No one is using hydrogen. Nitrogen is old and obsolete.

The current technology is "zero-cryogen" superconducting magnets. These use conventional niobium-titanium LTS magnets which are cooled by direct conduction to a heat exchanger in which is circulated a few grams of cold helium. This is a big change from the older generation of MRI technology which immersed the magnets in up to 150 kg of liquid helium, and used a "cold-head" to recondense helium which boiled off.

Zero cryogen magnets have several advantages, not just the fact that they don't need 100 kg+ of helium. The coolant circuit is sealed, so there is no leakage or boiloff. Similarly, there is no loss of coolant in the event of quench or emergency ramp down. A quench on an immersed magnet is a big problem, and recovery can take days. You can often recover a quench on a zero-cryogen magnet with a power cycle, which will initiate an automatic cool-down and ramp.