Rapid Whole-Knee Quantification of Cartilage Using T₁, T₂^*, and T_RAFF2 Mapping With Magnetic Resonance Fingerprinting

Quantitative Magnetic Resonance Imaging (MRI) holds great promise for the early detection of cartilage deterioration. Here, a Magnetic Resonance Fingerprinting (MRF) framework is proposed for comprehensive and rapid quantification of T₁, T₂^*, and T_RAFF2 with whole-knee coverage.

A MRF framework was developed to achieve quantification of Relaxation Along a Fictitious Field in the 2nd rotating frame of reference ( T_RAFF2) along with T₁ and T₂^*. The proposed sequence acquires 65 measurements of 25 high-resolution slices, interleaved with 7 inversion pulses and 40 RAFF2 trains, for whole-knee quantification in a total acquisition time of 3:25 min. Comparison with reference T₁, T₂^*, and T_RAFF2 methods was performed in phantom and in seven healthy subjects at 3 T. Repeatability (test-retest) with and without repositioning was also assessed.

Phantom measurements resulted in good agreement between MRF and the reference with mean biases of -54, 2, and 5 ms for T₁, T₂^*, and T_RAFF2, respectively. Complete characterization of the whole-knee cartilage was achieved for all subjects, and, for the femoral and tibial compartments, a good agreement between MRF and reference measurements was obtained. Across all subjects, the proposed MRF method yielded acceptable repeatability without repositioning ( R² ≥ 0.94) and with repositioning ( R² ≥ 0.57) for T₁, T₂^*, and T_RAFF2.

The short scan time combined with the whole-knee coverage makes the proposed MRF framework a promising candidate for the early assessment of cartilage degeneration with quantitative MRI, but further research may be warranted to improve repeatability after repositioning and assess clinical value in patients.