A tight interaction occurs between the brain vascular and neuronal activities: blood vessels supply neurons in oxygen and nutrients, and therefore support the neuronal activity. This essential interaction, called neurovascular coupling, is exploited in neuroimaging: detecting blood flow variations allows to detect brain activation. Functional ultrasound (fUS) does so with a very high sensitivity: it is capable of detecting very subtle changes in the cerebral blood volume. And it provides imaging performances inherent to the use of ultrasound waves, i.e. a large field of view covering the entire brain, and a resolution of several hundreds of microns.
To distinguish smaller vessels, researchers of the Physics for Medicine laboratory have developed a technique called ultrasound localization microscopy (ULM), achieving a much better spatial resolution than standard ultrasound. Let’s imagine that you try to capture a satellite view of a narrow road. It might be challenging to distinguish a narrow path from afar. Now, if a motorbike travels on that road with its headlight on, you might see its halo and the center of the halo will inform you accurately on the motorbike’s position, and therefore reveal the narrow road’s position. Localization microscopy relies on that same principle: a bright, point-like object can be localized accurately by pinpointing the center of its halo. In ULM, the “bright” objects are biocompatible micron-size bubbles, injected in the blood circulation. Tracking these micron-size bubbles as they travel in the blood stream reveals the location of blood vessels with a micron-size accuracy, and across large fields of view using ultrasound imaging. By accumulating the tracks of millions of microbubbles, the researchers have reconstructed unique pictures of the microvasculature anatomy at the whole-brain scale in rodents and in human patients, as published in previous studies (Demené et al, Science Translational Medicine 2017; Demeulenaere et al, eBioMedicine 2022). However, this technique is not fast and sensitive enough to catch dynamically the local changes of blood flow induced by the neuronal activity.
Source: Healthcare in Europe