MRI stands for magnetic resonance imaging. This type of scan uses magnetism and radio waves to build up a picture of the inside of the body. Below is an example of an MRI scan of the head.MRI is completely painless, but the scanner is very noisy.n MRI scan uses magnetism and radio waves to build up a picture of the inside of the body. It can show how deeply a tumour has grown into body tissues. For some types of cancer it can tell whether the tissue left behind after treatment is cancer or not. The scanner is a large machine with a doughnut shaped hole.