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Biomedical subjects

M Hilbert

Publications and source records attributed to M Hilbert.

16 recordsLinked to original sources
PubMed1998

[Intraoperative precision of mechanical, electromagnetic, infrared and laser-guided navigation systems in computer-assisted surgery].

Intraoperative precision in computer-assisted surgery depends on the characteristics of a navigation system, the precision of correlation between object and data set, the position, number and fixation of landmarks, and the parameters of the data set. The characteristics of a navigation system, in particular the immanent precision, can be detected by the use of the geometric model and navigation analyzer developed at the University of Regensburg with the support of Carl Zeiss, Germany. The precision of five navigation systems of different types and technology was measured: Viewing Wand (ISG, mechanical system), the SMN microscope (Carl Zeiss, infrared system with laser autofocus), the MKM system (Carl Zeiss, robot platform with laser autofocus) and the STP pointer (Leibinger, infrared system). The immanent precision of these systems ranges from 0.1 to 2.0 mm. An electromagnetic system (3-Space Digitizer, Polhemus) was compared; this produces serious spherical deviations of 10.0 to 20.0 mm in the presence of metal, surgical and rotating instruments, and circuits. The application of these different systems for craniomaxillofacial surgery is discussed.

Computer Systems↗
PubMed1998

[Comparative accuracy assessment between a mechanical (viewing wand) and a laser-controlled microscopic positioning system using a geometric test model].

The precision of a new laser-guided navigation system (the "MKM") was compared with the "Viewing Wand" mechanical navigation system. We describe the inherent deviations in each positioning system as well as errors caused by data acquisition and referencing between the CT data set used for navigation and the original object. Two thousand individual measurements were performed on geometric test models scanned by CT. The technical accuracy of the mechanical navigation system varied between 0.48 mm in the most favorable area of the working field and 1.8 mm in the more inaccurate areas. For the laser-guided system a precision of 0.27 mm was found for all areas of the working field. After referencing between the CT data set and the original object, the error of measurement increased in both navigation systems: i.e., 0.83 mm for the Viewing Wand and 0.49 mm for the MKM system.

Equipment Design↗
PubMed1998

[Development of a surgical simulator for interventions of the paranasal sinuses. Technical principles and initial prototype].

BACKGROUND: Traditional training methods for surgeons include anatomical studies on human cadavers. Limited availability and ethical problems led to the consideration of alternatives. The surgeon's level of training could be significantly increased by a interactive training system trough computer graphics and virtual reality (VR). METHODS: Two main issues addressed are the 3-D reconstruction process and 3-D interaction to guide the surgical instruments. To provide the virtual environment, a realistic representation of the region of interest with all relevant anatomical parts is required. This model has to be suitable for computer simulation, while preserving as accurately as possible important anatomic features. Therefore the concept of creating a 3-D representation semi-automatically was developed. Textures derived from endoscopic images are superimposed on the virtual anatomic structures and provide better realism. RESULTS: Intuitive handling of the surgical instruments is ensured by using the tracking technique. The system allows navigation via a virtual camera and interaction with the virtual anatomical structures. Currently the use of a force feedback system and the simulation of deformations of tissues is critical. CONCLUSIONS: The VR based simulation system offers an alternative to conventional training methods. The future role of surgical simulation depends on overcoming the current drawbacks to provide greater interactive realism: the integration of a force feedback system to simulate the resistance of anatomical structures and the simulation of tissue deformations--both currently under development.

Artificial Intelligence↗
PubMed1998

[Online infection recording within the scope of total quality management].

The continuous and exact recording of infections is a condition sine qua non for total quality management. Therefore, at the Diakoniekrankenhaus Rotenburg (Wümme) a program which offers the possibility of online recording of data was integrated into the hospital intranet. The recording is done with network clients. The recording of data is supported by a series of plausibility controls. The advantage consists in immediate evaluation of up to date and extensive statistics of infections. By integration into the existing system, relevant influences and consequences such as the prolongation of hospitalisation, use of material, and frequency of reoperation can by recognized and immediately considered with high validity.

Cross Infection↗
PubMed1997

Inherent precision of mechanical, infrared and laser-guided navigation systems for computer-assisted surgery.

