Potential clinical utility of 68Ga-DOTATATE PET/CT for detection and response assessment in cardiac sarcoidosis

Reference myocardial uptake values on somatostatin receptor-targeted PET: not yet in preference to visual assessment

“…Defining the specific reference range for each of the six areas of left ventricular myocardium was appropriate, since spillover signal from the abdomen artificially increases the inferior wall and inferolateral wall SUV. 11 However, and due to the difference in parameters used to report background myocardial uptake on SSTR-PET across published studies, the results of this study cannot be easily compared to those of the existing literature. For instance, Itani et al previously showed that, among individuals undergoing Ga-68 Dotatate for neuroendocrine tumor evaluation, myocardial SUVmean to blood pool ratios were in average 1.40 in those individuals without known cardiac disease (n = 23), and 2.03 among patients with known cardiac disease (n = 83), indicating an interesting correlation between risk factors, cardiac disease and myocardial SSTR-PET uptake.…”

“…In this sense, we decided to apply the suggested threshold to a control group of 20 consecutive patients without known CAD, heart failure or sarcoidosis, who underwent Ga-68 Dotatate PET/CT for neuroendocrine tumor indication, as well as our previously published cohort of 11 patients with CS (Figure 1). 11 For the control group, we measured Dotatate uptake at the interventricular septum, as this region of the heart seems to be the least affected by spill over activity. We observed that 40% and 20% of the control cohort had myocardial SUVmaxto-blood pool SUVmean ratios greater than 1.70 (95th percentile) and 2.00 (97.5th percentile), respectively (Figure 1), and consequently, they would be considered abnormal according to the upper limit reference values suggested by Kaushik's study.…”

“…17 Given the low target-to-background ratio, combined with the fact that prior studies mostly relied on subjective visual assessment, there is high variability in interpretation of SSTR-PET for myocardial inflammation. For example, the reported diagnostic performance of SSTR-PET for CS shows sensitivities ranging from 10 to 100%, 11 and significant inter-observer variability is seen even within a study. 18 Objective criteria, that can help distinguish the narrow difference in uptake between normal vs inflamed myocardium, are needed.…”

“…14,15 However, this low-level normal or basal uptake can still be an impediment for the evaluation of myocardial inflammation if the signal is not high-enough to differentiate from the basal uptake. For example, in a study by Lapa et al, the myocardium involved by active CS showed SUVmean of 2.0 ± 1.2 and SUVmax of 2.6 ± 1.2 on 68 Ga-DOTATOC PET/ CT. 16 Previously, we also found myocardial SUVmax in active CS to be only 2.4 ± 0.6 on 68 Ga-DOTATATE PET/CT, much lower than 9.7 ± 3.1 on 18 F-FDG PET/ CT. 11 Similarly, in a recent study on use of 68 Ga-DOTATOC PET/CT in patients with acute myocarditis, the average SUVmax of inflamed myocardium was only 1.8. 17 Given the low target-to-background ratio, combined with the fact that prior studies mostly relied on subjective visual assessment, there is high variability in interpretation of SSTR-PET for myocardial inflammation.…”

“…In our recent study on the use of 68 Ga-DOTATATE PET/ CT in 11 patients with CS, we found up to moderate levels of background myocardial DOTATATE uptake. 11 On a molecular level, this background uptake is mediated by on-target binding to SSTR. Smith et al performed messenger RNA analysis on cardiac biopsies in patients undergoing mitral valve replacement or coronary artery bypass surgery to show expression of SSTR in cardiomyocytes and cardiac fibroblasts.…”