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Florian Schwarzhans, Sylvia Desissaire, Stefan Steiner, Hemma Resch, Michael Pircher, Christoph K Hitzenberger, Clemens Vass, Georg Fischer; Real time eye-tracking and blinking compensation for artefact-free acquisition of polarisation-sensitive OCT volumes. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6082.
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To implement a technical solution for eliminating movement artefacts during acquisition of volumetric PS-OCT scans. This also includes detecting movement too large for the scanner to follow, as well as loss of signal caused by blinking.
The system used was a custombuilt prototype PS-OCT operating at 860nm with an A-Scan rate of 70kHz and a field of view of 28°x21° (1024 A-Scans x 250 B-Scans), with an integrated line scanning laser ophthalmoscope for tracking operating at 790nm and a refresh rate of 60Hz.A real-time tracking algorithm with sub-pixel accuracy based on frequency space registration techniques using a set of automatically selected and trained LSLO images as reference and the B-Scan corresponding LSLO image as moving frame was implemented on the graphics card using the CUDA framework on C++. The calculated spatial displacement is sent to the scanner to compensate for the detected motion. Additionally a quality parameter is calculated to indicate whether the current B-Scan can be accepted or if it needs to be retaken. Reasons for a low quality measure can be very large movement or loss of signal e.g. caused by blinking.
Several subjects were scanned with and without tracking, with the image centred at various retinal locations. The accuracy of the algorithm was analysed by scanning a single B-Scan position 250 times while the subject focused on a circularly moving fixation target with and without tracking turned on. Fig1 (left) shows that without tracking the scanned area moves with the gaze of the eye, whereas with tracking turned on the same position was scanned for all 250 B-Scans with next to no offset (Fig1 right).For demonstrating the quality control a whole volume scan was acquired with intentional blinking during the acquisition, again with and without tracking turned on. Fig2 (left) clearly shows the missing regions in the projection image caused by the blinks. With tracking turned on the B-Scans with low quality are automatically retaken, resulting in an artefact-free projection image (Fig2 right).
A real-time eye tracking technique, requiring no further operator actions on the tracking setup, with high accuracy and automatic rescan of low quality measurements was presented. This method has the potential to significantly increase the quality of acquired OCT measurements as well as to reduce the total imaging time.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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