A team led by Song Hu, professor of biomedical engineering at Washington University in St. Louis's McKelvey School of Engineering, working with colleagues at Northwestern University, has developed an imaging method that captures blood flow and oxygen levels in the brain at the resolution of individual red blood cells. The technique, called super-resolution functional photoacoustic microscopy, or SR-fPAM, follows cells as they move through vessels and registers the color change that signals how much oxygen they are carrying.
The approach exploits a quirk of physics. Hemoglobin, the oxygen-carrying molecule packed into red blood cells, absorbs light, and when hit with short laser pulses it emits ultrasound waves - the photoacoustic effect. Conventional photoacoustic microscopy can already image vessels without any injected dye or label, but it cannot resolve single cells in three dimensions. Hu's group got around that by building a microscope fast enough to reimage the same patch of brain every few milliseconds, tracing red blood cells moving single file through capillaries and in clusters through larger vessels, then computationally stacking those trajectories into a 3D map of the microvasculature.
The gap this fills matters for dementia research. Neuroscientists can already watch individual neurons fire, but the microscopic vessels that keep those neurons supplied with oxygen and nutrients have remained harder to study at a comparable scale. That blind spot has slowed progress on cerebral small vessel disease and its role in cognitive decline, an area of growing interest given the vascular contributions to stroke, vascular dementia and Alzheimer's disease.
For now the work has been demonstrated in the mouse brain, so its value lies in what it could reveal about how microvascular function breaks down in disease models rather than in any immediate clinical use. Still, a tool that shows oxygen delivery vessel by vessel, cell by cell, gives researchers a way to ask questions about brain blood supply that were previously out of reach.