MRI scanner. Magnetic resonance imaging (MRI) scanning is a diagnostic technique that produces 'slice' images through the body. The walls of the chamber contain a powerful cylindrical magnet, which forces the hydrogen atoms in the patient's tissues to align themselves parallel to each other. A pulse of radio waves then knocks the atoms out of alignment. As they fall back into alignment, they produce a detectable radio signal. MRI scans are usually used to study nervous tissue, for example the brain, and are helpful when looking for tumours or other abnormalities. helium