Angular compounding in Optical Coherence Tomography for speckle reduction and enhanced visualization of directional scattering in retinal OCT and OCT angiography images

Abstract

Purpose : To investigate the potential of angular compounding OCT to improve visualization and contrast of mouse retinal cellular and vascular morphology with OCT and OCTA by speckle reduction and incidence angle dependent color-coded directional scattering.

Methods : A SSOCT system operating at 100 kA-scans/s centered at 1050 nm was used to acquire directional (angular) OCT / OCTA volumes of mouse retina. Directional OCT / OCTA volumes were acquired by translating OCT imaging beam with respect to entrance pupil position of the dilated mouse eye. 21 OCT / OCTA volumes were acquired by shifting entrance pupil position to a maximum of 1 mm on either side of the pupil center with a step of 100 μm. Speckle-variance based OCTA was used to generate the retinal vascular beds. The volume registration and averaging of the directional OCT / OCTA images were implemented in Image J. We used incidence angle dependent color codding to visualize directional scattering properties of retinal structures. This novel imaging method was tested on mice models with different melanin pigmentation levels and retinal degeneration.

Results : The OCT / OCTA volumes of the same retinal region were acquired at different angles of incidence. The acquired OCT / OCTA volumes are registered and averaged with the proposed registration algorithm. As an example, the single incidence and angularly compounded (averaged) OCT / OCTA B-scans are shown in Fig 1. The normalized speckle contrast (NSC) metric was used to quantify speckle reduction as a function of the number of averaging frames . Example visualization of directional scattering by angle dependent color-coding of angularly compounded OCT images on the same data set is shown in Fig 2.

Conclusions : The angular compounding efficiently suppressed the speckle noise and enhanced the contrast of OCT and OCTA images. The proposed angle dependent color-coding of angularly compounded OCT and OCT images provided enhanced visualization of retinal cellular and vascular structures. Our volume registration allowed angular compounding without any distortion of vessel structures. The proposed angular compounding is found promising for retinal OCT applications due to the (i) easiness of implementation (ii) no need of active mechanism to decorrelate speckle patterns for averaging (iii) contrast enhancement over a large field of view .

This is a 2020 ARVO Annual Meeting abstract.