Brain tissue segmentation from the magnetic resonance (MR) images is having considerable importance in the medical research field and has been useful in many applications. Brain tissue is a complex structure and hence proper diagnosis of many brain disorders greatly depends upon accurate segmentation of three main tissues, namely, white matter (WM), gray matter (GM) and cerebro-spinal fluid (CSF) in brain MR images. This book investigates medical image segmentation methods across a range of modalities and clinical applications, covering MRI in brain tissue segmentation and MRI based MS lesion segmentation.The prime objective is to devise novel strategies and methodologies for an automated brain MR image segmentation scheme.This problem has been addressed in literature, but many key open issues still remains to be investigated. This book aims to address the segmentation problems and improve the segmentation accuracy. The comparative analysis of the proposed methods with existing methods should be especially useful to researchers working on this problem and may help to understand the complex classification and segmentation tasks of brain MRI tissues.