Accurate assessment of disease activity and joint damage in rheumatoid arthritis (RA) is important for monitoring of treatment efficiency and predicting outcome of the disease. Musculoskeletal ultrasonography (US) has become an important imaging technique in RA. US is able to detect both early inflammatory soft tissue lesions (e.g. synovitis, tenosynovitis, and bursitis) and early erosive bone lesions (e.g. erosions) in arthritic joint diseases. Studies show good correlation between US and Magnetic Resonance Imaging (MRI) in detection of inflammatory soft tissue lesions and erosive bone lesions.
Indocyanine green (ICG) enhanced fluorescence optical imaging (FOI) with Xiralite system is a novel diagnostic tool for the assessment of inflammation in joint diseases. ICG-FOI is an established technology for imaging of inflammation in animal models. In experimental models of arthritis, FOI findings corresponded to histologically proven synovitis . The feasibility of this approach in humans was tested, [2,3] and an FOI system with fixed optical geometry was developed (Xiralite X4; mivenion GmbH, Berlin, Germany).
FOI is performed with the commercial available Xiralite system by using 0.1 mg/kg bodyweight of indocyanine green as fluorophor. Images are acquired every second for 6 minutes, starting 10 seconds prior to intravenous fluorophor injection. Image interpretation is done for three defined phases of contrast enhancement in the finger tips: early (P1), intermediate (P2), and late phase (P3) and for an automatically generated composite image (PrimaVistaMode, PVM). An adequate interpretation of an FOI sequence requires a separate evaluation of all phases.
In the first large comparison study of FOI, US, MRI and clinical examination we found that FOI correlated significantly with disease activity scores (DAS28, US score, RAMRIS). Monitoring of disease activity and valid assessment of remission, the special target for RA treatment, are a crucial aspect with respect to the rapidly growing armamentarium of disease-modifying drugs. The data indicate that FOI may be an additional tool for the assessment of disease activity in arthritic conditions .
Another comparison study with early and very early untreated arthritis patients and healthy controlls without any sings of inflammatory joint diseases presents good results between MRI and FOI. Intrareader and interreader agreement were moderate to substantial (kappa 0.53-0.73). FOI showed positive findings in 0.5%>5% of normal joints in the control group.
ICG-enhanced FOI with the Xiralite system is a new imaging technology that allows a sensitive and valid assessment of inflammation in arthritis. FOI was comparable to 1.5 T magnetic resonance tomography MRI and ultrasound (US) in detecting synovitis and tenosynovitis. Thereby, it is a fast and safe imaging screening tool for patients with suspected arthritis. Furthermore, FOI is useful for objectifying treatment response and treatment monitoring. FOI was more sensitive than clinical examination (CE). In addition, FOI could be helpful in the differentiation of nail involvement and arthritis of distal interphalngeal joints (DIP) in patients with psoriasis and/or psoriasis arthritis. However, further investigations are needed for a comprehensive definition of FOI pathologies, advancement of methodical standards and evaluation of sensitivity to change and prognostic value.
Meier R, Krug C, Golovko D, et al. Indocyanine green-enhanced imaging of antigen- induced arthritis with an integrated optical imaging/radiography system. Arthritis Rheum 2010;62:2322–7.
Ebert B, Berger J, Voigt J, et al. Early detection of rheumatoid arthritis in humans by fluorescence imaging. Biomedical Optics, OSA Technical Digest (CD). Optical Society of America, 2008, p. BTuF19.
Fischer T, Gemeinhardt I, Wagner S, et al. Assessment of unspecific near-infrared dyes in laser-induced fluorescence imaging of experimental arthritis. Acad Radiol 2006;13:4–13.
Werner SG, Langer HE, Ohrndorf S et al. Inflammation assessment in patients with arthritis using a novel in vivo fluorescence optical imaging technology. Ann Rheum Dis. 2012 Apr;71(4):504-10.
Disclosure of Interest None Declared
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