Rapid volumetric gagCEST imaging of knee articular cartilage at 3 T: evaluation of improved dynamic range and an osteoarthritic population

Chemical exchange saturation transfer of glycosaminoglycans (GAG), gagCEST, is a quantitative MR technique that has potential for assessing cartilage proteoglycan content at field strengths of 7 Tesla (T) and higher. However, its utility at 3T remains unclear. The objective of this work was to implement a rapid volumetric gagCEST sequence with higher gagCEST asymmetry at 3T to evaluate its sensitivity to osteoarthritic changes in knee articular cartilage and in comparison to T(2) and T(1ρ) measures. We hypothesize that gagCEST asymmetry at 3T decreases with increasing severity of osteoarthritis (OA). Forty-two human volunteers, including ten healthy subjects and thirty-two subjects with medial OA, were included in the study. Knee injury and Osteoarthritis Outcome Scores (KOOS) were assessed for all subjects and Kellgren-Lawrence grading was performed for OA volunteers. Healthy subjects were scanned consecutively at 3T to assess repeatability of the volumetric gagCEST sequence at 3T. For healthy and OA subjects, gagCEST asymmetry and T(2) and T(1ρ) relaxation times were calculated for the femoral articular to assess sensitivity to OA severity. Volumetric gagCEST imaging had higher gagCEST asymmetry than single slice acquisitions (p = 0.015). Average scan-rescan coefficient of variation was 6.8%. There were no significant differences in average gagCEST asymmetry between younger and older healthy controls (p = 0.655) or between healthy controls and OA subjects (p = 0.310). T(2) and T(1ρ) relaxation times were elevated in OA subjects (p < 0.001 for both) compared to healthy controls and both were moderately correlated with total KOOS scores (rho = −0.181 and rho = −0.332 respectively). The gagCEST technique developed here, with volumetric scan times under 10 minutes and high gagCEST asymmetry at 3T, did not vary significantly between healthy subjects and those with mild-moderate osteoarthritis. This further supports a limited utility for gagCEST imaging at 3T for assessment of early changes in cartilage composition in osteoarthritis.