Biomedical subjects

Tim Lüth

Publications and source records attributed to Tim Lüth.

6 recordsLinked to original sources

PubMed2006

Evaluation of a navigation system for ENT with surgical efficiency criteria.

The aim of this study is the evaluation of a navigation system (NaviBase) for ENT surgery. For this purpose, a new methodology for the evaluation of surgical and ergonomic system properties has been developed. The practicability of the evaluation instruments will be examined using the example of the overall assessment of the system in comparison with the current surgical standard and with other systems using clinical efficiency criteria. The evaluation is based on 102 ENT surgical applications; of these, 89 were functional endoscopic sinus surgeries (FESS). The evaluation of surgical and ergonomic performance factors was performed by seven ENT surgeons. To evaluate surgical system properties, the Level of Quality (LOQ) in 89 cases of the FESS was determined. It compares the existing information of the surgeon with that of the navigation system on a scale of 0 to 100 and with a mean value of 50 and places it in a relationship to the clinical impact. The intraoperative change of the planned surgical strategy (Change of Surgical Strategy) was documented. The ergonomic factors of the system with the categories of Overall Confidence (Trust), awareness of the situation (Situation Awareness), influence on the operating team, requirements for specific skills (Skill Set Requirement), and cognitive load (Workload Shift) were recorded for all surgical procedures as Level of Reliance (LOR). In the evaluation of the surgical system properties, an average evaluation of the quality of the information, as an LOQ of 63.59, resulted. Every second application of the navigation system (47.9%), on average, led to a change in the surgical strategy. An extension/enhancement of the indication of the endonasal approach through the use of the navigation system was shown in 7 of 102 (6.8%) cases. The completion of the resection in the FESS was rated by 74% of group I and 11% of group II as better in comparison with the standard approach. Total confidence shows a positive evaluation of 3.35 in the LOR. To supplement the evaluation of the navigation system, the technical parameters were included. The maximum deviation, Amax, of the displayed position of the reference value amounted to 1.93 mm. The average deviation was at 1.29 mm with an SD above all values, sd, of 0.29. The subsequent economic evaluation resulted in an effective average extra expenditure of time of 1.35 minutes per case. The overall evaluation of the system imparts application-relevant information beyond the technical details and permits comparability between different assistance systems.

Endoscopy↗

PubMed2005

Physiological shift of facial skin and its influence on the change in precision of computer-assisted surgery.

Methods of recording landmarks on the facial skin without the use of markers have become increasingly accepted in image-guided surgery. However, position or muscular activity may change the skin's geometry and generate a lack of agreement between the facial contours recorded before and those recorded during the operation. In the present study, we measured this physiological shift of facial skin and evaluated its influence on the accuracy of stereotactic recording. We made laser-scans of the skin of 20 conscious patients while they were sitting and lying, both at rest and when smiling. The laser-scans were referenced to the corresponding computed tomographic dataset, and the accuracy of the recording was calculated. Gravitational or muscular shifts of the skin reduced the mean (S.D.) accuracy of recording to 1.7 (0.3)mm. The loss of accuracy was significantly correlated with the dynamic and gravitational wrinkling of the facial skin and with the body mass index of each patient.

Adolescent↗

PubMed2004

Advanced surface-recording techniques for computer-assisted oral and maxillofacial surgery.

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.

Ear, External↗

PubMed2004

Markerless laser registration in image-guided oral and maxillofacial surgery.

PURPOSE: The use of registration markers in computer-assisted surgery is combined with high logistic costs and efforts. Markerless patient registration using laser scan surface registration techniques is a new challenging method. The present study was performed to evaluate the clinical accuracy in finding defined target points within the surgical site after markerless patient registration in image-guided oral and maxillofacial surgery. PATIENTS AND METHODS: Twenty consecutive patients with different cranial diseases were scheduled for computer-assisted surgery. Data set alignment between the surgical site and the computed tomography (CT) data set was performed by markerless laser scan surface registration of the patient's face. Intraoral rigidly attached registration markers were used as target points, which had to be detected by an infrared pointer. The Surgical Segment Navigator SSN++ has been used for all procedures. SSN++ is an investigative product based on the SSN system that had previously been developed by the presenting authors with the support of Carl Zeiss (Oberkochen, Germany). SSN++ is connected to a Polaris infrared camera (Northern Digital, Waterloo, Ontario, Canada) and to a Minolta VI 900 3D digitizer (Tokyo, Japan) for high-resolution laser scanning. RESULTS: Minimal differences in shape between the laser scan surface and the surface generated from the CT data set could be detected. Nevertheless, high-resolution laser scan of the skin surface allows for a precise patient registration (mean deviation 1.1 mm, maximum deviation 1.8 mm). CONCLUSIONS: Radiation load, logistic costs, and efforts arising from the planning of computer-assisted surgery of the head can be reduced because native (markerless) CT data sets can be used for laser scan-based surface registration.

Data Display↗

PubMed2003

Laser-scan-based navigation in cranio-maxillofacial surgery.

BACKGROUND: In computer-assisted surgery, a correlation between a volume data set and the surgical site is required in order to localize the patient's head on the operating table. Registration markers are commonly used for this procedure. However, the marker registration is associated with high logistics, since the markers have to be placed prior to data set acquisition and have to be kept in their position until the patient enters the operating room. This study deals with a new markerless registration method in cranio-maxillofacial surgery that is based on a high-resolution laser-scan of the patient's (relaxed) skin surface. PATIENTS: 20 patients with tumours, bone malformations or foreign bodies, scheduled for computer-assisted surgery, were involved in the study. STUDY DESIGN: The clinically applied accuracy of the laser-scan-based registration was measured through additionally placed registration markers. The inherent precision of the laser-scan registration system was controlled in phantom studies. RESULTS: The clinically applied accuracy of the new laser-scan-based registration technique ranged between 0.2 and 1.8 mm with a mean deviation of 1.1mm and a standard deviation of 0.3 mm. CONCLUSION: The facial skin surface can serve as a sufficiently stable and invariable reference base in order to register patients for computer-assisted cranio-maxillofacial surgery.

Algorithms↗

PubMed2003

Soft tissue scanning for patient registration in image-guided surgery.

Prior to an image-guided surgical intervention, a correlation between the patient's data set and the surgical site is required. This study introduces a markerless registration method for cranio-maxillofacial surgery that is based on a high-resolution laser scan of the patient's skin surface. The Surgical Segment Navigator SSN++ rejects contaminated surface measurements in a way similar to the bluescreen technique. Acquisition of the spatial position and the corresponding surface color of each laser-scanned point facilitates this bluescreen method, removing points with a defined surface color, e.g., blue or green points. The accuracy of the laser-scan-based registration was measured via additional intraoral titanium-markers. These markers served only to check the accuracy of the markerless registration process. In twelve patients, the stability and accuracy of the data set alignment was evaluated for high-(300,000 surface points), medium-, and low-resolution (down to 3,750 surface points) laser scanning. The accuracy of the registration technique was best for high-resolution laser scanning (mean deviation 1.1 mm; maximum deviation 1.8 mm). Low-resolution laser scans revealed inaccuracies up to 6 mm.

Face↗