  We present an open-source software pipeline to create patient-specific left
atrial (LA) models with fibre orientations and a fibrosis map, suitable for
electrophysiology simulations. The semi-automatic pipeline takes as input a
contrast enhanced magnetic resonance angiogram, and a late gadolinium enhanced
(LGE) contrast magnetic resonance (CMR). Five operators were allocated 20 cases
each from a set of 50 CMR datasets to create a total of 100 models to evaluate
inter/intra-operator variability. Each output model consisted of (1) a labelled
surface mesh open at the pulmonary veins (PV) and mitral valve (MV), (2) fibre
orientations mapped from a diffusion tensor MRI human atlas, (3) fibrosis map
from the LGE-CMR scan, and (4) simulation of local activation time (LAT) and
phase singularity (PS) mapping. We evaluated reproducibility in our pipeline by
comparing agreement in shape of the output meshes, fibrosis distribution in the
LA body, and fibre orientations; simulations outputs were evaluated comparing
total activation times of LAT maps, mean conduction velocity (CV), and
structural similarity index measure (SSIM) of PS maps. Our workflow allows a
single model to be created in 16.72 +/- 12.25 minutes. Results in this abstract
are reported as inter/intra. Shape only differed noticeably with users'
selection of the MV and the length of the PV from the ostia to the distal end;
fibrosis agreement (0.91/0.99 ICC) and fibre orientation agreement (60.63/71.77
%) were high. LAT maps showed good agreement, the median of the absolute
difference of the total activation times was 2.02ms/1.37ms. The average of the
mean CV difference was -4.04mm/s / 2.1mm/s. PS maps showed a moderately good
agreement with SSIM of 0.648/0.608. Although we found notable differences in
the models due to user input, our tests show that operator variability was
comparable to that of image resolution or fibre estimation.
