Variable Temporal Interval OCTA Velocimetry Enables Wide-Range Hemodynamic Mapping in Hyperoxia Models

Purpose: The purpose of this study was to introduce variable interscan saturation alignment (VISA), an optical coherence tomography angiography (OCTA)-based method for wide-range flow velocimetry with angular tolerance, and validate its ability to quantify hyperoxia-induced hemodynamic changes in rat retina and cerebral cortex. Methods: VISA achieved 92.6% mean velocity estimation accuracy over 1.0 to 20.0 mm/s, with a strong linear association between estimated and preset velocities (R² = 0.996), and stable measurements across 35 degrees to 90 degrees. In vivo imaging resolved layer-specific blood flow. Hyperoxia reduced flow velocity in the superficial vascular plexus, deep capillary plexus, and choroid by 21.88 ± 17.71%, 20.00 ± 10.91%, and 24.81 ± 15.18%, respectively, and superficial cortical flow velocity by 5.67 ± 1.81% (P < 0.05). Results: In phantom studies, VISA achieved a mean velocity estimation accuracy of 92.6% across the 1.0 to 20.0 mm/s range, with strong linear association between measured and preset velocities (R² = 0.996), and maintained stable measurements across the tested incident angles of 35 degrees to 90 degrees at 4 preset flow velocities (7.5, 10.0, 12.5, and 15.0 mm/s). In vivo imaging resolved layer-specific blood flow in the retina and cerebral cortex. Hyperoxia induced significant reductions in flow velocity in the superficial vascular plexus, deep capillary plexus, and choroid by 21.88 ± 17.71%, 20.00 ± 10.91%, and 24.81 ± 15.18%, respectively, and reduced superficial cortical flow velocity by 5.67 ± 1.81% (P < 0.05). Conclusions: VISA enables wide-range quantitative OCTA velocimetry with angular tolerance under the tested phantom conditions and quantifies hyperoxia-induced microvascular responses in the rat retina and cerebral cortex, supporting volumetric flow mapping in retinal and cerebral microcirculation.