2.2 Cardiac CT scan
All patients received a contrast-enhanced CT scan 1 to 2 days before the ablation procedure. CT examinations of the left atrium (LA), PVs, aorta, and esophagus were performed on a 256-multidetector spiral CT scanner (Revolution™, GE Healthcare, Milwaukee, USA). The intravenous contrast (Iopamidol 370, Shanghai Pharmaceuticals Sine, China) was administered with a bolus track technique at a rate of 4ml/s through an antecubital vein. The scanning parameters are listed as follows: slice thickness 0.625mm, collimation of 64 × 0.5mm, the gantry rotation time was 350ms, tube voltage 120 kV, tube current 200–500mA (Smart control). The scanning procedure was started after the CT value of the center of the LA chamber (region of interest) was higher than 150, and all the CT angiographic images were obtained in the craniocaudal direction with a covering of the heart during a single breath-hold (within 3 seconds). All data were transferred to GE Advantage Windows Workstation (AW 4.6 system) for post-image processing. A volume rendering technique was performed to obtain three-dimensions (3D) images of the LA, and all multiplanar reconstruction images were gathered. The spatial resolution in all the 3D images was 0.30mm.