Magnetic Resonance (MR) has proven to be one of the most promising diagnostic modalities for the study of the brain. This highly flexible technique makes it possible to examine the brain’s interior structures as well as its activity at rest or under specific stimuli.Automatic tissue recognition (also known as segmentation) is an important and challenging task in the processing and analysis of brain MR images, and during the last decade a large number of software packages have been developed to classify the three major brain tissues: grey matter, white matter and cerebro spinal fluid.