A Fast Method to Reduce Decorrelation Tail Artifacts in OCT Angiography

Abstract

Purpose : Optical coherence tomography angiography (OCT-A) is prone to decorrelation tails, apparent flow in retinal tissue due to the blood flow within overlying vessels. Such artifacts can interfere with the interpretation of angiographic results. We present a fast practical approach for reducing these artifacts using slab images generated from two or more retinal layers.

Methods : A slab image can be generated by linearly or nonlinearly projecting the OCT-A cube data (generated using Optical Micro Angiography (OMAG^c) algorithms) within one or more layers. The artifact reduction method assumes that the observed lower slab image (I) is generated by additive mix of a signal from an upper slab (U) and a lower slab without artifacts (Î). The mixing problem can be formulated as Î=I-wU, where w∈[0.1] is the fraction of U added to Îto result in I. If the upper slab and the unknown lower slab with no artifacts do not have similar vessel patterns, w can be solved by minimizing the square of the normalized cross-correlation between U and Îas min_wγ²(U,I-wU). The explicit solution is w=Cov(U,I)/Var(U), which is rapidly computed.

Results : We have tested our method on 32 scans using CIRRUS HD-OCT 5000 with AngioPlex™ OCT Angiography (ZEISS, Dublin, CA), and 25 cases using PLEX™ Elite 9000 (ZEISS, Dublin, CA) with diseases such as Diabetic Retinopathy, wet and dry Age-related Macular Degeneration (AMD), Branch Retinal Vein Occlusion, Sickle Cell Disease, Central Retinal Artery Occlusion, Macular telangiectasia, and normal. Figure 1 and 2 show examples of decorrelation artifacts reduction by our method for two cases of Neovascular AMD.

Conclusions : We present a practical and fast method to reduce the decorrelation tail artifacts in OCT-A images. This artifact reduction technique also can be used to correct a whole OCT-A cube with a sliding slab that is segmentation-independent. Our approach is specifically useful for visualization and interpretation of a variety of retinal vascular diseases.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1: Neovascular AMD type 1 case from AngioPlex OCT: an intensity B-scan with two layer boundaries, corresponding slab with decorrelation tail artifacts, and with reduced artifacts. Note that choriocapillaris is not removed.

 

Figure 2: Neovascular AMD from PLEX Elite 9000: a flow B-scan with two layer boundaries, corresponding slab with decorrelation tail artifacts, and with reduced artifacts. Note that choriocapillaris is not removed.