An efficient R1ρ dispersion imaging method for human knee cartilage using constant magnetization prepared turbo-FLASH.

This work aimed to develop an efficient R1ρ dispersion imaging method for clinical studies of human knee cartilage at 3 T. Eight constant magnetizations (Mprep ) were prepared by tailoring both the duration and amplitude (ω1 ) of a fully refocused spin-lock preparation pulse. The limited Mprep dynamic range was expanded by the measure, equivalent to that with ω1  = ∞, from the magic angle location in the deep femoral cartilage. The developed protocol with Mprep  = 60% was demonstrated on one subject's bilateral and two subjects' unilateral asymptomatic knees. The repeatability of the proposed protocol was estimated by two repeated scans with a three-month gap for the last two subjects. The synthetic R1ρ and R2 derived from R1ρ dispersions were compared with the published references using state-of-the-art R1ρ and R2 mapping (MAPSS). The proposed protocol demonstrated good (<5%) repeatability quantified by the intra- and intersubject coefficients of variation in the femoral and tibial cartilage. The synthetic R1ρ (1/s) and the references were comparable in the femoral (23.0 ± 5.3 versus 24.1 ± 3.8, P = 0.67) and the tibial (29.1 ± 8.8 versus 27.1 ± 5.1, P = 0.62), but not the patellar (16.5 ± 4.9 versus 22.7 ± 1.6, P < 0.01) cartilage. The same trends were also observed for the current and the previous R2 . In conclusion, the developed R1ρ dispersion imaging scheme has been revealed to be not only efficient but also robust for clinical studies of human knee cartilage at 3 T.