Louisiana State University School of Veterinary of Medicine, Baton Rouge, LA, USA.
Yale University, Radiology and Biomedical Imaging, New Haven, CT, USA.
Sci Rep. 2019 Mar 5;9(1):3600. doi: 10.1038/s41598-019-39780-4.
Previous work has highlighted the complicated and distinctive dynamics that set signal evolution during a train of spin echoes, especially with nonuniform echo spacing applied to complex molecules like fats. The work presented here regards those signal patterns as codes that can be used as a contrast mechanism, capable of distinguishing mixtures of molecules with an imaging sequence, sidestepping many challenges of spectroscopy. For particular arrays of echo spacings, non-monotonic and distinctive signal evolution can be enhanced to improve contrast between target species. This work presents simulations that show how contrast between two molecules: (a) depends on the specific sequence of echo spacing, (b) is directly linked to the presence of J-coupling, and (c) can be relatively insensitive to variations in B0, T2 and B1. Imaging studies with oils demonstrate this phenomenon experimentally and also show that spin echo codes can be used for quantification. Finally, preliminary experiments apply the method to human liver in vivo, verifying that the presence of fat can lead to nonmonotonic codes like those seen in vitro. In summary, nonuniformly spaced echo trains introduce a new approach to molecular imaging of J-coupled species, such as lipids, which may have implications diagnosing metabolic diseases.
先前的工作已经强调了在一连串自旋回波中设置信号演变的复杂和独特动力学，特别是对于脂肪等复杂分子应用不均匀的回波间隔时。这里介绍的工作将这些信号模式视为可以用作对比机制的代码，能够区分分子混合物的成像序列，避开了光谱学的许多挑战。对于特定的回波间隔阵列，可以增强非单调和独特的信号演变，以提高目标物种之间的对比度。这项工作展示了如何通过模拟来实现两种分子之间的对比度：（a）取决于回声间隔的具体序列，（b）与 J 耦合的存在直接相关，（c）可以相对不敏感于 B0、T2 和 B1 的变化。油的成像研究实验证明了这种现象，也表明自旋回波码可用于定量分析。最后，初步实验将该方法应用于人体肝脏的体内实验，证实了脂肪的存在会导致像在体外观察到的非单调编码。总之，不均匀间隔的回波序列为 J 耦合物质（如脂质）的分子成像引入了一种新方法，这可能对诊断代谢疾病具有重要意义。
