The principles and applications of computed tomography

In computed tomography (CT) a thin fan-shaped x-ray beam is used to produce cross-sectional images of the patient in which there is a clear distinction between soft tissue, fat, air and bony structures. CT is associated with less scattered radiation than conventional radiography. The CT scanner comprises three basic components, namely the scanning gantry, a computer system and a display console. The greatest use for CT remains in the investigation of intra-cranial disease. In the rest of the body, CT is most commonly used for detecting and determining the extent of malignant disease. It contributes in the primary diagnosis of cancer as well as in the staging, monitoring of response to treatment and detection of recurrence. Inflammatory conditions such as abscesses and pancreatitis are well evaluated with CT. Cysts can be clearly distinguished and a further application is in chronic back pain where CT accurately demonstrates lumbar disc disease, spinal stinosis and facet joint disease. CT has certain important limitations. A solid mass may be benign or malignant and CT cannot always tell the difference. CT may not even be able to differentiate between neoplastic and infective processes and CT is also of limited value in studying the gastro-intestinal tract. 1 tab., 19 figs., 2 refs