@article {Dashorajnumed.121.262326, author = {Himanshu R Dashora and Joel S Rosenblum and Kaitlin A Quinn and Hugh Alessi and Elaine Novakovich and Babak Saboury and Mark A Ahlman and Peter Grayson}, title = {Comparing Semi-quantitative and Qualitative Methods of Vascular FDG-PET Activity Measurement in Large-Vessel Vasculitis}, elocation-id = {jnumed.121.262326}, year = {2021}, doi = {10.2967/jnumed.121.262326}, publisher = {Society of Nuclear Medicine}, abstract = {The study rationale was to assess the performance of qualitative and semi-quantitative scoring methods for 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) assessment in large-vessel vasculitis (LVV). Methods: Patients with giant cell arteritis (GCA) or Takayasu{\textquoteright}s arteritis (TAK) underwent clinical and imaging assessment, blinded to each other, within a prospective observational cohort. FDG-PET-CT scans were interpreted for active vasculitis by central reader assessment. Arterial FDG uptake was scored by qualitative visual assessment using the PET vascular activity score (PETVAS) and by semi-quantitative assessment using standardized uptake values (SUV) and target-to-background ratios (TBR) relative to liver/blood activity. Performance of each scoring method was assessed by intra-rater reliability using the intra-class coefficient (ICC) and area under receiver-operator characteristic curves (AUC), using physician assessment of clinical disease activity and reader interpretation of vascular PET activity as independent reference standards. Wilcoxon signed-rank test was used to analyze change in arterial FDG uptake over time. Results: Ninety-five patients (GCA=52; TAK=43) contributed 212 FDG-PET studies. The ICC for semi-quantitative evaluation [0.99 (range 0.98-1.00)] was greater than the ICC for qualitative evaluation [0.82 (range 0.56-0.93)]. PETVAS and TBR metrics were more strongly associated with reader interpretation of PET activity than SUV metrics. All assessment methods were significantly associated with physician assessment of clinical disease activity, but the semi-quantitative metric TBRLiver{\textlnot} achieved the highest AUC (0.66). Significant but weak correlations with C-reactive protein were observed for SUV metrics (r = 0.19, p\<0.01) and TBRLiver (r = 0.20, p\<0.01) but not for PETVAS. In response to increased treatment in 56 patients, arterial FDG uptake was significantly reduced when measured by semi-quantitative (TBRLiver 1.31 to 1.23, 6.1\% ∆, p\<0.0001) or qualitative (PETVAS 22 to 18, p\<0.0001) methods. Semi-quantitative metrics provided complementary information to qualitative evaluation in cases of severe vascular inflammation. Conclusion: Both qualitative and semi-quantitative methods to measure arterial FDG uptake are useful to assess and monitor vascular inflammation in LVV. Compared to qualitative metrics, semi-quantitative methods have superior reliability and better discriminate treatment response in cases of severe inflammation.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/early/2021/06/04/jnumed.121.262326}, eprint = {https://jnm.snmjournals.org/content/early/2021/06/04/jnumed.121.262326.full.pdf}, journal = {Journal of Nuclear Medicine} }