Cortical Fractional Anisotropy Research Articles

Early postnatal development of rat brain: In vivo diffusion tensor imaging

Perinatal hypoxia is a major cause of neurodevelopmental deficits. Neuronal migration patterns are particularly sensitive to perinatal hypoxia/ischemia and are associated with the clinical deficits. The rat model of hypoxia/ischemia at P7 mimics that of perinatal injury in humans. Before assessing the effects of postnatal injury on brain development, it is essential to determine the normal developmental trajectories of various brain structures in individual animals. In vivo longitudinal diffusion tensor imaging (DTI) was performed from postnatal day 0 (P0) to P56 on Wistar rats. The DTI metrics, mean diffusivity (MD), fractional anisotropy (FA), axial (lambdal) and radial (lambdat) diffusivities, were determined for four gray matter and eight white matter structures. The FA of the cortical plate and the body of corpus callosum decreased significantly during the first 3 weeks after birth. The decrease in the cortical plate's FA value was associated mainly with an increase in lambdat. The initial decrease in FA of corpus callosum was associated with a significant decrease in lambdal. The FA of corpus callosum increased during the rest of the observational period, which was mainly associated with a decrease in lambdat. The FA of gray matter structures, hippocampus, caudate putamen, and cortical mantle did not show significant changes between P0 and P56. In contrast, the majority of white matter structures showed significant changes between P0 and P56. These temporal changes in the DTI metrics were related to the neuronal and axonal pruning and myelination that are known to occur in the developing brain.

Clinical Implications of Increased Fractional Anisotropy in Meningitis Associated With Brain Abscess

To look for the clinical implications of increased cortical fractional anisotropy (FA) in meningitis patients associated with brain abscess. Diffusion tensor imaging was performed in 10 patients of meningitis associated with brain abscess and 10 controls. The region of interest analysis was performed to calculate FA and mean diffusivity values from the abscess cavity and cortical regions of patients (enhancing and nonenhancing meninges on postcontrast T1-weighted images) and controls. Significantly increased FA values with no change in mean diffusivity values were found in enhancing (FA = 0.113 +/- 0.023, P = 0.000) as well as nonenhancing (FA = 0.085 +/- 0.009, P = 0.000) cortical region of patients compared with controls (FA = 0.067 +/- 0.010). Increased FA values in the enhancing as well as nonenhancing cortical regions suggest diffuse inflammatory activity in the pia-arachnoid in meningitis patients. It also suggests that FA may be a better indicator of active and diffuse meningeal inflammation than postcontrast T1-weighted images.

Diffusion tensor imaging of the developing human cerebrum

Diffusion tensor imaging (DTI) was performed on 15 fresh spontaneously or therapeutically aborted normal fetuses and five term infants at different gestational ages. Regional cortical fractional anisotropy (FA) values were observed to increase with gestational age (GA) from 15 to 28 weeks, followed by a decrease through 36 weeks. The early increase in the cortical FA value, which has never been reported before, is consistent with neuronal migration from the germinal matrix. A statistically significant inverse correlation between GA and the FA values in the germinal matrix was observed (r = -0.81, P = 0.004). In addition, there was a significant difference in the FA values in the right and left frontal cortices (P = 0.007, sign test), suggesting cortical lateralization during the early stage of development. Our studies suggest that the DTI-estimated anisotropy could be useful in following neuronal migration, cortical maturation, and associated changes in the germinal matrix during early brain development.