Miller G Wilson, Mugler John P, Sá Rui C, Altes Talissa A, Prisk G Kim, Hopkins Susan R
Center for In-Vivo Hyperpolarized Gas MRI, Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, USA; Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
NMR Biomed. 2014 Dec;27(12):1542-56. doi: 10.1002/nbm.3156. Epub 2014 Jul 2.
The field of proton lung MRI is advancing on a variety of fronts. In the realm of functional imaging, it is now possible to use arterial spin labeling (ASL) and oxygen-enhanced imaging techniques to quantify regional perfusion and ventilation, respectively, in standard units of measurement. By combining these techniques into a single scan, it is also possible to quantify the local ventilation-perfusion ratio, which is the most important determinant of gas-exchange efficiency in the lung. To demonstrate potential for accurate and meaningful measurements of lung function, this technique was used to study gravitational gradients of ventilation, perfusion, and ventilation-perfusion ratio in healthy subjects, yielding quantitative results consistent with expected regional variations. Such techniques can also be applied in the time domain, providing new tools for studying temporal dynamics of lung function. Temporal ASL measurements showed increased spatial-temporal heterogeneity of pulmonary blood flow in healthy subjects exposed to hypoxia, suggesting sensitivity to active control mechanisms such as hypoxic pulmonary vasoconstriction, and illustrating that to fully examine the factors that govern lung function it is necessary to consider temporal as well as spatial variability. Further development to increase spatial coverage and improve robustness would enhance the clinical applicability of these new functional imaging tools. In the realm of structural imaging, pulse sequence techniques such as ultrashort echo-time radial k-space acquisition, ultrafast steady-state free precession, and imaging-based diaphragm triggering can be combined to overcome the significant challenges associated with proton MRI in the lung, enabling high-quality three-dimensional imaging of the whole lung in a clinically reasonable scan time. Images of healthy and cystic fibrosis subjects using these techniques demonstrate substantial promise for non-contrast pulmonary angiography and detailed depiction of airway disease. Although there is opportunity for further optimization, such approaches to structural lung imaging are ready for clinical testing.
质子肺部磁共振成像领域正在多个方面取得进展。在功能成像领域，现在可以使用动脉自旋标记（ASL）和氧增强成像技术，分别以标准测量单位量化局部灌注和通气。通过将这些技术整合到一次扫描中，还可以量化局部通气-灌注比，这是肺部气体交换效率的最重要决定因素。为了证明准确且有意义地测量肺功能的潜力，该技术被用于研究健康受试者通气、灌注和通气-灌注比的重力梯度，得出的定量结果与预期的区域变化一致。此类技术也可应用于时域，为研究肺功能的时间动态提供新工具。时域ASL测量显示，暴露于低氧环境的健康受试者肺血流的时空异质性增加，这表明该技术对诸如低氧性肺血管收缩等主动控制机制敏感，也说明要全面研究影响肺功能的因素，有必要考虑时间和空间变异性。进一步发展以增加空间覆盖范围并提高稳健性，将增强这些新功能成像工具的临床适用性。在结构成像领域，可以将诸如超短回波时间径向k空间采集、超快稳态自由进动和基于成像的膈肌触发等脉冲序列技术结合起来，以克服与肺部质子磁共振成像相关的重大挑战，从而在临床合理的扫描时间内实现全肺的高质量三维成像。使用这些技术对健康受试者和囊性纤维化患者进行成像，显示出在非对比剂肺血管造影和气道疾病详细描绘方面具有巨大潜力。尽管还有进一步优化的空间，但这种肺部结构成像方法已准备好进行临床试验。
