How Does MRT Work?
Magnetic resonance tomography is based on the magnetic properties of atomic nuclei, usually of the hydrogen nucleus which is very frequently found as an element in water in the human body.
When a person is in a magnetic resonance tomograph, certain atomic nuclei in his/her body are aligned like small bar magnets. Scientists specifically "disturb" this order using high-frequency radio waves thus making the atomic nuclei "tumble". When the radio signal is turned off, the nuclei gradually return to their initial position. The energy absorbed beforehand is released in the form of radio waves during this process. Using the strength and duration of the tumbling motion, researchers are able to differentiate between the different types of tissue and thus create images of the brain structures with a resolution of less than one millimetre.
The behaviour of atomic nuclei is different depending on the type of tissue. The stronger the magnetic field inside the tube, the clearer the differences between different types of tissue – anatomical differences become more evident.
With the magnetic field of 9.4 tesla, signals can be measured which are too weak for conventional devices. While these can only investigate hydrogen nuclei, the new hybrid device can also receive messages from oxygen and sodium nuclei in the brain.
A certain kind of MRT – functional magnetic resonance tomography (fMRT) – provides information on the brain regions that are supplied with more blood, for example, when patients solve problems or look at images. PET provides similar results, however, more selectively and with a sensitivity that is 1000 times higher. PET produces images of metabolic processes, brain activities and receptor occupancies.