MRI T2 mapping for quantitative assessment of venous oxygen saturation

心力衰竭、肺动脉高压和先天性心脏病会损害心脏的功能 心血管系统提供足够的氧气(O2)以满足器官不同的代谢需求 系统。在主肺动脉测量混合静脉血氧饱和度是一个准确的标志物。 全身输送血液和氧气，提供关键的诊断和预后价值。然而，一个真正的 混合性静脉饱和需要导管进入主肺动脉，可能作为一种 由于相关的侵袭性和风险水平而进行的诊断措施。一种非侵入性的手段来快速和 准确测量主肺动脉、心腔的氧饱和度(O2sat)，理想情况下 在身体的任何地方，不仅会减少侵入性导尿术的需要，而且还会 提供重要的生理信息，否则可能无法获得或无法获得。 在血液中，磁共振横向弛豫时间(T2)与血氧饱和度有关 Hb和MR弛豫法先前已被建议用于活体估计血氧饱和度； 然而，这些估计依赖于对每个患者进行不切实际的体外校准，结果是 已经被流诱导的人工产物破坏了。我们实验室以前开发的一种快速单次激发T2的技术 已修改映射以减少流动伪影，并提高在流动血液中测量T2的准确性。 结合这种改进的脉冲序列，我们提出了一种全新的求解Luz-Meiboom问题的方法 (L-M)方程，描述了T2和O2在血液中的关系。我们假设，使用 不同的准备脉冲计时以及容易获得的患者特定参数的直接测量 将支持非线性参数估计技术的应用提供准确的量化 评估心脏和深血管中的血氧，即使在可及性有限的位置也是如此 其他诊断技术。我们建议优化和验证这种非侵入性血氧测定仪的方法。 通过实现以下具体目标。目标1：我们将为采集参数TE定义适当的限制 并使用统计灵敏度分析来优化采集参数。目标2：我们 是否会在猪的分级低氧血症模型中经验性地验证来自T2的O2sat，从而使 在广泛的数值范围内同时采集T2和侵入性的O2sat测量。目标3：我们将 评估一小部分心力衰竭患者接受临床指征的肺动脉手术的可行性 留置导管测量混合静脉血氧饱和度。 通过解决T2准备脉冲的流动敏感性和由 将T2与O2sat之间的模型过于简化，我们预计精确度和重复性水平 这项技术将提高到心血管疾病患者临床应用所需的水平。 τ

Heart failure, pulmonary hypertension, and congenital heart disease can compromise the capacity of the cardiovascular system to deliver sufficient oxygen (O2) to meet the varying metabolic demands of the organ systems. Mixed venous oxygen saturation measured in the main pulmonary artery is an accurate marker of the systemic delivery of blood and oxygen that provides key diagnostic and prognostic value. However, a true mixed venous saturation requires catheter access to the main pulmonary artery and may be underutilized as a diagnostic measure due to the associated level of invasiveness and risk. A non-invasive means to quickly and accurately measure O2 saturation (O2sat) in the main pulmonary artery, the cardiac chambers, and ideally anywhere in the body, would not only reduce the need for invasive catheterization procedures, but would also provide important physiological information that may be otherwise unavailable or unobtainable. In the blood, the magnetic resonance transverse relaxation time (T2) is related to the oxygen saturation of hemoglobin, and MR relaxometry has been previously proposed for in vivo estimation of blood O2 saturation; however, these estimates have relied on an impractical in vitro calibration on each patient, and results have been corrupted by flow-induced artifacts. A technique previously developed in our lab for rapid, single-shot T2 mapping has been modified to reduce flow artifacts and improve the accuracy of T2 measured in flowing blood. Together with this modified pulse sequence, we propose an entirely new approach to solving the Luz-Meiboom (L-M) equation that describes the relationship between T2 and O2sat in blood. We hypothesize that the use of varied preparation pulse timing along with direct measurement of easily accessible patient specific parameters will support the application of non-linear parameter estimation techniques to provide an accurate quantitative assessment of blood O2sat in the heart and deep vessels, even in locations having limited accessibility with other diagnostic techniques. We propose to optimize and validate this approach to non-invasive blood oximetry by meeting the following specific aims. Aim 1: We will define appropriate limits for acquisition parameters TE and 180 in a flow phantom and optimize acquisition parameters using statistical sensitivity analysis. Aim 2: We will empirically validate O2sat derived from T2 in a porcine model of graded hypoxemia that enables simultaneous acquisition of T2 and invasive O2sat measurement over a broad range of values. Aim 3: We will evaluate feasibility in a small cohort of heart failure patients undergoing clinically indicated pulmonary artery catheterization for mixed venous O2sat measurement. By addressing the flow sensitivity of the T2 preparation pulse and the inaccuracies introduced by oversimplification of the model relating T2 to O2sat, we anticipate that the level of accuracy and reproducibility for this technique will be raised to that required for clinical application in patients with cardiovascular disease. τ