Exploratory comparison of diffusion-weighted whole-body imaging with background body signal suppression and 18F-FDG PET/CT for assessing disease activity in large-vessel vasculitis.

OBJECTIVES To compare diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) with ^18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) for assessing disease activity in large-vessel vasculitis (LVV), and to evaluate whether segment-level analysis provides complementary information beyond global grading.

METHODS We enrolled 25 patients with LVV (Takayasu arteritis [TAK], n = 11; giant cell arteritis [GCA], n = 14). Two blinded readers graded 11 arterial territories (18 segments) on a four-point visual scale for DWIBS and FDG-PET/CT. Global imaging grades were calculated as segment-averaged means. Correlations with serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were assessed.

RESULTS Global mean DWIBS grades correlated significantly with FDG-PET/CT grades (r = 0.72) and with CRP levels (r = 0.53). Territory-level mapping revealed diffuse central aortic involvement in GCA, whereas TAK showed more focal and segment-limited patterns. DWIBS demonstrated lower sensitivity in motion-prone regions but appeared to better reflect clinical activity and more frequently detected subclavian artery involvement in TAK compared with FDG-PET/CT. Residual vascular signals were also observed in some patients classified as being in clinical remission.

CONCLUSIONS DWIBS shows good agreement with FDG-PET/CT and provides a radiation- and contrast-free approach for assessing LVV. Global mean grades alone showed limited discriminatory power and may underestimate disease activity in focal or segment-limited involvement. Integrating segment-level imaging findings with clinical and laboratory markers may improve assessment of disease activity. Multicenter validation and longitudinal studies are warranted.