Cardiac MRI is gaining proponents thanks to its finesse in determining cardiac viability, assessing heart muscle damage after a heart attack, measuring left and right ejection fraction, and determining true ischemia - and rivaling nuclear stress tests and cardiac cath procedures.
Clinical experience is showing that cardiac MRI scans can take less time to evaluate heart function and anatomy compared to a series of other cardiac imaging exams.
"We can measure both left and right ejection fraction; we can look for evidence of blocked arteries; and we can do an assessment of previous heart attacks," says Tony Fuisz, director of cardiac MR at Washington (D.C.) Health Center. "The best attribute of MRI in this setting is the ability to combine multiple types of information in one study, so the patient has one 40-minute exam."
Washington Health Center is a tertiary care facility, which annually performs between 12,000 and 13,000 invasive cardiac procedures and approximately 1,500 cardiac studies. Most of the exams involve coronary artery disease and left ventricular function and may include viability imaging using the gadolinium contrast agent techniques and profusion imaging using Adenosine.
The most common use for MRI is to determine cardiac viability - to tell if a patient has any coronary lesions and to determine treatment. In this area, most practitioners consider MRI the gold standard.
"What is outstanding about cardiac MRI - which the other technologies have not offered so far - is the ability to very correctly predict how much of the heart muscle has been completely damaged," notes Deepika Gopal, MD, medical director for the cardiovascular MRI program at the North Texas Heart Center at Medical City Dallas Hospital. "This is the best test we have today for identification of completely dead myocardium, which is scarred heart muscle from prior damage."
The North Texas Heart Center began its foray into cardiac MR imaging last November. The facility, which performs five to 10 studies per week, also is using MRI with adenosine stress tests for perfusion imaging to detect how much of the heart muscle is dead, alive or at-risk.
Gopal prefers the adenosine stress test, adding that it is "superior to stress nuclear perfusion studies, because the MRI has increased spatial and temporal resolution in any kind of perfusion imaging in cardiology."
The North Atlanta (Ga.) Diagnostic & Cardiovascular Center (NADCC) has utilized a cardiac MRI unit for about two years, having performed some 500 studies over that time.
Stephen Frohwein, MD, NADCC's medical director for cardiovascular imaging, says some encouraging work is being done on MRI's potential role in evaluating coronary artery disease. Early research has found that 60 to 70 percent of patients get what Frohwein describes as an "adequate evaluation" of his or her coronary anatomy.
"But, that's not good enough when it comes to obstructive disease," he adds. "When you have a procedure, such as heart catheterization, that can tell nearly 100 percent of the time what is going on with the cardio vessels, a procedure that is not up to that par is not good enough - especially when it concerns something as serious as coronary artery disease."
If MRI does become a valuable tool in evaluating obstructive coronary disease and identifying plaque in arteries - perhaps with the help of the MR contrast agent gadolinium - Frohwein says physicians "may have the best test out there to evaluate the whole cardiac condition."
To some degree, the jury is still out on the most optimum magnet field strength to perform cardiac MRI. Right now, 1.5 tesla (T) magnets are in the market in great numbers and physicians are more than satisfied with image quality.
"The 1.5 tesla MRI has been the mainstay," says Sungkee Ahn, MD, director of MRI at American Radiology Services Inc. (ARS). "Just because of the small size and difficulty of the anatomy of heart - because it is moving - we have to image very fast. That precludes any low-field MR, because it cannot get the images fast enough."
ARS, based in Baltimore, Md., is about to launch its cardiac MRI service this summer. The company has more than 30 medical imaging sites in Maryland and Delaware.
ARS is adding cardiac MRI because of the modality's non-invasive nature and its non-radiation method to image the heart and evaluate the heart's anatomy and function non-invasively, Ahn says.
Lurking on the not-so-distant horizon are