Purpose: To determine the relationship between changes in the extracellular matrix (ECM) and T 1r and T 2 values in vivo. The ECM is composed of proteoglycan (PG), collagen, and water. It has been unclear which of the ECM constituents affects T 1r and T 2 mapping in living human cartilage.Materials and Methods: Sagittal T 1r and T 2 maps were preoperatively obtained from 20 knee osteoarthritis patients. Osteochondral samples harvested from the resected tibial plateaus during total knee arthroplasty were consistent with the MRIs of the patients' knees. Parameters that included histological grading of cartilage degeneration, glycosaminoglycan (GAG) content (which constitutes PG), presence of collagen anisotropy and water content were evaluated along with T 1r and T 2 values, and statistical analysis was performed using multiple regression analysis.Results: T 1r and T 2 values were significantly correlated with the degree of cartilage degeneration (b ¼ 0.397 and 0.357, respectively) and the GAG content (b ¼ À0.340 and À0.244, respectively). Conclusion:The present study demonstrated that T 1r and T 2 values reflect the GAG content of the cartilage and can indicate cartilage degeneration in vivo. Use of these parameters can facilitate the noninvasive diagnosis and evaluation of cartilage degeneration. OSTEOARTHRITIS (OA) IS a degenerative disease that affects the hyaline cartilage at the articular surface.Cartilage matrix breakdown is characterized by changes in the content of glycosaminoglycan (GAG), type II collagen, and water (1). It is difficult to detect these changes in the cartilage matrix using plain radiography or conventional magnetic resonance imaging (MRI) techniques (2,3). However, new MRI techniques that can detect changes in the extracellular matrix (ECM) have recently been developed. In particular, T 1r and T 2 mapping can quantify the ECM of the articular cartilage.The T 1r parameter describes the spin-lattice relaxation in the rotating frame (4). A ''spin-lock'' (SL) pulse is applied to the magnetization in the transverse plane at extremely low fields, and this spin-locked magnetization reflects the changes in the magnetic fields caused by water spin dynamics, such as the chemical exchange of protons. T 1r mapping is most sensitive to changes in the GAG content in the ECM (5-7). A previous in vitro study using a model with selective degradation of GAG by trypsinization revealed that increases in T 1r values correlated with decreases in the GAG content (6,7). The chemical exchanges between bulk water and the hydroxyl and amine groups of proteoglycan (PG) are considered important for the T 1r parameter's relaxation mechanism in articular cartilage (8). In addition, the chemical exchanges between the hydroxyl and amino groups of collagen and the water protons may affect the T 1r parameter; a previous study demonstrated that T 1r shows approximately exponential dependencies on molecular concentration using collagen solutions (9).The T 2 parameter is a spin-spin relaxation method related to the energy ch...

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Using T1ρ mapping to detect minimal changes, our study demonstrated that cartilage lesions are related to progressive degenerative cartilage changes during the early phase after ACLR.

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