Computed tomography (CT) comprises an X-ray tube and a bank of detectors that rotate around a patient, taking multiple exposures from different angles. The data from the detectors, essentially a density map of the body, is reconstructed to form an image which may be manipulated to any plane. The development of CT during the 1970s heralded the start of sophisticated cross-sectional imaging. Such cross-sectional images have, in turn, revolutionized the diagnostic investigation for many clinical conditions and demand for imaging grows inexorably; in 2006, an estimated 62 million CT studies were performed in the United States alone, almost five times the number in 1990. Increasingly, the radiation dose involved in CT has become a major issue and, alongside high-speed imaging, is the focus of current developments.
- The first CT machine was built in the early 1970s by Sir Godfrey Hounsfield.
- CT comprises an X-ray tube and a bank of detectors rotating around a patient to produce a dataset from which an image can be reconstructed.
- Current technology enables rapid acquisition (<10 s) of submillimetre resolution images.
- The contrast adjacent structures may be enhanced by the administration of oral, intravascular or rectal contrast medium.
- CT images may be displayed in any plane and manipulated in a number of ways depending on the clinical indication.
- There are innumerable indications for CT across many clinical specialties, with many other investigations becoming obsolete.
- CT exposes patients to a relatively high dose of radiation; efforts should be made to ensure that the investigation is necessary and that the technique employed uses the lowest dose possible while answering the clinical problem.
- Dual-energy CT enables one to determine the chemical composition of structures in addition to their morphology.
- There is currently extensive research in the use of CT perfusion imaging, adding functional information to the anatomical detail.
- CT machines are often combined with nuclear medicine machines to give hybrid functional and anatomical information.
Keywords: computed tomography; CT; clinical applications; development; radiation; X-ray