Accuracy assessment for navigated maxillo-facial surgery using an electromagnetic tracking device.

PURPOSE: To evaluate the accuracy and the usability of an electromagnetic tracking device in maxillo-facial surgery through testing on a phantom skull under operating room (OR) conditions. MATERIAL AND METHODS: A standard plastic skull phantom was equipped with a custom made model of the maxilla and with target markers and dental brackets. Imaging was performed with a computed tomography (CT) scanner. The extent and robustness of the electromagnetic tracking system's target registration error (TRE) was evaluated under various conditions. RESULTS: For each measurement a total of 243 registrations were performed with 5 point registration and 4374 registrations with 6 point registration. The average target registration error for the 5 point registration under OR conditions was 2.1 mm (SD 0.86) and 1.03 (SD 0.53) for the 6 point registration. Metallic instruments applied to the skull increased the TRE significantly in both registration methods. CONCLUSION: The electromagnetic tracking device showed a high accuracy and performed stable in both registration methods. Electromagnetic interference due to metallic instruments was significant but the extent of TRE was still acceptable in comparison to optical navigation devices. A benefit of EM tracking is the absence of line-of-sight hindrance. The test setting simulating OR conditions has proven suitable for further studies.

Comparative study of application accuracy of two frameless neuronavigation systems: experimental error assessment quantifying registration methods and clinically influencing factors.

This study aimed at comparing the accuracy of two commercial neuronavigation systems. Error assessment and quantification of clinical factors and surface registration, often resulting in decreased accuracy, were intended. Active (Stryker Navigation) and passive (VectorVision Sky, BrainLAB) neuronavigation systems were tested with an anthropomorphic phantom with a deformable layer, simulating skin and soft tissue. True coordinates measured by computer numerical control were compared with coordinates on image data and during navigation, to calculate software and system accuracy respectively. Comparison of image and navigation coordinates was used to evaluate navigation accuracy. Both systems achieved an overall accuracy of <1.5 mm. Stryker achieved better software accuracy, whereas BrainLAB better system and navigation accuracy. Factors with conspicuous influence (P<0.01) were imaging, instrument replacement, sterile cover drape and geometry of instruments. Precision data indicated by the systems did not reflect measured accuracy in general. Surface matching resulted in no improvement of accuracy, confirming former studies. Laser registration showed no differences compared to conventional pointers. Differences between the two systems were limited. Surface registration may improve inaccurate point-based registrations but does not in general affect overall accuracy. Accuracy feedback by the systems does not always match with true target accuracy and requires critical evaluation from the surgeon.

Accuracy of template-based dental implant placement.

PURPOSE: The accuracy of a system for image-guided dental implant planning and placement based on individually fabricated oral templates was investigated in a phantom study. MATERIALS AND METHODS: The study was performed on identical phantoms of a partially edentulous mandible. In one phantom mandible (the master model), pilot boreholes for dental implants were placed. Computerized tomography image data were then acquired. Using a system for template-based dental implant placement, identical boreholes were planned on the image data and then reproduced in the 10 remaining phantom mandibles (the "slave" models). The resulting positions were compared to the positions in the master model using a three-dimensional digitizer arm. RESULTS: The mean deviation of borehole apex positions in the slave phantoms, as compared to the master phantom, was 0.50+/-0.04 mm and was below 1 mm in 29 of 30 models. The accuracy was highly reproducible, irrespective of the template used and the surgeon involved. CONCLUSIONS: The use of templates for image-guided insertion of dental implants is a method with high and reproducible accuracy.

Clinical use of navigation based on cone-beam computer tomography in maxillofacial surgery.

