Surgical navigation systems are used widely among all fields of modern medicine, including, but not limited to ENT- and maxillofacial surgery. As a fundamental prerequisite for image-guided surgery, intraoperative registration, which maps image to patient coordinates, has been subject to many studies and developments. While registration methods have evolved from invasive procedures like fixed stereotactic frames and implanted fiducial markers toward surface-based registration and noninvasive markers fixed to the patient's skin, even the most sophisticated registration techniques produce an imperfect result. Due to errors introduced during the registration process, the projection of navigated instruments into image data deviates up to several millimeter from the actual position, depending on the applied registration method and the distance between the instrument and the fiducial markers. We propose a method that allows to automatically and continually improve registration accuracy during intraoperative navigation after the actual registration process has been completed. The projections of navigated instruments into image data are inspected and validated by the navigation software. Errors in image-to-patient registration are identified by calculating intersections between the virtual instruments' axes and surfaces of hard bone tissue extracted from the patient's image data. The information gained from the identification of such registration errors is then used to improve registration accuracy by adding an additional pair of registration points at every location where an error has been detected. The proposed method was integrated into a surgical navigation system based on paired points registration with anatomical landmarks. Experiments were conducted, where registrations with deliberately misplaced point pairs were corrected with automatic error correction. Results showed an improvement in registration quality in all cases.

The first clinical study for use of an automatic algorithm for recognition and reduction of faulty registration of a CT, navigation was successful. The findings suggest that by using automatic intraoperative registration DRS consisting inaccuracy can be reduced. In practice this means an efficient quality improvement of the Navigation.

Image-guided surgical navigation is on the rise in many different areas of modern medicine and is already an established standard in some disciplines like ear nose and throat (ENT) or maxillofacial surgery. When evaluating surgical navigation systems the absolute accuracy of the device is of major concern to the surgeon. The following work presents two different ways of measuring the accuracy of surgical navigation systems using the example of the KARL STORZ Navigation Panel Unit (NPU). According to these protocols the FDA approval of the NPU navigation system was prepared. In a first series of experiments the accuracy under realistic surgical conditions is evaluated with a phantom of a human head, which is manufactured in rapid-prototyping processes. In another series of experiments a custom registration board is used, which provides means to evaluate the accuracy under optimal conditions and also allows further measurements regarding the registration error, that are not possible with the phantom. In the experiments an accuracy of 1.44 mm ± 0.18 mm was measured in the surgical setup and 0.63 mm ± 0.07 mm under ideal conditions.

In this article a new navigated drill system for computer assisted ear, nose and throat (ENT) surgery is presented. The navigated drill and the microscope probe are part of a surgical navigation system for ENT-surgery. In particular, the accuracy of the new navigated drill is compared to an existing navigated drill experimentally under conditions close to the surgical workflow. For the technical accuracy experiment, the new navigated drill in combination with the new microscope probe and a particular navigated measurement board have been integrated, together with the current navigated drill, in a navigation system by a special navigation software with measuring function, based on a standard ENT navigation software. The developed navigated measurement board provided the implementation of reproducible experiments and the direct accuracy comparison of the two navigated instruments under the same conditions. Thereby, N = 15 accuracy experiments are performed with both navigated drill systems with three possible tracker positions. The distance between the planned and the touched points were calculated and compared. The average distances from the planned points to the touched points with the new navigated drill is in the left tracker position 1.10 mm, in the middle tracker position 1.14 mm and in the right tracker position 1.59 mm. In comparison to the existing drill, the new navigated drill, measured with each tracker position, is 0.62 mm more accurate.