Rapid Whole-Knee Quantification of Cartilage Using $T_{1}$, $T_{2}^*$, and $T_{RAFF2}$ 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
$T_{1}$
,
$T_{2}^*$
, and
$T_{RAFF2}$
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 (
$T_{RAFF2}$
) along with
$T_{1}$
and
$T_{2}^*$
. 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
$T_{1}$
,
$T_{2}^*$
, 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.
Results:
Phantom measurements resulted in good agreement between MRF and the reference with mean biases of −54, 2, and 5 ms for
$T_{1}$
,
$T_{2}^*$
, 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 (
$R^{2}\geq$
0.94) and with repositioning (
$R^{2}\geq$
0.57) for
$T_{1}$
,
$T_{2}^*$
, and
$T_{RAFF2}$
.
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.