Flow Sensitivity of CPMG Sequences with Variable Flip Refocusing and Implications for CSF Signal Uniformity in 3D-FSE Imaging
3D-FRFSE with variable flip refocusing is a means to acquire large volumetric datasets with T2-weighting in a relatively short time. CSF, however, may appear dark in regions of high flow. Here it is demonstrated that motion causes differing amounts of phase to accrue in different spin and stimulated echo pathways, resulting in signal loss when signal pathways do not add constructively. As refocusing flip angles decrease and/or net gradient area between refocusing RF pulses increases, the sensitivity to flow increases. In vivo imaging experiments demonstrate that uniformly bright CSF may be attained if minimum flip and net gradient area are limited.