PubMed Health⌕ Search

Biomedical subjects

W Kunert

Publications and source records attributed to W Kunert.

At least 19 recordsLinked to original sources
PubMed2000

The effect of high-definition imaging on surgical task efficiency in minimally invasive surgery: an experimental comparison between three-dimensional imaging and direct vision through a stereoscopic TEM rectoscope.

BACKGROUND: In 1995, when we first used a high-definition television (HDTV) video system during a laparoscopic cholecystectomy in Tuebingen, we were surprised by the excellence of the spatial impression achieved by an image with improved resolution. Although any improvement in vision systems entails a trade-off among cost, quality, and complexity, high-definition imaging may well become an essential part of 3-D video systems. The aim of this experimental study was to assess the impact of high definition on surgical task efficiency in minimally invasive surgery and to determine whether it is preferable to use a 3-D system or a 2-D system with perfect resolution and color--for instance, HDTV or the three-chip charge-coupled device (3CCD). METHODS: We compared a 3-D video system with the vision through a stereoscopic rectoscope for transanal endoscopic microsurgery (TEM). Because its stereoscopic direct vision is not restricted to either shutter technology or video resolution, TEM optics represents the state of the art. For objective comparison, inanimate phantom models with suturing tasks were set up. The setups allowed the approach of parallel instruments as in TEM operations or via a laparoscopic approach, with oblique instruments coming laterally. Both types of procedure were carried out by highly experienced laparoscopic surgeons as well as those inexperienced in endoscopic surgery. These volunteers worked under 3-D video vision and/or TEM vision. Altogether, the model tasks were performed by 54 different persons. RESULTS: The evaluation did not show a significant (p > 0.05) difference in performance time in all models, but there was a clear trend showing the benefit of a higher resolution. CONCLUSION: We found a tendency for both endoscopically inexperienced and experienced surgeons to benefit from the use of a system with improved resolution (direct vision) rather than a 3-D shutter video system.

Efficiency↗
PubMed1999

The role and future of endoscopic imaging systems.

Visual perception is the main sensory input from the environment in most situations of daily life. It is the only sensory input from the operating field in endoscopic surgery, and thus the qualities of the optical imaging system have a considerable impact on the course of the surgical intervention. Significant improvements have been made recently in various fields of science and engineering, influencing endoscopic imaging systems in experimental and clinical use. Among these are technologies that improve the endoscope itself in terms of providing new visual features, such as fogging prevention and plastic images, using new illumination techniques. Other developments concern the improvement of image resolution and color fidelity through new charge-coupled device (CCD) sensors or alternative techniques for image creation. Finally, the combination of endoscopic technologies with robotics provides for intuitive and more efficient direction of the line of sight.

Endoscopes↗
PubMed1999

Three-dimensional (3-D) video systems: bi-channel or single-channel optics?

BACKGROUND AND STUDY AIMS: This paper presents the results of a comparison between two different three-dimensional (3-D) video systems, one with single-channel optics, the other with bi-channel optics. The latter integrates two lens systems, each transferring one half of the stereoscopic image; the former uses only one lens system, similar to a two-dimensional (2-D) endoscope, which transfers the complete stereoscopic picture. MATERIAL AND METHODS: In our training centre for minimally invasive surgery, surgeons were involved in basic and advanced laparoscopic courses using both a 2-D system and the two 3-D video systems. They completed analog scale questionnaires in order to record a subjective impression of the relative convenience of operating in 2-D and 3-D vision, and to identify perceived deficiencies in the 3-D system. As an objective test, different experimental tasks were developed, in order to measure performance times and to count pre-defined errors made while using the two 3-D video systems and the 2-D system. RESULTS AND CONCLUSION: Using the bi-channel optical system, the surgeon has a heightened spatial perception, and can work faster and more safely than with a single-channel system. However, single-channel optics allow the use of an angulated endoscope, and the free rotation of the optics relative to the camera, which is necessary for some operative applications.

Cholecystectomy, Laparoscopic↗
PubMed1998

Comparative study of two-dimensional and three-dimensional vision systems for minimally invasive surgery.

BACKGROUND: The aim of this comparative study was to gain subjective and objective data to determine for which operative tasks three-dimensional (3-D) vision systems are superior to two-dimensional (2-D) systems and to demonstrate any advantages or disadvantages of 3-D systems. METHODS: A model with five standardized tasks including sewing and knotting was developed to objectively measure performance times and to count technical faults. In our training center for minimally invasive surgery, surgeons involved in basic and advanced laparoscopic courses trained using both 2-D and 3-D vision systems. They subsequently completed analog scale questionnaires to record a subjective impression of comparative ease of operation tasks under 2-D and 3-D vision and to identify perceived deficiencies in the 3-D system. RESULTS: Compared to 2-D vision, the objective performance time was significantly shorter and significantly less mistakes were made using 3-D vision. All operative tasks were subjectively judged significantly easier under 3-D vision. CONCLUSIONS: Users with a normal capability for spatial perception can perform standard tasks more quickly and safely using 3-D vision, and a greater benefit is apparent for more complicated surgical maneuvers.

