Clustering of atlas-defined cortical regions based on relaxation times and proton density.

Magnetic resonance parameters, such as longitudinal (T1) and transverse (T2) relaxation times and proton density (PD) provide intrinsic information about the human brain. In vivo quantification of these parameters may enable detection of subtle regional grey matter (GM) or white matter (WM) differences and permit neurological disease detection and monitoring. The aims of the study were to quantify T1, T2 and PD values in all cortical gray matter regions for a group of healthy volunteers scanned at 1.5 T and to cluster regions showing statistically distinguishable tissue characteristics. Using a combination of spoiled gradient recalled echo (SPGR) and fast spin echo (FSE) sequences, 3D T1, T2 and PD of the brain were measured at 1.5 T for twenty healthy young volunteers. Cortical GM volumes of interest (VOIs) were identified by transforming 56 labels from an atlas onto each subject volumes: 8 frontal, 5 parietal, 6 occipital and 9 temporal on both the left and right sides. T1, T2 and PD measurements within these anatomical regions were quantified and reported here. Correspondence analysis (CA) and hierarchical clustering (HC) were combined and applied to averaged T1, T2 and PD values within each VOI in order to identify groups of anatomical structures that are related statistically. Interestingly, except for one structure, all VOIs were grouped with left-right symmetry and showed an interesting pattern: the four lobes (frontal, occipital, parietal and temporal) were roughly clustered and the precentral and postcentral gyri were merged together. Our study shows that CA and HC analysis of MRI relaxation parameters and proton density can be used for cortical clustering of atlas-defined cortical regions.