State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, PR China; University of Chinese Academy of Sciences, Beijing 100049, PR China.
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, PR China.
J Magn Reson. 2018 May;290:29-37. doi: 10.1016/j.jmr.2018.03.003. Epub 2018 Mar 8.
Dynamic hyperpolarized (HP) Xe MRI is able to visualize the process of lung ventilation, which potentially provides unique information about lung physiology and pathophysiology. However, the longitudinal magnetization of HP Xe is nonrenewable, making it difficult to achieve high image quality while maintaining high temporal-spatial resolution in the pulmonary dynamic MRI. In this paper, we propose a new accelerated dynamic HP Xe MRI scheme incorporating the low-rank, sparse and gas-inflow effects (L + S + G) constraints. According to the gas-inflow effects of HP gas during the lung inspiratory process, a variable-flip-angle (VFA) strategy is designed to compensate for the rapid attenuation of the magnetization. After undersampling k-space data, an effective reconstruction algorithm considering the low-rank, sparse and gas-inflow effects constraints is developed to reconstruct dynamic MR images. In this way, the temporal and spatial resolution of dynamic MR images is improved and the artifacts are lessened. Simulation and in vivo experiments implemented on the phantom and healthy volunteers demonstrate that the proposed method is not only feasible and effective to compensate for the decay of the magnetization, but also has a significant improvement compared with the conventional reconstruction algorithms (P-values are less than 0.05). This confirms the superior performance of the proposed designs and their ability to maintain high quality and temporal-spatial resolution.
动态超极化（HP）氙 MRI 能够可视化肺部通气过程，这为肺部生理学和病理生理学提供了独特的信息。然而，HP Xe 的纵向磁化是不可再生的，这使得在保持高时间-空间分辨率的同时，难以实现高质量的肺部动态 MRI。在本文中，我们提出了一种新的加速动态 HP Xe MRI 方案，该方案结合了低秩、稀疏和气体流入效应（L+S+G）约束。根据肺部吸气过程中 HP 气体的气体流入效应，设计了一种可变翻转角（VFA）策略来补偿磁化的快速衰减。在欠采样 k 空间数据后，开发了一种考虑低秩、稀疏和气体流入效应约束的有效重建算法来重建动态 MRI 图像。这样，动态 MRI 图像的时间和空间分辨率得到了提高，伪影减少了。在体模和健康志愿者上进行的仿真和体内实验表明，所提出的方法不仅可以补偿磁化的衰减，而且与传统的重建算法相比具有显著的改进（P 值小于 0.05）。这证实了所提出的设计具有优越的性能，并且能够保持高质量和高时间-空间分辨率。
