Laminar fMRI using magnetization transfer contrast at 7 T

Conventional gradient-echo blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is limited in spatial specificity due to extravascular static dephasing around large draining veins. Although alternative contrasts based on cerebral blood volume (CBV) and cerebral blood flow can provide improved laminar specificity, they are typically constrained by reduced sensitivity and limited temporal efficiency. Here, we evaluate a specific-absorption-rate-efficient magnetization transfer contrast (MTC) implementation as a practical complementary approach for laminar fMRI. Using on-resonance, small-flip-angle binomial pulse trains, this approach selectively attenuates the extravascular tissue background while largely preserving the intravascular blood signal, thereby generating a CBV-weighted contrast with retained functional sensitivity. We evaluated MTC fMRI in the human primary motor (M1) and visual (V1) cortices at 7 T. In M1, MTC showed a double-peak laminar profile, with peaks in both superficial and deep cortical depths. In V1, MTC showed an activation shift toward the middle cortical depths and a steeper signal attenuation toward the cortical surface compared with conventional BOLD. These findings suggest that MTC fMRI provides a practical balance between spatial specificity, functional sensitivity, and acquisition efficiency, and may serve as a complementary approach for non-invasive investigations of depth-dependent functional organization in laminar fMRI.