Background/Purpose: Modern diagnostic imaging technologies including US and MRI become increasingly important in the management of rheumatic joint disorders. Semiquantitative scores, like the RAMRIS or the US7 – score aim at measuring disease activity especially for clinical trials. Most recently, fluorescence optical imaging (FOI) became clinically available for diagnostic imaging. Most recently, it has been shown that automatic, computer-based image analysis of FOI using dedicated software is technically feasible and offers high reproducibility. Measurement of areas of high signal intensity expressed as DACT value may provide a reliable quantitative readout for inflammatory activity. In this feasibility study we compared the results of visual reading of FOI using the semiquantitative scoring system FOIAS (fluorescence optical imaging activity score) for visually assessment with this automatic, computer-based algorithm for quantitative analysis.

Methods: 45 patients (34 f, mean age 55y, mean DAS28 4.2) were selected. First 4 readers analyzed all 45 image data sets individually, and then 2 of the four readers performed a consensus reading. For articular location of increased signal intensities (ISI) the FOIAS was used. For extraarticular location the signals were graded semiquantitatively on a scale of 0 to 2. These values were added to a single number representing the overall fluorescence signal intensity of the hands (cFOIAS, complete FOIAS).  For DACT the automatically generated composite images were generated. Using dedicated parameters of the histograms, automatic extraction of the hands from the image background was performed by the computer. The algorithm separated the hands from the forearm in a standardized manner by using a multiple of the length of the middle finger. A threshold in the fluorescence intensity curve was set to discriminate high and low intensity areas. The area of high intensity was calculated and the values of each patient were divided by the 90th percentile of normal individuals which was defined as reference value. DACT was expressed as high signal intensity area  _patient / healthy reference. DACT in healthy individual equaled 1. Then cFOIAS and DACT value were compared.

Results: Correlation of the cFOIAS and the DACT value was high, while all 4 readers and the consensus readings showed good interreader reliability. Two sample scatter plots are shown in the figure.

Conclusion: Assessment of disease activity in FOI using automated, computer-based algorithms correlated well with visual assessment with a scoring system. While the semiquantitative assessement is time consuming and can be biased by the reader, the automatic calculation may be an objective and fast tool for assessment of disease activity. Following work should concern to proof this and the potential value of DACT for monitoring of treatment response in longitudinal, interventional studies.