplitudes. These time‐varying fields cause additional phase accumulation, which must be compensated for to avoid image artifacts. In the case of gradient systems employing symmetric design, the concomitant fields are well described with second‐order spatial variation. Gradient systems employing asymmetric design additionally generate concomitant fields with global (zeroth‐order or B 0 ) and linear (first‐order) spatial dependence. Methods This work demonstrates a general solution to eliminate the zeroth‐order concomitant field by applying the correct B 0 frequency shift in real time to counteract the concomitant fields. Results are demonstrated for phase contrast, spiral, echo‐planar imaging (EPI), and fast spin‐echo imaging. Results A global phase offset is reduced in the phase‐contrast exam, and blurring is virtually eliminated in spiral images. The bulk image shift in the phase‐encode direction is compensated for in EPI, whereas signal loss, ghosting, and blurring are corrected in the fast‐spin echo images. Conclusion A user‐transparent method to compensate the zeroth‐order concomitant field term by center frequency shifting is proposed and implemented. This solution allows all the existing pulse sequences—both product and research—to be retained without any modifications. Magn Reson Med 79:1538–1544, 2018. © 2017 International Society for Magnetic Resonance in Medicine.