Pronounced ''cat'' scan, computerized tomography or CT is a technology tool to examine the brain in cross sections. The word ''tomography'' is derived from the Greek tomos meaning ''slice'' and graphein meaning ''to write.'' CT employs digital geometry to generate a three-dimensional (3-D) image of the internals of an object from a large series of 2-D x-ray images taken around a single axis of rotation. As multidimensional views of multiple axial slices are captured from various angles, x-rays on various paths through the CNS create contrast, which creates lighter or darker areas seen on the image. CT produces a volume of data that can be manipulated through a process known as windowing. Modern scanners allow this volume of data to be reformatted in various planes or as 3-D representations of structures. The trained reader can then read various anatomical sites.

The British scientist Sir Godfrey Newbold Hounsfield first conceived the idea in 1967 at the research branch of Electric and Musical Industries. The first machine was called an EMI scanner. An American Allan McLeod Cormack of Tufts University in Massachusetts independently invented a similar process. Together the two shared the 1979 Nobel Prize in Medicine for the invention.

CT has been used for over 30 years to look into the central nervous system (CNS) and other body systems. In medicine CT has been used to evaluate CNS lesions, tumors, or structural change, as well as areas when the blood-brain barrier has broken down. Early studies of ADHD using CT were useful in establishing some of the foundation information about brain structure. However, recently use has been limited because there is a risk of allergic reaction to the iodine-based contrast dyes that are commonly used. Although it is less expensive that MRI, it does expose the subject to ionizing radiation creating ethical concerns when used solely for research purposes.

Bibliography:

Gozal, David, and Dennis L. Molfese, eds. 2005. Attention deficit hyperactive disorder: From genes to patients. Totowa, NJ: Humana Press

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