[Protocol optimization of three-dimensional spiral CT of craniofacial bones].

Purpose: To identify and optimize parameters determining the diagnostic quality of three-dimensional surface models derived from craniofacial spiral CT.

Materials And Methods: Three dry bone skull specimens were scanned with 1-slice, 4-slice, and 16-slice spiral CT. A total of 60 surface models were calculated with variation of several parameters of the CT scan and calculation of the primary data set and SSD reformations.

[Laser-based quality assurance for robot-assisted milling at the base of the skull].

Background: Implanting active hearing devices in the lateral base of the skull requires high-precision, secure fixation of the electromagnetic transducer and long-life anchorage using osteosynthetic fixation plates referred to as mountain brackets. Nonlinear distortion in the acoustic signal path and consecutive implant loosening can only be avoided by exact osseous milling to create the necessary cavity bed while avoiding excessive milling. Robot technology is ideal for high-precision milling.

Automated registration of partially defective surfaces by local landmark identification.

Objective: In computer- and robot-assisted surgery, the term "registration" refers to the definition of the geometrical relationship between the coordinate system of a surgical planning system and that of the patient. Within the context of the development of a navigation and control system for computer- and robot-assisted surgery of the lateral skull base, it was desirable to realize an algorithm for automated registration of partially defective surfaces that is reliable and suitable for use in clinical practice.

Materials And Methods: A registration algorithm based on the use of local fingerprints for specific points on a surface (so-called "spin images") was developed.

Comparison of the implantability of electronic hearing devices in a virtual reality planning environment and in human temporal bones.

Objective: To develop a procedure using a virtual reality (VR) environment that permitted us to simulate the preoperative fitting of an electronic implantable hearing device (IHD) and assess its implantability.

Material And Methods: This was an experimental, prospective study based on VR simulations involving the pre- and postoperative comparison of the implantability of an IHD. The preoperative possibility of implanting an IHD in a VR environment was compared with the postoperative implantability of the device in the temporal bones of human cadavers and patients.

The use of hybrid stereolithographic models for the planning of complex craniofacial procedures.

Preoperative planning of orthognathic surgery is usually based on plaster cast models. Those are integrated in an articulator, simulating the movement of the jaws. We present a new procedure to combine the individual jaw anatomy by stereolithographical models with dental plaster casts, which are more accurately reproducing dental and bony anatomy.

[Analysis of artefacts by virtual endoscopy visualization of spiral CT data].

Purpose: Analysis of patterns and causes of artifacts found in endographic visualization of spiral CT data.

Materials And Methods: A straight perspex tube with a diameter of 20 mm was scanned in three different positions with ten scan protocols of varying table feed, increment, kernel, and signal to noise ratio (Tomoscan AVE, Philips). The resulting 30 CT datasets were visualized as a virtual endoscopy (VE) with ten different visualization protocols (Easy Vision 4.

[Use of VR (virtual reality) software for preoperative implantation fitting with an implantable hearing aid as an example].

Purpose: To prove the feasibility of a preoperative fitting test for an implantable hearing aid using a VR environment.

Methods: A high-resolution spiral CT was performed after mastoidectomy in 10 temporal bone specimens. The bony structures were segmented and merged with the Computer-Aided Design (CAD) data of the hearing aid in a VR environment.

Computer-aided surgical planning for implantation of hearing aids based on CT data in a VR environment.

A study was undertaken to assess the feasibility of a preoperative fitting test for an implantable hearing aid in a virtual reality (VR) environment. High-resolution spiral computed tomography (CT) of the mastoid bone was performed, and the results of a mastoidectomy were simulated with manual segmentation on a standard medical workstation. CT was also performed on a temporal bone specimen obtained at real mastoidectomy, and the bone margins were segmented automatically with threshold-based techniques.