2.2 MRI acquisition
Before the AF ablation, LGE-MRI was performed in all patients using a 1.5T MR system (Achieva; Philips Medical, Best, The Netherlands) equipped with a 5-channel cardiac coil. This scan technique has been previously reported.9 First, contrast-enhancement magnetic resonance angiography (CE-MRA) of the pulmonary vein (PV) - left atrial (LA) anatomy was obtained in the coronal plane using a breath-hold three-dimensional (3D) fast field echo sequence after the injection of 0.1 mmol/kg of a contrast agent (Gadobutrol, Gadovist, Bayer Yakuhin, Osaka, Japan).10 The purpose of the scanning in the coronal plane was to reduce the number of acquisition slices and shorten the breath-hold time. Next, 15 minutes after the contrast injection, LGE-MRI of the LA including the PVs was performed using a lateral 3D inversion recovery, respiratory navigation, ECG gating, and T1-fast field echo sequence.11 The CE-MRA and LGE-MRI images were transferred to customized software (MRI LADE Analysis; PixSpace Inc, Fukuoka, Japan) for image post-processing and an image analysis.