Department of Biomedical Engineering, Department of Biomedicine and Health Sciences, College of Medicine, The Catholic University of Korea, Seoul, 06591, Republic of Korea.
Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, 06591, Republic of Korea.
Med Phys. 2020 Mar;47(3):898-908. doi: 10.1002/mp.13982. Epub 2020 Jan 20.
Deformable lung phantoms have been proposed to investigate four-dimensional (4D) imaging and radiotherapy delivery techniques. However, most phantoms mimic only the lung and tumor without pulmonary airways. The purpose of this study was to develop a reproducible, deformable lung phantom with three-dimensional (3D)-printed airways.
The phantom consists of: (a) 3D-printed flexible airways, (b) flexible polyurethane foam infused with iodinated contrast agents, and (c) a motion platform. The airways were simulated using publicly available breath-hold computed tomography (CT) image datasets of a human lung through airway segmentation, computer-aided design modeling, and 3D printing with a rubber-like material. The lung was simulated by pouring liquid expanding foam into a mold with the 3D-printed airways attached. Iodinated contrast agents were infused into the lung phantom to emulate the density of the human lung. The lung/airways phantom was integrated into our previously developed motion platform, which allows for compression and decompression of the phantom in the superior-inferior direction. We quantified the reproducibility of the density (lung), motion/deformation (lung and airways), and position (airways) using breath-hold CT scans (with the phantom compressed and decompressed) repeated every two weeks over a 2-month period as well as 4D CT scans (with the phantom continuously compressed and decompressed) repeated twice over four weeks. The density reproducibility was quantified with a difference image (created by subtracting the rigidly registered baseline and the repeated images) in each of the compressed and decompressed states. Reproducibility of the motion/deformation was evaluated by comparing the baseline displacement vector fields (DVFs) derived from deformable image registration (DIR) between the compressed and decompressed phantom CT images with those of repeated scans and calculating the difference in the displacement vectors. Reproducibility of the airway position was quantified based on DIR between the baseline and repeated images.
For the breath-hold CT scans, the mean difference in lung density between baseline and week 8 was -1.3 (standard deviation 33.5) Hounsfield unit (HU) in the compressed state and 0.4 (36.8) HU in the decompressed state, while large local differences were observed around the high-contrast structures (caused by small misalignments). By visual inspection, the DVFs (between the compressed and decompressed states) at baseline and last time point (week 8 for the breath-hold CT scans) demonstrated a similar pattern. The mean lengths of displacement vector differences between baseline and week 8 were 0.5 (0.4) mm for the lung and 0.3 (0.2) mm for the airways. The mean airway displacements between baseline and week 8 were 0.6 (0.5) mm in the compressed state and 0.6 (0.4) mm in the decompressed state. We also observed similar results for the 4D CT scans (week 0 vs week 4) as well as for the breath-hold CT scans at other time points (week 0 vs weeks 2, 4, and 6).
We have developed a deformable lung phantom with 3D-printed airways based on a human lung CT image. Our findings indicate reproducible density, motion/deformation, and position. This phantom is based on widely available materials and technology, which represents advantages over other deformable phantoms.
变形肺体模已被提出用于研究四维（4D）成像和放射治疗技术。然而，大多数体模仅模仿肺和肿瘤，而不模仿肺气道。本研究的目的是开发一种可重复的、具有三维（3D）打印气道的变形肺体模。
该体模由：（a）3D 打印的柔性气道，（b）注入碘化对比剂的柔性聚氨酯泡沫，和（c）运动平台组成。气道通过对人体肺的呼吸暂停 CT（CT）图像数据集进行气道分割、计算机辅助设计建模和使用橡胶状材料的 3D 打印来模拟。通过将液体膨胀泡沫倒入附有 3D 打印气道的模具中，来模拟肺。将碘化对比剂注入肺体模中，以模拟人体肺的密度。将肺/气道体模集成到我们之前开发的运动平台中，该平台允许在上下方向上压缩和解压缩体模。我们使用呼吸暂停 CT 扫描（在压缩和解压缩体模时），在两个月的时间内每隔两周重复一次，以及 4D CT 扫描（在连续压缩和解压缩体模时），在四周内重复两次，来量化密度（肺）、运动/变形（肺和气道）和位置（气道）的可重复性。通过在每个压缩和减压状态下创建刚性注册基线和重复图像之间的差值图像，来量化密度的可重复性。通过比较基线变形图像配准（DIR）得出的压缩和减压体模 CT 图像之间的位移向量场（DVF），以及重复扫描的位移向量，来评估运动/变形的可重复性，并计算位移向量的差异。基于基线和重复图像之间的 DIR，来量化气道位置的可重复性。
对于呼吸暂停 CT 扫描，基线和第 8 周时肺密度的平均差值分别为在压缩状态下为-1.3（标准偏差 33.5）亨氏单位（HU），在减压状态下为 0.4（36.8）HU，而在高对比度结构周围观察到较大的局部差异（由于小的对位不准）。通过视觉检查，基线和最后时间点（呼吸暂停 CT 扫描的第 8 周）的 DIR （在压缩和减压状态之间）显示出相似的模式。基线和第 8 周之间的位移向量差值的平均值分别为肺为 0.5（0.4）mm，气道为 0.3（0.2）mm。基线和第 8 周之间的气道位移平均值分别为压缩状态下为 0.6（0.5）mm，减压状态下为 0.6（0.4）mm。我们还观察到 4D CT 扫描（第 0 周与第 4 周）以及其他时间点（第 0 周与第 2、4 和 6 周）的呼吸暂停 CT 扫描的类似结果。
我们已经基于人体肺 CT 图像开发了一种具有 3D 打印气道的可变形肺体模。我们的研究结果表明，密度、运动/变形和位置具有可重复性。这种体模基于广泛使用的材料和技术，相对于其他变形体模具有优势。
