Images of multi-walled carbon nanotubes (MWCNT) from the rodent inhalation study. Scanning electron microscopy images of MWCNT collected on the most populated stage of a Nano MOUDI, showing a well-dispersed material. The images represent four different magnifications indicated by the scale bars (20, 10, 5, and 1 um). The 5 μm scale bar had a pore size (dark circles) of 2.5 μm and the other three figures had a pore size of 0.1 μm. The mass median aerodynamic diameter of the material was 1.5 μm. The count mode aerodynamic diameter was ~400 nm.