Several methods can detect or infer the disruption of basic brain physiology; these methods include the techniques of computerized axial tomography, magnetic resonance imaging, positron emission tomography, single photon emission computed tomography, electroencephalography, magnetoencephalography, and magnetic resonance spectroscopy. Until recently any information on the actual function of the brain has been restricted to that deduced from the clinical examination, as most imaging methods have been limited to providing only anatomical references. In the past 10 years magnetic resonance has become a standard part of many neuroradiological practices. Tremendous advances in computed tomography have resulted in dramatic improvement in both image resolution and imaging times. During the 1990s, as interest shifts toward the analysis of brain function or dysfunction, the focus on the brain's electrical activity has resurged. Functional evaluation techniques, such as magnetoencephalography, began in the 1960s and early 1970s; sophistication in the technology has led to much shorter examination and analysis times, leading to further clinical utility. Magnetoencephalography, when combined with magnetic resonance images, forms a functional image of the brain, or magnetic source image. The advent of such methods for evaluating actual functional activity of the brain has resulted in new clinical applications for previous methods of brain imaging and the arrival of new clinical imaging modalities.