WHEN it was first unveiled four years ago in the US, it was called the 'full-monty X-ray'.

Not many were happy with it.

Even though Ms Susan Hallowell, the director of the US Transportation Security Administration's (TSA) security laboratory, showed her own X-ray image to demonstrate the technology to reporters, it did not make the cut.

The plan to put the machine in US airports was put on the backburner.

The reason: It showed too much.

On Friday, an improved version of the X-ray scanner was officially installed in Arizona's Phoenix airport.

LINE DRAWING

In the new scanner, the images have been adjusted to look something like a line drawing while still detecting concealed weapons.

The TSA will test the machine in Phoenix for 60 to 90 days before deploying machines in Los Angeles and New York's John F Kennedy Airport for additional testing.

'Every day the bad guys are working and improving their tools. We need to continue working to improve ours and introducing this technology is part of that work,' said TSA regional spokesman Nico Melendez.

Passengers selected for screening are asked to stand in front of the closet-size unit with the palms of their hands facing out.

Then they must turn around for a second screening from behind. A tiny laser beam scans the passenger from head to toe. The procedure takes about a minute.

A green or red light - for pass or fail - is pressed and shows up at the screening location.

During testing, the machine - costing US$100,000 ($154,000) will be used only as a backup.

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 per cent voluntary,' said Mr Melendez.

The first volunteer for scanning was a Vietnam War veteran traveling with his wife for a 40th wedding anniversary trip.

'He didn't have any problem with it whatsoever,' Mr Melendez told a local TV station.

During the process, light grey silhouettes produced by scans appeared on computer screens in a secure room a short distance away.

Those being scanned had the option of using a rectangular piece of lead to block imaging of their crotch.

One expert said the machine's altered image is ineffective, and the clear picture is an invasion of privacy.

'The more obscure they make the image, the more obscure the contraband, weapons and explosives,' said Mr Barry Steinhardt, director of the Technology and Liberty Project at the ACLU in Washington, DC.

TSA officials said they had worked with industry specialists to blur any images of body parts generated by the scan, and likened the resulting picture to a 'chalk outline' of a person.

It is not known if this machine will be adopted in airports in other parts of the world, including Changi.

Officials said the computer does not have the ability to save or store images, a concern expressed by privacy-rights groups.

Airport travellers had mixed opinions about the new device.

Some hoped it wouldn't slow down the process of getting through security. But very few seemed to have privacy concerns.

'If it's something that's going to improve safety, then I don't have any problem with it,' said Ms Ashley Houston, 32, as she waited for a plane to Albuquerque. 'I have nothing to hide.' - Wire services.