Development of multimodal experimental protocols for GAG quantification in articular cartilage using low field NMR

Osteoarthritis (OA) is an irreversible and degenerative disorder that affects articular car- tilage (AC). Currently, no screening methods have been established for the early detection of asymptomatic patients. To address this issue, the present study investigated the feasibility of quantifying gly- cosaminoglycan (GAG) concentration in AC using low-field nuclear magnetic resonance (NMR). Two experimental protocols aimed at using reference techniques to quantify GAG concentration were developed and tested on bovine samples. NMR measurements were performed employing a single-sided NMR instrument with a magnetic field strength of B0 = 0.327 T to acquire CPMG and saturation recovery (SR) data. The data were inverted via the UPEN algorithm to obtain the distribution of lon- gitudinal and transversal relaxation times T1 and T2. The average relaxation times, signal fraction of the fast-decaying T2 component, and novel parameters, such as the full width at half maximum of the distributions, were extracted from the curves. These were then correlated with the GAG concentration measured from both experimental protocols. The dGEMRIC technique was used as a reference method via T1 mapping with a 3T clinical scanner. The second reference method employed was contrast-enhanced X-ray computed tomography (CE-CT) using the CA4+ cationic contrast agent. Finally, the samples under- went indentation testing. The analysis identified water pools relevant to relaxation time distributions, along with a number of correlations between GAG concentration and NMR parameters, which may prove to be estimators of GAG concentration or biomarkers for the screening and early detection of OA in asymptomatic patients. Sample preparation, MRI, CE-CT and indentation testing have been conducted at IRCCS Rizzoli Orthopedic Institute during an internship period.