Substantial Flow-Related Contribution in FMRI Signal Observed in Human Visual Cortex at 4T

Xiao Wang¹, Wei Chen¹

It is a common practice to apply a short repetition time (TR) for acquiring more fMRI volumes within a given total imaging time, thus gaining contrast-to-noise ratio (CNR). However, both the task-evoked BOLD (T2/T2*) effect and flow-related component (R1) increases could contribute to the total percentage change of fMRI signal. This study aims to quantitatively evaluate the BOLD and flow contributions in the fMRI signal detected by gradient echo EPI in the human visual cortex during visual stimulation at 4T. The results show a substantially large flow-related contribution in the measured fMRI signal when TR is short. The observed flow-related enhancement in fMRI signal is likely attributed by perfusion change, and it benefits fMRI mapping in two aspects: improved CNR and specificity. The finding also suggests that the flow-related component needs to be considered in BOLD quantification (e.g., calibration of CMRO2).