Validation of Catalyst HD™ positioning performance using a deformable phantom

Abstract: Aim: The overall purpose for this master thesis was to evaluate the deformable algorithm of the optical surface scanning system Catalyst HDTM . The aim was to develop a method to evaluate the non-rigid registration algorithm using a deformable phantom and with it investigate the positioning accuracy of the depth calculation. Materials and Methods: As deformable phantom a modified breast implant was used. The silicone breast implant was modified by implanting six gold seeds as radio graphic markers as well as painting the surface in a skin toned colour for reflective purposes. The deformation was achieved by tilting the phantom in pitch direction using 3D-printed stands and wedges. The developed method was to compare the measured isocentric shift from the Catalyst HDTM -system with the true isocentric shift given from acquired high res- olution CT images. The measured isocentric shift was based on a match between a reference surface of the original state, with a live surface of the deformed state. The true isocentric shift was computed in the graphical user interface MICE Toolkit where the CT images of the deformed state was registered with the original state. The absolute difference between the measured- and true isocentric shift was evalu- ated against the level of deformity of the phantom. Results: For deformations less than 0.5 mm, related from clinically relevant pitch rotations of less than 10◦, the positioning accuracy of the deformable algorithm of Catalyst HD TM was found to be within 1.7 mm. For larger deformations of 1.5 mm, related to the clinically unrealistic pitch rotation of 19◦, the positioning accuracy was found to be within 3.1 mm. Conclusions: The positioning accuracy of the optical surface scanning system’s deformable depth calculation were within 2 mm for various levels of clinically rele- vant deformities.