Original Research

The impact of optic nerve movement on optic nerve magnetic resonance diffusion parameters

Anand Moodley, William I.D. Rae, Yarish Brijmohan, Miranda Durand, Catherine Connolly, Andrew Michowicz, Ahmed Bhigjee
South African Journal of Radiology | Vol 18, No 1 | a596 | DOI: https://doi.org/10.4102/sajr.v18i1.596 | © 2014 Anand Moodley, William I.D. Rae, Yarish Brijmohan, Miranda Durand, Catherine Connolly, Andrew Michowicz, Ahmed Bhigjee | This work is licensed under CC Attribution 4.0
Submitted: 05 March 2014 | Published: 15 December 2014

About the author(s)

Anand Moodley, Department of Neurology, Grey’s Hospital, University of KwaZulu-Natal, South Africa
William I.D. Rae, Department of Medical Physics, University of the Free State, South Africa
Yarish Brijmohan, Department of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal, South Africa
Miranda Durand, Department of Radiology, Grey’s Hospital, South Africa
Catherine Connolly, Biostatistics Unit, Medical Research Council, South Africa
Andrew Michowicz, Department of Medicine, Edendale Hospital, South Africa
Ahmed Bhigjee, Department of Neurology, University of KwaZulu-Natal, South Africa

Abstract

Background: Optic nerve diffusion imaging is a useful investigational tool of optic nerve microstructure, but is limited by eye-movement-induced optic nerve movement and artifacts from surrounding cerebrospinal fluid, fat, bone and air. Attempts at improving patient cooperation, thus voluntarily limiting eye movement during a standard diffusion imagingsequence, are usually futile. The aim of this study was to establish the impact of optic nerve movement on clinical diffusion parameters of the optic nerve.

Method: Twenty-nine healthy volunteers with intact vision and intact conjugate gaze were recruited and subjected to magnetic resonance diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) of the optic nerves. Twenty right eyes had nerve tracking done using single-shot echo-planar imaging at 20 time points over 3 minutes. Optic nerve movement measurements were correlated with diffusion parameters of apparent diffusion coefficient (ADC), mean diffusivity (MD), fractional anisotropy (FA) and anisotropic index(AI) using Spearman’s rank correlation.

Results: No significant correlations were noted between optic nerve movement parameters and ADC in the axial plane and MD of the optic nerve. Low to moderate negative correlations were noted between optic nerve movement parameters and AI and FA and positive correlation with ADC in the radial plane.

Conclusion: Optic nerve movement documented during the timespan of standard diffusion sequences (DWI and DTI) has a negative effect on the anisotropic diffusion parameters of the optic nerve. With greater eye movement, optic nerve diffusion appears less anisotropic owing to greater radial diffusion.


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