PET Myocardial Perfusion Imaging: 82Rb

Rubidium 82 (82Rb) is a positron emitter tracer, produced by the nuclear decay of Strontium-82 by electron capture via a commercially available generator. It is used for PET myocardial perfusion imaging (MPI) and quantification of myocardial blood flow (MBF) that has been shown accurate despite the limits of quantification intrinsic to non-diffusible tracers. The short physical half-life of 82Rb, 76 s, allows for an efficient fast protocol and let a considerable dosimetric advantage for the patient and staff but hinders the use of stress test, allowing only pharmacologic stressor tests. List mode 82Rb PET acquisition and a mono-compartmental model approach are recommended for MBF and myocardial flow reserve (MFR) quantification. Multimodality technique allows higher accuracy in defining ischemic vessel pertaining and calcified plaques of coronary vessels with a stronger clinical impact. Due to the diagnostic accuracy over the traditional MPI, quantitative 82Rb PET has been widely used to facilitate diagnosis, establish the patient’s workup, and predict successfully outcome in patients with obstructive and nonobstructive CAD. If the oxygen extraction is already maximal in basic conditions, an increase in the oxygen demand can be satisfied only with an increase in MBF that is in dependence of microcirculation, endothelial function, and metabolic factors. Impairment of these systems invalidates the flow and reduces the coronary reserve, thus affecting vasodilation in particular at the subendocardium, which is earlier affected by the ischemia. A strong clinical impact of MBF quantification is achieved also in patients with multivessels disease (MVD) or left main artery stenoses where MPI alone can underestimate the balanced ischemia, and in patients with intermediate pretest probability of CAD, where quantitative 82Rb PET allows a more accurate assessment of the ischemic burden and supports the clinical decision-making. A growing interest regards 82Rb PET in the study of suspect acute coronary syndrome and in cardiac allograft vasculopathy after transplant (HTx). Correlations between 82Rb PET MPI, invasive coronary angiography (ICA), and intravascular ultrasound (IVUS) confirmed that 82Rb PET MPI correlates with intravascular ultrasound and angiograms findings, so 82Rb PET MPI can be suggested to improve HTx patient’s management by reducing the frequency of invasive techniques and to establish the functional significance of cardiac allograft vasculopathy (CAV) involvement. Moreover MBF 82Rb can target viability assessment in those patients where clinical yield is likely to be highest. The monthly cost of acquiring the 82Sr/82Rb generator was initially considered prohibitive, but it is now clear that it can be amortized by scheduling a number of at least 30 patients for each generator and it can become economically sustainable in relation to a very high number of scans. 82Rb PET-MPI submits the patients at radiation dosimetry less than the SPECT-MPI; moreover, it should be emphasized that the limited dosimetry of 82Rb PET vs. the SPECT one regards both patients and the staff. A new trend of scientific research for 82Rb is emerging in the recent years in the field of oncology. On this purpose, 82Rb is a nonspecific radiotracer; therefore, the uptake by the tumor primarily depends on the tumor vascularization. Theoretically, the rationale of use of this radiotracer can be firstly identified in its capability to explore angiogenesis which, in turn, can directly correlate with the aggressiveness of the tumors.