Researchers at Stanford University have developed a new, non-invasive brain imaging technique that allows scientists to visualize cerebral vasculature and blood flow in remarkable detail. Although this technique was developed for use in mice, if it could be adapted for use in humans it has the potential to provide insights into conditions where blood flow in the brain is disrupted, for example strokes and migraines. The study has been published in Nature Photonics.

At present, brain imaging largely relies on CT and MRI scans and while they are certainly useful, they have limited spatial resolution. Alternatively, scientists can use fluorescence-based techniques and while these give a detailed image, they involve either thinning the skull or removing part of it, the trauma of which can affect the activity of the brain. Therefore, there exists a need for non-invasive techniques that also provide scientists with the necessary level of detail for in-depth studies, which is what the team of Stanford scientists have been working on.

Their novel technique is a two-step process. First, they inject photoluminescent carbon nanotubes directly into a live mouse’s bloodstream. Then, nearinfrared light, called NIR-lla light, is shone over the mouse’s skull, causing the nanotubes to fluoresce at a specific range of wavelengths. These wavelengths are optimal for reduced light scattering and consequently the researchers can image to a depth of greater than 2 mm in the mouse brain. This is an improvement on previous fluorescence-based imaging techniques which could only penetrate to a maximum depth of 1-2 mm.

Impressively, this new technique allows scientists to image blood flowing through single capillaries that are just a few microns in diameter. Moreover, it doesn’t seem to affect brain function.

“The NIR-lla light can pass through intact scalp skin and skull and penetrate millimetres into the brain, allowing us to see vasculature in an almost non-invasive way,” first author Guosong Hong said in a news-release. “All we have to remove is some hair.”

While the technique is currently only suitable for animals, it is still an extremely useful way to investigate human diseases that affect brain vasculature in animal models. There is also evidence to suggest that changes in blood flow within certain brain regions occur in some degenerative diseases, such as Alzheimer’s and Parkinson’s. This technique could therefore provide researchers with a window of opportunity to study the role of cerebral vasculature in such diseases.

The researchers would like to eventually adapt this technique to make it suitable for use in humans, but they’d need to significantly improve the penetration depth first. Furthermore, given that these nanotubes are currently not approved for human use, alternative fluorescent molecules may be required.