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Line-field OCT assists clear diagnosis of eye diseases

16 Aug 2017

Medical University of Vienna method corrects for aberrations digitally without adaptive lenses.

A new OCT technique developed by the Medical University of Vienna could help to provide aberration-free cellular-level resolution images of the retina, as an aid to the diagnosis of several different eye diseases.

Termed line-field OCT (LF-OCT), it tackles the unhelpful image aberrations to which existing techniques are prone through the application of a non-iterative digital aberration correction (DAC) process, designed by the project. The work was published in Optica.

"Our new technique enables us to make digital corrections without the need for expensive hardware-based adaptive lenses," commented Laurin Ginner of MedUniVienna.

"The linear illumination that is used allows very rapid frame rates, which are extremely important for these corrections. This enables us to correct aberrations over the entire three-dimensional volume of the retina."

At present, the only effective way to achieve high isotropic resolution in three dimensions during OCT retinal imaging is to incorporate adaptive optics into the procedure, countering the significant optical imperfections in the eye's natural optics. However, this approach can prove both complex and costly.

Computational correction of these aberrations has been an attractive alternative for some time, but has remained challenging to use for real-world in vivo scenarios, where the patient's eye makes numerous involuntary movements that interfere with the goal of pristine imaging.

In its published paper, the project describes an approach based on parallel OCT - an approach in which the sample is illuminated over a region rather than a raster-scanned point - using line-field illumination. This is combined with a DAC process designed to work over the full retinal volume, based on a core algorithm that does not require knowledge of system parameters such as pixel size, focus distance, or refractive index.

OCT angiography reveals valuable blood flow data
Tests on volunteers showed that applying this combination of LF-OCT and DAC could successfully be used at scan rates of up to 2.5 kHz, an essential factor if DAC is to adequately handle in vivo data and allow accurate imaging when it is applied to patients.

The project also investigated using the technique in OCT angiography (OCTA), in which multiple B-scans are rapidly acquired at the same position and then combined to reveal the fluctuating signal of flowing blood. The non-invasive nature of OCTA and its natural fit with established OCT procedures should allow it to become a major topic in ophthalmic imaging and diagnosis, according to the MedUniVienna group, and OCTA modalities are already of interest in clinical areas away from ophthalmology too.

When the project applied its DAC methods to functional OCTA data, it was able to successfully improve lateral resolution and increase the vascular contrast in out-of-focus regions, proving the potential value of the technique.

Team leader Rainer Leitgeb of the Christian Doppler Laboratory for Innovative Optical Imaging and its Translation into Medicine (Optramed), believes that a range of clinical applications might now benefit from the improved OCT modality.

"This technique can conceivably also be used for diagnosing neurodegenerative diseases," he said. "The eye is the window into the brain. Our hope is that the higher resolution will help to improve diagnostic accuracy in general."

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