A great evolution of the payment structure for imaging procedures is occurring. Soon, payers will reward cost-effective, high-quality procedures, while both healthcare providers and patients increasingly will demand efficient, diagnostically accurate nuclear cardiology procedures with low radiation exposure. Together these forces are positioning cardiovascular positron emission tomography (PET) to thrive.
Challenges ahead for SPECT
With single photon-emission computerized tomographic (SPECT) imaging (often referred to as thallium stress testing), a patient who is at rest is given a small dose of a radioactive tracer, and images are obtained. The patient then receives a second injection of the tracer and undergoes a “stress” while a second set of images is taken. The two rounds of images are compared to identify stress-related blockages in the coronary arteries or permanent damage to the heart, such as after myocardial infarction. SPECT imaging has been successful in identifying coronary artery disease (CAD) and assessing patients’ risk for future cardiac events; however, challenges exist in all advanced cardiac imaging, including SPECT. Now, cardiovascular PET is emerging as a distinctive alternative to SPECT, in part because PET can image disease states that SPECT cannot.
Cardiovascular PET uses tracers that are either cyclotron produced (FDG, NH3 ammonia) or, in the case of rubidium, where supply is ensured for the near- and long-term future. Cardiovascular PET perfusion with either NH3 ammonia or rubidium-82 has consistently been shown to have significantly higher diagnostic accuracy than current procedures, including SPECT and other noninvasive tests. With the greater accuracy comes higher image quality and lower radiation exposure to patients and staff. The higher diagnostic accuracy also translates into better physician and healthcare provider confidence and lower unnecessary downstream testing. The reliability of high image quality gives interpreting physicians more assurance to deem studies positive or negative without equivocal terminology, thereby increasing referring providers’ confidence. With cardiovascular PET, radiation exposure is consistently low, in the range of 2-5 mSV, which is one-fourth to one-third less than with current procedures.
The ability to assess myocardial blood flow is a unique advantage of cardiovascular PET that increases the accuracy of the test and makes it possible to identify other disease states, such as small-vessel disease, which is relatively common in diabetic patients. Data suggest that metabolic imaging with FDG-PET is the best means for assessing myocardial viability in patients with heart failure and candidates for bypass surgery. Inflammation imaging, especially for active cardiac sarcoid involvement, has become an important part of assessing patients with unexplained heart failure and lethal arrhythmias. FDG-PET imaging plays a role in assessing the presence and burden of disease as well as later examination to determine the effectiveness of treatment. Infection imaging offers a unique means of noninvasively identifying infection in areas of device placement, such as pacemakers and implantable cardioverter-defibrillators.
These and other attributes led the American Society of Nuclear Cardiology and the Society of Nuclear Medicine and Molecular Imaging to announce that cardiovascular PET is “preferred” in all patients who are referred for pharmacologic stress imaging and is “recommended” in certain subsets of patients who, regardless of exercise status, have a challenging body habitus, high risk for CAD and cardiac events or great concerns about radiation exposure (J Nucl Cardiol online Aug. 18, 2016).
PET’s economic sensibility
Does cardiovascular PET make good economic sense? The answer is a resounding yes. First, if the right instrumentation is chosen for the PET camera, all of the previously mentioned indications can be performed with the same camera. Thus, PET perfusion can be combined with FDG viability, infection and inflammation imaging. The camera also is more likely to be in full operation on a daily basis. Second, imaging protocols are shorter for PET than SPECT, allowing more PET studies to be performed on a single camera as well as improved lab efficiency. Third, downstream testing can be aimed at treatment, not at confirming diagnoses, which will be an important attribute as payment models move toward rewarding value. Finally, the availability of the radiopharmaceuticals used in PET imaging is steady and able to meet growing demand.
Health systems and practices would be wise to consider these new developments as they invest in cameras, technologies and tracers. Cardiovascular PET is moving into the mainstream of nuclear cardiac imaging and is likely to thrive in the years to come.