Coronary Flow Reserve (CFR) quantification, used in conjunction with Myocardial Perfusion Imaging (MPI), can potentially help to rule out Coronary Artery Disease (CAD). Coronary Flow Reserve compares the myocardial blood flow at peak hyperemia (stress) with the myocardial blood flow at rest.
Currently, most coronary flow reserve testing is performed during cardiac PET imaging, but advancements in technology and the software used to process the data are enabling SPECT cameras to perform CFR evaluation. The lower overall cost of SPECT makes this improvement a promising development for patients and the healthcare system. While this is a positive step, there are some important factors to examine and consider when exploring CFR imaging with a SPECT camera.
Adjustments for CFR testing with SPECT
Longer Test Times: CFR evaluation requires an additional 6-8 minutes of dynamic imaging at time of rest and at time of stress, prior to Myocardial Perfusion SPECT. Patients would no longer be injected and sent away for perfusion imaging at a later time, but rather they must be positioned for imaging at the time of injection. Although the camera may offer the additional benefit of CFR evaluation, the additional acquisition time requirements may lower patient throughput statistics.
No treadmill/exercise stress: Since the patient is positioned prior to the exam and will be imaged at the time of injection, this limits patients to a pharmaceutical stress procedure, which may not be the preferred method. This method will also increase the cost of performing the test and is currently only reimbursed when there is a documented reason that a patient is unable to physically perform a mechanical treadmill stress test.
Additional costs for an injector: The injection, both at rest and at stress, will need to be administered at a specific volume and rate, which will require an injector.
Additional costs for software: Currently, the CFR calculation is not a standard software application. Evaluating CFR may require an additional licensing cost depending on your software package.
No MPI clinical guideline requirement: Although CFR quantification can be a potential benefit in diagnosing triple vessel disease, it has not yet been established as a clinical guideline requirement or standard. As there is no clinical guideline or standard, there is currently no incremental reimbursement or payment to offset all of the various incremental costs associated with performing CFR quantification.
Effective calculations: As with all nuclear medicine studies, good count statistics are needed to produce clinically valid data. Factors such as reduced dose and patient size can easily affect count statistics. Physicians may still hesitate to call a study abnormal based solely on CFR quantification, especially if the perfusion images appear completely normal.
CFR testing is not yet standard practice with SPECT Myocardial Perfusion Imaging and is only applicable to a small subset of patients, but technological equipment updates are in the works. Stay tuned as progress continues.