Dynamic cardiac PET imaging: Technological improvements advancing future cardiac health

Excerpt

While PET, in conjunction with CT,1 has been an important tool in the management of oncology patients, accounting for 86% of PET scans by 2016,2 PET with attenuation and motion correction has significant potential for future cardiac applications, especially with the ability of PET to perform dynamic imaging to measure myocardial perfusion—myocardial blood flow (MBF) and coronary flow reserve (CFR), integrity of neural transmitters of the autonomic nervous system, and connecting cardiac efficiency with metabolism of myocardial substrates. Its potential is found with its excellent resolution and sensitivity, the ability to use tracers with a short half-life allowing higher doses, and possibly in the future the ability to use ¹⁸F perfusion agents that would eliminate the need of an onsite cyclotron. During dynamic imaging (a dynamic scan should be performed for every procedure), the high counts during the blood input phase can paralyze the camera electronics. Therefore, improved time-of-flight (TOF) electronics able to accept these high counts rates and quality control measures to determine the maximum allowable injected dose (as presented in this issue of the Journal by van Dijk and colleagues) for dynamic cardiac PET studies need to be implemented. However, there is a caveat: restricting the injected dose to meet the count rate capabilities during the input phase penalizes the ability to obtain high counts during the later phase of the dynamic study when the camera electronics are less likely to be paralyzed. Using constant infusion techniques can reduce high peak counts during the input phase, but this reduces the ability to accurately measure the frequency response of the transfer of blood to tissue compartments. Other approaches in the future such as using a library of input functions or blind estimation may alleviate the limitations of injecting a restricted dose for dynamic cardiac PET studies. Nevertheless, one needs to follow caution and consider the fact that the overall radiation burden to the U.S. population doubled from the early 1980s to 2006, and the contribution of nuclear cardiology procedures to ionizing radiation burden increased 10-fold.3 Thus new and improved hardware, software, and radiotracer developments play an important part in the performance of the PET system for dynamic cardiac applications to provide expected clinical benefit that outweighs the risks of the procedure. …