Simultaneous acquisition of T_1ρ and T₂ quantification in knee cartilage: Repeatability and diurnal variation

Purpose To develop a robust sequence that combines T_1ρ and T₂ quantifications and to examine the in vivo repeatability and diurnal variation of T_1ρ and T₂ quantifications in knee cartilage. Materials and Methods Six healthy volunteers were scanned in the morning and afternoon on 2 days using a combined T_1ρ and T ₂ quantification sequence developed in this study. Repeatability of T_1ρ and T₂ quantification was estimated using root-mean-square coefficients-of-variation (RMS-CV). T_1ρ and T₂ values from morning scans were compared to those from afternoon scans using paired t-tests. Results The overall RMS-CV of in vivo T _1ρ and T₂ quantification was 5.3% and 5.2%, respectively. The RMS-CV of am scans was 4.2% and 5.0% while the RMS-CV of pm scans was 6.0% and 6.3% for T_1ρ and T₂, respectively. No significant difference was found between T_1ρ or T₂ values in the morning and in the afternoon. Conclusion A sequence that combines T_1ρ and T₂ quantification with scan time less than 10 minutes and is robust to B₀ and B₁ inhomogeneity was developed with excellent repeatability. For a cohort with low-level daily activity, although no significant diurnal variation of cartilage MR relaxation times was observed, the afternoon scans had inferior repeatability compared to morning scans. J. Magn. Reson. Imaging 2014;39:1287-1293. © 2013 Wiley Periodicals, Inc.