Combination of 18F-fluorodeoxyglucose positron emission tomography/computed tomography and magnetic resonance imaging is an optimal way to evaluate rheumatoid arthritis in rats dynamically

Background Rheumatoid arthritis (RA) is a chronic, systemic autoimmune inflammatory disorder. Many methods have been used to observe the progress of RA. The purpose of this study was to observe the progress of RA in rats with F-18-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT), magnetic resonance (MR) imaging and arthritis score, and analyze the relationships among different methods in evaluation of RA. Methods Sixteen healthy Sprague Dawley (SD) rats about 8-week old were randomly assigned to a RA group and a control group. Bovine type II emulsified incomplete Freud's adjuvant was used to induce arthritis in the RA group. Arthritis score of the rats in two groups were recorded, and F-18-FDG PET/CT, MR imaging were performed both on the corresponding rats every 3 days. All the rats were sacrificed at week 5, and histopathological examination was performed on rat knees stained with haematoxylin and eosin. Results The arthritis score and the standard uptake value (SUV) of knee joints in RA rats increased with the progression of arthritis gradually. Both peaks of arthritis score and SUV appeared at 21 days after the first immune injection, then the arthritis score and SUV of knee joints decreased slowly. The arthritis scores of knee joints in RA rats were positively correlated with their SUV changes. The MR images were confirmed by the histopathological studies. Conclusion PET/CT can detect the earliest molecular metabolism changes of RA, and MR imaging can follow up the dynamical anatomical changes of RA, all of which indicated that PET/CT and MR imaging may be applied as useful tools to monitor the progress of RA.