Hundreds of hospitals are routinely performing a type of chest scan that experts say should be used rarely, subjecting patients to double doses of radiation and driving up health-care costs. In a double CT scan, patients get two imaging tests consecutively: one without dye and the other with dye injected into their veins. Providence Hospital in Northeast Washington and nearly one of every six hospitals in Virginia were among those performing double scans particularly frequently, according to the most recently published government Medicare data, from 2008. The government is taking a closer look at scans because imaging tests are among the fastest growing procedures in health care. Medicare’s Hospital Compare Web site publishes individual hospital rates of double chest scans, along with rates for several other kinds of imaging. Medicare doesn’t restrict the use of double scans or penalise those who perform lots of them. Nationwide, hospitals performed double scans on 5.4 percent of Medicare patients who received chest CTs in emergency rooms or hospital radiology units where they were referred by their doctors. Those scans totaled 76,781 in 2008. The overall number was certainly higher, as patients with private insurance, Medicaid or no coverage also get double scans, but no one tracks the number. Most hospitals used the double chest scans sparingly. The median rate was 2 percent of all Medicare patients who received chest scans, according to Hospital Compare data on 3,094 hospitals. But 618 hospitals performed the tests on at least 10 percent of Medicare patients getting a chest CT scan. Ninety-four of those hospitals performed double scans on at least half their patients getting chest scans. The highest rates “really raise a red flag,” says Paul L. Molina, chief of chest imaging at the University of North Carolina School of Medicine.