Purpose: Studies in OA commonly focus on a single joint. However, clinical outcomes such as quality of life questionnaires, physical performance-based tests, and systemic biochemical marker levels will be influenced by OA affecting multiple joints. Low dose computed tomography (CT) provides valuable information on the bony aspects of the joints, including osteophyte formation, sclerosis and joint space width with a relative high signal-to-noise ratio as a result of the high density of bone. Whole-body low dose CTs (WBLDCT) with an effective radiation dose <3 mSv (comparable to one year of background radiation) can be used to capture osteoarthritis of joints throughout the body. In the present study we developed an atlas describing a new scoring system for degenerative joint disease and tested its reliability. Methods: WBLDCTs from 198 patients in a cohort of clinical scans in our hospital (indications include cancer, vascular and infectious disease) were used to develop the atlas. The acromioclavicular, glenohumeral, hip, patellofemoral, tibiofemoral, facet and ankle joints and intervertebral discs were incorporated in the scoring system. The elbow is frequently positioned outside the field of view of the WBLDCT and was excluded. We modified existing radiographic and CT-based scoring instruments to four-grade scores per joint. Example images of scored items were collected in an atlas. The goal was to enable to reliably score all joints of a single patient in approximately 15 minutes. We produced a Whole-body OA grade by summing the grades of 24 separate joints (0-3) to obtain a score ranging from 0 to 72. We additionally calculated an Extremity-OA grade, by summing the grades of all joints except the intervertebral discs and facet joints. To test intra-observer reliability a medical doctor/researcher (WPG) scored 25 randomly selected WBLDCTs twice, with at least one week in between. To test inter-observer reliability the atlas was used as reference for the grading system by one radiologist in training with a subspecialization in musculoskeletal radiology (WF) and a fellowship-trained musculoskeletal radiologist with five years of experience (FJN). WF and FJN scored the same random sample of 25 scans independently. Scores for the IVD and facet joints were not yet available for FJN at the time of this interim analysis. Reliability was tested using Cohen’s kappa for binominal grade, squared weighted kappa for ordinal grade and Intraclass Correlation Coefficient (ICC) for continuous grades. In addition to kappa statistics, absolute agreement percentages for binominal and ordinal grades were assessed. All analyses were carried out in R v3.4.4 using IRR package v0.84. Results: The 25 patients (14 female) had a mean age (SD) of 54 (±17) years. Prevalence of OA scores per joint are shown in Table 1. Intra-observer reliability and agreement of the separate grades were good with kappa’s ranging from 0.79 to 0.95 and absolute agreement ranging from 67% to 92% (Table 2). Intra-observer reliability of the Whole-body OA grade and extremity OA grade were excellent with ICCs of 0.97 (95%-CI 0.94 to 0.99) and 0.95 (95%-CI 0.90 to 0.98). Inter-observer reliability and agreement of the separate grades were moderate to substantial with kappa’s ranging from 0.48 to 0.95 and absolute agreement ranging from 36% to 90% (Table 2). Inter- observer reliability of the Whole-body OA grade and extremity OA grade were excellent with ICCs of 0.95 (95%-CI 0.90 to 0.98) and 0.95 (95%-CI 0.90 to 0.98). Conclusions: We developed a novel grading system for osteoarthritis of the whole body using low-dose CTs. Subsequently we tested intra- and inter-observer reliability and agreement for scores per joint, the Whole-body OA grade, and Extremity-OA grade. In this interim analysis we consider the intra- and inter-observer reliability and agreement sufficient to be used in future research. An atlas was compiled to consistently teach new readers the grading system.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)