Depth Perception↗
PubMed1997

Paclitaxel inhibits arterial smooth muscle cell proliferation and migration in vitro and in vivo using local drug delivery.

BACKGROUND: The antineoplastic compound paclitaxel (Taxol) causes an increased assembly of extraordinarily stable microtubules. The present study was designed to characterize the effects of paclitaxel on proliferation and migration of human arterial smooth muscle cells (haSMCs) in vitro and on neointima formation in an in vivo experimental rabbit model. METHODS AND RESULTS: Both monocultures of haSMCs and cocultures with human arterial endothelial cells (haECs) were used. Cell growth after 4, 8, and 14 days was determined in the absence or presence of platelet-derived growth factor-AB (PDGF-AB), basic fibroblast growth factor (bFGF), or thrombin. Nonstop paclitaxel exposure, as well as single-dose applications of paclitaxel for 24 hours or even 20 minutes (0.1 to 10.0 micromol/L), caused a complete and prolonged inhibition of haSMC growth up to day 14, with an IC50 of 2.0 nmol/L. Mitogens or cocultures with stimulating haECs did not significantly attenuate paclitaxel-induced effects. Immunohistochemistry showed characteristic cytoskeletal changes predominantly in the microtubule network. Additionally, in 20 male New Zealand White rabbits, intimal plaques were produced by electrical stimulation. In 10 animals, paclitaxel was locally applied by use of microporous balloons. Histologically, the intima wall area, wall thickness, and degree of stenosis were reduced significantly in paclitaxel-treated animals compared with controls. CONCLUSIONS: Our data show that paclitaxel inhibits haSMC proliferation and migration in a dose-dependent manner in monocultures and cocultures even in the presence of mitogens. Furthermore, paclitaxel prevents neointima formation in rabbits after balloon angioplasty. The long-lasting effect after just several minutes' exposure time makes this lipophilic substance a promising candidate for local antiproliferative therapy of restenosis.

Animals↗
PubMed1997

Efficacy of low-molecular-weight heparin delivery with the Dispatch catheter following balloon angioplasty in the rabbit iliac artery.

Local drug delivery can be achieved with active injection systems or passive contact of a compound with the arterial wall. The Dispatch catheter allows for passive diffusion of drugs from drug compartments while preserving blood flow through the central conduit. The aim of this study was to investigate whether a reduction in neointima formation can be achieved by local delivery of a limited amount of a highly concentrated solution of the low-molecular-weight heparin Reviparin. In 16 New Zealand white rabbits, successful balloon dilatation was performed in both iliac arteries, followed by local delivery of 4 ml Reviparin (1,000 IU/ml). The arteries were harvested at 7, 28, or 56 d following the procedure. The intimal cell layers increased substantially between 7 and 28 d following balloon dilatation with or without local drug delivery. The medial cell layers showed only a little increase. Proliferation of smooth muscle cells reached an early peak after 7 d, with a significantly higher proliferation index following local delivery. The maximum amount of macrophages in the intima and media was detected after 28 d. The lumen area decreased with time and was 0.6 +/- 0.7 mm2 in the local delivery group at 56 d compared with 0.5 +/- 0.5 mm2 in the control group. In conclusion, local delivery of Reviparin with the Dispatch catheter is safe and feasible. However, the infusion of highly concentrated low-molecular-weight heparin over a short period of time did not result in a reduction of neointima formation and restenosis following balloon dilatation in the rabbit iliac artery.

Angioplasty, Balloon, Coronary↗
PubMed1997

[Optics with natural appearing added illumination].

Today's endoscopes use a central frontal illumination which creates huge contrast, no visible shadows, and gives an unnaturally flat impression. In the SIMIC project, a new type of optics has been developed that uses additional illumination fibres ending 3 mm behind the front lens. This gives a more natural and spatial impression of the body cavity, causes shadows that are an improvement when approaching tissue with an instrument, reduces blooming in the foreground, and improves detail reproduction in the background.

Endoscopes↗
PubMed1996

[Comparative study of various 2-D and 3-D vision systems in minimally invasive surgery].

The aim of this comparative study was to gain subjective and objective data to determine for which operative tasks it is useful to work with 3-D rather than 2-D vision systems and to show the advantages and disadvantages of 3-D systems. A series of five standardized tasks like sewing and tying knots was set up to measure performance times objectively and to count errors. Compared with 2-D vision, the performance time was 32% shorter and 43% fewer errors were made under 3-D vision (P < 0.001). In our endoscopic training centre, surgeons involved in basic and advanced laparoscopic courses trained using both 2-D and 3-D vision systems. They subsequently completed analogue scale questionnaires to record a subjective impression of comparative ease of operation tasks under 2-D and 3-D vision, and to identify perceived deficiencies in the 3-D system. In both courses, all operative tasks were judged significantly easier under 3-D vision (P < 0.001). It was concluded that users with a normal capacity for spatial perception can work faster and safer under 3-D vision, especially for more complicated surgical manoeuvres.

Animals↗
PubMed1996

Experimental telemanipulation in endoscopic surgery.

