The injection wouldn’t have been only for the pain, right? I mean, you wouldn’t need to bother with this type of injection if that was the point. Pain management is routine.
What I suspect your rheuma had in mind was an injection that targets the inflammation. Not a permanent fix obviously but probably still worth trying since clearing crystals with febuxostat is going to take a while (assuming you tolerate the drug).
My rheuma figures a well-done ultrasound is more informative than an MRI. Or maybe that depends on what you want to see. Based on SUA, physical exam and X-rays, serious permanent damage wasn’t expected in my case.
The advantage of MRIs is apparently that any qualified fool can do them. For the ultrasound though, I was to see a specific fellow.
In the end, if you’re 99% confident that the right course of action is going to be simple ULT whether or not a scan is done… well, in that case the cost/benefit of a scan is questionable.