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Biomedical subjects

S Hassfeld

Publications and source records attributed to S Hassfeld.

At least 73 records · Page 4Linked to original sources
PubMed1998

Tracing of thin tubular structures in computer tomographic data.

For many applications in diagnostics and in the planning of surgical interventions, specific structures have to be identified in a patient's volume data set. In this article we give an outline of how the detection of thin tubular structures (e.g., nerves and vessels) can be automated, requiring very little initialization from a human expert. We focused on the nervus alveolaris inferior in the lower jaw and were looking at three details: data acquisition, detection, and validation of accuracy. Our method can be easily adapted to many similar cases such as other nerves, arteries, and veins or bundles thereof.

Algorithms↗
PubMed1998

Navigation in maxillofacial and craniofacial surgery.

The standardized operational techniques available today make it possible to perform extensive surgeries for the treatment of craniofacial malformations and advanced tumors in this anatomically complex region. The new techniques of computer-assisted surgery allow us to interactively use the three-dimensional image data of the patient during surgery. Simulation of complex osteotomies in individual patients is now possible with the aid of new software developments for virtual cutting and shifting of bone segments. Intraoperative realization with navigation systems has been performed at our clinic for the past 4 years, and we have gained extensive experience from more than 100 clinical applications of mechanical and optoelectronic navigation systems. These passive localization systems supply the surgeon with direct intraoperative support while performing the surgeries. It is the primary goal of computer-assisted surgery to support the surgeon during diagnosis, operational planning, and intraoperative navigation. We can thereby achieve a reduction in operational risk and duration, which in turn results in a considerable stress reduction for the patient.

Craniofacial Abnormalities↗
PubMed1998

Possibilities and developments of intraoperative image-guided surgery in craniofacial surgery.

The standardised operational techniques of fronto-orbital osteotomy and the various modifications used today make it possible to perform extensive surgery for the treatment of craniofacial malformations and advanced tumours in this region, while also allowing for a good extra- and intracranial view. Osteotomies and resections in areas of the skull base that are normally hard to reach have been considerably facilitated and the operational risk has been lowered. Our aim is to achieve a further reduction of the operational risks and of the post-surgical morbidity rate through the use of techniques of computer-assisted surgery. Especially in the area of the complex anatomy of the skull base, use of the systems for the purpose of orientation and realisation of operational planning as well as for the control of how radical a tumour resection needs to be, have proved quite successful. Meanwhile, we have acquired experience in more than 100 clinical applications of mechanical and optoelectronical navigation systems. However, it is not possible to make changes to the presurgical data. Also, the flexibility of the system is still somewhat limited. By introducing a new referencing system, the flexibility and possible applications of navigation have been increased. The current possibilities and indications for the use of intraoperative navigation are discussed.

Computer Simulation↗
PubMed1998

[Neuronavigation. Methods and prospects].

With the recent developments in computer technology and the improvements in modern neuroimaging, frame-based stereotactic guidance for open microsurgical procedures has been increasingly replaced by neuronavigation, also called frameless stereotaxy. It allows transfer of individual patientís images onto the operative field to assist the neurosurgeon intraoperatively in defining the tumor margins or identifying functionally important brain areas. The different localization techniques employed are articulated position-sensing arms, infrared or ultrasound systems working with the principle of satellite navigation and robotic systems integrated with the operating microscope. In 200 operations performed with different systems (arm-based, robotic and infrared) the method proved to be helpful, enabling fewer invasive procedures to be performed. With a mean deviation of 2.87 +/- 1.9 mm for intraoperative localization, the accuracy was only slightly worse than in frame-based stereotaxy with deviations below 2 mm. Neuronavigation was most helpful for operations on deeply seated lesions, skull-base tumors and lesions in brain areas with high functionality. The major disadvantage is the use of preoperative data for navigation, leading to inaccuracies when anatomical structures are altered during the operation by resection of tumors or shift of intracranial soft tissue. Intraoperative magnetic resonance imaging (MRI) might be a solution for this problem. With the method of intraoperative MRI developed in our department it has already been possible to update neuronavigation with images reflecting intraoperative changes in anatomy. Therefore, neuronavigation is definitely a method with growing importance in operative routine, and it will also spread into other surgical specialties.

