The device is as bulky as its name – a man-sized magnet with a narrow, round opening through which the patient is pushed. The noise, which can only be endured with headphones, seems archaic. But the MRI provides excellent cross-sectional images of the internal organs, entirely without radiation exposure.
Evolution of magnetic resonance imaging
The principle of magnetic resonance has been known to scientists since the 1950s. Initially, it was used to visualize the chemical structure of complex molecules. Chemist Lauterbur and physicist Mansfield had the pioneering idea of using the phenomenon to gain insights into the human body; in 2003, they were awarded the Nobel Prize in Medicine for their work. Medical diagnostic equipment, which has existed since the early 1980s, has undergone a huge development over the past thirty years.
There are now full-body tomographs that scan the body from head to toe in 12 minutes. Whether it’s cartilage damage after injury or osteoarthritis, the extent of tissue damage after a heart attack or stroke, or early diagnosis of diseases such as multiple sclerosis or Alzheimer’s disease, magnetic resonance imaging (MRI) reliably provides color “maps” of the tissue being examined.
How does magnetic resonance imaging work?
Each atomic nucleus has an intrinsic angular momentum (nuclear spin), which generates a small electromagnetic field that normally points randomly in a crisscross pattern. If a stronger magnetic field is applied from the outside, these small fields all align themselves in the same way. This is why the core of the MRI machine is a giant magnet whose field is on average 10,000 to 30,000 times larger than the earth’s magnetic field.
Since the human body consists mainly of water, hydrogen atoms are particularly well suited for measurement. As soon as their nuclei are synchronized by the magnetic field, radio waves are sent into the tissue, bouncing off the nuclei and causing them to wobble – the resonance effect. This gives the nuclei energy – they become excited.
This is how the cross-sectional images are created
If the magnetic field is now turned off, the nuclei return to their original position, emitting this energy again in the form of electromagnetic waves. These signals are registered by highly sensitive receivers from different directions and converted into sectional images (tomograms) by computer.
Since the different types of tissue in the body contain different amounts of water (for example, fatty tissue contains a lot, bones a little), they emit more or fewer signals and thus present themselves differently, namely lighter or darker.
Loud examination
The name of the procedure – magnetic resonance imaging or magnetic resonance tomography (MRI) – is derived from the processes described. The examination itself is very loud; the examination rooms are soundproofed to protect the staff. To enable the patient to make himself heard in the tube, he is given a bell button shortly before the examination begins. During the preparation for the examination, he can talk to the staff by means of an intercom system.
