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.
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 micros 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.
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.
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.