Improved spoiling efficiency in dynamic RF-spoiled imaging by ghost phase modulation and temporal filtering.

ABSTRACT

PURPOSE: Radiofrequency-spoiled steady-state sequences offer rapid data acquisition with T1- or T2*-weighting. The spoiler gradients in these sequences must be large enough to suppress ghost artifacts, and are chosen empirically. However, certain factors such as the need to minimize gradient first moments or acoustic noise can limit the spoiler size and, hence, the ability to suppress ghosts. We present an acquisition and preprocessing strategy for improved spoiling efficiency in conventional and echo-shifted dynamic radiofrequency-spoiled 3D imaging. THEORY AND METHODS: By requiring each time-frame in a dynamic imaging sequence to contain a particular (restricted) number of total radiofrequency shots, the ghost signal can be made to alternate in sign every other frame. The ghost is then suppressed by Fourier transforming along the temporal dimension, and removing the Nyquist frequency in preprocessing (similar to UNFOLD). The method works for both Cartesian and non-Cartesian imaging. RESULTS: We demonstrate improved ghost suppression with the proposed approach, for both conventional and echo-shifted spoiled gradient echo imaging in stationary phantoms and in vivo. Cartesian echo-shifted spoiled gradient echo imaging produces two ghosts shifted in opposite directions, both of which are suppressed with our method. CONCLUSION: For a given spoiler gradient area, the proposed approach substantially suppresses the ghost signal in both conventional and echo-shifted dynamic radiofrequency-spoiled imaging. Magn Reson Med 752388-2393, 2016. © 2015 Wiley Periodicals, Inc.