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J Hesser

Publications and source records attributed to J Hesser.

16 recordsLinked to original sources
PubMed2004

Live-wires using path-graphs.

OBJECTIVES: This article discusses our new Path-Graph approach for the interactive Live-Wire segmentation method in 2D applied to pre-segmented data. Furthermore, we examine whether or not the Live-Lane extension provides advantages in combination with pre-segmentation. METHODS: We automatically over-segment the image data in a preprocessing step, using region growing with an automatic seed point generation. The Live-Wire algorithm is applied on this mosaic data by using the outlines of the homogeneous regions as the basis for graph building. We present a new definition of this underlying graph where the edges of the standard graphs are turning into vertices and the vertices of the new graph are defined by the edge connectivity in the standard graph. For better differentiation we name our new graph Path-Graph and the original defined graph Node-Graph. RESULTS: The quality evaluation is done by comparing our segmentation results with existing model data. We show that using the Path-Graph as basis for the Live-Wire algorithm instead of the Node-Graph allows for a finer segmentation. We achieve a reduction of incorrectly classified pixels by 20.66 per cent and a decrease of the mean boundary deviation by 11.61 per cent. Since savings on cost tree calculations are compensated by additional computation time required to compute the Live-Lanes, a performance loss of 2.41 per cent is measured. CONCLUSIONS: Our redefinition of the underlying graph increases the quality of the Live-Wire segmentation. The Live-Lane extension in combination with pre-segmentation is not justified for our data.

Algorithms↗
PubMed2002

[Cathi-training on virtual patients for catheter interventions].

In this paper we present a trainings system for catheter interventions, especially PCTAs also called ballon dilatation. Despite the large number of such interventions the education of the cardiologist is still based on learning on the patient. This means risk to the patient and additional cost. To overcome these problems we developed the CathI system (Catheter Instruction System), a realistic computerbased training system. It provides the physician with the same equipment found in a catheter laboratory, e.g. original control instruments for the flouroscopy system, syringes, catheters, and guide wires. CathI only replaces patient and C-arm by a virtual patient and a virtual x-ray system.

Angioplasty, Balloon, Coronary↗
PubMed2002

Operation planning of correction osteotomies in 3D.

This paper discusses an operation planning system for correction osteotomies. It is based on 3D data obtained from CT/MR of the bone and it allows to perform a 3D planning. The physician can individually determine anatomical landmarks for measuring geometric parameters of the bone like length, angle and torsion angle. In a virtual scene he or she can set a single cut or can remove/insert a wedge, dissecting the bones. The bone parts can be rearranged in 3D space. Optimization routines allow that the physician only defines the position of the cut, the orientation of the cut plane, the rearrangement of the bone and the optimization for the maximal overlap of the cortical bone can be processed automatically. The system is currently in use at the Trauma department at the University of Ulm. A case study shows the results by applying this system.

Bone Malalignment↗
PubMed2001

[Computer-assisted surgery: developments and prospects in 2001. Results of a workshop at Schloss Reisenburg, 23-24 November 2000].

The progress in computer assisted surgery (CAS) is influenced by new technologies in imaging as well as by the input of the users. At present, CAS procedures are established in dorsal spine instrumentation, prosthetics and long bone surgery. Present status and future of CAS was a topic of an expert meeting at the Reisensburg castle. Imaging will speed up in the future using multi-detector techniques. C-arm navigation will gain more information using the 3D technology intraoperatively. CT based navigation procedures are standard in spine and will be established in pelvic surgery. CAS in robotics at the moment means the use of robot-assistance. A new concept is the modality-based navigated surgery, which can be used at various skeletal locations. Visualization of patient data will improve using 3D semi-transparencies with real time update. In the future it will be mandatory to find algorithms to fuse the different possibilities and techniques. A new concept of surgical training is necessary to teach CAS procedures. Therefore discussion must go on to improve these systems.

Arthroplasty, Replacement, Knee↗
PubMed2001

[Computer assisted surgery, 2001 development and prospects. Results of a congress at Reisensburg Castle, 23-24 November 2000]].

