Abstract
Purpose :
Traditional raster scanning in optical coherence tomography (OCT) puts a lot of strain on the galvanometer scanners as they must continuously accelerate and deaccelerate the scan mirrors. This limits the maximum scan rate at which they can be operated. For applications where very high scan rates are essential, e.g. confocal laser scanning microscopy and 4D intra-surgical OCT, scan patterns which avoid sudden changes in scan direction are preferred. Examples of such patterns include Lissajous and spiral scan patterns. We demonstrate the use of spiral scan patterns for OCT and OCT angiography (OCTA) imaging of the human retina.
Methods :
We developed a point scanning ophthalmic swept-source OCT (SS-OCT), with a 100 kHz akinetic swept laser source (Insight Photonics, Longmont, CO, 1060nm central wavelength, 70nm tuning range) where we can drive the galvanometer scanners with arbitrary scan patterns. Spiral patterns with different radii and sampling densities were pre-calculated. Patterns with constant number of A-scans per “circle” were used for OCTA to maintain a constant temporal sampling. For structural OCT imaging, the number of A-scans per arc was increased in order to maintain a constant spatial sampling. For both, the acquisition time for a full volume of 250,000 A-scans was approximately 2.5s. After acquisition, the A-scans were remapped to a rectangular grid using the A-scan locations recorded during acquisition. OCTA images were then generated by calculating the speckle variance between neighboring arcs.
Results :
We show OCT structural en face images (Figure 1) as well as OCTA en face images (Figure 2) of the human retina, acquired with a 1.5 mm diameter spiral scan pattern. Because different scan patterns were used for OCT structural and OCTA imaging, Figure 1 and 2 are showing slightly different region of interests on the retina.
Conclusions :
We demonstrated OCTA imaging with spiral scan patterns. This may be valuable for applications where the maximum acquisition rate is otherwise limited by the maximum scanner frequency of a raster scan, like for example intra-surgical 4D OCT. Next steps include increasing the field of view and the investigation of motion correction and eye tracking methods for non-raster scan patterns.
This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.