 Neointimal coverage over stent strut is important for preventing the stent thrombosis. But, there is no data for the duration of complete formation of neointima om zotarolimus eluting stent ZES. Previously the investigational observational data at 9 months showed most of stent strut was covered with neointima. Therefore, the investigators investigated the evaluation of neointimal coverage on 3 months after ZES implantation using novel OCT system, which is powerful intravascular imaging system having the higher resolution power. 