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S Hassfeld

Publications and source records attributed to S Hassfeld.

At least 19 recordsLinked to original sources
PubMed2002

Semiautomated registration using new markers for assessing the accuracy of a navigation system.

OBJECTIVES: New markers are described that can be used for an improved registration procedure and for the exact comparison of navigation systems. The advantages of the markers are demonstrated, together with an automated segmentation algorithm for locating the centroid of the markers in image space. Compared to manual registration, this method shows an improved registration accuracy. MATERIALS AND METHODS: The new markers are detected completely automatically within all scan images. This allows a semiautomatic registration, as a preregistration is performed via the algorithm. Furthermore, the exact coordinates within one scan slice are now determined with the calculation procedure. The calculated data from the preregistration were matched up with a manual preregistration and some reference data, so as to confirm the quality of this new algorithm. The accuracies of several manual and semiautomatic registrations were also compared. RESULTS: The average deviation between the coordinates of the algorithm and the reference data (coordinate measuring machine) was 0.3 mm. The standard deviation amounted to 0.131 mm. Comparing several manual registrations with the reference data showed that the middle fiducial registration error (FRE) was between 0.7 and 2 mm. In comparison, the FRE remained constant at around 0.7 mm for the semiautomatic registration procedure. CONCLUSIONS: The measured results show a significant improvement in the preregistration data using the new markers together with the algorithm. This improvement leads to a reproducible and more accurate registration. The combination of the new marker type with the automated segmentation algorithm minimizes the human error factor, and provides the opportunity to directly compare image-guided and robotic systems.

Algorithms↗
PubMed2002

[Carcinoma cuniculatum of the oral cavity. A contribution to the differential diagnosis of potentially malignant papillary lesions of mouth mucosa].

Although carcinoma cuniculatum clinically appears to be malignant, histological evaluation often results in a false diagnosis of a benign papillomatous lesion or pseudoepitheliomatous hyperplasia, because the tumor usually displays a well differentiated tissue. In this report morphological and immunohistological features in a rare case of carcinoma cuniculatum of the oral cavity are described. Both clinical features and histomorphological evaluation must be taken into consideration when diagnosing the tumor.

Aged↗
PubMed2002

[3D-ultrasound: a valuable adjunct for therapy planning and follow-up of head and neck tumours].

AIM: The three-dimensional visualization of orofacial tumours and adjacent organs at risk of infiltration is an important requirement for staging, therapy planning and follow-up. Artifacts from the mandible or metal implants often reduce the diagnostic power of computed tomography (CT). The value of 3D-ultrasound (3D-US) in respect to the standard methods CT and magnetic resonance imaging (MRI) was therefore analyzed. METHOD: Between 9/97 and 10/99 the visualization of orofacial tumours in 243 patients by 3D-US was examined, classified on a five-point scale and compared to the corresponding CT and MRI scans. RESULTS: Complete visualization of the tumours was possible in 85.6 % by 3D-US, whereas the rates of MRI and CT were lower with 77.4 % and 61.3 % respectively, mainly because of artifacts. The best combinations of methods, 3D-US + CT (96.7 %) and 3D-US + MRI (95.1 %) gave almost equivalent results, whereas CT + MRI (83.5 %) was inferior. In 2.5 % of the cases none of the methods produced adequate results. CONCLUSION: By free selection of sectional planes and direct correlation to the clinical findings 3D-ultrasound can improve staging, therapy planning and follow-up of orofacial tumours, especially in the case of small tumour size, dental crowns/inlays, metal implants or contraindications to MRI.

Head and Neck Neoplasms↗
PubMed2002

[Cadaver study: robot-assisted cranial resection and implantation of titanium plates].

A processing chain for the prefabrication of individual titanium implants for cranioplasty was developed at the Ruhr-University Bochum. In patients with tumours a simultaneous resection of cranial bone and insertion of the individual implant is desirable. At first resection templates were used for this. New developments aim at a preoperative definition of resection trajectories for surgical robots corresponding to both the planning of the resection and the implant. This study used ovine cadaver skulls for robot resection experiments. The results demonstrate possible applications, limitations and necessary prerequisites in robot assisted cranial surgery.

Animals↗
PubMed2002

Symmetry considerations for volumetric implant-planning.

Symmetry Considerations can be used not only to plan the desired shape of reconstructured bone structures, but also to generate prototypes for soft tissue implants. The paper describes a system which allows to calculate a symmetry plane in the facial area automatically and computes proposals for implants or transplants. This is done by using a Simulated Annealing algorithm to determine the best reflection and morphologig operators to calculate the implant. The system presented has been used to calculate soft tissue implants in the facial area and a replacement for parts of the lower jaw.

Artifacts↗
PubMed2002

Evaluation of models.

Evaluation of models describing computer based technology is crucial for further evolution of medical progress. In this project, the research sites of the Sonderforschungsbereich 414 "Computer and sensor aided surgery" were linked for evaluation purposes. Topics of flow, morphology, function, and robotics in the field of cardiac and oromaxillofacial surgery are addressed. Key methods are animal models, phantoms, image processing and clinical studies in the setting of exactly defined circumstances. As an example, 3D evaluation of myocardial edema is presented. Heterogeneity of 3D distribution of induced myocardial edema was validated. Temporal dynamics of edema is described as an example. Based on such models, diagnostic and operation relevant planning data are offered to cardiac surgeons.

