Potential usefulness of ⁶⁸ Ga-citrate PET/CT in detecting infected lower limb prostheses

Background: Prosthetic joint infections may lead to failures of total joint arthroplasty. Radionuclide imaging can play a diagnostic role in identifying such infections, which require two-stage exchange arthroplasty (instead of simple revision surgery performed in non-infected cases). Although ¹⁸ F-FDG PET/CT has emerged as a novel diagnostic tool in this setting, the clinical usefulness of ⁶⁸ Ga-citrate PET/CT has not been previously investigated. This single-center prospective study was designed to address this issue. Methods: Between January 2016 and October 2017, we examined 34 patients with clinically proven or suspected prosthetic hip/knee joint infections scheduled to undergo surgery. All patients underwent ⁶⁸ Ga-citrate PET/CT scans and sequential ¹⁸ F-FDG PET/CT imaging for comparative purposes. Intraoperative findings and the results of microbiological analyses of surgical specimens served as gold standard. The diagnostic results were examined according to (1) image interpretation based on radiotracer uptake patterns and (2) quantitative analysis using volumes of interest (VOIs) to calculate standard uptake values (SUVs) and metabolic volumes (MVs). Results: A total of 26 (76%) patients were diagnosed as having infections. Based on radiotracer uptake pattern criteria, the sensitivity, specificity, and accuracy of ⁶⁸ Ga-citrate PET/CT and ¹⁸ F-FDG PET/CT were 92%, 88%, and 91% and 100%, 38%, and 85%, respectively. MV was significantly higher in the infected group when ⁶⁸ Ga-citrate PET/CT was used (422.45 vs. 303.65 cm ³ , p = 0.027), whereas no significant differences were observed on ¹⁸ F-FDG PET/CT. According to receiver operating characteristic (ROC) curve analysis, a cut-off value of 370.86 for MV resulted in a sensitivity of 61.5% and a specificity of 87.5% (area under curve: 0.75, 95% confidence interval: 0.57–0.88, p = 0.035). Conclusions: Subject to future confirmation, our data provide preliminary evidence that ⁶⁸ Ga-citrate PET/CT may have a complimentary role to ¹⁸ F-FDG PET/CT in detecting prosthetic joint infections, being characterized by a higher specificity and the possibility to discriminate between an infectious condition and sterile inflammation. Trial registration: This prospective study was registered at clinicaltrials.gov (registration number: NCT02855190).