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Tilman Schmoll, Michael Niederleithner, Anja Britten, Philipp Matten, Simon Bello, Sophie Kubach, Wolfgang Drexler, Rainer Leitgeb; MHz Swept Source Optical Coherence Tomography of the Choriocapillaris. Invest. Ophthalmol. Vis. Sci. 2021;62(11):63.
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© ARVO (1962-2015); The Authors (2016-present)
Resolving individual capillaries of the choriocapillaris with swept source optical coherence tomography (SS-OCT) angiography is challenging and has so far been limited to very small field of views (FOV). We present a MHz SS-OCT prototype, which provides high-contrast choriocapillaris (CC) images.
We developed a 1060 nm SS-OCT prototype, capable of A-scan rates up to 1.7 MHz. Its lateral resolution was 7.8 μm and its axial resolution was 9 μm in tissue. We acquired Angio 12 mm x 12 mm scans with a sampling of 1024 (A-scans) x 1024 (B-scans) x 4 (B-scan repetitions) and Angio 2.2 mm x 2.2 mm scans with a sampling of 320 x 300 x 10. To create CC en face images, we segmented the RPE and integrated over 3 pixels 20 μm below the RPE fit. To compare the prototype’s image quality to state of the art images, we acquired Angio 12 mm x 12 mm and Angio 3 mm x 3 mm scans of the same eye, using the 100 kHz mode of the Plex® Elite 9000 (ZEISS, Dublin, CA).
In Fig. 1a&b Angio 12 mm x 12 mm scans of the CC acquired at 100 kHz (a) and 1.7 MHz (b) are presented side by side. Especially when comparing the magnified views in the blue boxes, one can appreciate significantly more contrast in the higher resolution 1.7 MHz images. Fig. 1c-f show Angio scans over smaller FOV with higher sampling density. The Angio 3 mm x 3 mm scan with the commercial instrument is shown in c&d for the superficial and CC slab respectively. A corresponding Angio 3 mm x 3 mm image of the superficial slab is shown in Fig. 1f. Fig. 1e shows a 2.2 mm x 2.2 mm MHz Angio image of the CC at the location indicated by the yellow box in Fig. 1b. This illustrates that not only the sampling rate and lateral resolution, but also the sampling density strongly impact the ability to resolve individual capillaries of the CC.
We demonstrated that MHz A-scan rates paired with improved lateral resolution, can significantly improve the resolution of individual capillaries in the CC over a large FOV. We further show that increasing the lateral sampling and the number of B-scan repetitions can again significantly enhance the contrast of CC Angio images.
This is a 2021 Imaging in the Eye Conference abstract.
a) Angio 12mm x 12mm CC scan using commercial instrument, b) Angio 12mm x 12mm CC scan using MHz prototype, c) Angio 3mm x 3mm retina using commercial instrument, d) Angio CC image of the same scan as in c), e) densely sampled Angio CC using MHz prototype, f) Angio 3mm x 3mm retina using MHz prototype
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