Any noninvasive means of generating images of a living brain. Images of the anatomical structure of the brain can be obtained using computerized axial tomography (CAT) or magnetic resonance imaging (MRI). These are used for diagnosis of brain disease and injury. Images can also be obtained to show activity in the brain as various mental tasks are being performed, using positron emission tomography (PET) or functional magnetic resonance imaging (fMRI). Such functional neuroimaging is used for neurological research and to diagnose disease on a finer scale than is possible with the structural techniques.