flag with a nonzero-value for a tissue point, and [`fibre_x, fibre_y, fibre_z`]{} are $x$-, $y$- and $z$-components of the fibre orientation vector at that point. To reduce the size of the [[`.bbg`]{}]{} files, only the tissue points, that is points with nonzero [`status`]{} need to be specified, because the [BeatBox]{} solver will ignore the void points with zero status in any case. Although the original DT-MRI images data sets had $128\times128\times128$ voxels size, the actual dimensions of the foetal heart minimum bounding box were $67\times91\times128$, with $181070$ tissue points.

[[[ The raw DT-MRI anatomy data [@Pervolaraki-etal-2013] were segmented into the “tissue”/“not tissue” pixels discretion based on the MRI luminosity threshold, with the cartesian fiber angles at each voxel obtained from the diffusion-weighted DT-MRI images. Only this basic segmentaion of the raw DT-MRI anatomy data [@Pervolaraki-etal-2013] was taken into account in the computer simulation of cardiac re-entry dynamics, so we shall refer to it as the raw DT-MRI based anatomy model.]{}]{}]{}

[In the 2D model, the fibres vectors were projected into the plane, in order to construct the 2D diffusivity tensor. ]{}

[[[ Fig. \[HF\_slice\_x\_63\] shows the cross section of the 143 days of gestational age (DGA) foetal heart with already 