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Biomedical subjects

Martin Schweiger

Publications and source records attributed to Martin Schweiger.

11 recordsLinked to original sources
PubMed2005

A simplified technique for implantation of left ventricular epicardial leads for biventricular re-synchronization using video-assisted thoracoscopy (VATS).

OBJECTIVE: Cardiac re-synchronization therapy for treatment of heart failure requires transvenous insertion of both a right ventricular and left ventricular pacing lead. Implantation of the latter by way of the coronary sinus often fails. Therefore, alternative techniques for insertion are required. We applied a simple video-assisted surgical technique (VATS) using only two ports for the insertion of left-ventricular screw-in electrodes. METHODS: Fifteen patients (M: 10; F: 5; mean age: 62.2 years; range: 46-76 years) with heart failure meeting the ACC/AHA guidelines for implantation of biventricular pacing underwent transvenous insertion of the right atrial sensor lead and the right ventricular pacing lead. In all of them transvenous implantation of the left ventricular pacing lead failed, and they were planned for VATS. In right-lateral decubitus position and under single-lung ventilation a camera port and a flexible instrumentation port were inserted in the forth intercostal space. By using routine instruments, a T-shaped incision was made lateral to the phrenic nerve and an electrode was screwed in. The lead was guided subcutaneously to the pacemaker. RESULTS: Mean skin-to-skin operating time was 55+/-16 min, no conversion to thoracotomy was necessary. All patients were extubated in the operating room and remained in the intensive care unit for less than 24h. Chest tubes were removed after a mean of 1.6+/-0.5 days and the patients were discharged after a mean of 4+/-1.3 days. Intraoperative and postoperative pacing thresholds at 1 and 7 months were satisfactory in all cases and there was no lead dislocation. All but two patients had an improvement of their NYHA function class. There was neither surgical morbidity nor mortality. CONCLUSIONS: Video-assisted thoracoscopy over two ports seems to be an excellent alternative procedure for epicardial lead implantation. It is readily available and produces good pacing results at a short intervention time and tolerable stress for the patients.

Aged↗
PubMed2005

Local diffusion regularization method for optical tomography reconstruction by using robust statistics.

We formulate a solution to the diffuse optical tomography (DOT) inverse problem as the minimization of an energy functional of the solution and the data. For the solution prior we introduce a local diffusion regularization potential with a threshold based on robust statistics (the Hubert function). We compare results on simulated data for the Hubert function and two other standard regularization functionals, Tikhonov and total variation.

Algorithms↗
PubMed2005

The prognostic validity of the ventricular evoked response (VER) signals in cardiac transplantation.

INTRODUCTION: Computerized heart allograft rejection monitoring (CHARM) used for non-invasive rejection monitoring in heart transplant recipients is based on the analysis of ventricular evoked response (VER) signals. The aim of this study was to evaluate the prognostic validity of the Tslew(C), a parameter calculated from the VER. METHODS: During orthotopic heart transplantation, 2 unipolar fractally coated screw-in leads were implanted epimyocardially, one to the left and one to the right ventricle, and connected to a telemetric pacemaker. Recordings of intramyocardial electrograms were performed routinely at the hospital. Data processing was done, artifacts were eliminated, and trend curves of the patients were displayed. Tslew(C) was calculated from the tangent of VER and evaluated from 105 patients. The patients were divided into survivor and non-survivor groups. For statistical analysis, the 2-tailed t-test was performed. RESULTS: Patients in the non-survivors group compared with the control group showed a significantly lower Tslew(C) in the final follow-up (p < 0.001). The differences were even more impressive in patients with recorded intramyocardial electrograms 30 days before death or with a cardiac reason for death. Tests were performed to find an optimal prognostic threshold of the Tslew(C), and the value of 26 mV was finally found. CONCLUSION: Tslew(C) can function as prognostic factor after orthotopic heart transplantation. Further studies should be initiated to provide the prognostic threshold so that patients would not be forced to show up routinely every 4 weeks for follow-up visits. Patients would only have to be admitted to the hospital if the Tslew(C) were less than this prognostic threshold.

Cardiomyopathy, Dilated↗
PubMed2005

Linear and nonlinear reconstruction for optical tomography of phantoms with nonscattering regions.

Most research in optical imaging incorrectly assumes that light transport in nonscattering regions in the head may be modeled by use of the diffusion approximation. The effect of this assumption is examined in a series of experiments on tissue-equivalent phantoms. Images from cylindrical and head-shaped phantoms with and without clear regions [simulating the cerebrospinal fluid (CSF) filled ventricles] and a clear layer (simulating the CSF layer surrounding the brain) are reconstructed with linear and nonlinear reconstruction techniques. The results suggest that absorbing and scattering perturbations can be identified reliably with nonlinear reconstruction methods when the clear regions are also present in the reference data but that the quality of the image degrades considerably if the reference data does not contain these features. Linear reconstruction performs similarly to nonlinear reconstruction, provided the clear regions are present in the reference data, but otherwise linear reconstruction fails. This study supports the use of linear reconstruction for dynamic imaging but suggests that, in all cases, image quality is likely to improve if the clear regions are modeled correctly.

