Hillier Elizabeth, Covone Jason, Friedrich Matthias G
Faculty of Medicine and Health Sciences, McGill University; Faulty of Medicine and Dentistry, University of Alberta.
Faculty of Medicine and Health Sciences, McGill University.
J Vis Exp. 2022 Aug 17(186). doi: 10.3791/64149.
Oxygenation-sensitive cardiac magnetic resonance imaging (OS-CMR) is a diagnostic technique that uses the inherent paramagnetic properties of deoxyhemoglobin as an endogenous source of tissue contrast. Used in combination with standardized vasoactive breathing maneuvers (hyperventilation and apnea) as a potent non-pharmacologic vasomotor stimulus, OS-CMR can monitor changes in myocardial oxygenation. Quantifying such changes during the cardiac cycle and throughout vasoactive maneuvers can provide markers for coronary macro- and microvascular function and thereby circumvent the need for any extrinsic, intravenous contrast or pharmacologic stress agents. OS-CMR uses the well-known sensitivity of T2*-weighted images to blood oxygenation. Oxygenation-sensitive images can be acquired on any cardiac MRI scanner using a modified standard clinical steady-state free precession (SSFP) cine sequence, making this technique vendor-agnostic and easily implemented. As a vasoactive breathing maneuver, we apply a 4 min breathing protocol of 120 s of free breathing, 60 s of paced hyperventilation, followed by an expiratory breath-hold of at least 30 s. The regional and global response of myocardial tissue oxygenation to this maneuver can be assessed by tracking the signal intensity change. The change over the initial 30 s of the post-hyperventilation breath-hold, referred to as the breathing-induced myocardial oxygenation reserve (B-MORE) has been studied in healthy people and various pathologies. A detailed protocol for performing oxygen-sensitive CMR scans with vasoactive maneuvers is provided. As demonstrated in patients with microvascular dysfunction in yet incompletely understood conditions, such as inducible ischemia with no obstructive coronary artery stenosis (INOCA), heart failure with preserved ejection fraction (HFpEF), or microvascular dysfunction after heart transplantation, this approach provides unique, clinically important, and complementary information on coronary vascular function.
氧合敏感心脏磁共振成像（OS-CMR）是一种诊断技术，它利用脱氧血红蛋白固有的顺磁性特性作为组织对比的内源性来源。与标准化血管活性呼吸动作（过度通气和屏气）联合使用，作为一种有效的非药物血管运动刺激，OS-CMR可以监测心肌氧合的变化。在心动周期和整个血管活性动作过程中量化这些变化，可以为冠状动脉大血管和微血管功能提供标志物，从而无需任何外源性静脉造影剂或药物应激剂。OS-CMR利用了T2*加权图像对血液氧合的众所周知的敏感性。使用改良的标准临床稳态自由进动（SSFP）电影序列，可在任何心脏MRI扫描仪上采集氧合敏感图像，使该技术与设备供应商无关且易于实施。作为一种血管活性呼吸动作，我们应用一个4分钟的呼吸方案，包括120秒的自由呼吸、60秒的定频过度通气，然后进行至少30秒的呼气屏气。通过跟踪信号强度变化，可以评估心肌组织氧合对该动作的局部和整体反应。在健康人和各种病理情况下，已经对过度通气后屏气最初30秒内的变化进行了研究，这一变化被称为呼吸诱导心肌氧合储备（B-MORE）。本文提供了使用血管活性动作进行氧敏感CMR扫描的详细方案。正如在尚未完全了解的情况下微血管功能障碍患者中所证明的那样，例如在无阻塞性冠状动脉狭窄的诱导性缺血（INOCA）、射血分数保留的心力衰竭（HFpEF）或心脏移植后的微血管功能障碍患者中，这种方法提供了关于冠状动脉血管功能的独特、临床重要且互补的信息。
