Dr. Shawn Mikula, a neuroscientist then at the Max Planck Institute of Neurobiology, led a Whole Mouse Brain Volume Electron Microscopy Project with the ambitious goal of mapping the entire connectome of a mouse brain. Over several years he researched modifications to the "standard EM" chemical fixation and staining protocol, which traditionally only works for small tissue pieces because the osmium-based stain is prone to precipitation and barrier formation in larger volumes.
Mikula developed a protocol that overcomes this limitation — the key being the addition of a high concentration of formamide to the osmium tetroxide fixative, eliminating barrier formation and allowing uniform preservation and staining of an entire mouse brain. He published this protocol in Nature Methods (warranting the cover of the June 2015 issue).
Mikula was an official competitor from 2012. On two earlier occasions, brains he submitted were rejected after evaluation: the first showed large cortical cracks revealed by X-ray imaging; the second had non-uniform osmium penetration, leaving core regions such as the thalamus insufficiently preserved. In June 2015 we received a new official whole-mouse-brain entry and performed evaluation imaging, including X-ray micro-CT (16-micron voxel resolution) showing relatively uniform staining at that scale, followed by a statistical electron-microscopy survey for ultrastructure damage using diamond-polished coronal sections correlated back to the X-ray volume.