Brain Imaging

The blood–brain barrier vigorously limits what can get into and out of the brain, making our ability to understand brain function much more difficult than with any other organ in the body. The modern era of brain imaging began about a half-century ago with the introduction of computed axial tomography (CAT) and magnetic resonance imaging (MRI). Although CAT scanning shows brain structure in great detail and revolutionized the precision of medical diagnosis, including of brain disorders, it has had relatively little impact on psychiatry because most psychiatric illnesses do not involve visible abnormalities of the size, shape, or volume of brain structures. Similarly, although we have gained some insights from structural MRI, it primarily shows us the anatomy of the brain. Three other variants of MRI, however, have been extremely useful in studying psychiatric issues: functional magnetic resonance imaging, diffusion tensor imaging, and magnetic resonance spectroscopy.