Visualizing treatment delivery and deposition in mouse lungs using in vivo x-ray imaging

The complexity of lung diseases makes pre-clinical in vivo respiratory research in mouse lungs of great importance for a better understanding of physiology and therapeutic effects. Synchrotron-based imaging has been successfully applied to lung research studies, however longitudinal studies can be difficult to perform due to limited facility access. Laboratory-based x-ray sources, such as inverse Compton x-ray sources, remove this access limitation and opens up new possibilities for pre-clinical small-animal lung research at high spatial and temporal resolution. The in vivo visualization of drug deposition in mouse lungs is of interest, particularly in longitudinal research, because the therapeutic outcome is not only dependent on the delivered dose of the drug, but also on the spatial distribution of the drug. An additional advantage of this approach, when compared to other imaging techniques, is that anatomic and dynamic information is collected simultaneously. Here we report the use of dynamic x-ray phase-contrast imaging to observe pulmonary drug delivery via liquid instillation, and by inhalation of micro-droplets. Different liquid volumes (4 μl, 20 μl, 50 μl) were tested and a range of localized and global distributions were observed with a temporal resolution of up to 1.5 fps. The in vivo imaging results were confirmed by ex vivo x-ray and fluorescence imaging. This ability to visualize pulmonary substance deposition in live small animals has provided a better understanding of the two key methods of delivery; instillation and nebulization.