Mapping proteoglycan-bound water in cartilage: Improved specificity of matrix assessment using multiexponential transverse relaxation analysis

Association of MR parameters with cartilage matrix components remains an area of ongoing investigation. Multiexponential analysis of nonlocalized transverse relaxation data has previously been used to quantify water compartments associated with matrix macromolecules in cartilage. We extend this to mapping the proteoglycan (PG)-bound water fraction in cartilage, using mature and young bovine nasal cartilage model systems, toward the goal of matrix component-specific imaging. PG-bound water fraction from mature and young bovine nasal cartilage was 0.31 ± 0.04 and 0.22 ± 0.06, respectively, in agreement with biochemically derived PG content and PG-to-water weight ratios. Fourier transform infrared imaging spectroscopic-derived PG maps normalized by water content (IR-PG_ww) showed spatial correspondence with PG-bound water fraction maps. Extensive simulation analysis demonstrated that the accuracy and precision of our determination of PG-bound water fraction was within 2%, which is well-within the observed tissue differences. Our results demonstrate the feasibility of performing imaging-based multiexponential analysis of transverse relaxation data to map PG in cartilage.