Gall stone treatment?

I had pain in upper abdomen, After Ultrasound I came to know I have sludge in gall bladder, though they have not seen any stone. I had developed that during my pregnancy, Doctor said it will improve with time. Its been six months now I delivered my baby but I still suffer with pain ( attack) at least once a month. If I go for surgery then do I expect to remove gall bladder or is there any way to remove sludge only?