The Ammonia Option: PET/CT Myocardial Perfusion Imaging
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| PET/CT image. Source: Technical University of Munich, Munich, Germany |
PETNET Solutions, a Siemens Medical Solutions company, recently expanded its offerings and opened the door to myocardial perfusion imaging (MPI) with 13N-ammonia. The new option enables facilities without access to an onsite cyclotron to offer the cardiac scan. The patient benefits are significant as perfusion imaging with ammonia is a shorter and more convenient stress study than a traditional nuclear cardiac test.
In addition, the superior spatial resolution of PET results in fewer equivocal studies. It enables the quantification of perfusion and determination of coronary flow reserve, allowing for high sensitivity and predictive value in coronary artery disease detection and small vessel disease.
Premier PET Imaging of Jacksonville, Fla., the first center in the nation to offer “off-site” MPI with ammonia, started its MPI program in August 2006. The new service erases previous time and logistics barriers to MPI. “Prior to the PETNET program, the only option for PET centers to offer perfusion imaging required the use of rubidium-82 (82Rb) as a tracer. Unfortunately, 82Rb is an unrealistic option for many sites,” says Darren Miller, chief technical advisor. That’s because Rb-82 carries substantial initial costs in the form of an onsite Rb-82 generator. Without an established referral base, these purchases represent risky business. “PET centers can’t rely on a ‘build it and they will come’ business strategy,” continues Miller, “The PETNET Solutions ammonia program allows a center to start an MPI program at its own pace without large out-of-pocket costs.”
The program is a perfect match for this Jacksonville center which is committed to bringing imaging services on par with those offered in the university setting to the private sector, says Medical Director Michael Fagien, MD.
Quality imaging
There are economic benefits to ammonia MPI, but at Premier PET Imaging, economics is secondary to patient care. “The benefits to the patient are three-fold. It’s a much quicker, more convenient, and a higher image quality scan than traditional nuclear stress testing,” says Miller. The other PET-based option uses Rb-82 as a tracer, and allows no time between stress testing and the PET scan. With ammonia, the patient has about five minutes to recover from stress prior to the PET scan. The five-minute recovery period translates into fewer motion artifacts. In fact, ammonia MPI could be the new paradigm in cardiac stress testing. “Although 95 percent of patients still undergo conventional nuclear stress testing, a growing amount of clinical research shows cardiac PET imaging is superior,” shares Miller.
Several clinical studies have reported that cardiac PET stress/rest imaging results in a higher diagnostic accuracy than SPECT imaging. (See SPECT and PET in the Evaluation of Coronary Artery Disease, RadioGraphics 1999; 19:915-926; Impact of Myocardial Perfusion Imaging with PET and 82Rb on Downstream Invasive Procedure Utilization, Costs and Outcomes in Coronary Disease Management, J Nucl Med 2007; 48:1069-1076; and Clinical cardiac positron emission tomography: State of the Art, Circulation 1991;84(Suppl I):I-22—I-36.
Perfusion imaging with ammonia requires precise timing and attention to detail to maximize patient throughput and minimize scan time. Currently, Premier PET Imaging offers six ammonia MPI slots weekly. On the ammonia MPI day, PETNET Solutions schedules one radiopharmacist for an afternoon shift and converts its cyclotron from FDG to ammonia production.
Although patients are scheduled, the PET center does not place the order for ammonia until the patient arrives. As the PETNET Solutions radiopharmacist prepares the dose, the PET center readies the patient by completing paperwork, starting an IV and placing EKG leads. Typically, the ammonia dose arrives as the technologist starts the six-minute adenosine stress test.
Midway through the stress portion of the study, the tech injects the ammonia, which gives the patient several minutes to recover from the stress portion of the study. As the patient’s heart rate and pulse return to normal, the PET acquisition begins. “We’ve had a very positive response from patients and referring physicians,” confirms Miller.
In fact, the positive response is likely to grow the business. “The potential to increase the business is immense. We are under pressure to offer the procedure to more patients,” says Miller. Premier PET Imaging aims to meet local demands by tripling the number of slots dedicated to cardiac imaging. The limiting factor, says Miller, is the availability of ammonia. “Right now, cardiac imaging plays second fiddle to oncology imaging, but the market is rapidly changing.” The clinical rationale is sound, and demand for perfusion imaging is high. On the business side, more radio-pharmacy sites are investing in two cyclotrons, providing the flexibility to dedicate more time to ammonia production.
Ammonia PET MPI is clearly impacting patient management as well as proving to be quite cost-effective. A European study released last fall showed that PET changed patient management in 78% of the patients in a cost-effective fashion. (See: 13N-ammonia myocardial perfusion imaging with a PET/CT scanner: impact on clinical decision making and cost-effectiveness, Eur J Nucl Med Mol Imaging, 2007 Dec 5, DOI 10.1007/s00259-007-0647-3. Another study released last year in the Journal of Nuclear Medicine found that PET MPI performed in patients with intermediate pretest likelihood of coronary disease resulted in a 50% reduction in coronary angiograms, 30% cost savings and excellent clinical outcomes at one year when compared to SPECT imaging. (See: Impact of Myocardial Perfusion Imaging with PET and 82Rb on Downstream Invasive Procedure Utilization, Costs and Outcomes in Coronary Disease Management, J Nucl Med 2007; 48:1069-1076.)
Starting a program
It takes a fair amount of planning to begin an ammonia MPI program1. Currently, the half-life of ammonia limits availability to sites within a 20-minute radius of PETNET Solutions. “This procedure is a finely orchestrated assembly line. Centers need to assess traffic congestion and transport time at several times of day prior to beginning a program to minimize the chance of a dose expiring during transport,” explains Miller. The other prerequisite is a solid relationship between the PET center and the radiopharmacy. The program is a partnership that requires trust. The center needs to count on timely dose transportation, and the radiopharmacy requires volume to justify the cost of ammonia generation.
Other critical infrastructure includes staffing and education. Premier PET Imaging turns to an on-staff nuclear cardiologist to oversee the lion’s share of the ammonia MPI program and interprets the data. The supervising physician monitors the patients and administers the ammonia and adenosine. “It’s very important that a subspecialist is available and able to answer any questions a referring physician might have about the study,” Fagien says. The practice also implemented an educational marketing campaign to inform area cardiologists and non-cardiac referring physicians about the utility and benefits of perfusion imaging.
An improved paradigm
Ammonia MPI offers a best-of-both-worlds option. Image quality is superior to traditional nuclear cardiac stress testing and has long been considered the gold standard in MPI. Compared to traditional stress testing, ammonia MPI is more convenient for patients, and equally important, it allows PET centers to expand their clinical offerings and market a new service. “PET perfusion scans are another example of how the education and appropriate utilization of certain modalities parlays into both better clinical medicine and business,” sums Fagien.
1Pending PETNET pilot program evaluation