gms | German Medical Science

Objectives: Early onset osteoarthritis is associated with ultrastructural and compositional changes of cartilage, in particular with a loss of glycosaminoglycans (GAGs) and disorganization of the collagen matrix. Both changes remain elusive to morphological MRI. Their quantification and monitoring, however, would be crucial for early OA diagnosis as well as in the evaluation of anti-OA therapies. GagCEST is a very promising tool for the non-invasive evaluation of (GAG) content in articular cartilage. However, it is affected by many variables, thus rendering its application challenging.

To establish an optimized gagCEST protocol that enables robust and reproducible assessment of the glycosaminoglycan (GAG) content in knee cartilage at 7 Tesla within a clinically feasible measurement time.

Methods: Ten young and healthy volunteers (mean age 26 years; 5 males) were examined on a 7 Tesla MR system. Each volunteer was measured twice within one hour for reproducibility assessment. A custom-made fixation splint was used to address motion artifacts. A prototype segmented 3D RF-spoiled gradient-echo (GRE) sequence with selective RF presaturation using ten 60-ms hs2 pulses in the saturation pulse train was applied. The images were measured for 19 saturation offsets with a step of 92 Hz around the water resonance (Figure 1 [Fig. 1]).

For each evaluated region, i.e., weight bearing and non-weight bearing femoral cartilage, trochlear groove, patellar and tibial cartilage, regions of interest were placed on three adjacent slices on morphological images and consecutively transferred to gagCEST maps. For assessing reproducibility, a two-way mixed intraclass correlation coefficient (ICC) was calculated. Differences in MTR_asym between different regions were evaluated using ANOVA and Bonferroni corrected post hoc test.

Results and Conclusion: The optimization of the saturation scheme reduced the influence of field inhomogeneities, resulted in more uniform saturation, and allowed for good reproducibility, as demonstrated by an ICC of 0.77 in a clinically applicable measurement time (19:39 minutes). Whereas similar MTR_asym values were found for weight-bearing and non-weight-bearing femoral cartilage, lower values were observed in the trochlear groove (p = 0.028), patellar (p = 0.015) and tibial cartilage (p < 0.001) when compared to non-weight-bearing femoral cartilage.

Sensitivity to regional differences in GAG content and good reproducibility underline the potential of the optimized gagCEST protocol for assessing biochemical changes in articular cartilage that are associated with early stages of cartilage degeneration.