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How can magnets be used to look at what's inside you?

If you went to have an MRI (Magnetic Resonance Imaging) scan at hospital you would find yourself lying in a large doughnut-shaped magnet. This magnet is very strong and great care has to be taken to ensure that all moveable metal objects are away from the scanner before it’s switched on – otherwise keys, paperclips and, if unlucky, larger items could whizz though the air towards the MRI scanner.

Lying inside a magnet

MRI scans create two and three dimensional images of the different types of tissue inside of you that can then be examined by a radiologist to see if there is any damage or disease. This is possible because the fat and water in your body is 60% hydrogen. When you lie inside the magnet, each hydrogen nucleus lines up with the magnetic field like a needle on a compass.

A short pulse of radio waves then gives the hydrogen nuclei enough energy to briefly change direction. As the nuclei go back to their original orientation, they give off energy in the form of radio waves. The location of these radio waves and the type of tissue they belong to are detected up by the scanner which can then build up a detailed map of the inside of your body.

Magnets to study your brain

MRI can also be used to detect changes in your brain as you perform different tasks and experience different emotions. This application is called functional MRI (fMRI) and it works by detecting which parts of the brain are being supplied with higher levels of oxygenated blood compared to others. This can help neuropsychologists understand the function of different brain areas as well as helping the treatment of brain damaged patients.

You can have a go at creating fMRI images yourself.

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