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%.