Comparing BOLD contamination in CBV-based fMRI with conventional EPI and echo-planar time-resolved imaging (EPTI) at 7 T

Motivation: Non-BOLD functional imaging contrasts like CBV-weighted VASO-fMRI often use EPI-based readouts, which are prone to BOLD contamination from non-zero echo times and non-zero echo-train lengths. Goal(s): Echo-planar time-resolved Imaging (EPTI) is a new readout strategy that allows dense reconstruction of multiple echoes with minimal echo train length. Approach: This study evaluates residual BOLD effects in BOLD-corrected VASO using EPI and compares these to EPTI extrapolated to zero echo time. Results: Findings show that BOLD correction alone does not fully eliminate residual contamination in VASO, and that EPTI exhibits unexpected signal changes that may reflect residual BOLD or non-BOLD components. Impact: This work underscores the limitations of conventional BOLD correction techniques for VASO fMRI and evaluates EPTI for removing unwanted BOLD contamination. Both approaches appear unable to isolate pure CBV weighting in VASO data.