Cardiac PET/CT Steps into the Clinical Mainstream

According to the Centers for Disease Control and Prevention (CDC), heart disease has been the leading cause of death in the United States for the past 80 years and is a major cause of disability. The CDC estimates that approximately 61 million people in the United States have heart disease, and approximately 950,000 people die from the condition each year. Overall, heart disease contributes to approximately 40 percent of all deaths.

For women, heart disease statistics paint an even grimmer picture. According to the American Heart Association, cardiovascular disease accounts for more deaths in women per year in the United States than the next six causes of death combined.

Myocardial perfusion imaging (MPI), particularly quantitative MPI, with PET/CT has demonstrated superior sensitivity, specificity, and efficiency compared with SPECT studies. However, until recently, cardiac PET/CT imaging has largely been the purview of academic or research-based medical centers.

The primary reason for this situation lies in the Centers for Medicare & Medicaid (CMS) reimbursement-approved radiotracers utilized in the PET portion of a cardiac study. Nitrogen-13 (N-13) ammonia requires an on-site cyclotron, radiochemistry synthesis capabilities, and has an approximate 10-minute half-life. Although N-13 ammonia has enjoyed widespread use in scientific investigations, its production parameters have limited its clinical utilization.

The other CMS-approved cardiac PET radiotracer, rubidium-82 chloride (Rb-82), is a monovalent cationic analogue of potassium with a half-life of approximately 75 seconds. However, unlike N-13 ammonia, this radiotracer is produced in a commercially available generator (CardioGen-82 by Bracco Diagnostics) that can be delivered to a PET/CT practice via distribution channels throughout the United States.

The generator contains strontium-82 (Sr-82) in a lead-shielded elution column. The Sr-82 has a half-life of 25 days, which allows for the generator to be on-site for nearly four weeks before it needs replacing. The Rb-82 is eluted with saline by a computer-controlled infusion pump, connected via an intravenous tube to the patient. The generator is replenished every 10 minutes, allowing for Rb-82 to be utilized in a routine clinical setting for gated rest/pharmacological stress PET/CT MPI studies.

PET/CT cardiac imaging has demonstrated advantages over the more commonly performed nuclear stress tests. First and foremost, it has shown particular superiority in patients with a body-mass index (BMI) greater than 30, so abnormal results are more reliable. Cardiac PET/CT is also the clinical gold standard to determine the viability of heart tissue for revascularization, providing cardiac surgeons greater diagnostic confidence as to whether bypass surgery or transplantation is the appropriate treatment after a heart attack.

In addition to lower radiation exposure than other forms of nuclear stress testing, patients benefit from reduced exam time. For example, the entire test (rest and stress) can be completed in 45 minutes or less compared with the 3 to 4 hours required for SPECT stress testing.

Putting cardiac PET/CT into practice

Ronald Korn, MD, PhD, a board-certified radiologist and nuclear medicine physician, recognized the potential for cardiac PET/CT and developed a program for his Phoenix area private practice, Scottsdale Medical Imaging.

“The value of PET/CT is that cardiac SPECT studies can be difficult to interpret because of artifacts, problems with image acquisition, and the build of the patient,” Korn says. “PET/CT helps clarify the equivocal SPECT.”

When a patient is referred to Korn, the practice pre-qualifies him or her with their payor. If the patient is a Medicare beneficiary, the process is fairly straightforward, as CMS has approved the use of Rb-82 MPI PET studies since 1995. When it comes to private payors, pre-authorization can be a tricky matter.

“Most private insurance carriers provide pre-authorization for Rb-82 PET exams, although a few still consider it an investigational study and don’t give authorization,” Korn said. “However, the data are clear that PET/CT is the gold standard for MPI, so it is well beyond investigational.”

One of the primary reasons that cardiologists refer their equivocal or non-diagnostic SPECT cases to Korn for PET/CT MPI is the relationships that he has cultivated in his 11 years of Arizona-based practice.

“I spent the past 11 years building a very trusting relationship with cardiologists,” Korn notes. “As a result, in difficult nuclear cardiac cases, I’m often called upon in an advisory role to give a secondary opinion.”

Those relationships have allowed Korn to educate his referring physician base on the value of PET/CT MPI studies vs. SPECT imaging, particularly for overweight and obese patients. “We really focused our practice on patients who have a BMI greater than 25,” he notes.

In addition, because his practice is affiliated with a bariatric surgery center, he says that Scottsdale Medical Imaging is seeing more of these patients, whose weight puts them at greater risk for coronary artery disease.

“Not only is PET/CT superior to SPECT in these patients, but if you have a positive SPECT it generally results in downstream procedures and interventions, such as cardiac catheterization, being performed, sometimes unnecessarily,” Korn said. “PET/CT really does offer a very practical and useful application in reducing the number of patients that get unnecessary catheterizations.”

