A technique for 3D in vivo quantification of proton density and magnetization transfer coefficients of knee joint cartilage

Objective: To develop an MR-based method for the in vivo evaluation of the structural composition of articular cartilage. Design: Five sagittal magnetic resonance imaging (MRI) protocols were acqui red throughout the knee joint of 15 healthy volunteers and the boundaries o f the cartilage segmented from a previously validated sequence with high co ntrast between cartilage and surrounding tissue. The other sequences were m atched to these data, using a 3D least squares fit algorithm to exclude mot ion artefacts. In this way secondary images were computed that included inf ormation about the proton density (interstitial water content) and the magn etization transfer coefficient (macromolecules, collagen). The average sign al intensities of the 3D cartilage plates were extracted from these data se ts and related to a phantom. Results: The signal intensity data showed a high interindividual variabilit y for the proton density (patella 31%, lateral tibia 36%, medial tibia 29%) ; the patella displaying higher values than the tibia (P<0.001). There were high correlations between the three plates. The magnetization transfer coe fficient also showed high variability (patella 25%, lateral tibia 32%, medi al tibia 30%) with the lowest values in the medial tibia (P<0.01) and lower correlations between the plates. The slice-to-slice variation (medial to l ateral) ranged from 9% to 24%. Conclusion: An MR-based method has been developed for evaluating the proton density and magnetization transfer of articular cartilage in vivo and obse rving systematic differences between knee joint cartilage plates. The techn ique has the potential to supply information about the water content and co llagen of articular cartilage, in particular at the early state of osteoart hritic degeneration. (C) 2000 OsteoArthritis Research Society International .