MRI-based topographic parcellation of human cerebral white matter I. Technical foundations

We describe a virtually automatic comprehensive parcellation of the human c erebral central white matter, which is based upon T1-weighted MRI scans. Th e system, which is "rule-based," is developed from prior anatomic studies o f the human brain and experimental studies of connectivity in animals as el aborated in the companion manuscript. Boundaries which delineate anatomic s ubregions of the white matter are computed from the geometric features of a natomic landmarks visible in the imaging data. The fiber systems of the cen tral white matter are ordered topographically into three compartments, refl ecting the inferred arrangements of principal neural systems pathways. Thes e include an outer radiate (fibers principally radially aligned), an interm ediate sagittal (fibers principally sagittally aligned), and deep bridging (fibers bridging hemispheres or cortex and deep structures) compartments. E ach of these compartments is secondarily parcellated into smaller units to increase the anatomic specificity and spatial resolution of the system. The principal intended uses for this system of anatomic subdivision are for th e volumetric characterization of forebrain white matter in normal and abnor mal brains and for precision and specificity of localization in focal lesio n-deficit correlation studies. (C) 1999 Academic Press.