期刊
MAGNETIC RESONANCE IN MEDICINE
卷 52, 期 5, 页码 1052-1059出版社
WILEY
DOI: 10.1002/mrm.20260
关键词
CWS; MRI; diffusion; cytoplasm; viscosity
资金
- NCI NIH HHS [R24-CA83060] Funding Source: Medline
- NINDS NIH HHS [R01-NS41519, R01-NS35912, F32-NS43010] Funding Source: Medline
In the brain, on a macroscopic scale, diffusion of the intraneuronal constituent N-acetyl-L-aspartate (NAA) appears to be isotropic. In contrast, on a microscopic scale, NAA diffusion is likely highly anisotropic, with displacements perpendicular to neuronal fibers being markedly hindered, and parallel displacements less so. In this report we first substantiate that local anisotropy influences NAA diffusion in vivo by observing differing diffusivities parallel and perpendicular to human corpus callosum axonal fibers. We then extend our measurements to large voxels within rat brains. As expected, the macroscopic apparent diffusion coefficient (ADC) of NAA is practically isotropic due to averaging of the numerous and diverse fiber orientations. We demonstrate that the substantially non-mono-exponential diffusion-mediated MR signal decay vs. b value can be quantitatively explained by a theoretical model of NAA confined to an ensemble of differently oriented neuronal fibers. On the microscopic scale, NAA diffusion is found to be strongly anisotropic, with displacements occurring almost exclusively parallel to the local fiber axis. This parallel diffusivity, ADC(parallel to), is 0.36 +/- 0.01 mum(2)/ms, and ADC (perpendicular to) is essentially zero. From ADC(parallel to) the apparent viscosity of the neuron cytoplasm is estimated to be twice as large as that of a temperature-matched dilute aqueous solution. (C) 2004 Wiley-Liss, Inc.
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