BASIC PHYSICAL PRINCIPLES OF MAGNETIC RESONANCE IMAGING

Oslikavanje magnetskom rezonancijom je vrlo značajna dijagnostička metoda u suvremenoj medicini. Nezaobilazna je kod prikaza mnogih patoloških stanja mekih tkiva i organa. Za oslikavanje magnetskom rezonancijom koriste se uređaji sa snažnim magnetskim poljima, izvorima radiofrekventnih valova i gradijentima magnetskog polja. Ovo je metoda koja ne koristi ionizirajuće zračenje već se zasniva na principu magnetizacije i ekscitacije vodikovih jezgri radiofrekventnim valovima. Nakon ekscitacije vodikovih jezgri unutar ljudskog tijela dolazi do njihove relaksacije pri čemu se otpušta energija. Energija se detektira u prijemnim zavojnicama u kojima se inducira nastanak električnog signal. Signal se zatim kompjuterski obradi te pretvara u dvodimenzionalnu ili trodimenzionalnu sliku koja se upotrebljava u dijagnostici. Promatrano tkivo moguće je pobuditi na različite načine uz pomoć sekvenci. Razlikuju se dvije osnovne skupine, sekvence koje koriste spin te sekvence koje koriste gradijente magnetskog polja. Pomoću njih se dobivaju slike koje na drugačije načine prikazuju tkivo i olakšavaju dijagnostiku određene patologije. Osim morfologije mekih tkiva i organa, moguće je prikazati i njihovu vaskularizaciju te funkciju dijelova organa kao što su regije u mozgu. Oslikavanje magnetskom rezonancijom ima mnoge prednosti jer ne koristi štetno ionizirajuće zračenje, upotrebljavaju se kontrastna sredstva na bazi gadolinija koja rijetko uzrokuju nuspojave, a i sam prikaz koji nastaje je vrlo koristan kod dijagnostike mnogih stanja. Potrebno je poznavati i ograničenja u radu s magnetskom rezonancijom kako bi ova metoda bila što sigurnija za primjenu u svakodnevnoj dijagnostici.Magnetic resonance imaging is a very significant diagnostic method in modern medicine. It is a necessity in imaging of many pathological conditions of soft tissues and organs. The equipment that is used produces strong magnetic fields, radiofrequency waves and includes magnetic field gradients. This method does not use harmful ionising radiation, but is based on principles of magnetisation and excitation of hydrogen atoms with radiofrequency waves. After the excitation of hydrogen atoms within the human body, relaxation with energy release occurs. The energy is then detected in receiving coils, and electric signal is induced. Produced signal goes through computer processing and is transformed into two-dimensional and three-dimensional images that are used in diagnostics. Observed tissue can be excited in many different ways using sequences. There are two main groups of sequences, those that use spin and those that use magnetic field gradients. By sequencing, different types of images that present tissue in various ways can be obtained. Beside morphology of soft tissues and organs, it is also possible to image their vascularisation as well as the function of any part of the organ, such as stimulated regions of the brain. Magnetic resonance imaging has many advantages because it does not use harmful ionising radiation and it uses gadolinium contrast agents that are rarely associated with side effects. Also, obtained images are very useful in diagnosis of many different conditions. It is very important to be familiar with the limitations that are present in the work with magnetic resonance imaging, so that this method is as safe as possible in everyday diagnostics