The main technological developments in magnetic resonance imaging (MRI) for medical applications began in the 1970s. MRI involves using the radio-frequency part of the electromagnetic spectrum. Advanced Clinical Scientist trainees specialising in MRI physics will learn to safely operate different models of MRI scanner, running MR sequences to produce images of phantoms, healthy volunteers and patients. MRI techniques are based on the phenomenon of nuclear magnetic resonance, which occurs for atoms possessing a nucleus containing an odd number of protons and/or neutrons. This results in the atom possessing an intrinsic nuclear magnetic moment, causing it to act like a mini bar-magnet in the presence of an externally applied magnetic field. MRI scanners usually have specific clinical sequences pre-programmed so that a series of sequences can be run automatically to generate several different types of image within a single scanning session. The Clinical Scientist specialising in MRI physics might also help to optimise routine clinical sequences.