Independent component analysis of DTI reveals multivariate microstructural correlations of white matter in the human brain.

It has recently been demonstrated that specific patterns of correlation exist in diffusion tensor imaging (DTI) parameters across white matter tracts in the normal human brain. These microstructural correlations are thought to reflect phylogenetic and functional similarities between different axonal fiber pathways. However, this earlier work was limited in three major respects: (1) the analysis was restricted to only a dozen selected tracts; (2) the DTI measurements were averaged across whole tracts, whereas metrics such as fractional anisotropy (FA) are known to vary considerably within single tracts; and (3) a univariate measure of correlation was used. In this investigation, we perform an automated multivariate whole-brain voxel-based study of white matter FA correlations using independent component analysis (ICA) of tract-based spatial statistics computed from 3T DTI in 53 healthy adult volunteers. The resulting spatial maps of the independent components show voxels for which the FA values within each map co-vary across individuals. The strongest FA correlations were found in anatomically recognizable tracts and tract segments, either singly or in homologous pairs. Hence, ICA of DTI provides an automated unsupervised decomposition of the normal human brain into multiple separable microstructurally correlated white matter regions, many of which correspond to anatomically familiar classes of white matter pathways. Further research is needed to determine whether whole-brain ICA of DTI represents a novel alternative to tractography for feature extraction in studying the normal microstructure of human white matter as well as the abnormal white matter microstructure found in neurological and psychiatric disorders.

Efficacy of reductive ventricular osmotherapy in a swine model of traumatic brain injury.

BACKGROUND: The presence of osmotic gradients in the development of cerebral edema and the effectiveness of osmotherapy are well recognized. A modification of ventriculostomy catheters described in this article provides a method of osmotherapy that is not currently available. The reductive ventricular osmotherapy (RVOT) catheter removes free water from ventricular cerebrospinal fluid (CSF) by incorporating hollow fibers that remove water vapor, thereby providing osmotherapy without increasing osmotic load. OBJECTIVE: To increase osmolarity in the ventricular CSF through use of RVOT in vivo. METHODS: Twelve Yorkshire swine with contusional injury were randomized to external ventricular drainage (EVD) or RVOT for 12 hours. MR imaging was obtained. Serum, CSF, and brain ultrafiltrate were analyzed. Histology was compared using Fluor-Jade B and hematoxylin and eosin (H & E) stains. RESULTS: With RVOT, CSF osmolality increased from 292 ± 2.7 to 345 ± 8.0 mOsmol/kg (mean ± SE, P = 0.0006), and the apparent diffusion coefficient (ADC) in the injury region increased from 0.735 ± 0.047 to 1.135 ± .063 (P = 0.004) over 24 hours. With EVD controls, CSF osmolarity and ADC were not significantly changed. Histologically, all RVOT pigs showed no evidence of neuronal degeneration (Grade 1/4) compared to moderate degeneration (Grade 2.6 ± .4/4) seen in EVD treated animals (P = 0.02). The difference in intracranial pressure (ICP) by area under the curve approached significance at P = .065 by Mann Whitney test. CONCLUSION: RVOT can increase CSF osmolarity in vivo after experimental traumatic brain injury (TBI). In anticipated clinical use, only a slight increase in CSF osmolarity may be required to reduce cerebral edema.