re: common bile duct dilation

if an ultrasound shows a dialation of the common bile duct with no obstruction, would a Mrcp test be necessary? my gp, thinks the test shows only obstructions, wouldn't it be strange to have a radiologist Dr. recommend an Mrcp if the ultrasound shows no obstruction and obstructions are all the Mrcp test confirms or does not confirm? Does the Mrcp test show conditions other than just obstructions? i am having this test done on friday, i have no insurance so i am sure this is going to cost me a small fortune, but i really don't care about the cost, i just want to understand how i can acquire hepatitis from my thyroid med's(have graves' antibodies and hashimoto's, but graves' is currently in control)  to a dialated bile duct in less than 6 months of taking tapazole?. sorry for the structuring of my questions, i know i bounce to and fro, blame it on the strokes!.