Augmenting Auto-context with Global Geometric Features for Spinal Cord Segmentation

Anatomical shape variations are typically difficult to model and parametric or hand-crafted models can lead to ill-fitting segmentations. This difficulty can be addressed with a framework like autocontext, that learns to jointly detect and regularize a segmentation. However, mis-segmentation can still occur when a desired structure, such as the spinal cord, has few locally distinct features. High-level knowledge at a global scale (e.g. an MRI contains a single connected spinal cord) is needed to regularize these candidate segmentations. To encode highlevel knowledge, we propose to augment the auto-context framework with global geometric features extracted from the detected candidate shapes. Our classifier then learns these high-level rules and rejects falsely detected shapes. To validate our method we segment the spinal cords from 20 MRI volumes composed of patients with and without multiple sclerosis and demonstrate improvements in accuracy, speed, and manual effort required when compared to state-of-the-art methods.