So long as they stay under their critical temperature. If that changes… well, a lot of liquid helium is about to stop being liquid.
And that's one of the reasons why a permanent-magnet MRI is so interesting -- it doesn't depend on a constant supply of power (for the helium cooler) and gaseous helium (to replace lost gas), so the system is portable, and maintenance costs are likely to be much lower.
So long as they stay under their critical temperature. If that changes… well, a lot of liquid helium is about to stop being liquid.
And that's one of the reasons why a permanent-magnet MRI is so interesting -- it doesn't depend on a constant supply of power (for the helium cooler) and gaseous helium (to replace lost gas), so the system is portable, and maintenance costs are likely to be much lower.