In vivo Sub-regional dGEMRIC Analysis and Contrast Distribution in Clinical Studies of Human Knee Cartilage

Aims: This work was carried out to investigate whether considering cartilage depth in vivo dGEMRIC would provide additional information on the molecular content and changes in normal and diseased cartilage.

Methods: Study I was a longitudinal study on 23 healthy volunteers; Study II was a case-control study on 9 sedentary individuals and 8 elite runners. Study III was a longitudinal study on 30 patients with a history of medial meniscectomy. They were divided into three groups according to self-reported changes in level of physical activity. MRI measurements were performed in femoral knee cartilage pre- & post-injection of Gd-DTPA2-. Depth-wise times p.i. depending on the study group.

Results: Studies I and II: before contrast injection, T1 was higher in the superficial region than in the deep regions of the cartilage. Bulk gadolinium concentration was negatively related to cartilage thickness. Gd-DTPA2- uptake was significantly slower in the deep region than in the superficial region of the cartilage. Gd concentration in the superficial region was independent of cartilage thickness. A trend was seen towards lower Gd concentration in the superficial layer of weight-bearing cartilage in elite runners, than in sedentary individuals. More contrast agent seen in superficial non-weight-bearing cartilage than weight-bearing cartilage. In Study III, those who increased their physical activity showed a significant increase in dGEMRIC index in both superficial and deep layers in lateral weight-bearing cartilage. Those who decreased their physical activity showed a significant decrease in dGEMRIC index in the medial weight-bearing cartilage.

Conclusions: The higher pre-contrast T1 in the superficial region than in the deep region is an indication of a higher water content in superficial cartilage. The uptake of contrast agent was found to be from the superficial region of the cartilage, with diffusion into the deeper parts, and this affects the interpretation of bulk dGEMRIC measurements. The Gd concentration in the superficial layer supports dGEMRIC findings that cartilage has an adaptive capacity to exercise, leading to increased glycosaminoglycan (GAG) content throughout the cartilage. Decreasing physical activity leads to a decrease in GAG content in the cartilage. Variation in cartilage thickness is a source of error in dGEMRIC that should be considered when analysing bulk values.