New technique lifts x-ray fog

A chicken wing seen with a traditional x-ray (left) and using the new technique

Technology developed by Swiss-based researchers means that x-ray images could be sharper, offering better diagnostic results in the future.

Instead of the traditionally blurred pictures taken by radiologists or even security specialists, observers will be able to see the finer details of the person or object.

Researchers from the Federal Institute of Technology in Lausanne and the Paul Scherrer Institute (PSI), led by Franz Pfeiffer, have now demonstrated the practicality of a high-resolution technique known as dark-field x-ray imaging.

Normal x-rays only reveal shapes based on how much of the radiation passing through the structure under observation is absorbed, producing a contrast. But this produces foggy images with little fine detail.

The dark-field technique, already used for some microscopes using visible light, looks on the other hand at how the beam is modified when it passes through the sample.

“By analysing this beam, we can learn something about the microstructure,” Pfeiffer told swissinfo. “We can out find out for example if it is porous or has micro-cracks.”

According to the German-born researcher, these are the kinds of details that traditional x-rays cannot pick up.

Synchrotrons

The dark-field technique has been known for more than five years, but until now has only been possible using large particle accelerators known as synchrotrons, such as the one used at PSI.

But producing x-ray beams with these machines is inefficient and expensive, making the whole process of little practical use.

To overcome this drawback, Pfeiffer’s team designed small silicon filters containing tiny structures etched into their surface that work with conventional x-ray tubes, as can be found in hospitals or at security checkpoints.

Four images are taken of the sample, then software is used to analyse the results and produce the final picture.

There are plenty of potential applications, and not just in the medical field, although Pfeiffer says this is mostly likely place to start.

“You could use it to detect osteoporosis at an earlier stage for example,” he added. “Doctors need to know a patient’s bone porosity, density and if there are small fractures already present in the bones.”

Medicine and security

Other applications could include detection of tumours, and revealing dangerous cracks in materials used for aircraft propellers or turbines.

Security specialists could find the technology interesting too. Airport scanning devices would benefit from the extra resolution.

“You could distinguish between substances such as suntan lotion and powder-like ones such as drugs or even explosives,” Pfeiffer told swissinfo.

He says that adapting dark-field imaging to existing x-ray systems would not be a major technical problem. But producers of this equipment would have to be convinced that the investment is worthwhile.

“It should be possible to add the filtering system to current radiological devices,” says Pfeiffer. “But manufacturers would have to consider that it would still need some development before it could be produced.”

So how long will it be before users see higher resolution x-rays? Probably sooner than most people think according to the researcher: for breast scans the technique is already applicable, while other radiological tests should be possible within the next two years.

swissinfo, Scott Capper

Taking a closer look

X-ray images normally reveal the way different materials, including body tissue, absorb x-ray radiation. Areas that absorb this radiation strongly come out as white while those that don’t are black.

The new technique builds on dark-field microscopy, which is used by biologists to study cells under a light microscope.

Dark-field microscopy manages to improve image contrasts by only taking into account light scattered by a sample.

Pfeiffer’s technique is much the same: x-ray radiation that passes through the sample is ignored, and only rays that are scattered are measured.

The process gives better resolution, but also requires a stronger total dose of radiation, the only obvious drawback.