Aspie kids and MRIs?

My latest concern with Chayce is the pending MRI coming up on the 20th. My neurologist can't seem to give me a direct answer as to why my 4 year old needs this. To me it seems like "research" but on my dime. You can't see autism from an MRI. I DO know that! I don't want to tramatize my son and have him sedated for an MRI if it won't give us any further indication as to what Asperger Syndrome really is. I've looked it up as well and I see nothing. I think I will cancel it until someone can convince me that this is necessary.