早期慢阻肺小气道功能的超极化气体动态MRI研究

Air pollution (haze), smoking and population aging aggravate the development of chronic obstructive pulmonary diseases (COPD) in China. COPD is characterized by airflow limitation mainly caused by small airways diseases. The evaluation of small airways function is of great significance to the diagnosis and prognosis of COPD. However, both the clinical function tests (e.g. pulmonary function tests) and imaging modalities (e.g. CT, X-ray) make great challenges to evaluate small airways function. Consequently, the project utilizes hyperpolarized 129Xe gas, which is of high magnetic resonance sensitivity, to explore a novel approach to evaluate small airways function in early-stage COPD. Firstly, use variable sampling rates to acquire magnetic resonance signals based on the diffusion characteristics of gas, and then achieve hyperpolarized gas dynamic MRI by uniting time-space correlation. Secondly, develop an enhancement method of hyperpolarized gas magnetic resonance images to improve the quality of regions of interest. Thirdly, dynamically describe pulmonary airflow patterns by visualizing kinetics of hyperpolarized gas in the bronchi, bronchioles and alveoli, such as the diffusion velocity and direction, and airway resistance. Finally, construct a new model of small airways function based on the analysis of gas distribution, and then evaluate the pathological characteristics of early-stage COPD. Therefore, the project provides a novel technique for early diagnosis and treatment of COPD.

空气污染（雾霾）、吸烟和人口老龄化加速我国慢性阻塞性肺疾病（COPD）问题的恶性发展。小气道疾病是引起COPD气流受限的主要原因，其功能的评价对COPD的诊断和预后具有重要意义。目前临床常规功能检测（如肺功能检查）和影像手段（如CT、胸透）在小气道功能评价方面依然面临很大挑战性。本项目拟采用具有极高磁共振灵敏度的超极化129Xe气体，探索早期COPD小气道功能评价新方法：首先，利用气体在肺内的弥散特点以变采样率获取磁共振信号，并结合时-空域相关性实现超极化气体动态MRI；其次，发展符合超极化气体磁共振图像特色的增强方法，改善感兴趣区域的图像质量；然后，可视化超极化气体在支气管、细支气管及肺泡内的弥散速度和方向、气道阻力等动力学特性，动态描述肺内气流模式；最后，在分析肺内气体动态弥散过程基础上建立新的小气道功能模型，评估早期COPD的病变特征，以期为临床COPD的早诊断和早治疗提供新技术。

空气污染（雾霾）、吸烟和人口老龄化加速我国慢性阻塞性肺疾病（COPD）问题的恶性发展。小气道疾病是引起COPD气流受限的主要原因，其功能的评价对COPD的诊断和预后具有重要意义。目前临床常规功能检测（如肺功能检查）和影像手段（如CT、胸透）在小气道功能评价方面依然面临很大挑战性。本项目致力于肺部小气道功能的超极化气体动态MRI研究，可视化肺内超极化气体的动力学过程，动态描述肺内气流弥散过程，从而理解和评估小气道功能及变化特征。项目总体取得了良好的研究成果：1）受限于屏气时间和超极化磁共振矢量的衰减特性，提出了一种基于低秩+稀疏+气流效应的肺部动态气体MRI快速成像方法，其时间分辨率为445 ms/帧，空间分辨率为3 mm。该工作作为封面文章发表在Journal of Magnetic Resonance。2）针对恒定欠采样率无法兼顾成像速度肺部细节信息，构建了一种基于自适应采样率的肺部超极化129Xe动态成像方法，其时间分辨率为202 ms/帧，空间分辨率为3 mm，是世界上最快的超极化129Xe MRI采样速率。3）针对CS-MRI的局限，我们提出了一种coarse-to-fine级联卷积神经网络模型用于气体MRI重建，进一步提高重建速度和质量。这也是国际上首次将深度学习应用到气体MRI重建。4）为有效评估肺部微观结构参数，我们首次提出了一种基于深度残差密集网络的多b值气体DW-MRI重建方法，成像时间由18秒缩短至4.7秒，重建时间7.2 ms/层。项目执行期间共发表署课题号论文7篇SCI论文，包括IEEE Trans. Medical Imaging, IEEE Trans. Cybernetics, Magnetic Resonance in Medicine, European Radiology, Journal of Magnetic Resonance, IEEE Trans. Instrumentation & Measurement等；授权发明专利3项，软件著作权3项，培养博士生2名。