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Title: Analyzing infant head flatness and asymmetry using directional surface normal data from a craniofacial 3D model Authors:  Lasse Holmstrom - University of Oulu (Finland) [presenting]
Ville Vuollo - University of Oulu (Finland)
Henri Aarnivala - University of Oulu (Finland)
Virpi Harila - University of Oulu (Finland)
Tuomo Heikkinen - University of Oulu (Finland)
Pertti Pirttiniemi - University of Oulu (Finland)
Arja Marita Valkama - University of Oulu (Finland)
Abstract: Human skull deformation is analyzed using the distribution of head normal vector directions computed from a 3D image. Round head shape corresponds to a uniform distribution of normal vector directions and for a symmetrical head, the distribution exhibits symmetry across the plane that divides the head into left and right halves. Severity of head flatness and asymmetry can then be quantified by suitable functionals of the kernel estimate of the normal vector direction density. The density estimates can be visualized using a 2D contour plot of an area-preserving projection of the estimate to a planar disk. The numerical integration needed in evaluating the density functionals can be performed efficiently by employing an evenly spaced Fibonacci grid on the unit sphere. Using image data from 99 infants and clinical deformation ratings made by experts, our approach is compared with some recently suggested methods. The results show that the proposed method performs competitively. We also describe a novel scale space approach to assess the statistical significance of features in a general spherical density function.