Geometric modelling of the human torso using cubic Hermite elements

Abstract

We discuss the advantages and problems associated with fitting geometric data of the human torso obtained from magnetic resonance imaging, with high order (bicubic Hermite) surface elements. These elements preserve derivative (C 1 ) continuity across element boundaries and permit smooth anatomically accurate surfaces to be obtained with relatively few elements. These elements are fitted to the data with a new non-linear fitting procedure that minimises the error in the fit whilst maintaining C 1 continuity with non-linear constraints. Non-linear Sobelov smoothing is also incorporated into this fitting scheme. The structures fitted along with their corresponding Root Mean Squared (RMS) error, number of elements used and number of degrees-of-freedom (dof) per variable are: epicardium (0.91 mm, 40 elements, 142 dof), left lung (1.66 mm, 80 elements, 309 dof), right lung (1.69 mm, 80 elements, 309 dof), skeletal muscle surface (1.67 mm, 264 elements, 1010 dof), fat layer (1.79 mm, 264 e..