Quantification of Sodium Relaxation Times and Concentrations as Surrogates of Proteoglycan Content of Patellar CARTILAGE at 3T MRI

Sodium MRI has the potential to depict cartilage health accurately, but synovial fluid can influence the estimation of sodium parameters of cartilage. Therefore, this study aimed to reduce the impact of synovial fluid to render the quantitative compositional analyses of cartilage tissue technically more robust. Two dedicated protocols were applied for determining sodium [Formula: see text] and [Formula: see text] relaxation times. For each protocol, data were acquired from 10 healthy volunteers and one patient with patellar cartilage damage. Data recorded with multiple repetition times for [Formula: see text] measurement and multi-echo data acquired with an additional inversion recovery pulse for [Formula: see text] measurement were analysed using biexponential models to differentiate longitudinal relaxation components of cartilage ([Formula: see text]) and synovial fluid ([Formula: see text]), and short ([Formula: see text]) from long ([Formula: see text]) transversal relaxation components. Sodium relaxation times and concentration estimates in patellar cartilage were successfully determined: [Formula: see text] = 14.5 ± 0.7 ms; [Formula: see text] = 37.9 ± 2.9 ms; c([Formula: see text]-protocol) = 200 ± 48 mmol/L; [Formula: see text] = 0.4 ± 0.1 ms; [Formula: see text] = 12.6 ± 0.7 ms; c([Formula: see text]-protocol) = 215 ± 44 mmol/L for healthy volunteers. In conclusion, a robust determination of sodium relaxation times is possible at a clinical field strength of 3T to quantify sodium concentrations, which might be a valuable tool to determine cartilage health.