Abstract
Cranial deformation and deformational plagiocephaly (DP) in particular affect an important percentage of infants. The assessment and diagnosis of the deformation are commonly carried by manual measurements that provide low interuser accuracy. Another approach is the use of three-dimensional (3D) models. Nevertheless, in most cases, deformation measurements are carried out manually on the 3D model. It is necessary to develop methodologies for the detection of DP that are automatic, accurate and take profit on the high quantity of information of the 3D models. Spherical harmonics are proposed as a new methodology to identify DP from head 3D models. The ideal fitted ellipsoid for each head is computed and the orthogonal distances between head and ellipsoid are obtained. Finally, the distances are modelled using spherical harmonics. Spherical harmonic coefficients of degree 2 and order − 2 are identified as the correct ones to represent the asymmetry characteristic of DP. The obtained coefficient is compared to other anthropometric deformation indexes, such as Asymmetry Index, Oblique Cranial Length Ratio, Posterior Asymmetry Index and Anterior Asymmetry Index. The coefficient of degree 2 and order − 2 with a maximum degree of 4 is found to provide better results than the commonly computed anthropometric indexes in the detection of DP.
Highlights
Cranial deformation and deformational plagiocephaly (DP) in particular affect an important percentage of infants
With the presented approach given in Eq (1), all cranial 3D models could be reconstructed with a small error with only small maximum spherical harmonic degrees
In order to be able to compare the different parameters, the spherical harmonic coefficients of each 3D model have been multiplied 10 times (10x) and the Oblique Cranial Length Ratio (OCLR) has been normalized so a normal head would have an index of zero, yielding the new index OCLR-100. (Fig. 5)
Summary
Cranial deformation and deformational plagiocephaly (DP) in particular affect an important percentage of infants. The assessment and diagnosis of the deformation are commonly carried by manual measurements that provide low interuser accuracy. Another approach is the use of threedimensional (3D) models. Deformational Plagiocephaly (DP) is a deformation of the infant’s skull due to positional causes It consists of a flattening of an area of the head, resulting in a symmetry[1]. The use of 3D models to evaluate cranial deformation is becoming more common. Due to their high cost, they are not widely implemented in clinical practice
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