Abstract
Purpose: :
To image the blood flow dynamics within retinal vasculature quantitatively and pulse coherent in 4D with high temporal and spatial resolution using a gated acquisition approach for Doppler Optical Coherence Tomography (DOCT).
Methods: :
For measuring flow maps of full retinal volumes DOCT usually needs several seconds. Hence vessels that are scanned at the beginning are out of pulse phase with vessels at the end of the scanning pattern. This renders it difficult to acquire pulse coherent Doppler volume series. We therefore chose to use a gated approach by equipping such DOCT system with a pulse-oximeter and acquiring multiple DOCT volumes with synchronous pulse recording. In post processing, we divided the plethysmograph of a single heartbeat into 7 phases and assigned a corresponding pulse phase to each tomogram. According to the assigned heartbeat phase the tomograms were recombined to quasi instantaneous heartbeat phase coherent DOCT volumes in order to produce 4D videos covering a full heart beat cycle. At a pulse rate of 80bpm, each of the 7 pulse phases corresponds to 0.1s recording time, which again corresponds directly to the temporal resolution of the 4D blood flow video. To study the blood flow dynamics of the human retina in vivo, quantitative 4D flow videos over a full heartbeat cycle have been created for the optic nerve head (ONH) region and regions containing dichotomous vessel branches.
Results: :
The high temporal resolution of complete heartbeat phase coherent DOCT flow videos has been demonstrated. Such videos at hand we were able to quantify the blood flow within a whole DOCT ONH volume over time and investigate the flow and pulsation within each vessel of interest over time. Furthermore we demonstrated videos of dichotomous vessel branches, showing the flow distributions over time within each of the vessel branches. Each video was reconstructed out of an acquisition series of 30 volumes of 1000 A-scans x 100 B-scans, acquired at an acquisition speed of 60,000 A-lines/sec, resulting in an acquisition time of 1.6sec per volume.
Conclusions: :
Fully quantitative and pulse coherent 4D videos of the dynamics of human retinal blood flow have been shown. The visualization of flow dynamics may lead ultimately to a better understanding of major retinal diseases as well as an understanding of perfusion in complex vessel geometries.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • blood supply • retina