The New England Journal of Medicine has a brilliant research paper describing the first MRI scan capable of imaging the whole nervous system, plus a little something extra.
The technology is based on diffusion MRI, a technique which takes advantage of how water molecules move to separate out nerves from the rest of the body.
Water molecules bounce around inside all of the body tissues. Nerve fibres are long and thin, and so water molecules trapped inside are restricted in their movement – like jumping beans in a pipe.
Diffusion MRI works out which water molecules diffuse only along a fixed route (the nerves) and which are moving more freely (the rest of the body).
Of course, there could be some false positives in there, so the scan looks specifically for this diffusion effect only in tissue of the right density for nerve fibres.
Normal MRI scans are essentially density maps and to do this the scanner aligns the proton spins of the body’s hydrogen atoms using huge magnets. It then fires off a electromagnetic pulse which knocks the spins out of alignment. As the spins return to alignment (called the ‘relaxation time’) a radio signal is given off which differs depending on the type of tissue. This can be read, mapped and turned into a scan.
As an analogy, imagine if you had compasses with lots of different liquids inside. They’d all point north, but you could knock them out of alignment by giving them a shake. Slowly the needles would return to north, but the liquid inside would affect how quickly they moved. Just by measuring the speed of return you could work out the density of the liquid. Treacle would take longer than oil, oil longer than water.
So if you restrict the scan only to pick out tissue with the same density as nerve fibres, that also only has water molecules moving along a single route, you’ve got a very high-tech nerve mapper.
The researchers tweaked this process for the whole body and produced the first scan of the entire nervous system which they called ‘Whole-Body Magnetic Resonance Neurography’.
You may notice from the scans that as well as imaging the young man’s nervous system, it also gives a remarkably good likeness of his cock.
As it turns out, the prostate, testes, and penis also hit the sweet spot of restricting water molecule diffusion while giving off a similar radio signal to nerves.
Action potential? Oh give over.