Mouse embryos. Left: Virtual sections of a Theiler stage 21 mouse, paraformaldehyde-fixed and IKI-stained. Voxel size 9.0 μm. Center: Similar embryo, PTA-stained. Voxel size 9.6 μm. Right: Osmium-stained 12.5 dpc mouse embryo embedded and scanned in JB4 resin (standard TEM preparation). Voxel size 8.2 μm. Sample was prepared by R. Walsh (Life Sciences EM Facility, Penn State University), and the microCT scan was made in 2001 at the Mayo Clinic in the laboratory of Dr. Erik Ritman (Physiological Imaging Research Lab, Rochester MN). Additional Files 4 and 5 are QuickTime movies of this PTA-stained embryo and a stage 22 IKI-stained embryo.