Examination methods
All patients were fasted for more than 4 h before examination, and they were given an intravenous indwelling needle. Electrocardiogram leads were connected to measure their heart rate, and breath holding training was performed. Those with a faster heart rate were given β-receptor blockers to stabilize the patient’s heart rate (ensuring that the patient’s heart rate was stabilized within 74 beats/min).All patients were scanned with a 320-slice computed tomography (CT) machine (Toshiba Aquiline ONE), and the data were post-processed. The examinee was in a supine position, and their feet entered the machine first. Both arms were stretched straight and placed over their head. Three leads were applied to the bilateral subclavian sites and left rib lower margin, respectively, and the leads were connected with a machine to monitor real-time heart rate changes. Scanning was performed with the last breath of a single inhalation The scanning range was determined according to the anteroposterior and lateral view, from the lower part of the tracheal bifurcation to the diaphragm. The range covered the whole heart, which was 140–160 mm. A Mallinckrodt double-chamber high-pressure syringe was used to inject 60–65 ml of the non-ionic contrast agent iohexol at an injection rate of 4.5–5.0 ml/s. The volume and flow rate were adjusted according to the patient’s weight and vascular conditions. Then, 40 ml of normal saline was injected at the same rate. Monitoring started after 10 s of contrast agent injection. Observing the time–density curve, the left ventricle was chosen as the monitoring area. It was triggered manually, with a trigger threshold of 150 HU. Scanning parameters: The tube voltage was 120 kV, the scanning slice thickness and gap were both 0.5 mm, and the rotation speed was 0.35 s. All CT scans were performed in automatic regulation mode of the tube current during the cardiac cycle to reduce radiation dosages.