Diagram 1 shows a small Magnetic Resonance apparatus with which only the limbs of the body can be investigated.
It consists of a sitting / lying table, a magnet tunnel and an imaging and control console. It is normally equipped with a permanent magnet of 0.3 tesla.

Diagram 2 illustrates the similarity in properties between a charged atomic nucleus (right) and a gyroscope (left).
A spinning top (gyroscope) spins around its axis and has an angular moment C. In the presence of a gravitational field, (g), the gyroscope exhibits a precession movement (D).
Some charged atomic nuclei, e.g. 1H, have magnetic properties that can also be described by spin and magnetic moment (C). In the presence of an external magnetic field (B) the individual spins of the H atoms present can only take up certain orientations, in accordance with their energy.
Here too the spins exhibit a precession movement round the magnetic field. At equilibrium a magnetic moment M that is lined up with the axis of the external magnetic field will result for a large population of H atoms.
If an energy pulse (excitation) is supplied via a second magnetic field, which is perpendicular to the first (radio frequency transmitter) then the equilibrium is broken: the M vector changes in both size and orientation.

Following the disturbance caused by such a pulse the population of H atoms returns to equilibrium. This equilibrium recovery can be tracked by measuring the total magnetic moment as a function of time (relaxation); the relaxation behaviour and the relaxation time give information about the magnetic characteristics of the H atoms and their surroundings.

Diagram 3: MR-image of a bent knee that was reconstituted on either a monitor and/or on film via a laser printer.
This has been achieved using the recorded relaxation times that are then converted using suitable algorithms.
Relaxation measurements give an insight into the tissue structure and the distribution of the components in an organ, head or limb.

Diagram 4: shows a multi-functional classic machine in which the gantry ring (tunnel) is completely closed. Just as with the limb-MRI scanner, MRIs now exist with a broken circle to make investigations easier for claustrophobic patients. These mostly use super-conducting magnets of up to 1.5 Tesla. Just as in the CT the workstation / console is equipped with a powerful computer, a mobile table and a gantry with a magnet, radio frequency pulser and receiver.
In order to reduce interference and to protect the surroundings from the high magnetic field a Faraday cage surrounds the scanner.

Diagram 5: a cross-section of the tunnel with a patient in it. Under the influence of a strong magnetic field, the H atoms (the most prevalent atoms in the human body) are forced to orientate along one directional axis. When this magnetic field is interrupted relaxation occurs, and is detected by the radio-frequency pulser/receiver and transmitted in digital form to the computer. The computer processes the information further to produce an analogue image.

Diagram 6: MRI image of a skull.
Unlike radiography- or CT-investigation this method does not use X-rays. Moreover, CT and MR provide complementary image-information. Classic radiology still produces a projection of a surface structure onto a background structure.
Finally, only MR is able to give both an anatomical, as well as functional and physiological, status.