2.4 Thickness measurement of the LA
As shown in Figure 1 , the atrial wall thickness (AWT) was defined as the minimum distance from the manually determined endocardium to the epicardial border on the LGE-MRI. Regions of interest were manually drawn in specific atrial regions and the regions of interest -based AWT was estimated in the multiplanar reconstruction images perpendicular to the LA wall. To evaluate the AWT in the lesser LGE areas associated with AF drivers, a receiver operating characteristic (ROC) curve analysis was performed for the optimal values of the AWT predicting AF drivers.