More than 40 billion capillaries are tasked with carrying oxygen and nutrients to the far reaches of the human body, but not much is known about their inner workings.

Now a team from Northwestern University in the US has developed a new tool that images blood flow through these tiny, hair-like blood vessels, giving insight into this central portion of the human circulatory system.

Called spectral contrast optical coherence tomography angiography (SC-OCTA), the 3D-imaging technique can detect subtle changes in capillary organisation for early diagnosis of disease.

“There has been a progressive push to image smaller and smaller blood vessels and provide more comprehensive, functional information,” says study leader Vadim Backman. “Now we can see even the smallest capillaries and measure blood flow, oxygenation and metabolic rate.”

The study is reported in a paper published in the journal Light: Science and Applications.