Every human cell contains hydrogen atoms. When a patient is placed within a magnetic field, the hydrogen atoms in his/her cells align like small magnets. Then radiofrequency pulses producing an electromagnetic field are transmitted in a plane perpendicular to the magnet, resulting in the hydrogen atoms becoming excited and moving out of their original position. When the hydrogen atoms return to their baseline state, ie relax, energy is produced which can be transduced and, in turn, be translated into images. The returning signals vary according to the environment that the hydrogen atom is in, leading to different images - for example, differences between water- and fat-containing tissues. MRI scanning is therefore particularly useful at providing highly detailed images of soft tissues. MRI scanning can also provide images in various planes without movement of the patient.
This is a companion discussion topic for the original article at https://patient.info/doctor/investigations/magnetic-resonance-imaging