Response linearity of functional Quantitative Susceptibility Mapping (fQSM) and effect of reduced z-coverage: a pilot study

Motivation: fQSM quantitative and spatially-specific information on brain activity may be valuable in studying cortical substructures. However, fQSM response to varying stimulus intensity is unknown, and, as for QSM, reduced z-coverage may affect quantification. Goal(s): We aimed to assess fQSM linearity to stimulus intensity and its dependence on z-coverage. Approach: We employed visual stimuli with different contrasts and acquired whole-brain fQSM datasets that were truncated to simulate partial coverage. Results: We reported fQSM response linearity to different contrasts and, while extremely small coverage led to brain activity underestimation, whole-brain acquisitions were not necessary to obtain accurate results. Impact: Linearity and feasibility at reduced z-coverage, together with high spatial specificity, suggest that fQSM may provide added value to the functional study of cortical substructures.