A Transportation Security Administration agent scans airline passenger Kelsi Dunbar on Friday using the new backscatter X-ray technology that can see through people's clothes and show the body's contours at Sky Harbor Airport in Phoenix.

Phoenix ? The Phoenix airport on Friday became the first in the United States to test new X-ray technology that can see through people’s clothes and show the body’s contours with blush-inducing clarity.

Critics have said the high-resolution images created by the “backscatter” technology are too invasive. But the Transportation Security Administration adjusted the equipment to make the image look something like a line drawing, while still detecting concealed weapons.

During the testing, the machine will be used only as a backup screening measure. Passengers who fail the standard screening with a metal detector will be able to choose between the new device or a pat-down search.

“It’s 100 percent voluntary, so if the passenger doesn’t feel comfortable with it, the passenger doesn’t have to go through it,” TSA spokesman Nico Melendez said.

Passengers selected for screening by the device are asked to stand in front of the closet-size X-ray unit with the palms of their hands facing out. Then they must turn around for a second screening from behind. The procedure takes about a minute.

“It seems faster. I’m not uncomfortable with it,” said Kelsi Dunbar, 25, of Seattle, who chose the machine. “I trust TSA, and I trust that they are definitely trying to make things go quickly and smoothly in the airport.”

But one expert said the machine’s altered image is ineffective, while the clear picture is an invasion of privacy.

“The more obscure they make the image, the more obscure the contraband, weapons and explosives,” said Barry Steinhardt, director of the Technology and Liberty Project at the ACLU in Washington, D.C. “The graphic image is a strip-search. You shouldn’t have to be strip-searched to get on an airplane. Millions of Americans would regard them as pornographic.”

The security officer who works with the passenger going through the screening will never see the images the machine produces. The pictures will be viewed by another officer about 50 feet away who will not see the passenger, the TSA said.

The machine cannot store the images or transmit them.

“Once we’re done screening the passenger, the image is gone forever,” Melendez said.