2.3 3D Visualization and assessment of the tissue properties
To detect lesser LGE areas more sensitively, we used the same protocol as in our previous study.12 The 3D visualization method for the LGE was as follows. First, the LA in the LGE-MRI was semi-manually segmented by contouring the borders between the endocardium and epicardium of the atrium, including the PVs, with reference to the CE-MRA. Second, the mean value and standard deviation (SD) of the voxel intensity was measured on the “healthy” LA wall where no hyper-enhanced areas in LGE-MRA were involved. Third, we identified LGEs with an intensity of >1SD on the ”healthy” LA wall by a voxel intensity histogram analysis of the LA wall. Furthermore, the degree of the intensity was categorized by a color-coded scaling (green: >1SD: yellow: 2–3SD; red: >3SD). Finally, the 3D reconstruction, color-coded LGE, and volume-rendered LA and PV image generated from the CE-MRA were semi-automatically fused. In this study, atrial fibrosis was defined as an LGE site with a signal intensity of >1SD. To evaluate the fibrotic tissue properties, the fibrotic density was measured as the LGE-volume. The fibrotic density was defined as the volume ratio of an LGE signal intensity > 1SD (LGE-volume ratio). The details of the measurement can be found in the previous publication.7 In this study, the areas with an LGE-volume ratio of < 10% were defined as lesser LGE areas, and heterogenous LGE areas were defined as areas with an LGE-volume ratio of > 10%.