Macromolecule and water magnetization exchange modeling in articular cartilage

Magnetization exchange effects between the matrix macromolecules (e.g., col lagen and proteoglycan) and water were examined in normal, deuterated, and proteoglycan-depleted articular cartilage. Relaxation results (T-2, T-1 rho , and T-1) suggested that a four-site exchange scheme provided an accurate model for articular cartilage relaxation and interspin group coupling detai ls, Magnetization exchange within the collagen-bulk-water, proteoglycan-col lagen, and collagen fibrillar water-collagen cartilage subsystems were quan tified. Although collagen-bulk-water was the largest of the cartilage coupl ing subsystems (similar to 90% signal) and is exploited in MRI, the rates o f magnetization transfer (MT) within the latter subsystems were appreciably larger. Magnetization exchange rates for proteoglycan-collagen and collage n fibrillar water-collagen were 120 s(-1) and 4.4 s(-1), respectively. The observation of these latter two exchange subsystems suggested potential cli nical MRI-MT applications in detecting molecular abnormalities associated w ith osteoarthritis. (C) 2000 Wiley-Liss, Inc.