RSNA News - December 2004

Radiology Should Assume Leadership Role in Cardiac Imaging, Experts Say

This is a very serious issue for radiology. Cardiac imaging is an enormous field and will continue to grow.
— Martin J. Lipton, M.D.

Extraordinary technological advancements and increasing interest in cardiac imaging present a unique opportunity for radiologists, but are they prepared for the challenge?

"Radiologists are as prepared as cardiologists for CT studies of coronary calcium and for coronary angiograms. Radiologists must simply learn about cholesterol, Framingham risk score, and the National Cholesterol Education Protection Guidelines APT III," says Melvin E. Clouse, M.D., vice-chairman and director of research at Beth Israel Deaconess Medical Center and professor of radiology at Harvard Medical School. Dr. Clouse was a panelist during a focus session on cardiac imaging at RSNA 2004.

"Radiologists need to study and apply what we've learned in practice. The technology and the patients are here," he says.

The session, "Cardiac Imaging in the 21st Century: Is Radiology Ready for Prime Time?," was moderated by Martin J. Lipton, M.D.

"Interest in cardiac imaging has accelerated over the last few years because of scanners that are now able to provide high-speed, ECG-gated images of good diagnostic quality," says Dr. Lipton, a professor of radiology at Brigham and Women's Hospital in Boston.

In the past, radiologists were involved in cardiac imaging but times have changed. "In the last two to three decades, cardiologists have taken responsibility for nearly all of the cardiac imaging, including angiocardiography, echocardiography and at least half of nuclear medicine exams. These are the established diagnostic imaging tools for patient management," says Dr. Lipton, who is educated in both cardiology and radiology.

Now that cardiac CT and MR imaging are feasible, Dr. Lipton suggests radiology departments become vigorously involved. "This is a very serious issue for radiology," he says. "Cardiac imaging is an enormous field and will continue to grow."

As public demand for health information flourishes, the chance to reach and treat those with early heart disease also increases. "Incidents such as former President Clinton's heart surgery bring a heightened awareness to the detection of subclinical disease in completely asymptomatic individuals or those with minor symptoms previously thought not to be life threatening," adds focus session panelist David Bluemke, M.D., Ph.D. "These new technologies are largely focused on the evaluation of very early disease before people have heart attacks and strokes. Good examples of that are evaluations of coronary artery disease using MR angiography depicting plaque to identify the buildup of atherosclerotic lesions."

Hot Topics in Cardiac Imaging

Cardiac CT is not just a hot topic in cardiac imaging, it is also one of the hottest topics in medicine. Cardiac CT allows the entire heart to be scanned in approximately 10 to 15 seconds with a bolus injection of contrast material, which generates remarkable images of the coronary anatomy. Radiologists can examine cardiac function and coronary artery plaque while assessing cardiac structure for other diseases.

"It's a unique exam," says focus session panelist Thomas J. Brady, M.D., director of the cardiac MR/CT program at Massachusetts General Hospital and the Robbins Professor of Radiology at Harvard Medical School. "Cardiologists at Massachusetts General have used cardiac CT extensively and have significantly altered management of patients with coronary artery disease. They predict cardiac CT will replace diagnostic coronary angiography in the next several years. I believe that in the right situation with the right patient population, we can actually get patients to the catheter lab earlier and perhaps save more lives."

Another hot area is cardiac MR imaging. "It is in prime time right now, especially in the areas such as the evaluation of left and right ventricle function and myocardial viability," says Dr. Bluemke, an associate professor and clinical director of MRI at the Johns Hopkins Medical School in Baltimore, Md. "In the future, I believe that these MR imaging applications will be central within the realm of patient management for coronary disease."

Heart imaging is highly complex. Currently, 3D imaging of the heart can be performed within a breath hold. Left ventricle function can be rapidly determined and areas of myocardial viability can be established during one or more breath holds, avoiding more complicated diagnostic procedures.

In a very short period of time, viability imaging has become the gold standard for assessing myocardial viability using standard MR imaging contrast agents. Dr. Bluemke predicts that other novel approaches, such as MR assessment of unstable plaque, are soon to be developed and evaluated. "MR is the best noninvasive method for identifying substructure within atherosclerotic plaque and has been used to show regression of plaque after statin therapy," he says.

Contrast materials used in cardiac MR imaging are also being improved and used in novel ways. Dr. Bluemke says that the latest generation of intravascular contrast agents for MR imaging provides prolonged imaging periods of 10 to 15 minutes allowing much higher potential resolution of vascular detail, while existing contrast agents are being used to evaluate stem cell therapy of myocardial infarction and cardiomyopathy.

MR viability imaging of a patient after myocardial infarction with evidence of fibrosis in the territory of the left anterior descending coronary artery.

Image courtesy of David Bluemke, M.D., Ph.D.

Calcium Scoring

The coronary calcium score is also a controversial topic in cardiac imaging. Previously, it was thought that variability and reproducibility made the score unreliable. Dr. Clouse says this technology has now been validated for both electron beam and multidetector CT.

"The reproducibility and variability are such that radiologists should begin using it to detect early or asymptomatic disease so that patients can be treated to prevent progression," says Dr. Clouse, adding that the negative predictive value of a zero calcium score is approximately 97 percent.

He says total plaque burden is the most important predictor for future myocardial events. "Recently published research in The Journal of the American Medical Association indicates that the calcium score is additive to the Framingham risk score—the gold standard for predicting future myocardial events," says Dr. Clouse. "This proves the calcium score is an important predictor for future myocardial events. I think it should be used in those patients that are at intermediate and high risk."

Educating Residents in Cardiac Imaging

Major issues facing chairs of radiology departments today include recruiting and/or training the necessary cardiac imaging faculty and adequately educating residents. "Cardiac imaging is very complex," says Dr. Lipton. "Many aspects of cardiac diagnosis and management are clouded by the self-referral patterns of cardiologists. Radiologists should not use this as an excuse to deter them from participating and offering imaging services to referring physicians."

All the experts in the focus session agree however, that radiology must take an active role in cardiac imaging or run the risk of being left out of this burgeoning field.