Metabolic inflammatory volume and total inflammatory glycolysis: novel parameters to evaluate PET-CT disease activity in Takayasu arteritis.

ABSTRACT

OBJECTIVES: To evaluate diagnostic accuracy for active Takayasu arteritis (TAK) for two novel 18F-fluorodeoxyglucose PET-CT parameters, the inflammatory volume (MIV) and total inflammatory glycolysis (TIG), to quantitate volume of metabolically-active arterial tissue. METHODS: From a cohort of TAK (n = 36, 35 immunosuppressive-naïve), images of PET-CTs were reviewed for mean and maximum standardized uptake value (SUVmean and SUVmax), target-to-blood pool ratio (TBR), target-to-liver ratio (TLR), and PET Vasculitis Activity Score (PETVAS). Regions of interest were drawn to semiautomatically calculate MIV in areas of 18F-fluorodeoxyglucose uptake ≥ 1.5 SUVmean after excluding physiological tracer uptake. TIG was calculated by multiplying MIV with SUVmean. PET-CT parameters, ESR, CRP, and clinical disease activity scores were compared against the gold standard of physician global assessment of disease activity (PGA, active/inactive). RESULTS: Using dichotomized cut-offs for active TAK at SUVmax (≥ 2.21), SUVmean (≥ 1.58), TBR (≥ 2.31), TLR (≥ 1.22), PETVAS (various cut-offs), ESR (≥ 40 mm/hour), and CRP (≥ 6 mg/L), the novel indices MIV (≥ 1.8) and TIG (≥ 2.7) performed similar [area under the receiver operating characteristics curve (AUC) 0.873 for both] to SUVmax (AUC 0.841) and SUVmean (AUC 0.851), and better than TBR (AUC 0.773), TLR (AUC 0.773), PETVAS [≥ 5.5 (AUC 0.750), ≥ 10 (AUC 0.636), ≥ 15 (AUC 0.546)], ESR (AUC 0.748), or CRP (AUC 0.731). MIV and TIG had similar agreement with PGA or CRP as with SUVmax or SUVmean, and better agreement than TBR, TLR, or PETVAS cut-offs. CONCLUSIONS: MIV and TIG performed similarly, therefore, are viable alternatives to existing PET-CT parameters to assess TAK disease activity in this preliminary report. Key Points • MIV and TIG performed similar to SUVmax and SUVmax for disease activity assessment in TAK. • MIV and TIG distinguished active TAK better than TBR, TLR, PETVAS cut-offs, ESR, or CRP. • MIV and TIG had better agreement with PGA or CRP than TBR, TLR, or PETVAS cut-offs.