Multiple gradient echo sequence optimized for rapid, single‐scan mapping of R at high B0

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Abstract
A multiple-gradient-echo sequence is proposed for accurately mapping R in the presence of in-slice macroscopic susceptibility gradients. In-slice signal loss caused by background macroscopic susceptibility gradients is mitigated by combining three successive gradient-echo images whose slice refocus gradients are successively incremented. The optimum incrementation of slice-refocusing gradients was determined by numerical simulation. By repeating further cycles of three images in the same sequence, artifact-compensated data spanning a range of echo times (TEs) was acquired leading to single-scan, R maps that are quantitatively reflective of microscopic field inhomogeneities. The performance of the sequence was demonstrated at 3.0T, first with a doped aqueous phantom, and then on the head of a normal volunteer. That performance is compared quantitatively with previously published work. Magn Reson Med 48:867–876, 2002.