Microvascular specificity of spin-echo BOLD fMRI at 7T: the impact of EPI echo train length

Motivation: Macrovascular contributions to the BOLD signal reduce microvascular specificity, which can be alleviated by using SE sequences -refocusing local field inhomogeneities near large veins. Thus, the microvascular specificity of SE-EPI scan will rely on ETL duration, however, this dependence is not well-characterized in humans at 7T. Goal(s): Determining how microvascular-specific SE-EPI BOLD responses vary with ETL in humans at 7T. Approach: A biophysical model was developed and a validation experiment was conducted during a hyperoxic gas-challenge aiming at determining this goal. Results: Both our simulations and measurements indicate an increase in macrovascular contamination with longer ETL-durations, leading to a decrease in microvascular specificity. Impact: Through biophysical simulations and measurements, we show an increase in macrovascular contamination with longer ETL durations, leading to a substantial decrease in microvascular SE-BOLD specificity