Clinical Procedures - Computed Tomography (CT) Indications • Indications are manifold and too numerous to list. Contraindications • The standard radiation protection precautions apply. See separate topic • The patient must be able to lie flat and still for the duration of the scan • Examinations of the chest usually require the patient to hold their breath. Technology • The CT scanner houses an x-ray tube and rows of detectors which spin at 2-3 revolutions per second, creating a force of up to 25g • As the patient is moved through the machine, spiral data is acquired which is then converted to 'slices' by the software. Procedure This depends on the part of the body examined and the indications for the examination. • If indicated, the patient may be given oral contrast an hour or more before the examination • The patient lies (usually supine) on the scanner table: • Head-first for head and neck; feet-first for almost everything else • 'Scout' views are acquired which are brief swipes across the area of interest. The resultant images are then used by the radiographer to set the parameters for the scan • Most examinations involve IV iodinated contrast being given: • This is usually delivered via an IV cannula by an automatic pump-injection device, controlled remotely by the radiographer • Contrast may be hand-injected immediately before some scans • Depending on the part of the body examined, the patient may be asked to hold their breath via speakers in the machine. Microphones within the scanner allow the staff in the control room to hear the patient • The scan itself lasts no more than a couple of minutes. Time taken to transfer the patient onto the scanner and set up the IV injections will vary. Risks • IV contrast reactions including anaphylaxis and nephrotoxicity. IV contrast should not be given to patients with renal impairment unless in special circumstances. Check local guidance • Extravasation of IV contrast (pain, swelling, erythema).
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