The coronary images of invasive angiography and optical coherence tomography (or Coronary CT angiography) with FFR(Fractional Flow Reserve) values of the intermediate lesions (50-70% stenosis) will be prospectively registered.

Inclusion Criteria:

1. Patients who underwent coronary CT angiography because of chest pain
2. Patients who need OCT or FFR evaluation because of intermediate lesions according to invasive angiography (diameter stenosis of 50-70%)
3. Age: 20-80 yrs
4. Patients who consent and fully understand the protocol
5. Patients who consent the clinical follow-up
6. Patients who can be followed-up

Exclusion Criteria:

1. Patients who had contrast allergy
2. Patients who had unstable blood pressure needing the vasopressors
3. Patients who had severe left ventricular function (left ventricular ejection fraction<30%)
4. Chronic kidney disease who had Cr level of greater than 2.0 mg/dl
5. Patients whose expected survival is less than 12 months
6. Patients who had a severe valvular disease

Coronary artery disease