Association of cartilage T1ρ and T2 relaxation time measurement with hip osteoarthritis progression: A 5-year longitudinal study using voxel-based relaxometry and Z-score normalization

Objective

To study the longitudinal changes of cartilage $T_{1\rho }$ and $T_2$ relaxation time measurements in hip-OA patients.

Methods

A calibration study compared two scanner data, Scanner-1 (GE Discovery MR750 3.0T) with unilateral acquisition protocol and Scanner-2 (GE Signa Premier 3.0T) with bilateral acquisition protocol, using nine subjects(average age ​= ​40.33 ​± ​13.53 years, 5 females), including one hip-OA subject. Quantified parameters from the Scanner-2 were adjusted using voxel-based relaxometry(VBR) and Z-score normalization to reduce the inter-scanner variability. Eighteen hip-OA Subjects (age ​= ​53.11 ​± ​14.96 years, 12 females) were recruited to the longitudinal variability study from 2016, comprising five assessments at 1-year intervals. Baseline to 3rd-year data used unilateral acquisition with Scanner-1, while 4th-year data used bilateral acquisition with Scanner-2. A linear mixed-effects model(LME) assessed trajectory analyses, with acquisition year, age, sex, body mass index(BMI), and Kellgren-Lawrence(KL) score as predictor variables and cartilage mean $T_{1\rho }$ and $T_2$ values as outcomes.

Results

VBR analysis after Z-score normalization showed that only a few of the whole cartilage voxels had significant differences in $T_{1\rho }($femur-2.36 ​% and acetabular-3.23 ​%) and $T_2$ (femur-2.30 ​% and acetabular-2.94 ​%) values between the scanners. The LME analysis showed that the BMI predictor variable was significantly correlated with the femur $T_{1\rho }$ (p ​< ​0.0001) and $T_2$ (p ​< ​0.0001) and acetabular $T_{1\rho }$ (p ​< ​0.0001) and $T_2$ (p ​< ​0.0001) cartilage region.

Conclusion

The calibration study demonstrated the effectiveness of VBR and Z-score normalization in reducing inter-scanner variability. The longitudinal study revealed a significant correlation between $T_{1\rho }$ and $T_2$ values of the cartilage and BMI; also the $T_{1\rho }$ and $T_2$ values increased over time in some of the cartilage subregions.