Correlation of Laminated MR Appearance of Artcular Cartilage with Histology

PURPOSE: To determine the correlation of laminae of different signal intensities (SI) of articular cartilage,as seen on magnetic resonance (MR) imaging with histologic layes, using artificially constructed landmarks. MATERIALS AND METHODS: For a landmark that can exactly correlate the cartilage specimen with the MR image, five'V'-shaped markings of different depths were made on the surface of bovine patella. Both T1-weighted (TR/TE :300/14) and FSE T2-weighted images (TR/TE : 2000/53) were obtained on a 1.5T system with high gradient echostrength (25mT/m) and a voxel size of 78x78x2000 micrometer. Images were obtained with 1) changed frequency-encodingdirections on T1-weighted study, and 2) changed readout gradient strength (x2, x1/2) on T2-weighted sequence.Raw image data were transferred to a workstation and signal intensity profile was generated for each image. 1 : 1correlation of histologic specimens and MR images was performed. RESULTS: Line Profile through the cartilageshowed few peaks, suggesting changes in signal intensity profile in the cartilage. On the basis of artificiallandmarks, the histologic zone was accurately identified. The histologic tangential and transitional zonescorrelated with superficial high SI on T1WI, as well as high and low SII on T2WI. On T1WI, the radial zonecorrelated with a lamina of intermediate SI, and on T2WI, with a lamina for which SI gradually decreased from highto low. Additional well-defined low and intermediate SI bands were noted on bovine T1WI in the lower radial zone.In both T1 and T2 studies, calcified cartilage layers were of low SI. On T1-weighted study, changes in thedirection of frequency gradient did not lead to changes in the laminae. The alteration of readout gradientstrengths did not result in an inversely proportional difference in the thickness of the laminae. These becamemore distinct thus ruling out chemical shift and susceptibility artifacts. CONCLUSION: The laminated appearanceof articular cartilage, as seen on spin echo and fast spin-echo MR images, correlated with histologic layersrather than susceptibility or chemical shift artifacts.