Quantification of 18 F-fluoride uptake in progressive arthritis. Pathological effects in arthritic bone metabolism differed from 18 F-fluoride accumulation before clinical arthritis onset can be seen above an arbitrary baseline of 2 and 4 standardized uptake value (SUV) for fore and hindpaws, respectively. (A) Two days after onset of clinical arthritis at day 9, uptake of 18 F-fluoride in forelimbs was significantly enhanced (day 11). In chronic arthritis at days 18 and 25, 18 F-fluoride accumulation was further increased significantly compared to day 8, whereas in late chronic arthritis (day 39), tracer uptake was declining (n = 6 to 12 paws per time point). (B) Hindlimb pathological arthritic bone metabolism, reflected by 18 F-fluoride signaling in the tarsal joint and metatarsal bones, coincided with forelimb 18 F-fluoride signaling (n = 6 to 12 paws per time point). (C) High-level 18 F-fluoride uptake in distal femoral bone was similar at various time points in the course of arthritis pathogenesis, except for a significant decrease at day 39. (D) Low-level 18 F-fluoride uptake in medial cortical femoral bone was comparable at various time points of arthritis pathogenesis. *P < 0.05, **P < 0.01, ***P < 0.001.