Imaging Acquisition Technique Influences Interpretation of Positron Emission Tomography Vascular Activity in Large-Vessel Vasculitis

Abstract Objectives To determine the impact of imaging acquisition time on interpretation of disease activity on 18F-fluorodeoxyglucose positron emission tomography (PET) in large-vessel vasculitis (LVV) and assess the relationship between clinical features and image acquisition time. Methods Patients with giant cell arteritis (GCA) and Takayasu's arteritis (TAK) were recruited into a prospective, observational cohort. After a single injection of FDG, all patients underwent two sequential PET scans at one and two-hour time points. Images were interpreted for active vasculitis by subjective assessment, qualitative assessment, and semi-quantitative assessment. Agreement was assessed by percent agreement, Cohen's kappa, and McNemar's test. Multivariable logistic regression identified associations between PET activity and clinical variables. Results 79 patients (GCA=44, TAK=35) contributed 168 paired one and two-hour PET studies. A total of 94 out of 168 scans (56%) were interpreted as active at the one-hour time point, and 129 scans (77%) were interpreted as active at the two-hour time point (p Conclusions Imaging protocol significantly influences interpretation of PET activity in LVV. A substantial proportion of patients with LVV have PET activity only detected by delayed imaging. These patients were significantly more likely to have concomitant clinically-determined active disease.