special subjects
Computed Tomography (CT)
Disadvantages of CT
CT accounts for most diagnostic radiation exposure to patients collectively. If multiple scans are done, the total radiation dose may be relatively high, placing the patient at potential risk (see Risks of Medical Radiation ). Patients who have recurrent urinary tract stones or who have had major trauma are most likely to have multiple CT scans. The risk of radiation exposure versus benefit of the examination must always be considered because the effective radiation dose of one abdomen/pelvis CT is equal to approximately 385 single-view chest x-rays. Current practice dictates that CT scanning use the lowest radiation dose possible. Modern CT scanners and revised imaging protocols have dramatically lowered radiation exposure from CT. Also, newer, investigational methods are evaluating the use of even much lower radiation doses for certain CT scans and certain indications; in some cases, these doses would be comparable to the radiation delivered by x-rays. Some CT scans use IV contrast, which has certain risks (see Radiographic Contrast Agents and Contrast Reactions ). However, oral and rectal contrast also has risks, such as the following: If barium, given orally or rectally, extravasates outside the gastrointestinal tract lumen, it can induce severe inflammation in the peritoneal cavity. Iodinated oral contrast agents are used if there is a risk of intestinal perforation. Aspiration of iodinated contrast agents can induce severe Chemical pneumonitis . Barium retained in the intestinal tract can become hard and inspissated, potentially causing intestinal obstruction. 