Both of synovitis and joint effusion showed low signal intensity on T1WI, high signal intensity on T2WI and DWI. Although synovitis has a relatively lower signal intensity than joint effusion in T2WI, it is difficult to distinguish them due to similar contrast. Synovitis was judged by CE-MRI according to the definition by the OMERACT¹. The differentiation between bone erosion and cysts in OA is also extremely difficult without CE-MRI, since MRI bone erosion was enhanced based on either invading synovial tissue (pannus). Apparent diffusion coefficient (ADC) mapping provides a non-invasive mean of detecting synovitis and bone erosion in their early stage. To our knowledge, this is first study to investigate synovitis and bone erosion by using ADC mapping so far. The aim of study was to assess the value of ADC mapping in distinguishing synovitis from joint fluid , as well as bone erosion from cysts. 25 patients (6 male, 19 female, age = 50.68 ±7.96 years) with suspect RA who had swelling and pain of the wrists and hands. The MR imaging examinations were performed with using 3.0 T MR acquisition systems (Ingenia; Philips Healthcare, the Netherlands) by using a quadrature body coil to cover bilateral wrists and hands. The imaging parameters for transverse DWI: TR/TE, 4300 ms/58.9 ms; b value, 0 and 600 s/mm2, slice thickness/gap, 5 /0.5 mm; FOV, 300× 95 mm; and matrix, 152 × 63. Contrast-enhanced imaging (TR/TE, 10.308/2.052ms; flip angle, 10°; slice thickness/gap, 1.2 /0 mm; FOV, 300 × 300 mm; matrix, 320 × 320). Images were evaluated for the presence of synovitis and joint effusion in the wrist(distal radioulnar joint, radiocarpal joint, intercarpal-carpometa carpophalangeal joints) according to the EULAR-OMERACT rheumatoid arthritis MRI reference image atlas and joints of the hand including (metacarpophalangeal (MCP) joints I–V, proximal interphalangeal (PIP) joints I–V, the distal interphalangeal (DIP) joints II–V). T-test was used for the comparison between the mean ADC values of bone erosion and cysts, synovitis and joint effusion by using IBM SPSS Statistics 20.0 (Armonk, New York, USA). P < 0.01 was considered statistically significant. Differences between ADC values in synovitis and joint fluid, and bone erosion and cysts were compared using ROC analysis. 93 suspect synovitis and 70 suspect bone erosion were found by anatomical MRI. 53 synovitis (mean ADC values=1.63 ±0.375 x10^-3mm² /s), 40 joint fluid (mean ADC values=2.6 ±0.369 x10^-3mm² /s), 62 bone erosion(mean ADC values =1.61 ±0.39 x10^-3 mm² /s) and 8 cysts (mean ADC values =2.39 ±0.318 x10^-3 mm² /s) were found by CE- MRI. ADC value of synovitis was significantly lower than that of the joint effusion. ADC value of bone erosion was significantly lower than that of the cysts. ADC values of 2.0 10^-3mm² /s was found, distinguishing joint effusion from synovitis (specificity= 90 %, sensitivity=90 %; ROC AUC=0.974), and bone erosion from cysts (specificity= 90 %, sensitivity=87.5 %; ROC=AUC 0.952).DWI can reliably detect and characterize synovitis of wrist and hand. Inflamed lesions were seen as hyperintense relative to the surrounding presumably normal tissues on DWI due to the infiltration of the inflammatory cells which could demonstrate impeded molecular water mobility. Because it was very difficult to perform exact and reproducible ADC measurements in the small positive areas of wrist and hand with such complex anatomical structures. There have been no studies of the relation between apparent diffusion coefficient (ADC) values from changes of synovium and bone with RA², although measurement of ADC values is valuable for the diagnosis of bone tumors³ and arthritis such as sacroiliitis⁴. In our study, ADC values of bone erosion and synovitis were lower than cysts and joint effusion. We therefore conclude that measurement of ADC values could be effective in quantifying changes of inflammation in skeletal lesions.MR diffusion provides additional information to the routine MRI sequences rendering it an effective non-invasive tool in differentiating between synovitis and joint effusion, and bone erosion and cysts.