Testifying before skeptical House members, two TSA officials said imaging machines used for passenger screening have software that prevents the full-body images from being retained, stored or transmitted.
The officials, Robin Kane and Lee Kair, also said a single screening from a "backscatter" imaging machine produces radiation similar to a dose from about two minutes of flying at 30,000 feet.
The chairman of a House Oversight and Government Reform subcommittee, Republican Rep. Jason Chaffetz of Utah, said he isn't convinced privacy is being protected.
"Nobody has to look at my grandmother naked to secure an airplane," said Chaffetz, a frequent critic of the TSA.
A Columbia University radiology researcher, David Brenner, testified that despite a low individual risk, it's possible that radiation from backscatter machines could cause cancer in 100 people a year.
Brenner, director of Columbia's Center for Radiological Research, called the number "a best estimate," but acknowledged "this number is quite uncertain." He added that the cancer risk to each individual is as low as one in 10 million.
When TSA security officials Kane and Kair testified they were unaware of TSA ever retaining full body images of passengers, Chaffetz demanded to know why the answer wasn't an unequivocal "no."
"I'm frustrated by the lack of candor," Chaffetz said.
The TSA has installed two types of explosive-detecting machines that produce full body images: the "backscatter" that emits radiation and millimeter wave machines that do not. The agency says that with no concerns about radiation exposure, it uses both types to foster competition between manufacturers.
TSA also said it is testing a new type of imaging that will only show anomalies rather than a full body image.
Marc Rotenberg, executive director of the Electronic Privacy Information Center, expressed doubt about TSA's contention that it does not save images _ which are viewed in a separate area away from public security lines.
"We've obtained from the U.S. Marshals Service more than 100 images" from a Marshals' scanner at the U.S. Courthouse in Orlando, Rotenberg said. They were among 35,000 images that the Marshals acknowledged _ in a Freedom of Information response _ that they retained from the Orlando screenings.
He added that TSA has acknowledged, in a Freedom of Information response, storing and recording images while testing the machines.
"TSA has 2,000 images. They don't want the public to see this," he said. The TSA has refused to turn over the images.
The Center has filed a lawsuit to stop the TSA from using scans that show a naked image of a passenger's body. The group contends the machines violate privacy laws, religious freedom and the Fourth Amendment protections against unreasonable searches and seizures.
The TSA officials, who refused to sit on the same panel as Rotenberg because of the lawsuit, said the advanced imaging machines are vital to keep up with terrorist tactics.
"We have witnessed the evolution of this threat from checked baggage, to carry-on baggage, and now to air cargo and non-metallic explosives hidden on the body," Kane and Kair said in a joint statement.