Signal properties of split-spectrum amplitude decorrelation angiography for quantitative optical coherence tomography-based velocimetry

Retinal capillary density among healthy Egyptian and South Asian students: an optical coherence tomography angiography study

AIM

To compare the macular and optic nerve perfusion and vascular architecture using optical coherence tomography angiography (OCTA) in normal eyes of Egyptian (Caucasians) and South Asian (Asians) volunteers.

METHODS

Cross-sectional analytical OCTA study performed on 90 eyes of South Asian (n=45) and Egyptians (n=45) were analyzed. All participants underwent best-corrected visual acuity test, slit lamp, and fundus examination. OCTA images; macular 6×6 mm2 grid and optic nerve 4.5×4.5 mm2 grid were used to examine the parafoveal and peripapillary regions, respectively.

RESULTS

The mean capillary vessel density (CVD) in macular sectors among South Asians and Egyptians participants were (50.31%±2.53%, 51.2%±5.93%) and (49.71%±3.6%, 51.94%±4.79%) in superficial (SCP) and deep capillary plexuses (DCP), respectively (P>0.05). Mean CVD in both groups was higher in DCP compared to SCP in all sectors but was not significant (P>0.05). Mean foveal CVD increases with an increase in central retinal thickness in both SCP and DCP (P<0.001), among both groups. Mean area of the foveal avascular zone (FAZ) was 0.28±0.09 and 0.27±0.08 mm2 in South Asian and Egyptians, respectively. FAZ area decreases with an increase in the thickness and foveal CVD (P<0.001). Mean CVD in the peripapillary area was 48.23%±5.78% in South Asian and 49.52%±2.38% in Egyptian volunteers. The mean retinal nerve fiber layer thickness was found to be higher in the nasal quadrant among South Asian females than the Egyptian females (P<0.05).

CONCLUSION

No significant racial disparity is found in this study. The findings are helpful for assessing and improving the normative data on the differences in South Asian and Egyptian populations.

Monte Carlo-based realistic simulation of optical coherence tomography angiography

Optical coherence tomography angiography (OCTA) offers unparalleled capabilities for non-invasive detection of vessels. However, the lack of accurate models for light-tissue interaction in OCTA jeopardizes the development of the techniques to further extract quantitative information from the measurements. In this manuscript, we propose a Monte Carlo (MC)-based simulation method to precisely describe the signal formation of OCTA based on the fundamental theory of light-tissue interactions. A dynamic particle-fixed model is developed to depict the spatial-temporal behaviors of the tissue phantom: the particles are initialized and fixed in specific locations with wavelength-dependent scattering cross-sections and are allowed to travel over time. We then employ a full-spectrum MC engine to faithfully simulate the formation of OCT and OCTA images. A simulation on a vessel-mimicking phantom demonstrated that speckle characteristics in OCT as well as decorrelation maps in OCTA could be successfully reproduced. We further illustrate the usefulness of our method on the quantitative OCTA by extending it to simulate the gradual saturation of decorrelation in OCTA-based velocimetry. We believe our method will serve as a valuable tool for studying OCTA theory and inspire better solutions and metrics for non-invasive flow velocity measurement.

Dynamic inverse SNR-decorrelation OCT angiography with GPU acceleration

Dynamic OCT angiography (OCTA) is an attractive approach for monitoring stimulus-evoked hemodynamics; however, a 4D (3D space and time) dataset requires a long acquisition time and has a large data size, thereby posing a great challenge to data processing. This study proposed a GPU-based real-time data processing pipeline for dynamic inverse SNR-decorrelation OCTA (ID-OCTA), offering a measured line-process rate of 133 kHz for displaying OCT and OCTA cross-sections in real time. Real-time processing enabled automatic optimization of angiogram quality, which improved the vessel SNR, contrast-to-noise ratio, and connectivity by 14.37, 14.08, and 9.76%, respectively. Furthermore, motion-contrast 4D angiographic imaging of stimulus-evoked hemodynamics was achieved within a single trail in the mouse retina. Consequently, a flicker light stimulus evoked an apparent dilation of the retinal arterioles and venules and an elevation of the decorrelation value in the retinal plexuses. Therefore, GPU ID-OCTA enables real-time and high-quality angiographic imaging and is particularly suitable for hemodynamic studies.