Repeatability and age-related change of sodium in the knee articular cartilage measured with sodium MRI

Introduction Aging is one of the leading risk factors for osteoarthritis [1]. Proteoglycan, one of the major components of articular cartilage, undergoes loss and structural changes with aging [2]. Proteoglycan has a negative fixed charge density, which is balanced by positively charged sodium in the cartilage. Imaging of cartilage sodium is a potential tool to evaluate spatial proteoglycan content and cartilage degeneration [3]. Sodium MRI has been demonstrated as a desirable imaging modality to detect proteoglycan loss in cartilage [3,4]. The objectives of this study were twofold. The first was to understand the association between cartilage sodium content (as assessed with sodium MRI) and aging. We hypothesized that sodium content in cartilage would decrease with aging. The second objective was to test the repeatability of cartilage sodium content measurement using sodium MRI to assess the variability of the measurements at multiple time points.