 The study will enroll patients who have documented coronary artery disease and an indication for coronary angiography or CT angiography. Referred patients will be assessed for eligibility through phone calls followed by in-person interviews. Patents will be provided with the informed consent forms for CTA-CTP and iodine contrast if it is determined that participants are eligible for the study. Patients have the right to refuse to participate in the study and in that case participants will receive the regular care, per clinical guidelines. Baseline information will be collected from the patients after participants consent to participate in the study. Baseline data collection will happen at the same day that the patients will undergo CTA-CTP. The CTA-CTP acquisition takes less than 60 minutes after the patient is on the CT scanner table. Patient preparation time before patient is brought on the CT scanner depends on patients heart rate and the time that takes to reduce patients heart rate to a level that is appropriate for CTA-CTP acquisition. The blood sample will be obtained from the patients at the same day as CTA-CTP acquisition. Patients will be discharged to home at the same day participants undergo CTA-CTP. 