Going undercover

More than a century after their discovery, new uses are still being found for X-rays, with manufacturing being one of the latest sectors to adopt the technology, says E&T.

In June it was announced that Mexican officials had used X-ray scanning technology to uncover a large shipment of drugs hidden in the bodies of frozen sharks. Although it sounds bizarre, this incident highlights just how varied applications for X-ray technology can be. The technology has the potential to help in a whole range of situations - not just looking inside suitcases or checking for broken bones in hospitals, although this is what is often assumed.

One sector that is finding novel ways to deploy X-rays is the industrial sector. As X-ray technology itself develops, and the supporting electronics and software improve rapidly, there is a wide spectrum of industrial players finding new, inventive and sometimes surprising ways to exploit X-ray scanning technology.

In the industrial sector there is a straightforward reason to use the method: X-rays enable you to see inside components, objects or systems that are opaque or to examine products internally in a way that would be impossible with the naked eye or other vision inspection systems. For many industries the drive to see inside things is in order to pick up latent or hidden faults that cannot be identified simply by looking at or testing products. This could be anything from contaminants in baby food to misaligned auto components. In any of these cases the potential cost of not spotting these faults is massive.

The challenge in applying X-ray technology to industrial applications is different to healthcare and security applications. Of course anyone using X-rays wants to get the best images to help with the specific decision-making processes. However, time is an issue. Wasted time is inconvenient for healthcare and security; but wasted time in industry is wasted money. Real-time imaging is a critical concern for industrial X-ray engineers, and therefore achieving the best possible image in as short a time as possible is the desired goal.

Screening moves inline

While some products might have been screened using X-rays in the past, this typically happened as a final check at the end of the production line. The major development has therefore been the move to inline or online screening. This presents a whole range of new challenges and the potential for increasingly innovative X-ray solutions.

But such developments are not so much a convenience as a growing necessity. Customer expectations have increased to the extent that the demand is for products that won't fail in any way. Given the potential cost of faults, this has become a significant driver for industrial companies. Hence we have seen a proliferation of visual inspection systems and instrumentation systems, but ultimately it comes down to the component level. Here X-rays provide a unique solution. While there are certain specialist systems, such as ultrasound, that enable you to pick up specific kinds of faults in some situations, X-ray is the only nondestructive means to look inside closed objects in order to see a wide range of faults.

For example, medicines packaged in blister packs pose a serious problem for companies, because unfilled compartments could pose serious health risks and can also be a liability issue for the drug supplier. The aluminium foil used in the packaging eliminates a range of inspection techniques that could otherwise be used, including optical, microwave or RF.

Any inspection technique that is implemented will be required to see through the packaging, but be sensitive enough to detect the tablets. It also needs to be viable as a fully automated, high speed, inline inspection tool. To combat this problem, the 3DX-RAY company took its X-ray technology and developed a variety of software algorithms to identify rapidly and reliably any empty blisters, giving fully automated pass/fail detection. Using systems such as this, it is possible to inspect 400 blisters per second.

X-rays go 3D

Three-dimensional X-ray systems can be used in more complex applications, such as battery inspection. X-ray systems can accurately measure internal linear distances, alignments, the quality of internal electrical contacts, short circuits and misaligned components. The addition of a rotational and translation stage enables full 360º inspection of the component to take place in seconds.

New customer applications and demands have also driven significant advances in X-ray technology in the last decade. First and foremost, X-ray detector technology has improved dramatically and there are now completely new ways of acquiring images that did not exist before. Even in well-established X-ray techniques, such as line scanning, there have been significant advances in advanced digital processing techniques and sensor materials that have led to higher performance and more sensitive detectors. 

For example, digital X-ray detection can be loosely classified into either indirect or direct conversion systems. Indirect detectors have a scintillator that first converts X-rays into visible light. That light is then converted into an electric charge by means of photodetectors such as PiN photodiodes. Direct conversion detectors have an X-ray photoconductor that directly converts X-ray photons into an electric charge.

For indirect detectors, such as those generally deployed in line scanning techniques, recent advances in scintillator materials have brought forward devices that can convert an X-ray photon into a usable electrical signal with much higher efficiency. One example of these new materials is the transparent ceramic of Lu2O3:Eu. This has an extremely high density, with a light output in a narrow band at around 610nm, close to the maximum sensitivity of silicon-based photo detectors, maximising the conversion of light generated from a X-ray photon into a usable electronic signal. These new scintillator materials offer the opportunity for producing considerably more sensitive detection systems.

Direct conversion for higher resolution

Similar advances have also been seen in direct conversion technology with the gradual introduction of full-field imaging plates based on materials such as amorphous selenium. In a direct converter the X-ray photons interact with the material and create an electrical charge. That charge is then guided by a bias charge across the material directly to the readout electronics. Conversely, in an indirect system the X-ray interacts with the scintillator producing visible light that will be scattered and dispersed as it passes through the bulk of the material toward the photosensitive electronic detector. Direct detectors will therefore produce images with inherently less 'blur' and potentially offer higher resolutions for a given radiological geometry.

These improvements have also provided more scope to improve the design of X-ray systems, enabling smaller form factors and lower cost products. Almost as important has been the rapid improvement in the processing power available to X-ray engineers, as this has opened up new avenues to explore, such as the integration of advanced, high speed, in-line inspection systems into customers' production lines.

A further key factor has been the continuing popularity of X-ray technology in the healthcare and security sectors, as this has helped to drive down the cost of developing and manufacturing X-ray technology in general.

Cauliflowers ripe for the picking

These advances have been major enablers for some of the more unusual projects. For example, 3DX-RAY worked with two agricultural machine manufacturers to find a more economical and less wasteful way of selecting cauliflowers that were ready for picking for the supermarket shelf.

Usually it is very difficult to tell if a cauliflower is ready for harvest, as leaves envelop the vegetable. But the use of X-ray cameras enabled the company to develop a method of automatically identifying which cauliflowers were of the optimum size - while they were still growing - and a system to control the cutting heads to crop and later trim the vegetables.

Another innovative application is with a leading supplier of nuclear medicines and image-enhancing materials for use in medical treatment and diagnostic procedures. In disposing of its own and customer's waste it is necessary to meet, and often exceed, the strict regulatory requirements for the disposal of potentially hazardous materials through its waste decommissioning departments.

The requirements for a solution are relatively simple: without opening every sack of waste, produce an image of the contents so that a screener can readily identify the presence and location of any non-compliant items, and if any are found, also provide a visual representation of the surrounding items to ensure its safe and rapid retrieval through a hand search. Using 3D X-ray imaging techniques it is possible to deliver exactly this service.

These are just some of a myriad of applications that X-ray scanning has been used for. Whether it is vegetables, batteries, cars and catalytic converters, radioactive waste or determining the 'wrinkle' in metal cans, there is a vast quantity of objects that people need to see inside, and X-ray is proving itself a robust solution to even the most obscure problems.

Nick Fox is CTO of industrial X-ray specialist 3DX-RAY

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