Multimodal imaging for the detection of sub-micron particles in the gas-exchange region of the mammalian lung

The deposition sites of inhaled aerosols in the gas-exchange region of the lung represent one of the key parameters needed for the understanding of the interaction between these particles and lung tissue. In order to develop a method for three-dimensional imaging of sub-micron particles in lung tissue we applied gold particles (200 and 700 nm) to rat lungs by intratracheal instillation. The samples were scanned at TOMCAT, the beamline for TOmographic Microscopy and Coherent rAdiology experimenTs at the Swiss Light Source. The 200 nm particles were slightly below the detection capabilities of TOMCAT. Therefore, their localization was obtained only by electron microscopy. At a voxel size of 350 nm we observed single and clustered gold particles (700 nm) in alveoli, alveolar ducts, and small bronchioli. The locations of the gold particles were verified by transmission electron microscopical serial sections. We observed a very high correlation between these two imaging modalities. We conclude that a combination of x-ray tomographic microscopy and electron microscopy allows the full unrestricted 3D localization of particles smaller than the resolution of x-ray tomographic microscopy. We are planning to use this method for the verification of the simulation of particle deposition in the airway tree.