This is an imaging method, which uses magnetic characteristics of an atom´s nucleus, specifically protons (positively charged parts of the atom´s nucleus). Normally, the axes of these protons are turned in different directions. During the magnetic resonance, patient is placed to a strong magnetic field, which arranges the axes to the same direction. Then, the atom´s nucleus is “bombarded” by electromagnetic impulses which gives the atom´s nucleus some of their energy. When these impulses are ceased the atom starts to free itself from gained energy and it can do so in two ways which are marked as T1 and T2 relaxation. This energy release is recorded on coils in the form of voltage changes and then this information is processed by computed and presented graphically. Different tissues are distinguished by the value of the recorded voltage.

This principle is used also in cardiac magnetic resonance. It is a highly accurate method which is used in the diagnosis of myocarditis more and more. Myocarditis can be confirmed by this method with a degree of high accuracy and certainity.

CMRI also enables different types of heart projection, using different machine settings (so called sequences).

Firstly, it facilitates observing the heart´s function. A big advantage of CMRI is that changes to the heart structure and function (including ejection fraction) are observable in more details than when using other imaging methods (see video). Tissue structure can be observed by other sequences (e.g. oedema of heart muscle).

 

An important part of CMRI is, when medical experts administers patient a special contrast medium, containing gadolinium. In case of myocarditis, it is used to look for evidence of inflammatory changes in the myocardium, when some places of MRI “picture,” where possibly inflammation is taking (or took) place, are showed “brighter” than healthy heart tissue (see Picture 14). In medical terminology, it is called late gadolinium enhancement (LGE).  The principle of the contrast substance is that healthy tissues absorb the substance, vice versa in area of inflammation, the contrast substance stays in the spaces between the cells for a longer time and it shows as a “brighter” area. Apart from this, it is also possible to observe during this examination, whether pericardial effusion is present or not.

Picture 14: MRI of the heart (author: Clinic of Imaging Methods FN Motol)

A big advantage of this type of examination is its high accuracy rate and low load for the body. However, it is important to inform medical experts about metal parts in a patient´s body (for example joint prosthesis, pacemaker), because in some cases MRI could not be done due to the strong magnetic field. There are some disadvantages of CMRI like higher noise levels (which can be reduced by ear plugs).

Additionally, the narrow space of the machine can be quite claustrophobic and over a longer time of the examination which sometimes may take over an hour. Because of this from time to time small children are put to sleep during MRI.

Picture 15: MRI machine (author: Tomáš Vendiš)

Author of the opening picture: Clinic of Imaging Methods