Comparison between visual and numerical metrics for the evaluation of patients with Takayasu arteritis with 18F-FDG-PET

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The choice of metrics for defining active Takayasu arteritis (TAK) using fluorine-18-fluorodeoxyglucose (F-FDG)-PET remains controversial. The aim of this study was to compare in the same patients the diagnostic performance for the detection of active TAK of different metrics applied for the quantification of vascular F-FDG uptake with PET. Overall, 62 PET acquisitions were performed 90 min after F-FDG injection in 15 patients with TAK and analyzed retrospectively. The intensity of vascular F-FDG uptake was graded visually in comparison with the liver signal and with the numerical metrics, including maximum standard uptake value (SUV), maximum target to background ratio (TBR, ratio of SUVmax in the vessel wall and SUVmean of blood), most-diseased segment (MDS)-TBR (average of TBR from all active lesions), and global TBR (average TBR along the aorta and carotid arteries). The gold standard was disease activity identified using the National Institute of Health score for TAK. Using visual analysis, the definition of F-FDG-PET as positive in presence of at least one vascular lesion with a signal more than liver provided the best diagnostic performance for detecting active TAK with a specificity of 98%, a sensitivity of 62% and an accuracy of 89%. Using numerical metrics, SUVmax [SUVmax >3.3; area under the curve (AUC)=0.84] and TBRmax (TBRmax >2.3; AUC=0.84) offered the best diagnostic performance for the detection of active TAK in comparison with MDS-TBR (MDS-TBR>1.7; AUC=0.70) and global TBR (global TBR >1.4; AUC=0.51). In this study, we found that the analysis of the vascular region with the highest F-FDG uptake using either visual or numerical metrics provided the best diagnostic performance for the detection of active TAK with PET.