Animals↗
PubMed2002

AIDA--experiences in compensating the mutual weaknesses of knowledge-based and object-oriented development in a complex dental planning domain.

OBJECTIVES: Dentistry is a discipline with two properties that pose a serious challenge to knowledge based decision support: (1) It has to integrate six subdisciplines ranging from conservative measures to invasive disciplines, such as implantology; (2) A plan may have to cover a complex treatment often lasting one year or more. It is the aim of the AIDA-project to set up a planning strategy that is suited to incorporate all dental peculiarities in one methodology. METHODS: Generic tasks, that can be assigned to individual persons involved in dental treatment, have been designed with the help of KADS. They have been integrated into a planning super-structure for the planning of all dental solution alternatives, that can principally be applied on the basis of the given patient status. RESULTS: Besides an evaluation of the implemented planning system itself, it has been evaluated how well the development is supported by (1) knowledge-engineering methods and (2) object-oriented methods. CONCLUSION: Common knowledge-based tools are not powerful enough for the planning of complex dental constructions. Therefore, a solution combining object-oriented and knowledge-based methods is proposed.

Artificial Intelligence↗
PubMed2002

[Expanded reality in head surgery].

The preoperative planning of complex craniofacial surgical interventions is increasingly realized with the aid of appropriate planning systems in order to achieve high precision, minimal invasion and protection of risk areas. But the most important step from the planning to the actual intervention consists of providing the planning data intraoperatively in a reasonable and easy to handle way. In this regard, augmented reality is one of the most challenging and promising techniques to solve this problem. In this paper we present two different systems based on see-through glasses resp. a common video projector to directly visualize the planning data in the surgeon's field of view. The work is funded by the 'Deutsche Forschungsgemeinschaft (DFG)' and Stryker Leibinger Freiburg/Germany.

Computer Simulation↗
PubMed2001

[Magnetic resonance tomography for planning dental implantation].

PROBLEM: Three-dimensional imaging diagnostics are increasingly recommended before inserting dental implants in high-risk areas and in cases of severe alveolar atrophy. Since patients are exposed to considerable radiation with computed tomography (CT), the possibilities of employing magnetic resonance imaging (MRI) of the jaw as a diagnostic imaging method before inserting dental implants were examined. MATERIAL AND METHOD: Twelve patients and three volunteers were examined by MRI with T1-weighted, fat-suppressed sequences and conventional T1-weighted sequences. The patients wore a diagnostic splint including markers--in the form of capillaries filled with 0.025 x 10(-2) M gadolinium solution (1.5 mm in diameter)--in the planned implant's position and axis. RESULTS: The presentation of relevant anatomic structures and the three-dimensional accuracy of the markers were judged. Metal artefacts were evaluated in vitro. The MRI of the jaw and midface represents the mandibular canal, the maxillary sinus, and other decisive anatomic structures by detailed representation of the connective tissue surrounding the bone. Artefacts of metallic fillings reduce the image quality. CONCLUSION: Obtaining clinical findings and planning before inserting dental implants with the help of MRI can certainly be applied with toothless patients and facilitates three-dimensional planning by representing the exact location and angle of the drill tubes. Local restrictions result from metal extinction artefacts in jaws with teeth and in controls after having inserted titanium implants.

Adolescent↗
PubMed2001

Reliability of assessing interproximal bone loss by digital radiography: intrabony defects.

AIM: The aim of the present study was to assess the reproducibility and validity of linear measurements of interproximal bone loss in intrabony defects on digitized radiographic images after application of different filters and magnifications. METHODS: Immediately before surgery 50 radiographs of 50 periodontally diseased teeth exhibiting interproximal intrabony defects were obtained by a standardized technique in 50 patients. Intrasurgically the distances from the cementoenamel-junction (CEJ) to the alveolar crest (AC) and from the CEJ to the deepest extension of the bony defect (BD) were assessed. All radiographs were digitized by a flatbed scanner (resolution: 600x1200 dpi). Using the FRIACOM-soft ware, the linear distances CEJ to AC and CEJ to BD were measured at 50 intrabony defects on digitized but unchanged radiographic images and also after use of 2 different basic image processing modes (filters: enhancement of grey level differences, spreading of grey values) with 7-fold and 14-fold magnification by 2 different examiners. RESULTS: Repeated measures MANOVA revealed reproducibility of the measurement of the distance CEJ to AC to be significantly influenced by examiner (p=0.027) and filter in combination with the height of 2 wall component of the intrabony defect (p=0.066). For the distance CEJ to BD filters had significant influence on reproducibility in correlation with vertical angulation difference (p=0.001). On the average in this study radiographic measurements tended to overestimate the amount of bone loss as assessed by intrasurgical measurements (CEJ-AC: 0.74-1.91 mm; CEJ-DB: -0.04-0.77 mm). Validity of measurement of the distance CEJ-AC was shown to be significantly influenced by the depth of the intrabony defect (p<0.003). Validity of the distance CEJ-BD was significantly influenced by intrasurgically assessed bone loss (p=0.029), horizontal angulation (p=0.066). Filters influenced the validity only in combination with examiner (p<0.001). CONCLUSIONS: In this study, the chosen digital manipulations (filters: spreading, structure) of radiographic images failed to result in statistically significantly more reproducible or valid measurements of interproximal bone loss within intrabony defects when compared to the digitized but unchanged images. All radiographic assessments on the digitized images except for use of enhancement of grey level differences (structure) came close to the intrasurgical gold standard.

