EFFECTS OF COLLAGEN ORIENTATION ON MR-IMAGING CHARACTERISTICS OF BOVINE ARTICULAR-CARTILAGE

To determine the influence of collagen orientation on the magnetic res onance (MR) imaging appearance of articular cartilage, spin-echo MR im ages of normal bovine patellar specimens were obtained with the specim en rotated in 5-degrees increments between +75-degrees and -130-degree s. Hyperintense superficial, hypointense middle, and intermediate-inte nsity deep laminae were observed. Results of polarized light microscop y of histologic specimens confirmed the three zones, and transmission electron microscopy showed different collagen arrangements in the zone s. An anisotropic effect of rotation on signal intensity was evident e specially in the hypointense second lamina. Because of the preferentia l alignment of water molecules associated with collagen, angular rotat ion of the cartilage in the direction of minimum dipolar coupling (55- degrees to the magnetic field) caused the cartilage to have a homogene ous appearance. The MR imaging appearance of these layers is strongly influenced by an anisotropic arrangement of the collagen fibers and by the alignment of the specimen relative to the magnetic field.