Aarhus University reveals fine details of pulsing blood vessels

09 Sep 2025

Laser speckle contrast imaging shows how blood flow is regulated.

The way in which blood vessels rhythmically contract and relax, the process called vasomotion, helps to fine-tune blood flow and may play a role in clearing waste products from the brain.

For this reason disruptions in vasomotion have been linked to disorders such as Alzheimer's disease and strokes, but the details of how these vessel dynamics arise and spread have remained unclear.

A project at Aarhus University has now developed a new way to track vasomotion and its downstream consequences for blood flow, known as flowmotion, in awake mice subjects. The work was published in Neurophotonics.

"Despite recent advances and increasing interest, the comprehensive characterization of cerebral vasomotion remains challenging," said the team in its paper. "Vasomotion is a complex multidimensional phenomenon, manifesting simultaneously across space, time and frequency."

The Aarhus solution employed laser speckle contrast imaging (LSCI), in which the speckle effect caused by blood cells moving through blood vessels under laser illumination is used to capture details of vascular and arterial flow. Potential applications for this form of optical examination have included new ways to assess stroke risk in patients and detecting complications during labor.

In its study, Aarhus University used LSCI to capture the fleeting vascomotion events within the brain of an awake mouse in real time. The project combined the imaging with data analysis, including wavelet transforms to detect oscillations; a "pulsatility index" to map arteries and veins; and clustering algorithms to separate bursts of activity from quiet periods.

Complex dynamics studied through laser speckle

For its animal trials, the project designed a bespoke LSCI platform and applied it to the brains of awake mice subjects. Illumination was provided from a 785-nanometer source for recording sessions lasted 600 seconds, at an acquisition rate of 194 frames per second.

Results gave new insight into the complexity of blood flow, recorded by the speckle contrast technique. This revealed distinct intermittent periods of pronounced ("flare") and reduced ("silence") vasomotion activity, rather than a continuous steady process. The flares lasted on average about 80 seconds, followed by equally long silent intervals.

The strongest oscillations originated from the walls of small arteries, where vessel diameter fluctuated rhythmically. These oscillations propagated downstream as rhythmic changes in blood flow, reaching veins after a short delay of about a third of a second.

The team theorizes that arterial walls are the main drivers of this vasomotion in the brain, with this rhythmic activity spreading through the vascular network rather than appearing everywhere at once. These transient patterns provide new insights into how the brain regulates blood supply on a fine scale.

Beyond the immediate results, the work highlights the value of LSCI combined with advanced analysis for studying complex vascular dynamics, noted Aarhus University. A clearer understanding of vasomotion may shed light on its role in maintaining brain health, and how its breakdown could contribute to diseases marked by impaired blood flow and waste clearance.