Three-dimensional analysis and visualization of regional MR signal intensity distribution of articular cartilage

The aim of this study was to develop a technique for analyzing and visualizing the regional, three-dimensional signal intensity distribution of articular cartilage in MR images, as a potential surrogate marker of structural or biochemical alterations in early osteoarthritis. Exemplary MR-images of human patellae were acquired at a resolution of 1.5 x 0.31 x 0.31 mm(3), using a gradient-echo sequence with water excitation, and by combining three data sets to secondary images of proton density. After segmentation of the cartilage outlines, these were transferred to the other images. Contiguous slices were automatically divided into sub-regions that extend from the surface to the bone interface (layers) as well as from medial to lateral (sections). The signal intensity was then calculated and projected onto a three-dimensional representation of the articular surface, either by averaging through the depth (sections) or by visualizing the signal intensity at distinct levels in depth (layers). The exemplary data indicate that the reproducibility for regional analyses is in the same range as for the entire patellar cartilage, and that the distribution patterns of proton density delineated with MRI are in agreement with the literature. In conjunction with suitable MR protocols, this post-processing technique has potential to allow for detection and quantification of early degenerative processes in cartilage, before macro-morphological lesions occur.