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.

Regional dGEMRIC analysis in patients at risk of osteoarthritis provides additional information about activity related changes in cartilage structure

BACKGROUND

Previously, a positive effect of exercise on cartilage structure was indicated with delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC). However, in that study only one full-thickness region of interest (ROI) in the medial femoral condyle was analyzed.

PURPOSE

To improve the knowledge about exercise effects on cartilage structure by re-analyzing previous images with regional dGEMRIC analysis.

MATERIAL AND METHODS

Thirty patients (age range, 38-50 years) with a previous medial meniscus resection were divided into three groups according to self-reported change in physical activity (PA) level in a 4-month exercise intervention study: Group I (n = 11), increased PA level; Group II (n = 13), no change in PA level; and Group III (n = 6), reduced PA level. dGEMRIC index was analyzed at inclusion and after 4 months. Anterior (less load) and posterior (more load) ROIs of medial and lateral femoral condyles were analyzed, as well as superficial and deep cartilage regions.

RESULTS

Group I increased the dGEMRIC index in the posterior cartilage (P = 0.004). The increase was larger in the lateral (P = 0.005) than the medial compartment in both superficial and deep cartilage regions. The dGEMRIC index did not change in Group II. In Group III, the dGEMRIC index decreased in the medial posterior cartilage (P = 0.03).

CONCLUSION

In patients with a previous medial meniscectomy, the beneficial effect of exercise varies between different locations within the joint, the largest improvement being observed in lateral posterior cartilage, i.e. the load-bearing cartilage in the compartment without a meniscus lesion. The effects of exercise do not seem to vary with cartilage depth.

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) .