In vivo microCT arthrography (μCTa) can be used to measure both quantity (volumetric) and quality (glycosaminoglycan content) of cartilage. This study investigated the accuracy of four segmentation techniques to isolate cartilage from μCTa datasets and then used the most accurate one to investigate if the μCTa method could show osteoarthritic changes in rat models during longitudinal follow-up. Volumetric measurements and glycosaminoglycan contents of patellar cartilage from in vivo μCTa-scans were compared with an ex vivo gold standard μCT-scan. Cartilage was segmented with three global thresholds and one local threshold algorithm. Comparisons were made for healthy and osteoarthritic cartilage. Next, three rat models were investigated for 24 weeks using μCTa. Osteoarthritis was induced by injection with a chemical (mono-iodoacetate), a surgical intervention (grooves applied in articular cartilage), and via exercise (strenuous running). After euthanasia, all knee joints were isolated for histology. Local thresholds accurately segmented cartilage from in vivo μCTa scans and best measured cartilage quantity and glycosaminoglycan content. Each of the three osteoarthritic rat models showed a specific pattern of osteoarthritis progression. All μCTa results were comparable to histology. In vivo μCTa is a sensitive technique for imaging cartilage degradation. Local thresholds enhanced the sensitivity of this method and will probably more accurately detect disease-modulating effects from interventional strategies. The data from rat models may serve as a reference for the time sequence of cartilage degeneration during in vivo testing of new strategies in osteoarthritis treatment. Copyright

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Journal of Orthopaedic Research: a journal for musculoskeletal investigation
Erasmus MC: University Medical Center Rotterdam

Siebelt, M., Waarsing, J., Kops, N., Piscaer, T., Verhaar, J., Oei, E., & Weinans, H. (2011). Quantifying osteoarthritic cartilage changes accurately using in vivo microCT arthrography in three etiologically distinct rat models. Journal of Orthopaedic Research: a journal for musculoskeletal investigation, 29(11), 1788–1794. doi:10.1002/jor.21444