2.3 3D visualization and assessment of the tissue properties
The 3D visualization method for the LGE was as follows. First, the LA in LGE-MRI was segmented semi-manually by contouring the endocardial and epicardial borders of the atrium, including the PVs, while referring 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 hyperenhanced areas in LGE-MRA were involved. Third, a voxel intensity histogram analysis of the LA wall identified the LGEs as intensities >1SD on the “healthy” LA wall. Furthermore, the degree of intensity was categorized by a color-coded scaling (green: >1SD: yellow: 2–3SD; red: >3SD). Finally, a 3D reconstruction, color-coded LGE, and volume-rendered LA and PV image generated from the CE-MRA were fused semi-automatically. In this study, atrial fibrosis was defined as an LGE site with a signal intensity of >1SD. To evaluate the fibrotic tissue property, the fibrotic heterogeneity was defined as the value of the entropy (LGE-entropy) according to the Shannon formula: