The cumulative exposure to ionizing radiation used in medical diagnostic tests from dental and chest X-rays, mammograms, heart health exams and other procedures adds up, often reaching or surpassing the recommended lifetime limit of 100 milliSieverts (mSv) set by the American College of Radiology, according to a recent Harvard Medical School advisory.

Among the tests that emit ionizing radiation are computerized tomography (CT scans), cardiac catheterizations, coronary CT angiograms, cardiac calcium scoring and some types of stress tests. Heart tests that pose no radiation risk include electrocardiography (ECG), echocardiography, ultrasound and magnetic resonance imaging (MRI).

Dr. Warren Manning, chief of noninvasive cardiac imaging and testing at Beth Israel Deaconess Medical Center, in Boston, and a Harvard Medical School professor, advises, “One or two CT scans over a lifetime is appropriate. But if you have a condition that requires repeated monitoring, a test that does not expose you to ionizing radiation may be preferred.” Many radiologists take precautions to minimize clients’ radiation exposure, such as performing cardiac CT scans with one-sixth the conventional radiation dose.