Improved Cerebellar Tissue Classification on Magnetic Resonance Images of Brain

Purpose: To develop and implement a method for improved cerebellar tissue classification on the MRI of brain by au- tomatically isolating the cerebellum prior to segmentation. Materials and Methods: Dual fast spin echo (FSE) and fluid attenuation inversion recovery (FLAIR) images were acquired on 18 normal volunteers on a 3 T Philips scanner. The cerebellum was isolated from the rest of the brain using a symmetric inverse consistent nonlinear registration of individual brain with the parcellated template. The cerebel- lum was then separated by masking the anatomical image with individual FLAIR images. Tissues in both the cerebel- lum and rest of the brain were separately classified using hidden Markov random field (HMRF), a parametric method, and then combined to obtain tissue classification of the whole brain. The proposed method for tissue classification on real MR brain images was evaluated subjectively by two experts. The segmentation results on Brainweb images with varying noise and intensity nonuniformity levels were quantitatively compared with the ground truth by comput- ing the Dice similarity indices. Results: The proposed method significantly improved the cerebellar tissue classification on all normal volunteers in- cluded in this study without compromising the classifica- tion in remaining part of the brain. The average similarity indices for gray matter (GM) and white matter (WM) in the cerebellum are 89.81 (2.34) and 93.04 (2.41), demon- strating excellent performance of the proposed methodol- ogy. Conclusion: The proposed method significantly improved tissue classification in the cerebellum. The GM was over- estimated when segmentation was performed on the whole brain as a single object.