Comparative Study With Different Tracers (18F-FDG and 68Gallium Citrate) in the Diagnosis of Periprosthetic Joint Infection

This is an open-labelled two-arm pilot comparative prospective study. All the subjects will undergo image assessment in the two stages of exchange arthroplasty surgery. At the first stage, each enrolled subject will receive both FDG and Ga68 citrate PET/CT scans before the first operation for periprosthetic Joint Infection (PJI). Thus, the test results of FDG and Ga68 for each individual can be obtained. After the first operation, the surgery/biopsy proof can be obtained as the gold standard. The subjects those with PJI negative will complete the process at the first stage. And the second stage of this study will be based on the subjects with positive PJI from the first operation. They will receive both FDG and Ga68 citrate PET/MR scans after antibiotic bone cement was implanted. The sensitivity/accuracy of the two tracers for PET/MR can be calculated and compared. This stage is aimed to answer whether PET/MR scan is a feasible imaging tool to provide diagnostic information of infection control status after the resection arthroplasty of hip/knee PJIs, especially with the implantation of antibiotic loaded bone cement. In the second stage, the investigators shift the imaging modality to PET/MR based on the following reasons: (1) MRI itself has no radiation burden; (2) MRI provides more accurate tissue contrast information and therefore better anatomic delineation; and (3) currently there was no study indicating the existence of ABLC may hamper the interpretation of images. The study duration is expected to be completed in a period of 3 year. It plans to enrol a total of 40 evaluable subjects with suspicious. And we expect the PJI prevalence will be around 75%, i.e. the anticipated number of subjects of true PJI is around 30. The sample size and the prevanence is given based on the clinical availability and consideration.