To assess diagnostic accuracy,image quality and renal safety of a double low-dose coronary CTA protocol at coronary artery evaluation in patients with diabetes by using invasive coronary angiography(ICA) as the reference method and to compare the results with those obtained traditional dose protocol. The study will randomly include about 400 consecutive participants aged 18 to 80 years old who had been diagnosed with diabetes and suspected coronary artery disease.All participants undergo ICA and coronary CT angiography performed with a whole-heart CT scan.Coronary segment interpretability,image quality based on a four-point Likert scale,blood indicators of renal function will be accessed between double low-dose CTA protocol and traditional CTA protocol. Investigators hypothesize that an individualized coronary CTA protocol that appropriately reduces radiation dose and contrast dose does not affect image quality and diagnostic accuracy, and can reduce the risk of kidney damage in high-risk patients.

The study has been approved by the local ethics committee and allparticipants will be provided written informed consent. Iodixanol 320 mg/ml is injected followed by 30 ml of saline solution.In the test group,the tube voltage,contrast agent volume and flow rate are adapted to cardiac ejection fraction(EF) and body mass index(BMI)according to the pretest. participants in the contract group are injected 50 ml contrast agent with the flow rate of 5 ml/s in tube voltage of 120 kVp. All participants are scanned in automatic tube current.

Inclusion Criteria:

• age ≥ 18 years old and ≤ 80 years old;
• patients who have previously diagnosed diabetes;
• patients with suspected coronary artery disease and undergoing coronary CT angiography (CTA);
• Subjects are fully informed and provided written informed consent.

Exclusion Criteria:

• The exclusion criteria are pregnancy and lactation women or recent birth planners
• patients with Iodine contrast agent contraindications (such as a history of severe allergy history with iodine contrast agents, hyperthyroidism, etc.)
• patients with chronic kidney disease (Phase 4-5, eGFR <30 ml/min/1.73 m2)
• patients who have undergone coronary stent implantation or coronary artery bypass surgery
• patients who have received iodine contrast-related tests within 24 hours
• participated in other clinical trials within 3 months
• other circumstances that the investigator believes are not suitable for participation in the trial

This study belongs to a diagnostic test of CT angiography . All participants use the same contrast agent. The interventions on the two groups are different in scanning protocol of CTA. The examinees and image readers are blind, and the scanning technician is unblinded.