Why would I want to order a perfusion cardiac MRI on my patient instead of a nuclear perfusion (SPECT) study?
There are many possible reasons. These include:
• Higher spatial resolution
• Shorter exam time
• Absence of soft tissue attenuation artifacts
• No radiation
• The ability to assess other aspects of the heart better and more quantitatively, such as myocardial viability and ventricular and valvular function.
Is perfusion cardiac MRI more accurate than nuclear perfusion (SPECT) imaging?
In 2011, the CE-MARC trial showed cardiac MRI to be more accurate than SPECT in detecting obstructive coronary artery disease. Cardiac MRI also has the advantage of no radiation. It does not have the problem of soft tissue attenuation artifacts which can be problematic in obese patients, or in women with large breasts or breast implants. It also has higher spatial resolution, allowing visualization of perfusion within the myocardial wall. This may give MRI a unique advantage over SPECT for assessing balanced ischemia.
Why would I want to order a cardiac MRI on my patient with valvular disease if they've already had an echocardiogram?
There are many reasons. Most relate to the fact that MRI is a much more quantitative test. In patients with valvular regurgitation, MRI can better quantify how leaky the valve is. This is especially important for patients with mitral regurgitation when the regurgitant jet is eccentric. In patients with calcific valvular stenosis, it can better visualize the valve and directly assess how well it opens. In addition to assessing the valves themselves, MRI is also better at quantifying the effect of the valvular disease on the cardiac chambers. The difference between echocardiography and MRI can sometimes be startling. For example, MRI has demonstrated mild mitral regurgitation in some patients who were thought to have severe, eccentric mitral regurgitation based echocardiograms from nationally and internationally recognized centers. For more information on the value of cardiac MRI in assessing patients with mitral regurgitation, click here.
Should everyone with valvular disease get a cardiac MRI?
No. However, MRI is of great benefit to those patients whose valvular disease is thought to be significant enough to warrant serial follow-up studies as well as for those patients in whom one is trying to determine the timing of surgical intervention. It is also of great benefit when the degree of valvular disease is uncertain, because it can spare the patient a transesophageal echo.
How can cardiac MRI help me take care of my patients with heart failure?
Cardiac MRI can be extremely helpful in assessing patients with heart failure. Cardiac MRI is the standard of reference for determining ejection fraction; and, ejection fraction is often the key determinant for deciding whether a patient will benefit from an implantable cardioverter defibrillator (ICD). Also, cardiac MRI can be helpful in determining the cause of the heart failure, such as in those patients with myocardial scar (i.e. myocarditis), iron overload (i.e. hemochromatosis), and infiltration (i.e.amyloid).
Isn't the cost of cardiac MRI prohibitive?
No. Most physicians are surprised to learn that the reimbursement for cardiac MRI is similar to that of echocardiography, and significantly less than that for nuclear (SPECT) perfusion imaging.