Cardiac CT & MR: Defining the Strengths

Both cardiac CT and MR imaging are poised for continued growth. Efforts to improve MR’s simplicity and reduce the radiation exposure associated with CT will keep drawing both cardiologists and radiologists into the fold.

“Cardiac CT is experiencing enormous clinical growth,” says James Min, MD, assistant professor of medicine in radiology at Weill Medical College of Cornell University and director of cardiac CT at New York Presbyterian Hospital in New York City. “As more data accrue on CT, people are starting to gradually more and more see the great clinical impact the test can have on patient care. The test will become even more popular. Even now, the images are just exquisite.”


Show them the money

One drawback to cardiac CT is reimbursement or the lack thereof. The Centers for Medicare & Medicaid Services has said that it might consider the technical component of the exam to be the median average of local Medicare. That would come to $312.

“If reimbursement is not in that ballpark, nobody is going to buy a scanner,” says Min. Reimbursement has proven to be “a moving target,” he says. Medicare assigned experimental billing codes to drive data collection based on utilization patterns. Other payors then said that since Medicare considers the procedure experimental, they won’t pay. A “final” national coverage determination expected next March will probably just keep the issue in limbo, Min says.

Meanwhile, research has shown that the test is highly accurate and can rule out obstructive coronary disease. “We’ve seen a high amount of clinical acceptance,” Min says. In fact, the Society of Cardiovascular CT, formed in 2005, already has more than 4,000 members from a pool of 30,000 to 40,000 cardiologists in the United States. “Clearly, people like this test and think it’s going to be useful in managing patients with cardiac conditions.”

Min uses 64-slice GE Healthcare LightSpeed VCT and VCT XT with SnapShot Pulse and the GE Healthcare Advantage Workstation. The XT version offers prospective axial gating. By only exposing the patient at brief points in the heart’s cycle, radiation dose is reduced by 80 to 85 percent. He plans on purchasing another 64-slice scanner, solely for cardiac imaging, for an outpatient imaging center.

“We anticipate growth. We’re of the mind that it’s better to establish practice patterns early and worry about the money later.”

It can be tricky deciding when to jump into a new modality. Currently, cardiac CT is not a big moneymaker at most facilities, says Arthur Stillman, MD, professor of radiology and director of cardiothoracic imaging at Emory University School of Medicine in Atlanta, Ga. Stillman installed a Somatom Definition 64-slice scanner from Siemens Medical Systems in January. Depending on their situation, clinicians may want to wait until reimbursement improves. However, there is an advantage to being the leader in the local market. “Once established, it’s a powerful position to be in.”

Min favors getting into cardiac CT early. The private facilities that have made it work financially first and foremost provide a good service, he says. “The technology is there. If you wait four years and somebody else has set up shop—referral patterns are hard to break.”

Despite his satisfaction with the scanner, “until third-party payors are on board with this, we’re not going to see a lot of rapid growth,” Stillman says. More research on outcomes should help push payors along, he says. The technology is good for two large groups of patients: acute and chronic. “Most people don’t see this as a screening test for the worried well,” he says. “It probably isn’t worth the cost or even the radiation risk. But for someone with chest pain, it really changes the dynamics.”


Managing chest pain

Stillman says there is a lot of interest right now in acute chest pain. Patients with no changes seen in an electrocardiogram and unchanged enzymes make the cause of their chest pain unclear. “Oftentimes, these patients are admitted, they have multiple tests and are ultimately sent home because they don’t have a cardiac cause for chest pain. It’s very costly to do all of that.” Coronary CT angiography’s high negative predictive value makes it safe to send these patients home and several studies have demonstrated that.

Those with chronic chest pain are a much larger group. Up to 85 percent of patients at the typical cardiac cath lab don’t have acute chest pain. The COURAGE study, published earlier this year in The New England Journal of Medicine, found that the use of drug therapy is just as effective in preventing heart attacks or death when compared to a combination of drug therapy and stent implantation. “Those patients who had their angiography and stents could have been equally well treated medically at a substantial cost savings. You can argue that you can just document coronary disease, treat it medically and cath them later if necessary.”


