Kakkar, LS; Atkinson, D; Chan, RW; Siow, B; Ianus, A; Drobnjak, I; (2017) Sensitivity of OGSE activeax to microstructural dimensions on a clinical scanner. In: Hege, H-C and Hoffman, D and Johnson, CR and Polthier, K and Rumpf, M, (eds.) Computational Diffusion MRI MICCAI 2016. Mathematics and Visualization. (pp. pp. 85-97). Springer: Cham, Switzerland.

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Abstract

Axon diameter can play a key role in the function and performance of nerve pathways of the central and peripheral nervous system. Previously, a number of techniques to measure axon diameter using diffusion MR I have been proposed, majority of which uses single diffusion encoding (SDE) spin-echo sequence. However, recent theoretical research suggests that low-frequency oscillating gradient spin echo (OGSE) offers benefits over SDE for imaging diameters when fibres are of unknown orientation. Furthermore, it suggests that resolution limit for clinical scanners (gradient strength of 60–80 mT/m) is ~ 6 µm. Here we investigate the sensitivity of OGSE to fibre diameters experimentally on a clinical scanner, using microcapillaries of unknown orientation. We use the orientationally invariant OGSE ActiveAx method to image microcapillaries with diameters of 5, 10 or 20 µm. As predicted by theory, we find that 5 µm diameters are undistinguishable from zero. Furthermore, we find accurate and precise estimates for 10 and 20 µm. Finally, we find that low frequency oscillating gradient waveforms are optimal for accurate diameter estimation.

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