There are two types of scanning machines (what the Transportation Security Administration calls Advanced Imaging Technology) being installed at the nation’s airports. 

Backscatter machines use a narrow, low intensity X-ray beam which is scanned over the body’s surface at high speed.  The millimeter wave machine uses beams of radio frequency energy in the millimeter wave spectrum that are projected over the body’s surface at high speed from two antennas that rotate around the body.

By the end of 2010, some 500 scanners were deployed at the nation’s airports, with the number expected to double by the end of 2011. Taking the lead for sales to the TSA are Rapiscan Systems’ backscatter machines.  Rapiscan is the chief client of Michael Chertoff, who had been head of the Department of Homeland Security – where the TSA is based – from 2005 to 2009.  The Government Accountability Office estimates that direct costs associated with the scanners by the end of an expected 7-year-life cycle will be $2.4 billion. 

A Government Accountability Office report states that it remains “unclear” whether the machines would have detected the explosive material carried in his underwear by Umar Farouk Abdulmutallab.  A document obtained from the Transportation Security Administration as part of a FOIA request states that the scanners were intended to detect traditional weapons, liquids and such explosives as C4 – but not explosive powder.  They also find it hard to deal with folds in clothing or the body and cannot detect anything carried in body cavities.

They also have potential health risks, according to a group of biochemists and cancer experts from the University of California.