The technology is already used for screening checked luggage, but the cost and larger size of the CT scanners has held back their use for carry-on bags. TSA had expected to begin testing CT scanners for carry-on luggage by the end of 2016.CT scanners create a 3-D image that can be rotated to give screeners a better look. Suspicious bags can be pulled aside and opened by screeners.American Airlines, which is participating in the test, said the technology could let passengers leave laptops, liquids and aerosols in their carry-on bags, speeding up the trip through the airport.The test comes as U.S. officials scramble to deal with potential new threats, including reports that terrorists are developing bombs that can be disguised as laptop batteries.