In Vivo Surface Reconstruction of Three Signal-defined Intracortical Layers Using 5T 3D FLAIR MR Imaging

BackgroundIn vivo whole-cortex quantification of intracortical signal-defined layering on the routinely acquired structural MRI remains limited. PurposeTo develop and validate an automated framework to reconstruct three intracortical signal-defined layers from 5T three-dimensional (3D) T2-weighted fluid-attenuated inversion recovery (FLAIR) and to characterize whole-cortex morphometrics and regional organization across a prespecified cortical organizational framework. Materials and MethodsIn this retrospective study, 5T 3D FLAIR images were acquired between February and July 2024. Brain Multi-Layer Surface Reconstruction (BrainMLSR) reconstructed three intracortical signal-defined layers, and derived intracortical layer thickness and surface area measures and ratios. Performance was evaluated against manual annotations and assessed for test-retest repeatability (n=13) and cross-site feasibility (n=2). Paired two-tailed t-tests and linear mixed-effects models were used. A proof-of-concept analysis compared Heschls gyrus ratios between 19 patients with temporal lobe epilepsy (TLE) and 19 age-matched healthy controls (HC). ResultsA total of 270 healthy participants (mean age, 54.4{+/-}14.5 years; 146 men) were included. Agreement with manual hypointense-layer annotations was high (Dice, 0.960{+/-}0.003), and was similar in the cross-site dataset (Dice, 0.954{+/-}0.009). In the test-retest dataset, average symmetric surface distance was less than 0.1 mm. Across prespecified systems, thickness and surface area ratios varied by region; within an auditory-perisylvian hierarchy, banksSTS showed a localized turning point with an increased hyperintense layer thickness ratio and decreased hypointense layer thickness ratio, accompanied by inflections in surface area ratios (P < .001). In bilateral Heschls gyrus, hypointense (left: 0.619{+/-}0.262 vs 0.881{+/-}0.102; right: 0.607{+/-}0.310 vs 0.907{+/-}0.141 mm) and isointense (left: 0.406{+/-}0.225 vs 0.678{+/-}0.128; right: 0.478{+/-}0.232 vs 0.808{+/-}0.176 mm) layer thicknesses were lower in TLE than in HC (all P<.001). ConclusionBrainMLSR enabled accurate and repeatable in vivo reconstruction of three intracortical signal-defined layers from a single 5T 3D T2-weighted FLAIR acquisition and provided whole-cortex boundary-based morphometry with interpretable regional organization. Key ResultsO_LIIn this retrospective study of 270 participants, Brain Multi-Layer Surface Reconstruction (BrainMLSR) showed high agreement with hypointense-layer annotations (Dice, 0.960{+/-}0.003). C_LIO_LIWithin an auditory-perisylvian hierarchy, the hyperintense-layer thickness ratio peaked (0.620{+/-}0.003) and the hypointense-layer ratio was the lowest (0.156{+/-}0.002) in the bank of the superior temporal sulcus (P < .001). C_LIO_LIIn a proof-of-concept analysis, patients with temporal lobe epilepsy (vs healthy controls) had higher hyperintense-layer thicknesses ratio in the left hemisphere (0.523{+/-}0.085 vs 0.417{+/-}0.036, P<.001). C_LI SummaryAn automated multiple-layer surface reconstruction framework (BrainMLSR), applied to 5T 3D T2-weighted FLAIR images, produced reproducible whole-cortex, signal-defined laminar morphometry and demonstrated coherent patterns across prespecified cortical organizational framework.