Instead of X-ray scanners, European airports will use millimeter-wave scanners that utilize low-energy radio waves.

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Would any of us have objected to the deployment of millimeter-wave scanners had the technology been available then?

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Passengers who are asked to undergo a second screening can choose a pat-down search or the millimeter-wave test.

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In addition to the backscatter machines, the TSA has also deployed about 260 millimeter-wave machines which use radio waves and do not emit X-rays.

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The other uses millimeter-wave technology, which shows a detailed photo negative.

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The TSA plans to deploy 1, 275 backscatter and millimeter-wave scanners covering more than half its security lanes by the end of 2012 and 1, 800 covering nearly all the lanes by 2014.

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But while manufacturers of the less-intrusive "millimeter wave" machines found ways to use ATR software, backscatter machines have not.

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Backscatter machines use X-rays, while millimeter wave machines use radio waves.

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In the U.S., the TSA uses both types of scanners: 250 X-ray scanners and 264 millimeter wave scanners.

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These are the clear, cylindrical scanners using millimeter wave technology and sold by L-3 Communications.

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Rotenberg said he still has privacy concerns about millimeter wave machines, including what information is captured by the machine -- even if unseen by screeners -- and how long that information is retained.

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