Quantitative susceptibility and T1ρ mapping of knee articular cartilage at 3T

T1$\rho$ and Quantitative Susceptibility Mapping (QSM) are evolving as substrates for quantifying the progressive nature of knee osteoarthritis.

Objective

To evaluate the effects of spin lock time combinations on depth-dependent T1$\rho$ estimation, in adjunct to QSM, and characterize the degree of shared variance in QSM and T1$\rho$ for the quantitative measurement of articular cartilage.

Design

Twenty healthy participants (10 ​M/10F, 22.2 ​± ​3.4 years) underwent bilateral knee MRI using T1$\rho$ MAPPS sequences with varying TSLs ([0–120] ms), along with a 3D spoiled gradient echo for QSM. Five total TSL combinations were used for T1$\rho$ computation, and direct depth-based comparison. Depth-wide variance was assessed in comparison to QSM as a basis to assess for depth-specific variation in T1$\rho$ computations across healthy cartilage.

Results

Longer T1$\rho$ relaxation times were observed for TSL combinations with higher spin lock times. Depth-specific differences were documented for both QSM and T1$\rho$, with most change found at ∼60% depth of the cartilage, relative to the surface. Direct squared linear correlation revealed that most T1$\rho$ TSL combinations can explain over 30% of the variability in QSM, suggesting inherent shared sensitivity to cartilage microstructure.

Conclusions

T1$\rho$ mapping is subjective to the spin lock time combinations used for computation of relaxation times. When paired with QSM, both similarities and differences in signal sensitivity may be complementary to capture depth-wide changes in articular cartilage.