With the help of magnetic resonance imaging or nuclear spin resonance tomography, thin, layered images, so-called tomograms, can be generated of any part of the body from any angle without penetrating the body.

The largely stress-free diagnostic procedure which has been applied since the beginning of the 1980s works with strong magnetic fields and short radio impulses. It is based on so-called nuclear spin. This term describes the property of an atomic nucleus to turn on its own axis like a spinning top, changing it into a tiny magnet. The atomic nuclei of hydrogen, which are present in the body in large numbers, behave in exactly the same way.

In magnetic resonance imaging, the body is subjected to a magnetic field, which is approximately 30,000 times stronger than that of the earth. This artificial magnetic field causes the hydrogen atoms in the body to align themselves in one direction rather like compass needles in a magnetic field on earth.

Radio frequency coils send a short impulse with an exactly determined wave length and strength into the body. The pulse causes the aligned hydrogen atoms to spin. Once the impulse has ceased the atoms quickly return to their original positions. During this so-called relaxation time the hydrogen atoms emit resonance signals which are measured.

The signals received serve as the foundation for generating images of the inside of the body with the aid of computer processes such as those already developed for radiography and computer tomography. The various tissues appear on the screen in different levels of brightness. Tissues which are rich in water are very bright, tissues with a low water content are dark. Accordingly, bones can hardly be seen whilst tissues such as muscles, ligaments, tendons and organs can be recognised clearly in finely graduated tones of grey.