MRI uses large magnets and radio-frequency waves to produce high-quality still and moving pictures of the body's internal structures; no X-ray exposure is involved. The scan monitors energy changes in tissues reacting to magnetic forces. A computer analyzes these changes and creates a composite image of the tissues. The images can be shown in two or three spatial dimensions in either static or dynamic cine mode.
MRI is especially useful for evaluating the cardiovascular system. In addition to being non-invasive (not requiring an incision) and risk-free, MRI can image a large portion of the body, such as the chest, in one session. Because MRI acquires information about the heart as it is beating; it can create moving images of the heart throughout its pumping cycle. This allows MRI to display abnormalities in cardiac chamber contraction and to show abnormal patterns of blood flow in the heart and great vessels. Using MRI, physicians can obtain images of the chest and cardiovascular system from many angles. This allows better assessment of complex anatomic abnormalities than with other imaging techniques. Due to the development of new imaging techniques, MRI has the capability to identify areas of the heart muscle that are not receiving adequate blood supply from the coronary arteries. Aided by use of non-iodine-based enhancing agent (Gadolinium-DTPA), it can also clearly identify areas of the muscle that have become damaged as a result of infarction (heart attack).
Cardiac magnetic resonance imaging (MRI) has a wide range of clinical applications. Many of these applications are commonly employed in clinical practice for example, in the evaluation of congenital heart disease, cardiac masses, the pericardium, right ventricular dysplasia, and hibernating myocardium. Other applications, such as evaluation of myocardial perfusion and of valvular and ventricular function, are very accurately evaluated with MRI, but competing modalities such as single-photon emission computed tomography (SPECT) imaging and echocardiography are more commonly employed in clinical practice. Some applications, such as coronary artery imaging, are currently more accurately evaluated with other modalities.
One of the main advantages of cardiac MRI is the lack of ionizing radiation, which is substantial with SPECT and computed tomography (CT). The strength of cardiac MRI, as compared to CT, is its superior temporal and contrast resolution. However, the spatial resolution of CT is superior. While there are competing modalities for every clinical application of cardiac MRI, there is no one modality that can provide as comprehensive an evaluation as MRI. For this reason, cardiac MRI is often known as the "one-stop shop."