Brain Diseases↗
PubMed1998

[Low-dose computerized tomography of the jaw bone in pre-implantation diagnosis. Limits of dose reduction and accuracy of distance measurements].

Absorbed radiation doses delivered by computed tomography and panoramic radiography were measured in 16 anatomic sites using a head and neck phantom and thermoluminescent dosimetry. The recommended kilovoltage and scan time for dental scanning was reduced step by step, rating the quality of the low-dose scans. A reduction of up to 76% could be achieved without loss of diagnostic accuracy. Measured absorbed radiation dose ranges from 0.30 mGy (thyroid) to 29 mGy (skin) at 187.5 mAs and 1.0 mm-slices (25 mm scanning distance for maxilla, 30 mm for mandible). After reduction to 45 mAs, 0.07 mGy (thyroid) to 6.9 mGy (skin) was measured. Distance measurements on human jaw specimens were compared with corresponding CT image measurements. Average deviation was 0.1-0.3 mm. A dose reduction of 75% had no effect on the results. However, the doses of CT-scans reduced by 76% exceed by an average factor of 10 the doses of conventional panoramic radiography. Therefore, CT should be reserved for the planning of complex implant treatment in the direct vicinity of the maxillar sinus and nerves and for multiple implant insertion.

Body Burden↗
PubMed1998

[Odontogenic focus as the etiology of cerebral ischemia].

Recent studies have shown that acute infections, especially of the respiratory tract, are an important risk factor for cerebral ischemia. Additionally we know that chronic dental infections may be a risk for myocardial infarction and artherosclerosis. However, the connection between stroke and dental infections has hardly been examined so far. Therefore we performed a case-control study using a standardized questionaire and examination. We investigated 66 patients consecutive to a acute cerebral ischemia/stroke and 60 age- and sex-matched nonstroke neurological patients as a control group. Dental status was determined by a so called total dental index (TDI) which reflects primarily caries, periodontitis, periapical lesions, devital and missing teeth as well as by a panoramic index (PI). Specifically, older patients with cerebrovascular ischemia tended to have a significantly worse dental status and had more severe periodontitis and periapical lesions than control subjects. A predefined poor dental status was associated with cerebrovascular ischemia independent from other vascular risk factors and social status. In conclusion, poor dental health, mainly resulting from chronic dental infections, may be associated with an increased risk for cerebrovascular ischemia. The results must now be verified in larger studies. As chronic dental infections are a common and also easily treatable factor, their identification as a risk factor for stroke would be quite important in the field of preventive medicine.

Adult↗
PubMed1998

Preoperative planning and intraoperative navigation in skull base surgery.

Experience with the commercially available, 3-D navigation systems Viewing Wand (ISG, Mississauga, Ontario, Canada) and SPOCS (Aesculap, Germany) in skull base surgery is presented. Having meanwhile been tested in over 60 clinical trials, the systems achieved an accuracy of < or = 2.7 mm which, at the moment, we deem sufficiently acceptable to proceed with their clinical evaluation. There was no difference in intraoperative accuracy between the mechanical and the optical navigation systems. The systems proved to be very helpful in identifying the extent of the tumours and in visualizing the proximity of vital structures. 3-D-planning, simulation and intraoperative navigation especially facilitates surgery in anatomically complicated situations, without risk of damaging neighbouring structures. The SPOCS (Surgical Planning and Orientation Computer System) revealed a considerably improved flexibility in handling and a better integration into the surgical procedure in comparison with the relatively inflexible and space-demanding Viewing Wand arm. Especially, the 'offset' function of the SPOCS offers the possibility of a virtual elongation of the instrument and thus, in combination with the on-line visualization of the corresponding images, of a 'look ahead' operation. By using computer-assisted simulation and navigation systems, we can expect quality improvement and risk reduction. More extensive and radical interventions seem possible.

Computer Simulation↗
PubMed1998

CT-based 3D-planning for dental implantology.

