Pranav Bhagirath

78 Chapter 4 According to the current standard of care, trans-esophageal echocardiography was performed within 2 days prior to the procedure to exclude LAA thrombus. Patients with persistent AF had undergone electrical cardio-version 2-4 weeks prior to the ablation procedure. In addition, a standard contrast-enhanced computed tomography (CT) examination was performed to evaluate the PV morphology in all patients. Imaging protocol The complete workflow for image acquisition and post-processing is shown in figure 1 . The CMR examination was performed on a 1.5 Tesla Achieva (Philips Medical Systems, Best, Netherlands) using a sense cardiac phased-array receiver coil (Philips Medical Systems). The imaging protocol provided information about anatomical, functional and structural parameters. Steady state free precession (SSFP) cine imaging was performed in the 4 chamber and 2 chamber orientations covering the entire LA. Subsequently 3 dimensional (3-D) magnetic resonance angiography (MRA) of the LA was performed after 0.2 mmol/kg Dotarem (Guerbet Group, Villepente, France) contrast agent injection. This was followed by acquisition of 3-D balanced SSFP (bSSFP) images in transversal orientation providing whole-heart coverage. Late gadolinium enhanced (LGE) imaging was performed 20- 25 minutes after contrast injection using a free breathing 3-D ECG-triggered, inversion recovery gradient echo pulse sequence. Typical acquisition parameters are listed in table 1 . Table 1. Typical acquisition parameters. Pulse sequence Orientation Acq. voxel size TR/TE Flip angle Nav window SSFP 4- and 2-chamber 1.2 x 1.2 x 5.0 mm 3.8/1.9 ms 60-70° - 3-D MRA Axial 0.8 x 0.8 x 1.5 mm 2.4/0.9 ms 25° - 3-D bSSFP * Axial 0.6 x 0.6 x 0.8 mm 4.5/2.3 ms 90° 5mm 3-D IR GRE * ,+ Axial 1.3 x 1.3 x 2.5 mm 4.8/2.4 ms 25° 5mm SSFP indicates steady state free precession; MRA, magnetic resonance angiography; bSSFP, balanced SSFP; IR GRE, inversion recovery gradient echo; TR, repetition time; TE, echo time; Nav, navigator. *ECG gating was used to acquire views during the diastolic phase of the LA cardiac cycle. + The TI value for the scan was identified using a scout scan and was set at an intermediate between the optimal value to null blood and myocardium.