The author is a doctoral candidate at Polytechnique Montréal. Thanks to this article, which summarizes the theme of her research in medical imaging, she won the 2022 Acfas Research Popularization Competition.
Bo-doum, bo-doum, bo-doum… With each heartbeat, your heart pumps blood through the arteries to irrigate your entire body from head to toe. By applying two fingers under the jawbone, in the hollow of your neck, you can also feel the blood pulsing in your carotid artery. This major artery supplies the body’s most complex organ: your brain.
From the major arteries to the fine capillaries
The further one moves away from the heart to venture deep into the brain, the thinner and more fragile the vessels become. This is why the main arteries, such as the carotid artery, dilate with the passage of blood. They thus slow down its course and prevent it from surging like a torrent in the smallest blood vessels, which could not tolerate such pressure.
At the end of the road, in the capillaries – vessels thinner than a hair – the flow is very slow and is no longer subject to the back and forth of the cardiac cycle. This allows the blood to take time to exchange its nutrients and oxygen with the neurons, and rid them of the waste products they produce.
In my doctoral project, it is this blood circulation that I seek to observe in all the vessels of the brain, because it is crucial in determining its state of health.
See better to react in time
As we age, the arteries gradually lose their elasticity and dilate with difficulty. The blood pulse then gains ground: it spreads further and further in the blood vessels, to the capillaries. Abused, these can end up breaking and causing small hemorrhages in the brain. Neurons that were previously supplied by these vessels die, deprived of oxygen and nutrients. The multiplication of this type of event can gradually lead to cognitive decline, which results in loss of memory or attention. Eventually, illnesses such as dementia can occur.
Can we stop these cascading effects? This would require taking the problem to the root, because the first symptoms appear when the damage is already considerable. This is precisely the goal of the imaging technique that I am developing at the Ultrasound Laboratory of Jean Provost, at Polytechnique Montréal: to measure the pulsations of blood throughout the brain, from the main arteries to the smallest vessels. . The idea would be to be able to monitor their evolution over the months to possibly spot warning signs of dementia, in order to act before the disease sets in.
Millions of bubbles to see blood flow pulsating in the brain
Like an ultrasound performed on a pregnant woman, this technique is based on ultrasound imaging: it therefore requires neither surgery nor radiation. However, it requires the injection of millions of very small bubbles, already used today by doctors during certain medical imaging examinations to better visualize the blood. Driven by blood flow, these bubbles travel throughout the body for several minutes, before being naturally eliminated by breathing. During these few minutes, an ultrasound of the brain is performed by taking thousands of images per second, like a camera that would take a series of burst shots.
Subsequently, powerful algorithms are launched to find the bubbles in each of the images and follow them from one shot to another, in order to retrace the path they have traveled. After several hours of analysis, from all these images, we can reconstruct a film where we see the bubbles spreading in the brain to the rhythm of the pulse, both in the major arteries and in the smallest blood vessels. .
From this film, we can draw a lot of information on the size of the vessels, on the direction and the speed of the bubbles that have passed through there, but also and above all on the dynamics of the blood flow. In other words, for each vessel, we can know if the blood is pulsating or not.
Some challenges
So far, I have only tested this method on animals in the laboratory. I was thus able to measure blood pulsations in a mouse in small vessels only 30 μm (micrometers) in diameter (i.e. a little larger than a capillary), but also in the main arteries of the brain. It remains to be seen whether this technique is effective enough to identify the signs of a deterioration in the state of health in an aging mouse. Studies are underway in the laboratory to answer this question.
However, this method requires several challenges to be met before it can be applied to humans. It is based on ultrasounds which are sent to the brain, then which pass through the skin, tissues, blood and bubbles in order to make an image. Except that there is a problem, and not the least: the brain is protected by the skull, against which the ultrasounds bounce like on a brick wall. If the skull is thin enough, as it is in a mouse, this barrier is not too difficult to cross; but for a human skull, things get tough. However, in 2021, a team of French researchers achieved the feat of forming an image in humans, using a similar method. There is therefore good hope that the method I have developed will one day be applied in the clinic, and that it may eventually help to better detect the early signs of dementia.
#Dementia #understanding #role #blood #circulation
