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An excess of X-rays is bad for your health 鈥撀爓hich is why radiographers step out of the room before they zap you. Now a ghostly physics trick could reduce the dose needed for a clear image, because it requires only聽a small portion of the X-rays to pass through the object being imaged.

鈥淕host imaging has several benefits: reduced dose, super resolution, cheap and faster data collection,鈥� says Andrew Kingston at the Australian National University. Ghost imaging has been demonstrated with visible light rays, but Kingston and his colleagues showed for the first time how it could be done with X-rays.

They started with a series of聽X-ray beams, each聽in a聽unique, random, chequerboard-like pattern. Most of the rays in each beam reach a conventional digital camera that records the precise details of the chequerboard-like patterns. A small portion of the X-rays are reflected towards the object that is being imaged. They pass through the object and enter a camera with one large pixel that measures only the total brightness of the light.

By combining the chequerboard-like images that end up on the conventional camera and聽comparing them with the brightness captured by the single-pixel detector, the researchers are able to compute a full 3D image of the interior of the object. They tested their technique on a cylinder of aluminium, taking 28,000 measurements.

鈥淭he 鈥榞hostly鈥� thing is that most of the X-rays never pass through the object, yet all of the X-rays are used to construct the 3D ghost image,鈥� says David Paganin at Monash University in Australia, who also worked on the study.

This is similar to computed tomography (CT) scans that are in use today, Kingston says, but it has the potential to provide higher-resolution images with lower doses of X-rays.

The more you know about the object being ghost imaged, the fewer X-rays聽you need to聽find an anomaly. That means that聽ghost imaging could lower the dose for cancer screening, assuming we can get a decent model of聽what healthy tissue should look like in a person of a particular聽age and gender, Paganin says. This could also be useful for imaging delicate biological samples that can degrade with too much X-ray exposure.

Daniele Faccio at the University of Glasgow, UK, says this is a nice extension of ghost imaging, but it may not necessarily lower the dosage of the X-rays required to get a high-resolution image. 鈥淭here is no free lunch,鈥� he says, adding that an image comparable to standard CT scans may require more data.

鈥淏ut we should also bear in mind that there might be other reasons for preferring ghost tomography to standard tomography. If dosage per exposure is what counts, and not total integrated dosage, then ghost tomography may indeed have an advantage,鈥� he says.