In vivo 4D x-ray dark-field lung imaging in mice - Supplementary Information

X-ray dark-field imaging is well-suited to visualizing the health of the lungs because the alveoli create a strong dark-field signal. However, time-resolved and tomographic (i.e., 4D) dark-field imaging is challenging, since most x-ray dark-field techniques require multiple sample exposures, captured while scanning the position of crystals or gratings. Here, we present the first in vivo 4D x-ray dark-field lung imaging in mice. This was achieved by synchronizing the data acquisition process of a single-exposure grid-based imaging approach with the breath cycle. The short data acquisition time per dark-field projection made this approach feasible for 4D x-ray dark-field imaging by minimizing the motion-blurring effect, the total time required and the radiation dose imposed on the sample. Images were captured from a control mouse and from mouse models of muco-obstructive disease and lung cancer, where a change in the size of the alveoli was expected. This work demonstrates that the 4D dark-field signal provides complementary information that is inaccessible from conventional attenuation-based CT images, in particular, how the size of the alveoli from different parts of the lungs changes throughout a breath cycle, with examples shown across the different models. By quantifying the dark-field signal and relating it to other physical properties of the alveoli, this technique could be used to perform functional lung imaging that allows the assessment of both global and regional lung conditions where the size or expansion of the alveoli is affected.X射线暗场成像（X-ray dark-field imaging）非常适用于可视化肺部健康状态，这是因为肺泡能够产生较强的暗场信号。然而，时间分辨型断层（即四维，4D）暗场成像颇具挑战，因为多数X射线暗场技术需要多次样本曝光，且需在扫描晶体或光栅位置的同时完成拍摄。本研究首次实现了小鼠体内的四维X射线暗场肺部成像。该成果通过将单次曝光光栅基成像法的数据采集流程与呼吸周期同步得以实现。每个暗场投影的数据采集时长较短，这通过最小化运动模糊效应、总采集时长以及施加于样本的辐射剂量，使得该方法可应用于四维X射线暗场成像。本研究采集了对照小鼠以及黏液阻塞性疾病、肺癌小鼠模型的影像，上述模型的肺泡尺寸均预期发生变化。本研究表明，四维暗场信号可提供传统基于衰减的CT图像无法获取的补充信息，具体而言，能够展现肺部不同区域的肺泡尺寸在整个呼吸周期中的变化情况，不同疾病模型均展示了这一特性。通过对暗场信号进行量化，并将其与肺泡的其他物理特性相关联，该技术可用于实现功能性肺部成像，从而能够评估肺泡尺寸或扩张受到影响的全局与区域肺部状态。