Algorithms↗
PubMed2005

Gauss-Newton method for image reconstruction in diffuse optical tomography.

We present a regularized Gauss-Newton method for solving the inverse problem of parameter reconstruction from boundary data in frequency-domain diffuse optical tomography. To avoid the explicit formation and inversion of the Hessian which is often prohibitively expensive in terms of memory resources and runtime for large-scale problems, we propose to solve the normal equation at each Newton step by means of an iterative Krylov method, which accesses the Hessian only in the form of matrix-vector products. This allows us to represent the Hessian implicitly by the Jacobian and regularization term. Further we introduce transformation strategies for data and parameter space to improve the reconstruction performance. We present simultaneous reconstructions of absorption and scattering distributions using this method for a simulated test case and experimental phantom data.

Algorithms↗
PubMed2005

Diffuse optical tomography with spectral constraints and wavelength optimization.

We present an algorithm that explicitly utilizes the wavelength dependence of tissue optical properties for diffuse optical tomography. We have previously shown that the method gives superior separation of absorption and scattering. Here the technique is described and tested in detail, and optimum wavelength sets for a broad range of chromophore combinations are discovered and analyzed.

Algorithms↗
PubMed2005

Computational calibration method for optical tomography.

We propose a computational calibration method for optical tomography. The model of the calibration scheme is based on the rotation symmetry of source and detector positions in the measurement setup. The relative amplitude losses and phase shifts at the optic fibers are modeled by complex-valued coupling coefficients. The coupling coefficients can be estimated when optical tomography data from a homogeneous and isotropic object are given. Once these coupling coefficients have been estimated, any data measured with the same measurement setup can be corrected for the relative variation in the data due to source and detector losses. The final calibration of the data for the source and detector losses and the source calibration between the data and the forward model are obtained as part of the initial estimation for reconstruction. The calibration method was tested with simulations and measurements. The results show that the coupling coefficients of the sources and detectors can be estimated with good accuracy. Furthermore, the results show that the method can significantly improve the quality of reconstructed images.

Algorithms↗
PubMed2004

Managing controversy through consultation: a qualitative study of communication and trust around MMR vaccination decisions.

BACKGROUND: Controversy over the measles, mumps, and rubella (MMR) vaccine has reduced uptake, raising concerns of a future disease epidemic. AIMS: To explore parents' accounts of decision making relating to the MMR vaccine controversy, identifying uptake determinants and education needs. DESIGN OF STUDY: Qualitative interviews analysed using the 'framework' approach. SETTING: Five general practices in the Leeds area, 2002-2003. METHOD: Sixty-nine interviews conducted with parents of children aged between 4 and 5 years, and 12 interviews with primary care practitioners, managers and immunisation coordinators serving participating sites. Participants were interviewed one-to-one in a place of their choice. RESULTS: The vaccination decision is primarily a function of parental assessments of the relative acceptability and likelihood of possible outcomes. For most parents the evidence of science and medicine plays little role in the decision. Although local general practitioners and health visitors are trusted information sources, the influence of primary care providers on the vaccination decision is limited by concerns over consultation legitimacy, discussion opportunity, and perceptions of financial and political partiality. Parents and practitioners identify a need for new approaches to support decisions and learning when faced with this and similar healthcare controversies. These include new collaborative approaches to information exchange designed to transform rather than supplant existing parent knowledge as part of an ongoing learning process. CONCLUSION: The study identified new ways in which parents and practitioners need to be supported in order to increase understanding of medical science and secure more informed decisions in the face of health controversy.

Adult↗
PubMed2003

Uniqueness and wavelength optimization in continuous-wave multispectral diffuse optical tomography.

We derive conditions for the unique and simultaneous recovery of chromophore concentrations and scattering coefficients in multispectral continuous-wave diffuse optical tomography. These conditions depend strongly on measurement wavelengths. We introduce and demonstrate a general methodology for choosing those wavelengths, which yields superior separation of scattering from absorption and superior separation of one chromophore from another. Application of these concepts should significantly improve the fidelity of continuous-wave diffuse near-infrared optical tomography in tissues.

Computer Simulation↗
PubMed2003

Optical tomography of a realistic neonatal head phantom.

We have begun clinical trials of optical tomography of the neonatal brain. To validate this research, we have built and imaged an anatomically realistic, tissue-equivalent neonatal head phantom that is hollow, allowing contrasting objects to be placed inside it. Images were reconstructed by use of two finite-element meshes, one generated from a computed tomography image of the phantom and the other spherical. The phantom was filled with a liquid of the same optical properties as the outer region, and two perturbations were placed inside. These were successfully imaged with good separation between the absorption and scatter coefficients. The phantom was then refilled with a liquid of increased absorption compared with the background to simulate the brain, and the absolute properties of the two regions were found. These were used as a priori information for the complete reconstruction. Both perturbations were visible, superimposed on the increased absorption of the central region. The head-shaped mesh performed slightly better than the spherical mesh, particularly when the absorption of the central region of the phantom was increased.

Head↗