Multicomponent T₂ relaxation analysis in cartilage

MR techniques are sensitive to the early stages of osteoarthritis, characterized by disruption of collagen and loss of proteoglycan (PG), but are of limited specificity. Here, water compartments in normal and trypsin-degraded bovine nasal cartilage were identified using a nonnegative least squares rmultiexponential analysis of T₂ relaxation. Three components were detected: T_2,1 = 2, 3 ms, T_2,2 = 25.2 ms, and T _2,3 = 96.3 ms, with fractions w₁ = 8.2%, w₂ = 14.5%, and w₃ = 79.3%, respectively. Trypsinization resulted in increased (P < 0.01) values of T_2,2 = 64.2 ms and T_2,3 = 149.4 ms, supporting their assignment to water compartments that are bound and loosely associated with PG, respectively. The T₂ of the rapidly relaxing component was not altered by digestion, supporting assignment to relatively immobile collagen-bound water. Relaxation data were simulated for a range of TE, number of echoes, and SNR to guide selection of acquisition parameters and assess the accuracy and precision of experimental results. Based on this, the expected experimental accuracy of measured T₂s and associated weights was within 2% and 4% respectively, with precision within 1 % and 3%. These results demonstrate the potential of multiexponential T ₂ analysis to increase the specificity of MR characterization of cartilage.