Department of Radiation Oncology, NYU Langone Health, New York, NY 10016, United States of America.
Phys Med Biol. 2019 May 16;64(10):105019. doi: 10.1088/1361-6560/ab160c.
The aim of this work was to develop a novel hybrid 3D hyperpolarized (HP) gas tagging MRI (t-MRI) technique and to evaluate it for lung respiratory motion measurement with comparison to deformable image registrations (DIR) methods. Three healthy subjects underwent a hybrid MRI which combines 3D HP gas t-MRI with a low resolution (Low-R, 4.5 mm isotropic voxels) 3D proton MRI (p-MRI), plus a high resolution (High-R, 2.5 mm isotropic voxels) 3D p-MRI, during breath-holds at the end-of-inhalation (EOI) and the end-of-exhalation (EOE). Displacement vector field (DVF) of the lung motion was determined from the t-MRI images by tracking tagging grids and from the High-R p-MRI using three DIR methods (B-spline based method implemented by Velocity, Free Form Deformation by MIM, and B-spline by an open source software Elastix: denoted as A, B, and C, respectively), labeled as tDVF and dDVF, respectively. The tDVF from the HP gas t-MRI was used as ground-truth reference to evaluate performance of the three DIR methods. Differences in both magnitude and angle between the tDVF and dDVFs were analyzed. The mean lung motion of the three subjects was 37.3 mm, 8.9 mm and 12.9 mm, respectively. Relatively large discrepancies were observed between the tDVF and the dDVFs as compared to previously reported DIR errors. The mean ± standard deviation (SD) DVF magnitude difference was 8.3 ± 5.6 mm, 9.2 ± 4.5 mm, and 9.3 ± 6.1 mm, and the mean ± SD DVF angular difference was 29.1 ± 12.1°, 50.1 ± 28.6°, and 39.0 ± 6.3°, for the DIR Methods A, B, and C, respectively. These preliminary results showed that the hybrid HP gas t-MRI technique revealed different lung motion patterns as compared to the DIR methods. It may provide unique perspectives in developing and evaluating DIR of the lungs. Novelty and Significance We designed a MRI protocol that includes a novel hybrid MRI technique (3D HP gas t-MRI with a low resolution 3D p-MRI) plus a high resolution 3D p-MRI. We tested the novel hybrid MRI technique on three healthy subjects for measuring regional lung respiratory motion with comparison to deformable image registrations (DIR) methods, and observed relatively large discrepancies in lung motion between HP gas t-MRI and DIR methods.
这项工作的目的是开发一种新的混合 3D 极化（HP）气体标记 MRI（t-MRI）技术，并将其与可变形图像配准（DIR）方法进行比较，用于评估肺呼吸运动测量。三名健康受试者在吸气末（EOI）和呼气末（EOE）进行了一项混合 MRI，该 MRI 结合了 3D HP 气体 t-MRI 和低分辨率（Low-R，4.5mm 各向同性体素）3D 质子 MRI（p-MRI），外加高分辨率（High-R，2.5mm 各向同性体素）3D p-MRI。通过跟踪标记网格，从 t-MRI 图像中确定肺运动的位移矢量场（DVF），并使用三种 DIR 方法（由 Velocity 实现的基于 B 样条的方法、MIM 的自由变形和由开源软件 Elastix 实现的基于 B 样条：分别表示为 A、B 和 C）从 High-R p-MRI 中确定，分别标记为 tDVF 和 dDVF。将 HP 气体 t-MRI 中的 tDVF 用作地面真实参考，以评估三种 DIR 方法的性能。分析了 tDVF 和 dDVF 之间的大小和角度差异。三名受试者的平均肺运动分别为 37.3mm、8.9mm 和 12.9mm。与之前报道的 DIR 误差相比，tDVF 和 dDVF 之间观察到相对较大的差异。平均 ± 标准偏差（SD）DVF 幅度差分别为 8.3 ± 5.6 mm、9.2 ± 4.5 mm 和 9.3 ± 6.1 mm，平均 ± SD DVF 角度差分别为 29.1 ± 12.1°、50.1 ± 28.6°和 39.0 ± 6.3°，用于 DIR 方法 A、B 和 C。这些初步结果表明，混合 HP 气体 t-MRI 技术与 DIR 方法相比，揭示了不同的肺运动模式。它可能为开发和评估肺部 DIR 提供独特的视角。新颖性和意义我们设计了一种 MRI 协议，该协议包括一种新的混合 MRI 技术（具有低分辨率 3D p-MRI 的 3D HP 气体 t-MRI）和高分辨率 3D p-MRI。我们在三名健康受试者上测试了新的混合 MRI 技术，用于测量区域肺呼吸运动，并与可变形图像配准（DIR）方法进行比较，观察到 HP 气体 t-MRI 和 DIR 方法之间的肺运动存在相对较大的差异。
