  Ventricular coordinates are widely used as a versatile tool for various
applications that benefit from a description of local position within the
heart. However, the practical usefulness of ventricular coordinates is
determined by their ability to meet application-specific requirements. For
regression-based estimation of biventricular position, for example, a
consistent definition of coordinate directions in both ventricles is important.
For the transfer of data between different hearts as another use case, the
coordinate values are required to be consistent across different geometries.
Existing ventricular coordinate systems do not meet these requirements. We
first compare different approaches to compute coordinates and then present
Cobiveco, a consistent and intuitive biventricular coordinate system to
overcome these drawbacks. A novel one-way mapping error is introduced to assess
the consistency of the coordinates. Evaluation of mapping and linearity errors
on 36 patient geometries showed a more than 4-fold improvement compared to a
state-of-the-art method. Finally, we show two application examples underlining
the relevance for cardiac data processing. Cobiveco MATLAB code is available
under a permissive open-source license.
