Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).
BiomedEng Talks II: Biomedical Engineering: Talks II
10:15am - 11:15am
Session Chair: PD Dr. Stavroula Mougiakakou
Location:DCB, S379, 3rd floor, South Department of Chemistry and Biochemistry, 3rd floor South, Freiestrasse 3, 3012 Bern
Presentations T-025 to T-028
10:15am - 10:30am
HPC FSI Framework for the Simulation of Cardiovascular Flow Systems
Barna Errol Mario Becsek1, Maria Giuseppina Chiara Nestola2, Hadi Zolfaghari1, Dominik Obrist1, Rolf Krause2
1ARTORG Center for Biomedical Engineering Research, University of Bern, Switzerland; 2Institute of Computational Science, Università della Svizzera Italiana, Lugano, Switzerland
We have developed a fluid-structure (FSI) interaction simulation framework for high-performance computing (HPC). Our framework has been validated with benchmarks from literature as well as with analytical benchmark problems. We present a novel approach to handling multi-physics coupling that is based on the concept of immersed domains by employing a variational approach for transferring data. We implicitly solve the finite element elastodynamic equations of the solid domain and use finite differences to discretize the fluid in space. Our framework allows great flexibility in the choice of constitutive laws for elasticity including anisotropic and inhomogeneous materials.
We are currently applying the framework to investigate the hemodynamics of aortic valves with the goal of being able to predict the causes for pathologies such as aortic valve stenosis and regurgitation.
10:30am - 10:45am
Exploitation of Slow Macromolecular Diffusion for Baseline Estimation in MR Spectroscopy by 2D Simultaneous Fitting
André Döring, Victor Adalid, Chris Boesch, Roland Kreis
Department for BioMedical Research, Magnetic Resonance Spectroscopy and Methodology, University of Bern, Switzerland
Synopsis: MR spectroscopy (MRS) is a unique tool to provide information on human brain metabolites. The macromolecular baseline (MMBL) is a major feature of clinical MR spectra: a nuisance on one side that substantially complicates quantification of metabolite content, but a largely untapped source of patho-physiological information, on the other. However, state of the art MRS techniques reveal problems in MMBL prediction. In a new approach we exploit the slow diffusivity of heavy macromolecules in comparison to smaller metabolites for spectral segregation. We suggest to use a non-water-suppressed (nWS) diffusion-weighted MR spectroscopy (DWS) sequence in combination with simultaneous 2D modeling to define the MMBL in human brain.
Methods: A DWS sequence was used in 13 healthy subjects to record motion corrected spectra from occipital gray matter on a clinical 3T MR scanner. High quality spectra were obtained by collecting and averaging cohort-wide acquisitions. The MMBL and the apparent diffusion coefficients (ADCs) were estimated in a 2D simultaneous fit. Two models were investigated for the description of the MMBL: PreDefined Resonances (PDR) using prior knowledge conditions (adapted from 9.4T) and model-free approach simulating the MMBL by 80 Equally Spaced Resonances (ESR).
Results: The qualitative comparison of PDR vs. ESR reveals larger deviations between fit and measurement for PDR, indicating too restrictive predefinitions. The quantitative comparison of both models shows that the MMBL-definition method influences the ADC estimates and precisions for small metabolites. The ESR approach was found to yield a comparable feature-rich MMBL at 3T as usually found at higher field strengths.
Conclusion: It is shown that use of DWS in combination with 2D simultaneous fitting is suitable to define the MMBL solely based on diffusion properties even on clinical scanners. For instance, this technique can be applied in brain tumor diagnosis, classification and prognosis.
10:45am - 11:00am
Morphometric Investigation of the Canine Caudal Cervical Intervertebral Space: An ex-vivo CT Study
Sebastian Christoph Knell1, Antonio Pozzi1, Thomas Steffen2,3, Lucas Adam Smolders1
1Clinic for Small Animal Surgery, Vetsuisse Faculty, University of Zurich, Switzerland; 2Orthopedic Research Laboratory, University of Montreal, Canada; 3Musculoskeletal Research Unit, Vetsuisse Faculty, University of Zurich, Switzerland
Introduction: Implantation of an intervertebral disc (IVD) prosthesis is a novel treatment strategy for caudal cervical spondylomyelopathy in dogs. However, current prosthesis designs are suboptimal because of a mismatch between the prosthesis and the dimensions of the canine IVD space. The purpose of this study was to determine for C4-C5, C5-C6 and C6-C7 1) the size and shape of the cranial and caudal endplates and 2) the IVD space dimensions and angles in neutral position and in motion extremes.
Material and Methods: CT images were obtained from 5 canine spinal specimens, which were positioned in neutral position and thereafter loaded in flexion, extension and lateral bending. Images were used to determine and compare for C4-C5, C5-C6, and C6-C7: 1) height, width and shape of the cranial and caudal endplates, and 2) angle and dimensions of the IVD space in the different positions. A mixed model was used to compare between segments and postures for the outcome measures. Significance was set to p<0.05.
Results: Endplate size and shape, and IVD angle and dimensions were similar between the three tested segments. Endplate shape and size were significantly different between cranial and caudal endplates. Flexion induced a significant reduction in disc height in the ventral 36% of the IVD, whereas extension induced a significant decrease in the dorsal 20% of the IVD. The dimensions of the central 44% remained unchanged during all positions.
Discussion/Conclusion: The canine caudal cervical IVD space has unique dimensions and dynamic characteristics. These findings should be respected when designing IVD prostheses for canine cervical spondylomyelopathy.
The project was supported by the Small Animal Foundation, University of Zurich.
11:00am - 11:15am
Panoramic Opto-Electrical Mapping and Stimulation (POEMS) of the Heart
Michael Rieger, Stephan Rohr
Department of Physiology, University of Bern, Switzerland
Introduction and Aim: The use of optogenetic reporters and actuators of transmembrane voltage in cardiac tissue offers unprecedented possibilities to investigate basic mechanisms governing cardiac electrical function in both health and disease. Multimodal measurement systems suitable to simultaneously stimulate actuators and measure the electrical response in optogenetically-modified hearts are, however, still missing.
Methods and Results: We developed a prototype system permitting simultaneous optical- and electrical stimulation as well as optical- and electrical recording from Langendorff-perfused hearts. The system consists of a 3D heart container with embedded fiberoptic cables and silver electrodes. Electrical signals from electrodes are fed to custom-developed amplifiers for recording spatially resolved ventricular electrograms (EGs). At the same time, electrodes can be used to perform spatially defined electrical stimulation of the hearts. The fiberoptic cables serve to record signals from optogenetic reporters from the heart or to perform spatially defined stimulation of optogenetic actuators. Optical recordings are performed with a high-speed CMOS camera. Initial validation experiments of the POEMS system wild type mice (C57bl6) stained with Di-8-ANNEPS showed that the POEMS system permits the spatiotemporally resolved simultaneous detection of optical- and electrical signals from hearts in sinus rhythm.
Conclusion: The results of this study illustrate that high-density optical- and electrical stimulation and recording sites arranged as to form a tight container holding Langendorff-perfused hearts permits multimodal interrogation of the electrophysiological function of hearts ex vivo.