PubMed Health⌕ Search

Biomedical subjects

S Hassfeld

Publications and source records attributed to S Hassfeld.

At least 19 recordsLinked to original sources
PubMed2006

Clinical application of cone beam digital volume tomography in children with cleft lip and palate.

OBJECTIVES: The diagnostic advantages of digital volume tomography (DVT) over conventional imaging and computed tomography are demonstrated in terms of the respective radiation exposure. The potential role for three-dimensional imaging in cleft lip and palate patients is illustrated on the basis of clinical examples. METHODS: The radiation exposure resulting from scans using a cone beam DVT (NEW TOM QR-DVT 9000, Marburg, Germany) was measured with an Alderson-Rando-Phantom (The Phantom Laboratory, New York, NY) and compared with that resulting from other standard imaging modalities. The patient sample consisted of young children with cleft lip and palate on whom orthodontic and surgical treatment was planned on an interdisciplinary basis at the University-Hospital of Heidelberg. RESULTS: Digital volume tomography allows high-quality three-dimensional imaging of the premaxilla region, with an effective equivalent investigation dose of (110 kV, 5.4 mA) 0.342 mSv based on ICRP recommendations. While the effective equivalent investigation dose for DVT is higher than that for standard imaging techniques (for example digital panoramic radiograph Orthophos Plus DS Ceph (66 kV, 8 mA) 0.016 mSv), it is much lower than that for a normal CT scan (e.g. Picker International Inc., Highland Heights, OH) adjusted at (spiral 130 kV, 125 mA, and 30 mA, 1.5 s) 2.27 mSv. Digital volume tomography provides extensive data important in clinical decision making. CONCLUSIONS: The clinical examples show the good applicability of DVT with a reduced radiation dose.

Child, Preschool↗
PubMed2005

[Markerless patient registration. A new technique for image-guided surgery of the lateral base of the skull].

BACKGROUND: Markerless patient registration is a new procedure that may reduce logistical efforts and possibly also the radiation load on the patients prior to a computer-assisted intervention. Congruent surfaces, such as bone surfaces or skin surfaces, represented in a data set and in the surgical site, can be overlapped with the help of surface matching. Hitherto, these techniques were performed by using the periorbital and frontal skin of the face. The present clinical study assessed the usability of the auricle as a skin structure for markerless patient registration in lateral skull base surgery. PATIENTS AND METHODS: The periauricular precision of the navigation system SSN was investigated clinically in ten patients. Radiopaque registration markers in the periauricular region served as a target in order to evaluate the markerless registration method. RESULTS: Exact patient registration failed in five cases due to temporary deformation of the auricle caused by the head support during CT imaging. An excellent patient registration (mean target registration error = 0.9+/-0.2 mm) was found as long as the auricles had not been temporarily deformed during CT imaging. CONCLUSION: Laser-scan registration of the auricle reduces logistics in image-guided lateral skull base surgery. The problem of temporary deformation of the auricle during CT imaging might be solved by an appropriate opening in the head support at the level of the auricles.

Humans↗
PubMed2005

[Preoperative information].

BACKGROUND: Many empirical studies have identified the quality and communication of patient information as a major weak point in the treatment process. Patient information can be made considerably more effective by multimedia communication of contents tailored to the patient's needs. Computer-based training (CBT) takes the multimedia presentation one step further. METHODS: Using the Macromedia Director 8.5 authoring software, a multimedia system for pre-operative patient information was developed on CD-ROM for a limited area of oral and maxillofacial surgery. This information system was evaluated for quality assurance on the basis of a random sample of 85 patients in a test lasting about 20 min. Impressions were determined with regard to design features, motivation, understanding, the subjective communication of knowledge, the newly acquired competence and acceptance compared with other media (information leaflets, Internet, conventional information). RESULTS: The analysis of the program test revealed a hugely positive assessment of the interactive program in respect of layout, functionality and design as well as in respect of structuring and the subjective understanding of the underlying complaint, therapy and potential complications. In a comparison with other information media such as information leaflets and the Internet, the program was rated just as good or better by over 70% of the respondents. Only conventional consultation with a doctor came off better in a direct comparison. CONCLUSION: It was shown that the quality of preoperative patient information can be improved through multimedia presentation and that it would be sensible to make use of modern media for the purposes of giving patients graphic information.

