Airline passengers have already said bon voyage to the controversial backscatter X-ray security scanners, pulled from U.S. airports in 2013 over concerns about privacy and potential radiation risks. But the devices may be reintroduced in the future, in part because they produce superior images of many concealed threats.

Congress still wants to know whether these systems—currently used in prisons, in diamond mines, and by the military—produce safe levels of radiation for screeners and the people they screen.

Two years ago, researchers from the National Institute of Standards and Technology (NIST) produced a report stating that the radiation exposure levels produced by one widely used class of backscatter machines were in compliance with applicable national and international safety standards. To evaluate these results, as well as similar findings at other institutions, Congress ordered an independent third-party assessment of the backscatter systems to be carried out by a team selected by the National Academy of Sciences (NAS). Last week, NIST hosted the NAS study at its Gaithersburg, Maryland campus, in a lab that contains a government-surplus backscatter machine that once screened passengers at LaGuardia Airport.

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