“…Arterial embolization for hepatocellular carcinoma has been originally proposed by Yamada et al [1]. For this therapy, various kinds of obstructing materials, such as gelatin sponge, acrylic polymer matrices impregnated and embedded with porcine gelatin, PVA spheres, porous gelatin spheres, starch microspheres, chitosan microspheres have been developed [2][3][4][5]. Since these materials themselves do not absorb X-ray strongly, contrast media such as Lipiodol have been injected together with the materials to identify the extent of the obstructing region.…”