Quantification of the rotating frame relaxation time T2ρ: Comparison of balanced spin-lock and continuous-wave Malcolm-Levitt preparations.

Abstract

For the quantification of rotating frame relaxation times, the T_2ρ relaxation pathway plays an essential role. Nevertheless, T_2ρ imaging has been studied only to a small extent compared with T_1ρ, and preparation techniques for T_2ρ have so far been adapted from T_1ρ methods. In this work, two different preparation concepts are compared specifically for the use of T_2ρ mapping. The first approach involves transferring the balanced spin-locking (B-SL) concept of T_1ρ imaging. The second and newly proposed approach is a continuous-wave Malcolm-Levitt (CW-MLEV) pulse train with zero echo times and was motivated from T₂ preparation strategies. The modules are tested in Bloch simulations for their intrinsic sensitivity to field inhomogeneities and validated in phantom experiments. In addition, myocardial T_2ρ mapping was performed in mice as an exemplary application. Our results demonstrate that the CW-MLEV approach provides superior robustness and thus suggest that established methods of T_1ρ imaging are not best suited for T_2ρ experiments. In the presence of field inhomogeneities, the simulations indicated an increased banding compensation by a factor of 4.1 compared with B-SL. Quantification of left ventricular T_2ρ time in mice yielded more consistent results, and values in the range of 59.2-61.1 ms (R² = 0.986-0.992) were observed at 7 T.