False-colour magnetic resonance imaging (MRI) scan of healthy genitalia in a human male, seen from a side view (sagittal section). At centre left is the penis, coloured light blue. Within this light blue area a range of colours denote different tissue types: the pubic bone of the pelvis is coloured white. At lower centre, the circular dark blue structure is the scrotal sac containing the testes. Magnetic resonance imaging is a valuable diagnostic technique that uses a magnetic field and radio waves, instead of harmful X-rays, to create cross-sectional images of organs and structures within the body.