A system for 3D-planning for dental implantology is described. Since exact knowledge of the position of the nervus alv. inf. is critical, we present an algorithm for automated detection of this nerve, which requires only very little initial user interaction. To allow interactive implant placement on comparatively low-cost pc hardware we developed hybrid visualization techniques, which refrain from using large texture memory and raster engines.

Algorithms↗
PubMed1998

Virtual jaw: a 3D simulation for computer assisted surgery and education.

The jaw is one of the most complex joints in the human body. Its sliding and gliding movements are difficult to understand. Therefore, up to now there exist only mechanical simulations. But there is a strong need for a computer model of the jaw--the virtual jaw--to support physicians and surgeons in diagnoses and preoperative planning. During the preoperative planning of craniofacial operations for example, individual patient data has to be examined and the operation has to be simulated. In the education of physicians such a simulation system gives a much better understanding of the anatomy and functionality of the jaw than static images in text books do. The paper presents a 3D simulation of the human mastication apparatus which can be used for the preoperative planning of craniofacial surgeries as well as the education of dentists and surgeons. It consists of three interacting components: A kinematic model which defines the constraints of the articulation, a model for the mastication muscles and a 3D graphical interface.

Computer Graphics↗
PubMed1998

Neuronavigation--first experiences with three different commercially available systems.

Growing interest in neuronavigation also referred to as frameless stereotaxy has led to the development of various navigational devices employing different localization methods. In 152 procedures the authors have used neuronavigation. Cases included 89 intracranial- and 26 skull base tumours, 9 biopsies, 21 vascular and 7 functional procedures on 144 patients since July 1993. In 75 cases the lesions were located in eloquent areas. In 82% (124) MRI, 13% (18) CT and 5% (8) both imaging methods were employed. Three neuronavigational devices with different localization methods were used for the procedures. The Viewing Wand (VW, ISG, Canada), a multijointed arm was used in 101 procedures. In 15 cases the SPOCS (Aesculap, Germany) consisting of cameras detecting infrared light from LED's mounted on instruments and in 51 cases the microscope-integrated MKM (ZEISS, Germany) was investigated, 15 times two systems were used simultaneously. Mean time necessary for preoperative registration was 23 +/- 13 min (VW), 21 +/- 16 min (SPOCS) and 27 +/- 22 min (MKM) respectively. The mean accuracy of registration measured as RMS was 2.9 +/- 1.2 mm (VW), 3.3 +/- 0.9 mm (SPOCS) and 3.1 +/- 1.0 (MKM) respectively. Regarding intraoperative handling the VW was found to be a robust but sometimes bulky and hindering device whereas the SPOCS was more flexible but with the need of unobstructed visibility between cameras and pointers. The MKM without these restrictions required training to get used to handling.

Adolescent↗
PubMed1997

[Robotics in oral and maxillofacial surgery. Possibilities, chances, risks].

Robot systems are being tested in stereotactic neurosurgical interventions, orthopedic surgery of the hip or knee and advancal endoscopic systems for minimally invasive surgery. In contrast to most industrially manufactured products, objects for medical treatment are characterized by plasticity as well as by complex and individual forms. Thus, features of robots in this field have to be further developed in terms of advanced sensory and specific micromotoric systems. Safety and cooperation between surgeon and robot on the patient in the operating room have to be guaranteed. Extensive three-dimensional diagnosis, computer-aided planning and simulation of the intervention as well as sensory systems that monitor the actual performance of the operation are mandatory parts of this concept. In our interdisciplinary study, we aim to examine whether a robot-given a complete preoperative planning and simulation procedure-is able to perform certain surgical operations more precisely than the surgeon. Examples are drilling with depth control, shaping of bone surface by milling, sawing with defined depth in cranial osteotomies, defined preparation of implant sites and the positioning and insertion of dental and other surgical implants, whereby autonomous employment of the robot is not that which is aspired to in these interventions but rather the interactive support of the surgeon.

Humans↗
PubMed1997

Intraoperative guidance in maxillofacial and craniofacial surgery.

