基于SSFP BOLD MR技术建立一种内源性对比成像无创评价心肌缺血方法的研究

The detection of myocardial ischemia is expected to provide important information on the diagnosis of coronary heart disease and on interventional prevention to myocardial infarction (MI). Currently, magnetic resonance (MR) first-pass perfusion imaging is a widely-used exam to evaluate the myocardial blood flow; however, low spatial resolution, difficulty to perform and toxicity of gadolinium contrast agent are major drawbacks of this method. Non-contrast MR techniques for the detection of ischemic myocardium may address these problems. It is well known that the concentration of deoxyhemoglobin increases when ischemia happens. Deoxyhemoglobin, which contains Fe2+, may serve as a natural paramagnetic MR contrast agent and its level can be quantified by using blood oxygenation level-dependent (BOLD) MR. Therefore, we hypothesis that myocardial ischemia, characterized by low MR signal, can be detected by taking advantages of hypoxia of local myocardial blood flow. In preliminary studies, we have already built and optimized the sequence of SSFP BOLD MR on healthy canine models. Based on our previous work, the aim of the perspective study is to further verify the accuracy of SSFP BOLD MR in depicting regional myocardial blood flow on canine MI models and healthy volunteers by using first-pass MR perfusion imaging and PET/CT as references. The results of this study have the potential to provide an alternative strategy for the non-invasive diagnosis and real-time therapeutic evaluation of MI in clinical patients.

心肌缺血的精准检测可为冠心病的诊疗提供及时、必要的信息。MR首过灌注成像是目前评估心肌血流灌注情况的重要方法，但空间分辨率低、扫描难度高、含钆对比剂具有毒副作用是其不容忽视的问题。应用非对比剂MR方法检测心肌缺血可避免上述问题。我们最近采用内源性对比血氧饱和水平依赖技术（BOLD），以血管内固有的顺磁性脱氧血红蛋白为基本原理，行稳态自由进动的（SSFP）BOLD MR成像，已成功构建出扫描序列，并在活体健康犬心肌上验证了该技术的可靠性及高效性。本课题拟在此基础上，通过犬缺血心肌模型及健康志愿者验证，构建适用于心肌缺血患者的扫描序列，利用缺血心肌血流灌注的低氧状态获取不同于正常心肌的MR低信号来诊断心肌缺血，并与MR首过灌注及PET/CT成像进行对比验证，以期实现该技术对心肌缺血的精准检测。这种无创、无需对比剂、可重复、易操作的MR检测方法将为心肌缺血的无创诊断和实时治疗评估提供全新的策略。

在完成SSFP BOLD MR扫描序列的构建、于活体健康犬心肌上验证SSFP BOLD MR扫描技术的可靠性及有效性、成功制备犬急性心肌缺血模型的基础上，我们课题组进行了 SSFP BOLD MR扫描技术在犬急性缺血心肌模型上的有效验证、优化了适用于人心脏的SSFP BOLD MR扫描参数，并对SSFP BOLD MR扫描技术在健康志愿者心肌上以及在冠心病患者缺血心肌上进行了有效验证。我们发现：在无创无需外源性造影剂的情况下，利用体内固有的顺磁性脱氧血红蛋白，SSFP BOLD MR信号强度不光可间接反映犬的正常心肌和缺血心肌的局部血流情况，亦可有效反映人正常心肌及冠心病患者缺血心肌的局部血流情况。而且，虽然冠心病患者多有心率快、心律不齐等情况，但图像质量仍能满足诊断需要。由此，SSFP BOLD MR克服了MR首过灌注成像不容忽视的外源性对比剂、难操作、图像分辨率低等无法克服的问题，疑有缺血心肌的患者可使用这种MR检测方法进行无创、无需对比剂、可重复、易操作的检测，该方法可为缺血心肌的早期精准检测以及诊疗提供全新的策略。