Diffusion-weighted imaging of synovitis. Gonarthritis of the right knee in a 2-year-old girl with juvenile idiopathic arthritis (JIA). Marked synovial thickening and contrast enhancement accompanied by joint effusion are seen on transversal T1W TSE FS (a). DWI at b = 1000 with inverted gray scale depicts synovitis based on restricted diffusion on a corresponding transversal section acquired with 2 averages and 41s scan time (b). Joint effusion shows low signal on DWI and can be distinguished from the surrounding layer of synovitis. The unaffected left knee does not show inflammatory signal alterations on contrast-enhanced T1W imaging, nor on DWI. Overlay of colourised DWI b = 1000 data on coronal pre-contrast T1W TSE (c) with semi-automatic 3D image fusion.