Concomitant gradient field effects in spiral scans

Maxwell's equations imply that imaging gradients are accompanied by higher order spatially varying fields (concomitant fields) that can cause artifact s in MR imaging. The lowest order concomitant fields depend quadratically o n the imaging gradient amplitude and inversely on the static field strength . Time-varying concomitant fields that accompany the readout gradients of s piral scans cause unwanted phase accumulation during the readout, resulting in spatially dependent blurring. Concomitant field phase errors are indepe ndent of echo time and, therefore, cannot be detected using Dixon type fiel d map measurements that are normally used to deblur spiral scan images. Dat a acquisition methods that reduce concomitant field blurring increase off-r esonant spin blurring, and vice versa. Blurring caused by concomitant field s can be removed by variations of image reconstruction methods developed to correct for spatially dependent resonance offsets with nonrectangular k-sp ace trajectories. Magn Reson Med 41:103-112, 1999. (C) 1999 Wiley-Liss, Inc .