Bicubic Interpolation and Gradient-based Edge Detection with Skeletonization Segmentation (Bicubic-GES) on MR Optic Nerve Images for Examining NMOSD

The post-processing of optic nerve Magnetic Resonance (MR) images is very challenging due to their small size and the surrounding cerebrospinal fluid (CSF). This study proposed a new segmentation method called gradient-based edge detection with skeletonization (GES), which is specifically designed to segment the optic nerve acquired with T1-weighted magnetization-prepared 180° radio-frequency pulses and rapid gradient-echo (MPRAGE) without fat saturation (FATSAT). GES identifies the edges of the optic nerve based on the largest gradient changes of signal intensity from one region (optic nerve) to another region (CSF). The proposed GES method performed better than the well-known level set method (LSM) with higher Dice similarity coefficient (DSC) of 0.80 - 0.85 compared to 0.61 – 0.77 using LSM. Bicubic interpolation with a factor of 8 was applied before the segmentation process to increase the spatial resolution of the optic nerve. Five datasets of NMOSD patients, clinically diagnosed optic neuritis, were used in this study. The bicubic-GES processed optic nerve images were used for the area and volume measurements on the intraorbital portion of both left and right optic nerves. The measurement results were used to study the effect of Neuromyelitis Optica Spectrum Disorder (NMOSD) on the optic nerve The NMOSD causes optic neuritis and demyelination in the optic nerve. This study found that the affected optic nerve has a smaller volume than the normal contralateral optic nerve. Clinical Relevance — This study provides an additional tool to confirm the diagnosis of optic neuritis in NMOSD patients through the volume measurement on bicubic-GES processed optic nerve MR images.