What question do you ask to identify a good quality MRI machine vs a low quality one?

How many T?

T refers to Teslas, which are a measure of the strength of the magnetic field. Most medical MRIs are done at 1.5 T or less, with better quality images available from 3 T machines, and some used for research coming in at 7 T or more.

Frankly, though, there are ways to get around the "low quality" MRI, so it shouldn't have much of an impact on you (assuming you're not a researcher, which would appear to be the case given the question).