Visualizing cortical laminar architecture in the living human brain using next-generation ultra-high-gradient diffusion MRI.

Characterizing cortical laminar microstructure is essential for understanding human brain function. Leveraging the next-generation Connectome MRI scanner (maximum gradient strength = 500mT/m, slew rate = 600T/m/s), we characterized cortical laminar cytoarchitecture and myeloarchitecture through cortical depth-dependent analyses of soma and neurite density imaging (SANDI) metrics derived from diffusion MRI, enhanced by a super-resolution technique. SANDI revealed distinct laminar profiles: intra-soma signal fraction peaked at ~ 55% cortical depth, while intra-neurite signal fraction increased toward deeper layers, consistent with histological patterns. The visual cortex exhibited higher intra-soma signal fraction than the motor cortex, particularly in deeper layers. Moreover, intra-soma signal fraction correlated positively with cortical curvature in superficial layers and negatively in deeper layers, indicating layer-specific relationships between microstructure and cortical geometry. These findings demonstrate the feasibility of noninvasively mapping cortical laminar architecture, offering a potential surrogate for histology and enabling future studies of normative and pathological brain organization using commercially available high-performance gradient MRI systems.