CT scans are no more accurate than an ultrasound for the initial diagnosis of kidney stones, reports a study that was published recently in The New England Journal of Medicine. The study involved 15 medical centers.

Why should this finding concern you? CT scans deliver a large dose of radiation whereas an ultrasound does not. Radiation exposure is cumulative: it adds up over time. Healthy tissue can only tolerate so much radiation exposure before damage occurs. Ultrasound uses sonar – sound waves. CT scans are also more expensive than ultrasound exams.

Although many hospital emergency departments favor CT scans to diagnose kidney stones, an ultrasound should be the first step says the study’s lead author, Rebecca Smith-Bindman, MD, a professor at the University of California – San Francisco.