Seeing Blood Flow One Cell at a Time: A Dye-Free Way to Map Retinal Circulation
University of Pittsburgh researchers have developed an imaging method that tracks individual red blood cells (RBC) as they move through the tiniest blood vessels in the eye, without dyes, contrast agents, or specialized adaptive optics. By combining a wide-area scan with repeated, targeted circular scans, it turns a standard optical coherence tomography angiography (OCTA) system into a single-cell blood flow measurement tool.
Description
The technology works by first acquiring a large OCTA raster scan over a region of tissue to map the vascular network, then acquiring a repeated OCTA circular scan at specific capillary intersections within that region. Each circular scan consists of a series of temporally spaced A-scans taken at multiple points around a small circle, repeated many times at the same location. Because red blood cells scatter light differently than static tissue, this repeated sampling produces a temporal signal that reveals individual red blood cell passage events as they cross the circle. From this data, the system can calculate cell velocity in two independent ways: by measuring the time delay between two points where the circular scan crosses the same capillary, or by measuring the slope of a cell's passage trace where the scan crosses a capillary at an angle. The individual measurements can then be mapped back onto the larger vascular network to build three-dimensional hemodynamic maps spanning many vessels at once, including comparisons across different capillary layers.Applications
- Diagnostic imaging tools for ophthalmology clinics to assess microvascular health and detect early capillary dysfunction- Research instrumentation for studying retinal and other microvascular disease models
- Preclinical and clinical tools for evaluating pharmacologic effects on blood flow and vascular function
- Ocular tissue transplantation (e.g., corneal grafts)
- Add-on software/analysis modules for existing OCT/OCTA imaging platforms
Advantages
- Detects individual RBC passage events by combining a wide-area raster scan with localized, repeated circular scans at capillary intersections- Offers two independent methods for calculating RBC velocity, allowing cross-validation of measurements
- Generates 3D hemodynamic maps across hundreds of vessels, including comparisons among superficial, intermediate, and deep capillary layers
- Can build each circular scan from a B-scan averaged across repeated A-scans, supporting robust detection of cell passage events
- Uses high-repetition sampling improving the sensitivity and accuracy of individual RBC-event detection and yielding highly repeatable flux, velocity, and pulsatility measurements