Each MRI scanner comprises as follows:
- A magnet ,that generates a constant magnetic field, in which a patient is placed.;
- The gradient coils , that produce a weak alternating magnetic field in the central part of the main magnet. This field is called a gradient one. It allows selecting a study area of the part of a patient's body.
- The transmitting and receiving radio-frequency coils.;The transmitting coils are used to generate an excitation in the patient's body, while the receiving coils record responses coming from the excited areas.
- A computer ,controlling the work of coils, the processes of recording and processing of the measured signals, and the reconstruction of MR images.
- The radio-frequency coils for various body regions are necessary to produce a high-quality image.
Magnetic field is characterized by the magnetic field induction and measured in the units of "tesla" (T) named after a Serbian scientist Nikola Tesla.
There are several types of scanners (it all depends on the strength of a constant magnetic field):
- 0,01 Т — 0,1 Т → with a super weak field;
- 0,1 — 0,5 Т → with a weak field
- 0,5 — 1.0 Т → with a field of average strength;
- 1.0 — 2,0 Т → with a strong field;
- >2,0 Т → with a super strong field.
There are three types of magnets for MRI scanners: resistive, permanent, and superconductive.
The tomography scanners with the field of up to 0.3 T most commonly have the resistive and permanent magnets, and above 3.0 T — the superconductive magnets
The optimal magnetic field strength is a constant subject of discussion among experts.
More than 90% of magnetic resonance imaging scanners (MRI scanners) are the models with superconductive magnets (0.5–1.5 T ). The tomography scanners of a super strong field (over 3.0 T ) are very expensive to operate. In contrast, the permanent magnets are cheap and easy to operate.