Correlation between the oxygenation status of extrasynovial tissue in the wrist and disease activity in rheumatoid arthritis: a photoacoustic imaging study

Objective RA is characterized by hypoxia in the synovial tissue. While photoacoustic (PA) imaging offers a method for evaluating tissue oxygenation in RA patients, studies exploring the link between the oxygenation status of extrasynovial tissue in the wrist and disease activity remain scarce. We aimed to assess synovial oxygenation in RA patients using a multimodal photoacoustic-US (PA/US) imaging system and establish its correlation with disease activity.Methods A retrospective study was conducted on 111 patients with RA and 72 healthy controls from 2022 to 2023. Dual-wavelength PA imaging quantified oxygen saturation (So2) levels in the synovial membrane and peri-wrist region. Oxygenation states were categorized as hyperoxia, intermediate oxygenation, and hypoxia based on So2 values. The association between oxygenation levels and the clinical disease activity index was evaluated using a one-way analysis of variance, complemented by the Kruskal-Wallis test with Bonferroni adjustment.Results Of the patients with RA, 39 exhibited hyperoxia, 24 had intermediate oxygenation, and 48 had hypoxia in the wrist extrasynovial tissue. All of the control participants exhibited the hyperoxia status. Oxygenation levels in patients with RA correlated with clinical metrics. Patients with intermediate oxygenation had a lower disease activity index compared with those with hypoxia and hyperoxia.Conclusion A significant correlation was found to exist between wrist extrasynovial tissue oxygenation and disease activity in patients with RA.