We are already starting to hit critical points with regard to helium supply, however we’ll soon be hitting critical points with regard to supply of other materials used in other computer aided imaging techniques. Without significant innovation, we’ve likely hit the field cap for widespread MRI at 7T, which still isn’t good enough. Eventually even tomography techniques are going to feel the bite of materials scarcity.
Ultrasonic techniques don’t completely solve the latter problem, but they at least give us a much longer window before it becomes a problem again and in the meantime would allow far more portable and less expensive devices.
We’ve got a window of maybe four to five years before MRI starts to become exotic, and not too much longer after that until tomography becomes exotic.