I’m confused by what you are trying to say.
There exists no 4 year IR residency. Many of them are categorical with internship+3 years DR+2 years IR=6 years at minimum, before tacking on any additional neuro IR specific training.
if you go to a place like MGH where “minifellowships” are equivalent to fellowships, you can shave a tiny bit of time off depending on where you do neuro IR, but it’s often a wash as the neuroradiology fellowship in those places is 2 years long.
it is faster to enter Neuro IR through DR. In all cases, it’s longer than Neurosurgery at 7 years.