How to skin a scatter plot

Introduction: First Trimester Screening regards to an ultrasound measurement of the nuchal translucency (NT), and valuation of free ß-hCG and PAPP-A. Latest studies suggest to plot these values into a three dimensional scatter diagram. This method was called AFS–3D. Typically, the plots of fetuses with the same chromosomal disorders are found close to each other. In this study a new algorithm was developed to compute a hull around the scatter plots of a given karyotype.

Methods: A scatter plot was created accorting to NT, PAPP-A and fß-hCG. Based on this, the following volume operations were performed: creating voxels, filling gaps, stalked voxel removing, erasing subordinate voxelcluster, smoothing, foamshaping, vertex detection, computing outlines, checking outline direction, creating triangle strips, and computing normal vectors and average normal vectors. The triangle list can finally be rendered with Phong shading as a three dimensional computer graphic, which can interactively be rotated.

Discussion: This algorithm is like laying a skin around a given cloud of points. The resulting polygon depends on the density of the scatter plot, the width of the voxels and the choice of the cut off. The size of the sphere at foamshaping also affects the smoothness of the hull.

The algorithm is so constructed that differentest shapes can automatically be created. Anyhow, the result will not be satisfying if the voxels are too small at too few scatter plots. In this case it is more efficient to render just a fewer number of voxels, which then become larger. This however results in chiseled polygones. Further development could increase the number of vertices, e.g. by Beziér-curves or splines.

AFS-3D - PAPP-A - Scatter plot - fß-hCG - nuchal translucency