Higher temperature super conductors and advances in technologies I guess. The machines are cooled with liquid helium which is expensive and requires a lot of additional tech. If you can live with a lower signal-to-noise ratio you can have lower magnetic field strength and you can maybe use liquid nitrogen. Still not stuff you want to have at home in significant amounts.

Additionally you need a very homogenious magnetic field. This is accomplished by rotating the field very fast by rotating the reels (part of why the machines are so loud). If we find another way to fix this or find a way to deal with it (possibly a supercomputer with supersoftware) cost and size might go down. But this was the best solution available which indicates the size of the problem.

MRI machines need liquid helium [1], so probably never?

[1] http://en.wikipedia.org/wiki/Magnetic_resonance_imaging#How_...

In addition to hardware there is expensive analyais by highly trained profesionals.

Pretty common? It's at most exceedingly rare.