Cardiac PET/CT Steps into the Clinical Mainstream

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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