¹H magnetic resonance spectroscopy of nanomelic chicken cartilage: Effect of aggrecan depletion on cartilage T₂

Objective: To determine the effect of proteoglycan depletion on cartilage proton magnetic resonance (MR) spectroscopy T₂ using nanomelic chicken cartilage, a genetic mutant that completely lacks aggrecan. Design: Proton MR spectroscopic T₂ measurements of normal embryonic and nanomelic femoral epiphyseal cartilage were obtained using a 96-echo pulse sequence with inter-echo delay times increased logarithmically over the TE period of 60 μs to 1.7 s. The relative intensity and distribution of cartilage T₂ components were determined by fitting signal decay curves to a multi-exponential function. The number of T₂ components in the signal decay curves was determined by the degree of freedom limited r² of the fit. Results: For normal fetal chicken cartilage, 97.6±0.2% (mean±95% confidence interval) of the total signal comprises a long T₂ component (179.1±1.3 ms) with a relatively small short T₂ component (0.5±0.4 ms). The T₂ distribution for nanomelic cartilage is more heterogeneous with four components identified: two short T₂ components (0.5±0.02 and 7.3±0.6 ms), a large intermediate component (56.4±5.6 ms), and a broadly distributed long component (137.5±16.6 ms). In nanomelic cartilage there is greater heterogeneity of cartilage T₂ indicating greater variation in water proton mobility and exchange of water with the extracellular matrix. Conclusion: Absence of aggrecan in the extracellular cartilage matrix produces greater heterogeneity in cartilage T₂, but will not increase T₂ as has been previously reported with degenerative change of the collagen matrix.