TU Delft sharpens optical images

08 December 2015 by Communication TNW

Researchers at TU Delft have succeeded in improving the capabilities of optical coherence tomography (OCT), an imaging technique used to gauge retinal health. The researchers, from the faculties of 3mE and Applied Sciences, publish their findings in the journal Optics Letters on 15 December.

The researchers of TU Delft are focusing on improving optical coherence tomography (OCT). This is a cross-sectional imaging technique which works in much the same way as ultrasound scanning, but using light rather than sonic waves. “By far the most important applications of OCT are in ophthalmology,” says Jeroen Kalkman of the Faculty of Applied Sciences (ImPhys department), one of the authors of the paper. “It enables hospitals to examine the state of the retina, in particular its blood vessels.”

Wavefront sensor
There is one problem with the current OCT method, though. To achieve high-resolution images of the retina, the patient’s pupil has to be widened artificially. But this in turn produces aberrations, which distort the image.

“This issue can be solved by using a combination of a wavefront sensor and an actuator,” Kalkman explains. “That’s a technique also used in astronomy to reverse distortions in images of stars. And it works well enough, but it also has some significant disadvantages.” Specifically, it is fairly complex, quite expensive and degrades the final image.

Smart algorithms
According to Professor Michel Verhaegen of the Delft Centre for Systems and Control at the Faculty of 3mE, another of the paper’s authors, “What you would rather do is utilise the information about the wavefront which is contained in the original image, without having to deploy that expensive sensor. Everything you need is actually there already.”

“It’s a question of developing smarter algorithms to recover the information,” Kalkman continues. “Doctoral candidate Hans Verstraete and researcher Sander Wahls have been creating and testing new algorithms, with some surprising results. The best working one they have come up with gives us good, sharp images at least ten times faster than previous methods being used under the same conditions. And with no need for a wavefront sensor!”

Rods and cones
At the same time, Kalkman stresses that this publication is only a first step towards practical application of the team’s work in optical medicine. “It could take ten years before this technique becomes a standard ophthalmological practice. At the moment we are trying to improve it even more, so that in the future we can obtain good images of the retina’s well-known rods and cones, which are only about 5 micrometres in size.”

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