Principal Diffusion Direction in Peritumoral Fiber Tracts: Color Map Patterns and Directional Statistics

The ability of diffusion tensor imaging (DTI) to probe the ultrastructural properties of biological tissues presents new possibilities for DTI‐based tissue characterization, with the potential for greater pathologic specificity than conventional imaging methods. This is urgently needed in the diagnosis and treatment of cerebral neoplasms, where clinical decisions depend on the ability to discriminate tumor‐involved from uninvolved tissue, a major shortcoming of conventional imaging. Several investigators have attempted to make this determination on the basis of the apparent diffusion coefficient (ADC) or the fractional anisotropy (FA), with mixed results. The directionally encoded color map, with hues reflecting tensor orientation and intensity weighted by FA, provides an aesthetic and informative summary of DTI features throughout the brain in an easily interpreted format. The use of these maps is becoming increasingly common in both basic and clinical research, as well as in purely clinical settings. These examples serve to demonstrate our approach to the quantitation of regional diffusion tensor distributions using directional statistical methods.