Diffusion tensor imaging and axonal tracking in the human brainstem

Diffusion tensor MRI was used to demonstrate in vivo anatomical mapping of brainstem axonal connections. It was possible to identify the corticospinal tract (CST), medial lemniscus, and the superior, medial, and inferior cere bellar peduncles. In addition, the cerebral peduncle could be subparcellate d into component tracts, namely, the frontopontine tract, the CST, and the temporo-/parieto-/occipitopontine tract. Anatomical landmarks and tracking thresholds were established for each fiber and, using these standards, repr oducibility of automated tracking as assessed by intra- and interrater reli ability was found to be high (kappa > 0.82). Reconstructed fibers correspon ded well to existing anatomical knowledge, validating the tracking. Informa tion on the location of individual tracts was coregistered with quantitativ e MRI maps to automatically measure MRI parameters on a tract-by-tract basi s. The results reveal that each tract has a unique spatial signature in ter ms of water relaxation and diffusion anisotropy. (C) 2001 Academic Press.