The last time I had an MRI, there were no gowns smaller than a large.  I could have wrapped it around my body twice.. It was falling off and very uncomfortable but it isn't feasible to have smalls because so many of the patients are supersize.  They love working with small people; we're so much easier to maneuver ( I have to be sedated).  The first time I had an epidural the doctor was thrilled because he could better find the correct spot because he could easily see my vertebrae.  He said most of his patients are fat and it's hard to place the needle with no landmarks to guide him.