UNFOLD using a temporal subtraction and spectral energy comparison technique.

In dynamic MRI, several methods have been demonstrated to increase acquisition speed by decreasing the number of sequential phase encodings. The UNFOLD technique interleaves the measurements of k-space, reconstructs aliased images from each k-space interleaf, and applies a temporal low-pass filter to obtain the nonaliased images. However, low-pass filter resolution of the nonaliased images fails if there is overlap between the spatially aliased temporal spectra. In this study a subtraction method was used to remove the static portion of the image. The aliased and nonaliased dynamic portions are then resolved by comparing the temporal energy of bands in the power spectrum. This method was combined with the 3D 2 x 2 UNFOLD (a factor of 2 interleaves in two directions) technique. The combination resulted in a factor of 4 improvement in acquisition speed. Application of this method to a time-resolved, contrast-enhanced flow phantom study is presented. Copyright 2002 Wiley-Liss, Inc.