The only interesting question in here so far and also the only one that got a downvote from someone. 4 microns is about the size of the cell body of the smalles

The only interesting question in here so far and also the only one that got a downvote from someone. 4 microns is about the size of the cell body of the smallest neurons so this technique could potentially give you the position of every neuron in the brain but isn't going to pick up the dendrites and synapses. You'd need resolution closer to 10 nanometers for that. 1 micrometer (micron) = 1000 nanometers