The intracranial boundary detection and RF inhomogeneity correction techniques presented in this thesis capitalize on several properties of magnetic resonance images. Therefore, some knowledge of magnetic resonance imaging (MRI) and the data produced by MRI scanners is necessary. This chapter introduces the basic principles of MRI and describes some important characteristics of MRI data, such as the partial volume effect and RF inhomogeneity. A detailed review of the physics of MRI falls outside the scope of this manuscript. Refer to [8] or [40] for a complete description of MRI.