The authors' experiences with intraoperative computer assisted guidance in interventions in oromaxillofacial and craniofacial surgery are reported. The guidance system SPOCS (Surgical Planning and Orientation Computer Systems, Aesculap, Germany) consists of an infrared light emitting system of diodes and camera, an imaging workstation and assorted freehand instruments. The software is an updated version of the well-known Viewing Wand software (ISG Technologies, Canada). In tests on phantoms, the system proved a mean accuracy of less than 1.5 mm. Within the last 15 clinical tests, the system has achieved an accuracy better than 3 mm which, at the moment, the authors estimate to be sufficient to proceed with its clinical evaluation. Using bone screws to register the patient's position, an accuracy in the range of less than 2 mm in relation to bony reference points has been achieved. By visualizing the tip of the instrument in real time, this technique allows surgical interventions, even in anatomically complicated situations, without endangering vital neighbouring structures. The 'offset' function of the software, by which the surgeon can elongate the tip of the instrument virtually, allows the surgeon to analyse structures before they are penetrated by the instrument as in a 'look ahead' operation. The authors expect computer assisted simulation and guidance systems to improve surgical quality and reduce the risks associated with surgical interventions.

Adolescent↗
PubMed1996

Intraoperative computer-assisted neuronavigation in functional neurosurgery.

The clinical experience with a frameless computer-assisted neuronavigational system (ISG. Canada) used in functional neurosurgery is described. The advantage of image-guided surgery is stressed for functional procedures of the cortex with delineation of the gyral pattern, e.g. motor cortex stimulation and procedures at the base of the skull with triplanar and three-dimensional reconstruction of the bony landmarks. A general use of the device for aiming at subcortical targets cannot be recommended. Limitations are the accuracy (< or = 2.2 mm) and software deficiencies and the lack of a reliable fixation of the position sensing arm (wand).

Cerebral Cortex↗
PubMed1996

A communication system supporting simultaneous planning and execution in cranio-maxillo-facial surgery.

This paper describes the development of a system for simultaneous planning and execution of surgical operations in the cranio-maxillo-facial area. Simultaneous planning and execution is the process of taking an implicit task description, planning a sequence of explicit execution commands (e.g. for robots) and monitoring their execution. As the execution planning process is run completely on-line, during the execution of the assembly task, the planning process is highly reactive, based on sensor information about the robot's present environment. In order to meet the problem that medical data are usually complex and need time-consuming preprocessing, an appropriate architecture for evaluating sensor data has been developed. In this paper, a detailed presentation of the phases of execution planning and sensor data evaluation is given. As an example, the execution of a LeFort I osteotomy is presented.

Computer Communication Networks↗
PubMed1996

Simultaneous planning and execution in cranio- and maxillofacial surgery.

This paper describes the development of a system for simultaneous planning and execution of surgical operations in the cranio-maxillo facial area. Simultaneous planning and execution is the process of taking an implicit task description, planning a sequence of explicit execution commands e.g. for robots and monitoring their execution. As the execution planning process is running completely on-line, that means during the actual execution of the assembly task, the planning process is highly reactive based on sensor information about the robot's present environment. In order to meet the problem that medical data is usually complex and needs time-costly preprocessing an appropriate architecture for evaluating sensor data has been developed. In this paper, a detailed presentation of the phases of execution planning and sensor data evaluation is given. As an example, the execution of a LeFort I osteotomy is presented.

Algorithms↗
PubMed1995

Masseter inhibitory reflex threshold: a novel technique for electrophysiological investigation of trigeminal nerve lesions.

The masseter inhibitory reflex was investigated in 60 healthy volunteers, in 38 patients with trigeminal nerve branch lesions in the majority due to dental surgery, and in 9 patients with facial sensory loss and weakness caused by brain hemisphere lesions. The reflex threshold (TR) was almost symmetric both in normal subjects and in the patients with hemisphere lesions. In peripheral trigeminal hypaesthesia, elevation of TR on the lesioned side proved the most sensitive electrophysiological parameter. There was, moreover, some correspondence between the degree of sensory loss in hypaesthesic skin areas and elevation of TR, and recovery from the lesion was associated with TR normalization. Supratentorial lesions, in contrast, may influence the reflex pattern rather than reflex excitability.

Adolescent↗