Pyramid-based stitching approach of multiple PS-OCT volumes for wide field PS-OCT data

Abstract

Purpose : To implement a technical solution for stitching a set of volumetric PS-OCT scan projections acquired at different retinal positions to generate wide field projection images of polarization data.

Methods : The systems used were a custom built 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 and a Nonmyd WX-3D fundus camera.
Volumetric OCT data was acquired at 7 different fundus positions with 3 scans per position for added signal quality totalling in 21 volumes. A 45° field of view fundus image was used as reference for stitching. As a first step all 3 volumetric intensity OCT projections are registered against one another, using a frequency space rigid registration technique and an average intensity projection for this sector is calculated to achieve a higher signal to noise ratio. This image is then compensated for optical distortions and registered against the fundus image. To remove residual optical distortions, the image is split in 4 quarters and each quarter is registered to the fundus once more, considering a probability map as to where that quarter should be in the fundus image. This process is recursively repeated 3 times generating a total of 149 registration point pairs. After filtering out bad matching point pairs a second order polynomial is estimated in order to get the transformation allowing for the best registration result. This process is repeated for all 7 sectors.

Results : Several subjects were scanned and stitched and the results were visually examined by looking for double contours of the retinal vessels on the stitched image. Even though the stitched images cover a wider field of view (up to 50°) than the original fundus image they are stitched correctly up to the outer most part of the reference image (Fig 1). Based on the stitching information wide field maps of retardation as well as retinal axis orientation have been created (Fig 2).

Conclusions : A technique for stitching several arbitrary OCT projections in to a high quality wide field of view projection image requiring no user input has been presented. This allows an anatomical correct topographical high resolution wide field analysis of arbitrary OCT projection data.

This is a 2020 ARVO Annual Meeting abstract.