In vivo qualitative assessments of articular cartilage in the rabbit knee with high-resolution MRI at 3 T.

Proteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high-resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One-millimeter thick coronal images were obtained at 3 T with a 97 x 97 microm(2) pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an approximately 2-fold greater Gd(DTPA)(2-)-induced decrease in T(1) relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two-point method was tested as an alternative to the more time-consuming multipoint method typically used to measure T(1) changes. Kinetics of Gd(DTPA)(2-) uptake were observed with a 10-min time resolution. The diffusive transport of Gd(DTPA)(2-) was characterized by a T(1) decrease approximately 2-fold faster in papain-treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T(1) variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA)(2-)-MRI may help in identifying new active compounds during efficacy studies on cartilage protection.