The purpose of this study is to compare clinical outcomes between quantitative coronary angiography -guided and Intravascular ultrasound -guided strategy in patients with significant coronary artery disease undergoing sirolimus-eluting Orsiro/Orsiro mission stent implantation.

Inclusion Criteria:

1. Men or women at least 19years of age
2. Typical chest pain or objective evidence of myocardial ischemia suitable for elective PCI
3. Significant coronary artery lesions suitable for sirolimus-eluting Orsiro/Orsiro mission stent implantation
4. The patient or guardian agrees to the study protocol and the schedule of clinical follow-up, and provides informed, written consent, as approved by the appropriate Institutional Review Board/Ethical Committee of the respective clinical site.

Exclusion Criteria:

1. Angiographic exclusion criteria: any of the followings 1)Bypass graft lesions 2)Impaired delivery of IVUS is expected:

   • Extreme angulation (≥90°) proximal to or within the target lesion.
   • Excessive tortuosity (≥ two 45° angles) proximal to or within the target lesion.
   • Heavy calcification proximal to or within the target lesion.

2. Previous percutaneous coronary intervention within 6 months before the index procedure

3. Previous BVS (bioresorbable vascular scaffold) implantation

4. Left ventricular ejection fraction (LVEF) < 30%

5. Hypersensitivity or contraindication to device material and its degradants and cobalt, chromium, nickel, platinum, tungsten, acrylic and fluoro polymers that cannot be adequately pre-medicated.

6. Persistent thrombocytopenia (platelet count <100,000/µl)

7. Any history of hemorrhagic stroke or intracranial hemorrhage, Transient ischemic attack or ischemic stroke within the past 6 months

8. A known intolerance to antiplatelet agents (aspirin, clopidogrel, prasugrel or ticagrelor)

9. Any surgery requiring general anesthesia or discontinuation of aspirin and/or an ADP antagonist is planned within 12 months after the procedure.

10. A diagnosis of cancer (other than superficial squamous or basal cell skin cancer) in the past 3 years or current treatment for the active cancer.

11. Any clinically significant abnormality identified at the screening visit, physical examination, laboratory tests, or electrocardiogram which, in the judgment of the Investigator, would preclude safe completion of the study.

12. Hepatic disease or biliary tract obstruction, or significant hepatic enzyme elevation (ALT or AST > 3 times upper limit of normal).

13. Life expectancy < 1 years for any non-cardiac or cardiac causes

14. Unwillingness or inability to comply with the procedures described in this protocol.

15. Patient's pregnant or breast-feeding or child-bearing potential.