According to CT technology development, cardiac CT is very useful examination as noninvasive examination and the accuracy in locating lesions has increased to 95%. Specifically, cardiac CT has been performing a gateway role in reducing invasive cardiac angiography implemented solely for the purpose of diagnosis because of the invasive testing of makeshift cardiac angiography. However, cardiac CT also comes with the disadvantage that patients cannot avoid being exposed to radiation, so there has been much effort in appealing to reduce exposed radiation dose. Of these methods, the most effective is the method of repeatedly reconstitution by way of synchronized prospective ECG while using low tube-based potential. According to recent studies, the SNR(Signal Noise Ratio) and CNR(Contrast Noise Ratio) values representing image quality have been higher compared to the combined method of image reconstruction by makeshift filtered back projection and condition of image acquisition by patient BMI. Also, the administered amount of contrast agent can be reduced for achieving the same contrast effect due to the advantage of the increased effect of contrast enhancement by using low tube voltage. Therefore, the efficacy studies of using low concentration of contrast agents in conditions of using low tube voltage are being processed.

This study intends to prove that image quality does not deteriorate by suitable image reconstruction method with low concentration contrast agent compared to the combined method of the makeshift filtered back projection image reconstruction method and the conditions of image acquisition according to BMI with general amount of contrast agent.

Inclusion Criteria:

• Adults at least 20 years old
• Subject who had requested a coronary CT angiography as per a clinical disease

Exclusion Criteria:

• Subject suspected as having myocardial infarction, unstable angina pectoris, coronary artery disease
• Subject with heart attack within 40 days prior to the CT scan
• Subject with diagnosed complicated heart anomaly
• BMI (body mass index) > 35kg/m2
• Serum creatinine ≥1.5mg/dl of renal insufficiency
• Subject with pregnancy or unknown pregnancy
• Subject with history of hypersensitivity reaction of contrast agents
• Subject has contraindication of using nitroglycerine
• Subject has plan to participate or enrolled in other randomized clinical trial for cardiovascular disease.
• Subject has contraindication of using adenosine (e.g. bronchial asthma, 2-3 degree AV block, sick sinus syndrome, SBP (systolic blood pressure) less than 90mmHg, recent prescribed history of dipyridamole, hypersensitivity of adenosine)