VOA标准英语2010年-Airport Body Scanners Called Safe If P（在线收听）

"Compared to the dose level of a medical chest x-ray, a backscatter scan is thousands of times lower."

Since the Christmas Day attempted bombing of a U.S. airliner, airports are looking for ways to tighten security.  One method being adopted by some and considered by others is the full body scanner.  A Johns Hopkins university professor says the scanners can be used safely and protect privacy at the same time. 

A young Nigerian – Umar Farouk Abdulmutallab – pleaded not guilty early this year to charges he smuggled explosives aboard an airliner by hiding them in his underwear.  He was traveling on a Northwest Airlines flight from Amsterdam to Detroit.  There were 300 people on board.

Many say a full body scanner would have detected the explosives before he boarded the plane.

However, the scanners have raised questions about safety and privacy.  For example, would the scanners give passengers large doses of x-rays?
   
Mahadevappa Mahesh says no. He’s chief physicist at Johns Hopkins Hospital in Baltimore, Maryland, and associate professor of radiology and medicine at the Johns Hopkins School of Medicine. 

He says two technologies are currently being used in the scanners.  One is Millimeter Wave Technology, the other is Backscatter Technology.

“The Millimeter Radio Wave Technology does not does not use x-rays.  The radio waves are similar to the radio waves produced by cell phones and so forth.  The second one, the Backscatter system, uses x-rays to scan,” he says.

The backscatter system, he says, provides good images.  But some worry about the dose of radiation a person might get by standing in front of a full body scanner.

“The x-rays are not strong (enough) to penetrate the body.  They just reflect off the body.  X-rays are captured by a detector and the detector creates an image,” he says.

But just how safe is it?

“The radiation dose levels in these body scanners are quite low.  Let me compare it to a medical chest x-ray.  Compared to the dose level of a medical chest x-ray, a backscatter scan is thousands of times lower.  The other way to put it in perspective is one has to undergo nearly a thousand to two thousand of the backscatter scans before they get a dose equaling the one chest x-ray,” he says.

The Johns Hopkins physicist says everyone is exposed to radiation everyday and at much higher doses than those emitted by the backscatter scan.

“There’s cosmic radiation, radiation from the earth and so forth.  Compared to that, we need really 100 to 200 scans to be equal to one day of background radiation,” he says.

And he says from take-off to landing, you’re being dosed with enough radiation equal to 40 to 80 backscatter scans. 

Privacy

Mahesh says because the radiation emitted is so low, the security benefits far outweigh the risks.

 
AFP
This file combination of images taken on October 13, 2009 shows an airport staff member (L) demonstrating a full body scan at Manchester Airport in Manchester, England

“Typically, they are installing two of them. So, simultaneously they can take the front and back image.  So, anything taped onto the surface of the body should show up on the image.  That’s the idea,” he says.

It’s those images that have raised concerns about privacy.  In other words, who sees them?  Professor Mahesh believes these concerns can be addressed.

“In the airport, they’re trying to keep these viewing stations far away from the scanners.  So the same security guy who’s asking a person to go through the scan is not the one who’s seeing the images.  Therefore, it is remotely seen somewhere in a controlled area where the guys who are watching these images are seeing nothing but these images all day,” he says.

And, he says, the images can be adjusted somewhat to enhance privacy without losing the security benefits.

“Some of the images I have seen are more like a ghost image, with anything taped on the surface (of the body) highlighting.  That way it will negate some of the revealing details of the body.  These manufacturers are also guaranteeing that the systems do not have a long-term saving mechanism.  So the images are not saved and they’re supposed to be purged then and there, once the screening is done,” he says.

The Johns Hopkins University professor does warn, however, that the scanners must be properly maintained to ensure radiation emissions remain low.

“For example, if the scanners are installed in some African country and after two years it breaks down and somebody comes and does the repair, it needs to be verified by a third party so that radiation dose levels are within standards,” he says.

Mahesh has published his findings on airport full-body scanners in the British Medical Journal.