Generation of combined-modality tetrahedral meshes

Registering and combining anatomical components from different image modalities, like MRI and CT that have different tissue contrast, could result in patient-specific models that more closely represent anatomical structures than a model based on either modality alone. In this study, we combined a pair of CT and MRI scans of a pig thorax from two different subjects to make a tetrahedral mesh. Registration of the images is a challenging step in any multimodal imaging and we compared four different registration techniques including rigid, affine, thin plate spline morphing (TPSM), and iterative closest point (ICP), to superimpose the segmented bones from the CT scan on the soft tissues segmented from the MRI. We achieved best visual results with TPSM and affine techniques, which both resulted in the bones remaining close to, but not overlapping, important soft tissue. We also compared simulated results from computing ECGs and defibrillation potentials based on the original MRI model and combined geometric models of the torso. Both qualitatively and quantitatively, the combined geometric models performed similarly to the original MRI model.