Clinical and Experimental Rheumatology 2009; 27: 580-586. Multimodal optical and Gd-based nanoparticles for imaging in inflammatory arthritis J.S. Kim 1 , H. An 2 , W.J. Rieter 1 , D. Esserman 3 , K.M.L. Taylor-Pashow 1 , R.B Sartor 4 , W. Lin 2 , W. Lin 1 , T.K. Tarrant 5 1 Department of Chemistry, 2 Department of Radiology, 3 School of Medicine and School of Public Health, 4 Division of Gastroenterology and Hepatology, Department of Medicine, 5 Thurston Arthritis Research Center and the Department of Medicine, Division of Rheumatology, Allergy, and Immunology, University of North Carolina School of Medicine, Chapel Hill, USA. Abstract Objective This report documents a multimodal nanoparticle (MNP) contrast agent, containing embedded luminophores and surface-immobilized gadolinium chelates, as a contrast agent of inflamed synovium in a collagen induced arthritis (CIA) model. Methods DBA-1J mice were immunized for CIA and imaged after disease onset by two independent modalities. After intravenous administration of MNP contrast, optical and magnetic resonance images were obtained and clinical disease was scored, which was followed by processing of hindlimbs for immunofluorescence and confocal microscopy. Results We show a correlation between disease severity and MNP optical luminescence that is dose dependent. Immunofluorescence of hindlimb sections reveal that MNP-labeled cells are monocytes/macrophages within the inflamed synovium. Magnetic resonance (MR) relaxation time maps, which determine the quantitative measure of T1 and T2 values at each imaging voxel, demonstrated a decreasing T2 signal in actively inflamed joints that was more pronounced earlier rather than later during disease. Conclusions MNPs containing surface-immobilized gadolinium chelates and embedded luminophores are potential dual-modality contrast agents in inflammatory arthritis and localize to monocytes/macrophages within inflamed synovium. Key words Nanostructures, arthritis, inflammation, magnetic resonance imaging, macrophages, monocytes, diagnostic imaging.