Robson Matthew D, Piechnik Stefan K, Tunnicliffe Elizabeth M, Neubauer Stefan
Division of Cardiovascular Medicine, Radcliffe Department of Medicine, Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, John Radcliffe Hospital, Oxford, UK.
Magn Reson Med. 2013 Sep;70(3):664-70. doi: 10.1002/mrm.24867. Epub 2013 Jul 15.
Quantitative mapping of the native T1 of the heart using the modified look-locker inversion recovery (MOLLI) technique provides high quality diagnostic information without requiring contrast agents. Previous work has considered the effects of T2 relaxation on MOLLI T1 measurements, finding that the T1 measured by MOLLI is biased, and that Saturation-recovery single-Shot Acquisition generates a more precise T1. However, despite detailed experiments and simulation the exact relaxation times observed in vivo remain unexplained, but might be due to magnetization transfer (MT).
We used an MT simulation based on the Bloch-McConnell equations to evaluate the most common MOLLI and saturation-recovery single-shot acquisition sequence variants.
For myocardial tissue we find that the T1 measured by saturation-recovery single-shot acquisition is insensitive to MT and T2, whereas MT reduces the T1 measured by MOLLI (>10%) in addition to the effects due to T2 relaxation.
The consequences of this T1 underestimation by MOLLI are relevant. Increases in the actual T1 and T2 and decreases in MT will all result in an increase in T1 measured by MOLLI. Myocardial infarction demonstrates increased native T1 and T2 and decreased MT, indicating that these biases enhance the sensitivity of MOLLI to detect this and possibly other cardiovascular disease states.
使用改良的锁相环反转恢复（MOLLI）技术对心脏的固有T1进行定量映射，无需使用造影剂即可提供高质量的诊断信息。先前的研究考虑了T2弛豫对MOLLI T1测量的影响，发现MOLLI测量的T1存在偏差，并且饱和恢复单次采集可产生更精确的T1。然而，尽管进行了详细的实验和模拟，但体内观察到的确切弛豫时间仍无法解释，可能是由于磁化传递（MT）所致。
我们使用基于Bloch-McConnell方程的MT模拟来评估最常见的MOLLI和饱和恢复单次采集序列变体。
对于心肌组织，我们发现饱和恢复单次采集测量的T1对MT和T2不敏感，而MT除了T2弛豫的影响外，还会降低MOLLI测量的T1（>10%）。
MOLLI对T1的低估所带来的后果是相关的。实际T1和T2的增加以及MT的减少都会导致MOLLI测量的T1增加。心肌梗死表现为固有T1和T2增加以及MT减少，表明这些偏差增强了MOLLI检测这种疾病以及可能其他心血管疾病状态的敏感性。
