There are NO alternatives. There's nothing else that stays liquid at 4 K and absolutely nothing else comes close.
We use a lot in our MR scanners.
The tech is changing and magnets are using far far less.
Super-conduction at higher temperatures has made progress too.
So while you are right that nothing else stays liquid at those temps, we won’t be needing nearly as much helium in radiology in the next few years.
The new generation use something like 700ml of helium, where the standard was hundreds of litres. https://magneticsmag.com/siemens-healthineers-gets-fda-clear...
How many loans for MRI machines that require helium haven't been paid back yet?
They use a lot when installed, but rarely need top-ups.
They are shipped full of helium and chilled, but aren’t ramped up (so aren’t superconducting magnets until after commissioning).
All these "we're going to run out" stories pretend that engineering cannot adapt to changing cost structures, which is just total nonsense.
Sure, there is nothing that can be directly substituted for how we use Helium today, but clearly we're using Helium inefficiently today and the answer is that once markets force us to change, we will find more efficient ways.