Beyond the depth-of-focus limit in connectomics

A fundamental limit in imaging is the depth of focus of DOF=5.4(transverse resolution squared)/λ. Because X rays offer high penetration with low multiple scattering, they are ideal for studies in connectomics where one wishes to obtain a map of all synaptic connections in the brain. Connectomics in the mouse is a major near-term goal in neurobiology, and the ESRF has committed to developing a nanotomography end-station designed to offer scalable imaging capabilities. However, while a whole mouse brain is approximately 1 cm in its longest direction, achieving sub-20 nanometer resolution (as required for highly accurate synapse detection) at 34 keV implies a depth-of-focus limit of 59 micrometers. This would seem to thwart full use of the penetration and resolution potential of X rays in connectomics, and in other studies. We propose to acquire mouse brain data that can be used to overcome this limit, using a multislice model that has worked well in simulation studies.