Thermal imaging may help catch terrorists

Deboshree Basu-Choudhuri London

A revolutionary new lie detector, incorporating a high definition thermal imaging camera that can detect thermal pattern changes around the eyes, has been developed (Nature 2002;415:35).

To test the camera 20 volunteers were asked to commit a mock crime--to stab a mannequin and grab $20 from its hand--and then to proclaim their innocence. The camera imaged their faces while they were questioned (figure). Volunteers in a control group were not aware of the crime. The camera correctly categorised 83% of the volunteers (75% of the test group were correctly found guilty and 90% of the control group were correctly found innocent).

Thermal images from the camera obtained before (top) and after (bottom) lying in response to the question:
"Did you steal $20?" T_min =29°C (black and T_max=38°C (cyan areas show the highest temperatures)

Thermal imaging cameras enable rapid analysis of changes in blood flow around the eyes. Auditory startling can, however, produce similar blood flow changes to lying (Lancet 2001;357:1757). If thermal changes occur independently of auditory startling then the camera can be used as a lie detector. The near instantaneous rush of blood to the eyes, during shock or lying, is suspected to be the result of adrenaline (epinephrine) mediated facial vasodilatation. It is the thermal signature of the primitive "fight or flight" response.

When a person is truthful there are no significant physiological changes, and the body functions normally. This is not the case when a person lies. Polygraph lie detectors measure changes in pulse rate, respiratory rate, and skin conductance, and they have a similar success rate to the thermal imaging camera.

Identifying suspected terrorists is the aim of high throughput security screening at airports and building entrances. At present, answers to questions such as, "Are you carrying any sharp instruments or explosives?" are assessed subjectively and deception is difficult to detect.

Using a thermal imaging camera can be quicker than using a polygraph and the results can be analysed rapidly by trained staff without the need for physical contact. The experiment to test the thermal imaging camera success rate was based on a small sample, but the results are encouraging and the potential for security applications is great.



studentBMJ 2002;10:1-44 February ISSN 0966-6494