Enhanced vascular contrast with angular compounded OCT angiography in quantitative bidirectional Doppler OCT at 400kHz

Abstract

 

Purpose

 

Bidirectional split spectrum DOCT allows performing non-invasive optical angiography (OA) based on calculating the speckle variance image together with quantitative absolute flow measurement. We propose coregistration of the three-dimensional (3D) OA image of both beams to suppress speckle and increase the vascular contrast for in vivo retinal data.

 

Methods

 

The swept source dual beam bidirectional OCT operates at 200 kA-scans/s centered at 1050nm and uses a spinning Dove prism that rotates both beams in the eye pupil plane for angle independent quantitative flow assessment. A 16° OA with 800x400 lateral sampling points is acquired in 7.8s. The implemented AC technique registers two en-face images obtained from different viewing angles using an angular transformation matrix. Subsequent averaging of both speckle variance images allows increasing the vascular contrast.

 

Results

 

We measured the absolute blood flow in retinal arteries and veins of healthy volunteers with angle-independent precision of 3% relative standard deviation in the range of 35-45µl/min. In Fig. 1(b) and 1(c) we compare enface projections of OA images of the parafoveal region obtained by maximum intensity projection over a depth range indicated in Fig. 1(a). We can appreciate the significant increase in contrast especially in the microvascular structure (Fig. 1(c)).

 

Conclusions

 

Our results demonstrate, that angular compounded OA with bidirectional DOCT allows for assessment of complementary qualitative and quantitative flow information without compromising vascular contrast. Both, 3D OA of retinal micro-vasculature and absolute retinal flow information are important biomarkers in specific ocular diseases which are not accessible with state-of-the-art fluorescein and indocyanine green angiography.  

 

Fig. 1. (a) Tomogram across the fovea centralis and indicating the depth range (red box) to calculate optical angiographies via maximum intensity projection. (b) and (c) show enface OA images prior and after angular compounding.