From Localization to Pathways: The Continuing Evolution of Diffusion Tensor Imaging

Abstract

nnate curiosity about the functional organization and connections within the brain has driven centuries of exploI rations in cortical stimulation, neural dissection, and technological developments. Increased understanding of neural networks, and their distortion by pathology, has led to paradigm shifts in neurosurgical management of diseases. The pioneering work of Broca, Penfield, and others helped map the cortical topography of the brain. Knowledge of the subcortical white matter tracts and their extension to the spinal cord has been more limited. Traditional methods of white matter tract investigations involved tracer injections in primates and postmortem dissections. The insight that the flow of water reflects surrounding obstacles such as cellular masses and myelinated fibers underlies the basis of diffusion imaging. Namely, water molecules diffuse along existent white matter tracts but are impeded orthogonal to those tracts. Mathematical models of diffusion maps collected in multiple directions, such as diffusion tensor, can generate a 3-dimensional Gaussian curve of water displacement, with the peak representing the dominant flow pattern, or by correlation, the presumed parallel fiber trajectory. The ability of diffusion tensor imaging (DTI) to offer in vivo insights into physiological tracts, as well as their derailment by pathology, marked an exciting new era.