Automated patient tracking for 3D-navigation with ultrasound

Surgical 3D-navigation assists the surgeon in locating the resected anatomy with millimetric accuracy. It contributes to the safety of the intervention and is an established standard of treatment in functional endoscopic sinus surgery (FESS). The manual selection of paired points on the patient and in the volumetric data is the main source of errors by registration. The procedure is made less prone to human errors through the application of the iterative closest point (ICP) algorithm for surface registration of the occipital bone, palpated intraoperatively with A-mode ultrasound, to the preoperative CT-image. Two stepper motors position the ultrasound sensor posterior to the patient’s head with sub-millimetric accuracy. The transit-time of the echoes from bone is measured to calculate the surface points on skull. The quality of the surface matching is evaluated through a color map of the closest-point distances, as well as by the mean distance and the standard deviation.