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To study the early change of bone matrix and soft tissue around articulation in adjuvant-induced arthritic (AIA) rats non-invasively by X-ray phase-contrast imaging (XPCI), a new imaging method.Adjuvant-induced arthritis was established in male Sprague-Dawley (SD) rats (n=6, age 40 days) by subcutaneous injection of Freund's complete adjuvant (FCA) into the left hindpaw. In vivo XPCI evaluation of the early soft tissue and bone changes in AIA rats was consecutively performed and correlated with changes in volumes of right hindpaws and body weights. In comparison, the changes in the AIA rats were also evaluated with absorption-contrast imaging using the same X-ray source as XPCI and conventional radiography at the same time. After the imaging evaluation, AIA rats were subjected to histological examination.There was significant difference between the score of XPCI and the other two methods in demonstrating soft tissue (P<0.01), bone details (P<0.01) and lesions (P<0.001). By day 10 after subcutaneous injection of FCA, bone changes in the right hindpaw were not obvious, but swelling of soft tissue appeared. By day 12, bone erosion in the articular facet and the area around the articular facet, was detected, along with osteoporosis, and swelling of soft tissue was aggravated. By day 14 bone erosions became fused and expanded, especially in the margin area around the articular facet. At day 16 bone erosion still existed. Joint interspaces seemed wider than normal, and swelling of soft tissue was significant. By day 18 periosteal new bone formation was seen definitely, destruction of bone decreased, bone density around the articular was enhanced, and swelling of soft tissue was relieved. XPCI could clearly distinguish all these alterations, which could not be demonstrated by absorption-contrast imaging and conventional radiography. During the test period, the volume of the right hindpaw and the body weight of the AIA rats also changed significantly compared with the normal rat. Histological examination confirmed that adjuvant-induced arthritis had occurred in all rats of the adjuvant group.Osteoporosis, bone erosion and periosteal new bone formation take place at the early stage of adjuvant-induced arthritis. XPCI can evaluate non-invasively these subtle bone changes that are “blind areas” for conventional radiography.