It is concluded that DTI abnormalities in the regions of CC were more in patients with moderate TBI compared to mild TBI and this was associated with relatively poor neuropsychological outcome 6 months post-injury.

Purpose:To detect lesion-related focal Wallerian degeneration (WD) changes in different segments of the corpus callosum (CC) in patients with large middle cerebral arterial (MCA) territory stroke using diffusion tensor imaging (DTI). Materials and Methods:Eight patients underwent DTI scans at three different time points: six to eight weeks, 10 -12 weeks, and beyond six months of stroke onset. Eight healthy age-matched controls were also scanned using the same protocol at three different time points. Region-of-interest (ROI) analysis was performed on seven segments of the CC to determine the fractional anisotropy (FA), mean diffusivity (MD), and corresponding callosal cross-sectional areas. Results:On repeated-measures analysis of variance (ANOVA), a significant reduction in the FA values was observed from the first to the third study compared to controls, reflecting temporal degeneration in the rostrum, genu, rostral body, anterior midbody, and splenium of the CC. However, a significant temporal elevation in MD values was observed in only the rostral body and anterior midbody of the CC. This was associated with a significant regionspecific reduction in the cross-sectional areas at time points beyond six months, and appears to be consistent with the loss of callosal structural components due to interruption of the cortico-callosal fibers secondary to WD. Conclusion:These results indicate that cortico-callosal topographical changes exhibit a significant temporal decline in observed FA values that is suggestive of corticocallosal WD in patients with large MCA territory stroke.

Summary: Purpose:The main objective of this study was to use diffusion tensor imaging (DTI) to search and quantify the extent of abnormality beyond the obvious lesions seen on the T 2 and fluid-attenuation inversion recovery (FLAIR) magnetic resonance images in patients with chronic traumatic brain injury (TBI) with and without epilepsy.Methods: DTI was performed on 23 chronic TBI patients (with late posttraumatic epilepsy, n = 14; without epilepsy, n = 9) and 11 age-matched controls. The ratios of fractional anisotropy (FA) and mean diffusivity (MD) between the regions of interest beyond the T 2 /FLAIR-visualized abnormality and the corresponding contralateral normal-appearing region were calculated. FA and MD ratios were compared for relative changes in these parameters among the TBI subjects with and without epilepsy and controls. Tissue volumes exhibiting abnormalities on DTI also were measured in these patients. Results:The mean regional FA ratio was significantly lower, whereas the mean regional MD value was higher in patients with TBI compared with controls. The mean regional FA ratio was significantly lower in TBI patients with epilepsy (0.57 ± 0.059) than in those without epilepsy (0.68 ± 0.039). Although the regional MD ratio was higher in TBI patients with epilepsy (1.15 ± 0.140) relative to those without epilepsy (1.09 ± 0.141), the difference did not reach statistical significance. The tissue volume with low FA value also was found to be higher in TBI patients with epilepsy than without.Conclusions: Severity of injury as predicted by the DTIderived increased volume of microstructure damage is associated with delayed posttraumatic epilepsy in TBI patients. These findings could be valuable in predicting epileptogenesis in patients with chronic TBI. Key Words: Diffusion tensor imaging-Traumatic brain injury-Posttraumatic epilepsyFractional anisotropy-Magnetic resonance imaging. Traumatic brain injury (TBI) is one of the most common causes of morbidity and mortality in developed countries, and posttraumatic epilepsy (PTE) is the major sequela (1,2). PTE is classified into three groups, depending on when seizures occur after TBI: (a) within 24 h, (b) during the first week, and (c) after >1 week (3,4). The first two groups are termed early PTE and are the result of direct response to the brain damage. The third category represents late PTE. The severity and type of brain injury appear to correlate with the incidence of PTE. The factors that are known to contribute to the risk of PTE are duration of unconsciousness, dura penetration, degree of direct cortical damage, and genetic predisposition to epilepsy (5). Structural damage resulting from trauma itself, or hypoxic damage and subsequent scarring and inadequate blood flow also are the major contributing factors to the risk of PTE. The investigation and management of patients after

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Restricted diffusion in brain abscess is assumed to be due to a combination of inflammatory cells, necrotic debris, viscosity, and macromolecules present in the pus. We performed diffusion-weighted imaging (DWI) on 41 patients with proven brain abscesses (36 pyogenic and five tuberculous), and correlated the apparent diffusion coefficient (ADC) from the abscess cavity with viable cell density, viscosity, and extracellular-protein content quantified from the pus. On the basis of the correlation between cell density and ADC in animal tumor models and human tumors in the literature, we assumed that the restricted ADC represents the cellular portion in the abscess cavity. We calculated restricted and unrestricted lesion volumes, and modeled cell density over the restricted area with viable cell density per mm 3 obtained from the pus. The mean restricted ADC in the cavity (0.65 ؎ 0.01 ؋ 10 -3 mm 2 /s) correlated inversely with restricted cell density in both the pyogenic (r ‫؍‬ -0.90, P ‫؍‬ <0.05) and tuberculous (0.60 ؎ 0.04 ؋ 10 -3 mm 2 /s, r ‫؍‬ -0.94, P ‫؍‬ <0.05) abscesses. We conclude that viable cell density is the main biological parameter responsible for restricted diffusion in brain abscess, and it is not influenced by the etiological agents responsible for its causation. Magn Reson Med 54:878 -885, 2005.