Water excitation may induce signal asymmetries in the bSSFP profile which affects parametric mapping

Motivation: Unsuppressed fat signal impairs the visualization of small anatomical structures and the quantification of relaxation times. Phase-cycled bSSFP can map both T1 and T2 relaxation times but not when fat is within the same voxel. Goal(s): To test the effect of different water excitation methods on relaxation time quantification and fat suppression in phase-cycled bSSFP. Approach: Conventional and off-resonant water excitation pulses were implemented in phase-cycled bSSFP sequences and experiments were performed in phantoms and knees of healthy subjects. Results: A few water excitation approaches were excellent while others induced signal asymmetries in the bSSFP profile, which affected T1 and T2 mapping. Impact: Using advanced water excitation pulses enabled fat-free multiparametric mapping with phase-cycled bSSFP. This benefits relaxometry that may be confounded by fat, which is particularly interesting for quantitative imaging in pathologies such as metabolic dysfunction-associated steatotic liver disease, where fat accumulates.