Nuclear test for gall bladder, can anyone give me information on this test and is it accurate?

I have already had two ultra sounds and two cat scans in the past three years and they haven't found anything as of yet. My liver,pancreas,kidneys are good. But, I have gall bladder attacks and I could handle it every once in a while, but when the pain didn't stop - I went back to the Doc and said, "something is not right with me and we have to find out what it is. She ordered a nuclear test to see if there is any obstructions anywhere, I just wan't the pain to stop. Any advice?