¹⁸F-sodium fluoride PET/CT as a complementary measure of osteoblastic disease burden in axial spondyloarthritis: a prospective exploratory study

Purpose To determine whether SIJ ¹⁸F-NaF uptake is associated with MRI-defined inflammation and structural damage and whether it provides a complementary measure of osteoblastic disease burden.Methods In this prospective exploratory study, 43 adults with chronic low back pain underwent pelvic radiography, sacroiliac joint (SIJ)-MRI, and whole-body ¹⁸F-NaF PET/CT and were classified as having radiographic axial spondyloarthritis or ankylosing spondylitis (AS; n = 29), non-radiographic axial spondyloarthritis (nr-axSpA; n = 5), or degenerative joint disease (DJD; n = 9). MRI was evaluated using SPARCC inflammation and structural scores. SIJ uptake was assessed visually and quantified using SUVmax. The primary endpoint was the correlation between SIJ SUVmax and the SPARCC structural score.Results SIJ SUVmax correlated with the SPARCC inflammation (ρ = 0.629) and structural (ρ = 0.606) scores (both p Conclusion SIJ ¹⁸F-NaF uptake was associated with both MRI-defined inflammation and structural burden in patients with AS, including those without active inflammation on MRI. SIJ SUVmax warrants evaluation as a complementary quantitative imaging biomarker of osteoblastic disease burden, but all derived thresholds require external validation.