Limited three-view intravenous urography is recommended in pregnancy to evaluate urolithiasis if initial ultrasonography findings are negative or equivocal. Cholescintigraphy has better discrimination to diagnose acute cholecystitis than CT in patients with equivocal ultrasonography results. Use of intravenous contrast media with abdominopelvic CT significantly increases the diagnostic accuracy for appendicitis. Sestamibi radioisotope has less radiation than thallium for myocardial perfusion imaging. Headache merits neuroimaging in special circumstances only. Although noncontrast CT of the head is needed to rule out bleeding in patients with suspected stroke within the first three hours of symptom onset, diffusion-weighted imaging with magnetic resonance of the head and neck is superior to CT within three to 24 hours of symptom onset. Appropriate use of imaging based on guidelines for specific clinical conditions can reduce these risks. Gadolinium contrast media should be avoided in patients with stage 4 or 5 chronic kidney disease because of the risk of nephrogenic systemic fibrosis. It is predicted that 2 percent of future cancers will be caused by radiation from computed tomography (CT) exposure. The increase in volume of imaging between 19 has led to a sixfold increase in annual per capita radiation exposure. Risks of diagnostic imaging include cancer from radiation exposure and nephrogenic systemic fibrosis.
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