2.2 MRI acquisition
All patients underwent contrast-enhanced MRI using a 1.5-T MR system (Achieva; Philips Medical, Best, The Netherlands) equipped with a 5-channel cardiac coil before the AF ablation. This scan technique has been previously reported.5 First, contrast-enhancement magnetic resonance angiography (CE-MRA) of the pulmonary vein (PV) - left atrium (LA) anatomy was acquired with a breath-hold three-dimensional (3D) fast field echo (FFE) sequence in the coronal plane during the first pass of a contrast agent (gadobutrol, Gadovist; Bayer Yakuhin, Osaka, Japan) injection at a dose of 0.1 mmol/kg.6
The purpose of the scanning in the coronal plane was to reduce the number of acquisition slices and shorten the breath-hold time. Then the LGE-MRI of the LA with the PVs was acquired using a 3D inversion recovery, respiration navigated, electrocardiogram-gated, T1-FFE sequence in the transverse plane 15 minutes after the contrast injection.7 The typical parameters were as follows: repetition time/ echo time = 4.7/1.5 ms, voxel size = 1.43 × 1.43 × 2.40 mm (reconstructed to 0.63 × 0.63 × 1.20 mm), flip angle = 15°, SENSE factor = 1.8, and 80 reference lines. The inversion time was set at 280 to 320 ms, using a Look-Locker scan. The data acquisition was performed during the mid-diastolic phase of the left ventricle. The typical scan time for the LGE-MRI study was 7 to 12 minutes depending on the patient’s heart rate and respiration pattern. The images of the CE-MRA, and LGE-MRI were transferred to customized software (MRI LADE Analysis; PixSpace Inc, Fukuoka, Japan) for a further image post processing and image analysis.