Pre-contrast T1 and cartilage thickness as confounding factors in dGEMRIC when evaluating human cartilage adaptation to physical activity.

BACKGROUND: The dGEMRIC (delayed Gadolinium-Enhanced MRI of Cartilage) technique has been used in numerous studies for quantitative in vivo evaluation of the relative glycosaminoglycan (GAG) content in cartilage. The purpose of this study was to determine the influence of pre-contrast T1 and cartilage thickness when assessing knee joint cartilage quality with dGEMRIC. METHODS: Cartilage thickness and T1 relaxation time were measured in the central part of the femoral condyles before and two hours after intravenous Gd-DTPA2- administration in 17 healthy volunteers from a previous study divided into two groups: 9 sedentary volunteers and 8 exercising elite runners. Results were analyzed in superficial and a deep weight-bearing, as well as in non-weight-bearing regions of interest. RESULTS: In the medial compartment, the cartilage was thicker in the exercising group, in weight-bearing and non-weight-bearing segments. In most of the segments, the T1 pre-contrast value was longer in the exercising group compared to the sedentary group. Both groups had a longer pre-contrast T1 in the superficial cartilage than in the deep cartilage. In the superficial cartilage, the gadolinium concentration was independent of cartilage thickness. In contrast, there was a linear correlation between the gadolinium concentration and cartilage thickness in the deep cartilage region. CONCLUSION: Cartilage pre-contrast T1 and thickness are sources of error in dGEMRIC that should be considered when analysing bulk values. Our results indicate that differences in cartilage structure due to exercise and weight-bearing may be less pronounced than previously demonstrated.

In vivo transport of Gd-DTPA(2-) in human knee cartilage assessed by depth-wise dGEMRIC analysis.

PURPOSE: To investigate the transport of Gd-DTPA(2-) in different layers of femoral knee cartilage in vivo. MATERIALS AND METHODS: T(1) measurements (1.5 Tesla) were performed in femoral knee cartilage of 23 healthy volunteers. The weight-bearing central cartilage was analyzed before contrast and at eight time points after an intravenous injection of Gd-DTPA(2-) : 12-60 min (4 volunteers) and 1-4 h (19 volunteers). Three regions of interest were segmented manually: deep, middle, and superficial. RESULTS: Before contrast injection, a depth-wise variation of T(1) was observed with 50% higher values in the superficial region compared with the deep region. In the deep region, the uptake of Gd-DTPA(2-) was not detected until 36 min and the concentration increased until 240 min, whereas in the superficial region, the uptake was seen already at 12 min and the concentration decreased after 180 min (P < 0.01). There was a difference between medial and lateral compartment regarding bulk, but not superficial Gd-DTPA(2-) concentration. The bulk gadolinium concentration was negatively related to the cartilage thickness (r = -0.68; P < 0.01). CONCLUSION: The depth-wise and thickness dependent variations in Gd-DTPA(2) transport influence the interpretation of bulk dGEMRIC analysis in vivo. In thick cartilage, incomplete penetration of Gd-DTPA(2) will yield a falsely too long T(1) .