Adolescent↗
PubMed2005

Image-guided removal of foreign bodies.

Foreign bodies are common in the head and face. We investigated the use of image-guided navigation systems for the removal of foreign bodies in 10 patients between 1998 and 2004. In all cases foreign bodies were retrieved. There were no major complications. Image-guided removal of foreign bodies is safe and valuable.

Adolescent↗
PubMed2005

[A new method for computer-assisted orbitotomies].

BACKGROUND: Surgical planning and tumor margins from preoperative image data sets can be transferred to the surgical site by use of computer-assisted navigation systems. Usually registration markers are placed prior to image data acquisition in order to correlate the patient's preoperative image data set with his/her position in the operating room. Pointers are commonly used for navigation, and the position of the pointer within the surgical site is compared to its position within the image data set. With a new navigation system, patient registration can be performed without registration markers. Tumor margins and osteotomy lines can be projected onto the surgical site. MATERIALS AND METHODS: With the new navigation system, which has been developed by the Sonderforschungsbereich 414 of the Deutsche Forschungsgemeinschaft, markerless patient registration is performed using the contours of the patient's face. A scanner is mounted above the operating table, which detects the surface of the surgical site intraoperatively. Osteotomy lines and tumor margins are projected onto this surface using an intense beamer. The procedure is illustrated for a patient with a meningeal tumor of the orbit. RESULTS: Patients can be registered with an accuracy of 1 mm. Pointers are not required to transfer the data on the surgical site. Furthermore, monitors are no longer required, since the information is projected directly on the patient's surface. CONCLUSIONS: Surgical planning and tumor margins can exactly be visualized within the surgical site. Ergonomics are especially improved for navigated orbitotomies via a coronal approach.

Adult↗
PubMed2005

Robot-assisted craniotomy.

In the Special Research Centre 414 of the German Research Funding (DFG, Bonn) a system for robot-assisted cranial surgery was developed. It is designed for the accurate and safe execution of craniotomies and repositioning of bone pieces. The system is intended for use in the surgical therapy of craniosynostosis. Preoperatively, CT imaging is performed. In a computerized planning system the position and shape of the intended craniotomy is intuitively planned on a virtual model of the patient's skull. Intraoperatively, after conventional removal of the covering soft tissue, the robot performs the craniotomy autonomously. Extensive testing in phantom studies and animal tests confirmed the reliability and accuracy of the system. A thorough risk analysis of the system was performed. In this paper, the first clinical use of the system on a patient is described and the clinical importance is discussed.

Bone Cysts↗
PubMed2005

Risk analysis and safety assessment in surgical robotics: a case study on a biopsy robot.

One of the most important issues in medical robotics is safety and integration into the clinical workflow. If a robot is not safe and its use is complicated by difficult handling and complex user interfaces physicians would not use a robotic system during clinical patient trials, whatever the other advantages are. However, there are only few publications on this topic, in particular on risk management in developing a robotic prototype (for clinical trials). In this paper risk management and the safety of using robot-assisted surgery equipment are discussed and demonstrated exemplarily in the process of developing a prototype biopsy robot.

Journal Article↗
PubMed2005

Detection of foreign bodies of the head with digital volume tomography.

OBJECTIVES: Foreign bodies occur as a sequela of trauma or therapeutic interventions. If the risks are not too high, therapy of choice is the removal of the foreign body. This is only possible if the existence of a foreign body is detected and it is localized accurately. METHODS: The suitability of digital volume tomography (DVT) for the detection and localization of foreign bodies was investigated. Samples of various materials that are typically found as foreign bodies in the head and neck region were used. RESULTS: All materials investigated are principally detectable with DVT. Highly radiopaque material was detectable down to small sizes. The detectability of less radiopaque substances like wood and resins was poor when located in soft tissue. CONCLUSION: DVT is an appropriate tool for the detection of radiopaque foreign bodies. However, foreign bodies made of wood and resin, although detectable by DVT, can be missed when located in muscular tissue. The detectability decreases further when the foreign body is located adjacent to a highly radiopaque tissue like bone. This has to be taken into consideration when using DVT for foreign body detection.

