[Registration using three-dimensional laser surface scanning for navigation in oral and craniomaxillofacial surgery]

Comparison of Laser versus Surface-Touch Registration for Image-Guided Sinus Surgery

Background

Use of image-guidance systems has become more popular in endoscopic sinus surgery. The laser registration technique has been used previously; however, a less expensive surface-touch registration technique recently has been developed. We compared the accuracy and speed of laser and surface-touch registration techniques.

Methods

Localization accuracy after laser and surface-touch registration was examined after 15 endoscopic sinonasal procedures between July and September 2004. Compared anatomic locations included the nasofrontal angle, nasolabial angle, posterior maxillary wall, skull base, and posterior vomer. For each localization point, the degree of error (in millimeters) was measured in superior–inferior (SI), anterior–posterior (AP), and right-left (RL) dimensions. The length of time for each registration procedure was recorded for both techniques.

Results

Laser registration was significantly faster (mean, 20 seconds) than surface-touch registration (mean, 20 seconds versus 63 seconds, respectively; p < 0.05). Laser registration was accurate within 0.3 mm in the SI direction, 0.4 mm in the AP direction, and 0.4 mm in the RL direction. Surface-touch registration was accurate within 0.3 mm in the SI direction, 0.4 mm in the AP direction, and 0.3 mm in the RL direction. There was no significant difference between techniques for any anatomic point. In 97.7% of all points, accuracy was within 2 mm or less for both the laser and surface-touch registration.

Conclusion

Surface-touch registration is significantly slower than laser registration but has virtually no difference in accuracy. Both techniques compare very favorably to the accuracy of other systems reported in the literature.

Registration strategy using occlusal splint based on augmented reality for mandibular angle oblique split osteotomy

BACKGROUND

An augmented reality tool allows for visual tracking of real anatomic structures in superposition with volume-rendered computed tomographic or magnetic resonance imaging scans and thus can be used for navigated translocation of important structures during operation. In this feasibility study, ARToolKit was used in mandibular angle oblique split osteotomy to define the cutting planes according to an operative plan.

METHODS

We overlay the operative plan on the model of a mandible made by rapid prototyping technology, and the technology was successfully used in 15 patients. Before the operation, all patients underwent computed tomographic scan, and dental casts were prepared by surgeons. Then, surgeons make the occlusal splint according to a dental cast to fix the marker, which can be recognized by the ARToolKit. The occlusal splint and marker were transformed to three-dimensional data using a laser scanner, and a programmer that runs on a personal computer named Rapidform matches the marker and the mandible image to generate the virtual image. By this step, the virtual image describing the marker, occlusal splint, and the mandible image of the patient are integrated. During the operation, the operative plan was overlaid on the rapid prototyping model of the mandible as soon as the ARToolKit recognized the marker.

RESULTS

The technology was successfully used in 15 patients; the virtual image of the mandible and the cutting-plane both overlaid the real model of the mandible.

CONCLUSIONS

This study has reported a new and effective way for mandibular angle oblique split osteotomy, and using occlusal splint might be a powerful option for the registration of augmented reality. Augmented reality tools like ARToolKit may be helpful for control of maxillary translocation in orthognathic surgery.

[Clinical efficiency and the influence of human factors on ear, nose, and throat navigation systems]

BACKGROUND

The aim of this study was to evaluate the Navibase navigation system for ear, nose, and throat (ENT) surgery. A new methodology for evaluating surgical and human factors is developed.

PATIENTS AND METHODS

The evaluation is based on 102 ENT surgical applications, including 89 cases of functional endoscopic sinus surgery (FESS). The evaluation of surgical and human factors was performed by seven ENT surgeons. To evaluate surgical performance, level of quality (LOQ) in the 89 cases of FESS was determined, comparing the surgeon's own impressions with those of the navigation system on a scale from 0 to 100 and further comparing them with clinical results. Intraoperative changes in surgical strategy were documented. The human factors of total confidence (trust), situation awareness, skill set requirement and workload shift were recorded as level of reliance (LOR).

RESULTS

The maximum deviation amounted to 1.93 mm. Averaging the quality of information resulted in an LOQ of 63.59. Every second application of the navigation system (47.9%) led to a change in surgical strategy. Total confidence showed a positive evaluation of 3.35 points in LOR.

CONCLUSION

Application-relevant information relevant to the application beyond only technical details permits comparison with other assisting systems.

Genauigkeit und Präzision in der Bewertung von chirurgischen Navigations- und Assistenzsystemen

Accuracy represents the outstanding criterion for navigation systems. Surgeons have noticed a great discrepancy between the values from the literature and system specifications on one hand, and intraoperative accuracy on the other. A unitary understanding for the term accuracy does not exist in clinical practice. Furthermore, an incorrect equality for the terms precision and accuracy can be found in the literature. On top of this, clinical accuracy differs from mechanical (technical) accuracy. From a clinical point of view, we had to deal with remarkably many different terms all describing accuracy. This study has the goals of: 1. Defining "accuracy" and related terms, 2. Differentiating between "precision" and "accuracy", 3. Deriving the term "surgical accuracy", 4. Recommending use of the the term "surgical accuracy" for a navigation system. To a great extent, definitions were applied from the International Standardisation Organisation-ISO and the norm from the Deutsches Institut für Normung e.V.-DIN (the German Institute for Standardization). For defining surgical accuracy, the terms reference value, expectation, accuracy and precision are of major interest. Surgical accuracy should indicate the maximum values for the deviation between test results and the reference value (true value) A(max), and additionally indicate precision P(surg). As a basis for measurements, a standardized technical model was used. Coordinates of the model were acquired by CT. To determine statistically and reality relevant results for head surgery, 50 measurements with an accuracy of 50, 75, 100 and 150 mm from the centre of the registration geometry are adequate. In the future, we recommend labeling the system's overall performance with the following specifications: maximum accuracy deviation A(max), precision P and information on the measurement method. This could be displayed on a seal of quality.