In vivo Analysis of Optic Nerve in an Elderly Population Using Diffusion Magnetic Resonance Imaging Tractography

Abstract

Purpose: To quantitatively investigate the microstructural properties of the optic nerve (ON) in vivo using diffusion magnetic resonance imaging (dMRI) tractography in an elderly population and to determine the differences between the ON diffusion properties stratified by basic demographics Methods: We measured fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD) of the intraorbital ON in cognitively normal controls selected from the Alzheimer’s Disease Neuroimaging Initiative 3 database (n = 132, mean age 74.5 ± 8.2 years) using dMRI probabilistic tractography and evaluated the correlation between diffusion parameters and demographic factors. Diffusion parameters were measured in 20 equidistant nodes along the tract. Results: The mean FA of the entire intraorbital ON was 0.346 ± 0.078 and the mean MD was 1.266 ± 0.196 μm2/s. The mean RD was 1.009 ± 0.195 μm2/s and the mean AD was 1.764 ± 0.210 μm2/s. FA gradually increased from 0.250 to 0.404 toward the orbital apex, whereas MD, RD and AD decreased from 1.529 to 1.121 μm2/s, from 1.323 to 0.851 μm2/s, and from 1.950 to 1.659 μm2/s, respectively. The multiple linear regression model showed a negative correlation between FA and age in all 20 nodes, and FA in females was significantly higher thant males. However, MD showed no significant correlation with age, and the MD of the anterior 19 nodes correlated with sex. Females had significantly lower RD in all nodes of the intraorbital ON, and RD was correlated with age in a fourth of the ON. Meanwhile, no variable was entered into the multiple linear regression model by a stepwise entry for AD except for the first node. Conclusions: We measured the diffusion properties along the intraorbital ON using dMRI tractography in an elderly cognitively normal population. FA had an inverse relationship with MD, where the FA gradually decreased with age and toward the eye globe, and the MD showed the opposite trend. Females had higher FA and lower MD and RD than males. The diffusion properties detected by dMRI tractography may substantially reflect the microstructure of the ON.