Rapid Whole-Knee Quantification of Cartilage Using <inline-formula><tex-math notation="LaTeX">$T_{1}$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$T_{2}^*$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$T_{RAFF2}$</tex-math></inline-formula> Mapping With Magnetic Resonance Fingerprinting

Objective: 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 <inline-formula><tex-math notation="LaTeX">$T_{1}$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$T_{2}^*$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$T_{RAFF2}$</tex-math></inline-formula> with whole-knee coverage. Methods: A MRF framework was developed to achieve quantification of Relaxation Along a Fictitious Field in the 2nd rotating frame of reference (<inline-formula><tex-math notation="LaTeX">$T_{RAFF2}$</tex-math></inline-formula>) along with <inline-formula><tex-math notation="LaTeX">$T_{1}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$T_{2}^*$</tex-math></inline-formula>. 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 <inline-formula><tex-math notation="LaTeX">$T_{1}$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$T_{2}^*$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$T_{RAFF2}$</tex-math></inline-formula> methods was performed in phantom and in seven healthy subjects at 3 T. Repeatability (test-retest) with and without repositioning was also assessed. Results: Phantom measurements resulted in good agreement between MRF and the reference with mean biases of −54, 2, and 5 ms for <inline-formula><tex-math notation="LaTeX">$T_{1}$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$T_{2}^*$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$T_{RAFF2}$</tex-math></inline-formula>, 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 (<inline-formula><tex-math notation="LaTeX">$R^{2}\geq$</tex-math></inline-formula> 0.94) and with repositioning (<inline-formula><tex-math notation="LaTeX">$R^{2}\geq$</tex-math></inline-formula> 0.57) for <inline-formula><tex-math notation="LaTeX">$T_{1}$</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">$T_{2}^*$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$T_{RAFF2}$</tex-math></inline-formula>. Significance: 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.