Optic Nerve Cross-Sectional Area Measurement with High-Resolution, Isotropic MRI in Optic Neuritis (P6.159)

OBJECTIVE: To develop a method of optic nerve (ON) segmentation with high-resolution, isotropic MRI. BACKGROUND: More than half of multiple sclerosis (MS) patients develop optic nerve lesions resulting in nerve atrophy, making optic neuritis useful to study the natural history of an isolated MS lesion. Yet high quality imaging of the ON is difficult due to its small size and tortuosity, leading to partial-volume effects and segmentation errors. High-resolution, isotropic images could be reoriented to be perpendicular to the ON’s long axis, allowing more accurate cross-sectional area measurement. DESIGN/METHODS: Five patients (mean age: 35 years, 3 women) underwent 3T MRI within 3 weeks of optic neuritis onset (3 with high-risk brain MRIs and 2 with MS) and 1 and 12 months after steroid treatment (by which time all had diagnosed MS). ON images were acquired with a T2-SPACE (Siemens) sequence at 600µm isotropic resolution (7.5min) with a customized coil. Images were reformatted orthogonal to the ON. To maximize image quality, reformatted images were averaged in sequential batches of three. Thus, each image represents a straightened 1.8mm portion of the ON. After manual segmentation, average cross-sectional area of unaffected and affected ONs was calculated. RESULTS: After exclusion of images with motion or other artifacts, all images were analyzed from the 15 cases. The mean coefficient of variation in unaffected eyes between baseline and month 1 was 6.4[percnt]. There was no cross-sectional area difference between unaffected (5.28±0.73mm2) and affected ONs (5.00±0.17mm2) at baseline. A year later, affected ONs were 8.2[percnt]±2[percnt] smaller than unaffected ONs (p=0.02). CONCLUSIONS: Preliminary results demonstrate that our method of high-resolution ON area measurement captures optic nerve atrophy 12 months after optic neuritis. Future work with a larger cohort will assess whether our method could be refined to improve precision and adapted as an imaging marker for disease. Study supported by: Intramural research program, NIH/NINDS Disclosure: Dr. Gao has nothing to disclose. Dr. Liu has nothing to disclose. Dr. Nair has nothing to disclose. Dr. Cortese has nothing to disclose. Dr. McFarland has nothing to disclose. Dr. Raz has nothing to disclose. Dr. Levin has nothing to disclose. Dr. Katz has nothing to disclose. Dr. Reich has nothing to disclose.