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. Author manuscript; available in PMC: 2015 Aug 1.
Published in final edited form as: NMR Biomed. 2014 May 17;27(8):897–906. doi: 10.1002/nbm.3133

Fig. 6. EXTREME SHIM CHALLENGE – STEEL ELECTRODE.

Fig. 6

Extreme shim challenge. A: Magnetic field distribution with the use of a (magnetic) steel electrodes for whisker stimulation. For three 2-mm EPI slices the corresponding four 0.5-mm field maps are shown. A several thousand Hertz frequency spread is observed with both severe in-plane and through-plane components. B: While second order SH shimming removes the bulk of the distortion, significant field imperfections remain (left). The combination of in-slice imperfections and through-slice components, i.e. field variations across the four field maps contributing to the same EPI slice, lead to image distortion and signal dropout with EPI (right). C: Single-step DYNAMITE shimming removed large part of the extreme field challenge (left) and, thereby, allowed reasonable EPI quality throughout the brain (right).