Total-Body ¹⁸F-FDG PET/CT in Autoimmune Inflammatory Arthritis at Ultra-Low Dose: Initial Observations

Abstract

Autoimmune inflammatory arthritides (AIA), such as psoriatic arthritis (PsA) and rheumatoid arthritis (RA), are chronic systemic conditions that affect multiple joints of the body. Recently, total-body (TB) PET/CT scanners have become available that exhibit superior technical characteristics (total-body coverage, geometric sensitivity) that could benefit AIA evaluation, compared to conventional PET/CT systems. The objectives of this work were to (1) assess the performance of an ultra-low-dose, ¹⁸F-FDG TB-PET/CT acquisition protocol for evaluating systemic joint involvement in AIA; and (2) report the association of TB-PET/CT measures with joint-by-joint rheumatologic examination and standardized rheumatologic outcome measures. Methods: Thirty participants (24 with AIA and 6 with osteoarthritis (OA)), were prospectively enrolled in this single-center, observational study. All participants underwent a TB-PET/CT scan for 20 min starting at 40 min after intravenous injection of 78.1±4.7 MBq of ¹⁸F-FDG. Qualitative and quantitative evaluation of ¹⁸F-FDG uptake and joint involvement were performed from the resulting images and compared with the rheumatologic assessments. Results: TB-PET/CT enabled the visualization of ¹⁸F-FDG uptake at joints of the entire body, including those of the hands and feet, in a single bed position, and in the same phase of radiotracer uptake. A range of pathologies consistent with AIA (and non-AIA in the OA group) were visualized, and the feasibility of extracting PET measures from joints examined by rheumatologic assessments was demonstrated. Out of 1997 evaluable joints, there was concordance between TB-PET qualitative assessments and joint-by-joint rheumatologic evaluation in the AIA and non-AIA cohorts for 69.9% and 91.1% joints, respectively, while an additional 20.1% and 8.8% joints, respectively, deemed negative on rheumatologic examination showed PET-positivity. On the other hand, 10.0% and 0% joints in the AIA and non-AIA cohorts, respectively, were positive on rheumatologic evaluation but negative on TB-PET. Quantitative measures from TB-PET in the AIA cohort demonstrated a moderate to strong correlation (Spearman's ρ=0.53-0.70, p<0.05) with the rheumatologic outcome measures. Conclusion: Systemic joint evaluation in AIA (and non-AIA) is feasible with a TB-PET/CT system and an ultra-low-dose protocol. Our results provide the foundation for future larger studies to evaluate the possible improvements in AIA joint assessment via the TB-PET/CT technology.