Fig. 2

Illustration of important steps of the study on a canine cadaver head. (A) Canine cadaver head with the four pins for the registration process in place: on both sides of the zygomatic arch, paramedian over the frontal sinus and into the occipital protuberance (red circles). After the placement of the four pins a CT scan of the skull was made. (B) 3D reconstruction of a cadaver head with the four K-wire pins in position. On each tip of the pins, a marker point for the registration process was set (green dots). (C) Canine cadaver head after placement of the patient tracker with the three reflective spheres paramedian over the frontal sinus (yellow ellipse). The two pins on both sides of the zygomatic arch are also visible (red circles). The patient tracker and the four pins were needed for the registration process of the skull. Thereby, the real operation situs was matched with the preoperative CT images of the skull