I. Introduction
Magnetic Resonance Imaging (MRI) is widely applied to diagnose a variety of diseases. MRI has several advantages which include the high contrast among different soft tissues and relatively high spatial resolution [1]. The brain MR image segmentation is a precondition for analyzing related brain diseases. As the manual segmentation is easily influenced by the subjective factors, the automatic segmentation is a key problem in the field of biomedical image processing research.