BACKGROUND: The purpose of this work was to evaluate different magnetization preparation and readout sequences for modified Look-Locker inversion recovery (MOLLI) toward improved T1 mapping in the heart. Elements investigated include: catalyzation sequences to prepare the magnetization before readout, alternate k-space trajectories, a spoiled gradient recalled echo readout, and a 5b(3b)3b MOLLI sampling scheme ('b' denoting beats).
METHODS: Conventional 3b(3b)3b(3b)5b MOLLI with a linear k-space trajectory was compared to four variants in simulations, in vitro and in vivo (at 3T). Variants were centric conventional MOLLI, centric-paired conventional MOLLI, linear 5b(3b)3b MOLLI and spoiled gradient recalled echo MOLLI. Each of these was applied with three magnetization catalyzation methods, and T1 measurement accuracy and precision were evaluated in simulations via a Monte Carlo algorithm, in a set of calibrated phantoms, and in ten healthy volunteers. Contrast-to-noise, heart rate dependence and B1+ dependence were also evaluated.
RESULTS: A linear k-space trajectory was superior in vitro to centric and centric-paired trajectories. Of the catalyzation methods, preparation of transverse magnetization only-using a linearly increasing flip angle catalyzation-improved MOLLI T1 measurement accuracy, precision, and map quality versus methods that include catalyzation of the longitudinal magnetization. The 5b(3b)3b MOLLI scheme offered comparable native T1 measurement accuracy and precision to conventional MOLLI, despite its shortened acquisition.
CONCLUSIONS: MOLLI T1 measurement accuracy, precision, and map quality depend on the method of catalyzation of magnetization prior to image acquisition, as well as on the readout method and MOLLI sampling scheme used.
- T1 mapping
- tissue characterization
- steady-state free precession
- transient signal oscillations