COVID-19 vaccination, implications for PET/CT image interpretation and future perspectives

Introduction: The present paper aims to systematically review the literature on COVID-19 vaccine-related findings in patients undergoing PET/CT. Methods: The search algorithms included the following combination of terms: "PET" OR "positron emission tomography" AND "COVID"; "PET" OR "positron emission tomography" AND "COVID" AND "vaccination"; "PET" OR "positron emission tomography" AND "COVID", AND "autoimmune". Results: We selected 17 articles which were assessed for quality and included in the systematic analysis. The most frequent vaccine-related signs on PET/CT were the deltoid [18F]FDG uptake and axillary hypermetabolic lymph nodes, which were described in 8-71% and 7-90% of the patients, respectively. Similarly, frequency of these findings using other tracers than [18F]FDG was greatly variable. This large variability was related to the variability in time elapsed between vaccination and PET/CT, and the criteria used to define positivity. In addition, vaccine-related findings were detected more frequently in young and immunocompetent patients than in elderly and immunocompromised ones. Discussion: Therefore, awareness on vaccination status (timing, patient characteristics, and concurrent therapies) and knowledge on patterns of radiopharmaceutical uptake are necessary to properly interpret PET/CT findings.