TRIM: TR independent multislice imaging

This article introduces a novel concept to overcome the dependence of image contrast on spatial positioning parameters such as the number of slices and slice separation in multislice measurements: TR-independent multislice (TRIM) acquisition allows the number of slices in a single measurement to remain independent of the repetition time TR. Ramped TRIM (rTRIM) allows the distance between the sections excited in each repetition to remain independent of the distance between the reconstructed slices. Even images from overlapping slices can be acquired without crosstalk between the images of adjacent slices due to spatially overlapping excitation profiles. This concept is based on a special reordering scheme: Within a single TR acquisition, steps are only taken from a fraction of all slices. This necessitates attribution of different phase-encoding steps to different slices within each repetition cycle. The reordering scheme can be derived by the use of a design matrix. The imaging properties of the technique are discussed theoretically and illustrated by a point spread function analysis based on simulations and phantom measurements. Potential sources of artifacts are identified and methods for their prevention are developed. Optimized implementations with different T1-weighted sequences such as spin echo (SE), turbo spin echo (TSE), and spoiled gradient echo acquisitions are shown on normal volunteers with imaging parameters used in routine diagnosis