Coloured X-ray showing gallstones within the gall bladder (red, pear-shaped). Gallstones, hard masses formed by bile pigments, cholesterol and calcium salts, are seen as green areas in the gall bladder. The technique used to obtain this image is known as endoscopic cholangiography. The contrast medium is injected into the common bile duct (bent tube at centre) with an endoscope which is passed via the mouth, stomach and duodenum. Gallstones that do not cause symptoms may be safely left untreated. If the symptoms are severe a cholecystectomy, the surgical removal of the gallbladder, may be carried out.