The pipeline for EM + Atlas based brain tissue segmentation.Brain tissue segmentation is one of the primary tools in analysing brain tissues. In previous labs, Expectation Maximization (EM) and Atlas construction strategies, which are widely-used approaches for brain tissue segmentation, were implemented from scratch. This course-work is a continuation of our registration lab where we built probabilistic atlas for brain tissue segmentation. Here, We are combining EM with Atlas for segmenting Cerebrospinal fluid (CSF) with label 1, White Matter (WM) with label 2, and Gray Matter (GM) with label 3. In this report, we propose a solution of 5 complexity levels, namely: