Pulmonary vascular biomechanics imaged with synchrotron phase contrast microtomography in live rats

Introduction: In vivo micromechanics of individual pulmonary blood vessels are challenging to assess in vivo due to insufficient temporal and spatial resolution of current imaging techniques. We developed a time-resolved synchrotron radiation phase-contrast CT technique which allows imaging the lungs in vivo down to the alveolar length scale. Here we describe the image processing methodology allowing for the quantitative assessment of vascular strain during breathing in rat lung. Methods: The experiment was performed in 3 anesthetized, muscle-relaxed and ventilated adult rats. Images were acquired using a fast camera (PCO Edge 5.5), with a pixel size of 6 µm and 10 ms time resolution. 3D images of the lung region of interest were reconstructed at 78 time points within a breath. Acinar and vascular structures were segmented at each time point and incremental registration-based voxel-by-voxel displacement was computed with reference to the start of inspiration and displayed as a function of time. Results: Figure 1A shows a quantitative map of the relative regional acinar volume change between the minimal and maximal pressure points during the breathing cycle. Figure 1B shows the regions of interest where regional strain is displayed within blood vessels (1C). A typical pulse-wave deformation was observed within a larger artery which was significantly damped in smaller caliber vessels. Conclusions: Our results demonstrate the feasibility of mapping regional vascular strain in in vivo rat lungs at 6 µm resolution. The ability to map the dynamics of mechanical strain in pulmonary blood vessels offers a unique tool to study mechanisms leading to ventilator-induced lung injury.