In the medical arena, initial exams are usually done by X-rays. But when doctors need a more comprehensive view to detect cancer or examine small and complex fractures, what do they use? They turn to the cross-sectional and 3-dimensional (3-D) images generated during a Computed Tomography (CT) scan. The same theory holds true for CT explosives detection systems (EDS).
Comparing single and multi-view x-ray to CT EDS
In today’s busy airport ecosystem, there is no time to waste. High-precision, CT EDS solutions produce 3-D representations of everything in each bag that is scanned. This helps operators make critical, informed decisions. It’s a simple premise with important results: the more they can see, the greater their ability to find threats. The more they can see, the greater their ability to quickly clear items that are non-threats.
| Non-CT X-ray producing 2-D images | CT X-ray producing 3-D images | |
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In comparing the visual clarity of 3-D images to 2-dimensional (2-D) imagery of single or multi-view X-ray the differences are clear. With 2-D, it’s difficult to differentiate between objects, especially in cluttered luggage. In contrast, the 3-D images leads to quick identification and better understanding of the relationship between objects. |
| Creating a 2-D image | |
| How are 2-D images created in non-CT X-ray? Substances are identified by measuring the attenuation (reduction in intensity) of X-rays as they pass through the substance. The results are displayed in a 2-D image with different colours or grayscale levels to highlight different substances. Challenges with 2-D X-ray include: • Higher false alarm rates (FAR), resulting in decreased operational efficiencies. • Difficulties in differentiating between objects, as objects become super-imposed in cluttered bags. |
2-D image from single or multi-view x-ray  |
Creating a 3-D image
With CT EDS, thousands of X-ray measurements are taken from all around each item. These measurements are used to create a 3-D image of the entire item and its contents. A 3-D CT image is constructed from hundreds of 2-D cross-sectional images, called slices. These slices are in reference to what the image being scanned would look like if it were sliced open.
Benefits include:
• Automatic, accurate detection and categorisation of threats using the fundamental physics of CT, density measurement and comparison to known densities of threats.
• Ability to identify and quantify substances with much greater accuracy and a clean, clear actionable image.
• Better clear rates as operators can see the object from any angle and therefore remove obstruction.
• Decreased automatic FAR.
• Gives operators the ability to manipulate and rotate the image, and individual items in the bag, in a way that feels natural and intuitive.
3-D image from a CT X-ray
Evolving OSARP protocols
The benefits of higher detection offered in Smiths Detection’s CT EDS systems create the need for new on-screen alarm resolution protocols (OSARP) to further enhance operator performance.
Smiths Detection’s OSARP improves screeners’, performance in the presence of highly-cluttered passenger bags.
Object Oriented viewing, which is the basis of modern OSARP, helps operators:
• Easily evaluate a set of rules relating to the alarming object and its surroundings.
• Follow rules that are simple, measurable, and easy to memorize.
• Follow a fixed order of on-screen image tools on the EDS graphical user interface and seek proof of the alarming object’s innocuousness.
The benefits of 3-D images produced by CT EDS systems facilitated by an advanced OSARP are clear: lower FAR, better clear rates, and more accurate detection. As threats continue to evolve in complexity, equipping operators with the latest tools and technology helps ensure both safety and overall operational efficiencies. 
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