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Indocyanine green-enhanced fluorescence optical imaging in patients with early and very early arthritis: a comparative study with magnetic resonance imaging.

OBJECTIVE
Indocyanine green-enhanced fluorescence optical imaging (FOI) is a novel diagnostic tool for the assessment of inflammation in arthritis. We undertook this study to compare FOI with magnetic resonance imaging (MRI) in 32 patients with early and very early untreated arthritis (mean disease duration 7.1 months).


METHODS
FOI images were acquired with the commercially available Xiralite system. Image interpretation was done for an early phase (phase 1), an intermediate phase (phase 2), and a late phase (phase 3), and for an electronically generated composite image. The results were compared with those of clinical examination (960 joints) and contrast (gadolinium)-enhanced 1.5T MRI (382 joints) of the clinically more affected hand. Additionally, we evaluated FOI in a control group of 46 subjects without any signs of inflammatory joint disease (1,380 joints).


RESULTS
With MRI as the reference method, the sensitivity of FOI was 86% and the specificity was 63%, while the composite image, phase 1, and phase 3 reached high specificities (87%, 90%, and 88%, respectively). The results differed considerably between the composite image and the phases. FOI did not detect inflammation in 11 joint regions that showed palmar tenosynovitis on MRI. Intrareader and interreader agreements were moderate to substantial (κ = 0.55-0.73). In the control group, FOI showed positive findings in 5% of normal joints in phase 2.


CONCLUSION
Further multicenter studies will address the question of whether FOI allows sensitive and reliable detection of inflammatory changes in early arthritis, as suggested by our initial findings. If this is confirmed, FOI has the potential to be a sensitive and valuable tool for monitoring disease activity on site in clinical settings and for serving as an outcome parameter in clinical trials.