Current neuroimaging is no where near single neuron-fidelity. In other words, there is no such scan nor is there reason to expect one anytime soon.
Wei_Dai wasn't saying there was. He was supposing that conventional brain scans produce data which is entangled with your particular brain; and that it's possible a sufficient number of such scans could enable a future superintelligence to reconstruct you to a sufficient level of fidelity. If FAI is coming but I buy the farm first, I would prefer lots of MRIs + a frozen brain to just a frozen brain; and I would prefer lots of MRIs to nothing at all.
edit: I do, of course, think the entangling is weak enough that 10GB of head MRIs << 10GB of mind state.
Paul Christiano recently suggested that we can use neuroimaging to form a complete mathematical characterization of a human brain, which a sufficiently powerful superintelligence would be able to reconstruct into a working mind, and the neuroimaging part is already possible today, or close to being possible.
Paul was using this idea as part of an FAI design proposal, but I'm highlighting it here since it seems to have independent value as an alternative or supplement to cryonics. That is, instead of (or in addition to) trying to get your body to be frozen and then preserved in liquid nitrogen after you die, you periodically take neuroimaging scans of your brain and save them to multiple backup locations (1010 bits is only about 1 gigabyte), in the hope that a friendly AI or posthuman will eventually use the scans to reconstruct your mind.
Are there any neuroimaging experts around who can tell us how feasible this really is, and how much such a scan might cost, now or in the near future?
ETA: Given the presence of thermal noise and the fact that a set of neuroimaging data may contain redundant or irrelevant information, 1010 bits ought to be regarded as just a rough lower bound on how much data needs to be collected and stored. Thanks to commenters who pointed this out.