This investigation detects the inherent precision of four navigation systems, of different structural type, for computer-assisted surgery, ranging from 0.1 to 1.8 mm: the Viewing Wand with a mechanical arm, and three new systems, the SMN microscope and STP pointer with infrared technology and the MKM system with laser autofocus. For this purpose, a new standard to detect separately the inherent deviations of navigation systems from the deviations caused by acquisition of CT data sets, is introduced. The measurements are performed within a complete three-dimensional room, consisting of three orthogonal planes of a geometric model. The method introduced is valid for regular measurements of the inherent precision of navigation systems for quality assurance in order to prevent intraoperative failure caused by insufficient potentiometers, infrared transmitters or receivers.

Computer Systems↗
PubMed1997

MRI of inner ear and facial nerve pathology using 3D MP-RAGE and 3D CISS sequences.

The aim of this study was to evaluate 3D CISS, unenhanced 3D MP-RAGE and contrast enhanced 3D MP-RAGE for the diagnosis of neoplastic, vascular and inflammatory lesions of the cerebellopontine angle, the inner auditory canal, the labyrinth and the facial nerve 42 MR examinations were performed on a total of 38 patients (25 males, 13 females; aged 1-77 years, mean age 43 +/- 20 years) using a 1.5 T MR unit. A T2* weighted 3D CISS sequence (TR 14.65 ms, TE 21 ms, flip angle 65 degrees, voxel size 0.7 x 0.7 x 0.7 mm3) and a T1 weighted 3D MP-RAGE sequence (TR 12.5 ms, TE 5 ms, T1 300 ms, flip angle 15 degrees, voxel size 1.0 x 0.9 x 0.9 mm3) with and without contrast medium (gadolinium-DTPA, 0.1 mmol kg-1 body weight) were used. Results of contrast enhanced 3D MP-RAGE-pathological enhancement was found in the following lesions: schwannomas of the cerebellopontine angle (CPA) and the internal auditory canal (IAC), 4; schwannomas of the IAC, 7 and labyrinthine tumours, 3; posterior fossa lymphoma, 1; meatal meningioma, 1; acute labyrinthitis, 15 and neuritis of the seventh cranial nerve, 10. Results of 3D CISS-filling defects were found with the following lesions: schwannomas of the CPA, the IAC or labyrinth, 14; lymphoma, 1; meningioma, 1; labyrinthine fibrosis, 13 and scar in the IAC, 4. These results suggest that unenhanced and contrast enhanced 3D MP-RAGE and 3D CISS are complementary MR imaging modalities. T1 weighted 3D MP-RAGE is preferred to T1 weighted 2D (turbo) spin echo sequences because of the multiplanar reconstruction possibilities of 3D sequences, which are very useful in the case of the inner ear and facial nerve.

Acute Disease↗
PubMed1997

Virtual reality in endonasal surgery.

Virtual environments provide a new dimension of graphic simulation. The interaction between the human and the computer is now intuitive for the user. The use of virtual reality (VR) gives the user the feeling of participating in a (computer generated) scenario very much like reality. This feeling is an essential requirement for simulation of surgical interventions using digital data. Especially in the fields of sinus and skull-base surgery, computer assisted simulation could present a valuable and effective alternative method for honing endoscopic skills. Traditionally, surgeons gain experience through anatomic preparation and education by more experienced colleagues. Landmarks like skull base, carotid arteria or optical nerve have to be identified intraoperatively in order to orientate in this critical region. Highly sensitive structures can be damaged most easily. The quality of surgical skills can be characterized as the sum of knowledge, individual experience and manual dexterity. It is conceivable that a surgeon's level of training and experience could be significantly increased by use of VR. With this in mind, a VR-based simulator for procedures in sinus surgery will improve most of these parts. To provide the virtual environment, a realistic representation of the region of interest with all relevant anatomical structures is required. Based on data from tomographic imaging studies, a three-dimensional representation of the paranasal sinuses is semiautomatically reconstructed. Textures derived from endoscopic images are superimposed on the virtual anatomic structures and provide better realism. Two main components of the VR interface can be distinguished: the 3-D interaction to guide the surgical instruments and the 2-D graphical user interface for visual feedback and control of the session. Moreover, the 3-D interaction has to be realized by means of Virtual Reality techniques providing a simulation of an endoscope and an intuitive handling of other surgical instruments.

Computer Simulation↗
PubMed1997

[Precision of computer-assisted systems in profile reconstructive interventions on the face].

In this investigation we compared the precision of different computer-aided systems for positioning osteotomized segments to reconstruct craniofacial asymmetries. The accuracy of a mechanical navigation system, a laser-guided navigation system and the precision of templates moulded on stereolithographic models are compared, using measurements on geometrical objects, anatomical specimens and clinical application. The precision of a mechanical navigation system is 0.5 mm, and a laser-guided system 0.3 mm. The accuracy of a computer and template guided application is 1 mm.

