New ghost imaging technique could make x-rays safer

While the huge diagnostic benefits of x-rays are undoubted, they are the most common human-made source of radiation affecting the population.

The advantages of the many forms of medical imaging diagnosis such as CT, fluoroscopy and mammography are limited by the potential health hazards of ionising radiation.

Health risks such as skin burns and acute radiation syndrome can occur when doses of radiation exceed certain levels, while low doses of ionising radiation over a prolonged time can increase the risk of longer term effects such as cancer.

A research team led by Dr Daniele Pelliccia from RMIT’s School of Science has reported the first experimental demonstration of x-ray ghost imaging. The technique will enable the use of conventional detectors, which are faster and more sensitive than cameras for clinical x-rays, to reduce the amount of x-rays that are required for a scan

“Conventional imaging works by using a camera to measure the distribution and colour of light that has interacted with objects,” Pelliccia said.

“Ghost imaging instead is an indirect technique, in which most of the light used for the experiment never actually interacts with the sample. To achieve this, we need to use not one but two identical light beams (or x-ray beams) that are highly structured with some form of detailed pattern.

“The first beam is sent to the sample, and only the total intensity transmitted or reflected by the specimen is recorded by a point detector known as a ‘bucket’. Next, the second beam is measured by a camera without interacting with the sample. This process is repeated many times, changing the pattern in the illumination each time.

“In this way the sample image is never measured directly: the camera always measures an empty beam. Indeed, most of the photons in the illumination beam never pass through the object to form an image.”

The sample image can still be retrieved through a computer which processes data from the outputs of the two detectors. The trick is that the illumination patterns are known, and this information can be used to extract the actual sample image, the ghost image.

Ghost imaging was previously realised using visible light and infrared, and it is being actively studied for satellite imaging through turbulent atmosphere and remote sensing.

The research team includes scientists from the European Synchrotron in Grenoble, France, where the experiment was conducted, and from Monash University and Soleil, the French synchrotron facility. The work is supported by funding from RMIT University and the Australian Synchrotron

The findings of the first experimental demonstration of x-ray ghost imaging have been published in Physical Review Letters, in the prestigious Editors’ Suggestion section of the journal. 

The researchers are now endeavouring to translate their results to conventional x-ray beams, to be used in clinical practice.

Story: Pauline Charleston