Sorry you've not had an answer to your questions Becky.
I had 2 MRIs completed... 1 session, but part without contrast, part with contrast.
The non-contrast portion was 'normal', the contrast portion is where they found my lesions.
I've spoken with folks who were diagnosed with MS without having any lesions present on their MRI.
We're all so very unique!
As for how metal affects an MRI, I'm not sure.. other than my neuro freaks at the littlest piece of metal that COULD affect an MRI.
I'm sorry I can't answer your other questions, but I'm certain someone else will have more insight.