Your doctor owns a CT scanner or has a financial interest in an imaging center

An in-office CT might seem convenient, but it carries an inherent financial conflict of interest. And studies have found that physicians who own scanners or are part owners of radiology clinics use imaging substantially more than others. If your doctor owns a scanner, ask why you need the CT or whether another test might be an option. And if he is sending you to a radiology clinic, ask whether he is financially affiliated with it.

Your doctor recommends a “whole-body” CT scan

Those scans are often touted as a way to detect early signs of cancer and heart disease. But most scans—and up to 80 percent in older people—have at least one abnormality that shows up on the exam. Almost all of the abnormalities are harmless, yet about one-third of patients are referred to follow-up imaging, according to a 2013 study. And whole-body CT scans expose you to much more radiation than regular CT scans. One study determined that for every 1,250 45-year-old adults who have the exam, one will die of cancer as a result. Yet it’s unknown how many lives the scans might save.

Your dentist recommends a 3D dental shot

The CT technique, called cone-beam CT, exposes children to about six times more radiation than traditional dental X-rays. The American Dental Association says that children rarely need them before orthodontic procedures. And several studies have shown that for any given dose of radiation, children are three to four times more likely than adults to develop malignancies, in part because their cells are more sensitive to radiation.