Adult↗
PubMed2001

Computer-based intraoral image analysis of the clinical plaque removing capacity of 3 manual toothbrushes.

BACKGROUND: (I) Introducing an intraoral camera system with a special positioner to allow computer-based analysis of reproducible images on lingual tooth surfaces and (II) comparing plaque removal by three manual toothbrushes with different brushhead designs (convex, multilevel and flat trimmed) on lingual mandibular tooth surfaces. METHOD: In a clinical single-blind, crossover, 24-h plaque-regrowth study on 25 subjects, a computer-based index (PPI) was used to evaluate pre- and postbrushing plaque on lingual surfaces of mandibular premolars and molars. Subjects brushed their teeth under standardized conditions at three visits, each time with a different, randomly assigned toothbrush. RESULTS: The intraoral camera system allowed a reproducible and relatively convenient access to the lingual surfaces of the mandibular teeth and provided an increase in objectivity. Overall, each brush achieved statistically significant plaque removal, however, none reached clinical relevance. The multilevel brush was superior at specific sites, but failed to show statistically significant superiority in terms of overall plaque reduction. Without regard of the toothbrush used, the right handed subjects were less efficient in removing plaque from the right side compared to the left. CONCLUSIONS: The method is able to detect even small differences in plaque reduction. None of the different brushhead designs was able to compensate an insufficient brushing techniques.

Adult↗
PubMed2001

Computer assisted oral and maxillofacial surgery--a review and an assessment of technology.

Advances in the basic scientific research within the field of computer assisted oral and maxillofacial surgery have enabled us to introduce features of these techniques into routine clinical practice. In order to simulate complex surgery with the aid of a computer, the diagnostic image data and especially various imaging modalities including computer tomography (CT), magnetic resonance imaging (MRI) and Ultrasound (US) must be arranged in relation to each other, thus enabling a rapid switching between the various modalities as well as the viewing of superimposed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft and hard tissues are required. We must develop ergonomic and user friendly interactive methods for the surgeon, thus allowing for a precise and fast entry of the planned surgical procedure in the planning and simulation phase. During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today and within this article we present a review of the development of this rapidly evolving technique. Future intraoperative assistance takes the form of such passive tools for the support of intraoperative orientation as well as so-called 'tracking systems' (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. The techniques of virtual reality and computer assisted surgery are increasingly important in their medical applications. Many applications are still being developed or are still in the form of a prototype. It is already clear, however, that developments in this area will have a considerable effect on a surgeon's routine work.

Computer Simulation↗
PubMed2001

Radiographic defect depth and width for prognosis and description of periodontal healing of infrabony defects.

BACKGROUND: The aims of the present study were to evaluate 1) defect depth and width as a prognostic factor and 2) change in defect width as a describing parameter of periodontal healing in infrabony defects treated by regenerative therapy after 6 and 24 months. METHODS: In 24 patients with advanced periodontitis, 39 infrabony defects were treated by guided tissue regeneration (GTR) using expanded polytetrafluoroethylene (ePTFE) (n = 7) or bioabsorbable barriers (n = 32). Clinical parameters were assessed and 39 standardized radiographs (in triplicate) were taken before and 6 and 24 months after surgery. Using a computer-assisted analysis, the depth, width, and angle of the bony defects were measured. RESULTS: Statistically significant vertical clinical attachment gains (CAL-V: 3.15 +/- 1.63 mm to 3.31 +/- 1.65 mm; P<0.001) and bony fill (1.30 +/- 2.53 mm; P<0.01 to 1.54 +/- 2.70 mm; P<0.005) were observed 6 and 24 months postsurgically. In a multilevel regression analysis CAL-V gain was predicted by baseline CAL-V (P <0.0001), actual smoking (P <0.05), and age (P <0.1). Bony fill could be predicted by baseline height of the infrabony component (P<0.0001), gingival index at baseline (P<0.05), and actual smoking (P <0.01). In narrow (<26 degrees) and deep (> or = 3 mm) infrabony defects bony fill was more pronounced than in wide and shallow defects (P <0.05). CONCLUSIONS: Improvement achieved by guided tissue regeneration in infrabony defects can be maintained up to 24 months after surgery. Narrow and deep infrabony defects respond radiographically and to some extent clinically more favorably to GTR therapy than wide and shallow defects. However, depth of the infrabony component was a stronger prognostic parameter than defect angle. Actual smoking impairs the results of GTR therapy in infrabony defects.

Adult↗