Contrast Media↗
PubMed2005

Geometric accuracy of the NewTom 9000 Cone Beam CT.

OBJECTIVES: To determine the geometric accuracy of digital volume tomograms to assess their usability for implant planning. METHODS: A measuring object with 216 measuring points, whose geometry is exactly known, is X-rayed with a NewTom 9000 cone beam scanner; thereafter the geometry of the volume tomogram of the object is compared with the original body. RESULTS: Considering all three coordinate axes, geometric mean deviations of 0.13 +/- 0.09 mm with a maximum deviation of 0.3 mm were determined. These geometric deviations are below the resolution power of the volume tomograph. CONCLUSION: The digital volume tomographies of NewTom 9000 present images which are geometrically correct and, from a geometrical point of view, suitable for three-dimensional implant planning.

Dental Implantation, Endosseous↗
PubMed2005

Geometric accuracy of magnetic resonance imaging of the mandibular nerve.

OBJECTIVES: Magnetic resonance imaging (MRI) is not routinely used for dental implant planning. A prerequisite for dental implant planning is the accurate imaging of risk structures like the mandibular nerve. The geometric accuracy of the imaging of the mandibular nerve was investigated. METHODS: Two human cadaver heads were scanned using MRI. Computed tomography (CT) scans of the same heads were used as a benchmark. Using a stereotactic frame, corresponding images of MRI and CT were superimposed and the concordance of the images of the mandibular nerve in MRI with those of the mandibular canal in CT was assessed. RESULTS: The geometric accuracy of the mandibular nerve in MRI was as good as that of the mandibular canal in CT imaging. CONCLUSIONS: MRI of the mandibular nerve is sufficiently accurate for the use of this imaging method in dental implant planning.

Artifacts↗
PubMed2004

Automated laser registration in image-guided surgery: evaluation of the correlation between laser scan resolution and navigation accuracy.

Markerless patient registration based on the facial skin surface makes logistics prior to image-guided surgery much easier, as it is not necessary to place and measure registration markers. A laser scan registration of the surgical site takes the place of conventional marker-based registration. In a clinical study, the stability and accuracy of markerless patient registration was evaluated in 12 patients. Intraoral titanium markers served as targets for the infrared-pointer of the navigation system in order to check the accuracy of the markerless registration process. The correlation between laser scan resolution and navigation accuracy was checked using seven different laser scan resolutions (a cloud of 300,000 laser scan points down to 3750 laser scan points of the surgical site). The markerless patient registration was successful as long as high laser scan resolution was used (30,000 laser scan points and more): the titanium markers were detected with a mean deviation of 1.1 +/- 0.2 mm. Low resolution laser scans (6000 laser scan points of the surgical site and less) revealed inaccuracies up to 6 mm.

Humans↗
PubMed2004

Robots in the operating theatre--chances and challenges.

The use of surgical robots and manipulators is still being frequently discussed in the mass media as well as in the scientific community. Although it was already noted in 1985 that the first patient was treated by a joint team of robot and surgeon, today such systems are not routinely used. This can be explained by the high complexity of such systems and the often limited usability, but also, that it is difficult for surgeons to accept "automatic" machines. In this paper the possibilities and chances of robots and manipulators will be explained and it will be shown that robots will never work alone in the operating theatre as it is common in industry today. On the other hand, also limitations and challenges will be outlined. Therefore first a review on today's systems is given in different disciplines including oral- and cranio-maxillofacial surgery, then advantages and disadvantages are shown.

Equipment Design↗
PubMed2004

High-resolution laser surface scanning for patient registration in cranial computer-assisted surgery.

