In vivo molecular imaging of experimental joint inflammation by combined 18F-FDG positron emission tomography and computed tomography

Introduction The purpose of this work was to establish and validate combined small animal positron emission tomography - computed tomography (PET/CT) as a new in vivo imaging method for visualisation and quantification of joint inflammation. Methods Signalling of radioisotope .sup.18F labelled Fluorodeoxyglucose (.sup.18F-FDG) injected in mice with glucose-6-phosphate isomerase (G6PI)-induced arthritis was analysed by PET/CT. Accumulation of .sup.18F-FDG in tissue was quantified by PET measurement, whereas high definition CT delivered anatomical information. The fusion of both images revealed in detail spatial and temporal distribution and metabolism of .sup.18F-FDG. Results A distinct .sup.18F-FDG signal could be measured by PET in carpal and tarsal joints, from mice with early or established arthritis. In contrast, no accumulation of .sup.18F-FDG was detectable before arthritis onset. Comparison of .sup.18F-FDG joint uptake with histopathological evaluation revealed a significant correlation of both methods. Conclusions Small animal PET/CT using .sup.18F-FDG is a feasible method for monitoring and, more importantly, quantitative assessment of inflammation in G6PI-arthritis. Since it is possible to perform repeated non-invasive measurements in vivo, not only numbers of animals in preclinical studies can markedly be reduced by this method, but also longitudinal studies come into reach, e. g. for individual flare-up reactions or monitoring therapy response in progressive arthritis. Keywords: Positron Emission Tomography, Histopathological Assessment, Arthritis Severity, Experimental Arthritis, Positron Emission Tomography Measurement