The authors introduce the Hybrid Volumetric Ventriculoid (HVV), a model for quantitatively analysing 3-D Left Ventricular (LV) geometry and motion from tagged MR (SPAMM) images. It is the first model (in parallel with Park et al., 1995) which is both hybrid and volumetric. It is hybrid in that it is comprised of a global (parametric) component and a local (explicit) component which form a composite model capable of resembling an LV with arbitrary precision. Among other advantages, this formulation allows the model to provide a concise description of the LV's gross shape for comparison with a "normal" population while at the same time being detailed enough to recover local material measures (i.e., strain). Since the HVV is volumetric it may be deformed directly from myocardial MR tag intersection displacements without prior processing. Deformation is cast as an energy minimization in which lower energies imply a better fit. The authors' paradigm extends the state of the art myocardial motion recovery to directly include myocardial contour information. This improves the overall model fit by helping to overcome the inherent sparsity of MR-tag data. the authors apply an HVV to volunteer multi-slice, multi-phase SPAMM data sets taken from orthogonal views and report LV strain, as well as motion parameters quantifying myocardial thickening.
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