Influence of the Size and Curvedness of Neural Projections on the Orientationally Averaged Diffusion MR Signal [Elektronisk resurs]

• Neuronal and glial projections can be envisioned to be tubes of infinitesimal diameter as far as diffusion magnetic resonance (MR) measurements via clinical scanners are concerned. Recent experimental studies indicate that the decay of the orientationally-averaged signal in white-matter may be characterized by the power-law, $\barE(q)\propto q^-1$, where $q$ is the wavenumber determined by the parameters of the pulsed field gradient measurements. \revisnOne particular study by McKinnon ηl. \citeMcKinnon17 reports a distinctively faster decay in gray-matter. Here, we assess the role of the size and curvature of the neurites and glial arborizations in these experimental findings. To this end, we studied the signal decay for diffusion along general curves at all three temporal regimes of the traditional pulsed field gradient measurements. \revisnWe show that for curvy projections, employment of longer pulse durations leads to a disappearance of the $q^-1$ decay, while such decay is robust when narrow gradient pulses are used. Thus, \revisnin clinical acquisitions, the lack of such a decay for a fibrous specimen \revisncan be seen as indicative of fibers that are \revisncurved. We note that the above discussion is valid for an intermediate range of $q$-values as the true asymptotic behavior of the signal decay is characterized by the Debye-Porod law, which suggests the dependence $\barE(q)\propto q^-4$ at very large $q$-values. This study is expected to provide insights for interpreting the diffusion-weighted images of the central nervous system and aid in the design of acquisition strategies. 

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