CARDIAC MAGNETIC RESONANCE IMAGING
Cardiac magnetic resonance imaging (MRI) does not use radiation and is based on fundamental principles related to the presence of water in all tissues. Since two protons are contained in a water molecule, when put in a magnetic field, they can be aligned. If the magnetic field is turned off, the photons can return to their original position and generate a radio signal that can be detected and quantitated for an image. The images obtained can help assess ventricular function, aortic disease, ischemic heart disease, cardiomyopathies, pericardial disease, valvular heart disease, cardiac masses, congenital heart disease, pulmonary vascular disease, and coronary artery bypass grafting. In the near future, electrophysiologists will be using cardiac MRI to evaluate atrial morphology before atrial fibrillation ablation therapy (see Plates 3-20 and 3-21).
Most
cardiac MR images are obtained using gadolinium as a contrast agent. Although
gadolinium is generally benign, some patients have developed devastating
problems, including nephrogenic systemic fibrosis, a serious occasionally fatal
condition.
At this
time, most radiologists will not perform cardiac MRI in patients who have
implantable devices such as pacemakers or defibrillators. However, some device
companies are producing MR-compatible devices, and all devices will probably be
MR compatible in the future.