Data Collection↗
PubMed1995

Epidermal damage and limited coagulation depth with the flashlamp-pumped pulsed dye laser: a histochemical study.

To investigate vessel coagulation depth and tissue damage in therapy with the flashlamp-pumped pulsed dye laser (585 nm, 5 mm spot size, 450 microsecond pulse duration, 6-8 J/cm2), we used the nitroblue-tetrazolium chloride stain in 22 post-treatment biopsy specimens from patients with port wine stain. With this method, thermally damaged tissue can be easily differentiated from unchanged tissue to the level of single cells. The results showed that in superficial port wine stain vessels up to 150 microns in diameter, vessel coagulation was complete and selective without further dermal damage. With the increase of vessel diameter, strong superficial hemoglobin absorption led to only partial vessel-wall coagulation and, in some cases, to superficial dermal damage. Likewise, deeper vessels were not coagulated because of shadow effects by superficial vessel layers. Thus, the overall vessel-wall coagulation depth of the flashlamp-pumped dye laser was limited to a maximum of 0.65 mm (mean 0.37 mm). In addition, some degree of epidermal damage was present in most specimens, which significantly increased with epidermal melanin content and resulted in epidermal coagulation and blistering in pigmented skin. Our results explain the occurrence of crusting, hyperpigmentation, and hypopigmentation in therapy with the flashlamp-pumped dye laser and its limited effect on dark or hypertrophic port wine stains in adults featuring large vessel diameters or multiple vessel layers.

Adult↗
PubMed1994

Autosomal dominant spondylarthropathy due to a type II procollagen gene (COL2A1) point mutation.

Osteoarthrosis represents a very common disease with heterogeneous etiology. In some pedigrees linkage of the condition with the type II collagen gene (COL2A1) has been established, but information on the underlying gene defect is still incomplete as only one mutation causing this phenotype has been identified. We analyzed the COL2A1 gene in a 27-year-old woman and her 47-year-old mother presenting with severe premature osteoarthrosis and X-ray signs compatible with mild spondyloepiphyseal dysplasia. Examination of the complete gene in both patients was done by amplification of all 54 exons, screening of the PCR products by SSCP-analysis, and subsequent sequencing. In mother and daughter a G to A transition at the 5'-end of exon 21 was detected, leading to a substitution of serine for glycine at position 274 of the triple helical domain. The mutation was not present in unaffected family members or in healthy control individuals. The autosomal dominant spondylarthropathies may represent the less severe entities of the clinical spectrum of type II collagenopathies.

Adult↗
PubMed1993

Structural relationships of homologous proteins as a fundamental principle in homology modeling.

Protein structure prediction is based mainly on the modeling of proteins by homology to known structures; this knowledge-based approach is the most promising method to date. Although it is used in the whole area of protein research, no general rules concerning the quality and applicability of concepts and procedures used in homology modeling have been put forward yet. Therefore, the main goal of the present work is to provide tools for the assessment of accuracy of modeling at a given level of sequence homology. A large set of known structures from different conformational and functional classes, but various degrees of homology was selected. Pairwise structure superpositions were performed. Starting with the definition of the structurally conserved regions and determination of topologically correct sequence alignments, we correlated geometrical properties with sequence homology (defined by the 250 PAM Dayhoff Matrix) and identity. It is shown that both the topological differences of the protein backbones and the relative positions of corresponding side chains diverge with decreasing sequence identity. Below 50% identity, the deviation in regions that are structurally not conserved continually increases, thus implying that with decreasing sequence identity modeling has to take into account more and more structurally diverging loop regions that are difficult to predict.

Bacterial Proteins↗
PubMed1993

Kniest and Stickler dysplasia phenotypes caused by collagen type II gene (COL2A1) defect.

Kniest and Stickler dysplasia are two chondrodysplasias characterized by specific phenotypes. No basic defect has been found in patients with Kniest dysplasia, whereas Stickler dysplasia is one of four chondrodysplasias for which mutations of type II procollagen gene (COL2A1) have been identified. We studied a 2-year-old girl presenting with manifestations of Kniest dysplasia and her mother showing a Stickler phenotype. Analysing COL2A1 in both patients, we detected the same 28 basepair deletion spanning the 3'-exon/intron boundary of exon 12 in mother and daughter. We were able to prove a somatic mosaic status for this mutation in the mother which accounts for her milder Stickler-like phenotype.

Adult↗