Gradient Echo Sampling of a Spin Echo (GESSE) linescans for human laminar fMRI at 7T: combining echoes to vary functional contrast and sensitivity

Motivation: Resolving distinct functional activation and connectivity within cerebral cortical layers requires high imaging resolutions and microvascular specificity along with sufficient sensitivity—a major challenge for current fMRI methodologies. Goal(s): To measure capillary-weighted spin-echo-BOLD fMRI signals in human cerebral cortex, with 500-micron resolution in the radial direction (i.e., perpendicular to the cortical surface). Approach: We used a novel “linescan” technique that samples a single spin echo with multiple gradient echoes. Results: We provide the first demonstration of T2-weighted BOLD activation via linescan fMRI in humans and show that the multiple gradient echoes can be combined in various ways to manipulate functional contrast and sensitivity. Impact: Our novel LS-GESSE technique allows for controlled trade-offs between sensitivity and specificity and should help enable the measurement of microvascular fMRI signals at spatial resolutions approaching the thickness of individual cortical layers, facilitating noninvasive studies of cortical dynamics and circuitry.