OBJECTIVE: Markerless patient registration is a new procedure that may reduce logistical efforts and possibly also the radiation load on the patients prior to a computer-assisted intervention. Congruent surfaces, such as bone surfaces or skin surfaces, represented in a data set and in the surgical site, can be overlapped using surface-matching. Previous studies describing this kind of markerless registration, however, show inaccuracies of up to 10 mm during computer-assisted navigation. Furthermore, these systems use less than 1000 surface points of the soft tissue surface in order to establish a correlation between the patient and the data set. Previous papers did not answer the question whether it is this scanning resolution that induces these inaccuracies in registration or rather intraoperative skin deformations. STUDY DESIGN: In the present study therefore a new navigation system (SSN++) was used which is able to register up to 180,000 surface points of the surgical site. SSN++ is an infrared navigation system enlarged by a Minolta VI 900 3D volume digitizer. Three different kinds of laser scan-resolution were used for data correlation. An additional congruence analysis was performed in order to assess the geometry of the matched skin surfaces. 22 patients suffering from different cranial diseases (tumors, bony malformations, foreign bodies) were prepared for a computer-assisted intervention. Intraoral titanium-markers, rigidly fixed on the patients by a maxillary splint, were placed as targets while the CT data sets were made. These targets were - after markerless laser scan registration of the patients - supposed to serve for validating the new high-resolution navigation system SSN++. RESULTS: The accuracy of markerless laser scan registration depends on the intraoperative laser scan's resolution. A high accuracy of the data correlation can be achieved if the number of the laser scan cloud points is about the same as the number of voxels of the corresponding surface on the CT data set. A reduction of the laser scan cloud points to less than 10 % compared to the number of voxels of the CT surface, however, leads to a significant loss of accuracy after markerless patient registration. CONCLUSION: 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.

Brain Diseases↗
PubMed2003

[New concepts in image assisted surgery: automated patient registration based on the jaw and external ear].

OBJECTIVE: Automatic and marker less patient registration based on natural anatomical interfaces may considerably reduce the radiation load and logistical input prior to computer-assisted surgical interventions, as it is not necessary to place and measure reference markers. The present study was to find out if, apart from the facial skin, also auricles as well as the upper and lower jaw can be used as anatomical interfaces for the intraoperative registration of the patient's position. MATERIAL AND METHOD: Prior to surgical intervention the positions of 20 patients were registered by a high-resolution 3D laser scan and correlated with the preoperative CT data set. Tumors, skeletal malformations, and foreign bodies were indications for surgical intervention. Auricles as well as the upper and lower jaw were used to register the patient's positions. The accuracy of this basically marker less method was clinically evaluated through the additionally placed conventional registration markers. RESULTS AND CONCLUSION: The marker less patient registration based on natural anatomical interfaces was successful in the upper jaw (deviation: 0.8+/-0.3 mm). The tongue and mobile floor of the mouth led to geometric incongruence and inadequate laser registration in the lower jaw. As far as the auricles were concerned, high accuracy could only be achieved as long as the auricles had not been deformed during CT imaging (deviation: 1.9+/-0.9 mm). The usual CT acquisition with a conventional head support, however, led to temporary auricular deformations in more than half of the patients, which made an exact laser scan registration impossible.

Artifacts↗
PubMed2003

AIDA: web agents in dental treatment planning.

The objective of the AIDA project (Artificial Intelligent Dental Agents, http://aida.uni-hd.de) is the analysis of dental decision-making, the design of a computer-based decision support system, as well as the testing of the decision structure in interactions with dental experts, practicing dentists, and patients. The planning of the solution alternatives for an individual patient is based on a top-down structure for dental decision-making, aiming at a standardization of the argumentation. From a theoretical point of view, decision support can be provided only for anticipated decisions (planning). Moreover, only parts of these anticipated decisions can be supported. Accordingly, a separation of these partial aspects has to take place before one is able to build decision support systems. For prosthetic dentistry, clinicians have been shown how to use individual patient findings to sketch the possible treatment alternatives and later derive guidelines for the treatment. The planning module for fixed prostheses has already been integrated into a software agent. Planning modules for other types of prostheses are currently specified, implemented, and verified.

Decision Support Systems, Clinical↗
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↗