In addition to providing greater diagnostic certainty for cardiologists, PET/CT has the side benefit, through the CT portion of the exam, of capturing thoracic anatomic information. These images have allowed Korn, through his extensive radiological education and experience, to discover malignancies for which the patient did not present, also known as “incidentalomas.”

“The same patients who are at risk for coronary artery disease because of smoking or other bad habits are also at risk for lung cancer,” he notes. “We’ve found in about 1 to 2 percent of our population an incidental finding that required aggressive evaluation for cancer.”

Korn also has found unsuspected aneurysms with the CT portion of the exam. As part of their cardiac imaging protocol, Scottsdale Medical Imaging performs coronary CT artery calcification scoring to evaluate plaque build up. If a patient presents as intermediate to high risk, or if the referring physician wants to find out the functional significance of the patient’s calcium score, the patient is referred for a PET/CT.

Building the practice

Inaugurating a cardiac PET/CT practice for cardiologists or radiologists is not simply a matter of throwing open the doors and announcing to the world that a group is providing these imaging services. A practice has to build relationships with cardiologists in their area and assure them that they are providing a complementary service, not competition, for patients.

“It is a process of gaining their trust,” Korn says. “SPECT imaging is not going away in the near future. But there are certain patients in which cardiologists are going to have a really difficult time interpreting their SPECT studies. We’re offering them a solution for their most difficult patients.”

To Korn, this approach has been received very well by cardiologists in the Phoenix area. Once they realized that Scottsdale Medical Imaging was providing a service for their overflow and difficult cases and not competing with them, they began referring their patients to the practice for cardiac PET/CT.

“We turned our rubidium imaging into more of a consultation service than cardiac PET/CT service,” Korn says. “That has been fairly effective and has helped to grow the practice.”

Another element to building a successful cardiac PET/CT service line is to provide prompt follow up on the results to the referring clinician.

“Every MPI PET/CT that has a positive or negative value is communicated to the referring cardiologist within a few hours of completing the exam,” Korn says. “We also follow up on the patient’s status so that we become part of the clinical team rather than separate from it. That helped a lot in building our consultative relationships.”

In addition, when providing in-patient service at Scottsdale Healthcare, Korn and his colleagues at Scottsdale Medical Imaging read the in-patient SPECT exams. When there are equivocal or non-diagnostic SPECT studies, they have been able to use the radiology report to educate both patients and clinicians on the benefits of obtaining a cardiac PET/CT exam. “I think this is a very useful way of appropriately utilizing the practice to build the practice,” he says.

Referring physician education has proven to be one of the most effective tools that Scottsdale Medical Imaging has used to grow its cardiac PET/CT service.

“We brought out a variety of nationally recognized experts who met one-on-one with cardiologists in our area to explain the benefits of PET/CT MPI,” Korn says. “We found this to be very effective in building the practice.”

Even with a strong reputation among cardiologists, Scottsdale Medical Imaging did not see a rush of patients when it first offered PET/CT MPI. “In the beginning, we were seeing about one patient per week,” Korn says. “Now we’re seeing about five a day for PET/CT MPI. We absolutely could be doing more, but because we only have one PET/CT system it needs to be used for oncology as well. So we have to balance myocardial perfusion imaging with oncology.”

Korn says that Scottsdale Medical Imaging has one of the busiest PET/CT oncology practices in the Southwest. As the demand for MPI on the system has grown, the practice is considering adding more time on the PET/CT system to handle the demand.

“What we hope is that if we can get up to eight PET/CT MPI patients a day, we can open another bay of myocardial perfusion imaging,” he says. “What we’re doing is baby steps; as the volume grows we’ll be able to open up more and more slots.”

Lessons learned

The Scottsdale Medical Imaging PET/CT MPI service line has been in development and practice for about the past two years. Given the opportunity to open the service in a new area, there are a few things that Korn would do differently.

“I would be absolutely certain that the contracts we have with private payors include the use of rubidium for myocardial perfusion imaging,” he says. “That is essential because the radiotracer used to conduct this study is very expensive. If you don’t get paid for it, it really hurts your bottom line.

“Secondly, I would be a little more aggressive in getting together a dedicated PET/CT MPI team. That includes the radiologists, technologists, a nurse to administer pharmaceuticals, scheduling, and billing personnel.

“The PET/CT technologists are well educated about oncologic imaging, but cardiac imaging on the system has its own set of protocols and requirements that they need to master. In addition, the radiologists should be advanced cardiac life support certified so that a cardiologist does not need to be present to perform the stress testing, which will give you a lot more flexibility as to when you can schedule these exams.

“I would spend a lot of time educating cardiologists about the service and emphasizing that it will be complementary to their practice and not in competition with them.

“Lastly, I would make sure to use as near to state-of-the-art equipment as possible, where you’re able to do things like cardiac gating to measure ejection fraction; which is an essential part of our interpretation of these scans.”