There is an urgent need to devise technologies to identify individuals intending to perform acts of terrorism

Mayo clinic team

Blood flow to the surface of the skin around the eyes increases when someone tells a lie.

The tiny hot spots are invisible to the naked eye but can be measured by thermal imaging, says a team led by James Levine of the Mayo Clinic in Rochester, Minnesota.

The researchers believe the new test could be used undercover at airports to identify potential terrorists.

They write in the journal Nature: "There is an urgent need to devise technologies that can be used for automated, high-throughput screening to identify individuals intending to perform acts of terrorism."

At present, airports have to rely on a passenger's response to brief questions such as: "Did you pack your own bags?"

Hands-off approach

The new system was tested on 20 volunteers who were told to carry out a fake crime.

The individuals were asked to stab a mannequin and rob it of $20, before pleading their innocence when questioned.

Another group of people who had no knowledge of the crime were also tested with thermal imaging.

Using the equipment, the scientists managed to correctly identify as guilty seventy-five percent of the "criminals", while 90% of the "innocent" group were successfully cleared of blame.

The results were as good as those from a traditional polygraph, or lie-detector test.

The best technology we have available to us... is the human brain

Philip Baum, Airport Security International

Polygraphs, which have been used for many years, are accepted in some courts of law.

They monitor physiological signs like breathing, sweat production and cardiovascular activity. But they have to be carried out by highly trained operators and the results take time to analyse.

The new method has the advantage that it is instant and can be used without physical contact by untrained staff in a variety of different situations.

Philip Baum, Editor of Aviation Security International, said further trials of the test were needed under real-life conditions.

He told BBC News Online: "It shows promise but there's a long way to go.

"We can't become overly reliant on technology except for the best technology we have available to us and that is the human brain."