Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO

Abstract

 

Purpose

 

To visualize the retinal and choroidal micro-vasculature with phase-resolved (Doppler) OCT angiography without eye motion artifacts.

 

Methods

 

A phase-resolved optical frequency domain imaging (OFDI) system at 1040 nm was combined with a tracking scanning laser ophthalmoscope (TSLO) at 840 nm. The TSLO imaged the retina over a 4° (1.2 × 1.2 mm²) field-of-view (FOV) and analyzed lateral retinal motion at 960 Hz. The reported eye motion was used to correct the OFDI galvanometer scanners in real-time to lock the OCT scan grid onto the retina. The OFDI system scanned the retina over a 6.7° FOV (2.0 × 2.0 mm²) in 6s. Blood flow was evaluated by inter-B-scan phase-difference calculation between two B-scans from the same location with a 10 ms time-interval. The lowest visualized flow velocity was 0.15±0.04 mm/s for a 89° Doppler angle. Angiography was performed on the foveal micro-vasculature of a healthy volunteer. En-face images were created from pre-processed 3D datasets (300 B-scan locations, 1000 A-scans/B-scan) by integration of the absolute phase-difference signals over depth.

 

Results

 

Real-time eye tracking successfully corrected discontinuities from eye drift. Additionally the TSLO was able to detect tracking failures during (micro-)saccades which enabled the OFDI to rescan motion corrupted B-scans in real-time. This resulted in a retained vasculature pattern throughout multiple datasets and allowed dataset compounding to increase the angiogram quality. In Fig. 1 angiograms are shown of the upper (nerve fiber layer up to inner plexiform layer) and the lower (inner nuclear layer up to outer plexiform layer) retinal vasculature. Individual capillaries are clearly observed. In Fig. 2 angiograms are shown of the choriocapillaris and the choroid. We show for the first time the mesh-like network of the choriocapillaris with phase-resolved OCT. Several typical pores (openings) are marked with arrows in the inset. The choroid angiogram shows an unorderly dense network of large blood vessels.

 

Conclusions

 

Eye motion was successfully reduced in real-time in phase-resolved OCT angiography imaging. The created high-quality angiograms show individual capillaries with high contrast and might have the potential to study subtle hemodynamic changes during disease.

 

 

Angiograms of the upper (A) and lower (B) retinal vasculature.

 

 

Angiograms of the choriocapillaris (A) and the choroid (B).

 

Keywords: 524 eye movements: recording techniques • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 436 blood supply