Field mapping without reference scan using asymmetric echo-planar techniques.
Improvements in Bo mapping and shimming were achieved by measuring the static field information in multiple subsequent echoes generated by an asymmetric echo-planar readout gradient train. With careful compensation, eddy current effects were shown to affect the adjustment of the shim coils minimally. In addition to reducing the time required for field mapping by two-fold, the sensitivity was simultaneously optimized irrespective of the prevalent T2* present, thereby minimizing the error of the static field measurement to below 0.1 Hz. With adiabatic low flip-angle excitation, the time required for field mapping was below 1 second.
Gruetter
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Department of Radiology, University of Minnesota, Minneapolis, USA. gruetter@cmrr.umn.edu
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D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D005583:Fourier Analysis; D006801:Humans; D019047:Phantoms, Imaging / Q000706:statistics & numerical data; D012984:Software; D013997:Time Factors