 Tetsuya Wada |
 Yoshitaka Asano |
Approximately 80% of nonfatal traumatic brain injuries (TBIs) are classified as mild. Although they occur often, the pathophysiological, neurophysiological, and neuropsychological mechanisms of mild TBI (MTBI) remain poorly understood. Clinically, TBI is associated with the cognitive disturbances that often cause problems in family, school, work, or other social settings. We have experienced many patients with MTBI who complained of neurocognitive symptoms though they had no morphological brain lesions on conventional MR imaging. We also found them difficult to treat. Previous meta-analytic studies have concluded that patients with MTBI with chronically impaired cognitive test performances were faking their deficits or that the cause of their poor performance was not brain-based. However, we thought that not all cases could be explained in this way.
Brain damage, which is referred to as diffuse axonal injury following MTBI, is a compromise of neural tissue; it is often subtle and difficult to detect. Diagnostic imaging of MTBI can increase our understanding of the clinical symptoms and help determine treatment strategies. In particular, DTI is a modality that has been developed as a tool to investigate the integrity of brain tissues such as white matter tracts and uncover discrete axonal injury. Diffusion anisotropy describes how variable the diffusion is in different directions. It is most commonly quantified in a ratio of axial-to-radial diffusivity known as fractional anisotropy (FA).