Evaluation of articular cartilage with quantitative MRI in an equine model of post‐traumatic osteoarthritis

Chondral lesions lead to degenerative changes in the surrounding cartilage tissue, increasing the risk of developing post‐traumatic osteoarthritis (PTOA). This study aimed to investigate the feasibility of quantitative magnetic resonance imaging (qMRI) for evaluation of articular cartilage in PTOA. Articular explants containing surgically induced and repaired chondral lesions were obtained from the stifle joints of seven Shetland ponies (14 samples). Three age‐matched nonoperated ponies served as controls (six samples). The samples were imaged at 9.4 T. The measured qMRI parameters included T(1), T(2), continuous‐wave T(1ρ) (CWT(1ρ)), adiabatic T(1ρ) (AdT(1ρ)), and T(2ρ) (AdT(2ρ)) and relaxation along a fictitious field (T(RAFF)). For reference, cartilage equilibrium and dynamic moduli, proteoglycan content and collagen fiber orientation were determined. Mean values and profiles from full‐thickness cartilage regions of interest, at increasing distances from the lesions, were used to compare experimental against control and to correlate qMRI with the references. Significant alterations were detected by qMRI parameters, including prolonged T(1), CWT(1ρ), and AdT(1ρ) in the regions adjacent to the lesions. The changes were confirmed by the reference methods. CWT(1ρ) was more strongly associated with the reference measurements and prolonged in the affected regions at lower spin‐locking amplitudes. Moderate to strong correlations were found between all qMRI parameters and the reference parameters (ρ = −0.531 to −0.757). T(1), low spin‐lock amplitude CWT(1ρ), and AdT(1ρ) were most responsive to changes in visually intact cartilage adjacent to the lesions. In the context of PTOA, these findings highlight the potential of T(1), CWT(1ρ), and AdT(1ρ) in evaluation of compositional and structural changes in cartilage.