MR knowledge needed

Cardiac MR also is growing, but the biggest obstacle is the small number of locations where clinicians can train, says Tony Fuisz, MD, cardiologist at Washington Hospital Center in Washington, D.C. Fuisz uses the MR suite from Philips Medical Systems as well as 1.5T and 3T scanners from Philips.

“A certain amount of technical background and knowledge is needed to perform these studies well but the number of places to learn is small,” he says. To address the problem, the American College of Radiology is ensuring a radiology presence in cardiac MR by including the modality on the exams given to graduating radiology residents. On the cardiology side, there is an effort underway to include cardiac MR in training programs. Despite these efforts, the modality “almost always requires someone to invest more time to learn.”

Cardiac MR has taken a lesson from CT, which offers one-button studies, says Fuisz. “Cardiac MR has gotten significantly simpler in the last 10 years.”

Once learned, the modality is good for a wide range of patients who are potential candidates. “In any given day, we might go from a patient with a complex congenital heart problem to a patient with chest pain and enzyme rise and might diagnosis a myocardial infarction.” The wide range of applications separates cardiac MR from cardiac CT. Fuisz says that the focus in cardiology is moving away from treating patients with catheters and other invasive procedures and toward earlier diagnosis of problems—at a point where they can be effectively treated with pharmaceuticals.


A novel technique

Timothy Albert, MD, director of cardiovascular imaging center at Ryan Ranch in Salinas Valley Hospital, Salinas, Calif., and assistant consulting professor of medicine at Duke University, looks at utilization of cardiac MR. “For cardiologists, it’s a very novel technique,” he says. He has worked to simplify it, define protocols and make the uses clear.

Albert has been working with Toshiba America Medical Systems for about a year and uses the company’s Aquilion 64-slice scanner and Vantage MR system powered by Atlas. He did an advanced fellowship at Duke University at their cardiovascular MR center and then started the cardiovascular imaging center in Salinas. He now works with both Toshiba and Duke in a joint research relationship.

“Even amongst physicians, there is deep confusion between CT and MR. I look at them as being synergistic tools,” he says. There is a lot of overlap but they also have unique strengths they bring to cardiovascular patients. MR is used extensively for cardiac valve assessment, heart structure assessment, scar from prior heart attacks, and diagnosis of a previous heart attack. “We are finding that more and more patients have silent myocardial infarctions (MIs),” Albert says. A recent study showed that about 20 percent of people over 70 have had a silent MI and the only way to definitively diagnosis that is with MR.

Albert also is working on setting up stress MR/perfusion testing. “MR is the newest tool for stress testing,” he says, because it allows for viewing of structure and function and higher resolution images of blood flow to the heart.

Physicians struggle with how MR fits into their practice, says Albert. “MR has so many different applications and affects so many different tests we already do. It’s hard to pin it to one category.” MR, however, has the benefit of having well-established and universally accepted billing codes. “MR is maybe a little harder to apply in practice but the billing isn’t as unknown.”


Coming soon

Both CT and MR are going to be dominant technologies in cardiovascular imaging, says Albert. While vendors are working on reducing the radiation exposure involved in CT, “I still think MR has the potential to do all of these things and do them more safely.” MR has to achieve higher resolution coronary imaging, he says, but “that’s something that’s being worked on aggressively. Once that hurdle is overcome, you’ve really got MR doing a lot, if not everything, CT was doing without the inherent risks of CT.”

Albert agrees that MR will be better than CT in the future. Since age is the most common predictor of coronary calcification, the Baby Boomers may not be the best population for CT. Plus, anyone with kidney problems will have a problem with the contrast required for CT.

Both technologies need further development, says Min. “64-slice is going to be the workhorse for the next 4 to 6 years. There are definitely going to be advances in spatial resolution, number of detectors, maybe even a complete rehaul of engineering design. But, the next true generation of scanners will come in 5 to 7 years, not 3 to 5.”

A bigger issue than technological improvements might be an increasing need to image patients. “The number of patients far exceeds the number of individuals trained to evaluate the images,” says Stillman. Fortunately, interest in education is growing.