En Face Doppler Optical Coherence Tomography Measurement of Total Retinal Blood Flow at 100,000 Axial Scans per Second Using Pulse Oximetry Cardiac Gating

Abstract

 

Purpose

 

En face Doppler Optical Coherence Tomography (OCT) of the human optic disc enables quantitative assessment of total retinal blood flow without manual vessel angle measurements. However, such assessment requires a full volumetric scan for every time point, necessitating high imaging speed to resolve pulsatility. We demonstrate a pulse-oximeter-gated approach to measure pulsatile total retinal blood flow with swept-source OCT systems at 100kHz axial scan (A-scan) rate, which can be adapted to commercially available instruments.

 

Methods

 

Doppler imaging was performed using a swept-source OCT system at 1050nm with a 100kHz A-scan rate. The cardiac gating algorithm analyzed the plethysmographic waveform measured by the pulse oximeter to initiate acquisition at desired phases of the cardiac cycle. A blood flow measurement consisted of nine volumes where each volume comprised 600×80 A-scans covering a 1.5mm×2mm area of the optic disc. Automated processing software segmented the en face flow of the arteries, unwrapped the Doppler phase, and integrated the axial velocity to yield total retinal blood flow at the plane of central or hemiretinal arteries depending on optimal Doppler signal. Three measurements were taken from one eye in each of six healthy subjects (average age 27.5 years, range 23 to 31) to evaluate repeatability.

 

Results

 

Fig 1(A) shows three representative pulsatile blood flow waveforms from a healthy subject. Fig 1(B) shows the OCT fundus image and Fig 1(C) shows axial flow velocity at four different cardiac stages. Fig 2 summarizes the mean blood flow measurements in six healthy subjects.

 

Conclusions

 

These results demonstrate a novel method to measure pulsatile total retinal blood flow using imaging speeds currently obtainable with commercial OCT systems. With further validation, this method can potentially monitor blood flow abnormalities in ocular diseases such as glaucoma and diabetic retinopathy.

 

 

Fig 1. (A) Pulsatile waveforms obtained by three total retinal blood flow measurements from a single subject. (B) Fundus view of the Doppler OCT volume. (C) Axial flow velocity in an en face plane showing pulsating retinal arteries measured in Session 3 at four different cardiac stages marked in (A). Scale bars 500µm.

 

 

Fig. 2. Results of total retinal blood flow measurement taken three times in each of six healthy subjects.

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 436 blood supply • 627 optic disc