Cerebrospinal fluid motion in the brain captured in remarkable detail

Cerebrospinal fluid (CSF) is a clear and watery liquid that flows in and around the brain and spinal cord. Its functions include protecting parts of the nervous system, delivering nutrients and removing metabolic waste.

Some neurological diseases, including Alzheimer’s disease, have been linked to the abnormal accumulation of proteins in the brain, which can cause damage to neurons. This accumulation of proteins could potentially be linked to variations in the flow of CSF in specific brain regions.

Researchers at Leiden University Medical Center, University of Amsterdam and the German Center for Neurodegenerative Diseases (DZNE) recently developed a new approach to study the motion of CSF, which is based on the widely used imaging technique magnetic resonance imaging (MRI).

This approach, outlined in a paper published in Nature Neuroscience, allowed them to uncover CSF mobility patterns linked with the build-up of amyloid protein in vessel walls, a condition known as cerebral amyloid angiopathy (CAA).

“As most techniques investigating the brain clearance system were invasive or low-resolution, we wanted to develop a non-invasive technique that could image how CSF moves with high spatial resolution throughout the human brain,” Matthias van Osch and Lydiane Hirschler, senior author and first author of the paper, respectively, told Medical Xpress.

“We were pointed towards the topic of brain clearance by a visiting researcher developing simulation methods studying the driving forces of brain clearance. Then we found out that no proper non-invasive sequences were available.”

A new tool to explore brain fluid dynamics

The new imaging technique developed by van Osch, Hirschler and their colleagues allows scientists to observe the movement of CSF in detail, also around tiny vessels that dive deep into the brain and lie closer to where many toxic proteins are produced. Their approach firstly isolates CSF signals and then encodes its motion in different areas of the brain.

“Since the brain clearance system depends on CSF channels that run alongside blood vessels, it is crucial to separate the CSF signal from the slow-moving blood signal before motion encoding,” explained van Osch and Hirschler.

“This ensures that the measured dynamics truly reflect CSF flow rather than blood flow. In addition, our method employs a high spatial resolution readout, allowing us to visualize the clearance pathways in fine detail.”

To collect images with high spatial resolution, the researchers employed ultrahigh field (7 Tesla) MRI. In initial tests, the new approach was found to perform remarkably well. To achieve high spatial resolution, however, requires relatively long scanning times, ranging between 30 to 40 minutes.

“The scan duration could be reduced using advanced reconstruction techniques, which is a research line that we are currently pursuing,” said the authors.

Advancing the study and treatment of various disorders

As part of their recent study, van Osch, Hirschler and their colleagues used their MRI-based approach to map the motion of CSF in a group of healthy volunteers. They then also scanned a group of patients diagnosed with CAA, to compare how CSF moved around blood vessels in their brains to how it moved around the same vessels in the brains of individuals without this condition.

Interestingly, they found that the movement of CSF was different in patients with CAA, following specific patterns. This supports the hypothesis that impairments in CSF mobility are linked to the undesired build-up of specific proteins.

“We believe our technique represents a significant step forward in the non-invasive investigation of the human CSF-mediated brain clearance system,” said van Osch and Hirschler. “It opens a new window to study this system in detail and, importantly, makes it feasible to examine larger cohorts and patient populations.”

Using their newly introduced approach, the researchers have already gathered some interesting insights. Firstly, they found that the cardiac cycle is a key driver of CSF movement in larger brain regions.

It was also shown that enhancing the slow pulsation of blood vessels (i.e. vasomotion) enhances CSF mobility. “We also observed that in smaller CSF spaces along penetrating vessels in the white matter, respiration and vasomotion become equal important driving forces to the cardiac cycle,” said van Osch and Hirschler.

“Moreover, in cerebral amyloid angiopathy, we measured preserved CSF mobility deeper in the brain in combination with enhanced CSF mobility around the middle cerebral artery.”

This recent study introduced a very promising method to study the motion of CSF in the human brain with high precision and without relying on invasive, contrast agent-based procedures.

In the future, the technique developed by the researchers could be used to study CSF mobility in the context of other neurological conditions, including neurodegenerative diseases and sleep disorders. This could in turn contribute to the development of new therapeutic interventions and treatments for these conditions.

“We are currently investigating how CSF mobility changes during sleep and in patients with neurodegenerative disorders,” added the authors.

“By exploring these dynamics, we aim to better understand how alterations in CSF motion relate to waste clearance in the brain and how these processes may be disrupted in disease.”

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