Magnetic Resonance Technology: a replacement for existing airport screening systems?23 Apr 2012
Just imagine that there were a technology that could screen passengers and baggage at the same time without the need to divest or extract articles for separate examination. Science fiction? Perhaps not. Viktor Vegh explains how MRI scans, routinely used in medical examinations, may hold the solution for the aviation security screening solution of the future.
The technology of current airport screening systems was developed in the 1970s and it is extensively used across the world today. Although we have seen the advent of improved instrumentation, primarily based on X-ray technology, the screening process is still erroneous. A false judgement of a possibly hazardous and dangerous substance can be due to an incorrect instrument reading (Type I error) or by accepting to transport a person or baggage when they should have been subject to secondary scans (Type II error).
Type I and Type II errors have to be reduced to improve screening precision at airports.
To improve the detection of liquid explosives, for example, new X-ray scanners utilising large numbers of detectors have recently been developed. These systems enable a reduction in Type I errors through an improvement in object classification by comparing screen data to a database of substances. Importantly, if a substance has not been classified (which means listed in the database) the system fails. To combat Type II errors, a process that removes human judgement needs to be incorporated as part of airport security. Human judgement involves the examination of X-ray images, resolution of metal detector alarms, performing body scans with a metal detection wand, physically searching baggage, and maintaining order in an otherwise hectic environment. Therefore, it is not hard to imagine that Type II errors are frequent in airport screening.
A robust solution is one that is capable of screening for various substances.
For decades the National Research Council has studied airline passenger security and maintains that the ideal detection system in airports is one that is capable of identifying both metallic and non-metallic objects of hazardous or dangerous nature with a low level of Type I errors. Recently, a large amount of emphasis has been placed on monitoring liquids, as they may be used in the manufacture of liquid explosives. The screening information provided to instrument operators should be delivered rapidly, which is sufficiently informative to be able to make an accurate human judgement. It is unclear whether the well-established X-ray technology, or recent fluorescence developments for airport screening, can fill the gap.
Magnetic resonance (MR) technology has also been around since the 1970s, and it is routinely used in hospitals to non-invasively scan patients in detail. Scans are primarily used for diagnosis, which is not dissimilar in nature to diagnosing objects, such as determining the contents of baggage. This is because an MR image of a patient can, for example, reveal locations of tumours, which are substances elucidating a different chemical structure to the rest of the body. Hence, the screening process is established, but its application outside medical imaging has been limited.
The MR technique of nuclear magnetic resonance (NMR) spectroscopy probes the bulk chemical environment of an object, from which the object make-up can be deduced. Magnetic Resonance Spectroscopy (MRS), on the other hand, can localise the chemical environment and deduce its constituents. Hence, MR techniques are capable of resolving information about a sample in 3D with great accuracy. These abilities provide great advantages over 2D X-ray scanners. So, why is it that we do not have MR based screening devices in airports? And, might they be the future?
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