Development and clinical evaluation of UTE sequences for functional lung imaging

磁共振成像(MRI)允许在没有电离辐射的情况下进行横断面成像，这使得它的使用特别适合医疗辐射应用的高风险群体。肺部MRI一直受到肺实质物理条件的限制，但最新的超短回波时间(UTE)MRI序列提供了更高的信噪比，从而显著改善了肺部的图像质量。研究表明，UTE MRI和计算机断层扫描在肺形态方面的许多适应症上具有类似的性能。尽管现代UTE序列的诊断潜力表明它们也可用于肺功能成像，但这一应用领域仍未被广泛探索。在研究项目的第一个资助期内，开发了用于功能性肺MRI的2D和3D UTE序列并进行了临床测试。开发工作包括制定用于测量肺通气量和对比灌注的3D UTE序列，并开发了2D单层和2D同时多层UTE序列，用于通过流入效应无对比测量肺灌注量。探索性研究已经测试和比较了呼吸方案，成功地验证了呼吸测量的重复性及其与肺功能测试的一致性，并展示了UTE序列在囊性纤维化患者功能成像中的潜在应用。尽管取得了这些成功，但仍然存在局限性，阻碍了UTE序列在功能性肺MRI的临床应用，最显著的是大多数方法依赖于屏气动作。在第二个资助期内，开发的技术将得到扩展和改进：自由呼吸数据采集的实施将使所有患者都可以使用功能性UTE-MRI，无论他们的呼吸顺应性如何。开发同时激发多个切片的序列将进一步减少扫描时间，集成误差图将允许立即评估功能测量的可靠性。系统地研究流入相关实质信号变化与采集参数之间的相关性将导致用于定量灌注成像的非造影剂方案。这些进展将在对具有代表性的患者集体进行的探索性研究中进行测试和验证。其中，目标参数是图像质量和功能测量与临床建立的方法的一致性。在项目结束时，基于UTE序列的无对比度肺MRI应该可用，它允许在短检查时间内对肺实质进行高分辨率成像，提供可量化的功能信息。根据个体的呼吸顺应性，可以在屏气或自由呼吸期间选择数据采集，并通过误差指数评估功能测量的有效性。

Magnetic resonance imaging (MRI) allows cross-sectional imaging without ionizing radiation, making its use particularly desirable for high-risk groups of medical radiation applications. Pulmonary MRI has been limited by physical conditions in the lung parenchyma, but latest ultrashort echo time (UTE) MRI sequences provide an improved signal-to-noise ratio and thus significantly better image quality in the lung. Studies show comparable performance of UTE MRI and computed tomography for many indications regarding lung morphology. Although the diagnostic potential of modern UTE sequences suggests their use also in functional lung imaging, this field of application was widely unexplored. During the first funding period of the research project, 2D and 3D UTE sequences for functional lung MRI were developed and clinically tested. Developmental work included the elaboration of 3D UTE sequences for measuring lung ventilation and contrast perfusion, and both 2D single-slice and 2D simultaneous multi-slice UTE sequences were developed for contrast-free measurements of lung perfusion via the inflow effect. Exploratory studies have tested and compared respiratory protocols, successfully verified the reproducibility of ventilation measurements and their agreement with pulmonary function testing, and demonstrated the potential application of UTE sequences for functional imaging in patients with cystic fibrosis, among others. Despite these successes, limitations still exist that hinder the widespread clinical use of UTE sequences for functional lung MRI, most notably the dependence of most methods on breath-hold maneuvers. Within the second funding period, the techniques developed will be expanded and improved: Implementation of free-breathing data acquisition will make functional UTE-MRI accessible to all patients regardless of their breathing compliance. Development of sequences with simultaneous excitation of multiple slices will further reduce scan time, and integration of error maps will allow immediate assessment of the reliability of functional measurements. Systematic investigation of the dependencies between inflow-related parenchymal signal changes and acquisition parameters will lead to a non-contrast protocol for quantitative perfusion imaging. The developments will be tested and validated in exploratory studies on representative patient collectives. Among others, target parameters are the image quality and the agreement of the functional measurements with clinically established methods. At the end of the project, a contrast-free lung MRI based on UTE sequences should be available, which allows high-resolution imaging of the lung parenchyma in a short examination time providing quantifiable functional information. Depending on the individual respiratory compliance, it is then possible to choose between data acquisition during breath-hold or free-breathing and to assess the validity of the functional measurements through error indices.