On the UNFOLD method

Abstract

A graphical formalism is presented, showing that “UNaliasing by Fourier‐encoding the Overlaps Using the temporaL Dimension” (UNFOLD) is equivalent to sampling k‐t‐space in a sheared grid pattern. Discrete regular sampling in k‐t‐space leads to periodic replication of the support region in x‐f‐space. Thus, the maximum acceleration achievable by UNFOLD is equivalent to the maximum packing of support regions in x‐f‐space. When the support region is separable along the x and f axes, the reconstruction can be performed separately for each k. UNFOLD can be combined with SiMultaneous Acquisition of Spatial Harmonics (SMASH) to further accelerate acquisition. However, a straightforward combination of the methods has been shown to result in a size restriction, which limits the portion of the field of view (FOV) with a larger temporal bandwidth to only a quarter of the FOV. Two solutions are presented to overcome this restriction. Magn Reson Med 47:202–207, 2002.