Issue 3: A Delve into MRI
What are MRI scans and how do they work? Well, it’s all to do with Physics!
- MRI scans use strong magnetic fields and radio waves to produce detailed images of the inside of the body including the
- MRI machines are tube-shaped When you go into an MRI scanner, the strong magnetic fields change the direction of tiny molecules of water in the body for a very short time. This is completely harmless.
- When the radio waves are turned off, the molecules of water move back to their original position. When they move back to their original position, they produce faint signals. These signals are sent to a computer and converted into an image of the brain.
- An MRI scanner generates lots of different images of the brain. You can think of each image as being a slice of bread- just like that which would come out of a massive bread slicer!
Advantages of MRI scans: what does a stroke look like on MRI?
- The image below on the left is a CT scan of a brain with a stroke. CT scans take a fast series of X-ray pictures. This is different to MRI scans, because MRI scans use radio waves and strong magnetic fields.
- This means that the image produced in a CT scan is less detailed than an MRI scan. To see this, compare the two images below.
- These are two images of the same stroke. You can see a white region in the MRI image (right hand side). This is the stroke. There isn’t a white region on the CT scan (left hand side). This is because the CT scan is less detailed, so it isn’t picking up the stroke.
- Depending on the size and location of your stroke, a CT scan may be good enough to show where the stroke is.
So, what actually causes the stroke to show up as white on an MRI scan?
- MRI measures the movement of water within the body.
- When water cannot move between cells of the brain so well, it shows up as This is what researchers like George and Laura call restricted diffusivity.
- The reason that water cannot move between the cells of the brain so well after a stroke is because the stroke causes the death of lots of brain cells. This is why the stroke shows up as white on an MRI scan.
- But why is the rest of the brain dark? Well, dark regions show areas where water can easily move between different cells of the brain. The dark areas are healthy brain areas with no stroke.
- As a result, dark regions show healthy brain areas and white regions show damaged brain Because of this, Doctors and researchers can compare these light and dark regions on an MRI scan to tell them details about the stroke.
Where to go from here:
If you would like to learn more about MRI scanning, here is a good place to start: https://www.mayoclinic.org/tests-procedures/mri/about/pac-20384768