Comparative Study of Optical Coherence Tomography Angiography and Phase-Resolved Doppler Optical Coherence Tomography for Measurement of Retinal Blood Vessels Caliber

Abstract

Purpose: To compare the accuracy of Doppler optical coherence tomography (DOCT) and OCT angiography (OCTA) for measuring retinal blood vessel caliber at different flow rates.

Methods: A research-grade 1060-nm OCT system with 3.5-μm axial resolution in retinal tissue and 92,000 A scan/s image acquisition rate was used in this study. DOCT and OCTA measurements were acquired both from a flow phantom and in vivo from retinal blood vessels in six male Brown Norway rats. The total retinal blood flow (TRBF) was modified from baseline to 70% and 20% of baseline by reducing the ocular perfusion pressure (OPP). The retinal blood vessel caliber (RBVC) was measured from OCTA and DOCT images. The caliber measurements were conducted by two separate graders using a custom MATLAB-based image processing algorithm.

Results: The RBVC measured with OCTA and DOCT for normal blood flow rates were not significantly different (56.69 ± 12.17 and 57.17 ± 9.46 μm, P = 0.27, respectively). However, significant differences were detected when TRBF was reduced to 70% (55.69 ± 11.56 vs. 50.62 ± 8.85 μm, P < 0.01) and 20% (50.29 ± 9.29 vs. 44.88 ± 7.13 μm, P < 0.01) of baseline.

Conclusions: Reduced TRBF resulted in inaccuracy of the RBVC measurements with DOCT in both the phantom and animal study. This result suggests that OCTA is a more accurate tool for RBVC evaluation when applied to retinal diseases associated with reduced TRBF, such as glaucoma and diabetic retinopathy.

Translational relevance: Results from this study are directly applicable to clinical studies of retinal blood flow measured with OCTA and DOCT.

Keywords: doppler optical coherence tomography; ocular perfusion pressure; optical coherence tomography angiography; retinal imaging.

Figure 1

Glass capillary phantom caliber measurements, (A) en face OCTA image acquired at 25-μL/min flow velocity. (B) Corresponding DOCT B-scan.

Figure 2

Overlaid DOCT image and OCTA image before/after application of the cross-correlation registration.

Figure 3

Measurement of the retinal blood vessel caliber from a presentative en face OCTA image and DOCT image. (A) Overlaid en face DOCT and OCTA images after registration. (B) Magnified view of the arear in 3A marked with the green dashed square that illustrates the measurement of RBVC from an OCTA en face image. (C) The corresponding DOCT B-scan (location labelled with the yellow line in [A], to illustrate the measurement of the RBVC).

Figure 4

(A) Calibers measured from both OCTA and DOCT images at different flow rates. *Significant difference between the glass capillary calibers measured by OCTA and DOCT. Data are presented as Mean ± SD. (B) Phase differences across the capillary phantom for different flow rates.

Figure 5

Correlation of vessel calibers measured by both graders on OCTA and DOCT images. Total number of samples is 345, measured at baseline and at increased OPP levels.

Figure 6

Comparison of RBVC measured by DOCT and OCTA for different OPP levels: (A) baseline level of 100 mm Hg; (B) 70 mm Hg; (C) 50 mm Hg.

Figure 7

Bland-Altman plots comparing arterial and venal calibers measured by OCTA and DOCT for different OPP levels: (A) baseline, (B) 70 mm Hg, (C) and 50 mm Hg. Red squares represent retinal veins and blue circles represent retinal arteries.