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D.A. Lee, D. Mulvihill, K.Q. Cheng, D. Jenkins; Diffusion Tensor Imaging of the Living Human Optic Nerve From the Neonatal Period to the Adult . Invest. Ophthalmol. Vis. Sci. 2006;47(13):735.
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Optic nerve demyelination and axonal loss play an important role in white matter disorders such as optic neuropathy. Conventional MRI techniques such as T1 and T2–weighted MRI are significantly more sensitive in detecting brain tissue damage than ultrasound or CT scans. However, signal intensity changes on T1– and T2–weighted MRI images can be difficult to detect particularly for early optic nerve damage. We investigated the fractional anisotropy (FA) in human optic nerves during brain development using diffusion tensor imaging (DTI) and quantitatively assessed of optic nerve damage from white matter injury unavailable with conventional MRI.
DTI was performed on all patients in additional to the conventional MRI scans. The DTI data was acquired in a single–shot echo planar sequence with six gradient directions. The imaging parameters are field–of–view (FOV) of 24x36 cm, section thickness of 5 mm at 1–mm intervals, matrix 256 × 128, and the b value of 0 and 1000 s/mm2. All DTI data was transferred to a workstation for off–line postprocessing. Multiple small circular regions of interest (ROI) were placed in the optic nerve. Values of FA were measured in 5 neonates, 2 young and 3 adults.
Mean FA of optic nerves was 0.4165 (SD ± 0.0595) in neonates (near term or full term), 0.4660 (SD ± 0.0432) in young adults (ages 10 to 14 years), and 0.4384 (SD ± 0.0216) in adults (ages 50–80 years). There is a significant difference (P=0.03) in FA values between neonates and young adults age group, but no difference between young adults and adults. Continuous increases of FA in optic nerves from birth into teenage years suggest continuing maturation and organization of deep tracts undetectable on conventional MRI. The lower values of FA in the adult group indicated that these patients may have some optic nerve damage or natural white matter atrophy.
DTI can be a useful tool for quantifying white matter damage in human optic nerves. Further study involving patients with different types of optic neuropathy is in progress.
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