The progress in computer assisted surgery (CAS) is influenced by new technologies in imaging as well as by the input of the users. At present, CAS procedures are established in dorsal spine instrumentation, prosthetics and long bone surgery. Present status and future of CAS was a topic of an expert meeting at the Reisensburg castle. Imaging will speed up in the future using multi-detector techniques. C-arm navigation will gain more information using the 3D technology intraoperatively. CT based navigation procedures are standard in spine and will be established in pelvic surgery. CAS in robotics at the moment means the use of robot-assistance. A new concept is the modality-based navigated surgery, which can be used at various skeletal locations. Visualization of patient data will improve using 3D semi-transparencies with real time update. In the future it will be mandatory to find algorithms to fuse the different possibilities and techniques. A new concept of surgical training is necessary to teach CAS procedures. Therefore discussion must go on to improve these systems.

Forecasting↗
PubMed2001

Computer assisted treatment of pelvis fractures.

The presented approach is the realization of a minimal invasive treatment of pelvis fractures using the computer aided surgery (CAS). Main problem of tracking of major bone fragments after reposition is solved by implementing of 3D ultrasound to obtain intraoperative bone surfaces. Preoperative and intraoperative data sets are matched. Major fragments are tracked. The real time navigation is possible.

Feasibility Studies↗
PubMed2001

Computer simulation of osteotomy correction.

This paper describes a novel approach to correct osteotomy deformities of long bones using virtual reality and image processing techniques on personal computers. The discussed method allows to simulate osteotomy corrections by implementing a single cut and a rearrangement of the dissected bone parts. It allows the surgeon to directly control the pre-operative situation and the post-operative result of the simulation by comparing bone-length, angles, and torsion of the bone. In addition, he or she obtains the coordinates and angles of the planned cut relative to anatomical landmarks.

Bone Malalignment↗
PubMed1997

Real-time direct volume rendering in functional magnetic resonance imaging.

Direct volume rendering is a visualization method that allows display of all information hidden in three-dimensional data sets of, for example, computed tomography or magnetic resonance imaging (MRI). In contrast to commonly used surface rendering methods, these algorithms need no preprocessing but suffer from a high computational complexity. A real-time rendering system, VIRIM (Vitec: Visualization Technology GmbH, Mannheim, Germany), cuts down rendering times of minutes on normal workstations to an interactive rate of 1 second or less. The immediate visual feedback allows interactive steering of the visualization process to achieve insight into the internal three-dimensional structure of objects. Additional information is obtained by using an interactive gray-value segmentation tool that both allows segmentation of the data set according to bone, tissue, and liquor and display of multifunctional data sets (e.g., functional MRI [fMRI] data sets). Thus, real-time direct volume rendering allows segmentation and volume data processing of functional and anatomical MR data sets simultaneously. As this method can be integrated in the clinical routine, it is of great importance for real-time motion artifact detection and the interpretation of fMRI data acquired during cognitive experiments with normal subjects and psychiatric patients. Because of the free programmability of VIRIM, more complex matching procedures are currently being investigated for future implementation.

Brain↗
PubMed1991

Cardiovascular responses to norepinephrine and arginine vasopressin infusion in chronically catheterized fetal lambs.

Fetal cardiovascular responses to infused norepinephrine (NE) and arginine vasopressin (AVP) were compared in bilaterally vagotomized and chronically catheterized (control) fetal lambs. In the control fetuses, NE infusion was characterized during the first five minutes by a decreased fetal heart rate (FHR) and increased mean arterial blood pressure (MABP) and by a preejection period (PEP) followed by a gradual return to the original values. NE infusion in vagotomized fetuses was followed by tachycardia, decreased PEP without the initial prolongation and an MABP response similar to that in the controls. AVP in control fetuses caused a persistent decrease in the FHR and increase in MABP and PEP. Vagotomy affected only the FHR response: the decrease was persistent but smaller. AVP produced persistent fetal cardiovascular responses regardless of vagotomy; however, the biphasic response FHR pattern, suggestive of NE tachyphylaxis, was eliminated by vagotomy.

Animals↗
PubMed1990

A randomized trial of routine prenatal ultrasound.

