Magnetic-Resonance Imaging
Effective diagnostic procedures make lives of doctors and patients better. Physicians get more information so that is why they may make diagnosis more precisely. Patients also gain from this situation – as a minimum, the way they should overcome visiting doctors, shortens.
MR-tomograph functioning is based on the effect of an intense magnetic field that makes the sole protons of hydrogen nucleus that are a part of water in the human’s body, to precess similar to a compass needle when it is placed near to a magnet. This precess goes on on a frequency allowing protons uptaking and transferring radio-waves that help to create 3D image. As a result, we get an image of internal organs, blood vessels, different tissues of the body. The scans are viewed on the computer monitor but it’s always possible to print them out or to copy to electronic media.
Peter Mansfield, a Professor of Physical faculty of Nottingham University has been researching a nuclear magnetic resonance, spectrometry in particular, for the whole life. In 1962 working on his thesis Mansfield had shown how radio signal obtained from a device, might be mathematically processed and transferred into an image. The invention of Peter Mansfield had only theoretical significance at first. It got its huge practical value together with a new MRI method that offered by Paul Lauterbur. Revolutionary MRI method has been waiting for its well-deserved honor for about 30 years. In the beginning of October 2003 the Nobel Committee had announced that the prize for medicine and physiology will be awarded for invention of a method of magnetic-resonance tomography. Two names were announced: Paul Lauterbur and Sir Peter Mansfield.
It’s necessary to know the difference between magnetic-resonance tomography (MRT) and computer tomography (CT).
Advantages of MRT over CT:
· Exposure of electromagnetic field that is safe for a human forms the basis of MRT; it can be performed for pregnant women and children;
· The MR-image is more precise, quality and informational, especially in soft tissues research;
· During MRI process the patient is not exposed to radiation; this allows repeating the observations of one and the same person many times.
Disadvantages of MRT over CT:
· CT will be informative for visualization of bone tissues;
· It’s forbidden to perform MRT to the patients that have metal implants in their bodies (i.e.vascular stents, prosthetic implants) or electronic life-saving devices (insulin pumps, peacemakers).
· It is necessary to remember that it’s not overcaution. For reference: the MRT magnet power of 1,5 T is 1,5 times greater than the electric magnet power working on a salvage yard.
· MRT is more sensible to patient’s movements during the procedure: event insignificant movement of a patient may lead to decrease of image quality.
MR-tomographs are classified according to magnetic field power. There are three types of machines:
- Low-field (up to 1,0 T);
- High-field (1,5 – 3,0 T);
- High-field (from 3,5 T).
Depending on constructions there are open and closed tomographs. Closed tomograph is a cylinder (tunnel) where to a patient is placed on a rolling table. Open tomograph looks like two “patches” between which that patient is placed. Open tomographs are intended for the patients with a limited space fear or when the patient’s weight exceeds 130 kg. The results of an open tomograph are less informative. The mastodons of electronic world are the leaders in the sphere of modern tomograph-construction: Siemens, General Electric, Philips, Hitachi. Only such huge companies may allow elaboration of very complex equipment which price amounts to more than 100 million RUR per one machine.
The Federal Neurosurgical Center (Novosibirsk) is equipped with 2 high-field machines of closed type:
1. 1,5 T Magnetom Avanto MRT from “Siemens” (Germany) from 2012;
2. 3,0 T Ingenia from “Philips” (The Netherlands) from 2018.
The MRT consists of the following items:
- The MRT machine itself placed in a treatment room;
- Control room where the laboratory technician sits;
- Technical rooms with MRT control boxes;
- MRT cooling systems with one part inside and the other one is outside.
Apart from the above-mentioned rooms, there is a cabinet for an X-ray department doctor who reports the images.
Magnetic resonance effect forms a basis of MRT machine functioning. The tomograph itself, its ring area (gentry), is a high-filed magnet providing constant magnetic field. Significant heat amount is generated in the process of high-field magnetic coils functioning. To keep them in a superconductive state, it’s necessary to always maintain temperature close to absolute zero (-273 C0). This mission execution is reached thanks to liquid helium cooling.
It is exactly liquid helium that is used as a cooling agent of the build-in cooling systems of a magnet because its boiling temperature is the lowest, -269 C0. Besides, it is chemically passive; it’s not flammable and nontoxic. In the process of steaming helium compensates inner heat exposure and provides temperature stability of superconductor. In cases of low temperatures that may be reached thanks to liquid helium existence, superconductive metals start getting strictly zero-point electric resistance due to which they create high magnetic field allowing MRT-machine functioning.
MRT 1,5 and MRT 3,0 T are essential and extremely useful. Having common functioning principle, the patients nowadays have only to have a classical 1,5 T imaging that may provide an objective and precise picture. Screening on a more powerful machine, 3,0 T, is recommended in the following cases:
- In cases of heart and coronary vessels MRT;
- In cases of planning of complex brain or spine surgery;
- In cases of foot or hand MRT; MRT of carpal joints to better examine all small bones and cartilages;
- In cases if epilepsy diagnostics;
- In cases of pinus and thymus gland MRT.
