X-Ray-Based Detection Systems

The standard airport hand-baggage scanner has a fan-shaped or scanning x-ray beam that is transmitted through the object to be inspected. The absorption of x-rays is usually measured by a line of detectors, and a high-resolution image, derived from the degree of absorption of the beam, is produced. The image depends primarily on the density of objects located in the bag along the beam of the x-ray. These devices cannot distinguish between a thin sheet of a strong absorber, such as a metal, and a thick slab of a weak absorber. Simple x-ray systems rely on humans to serve as pattern recognition devices; in the absence of advanced computer pattern recognition techniques, they are very dependent on human factors, i.e., the training and quality of the observer.