EU-funded VOXEL project develop an innovative way to create three-dimensional imaging without the high doses of X-ray radiation by adapting a technique called plenoptic imaging.
Doctors have used computed tomography scans, or CT scans, to greatly improve the diagnosis and treatment of illnesses such as cancer and cardiovascular disease. But a major problem limits their use: they deliver high doses of radiation that can harm patients nearly as much as their ailment.
Enter the EU-funded VOXEL project which set out to develop an innovative way to create three-dimensional imaging. The result is special cameras that can deliver 3D images but without the high doses of radiation.
‘Reports show that in Germany in 2013, although CT scans only represented 7 % of all X-rays performed, they conveyed 60 % of the radiation that patients received,’ says Marta Fajardo, project coordinator and assistant professor at the Instituto Superior Técnico in Lisbon, Portugal. ‘We built several prototype cameras. As an alternative to CT, they enable 3D X-ray imagines in very few exposures, meaning less radiation for the patient.’
A new perspective on 3D imaging
CT scans make images by taking thousands of flat, two-dimensional photos in order to reconstruct a 3D image. The problem is that each photo injects ionising radiation into the patient. As photos multiply, radiation levels rise.
To counter this, VOXEL’s breakthrough idea was to adapt a technique called plenoptic imaging to X-ray radiation. Plenoptic cameras capture information about the direction that light rays, including X-rays, are travelling in space, as opposed to a normal camera that captures only light intensity.
Because researchers can use the information about light direction captured by plenoptic cameras to reconstruct 3D images, there is no need to take thousands of 2D photos. Images of important structures like blood vessels can be made from a single exposure, lowering the average radiation dose significantly.
A major part of the work was using the right algorithms to manipulate the captured information. ‘First, we demonstrated that plenoptic imagining is mathematically equivalent to a limited-angle tomography problem,’ Fajardo says. ‘Then we could simply reformat plenoptic imaging as tomography data and apply image reconstruction algorithms to obtain much better images.’
But the biggest challenge remained engineering the cameras. ‘The higher the photon energy, the harder it is to manufacture the optics for a plenoptic camera,’ she says. ‘You need X-rays of different energies for different tasks.’ The solution was to develop one camera prototype that used lower-energy X-rays for tiny structures like cells. Then, another that used higher-energy X-rays for larger objects, such as small animals or human organs.
Less radiation, healthier patients
‘The low-energy X-ray camera belongs to a niche market,’ she explains. ‘But the high-energy X-ray prototype has huge medical potential, although it still requires some development.’
Results from the project, which was awarded a Future Emerging Technologies grant, will soon be submitted for publication in the international science journal Nature Photonics.>>