Image-guidance in maxillofacial surgery is based predominantly on computed tomographic (CT) images. Its main disadvantage is the considerable amount of radiation to which the patient is exposed, and dental metal artefacts. Recently, a new class of devices based on the concept of cone-beam computed tomography (CBCT) has been introduced for maxillofacial imaging, which we have investigated. In a clinical study, the first seven patients to be operated using a navigation system based on CBCT images, were evaluated. In all cases patient to image recording was uneventful and the surgical objective was reached. The guidance given by the navigation system was helpful. CBCT is an alternative to conventional CT, gives a lower dose of radiation, and costs less. Limitations in the quality of the images and the size of the field of view may restrict its use. It is suitable for image-guided surgery using a navigation system as long as the images show enough of the relevant anatomy and pathology.

Orthodontic archwire in the nasal cavity. A case report.

We present the unusual case of a patient who lost an orthodontic archwire after having, via manipulation, detached it from the brackets. It was only on a routine radiograph at the end of treatment that the archwire was found in the patient's nasal cavity, where it had failed to cause any symptoms! We discuss the treatment following the inhalation and ingestion of foreign bodies in orthodontics, as well as their prevention.

The accuracy of image guided surgery based on cone beam computer tomography image data.

OBJECTIVE: The objective of this study was to verify if accurate patient-to-image registration for precision navigation in maxillofacial surgery is possible based on cone beam computed tomography (CBCT) image data. STUDY DESIGN: A maxillary registration template was placed on a standard plastic skull phantom that was equipped with a custom made model of the maxilla and with target markers. Imaging was performed with a CBCT device (Newtom 9000 Digital Volume Tomograph (DVT), QR s.r.l., Verona, Italy) and a computed tomography (CT) scanner (Somatom 4, Siemens, Forchheim, Germany). Using an infrared navigation system (Polaris, NDI, Waterloo, Ontario), multiple pair-point registration of both image data sets and the phantom were performed. The target registration error (TRE) was evaluated. RESULTS: A total of 243 registrations were performed for either image data set. The spatial distribution of TRE on the skull showed increasing inaccuracy with growing distance from the registration markers. The average target registration error was 1.50 +/- 0.82 mm with CBCT and 1.57 +/- 0.84 mm with CT image data and did not differ significantly. Error distribution correlated strongly between CT- and CBCT-based registration. CONCLUSIONS: The overall registration accuracy based on CBCT image data was similar to CT. The strong correlation of the geometric distribution of TRE between CT- and CBCT-based measurements proves that CBCT can be equivalent to CT in image-guided maxillofacial surgery.

System design of a hand-held mobile robot for craniotomy.

This contribution reports the development and initial testing of a Mobile Robot System for Surgical Craniotomy, the Craniostar. A kinematic system based on a unicycle robot is analysed to provide local positioning through two spiked wheels gripping directly onto a patients skull. A control system based on a shared control system between both the Surgeon and Robot is employed in a hand-held design that is tested initially on plastic phantom and swine skulls. Results indicate that the system has substantially lower risk than present robotically assisted craniotomies, and despite being a hand-held mobile robot, the Craniostar is still capable of sub-millimetre accuracy in tracking along a trajectory and thus achieving an accurate transfer of pre-surgical plan to the operating room procedure, without the large impact of current medical robots based on modified industrial robots.

Projector-based augmented reality for intuitive intraoperative guidance in image-guided 3D interstitial brachytherapy.

PURPOSE: The aim of this study is to implement augmented reality in real-time image-guided interstitial brachytherapy to allow an intuitive real-time intraoperative orientation. METHODS AND MATERIALS: The developed system consists of a common video projector, two high-resolution charge coupled device cameras, and an off-the-shelf notebook. The projector was used as a scanning device by projecting coded-light patterns to register the patient and superimpose the operating field with planning data and additional information in arbitrary colors. Subsequent movements of the nonfixed patient were detected by means of stereoscopically tracking passive markers attached to the patient. RESULTS: In a first clinical study, we evaluated the whole process chain from image acquisition to data projection and determined overall accuracy with 10 patients undergoing implantation. The described method enabled the surgeon to visualize planning data on top of any preoperatively segmented and triangulated surface (skin) with direct line of sight during the operation. Furthermore, the tracking system allowed dynamic adjustment of the data to the patient's current position and therefore eliminated the need for rigid fixation. Because of soft-part displacement, we obtained an average deviation of 1.1 mm by moving the patient, whereas changing the projector's position resulted in an average deviation of 0.9 mm. Mean deviation of all needles of an implant was 1.4 mm (range, 0.3-2.7 mm). CONCLUSIONS: The developed low-cost augmented-reality system proved to be accurate and feasible in interstitial brachytherapy. The system meets clinical demands and enables intuitive real-time intraoperative orientation and monitoring of needle implantation.

