Area at Risk, Myocardial Infarction, and Myocardial Salvage

在过去的几年中，我们证明了t2加权MRI可以检测与心肌梗死相关的缺血危险区域。这意味着单次MRI检查能够根据t2加权图像确定冠状动脉闭塞期间有多少心肌受到损害，以及通过常规延迟增强图像确定有多少心肌永久性梗死。这种模式的美妙之处在于，两种检测方法都可以在心肌梗死后1-7天内进行，这比基于急诊室的SPECT方法可行得多，后者可能会干扰患者的急性稳定（Aletras等）。发行量2006;113: 1865)。

Over the past few years, we demonstrated that T2-weighted MRI can detect the ischemic area at risk associated with a myocardial infarction. This means that a single MRI examination is capable of determining how much myocardium was jeopardized during the coronary occlusion based on T2-weighted images and how much was permanently infarcted using conventional delayed enhancement images. The beauty of this paradigm is that both determinations can be made 1-7 days after the myocardial infarction - something much more feasible than emergency room based SPECT methods that might interfere with acute stabilization of the patient (Aletras et al. Circulation 2006; 113: 1865). This methodology opens up the possibilities of studying treatments that might modulate the size of acute myocardial infarction. Determining what myocardium was ischemic during an acute coronary occlusion is potentially valuable clinically and for research purposes (Arai AE et al. J Cardiovasc Pharmacol Ther. 2011;16(3-4):313-20 and Schwartz Longacre Let al. Circulation. 2011;124(10):1172-9). While manganese contrast agents can determine area at risk (Natanzon A et al. Radiology. 2005 Sep;236(3):859-66), preliminary experience with a manganese based contrast agent in humans suggested this agent may have too many side effects to be clinically useful. Next, we found that T2-weighted MRI can determine the area at risk in acute MI and is thus complementary to delayed enhancement imaging in acute reperfused MI (Aletras et al. Circulation 2006; 113: 1865) and in non-reperfused myocardial infarction (Tilak et al. Investigative Radiology 2008; 43: 7-15). We developed 2 new methods for imaging myocardial edema associated with acute coronary syndrome (Kellman et al Magn Resonance Med 2007; 57: 891) and a second method that may offer better signal to noise ratio but is more difficult to implement (Aletras AH et al Magn Reson Med 2008; 59: 229). The T2-prep SSFP method markedly improved the diagnostic accuracy of determining the coronary territory associated with an acute myocardial infarction (Kellman et al Magn Resonance Med 2007; 57: 891). The T2-prep SSFP method also works well in humans and correlates with coronary angiographic measures of area at risk (Berry C et al. Circ Cardiovasc Imaging. 2010;3:527-535). More recently, we found that T2-weighted imaging can also detect intramyocardial hemorrhage with excellent sensitivity and specificity (Payne AR et al. Circ Cardiovasc Imaging. 2011 Sep 19). We extended the pathophysiological understanding of MRI abnormalities associated with the area at risk. Consistent with myocardial edema, the T1 of the area at risk is also abnormal (Ugander M et al. JACC Cardiovasc Imaging. 2012; 5(6): 596-603). This study used quantitative images of T1 and T2 and compared with pathology and microspheres for reference standard measurements of infarction and area at risk. The boundaries of perfusion defects associated with the area at risk have been explored with high resolution MRI, CT, and direct visualization of fluorescent perticles (van der Pals et al. Eur Heart J Cardiovasc Imaging 2015). These studies show a perfusion gradient at the borders of the area at risk and a less severe transmural extent of infarction. The kinetics of gadolinium wash-in and wash-out of salvaged myocardium, acutely infarcted myocardium, and in remote myocardium were studied in humans (Hammer-Hansen et al. Eur Heart Cardiovascular Imaging 2015). This study provides a mechanism for why gadolinium can over-estimate infarct size in acute myocardial infarction.