急性缺血缺氧心肌损伤的早期检出和综合防治是目前医学界的重点研究方向，而梗死后心肌活力的判断对血运重建和功能恢复至关重要。缺血梗死后，局部代谢异常导致三磷酸腺苷（ATP）迅速消耗、磷酸肌酸（PCr）及游离肌酸（Cr）浓度均减低，因此基于心脏肌酸能量代谢的量化评价手段可为早期检测和及时评价心肌活性提供新方法和新思路。传统方法磁共振波谱成像（31P、1H-MRS）在空间分辨率和可重复性等方面均不同程度受限。因此，我们拟采用基于肌酸代谢的化学交换饱和转移（CrCEST）成像新技术，定量分析急性缺血心肌内肌酸代谢变化，实现心肌活性的早期评价；通过与31P、1H-MRS和延迟增强成像（LGE）的对比分析，优化CrCEST序列并实现临床转化，为临床早期诊断和治疗决策提供科学依据。

Currently, early diagnosis and comprehensive prevention for acute hypoxic-ischemic myocardial injury are increasingly focused in clinical practice, and early detection of myocardial viability has a vital role in determining revascularization and function recovery after myocardial infarction. During ischemia, adenosine triphosphate (ATP) depleted quickly, and phosphocreatine (PCr) and free creatine (Cr) concentrations reduced sharply due to emerging local metabolic abnormalities. As a new methods and strategies, therefore, quantitative assessment of creatine metabolism in infarcted myocardium is essential for early detection and promptly evaluation of myocardial viability. However, conventional magnetic resonance spectroscopy (31P, 1H-MRS) is limited in creatine metabolites measurement in vivo for some drawbacks including spatial resolution and repeatability to some extent. Herein, we hypothesize that creatine-sensitive chemical exchange saturation transfer (CrCEST) MR imaging may serve as a new surrogate metabolic imaging marker for hypoxic-ischemic myocardial viability. In this proposal, we intend to explore the optimal creatine-based chemical exchange saturation transfer (CrCEST) sequence and validate the feasibility of assessment the acute myocardial viability with this new method. In comparison with 31P,1H-MRS and late gadolinium enhancement (LGE) images, the myocardial viability will be assessed quantitatively and dynamically with the creatine-sensitive CrCEST imaging with high sensitivity and accuracy. We are hopeful that this project would further achieve CrCEST clinical translation and provide scientific evidences for making early diagnosis and prompt therapeutic decisions for acute hypoxic-ischemic myocardial injury.

本研究采用Siemens 3.0T MRI对不同浓度肌酸（Cr）的体外模型分别进行基础序列、优化后的非心电门控和心电门控CrEST序列成像，以完成序列优化。心电门控CrEST序列和非心电门控CrEST序列获得的图像的SNR要高于基础序列；与基础CrEST序列相比，优化后的心电门控CrEST序列可获得较高SNR的CrEST图像。正常、急性、及、慢性期心肌梗死（myocardial infarction，MI）模型动物分别接受优化后的磁共振CEST成像及延迟强化（late gadolinium enhanced, LGE）扫描，观察心肌基于肌酸（1.8ppm）代谢的CEST对比图中显示的心肌代谢降低区域，并将CEST及LGE扫描相应节段进行对照分析。在心梗动物模型中，拟合Z谱CEST显示频率为1.8ppm时，梗死心肌信号均降低。急、慢性MI模型心肌的CEST对比度均较正常对照组明显降低。此外，慢性期MI的CEST对比较急性期进一步降低。对于MI动物，梗死区域的CEST对比度低于对侧正常区域。基于肌酸代谢的CEST成像显示的梗死区域与LGE基本一致。基于肌酸代谢的CEST成像技术能无创地显示心肌梗死后心肌组织损伤并评价局部心肌活性。