Template-based registration for image-guided skull base surgery.

OBJECTIVES: To evaluate whether patient-to-image registration with the use of a maxillary template is sufficiently accurate for image guided skull base surgery. STUDY DESIGN AND SETTING: In an experimental phantom study, pair-point registration of a skull phantom to its CT image data was performed with 243 different configurations of a maxillary template with markers. Then artificial skull mounted target markers were located with an infrared tracking device as used in navigation systems. RESULTS: The average target registration error was 1.57 mm in the anterior skull base (95% confidence interval, 1.53 to 1.61 mm), but 3.31 mm in the lateral skull base (95% confidence interval, 3.26 to 3.37 mm). CONCLUSIONS: Fiducial marker registration based on a maxillary template is sufficiently accurate for image-guided surgery in the anterior skull base, but not for the lateral skull base. SIGNIFICANCE: Template-based registration is an accurate yet noninvasive registration method for frontal skull base surgery.

Inverted papilloma of paranasal sinuses.

INTRODUCTION: Inverted papilloma (Schneiderian papilloma) is a primarily benign lesion that occurs in the nasal cavity and paranasal sinuses. Clinical problems include a tendency towards local destruction, recurrence and malignant transformation into squamous cell carcinoma. Hence, complete surgical removal is the therapy of choice and a meticulous follow-up is mandatory. STUDY DESIGN: This is a review including a short introduction to the different histological types of nasal papilloma, their pathogenesis and the clinical and histopathological diagnosis. Staging systems, therapeutic approaches, and surgical concepts are discussed. RESULT: The detection and definition of factors that allow a prognosis of recurrence or malignant transformation of inverted papilloma is an active field of research. The results of studies dealing with the definition of prognostic factors, that investigated immunohistochemical methods, virus detection, molecular genetics, and histomorphological studies are discussed including our own results on the prognostic value of histology. A concept for the diagnosis, management, therapy and follow-up of inverted papilloma is proposed.

Age- and tooth-related pulp cavity signal intensity changes in healthy teeth: a comparative magnetic resonance imaging analysis.

OBJECTIVE: To determine if it is possible to measure age-related pulp cavity signal intensity changes by using magnetic resonance imaging (MRI). STUDY DESIGN: Dental pulp cavity signal intensities were assessed in 92 test subjects on the basis of MRI signal intensity measurements at freely defined regions of interest by using T1 gradient echo sequences before and after contrast-agent administration. Relative signal intensity differences were calculated and provided the basis for age- and tooth-related comparisons. RESULTS: Significant signal intensity differences were noted between the oldest (born between 1930 and 1959) and the youngest (born after 1980) test subjects and the other groups (P < .05). In addition, the first molars showed significantly lower signal intensity differences than the second molars (P < .05). CONCLUSION: Magnetic resonance imaging can be used to determine pulp cavity signal-intensity changes with age.

Augmented reality with fibre optics.

In this paper we present the concept and the first results of the Fibre Optic Pointer - a miniaturized Augmented Reality system for craniofacial surgery. The objective is the integration into surgical instruments.

Template-based registration for image-guided maxillofacial surgery.

