This 3D image of a developing mouse head at an early embryonic stage was created using high-resolution episcopic microscopy (HREM). In HREM, samples are embedded in a plastic that has been stained with eosin, a fluorescent dye. A microtome is used to slice away fine sections of the sample – as thin as 2 microns – then an image of the remaining block is captured after each slice is taken. Using computer software, different structures within the head can be visualised. Colour channels can be added to the 3D reconstruction to highlight tissue density, as shown here. (Image: NIMR, MRC) [NewScientist]