The markerless laser scan registration of the surgical site may achieve the same accuracy as a patient registration made by rigidly fixed titanium screws (mean accuracy: 1.2 mm) as long as a high-resolution laser scan is being used.
For many applications in diagnostics and in the planning of surgical interventions, specific structures have to be identified in a patient's volume data set. In this article we give an outline of how the detection of thin tubular structures (e.g., nerves and vessels) can be automated, requiring very little initialization from a human expert. We focused on the nervus alveolaris inferior in the lower jaw and were looking at three details: data acquisition, detection, and validation of accuracy. Our method can be easily adapted to many similar cases such as other nerves, arteries, and veins or bundles thereof.
Markerless recording of patients based on natural anatomical surfaces makes planning of computer-assisted surgery much easier, as it is not necessary to place and measure markers. Recording of the surgical site with a laser scan takes the place of conventional marker-based recording. We have used auricles as well as the maxilla and mandible as reproducible surfaces. The geometric congruence of the laser scanned surface with the corresponding surface in the computed tomographs data-set and the applied intraoperative accuracy after recording with a laser scanner have been evaluated, and the system was successful in the maxilla (mean precision: 0.8mm, standard deviation: 0.3mm). In the mandible, the tongue and mobile floor of the mouth led to geometric incongruence and inadequate laser scanning. An exact recording using auricles was possible only as long as the auricles had not been temporarily deformed by the head support during CT imaging.
This paper presents telemedicine as an extension of a teleradiology framework through tools for virtual surgery. To classify the described methods and applications, the research field of virtual reality (VR) is broadly reviewed. Differences with respect to technical equipment, methodological requirements and areas of application are pointed out. Desktop VR, augmented reality, and virtual reality are differentiated and discussed in some typical contexts of diagnostic support, surgical planning, therapeutic procedures, simulation and training. Visualization techniques are compared as a prerequisite for virtual reality and assigned to distinct levels of immersion. The advantage of a hybrid visualization kernel is emphasized with respect to the desktop VR applications that are subsequently shown. Moreover, software design aspects are considered by outlining functional openness in the architecture of the host system. Here, a teleradiology workstation was extended by dedicated tools for surgical planning through a plug-in mechanism. Examples of recent areas of application are introduced such as liver tumor resection planning, diagnostic support in heart surgery, and craniofacial surgery planning. In the future, surgical planning systems will become more important. They will benefit from improvements in image acquisition and communication, new image processing approaches, and techniques for data presentation. This will facilitate preoperative planning and intraoperative applications.
The authors' experiences with intraoperative computer assisted guidance in interventions in oromaxillofacial and craniofacial surgery are reported. The guidance system SPOCS (Surgical Planning and Orientation Computer Systems, Aesculap, Germany) consists of an infrared light emitting system of diodes and camera, an imaging workstation and assorted freehand instruments. The software is an updated version of the well-known Viewing Wand software (ISG Technologies, Canada). In tests on phantoms, the system proved a mean accuracy of less than 1.5 mm. Within the last 15 clinical tests, the system has achieved an accuracy better than 3 mm which, at the moment, the authors estimate to be sufficient to proceed with its clinical evaluation. Using bone screws to register the patient's position, an accuracy in the range of less than 2 mm in relation to bony reference points has been achieved. By visualizing the tip of the instrument in real time, this technique allows surgical interventions, even in anatomically complicated situations, without endangering vital neighbouring structures. The 'offset' function of the software, by which the surgeon can elongate the tip of the instrument virtually, allows the surgeon to analyse structures before they are penetrated by the instrument as in a 'look ahead' operation. The authors expect computer assisted simulation and guidance systems to improve surgical quality and reduce the risks associated with surgical interventions.
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