TY - JOUR
T1 - On the nature of the NAA diffusion attenuated MR signal in the central nervous system
AU - Kroenke, Christopher D.
AU - Ackerman, Joseph J.H.
AU - Yablonskiy, Dmitriy A.
PY - 2004/11
Y1 - 2004/11
N2 - 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-monoexponential 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∥, is 0.36 ± 0.01 μm 2/ms, and ADC⊥ is essentially zero. From ADC ∥ the apparent viscosity of the neuron cytoplasm is estimated to be twice as large as that of a temperature-matched dilute aqueous solution.
AB - 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-monoexponential 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∥, is 0.36 ± 0.01 μm 2/ms, and ADC⊥ is essentially zero. From ADC ∥ the apparent viscosity of the neuron cytoplasm is estimated to be twice as large as that of a temperature-matched dilute aqueous solution.
KW - CWS
KW - Cytoplasm
KW - Diffusion
KW - MRI
KW - Viscosity
UR - http://www.scopus.com/inward/record.url?scp=7544232782&partnerID=8YFLogxK
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U2 - 10.1002/mrm.20260
DO - 10.1002/mrm.20260
M3 - Article
C2 - 15508157
AN - SCOPUS:7544232782
SN - 0740-3194
VL - 52
SP - 1052
EP - 1059
JO - Magnetic Resonance in Medicine
JF - Magnetic Resonance in Medicine
IS - 5
ER -