Image-based ghost correction for interleaved EPI.

A new image-based ghost correction technique is described for general interleaved EPI. This technique works reliably with both even- and odd-number interleaved EPI sequences. It estimates the phase distortions causing the ghosts as a general function of (x,y) even in the presence of a significant overlap of parent image and ghosts. If the phase distortion is assumed to be a function of x (frequency-encode direction) only, the new technique is similar to a recently published correction method for general interleaved EPI (Hennel. J Magn Reson 1998;134:206-213). However, that study concluded that the method for general interleaved EPI did not work. It showed that the SNRs of the edge pixels were too low to accurately estimate the phase distortion. The new technique utilizes not one, but many pixels in the image for estimating the phase distortion. The technique requires a user-defined ROI to outline the parent image and identify so-called eligible pixels for estimating the phase distortion. When all eligible pixels are used, the SNR of the phase distortion estimate is comparable to that obtained in single-shot EPI. This study provides the first examples of high-quality, image-based correction of multiple ghosts in general interleaved EPI. Magn Reson Med 45:96-108, 2001.