In response to a passenger smuggling plastic explosives hidden in his underwear onto a Detroit-bound airliner on Christmas Day, 2009, the Transportation Security Administration (TSA), a department of the US Department of Homeland Security, began pushing forward with its plan to place full-body scanners in all American airports. Thus far, the TSA has deployed 486 scanners in 78 airports in the United States, with an estimated 1000 scanners to be deployed by the end of 2011.
There are 2 types of full-body scanners in use. Each generates a detailed outline of the human body for the purpose of identifying contraband hidden under clothing. The millimeter-wave scanners emit extremely low-energy waves—each scan delivers a small fraction of the energy of a cell phone—and the scanners capture the reflected energy. The backscatter x-ray scanner, the type used more commonly in the United States, uses very low dose x-rays, similar to those used in medical imaging. In contrast to x-rays used for medical imaging in which variation in the transmission of x-rays through the body is used to generate an image, backscatter scanners detect radiation that reflects off of the person imaged. When radiation passes through air, it deposits energy into the tissue that absorbs it, and with the backscatter technology, all of the energy of the scan is absorbed by the most superficial tissues of the body, such as the skin.