Molecular imaging for evaluation of synovitis associated with osteoarthritis: a narrative review

Recent evidence highlights the role of low-grade synovial inflammation in the progression of osteoarthritis (OA). Inflamed synovium of OA joints detected by imaging modalities are associated with subsequent progression of OA. In this sense, detecting and quantifying synovitis of OA by imaging modalities may be valuable in predicting OA progressors as well as in improving our understanding of OA progression. Of the several imaging modalities, molecular imaging such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) has an advantage of visualizing the cellular or subcellular events of the tissues. Depending on the radiotracers used, molecular imaging method can potentially detect and visualize various aspects of synovial inflammation. This narrative review summarizes the recent progresses of imaging modalities in assessing inflammation and OA synovitis and focuses on novel radiotracers. Recent studies about imaging modalities including ultrasonography (US), magnetic resonance imaging (MRI), and molecular imaging that were used to detect and quantify inflammation and OA synovitis are summarized. Novel radiotracers specifically targeting the components of inflammation have been developed. These tracers may show promise in detecting inflamed synovium of OA and help in expanding our understanding of OA progression.