Nine hundred fifteen of 2171 pregnant patients had no indication for ultrasound at their first prenatal visit and were randomly assigned to receive either a single routine screening ultrasound or usual prenatal care. The estimated date of confinement was altered in 24.9% of routine-ultrasound patients and in 11.6% of usual-care patients through ultrasound examinations obtained for a subsequent clinical indication. Of these, 8.3% of routine-ultrasound and 5.2% of usual-care patients had gestational age errors of 2 weeks or more. There were no differences between the groups in inductions for post-dates pregnancy (7.0 versus 7.5%; P = .87), total inductions (22.6 versus 24.9%; P = .61), or adverse perinatal outcomes (6.7 versus 8.3%; P = .63). Both sets of twins were detected in the screened group. In the usual-care group, five of seven pairs of twins (71%) were diagnosed by 24 weeks' gestation. There was no benefit found from routine ultrasound as performed in this study.

Adult↗
PubMed1987

Effects of norepinephrine on lung fluid flow rate in the chronically catheterized fetal lamb.

The influence of norepinephrine on lung fluid flow rate was studied in seven chronically catheterized fetal lambs. Lung fluid was collected through a catheter inserted into the fetal trachea. In six experiments, continuous saline solution infusion for 1 hour followed by equivolumnar norepinephrine (3.0 micrograms/min) for 1 hour via the fetal jugular vein was carried out. In three additional experiments (two fetuses), a 3.0 mg intravenous bolus of propranolol was administered before norepinephrine infusion. Saline solution infusion did not influence the lung fluid flow rate or fetal biophysical and biochemical parameters. Norepinephrine increased fetal blood pressure by 22% and decreased lung fluid flow by 45% from control values. Lung fluid flow rate recovered within 2 hours after the end of the norepinephrine infusion. Pretreatment with propranolol did not alter the results. In addition to previous reports that demonstrated beta-sympathomimetic agonist-enhanced reabsorption of lung fluid from fetal alveolar epithelial cells, our present results suggest that a reduction in fetal lung fluid secretion may be implemented as well through stimulation of alpha-sympathomimetic receptor sites in the pulmonary vasculature.

Animals↗
PubMed1985

Experimentally produced sinusoidal fetal heart rate pattern in the chronically instrumented fetal lamb.

A sinusoidal fetal heart rate and elevated fetal arginine vasopressin levels were found in two bled fetal lambs. Arginine vasopressin was continuously infused intravenously in chronically instrumented fetal lambs at rates ranging between 1.0 and 90 mlU/kg/min. No sinusoidal heart rate occurred in 21 experiments on six control animals with intact vagal nerves. Atropine at doses less than 0.4 mg had no effect (six experiments on three animals). Higher doses of atropine (greater than 1.2 mg) resulted in sinusoidal heart rate (24 experiments on six animals). Twenty-three infusions were performed in five bilaterally vagotomized fetuses, and the sinusoidal heart rate was successfully induced in 17 experiments. The arginine vasopressin infusion rate was less than 1.5 mlU/kg/min on the six occasions in which the sinusoidal heart rate did not appear. All sinusoidal heart rate patterns were associated with fluctuation of fetal arterial pressure at the same frequency. There was a linear correlation between the amplitude of sinusoidal heart rate and magnitude of arterial blood pressure fluctuation. The amplitude of sinusoidal heart rate increased with the concentration of arginine vasopressin infused. Modification of sinusoidal heart rate pattern was attempted with use of sympathetic agonists and antagonists. The possible etiology and mechanisms of sinusoidal heart rate pattern are discussed.

Animals↗
PubMed1981

Some epidemiologic studies of HBSAg in Greece.

In an epidemiologic study in 17 villages from different areas of Greece, 2898 persons were examined in order to find possible relations between HBSAg prevalence, altitude and endemic goitre morbidity. A lower prevalence with a significant difference was found in areas with a high altitude as compared with those with a low one, in endemic goitre than non-endemic areas, and in low altitude endemic than in low altitude non-endemic areas. Goitrous subjects had a lower HBSAg prevalence than non-goitrous subjects, but the difference was of borderline significance. The results can probably be explained by the presence of an environmental factor associated with altitude acting together with a host factor predisposing to endemic goitre and favouring the immunity to HBV infection.

Altitude↗