Today's rigid endoscopic instruments limit the intracorporeal mobility of the surgical tool and are a severe impediment for the further spread of endoscopic techniques in operative medicine. Since 1992 flexible, steerable instruments with additional links for pivoting and rotating the tip have been developed and experimentally evaluated. The latest versions of this series of instruments are equipped with electromotors for better handling. The next aim in this development is a fully mobile telemanipulator with six motion axes dedicated to use in endoscopic surgery. Its first tests are planned for 1995. For successful operation of an electric telemanipulator, the man-machine interface (MMI) is of cardinal importance. For the definition of surgical requirements for the MMI, a conventional master-slave manipulator designed for technical application was modified for use in guiding a laparoscopic instrument. Master and slave sites of the system were 1.3 km apart and linked by means of a fiber-optic cable. Using this modified telepresence system, remote laparoscopic cholecystectomy was feasible in a phantom model. In a standardized test series using a test parcours, different parameters of the control system were modified, and their influence on the execution time of the parcours tasks was recorded. Well-suited parameter configurations were found and allowed experimental verification and completion of the important aspects of our concepts for development of an endoscopic manipulator MMI.

Cholecystectomy, Laparoscopic↗
PubMed1996

[Minimally invasive ENT surgery. Progress due to modern technology].

Three fundamentals have to be fulfilled to optimize minimally, invasive surgery: three-dimensional imaging, free maneuverability of the instruments, sensorial feedback. Projection of two pictures from a stereoendoscope and subsequent separation with a LCD shutter allows three-dimensional videoendoscopy to be performed. A high-frequency shutter technique (100/120 Hz) presents pictures from the two video cameras to the right and left eye, respectively, so that the surgeon has spatial vision of the operative field. Steerable instruments have four component: a control unit, rigid shaft, steerable multi-joints, distal effector. The steerable multi-joints give two additional degrees of freedom compared to conventional rigid instruments in endoscopic surgery. For intuitive movements, however, an electronic control system is necessary that is comparable to the "master-slave" principle in remote technology. A remote manipulator system with six degrees of freedom is now available. Additionally, a multifunctional distal tip permits different surgical steps to be performed without changing the instrument. For better control of the instrument and the operative procedure tactile feedback can be achieved with appropriate microsensor systems. Recent projects suggest that an artificial sensor system can be established within the foreseeable future.

Endoscopes↗
PubMed1996

[Comparative study of endoscopic 2-D and 3-D imaging systems].

The aim of this comparative study is to gain subjective and objective data to determine for which operative task it is more useful to work with 3-D than 2-D vision systems, in order to show the advantages and disadvantages of 3-D systems. A parcour with five standardized tasks, e.g., sewing and knotting, were built to measure performance times objectively and to count faults. Compared to 2-D vision the performance time was 32% shorter and 43% less faults were made under 3-D vision (p < 0.001). In our endoscopy training centre, surgeons involved in basic and advanced laparoscopy courses were trained to use both 2-D and 3-D vision systems. They subsequently completed analogue scale questionnaires to record a subjective impression of comparative ease of operative tasks under 2-D and 3-D vision, and to identify perceived deficiencies in the 3-D system. In both course, all operative tasks were judged significantly easier under 3-D vision (p < 0.001). It was concluded that users with a normal capability for spatial perception can work faster and safer under 3-D vision, especially for more complicated surgical manoeuvres.

Attitude of Health Personnel↗
PubMed1993

Intelligent surgical instrument system ISIS. Concept and preliminary experimental application of components and prototypes.

The recent progress in endoscopic surgery, which is highlighted by the complexity of fundoplication, stomach surgery and colorectal surgery, has revealed major restrictions with difficult surgical manipulations. Mobilisation, dissection and suturing techniques are hampered mainly by the limited degrees of freedom of the conventional rigid instruments (translation along and rotation around the longitudinal axis and the limited play in the access channel). The frequent interchange of instruments such as coagulation forceps, scissors and suction-irrigation probe is time-consuming. We have established an interdisciplinary development model with the aim of improving surgical technology, instrument systems, the operation theatre and its environment. Concepts of electronic instrument control and sensoric feedback, and the features of the surgical man-machine-interface are described. The first prototypes of an intelligent steerable instrument system, ISIS, and its optional effectors, e.g. semiautomatic sewing device and multifunctional coagulation instrument, were tested in phantom and animal experiments. System analysis will lead to specially designed operating theatres (minimal invasive surgical operating system MINOS).

Dissection↗
PubMed1990

[An extragonadal retroperitoneal endodermal sinus tumor--results of treatment and treatment sequelae in a 3-year-old boy].

A case of an extragonadal endodermal sinus tumour in a three-year old boy is presented. Complete resection of the retroperitoneal tumour was possible after initial chemotherapy. Combined radio-chemotherapy after tumour removal led to complete remission now lasting for more than 5 years. There was unilateral renal atrophy and diverticulum of the stomach as treatment related complications. The favourable prognosis of this tumour due to intensified treatment is discussed in relation to treatment sequelae. The interdisciplinary approach in treatment of cancer in children is emphasized.

Child, Preschool↗