| Research Abstract |
<Introduction>cerebral vascular disorder is one of the most fatal diseases despite current advances in medical science. Acute cerebral infarction causes a long-term, serious sequelae because of lack of any established therapy to treat this disorder. In the diagnosis of acute cerebral ischemia, it is important to understand the extent of reversible ischemic penumbra, to distinguish it from unsalvageable infarcted tissues, and to determine appropriate therapies. However, methods that enable non-invasive observation of pathophysiologic state of the affected brain tissue have been limited. The measurement of random diffusional motion of water molecules in the human CNS is of great interest because it provides early alteration of CNS injury. In human brain, the diffusional motion of water is impeded by tissue structure such as cell membranes, myelin sheaths and white matter fiber tracts. The purpose of the present study was to clarify precise diffusion properties of water during early focal
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, cerebral ischemia using diffusion tensor analysis at a 7-tesla magnet.
<Material and Method> we studied 8 Wistar rats (250-350g, in body weight) for control and 10 with hemispheric infarct. All experiments were performed using a 7.05 T horizontal spectrometer (UNITY plus-SIS 300/183, Varian) equipped with an actively shielded gradient up to 120 mT/m per axis using a quadrature coil, 38mm in inner diameter. We used diffusion weighted spin-echo sequences (TR/TE = 3000/40msec, Δ/δ = 19/12lmsec, 2mm slice thickness, FOV=3x3cmィイD12ィエD1, NEX = 2, 256xl28 pixel matrix, gradient strength = 6gauss/cm per axis) for diffusion tensor analysis. Diffusion gradients (b-value of 557 s/mmィイD12ィエD1 per axis) were always applied on two axes simultaneously around the 180° pulse. Diffusion properties were measured along 6 noncollinear directions : (Gx, Gy, Gz) = [(0, 0. 0), (1, 0, 1), (-1, 0, 1), (0, 1, 1), (0, 1, -1), (1, 1, 0), (1, -1, 0)]. The six elements of the diffusion tensor D were estimated in each voxel using multivariate regression, and the eigenvalues (λ) were determined. Maps of Trace (D)/3 (ADC), and the fractional anisotropy (FA) were generated on a voxel-by-voxel basis. Values for ADC, and FA were determined in regions of gray and white matter, and basal ganglia in both hemispheres.
<Results> The measured ADC and FA values of distilled water were 2.10±0.04x10ィイD1-3ィエD1mmィイD12ィエD1/s and 0.06±0.029. The ADC and FA values in 8 normal rats were as follows, right gray matter 0.76±0.15 (mean ± standard deviation x 10ィイD1-3ィエD1mmィイD12ィエD1/s), 0.38±0.18 (mean ± standard deviation), left gray matter 0.73±0.17, 0.35±0.16, right white matter 0.72±0.14, 0.52±0.13, left white matter 0.74±0.13, 0.55±0.15, right basal ganglia 0.72±0.12, 0.32±0.15, left basal ganglia 0.75±0.13, 0.37±0.18. Comparisons of ADC and FA between the left and right hemisphere demonstrated no statistically significant difference in controls. For FA, the difference between gray matter and white matter and between basal ganglia and white matter were significant. The ADC and FA values in 10 rats with hemispheric infarct were as follows, right gray matter 0.73±0.16, 0.36±0.17, left gray matter 0.48±0.21, 0.38±0.18, right white matter 0.75±0.18. 0.51±0.18, left white matter 0.55±0.19, 0.45±0.22, right basal ganglia 0.73±0.12, 0.37±0.15, left basal ganglia 0.44±0.22, 0.35±0.19, A11 ADC values in the ischemic hemisphere were statistically lower than those in the contralateral hemisphere. FA in the ischemic white matter was also significantly lower than that in the contralateral hemisphere.
<Conclusion> This study suggests that diffusion tensor analysis may be robust enough to perceive changes in diffusion properties of ischemic neuronal tissue. Further data from much larger materials and human patients are required to validate this method. Less
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