Marty Benjamin, Vignaud Alexandre, Greiser Andreas, Robert Benjamin, de Sousa Paulo Loureiro, Carlier Pierre G
Institute of Myology, NMR Laboratory, Paris, France; CEA, DSV, I2BM, MIRCen, IdM NMR Laboratory, Paris, France; UPMC University Paris 06, Paris, France.
CEA, DSV, I2BM, NeuroSpin, UNIRS, Gif-sur-Yvette, France.
PLoS One. 2015 May 11;10(5):e0126766. doi: 10.1371/journal.pone.0126766. eCollection 2015.
Modified Look-Locker Inversion recovery (MOLLI) sequence is increasingly performed for myocardial T1 mapping but is known to underestimate T1 values. The aim of the study was to quantitatively analyze several sources of errors when T1 maps are derived using standard post-processing of the sequence and to propose a reconstruction approach that takes into account inversion efficacy (η), T2 relaxation during balanced steady-state free-precession readouts and B1+ inhomogeneities. Contributions of the different sources of error were analyzed using Bloch equations simulations of MOLLI sequence. Bloch simulations were then combined with the acquisition of fast B1+ and T2 maps to derive more accurate T1 maps. This novel approach was evaluated on phantoms and on five healthy volunteers. Simulations show that T2 variations, B1+ heterogeneities and inversion efficiency represent major confounders for T1 mapping when MOLLI is processed with standard 3-parameters fitting. In vitro data indicate that T1 values are accurately derived with the simulation approach and in vivo data suggest that myocardium T1 are 15% underestimated when processed with the standard 3-parameters fitting. At the cost of additional acquisitions, this method might be suitable in clinical research protocols for precise tissue characterization as it decorrelates T1 and T2 effects on parametric maps provided by MOLLI sequence and avoids inaccuracies when B1+ is not homogenous throughout the myocardium.
改良Look-Locker反转恢复（MOLLI）序列越来越多地用于心肌T1映射，但已知会低估T1值。本研究的目的是定量分析使用该序列的标准后处理得出T1映射时的几种误差来源，并提出一种考虑反转效率（η）、平衡稳态自由进动读出期间的T2弛豫以及B1 +不均匀性的重建方法。使用MOLLI序列的布洛赫方程模拟分析了不同误差来源的贡献。然后将布洛赫模拟与快速B1 +和T2映射的采集相结合，以得出更准确的T1映射。在体模和五名健康志愿者身上对这种新方法进行了评估。模拟表明，当用标准三参数拟合处理MOLLI时，T2变化、B1 +不均匀性和反转效率是T1映射的主要混杂因素。体外数据表明，模拟方法能准确得出T1值，体内数据表明，用标准三参数拟合处理时，心肌T1值被低估了15%。以额外采集为代价，这种方法可能适用于临床研究方案中的精确组织表征，因为它消除了T1和T2对MOLLI序列提供的参数图的影响，并且当整个心肌中的B1 +不均匀时可避免不准确。
