Abstract: In this Review paper, it is intended to summarize and compare the methods of automatic detection of brain tumor through Magnetic Resonance Image (MRI) used in different stages of Computer Aided Detection System (CAD).In particular, Image Acquisition, preprocessing and enhancement, segmentation steps are studied and compared. In Preprocessing and Enhancement stage, medical image is converted into standard format with contrast manipulation, noise reduction by background removal, edge sharpening, filtering process and removal of film artificates. Segmentation determines as the process of dividing an image into disjoint homogenous regions of a medical image. The amount of resources required to describe large set of data is simplified and selected in for tissue segmentation.