Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is another imaging technique that obtains images of the cardiovascular system non-invasively. In contrast to CT and nuclear techniques, MRI does not require ionizing radiation to produce pictures of the human body. Instead, MR works by applying what is referred to as a radiofrequency pulse (a radio wave) to human tissue, imparts energy to the tissue, and then observing the rate at which that energy dissipates from the tissue. The application of the radiofrequency pulse is painless and does not create tissue damage.
MRI is used for a wide range of cardiovascular applications. MRI, like echocardiography, provides excellent evaluation of heart function. Images of the beating heart can be generated to assess for the strength, timing and coordination of heart muscle contraction. The velocity and direction of blood flow can be ascertained with great accuracy.
Heart valve function is reliably assessed with MRI, which is outstanding for localizing and characterizing masses related to the heart as well. MRI is widely used in the assessment of congenital cardiovascular disease, both for initial diagnosis and the evaluation of the success of therapies such as surgery and stent placement. MRI is also a very powerful tool for assessing cardiomyopathies (diseases of the heart muscle), as well as assessing conditions affecting the pericardium (the lining of the heart).
MRI is an excellent test to evaluate the main blood vessels entering and leaving the heart. When intravenous contrast is injected for MRI studies, the resulting images, often referred to as magnetic resonance angiography (MRA), are exquisite. Much like 18F-PET, MRI can be used to assess for heart muscle viability and direct the need for revascularization therapy.
Finally, relatively recent innovations have allowed MRI to be used for the assessment of suspected coronary artery disease. Images are obtained at rest and then stress is applied to the heart, usually by the use of certain drugs to increase the heart rate. Intravenous contrast based on a heavy metal called gadolinium, is injected to create a map of blood flow to all areas of the heart.
Coronary arteries with narrowing in the range of 60 – 70 percent or greater will not allow sufficient contrast opacified blood flow to reach heart muscle, whereas other coronary arteries allow the injected intravenous contrast material to reach healthy heart muscle, creating a difference in enhancement between affected and unaffected areas. As the heart beats, when blood flow is restricted by areas of significant CAD, these regions of heart muscle do not enhance, or “light up”.
Much like coronary CTA, MRI may directly visualize the coronary artery lumen and wall through a procedure called coronary artery magnetic resonance angiography (MRA), or coronary MRA. Because MRI and MRA techniques do not use ionizing radiation, they enjoy a major advantage over CT, nuclear perfusion techniques and catheter coronary angiography, all of which employ ionizing radiation to create medical images.
Nevertheless, coronary MRA is a rather demanding technique to perform because the heart and coronary vessels are moving and because of motion related to the diaphragm. Additionally, examining the small coronary vessels requires very high spatial resolution. For this reason, most investigators favor the use of CT if non-invasive anatomic imaging is required. However, in selected circumstances, particularly suspected anomalous coronary arteries in younger patients, coronary MRA may be quite useful. Other abnormalities of the coronary arteries, particularly in young patients, may be well evaluated with MRA.
Managing Complex Conditions
Patients with the following conditions in addition to coronary artery disease may particularly benefit from diagnostic and imaging procedures:
- Metabolic syndrome
- Renal insufficiency (kidney failure)
- Lung disease
To manage these patients, diabetes specialists and other specialists are available to join our decision making team, as appropriate.
Our physicians are at the forefront when it comes to the latest treatment and therapies for coronary artery disease. Some of the advanced treatments and procedures offered within the Coronary Artery Disease Program include:
- High-risk coronary artery interventions
- Off-pump (beating heart) bypass procedures, in addition to traditional bypass surgery
- Percutaneous coronary intervention
- Minimally invasive techniques and medications to control symptoms
- Coronary artery disease prevention