PURPOSE: Fiducial marker registration using bone screws is a proved and tested method for patient-to-image registration for image-guided surgery of the head. The use of intraoral fiducial markers mounted on a template for the maxillary dentition is a less invasive alternative and is in use for intraoral image-guided surgery. The aim of this study was to verify if this method is sufficiently accurate for extraoral use. MATERIALS AND METHODS: Registration was performed using 243 different configurations of fiducial markers mounted on a maxillary template. The accuracy of the identification of artificial skull-mounted targets located in surgically relevant locations was determined for each registration. RESULTS: Targeting accuracy was sufficient for image-guided surgery of the maxilla, the midface, the orbit, and the pterygopalatine fossa. In the regions of the calvarium, however, average target registration error was > or =1.5 mm. Average target registration error was >3 mm. CONCLUSION: Fiducial marker registration based on a maxillary template is a safe and non-invasive alternative to bone-mounted fiducial markers for image-guided surgery in the regions of orbit, face, maxilla, and pterygopalatine fossa.

Accuracy of image-guided implantology.

OBJECTIVES: The accuracy of two commercially available systems for image-guided dental implant insertion based on infrared tracking cameras was compared with manual implantation. MATERIAL AND METHODS: Phantoms of partially edentulous mandibles were used. In a master phantom, pilot boreholes for dental implants were placed. These boreholes were reproduced in slave phantoms using either of the two image-guided systems and manual implantation. The resulting positions were determined using a coordinate measurement machine and compared with the master model. RESULTS: In comparison with manual implantation, the difference of borehole positions to the master phantom was significantly lower using either of the systems for image-guided implant insertion. CONCLUSION: Image-guided insertion of dental implants is significantly more accurate than manual insertion. However, the accuracy that can be achieved with manual implantation is sufficient for most clinical situations.

Infiltrating basal cell carcinoma of the neck 34 years after irradiation of an haemangioma in early childhood. A case-report.

A case of a 34-year-old Caucasian male is presented with a basal cell carcinoma deeply infiltrating the structures of the neck, including skeletal muscles and reaching the parotid gland. Radical surgical removal under meticulous histological control was performed. 18 months postoperatively, the patient is still free of recurrence. Thirty years ago the patient had undergone radiotherapy for an infantile haemangioma of the skin of the neck. The effects of this treatment when given in childhood in the aetiology of a basal cell carcinoma are discussed.

Artefacts in magnetic resonance imaging caused by dental material.

A common problem in computer tomography (CT) based imaging of the oral cavity is artefacts caused by dental restorations. The aim of this study was to investigate whether magnetic resonance imaging (MRI) of the oral cavity would be less affected than CT by artefacts caused by typical dental restorative alloys. In order to assess the extent of artefact generation, corresponding MRI scans of the same anatomic region with and without dental metal restorations were matched using a stereotactic frame. MRI imaging of the oral and maxillofacial region could be performed without reduction of the image quality by metallic dental restorations made from titanium, gold or amalgam. Dental restorations made from titanium, gold or amalgam did not reduce the image quality of the MRI sequence used in imaging of the oral and maxillofacial region for dental implant planning. In this respect MRI is superior to CT in implant planning.

Intraoperative augmented reality: the surgeons view.

Augmented Reality (AR) is a promising tool for intraoperative visualization. Two different AR systems, one projector based, one based on see-through glasses were used on patients. The task was the transfer of preoperative planning into the intraoperative reality, or the visualization of space occupying lesions, respectively. The intraoperative application of both systems is discussed from the surgeons point of view.

Visualization of surgical 3D information with projector-based augmented reality.

For visualizing surgical information (operation plans) directly onto the patient a projector-based augmented reality system is used for cranio-maxillofacial surgery. A prototype is introduced which has been evaluated in the first clinical cases. In a new setup with a second video projector it is now possible to give additionally 3D information for localization and orientation (6DoF). With this method the repositioning of a bone segment is intuitive and exact applicable.