Dr. Martin Weiser

Projects as a project leader

• CH20

  Stochasticity driving robust pattern formation in brain wiring

  Dr. Max von Kleist / Dr. Martin Weiser

  Project heads: Dr. Max von Kleist / Dr. Martin Weiser
  Project members: Marian Moldenhauer / Maureen Smith
  Duration: 01.06.2017 - 31.12.2019
  Status: running
  Located at: Freie Universität Berlin
  

  Description

  During brain development, synaptic connection patterns are formed in an extremely robust manner. As the interconnection patterns are much too complex to be encoded directly in the genome, they must emerge from simpler rules. In this project we investigate mechanistic stochastic models of axon growth and filopodial dynamics, checking whether their simulation leads to connection patterns and dynamics as observed in vivo, and with the same robustness.
  
  http://www.zib.de/projects/BrainWiring

• CH8

  X-ray based anatomy reconstruction with low radiation exposure

  Hon.-Prof. Hans-Christian Hege / Dr. Martin Weiser / Dr.-Ing. Stefan Zachow

  Project heads: Hon.-Prof. Hans-Christian Hege / Dr. Martin Weiser / Dr.-Ing. Stefan Zachow
  Project members: Dennis Jentsch
  Duration: -
  Status: completed
  Located at: Konrad-Zuse-Zentrum für Informationstechnik Berlin
  

  Description

  Medical imaging is essential in diagnostics and surgery planning. For representation of bony structures different imaging modalities are used; the leading methods are X-ray projection (projectional radiography) and CT. Disadvantage of these imaging techniques is the ionization caused by X-rays, particularly in CT, where the dose is 250-500 times higher than in classic X-ray projection. From the clinical perspective therefore one would like to replace CT acquisitions by a few possible X-ray projections. The project deals with the ill-posed inverse problem of 3D reconstruction of bony structures from 2D radiographs. Virtual radiographs are generated from virtual bone structure models; these are compared with clinical patient images and incrementally changed until a sufficiently accurate bone model is found whose virtual projections fit to the measured data. By using a statistical shape model as prior knowledge it is possible to formulate a well-posed optimization problem in a Bayesian setting. Using gradient methods and multilevel/multiresolution methods for both the reconstruction parameters and image data, good computational performance is achieved. Uncertainty quantification techniques can be applied to describe the spatially varying accuracy of the reconstructed model. Finding best X-ray projections (recording directions) minimizing both uncertainty and radiation exposure leads to a design of experiments problem. Two flavors of this design optimization are considered: An all-at-once approach finding the best image acquisition setup before any X-ray projections are performed, and a sequential approach determining the best next projection direction based on the accumulated knowledge gained from the previously taken images.
  
  http://www.zib.de/projects/x-ray-based-anatomy-reconstruction-low-radiation-exposure

• CH9

  Adaptive algorithms for optimization of hip implant positioning

  Dr. Martin Weiser / Dr.-Ing. Stefan Zachow

  Project heads: Dr. Martin Weiser / Dr.-Ing. Stefan Zachow
  Project members: Marian Moldenhauer
  Duration: -
  Status: completed
  Located at: Konrad-Zuse-Zentrum für Informationstechnik Berlin
  

  Description

  This project aims at a software environment supporting computer-assisted planning for total hip joint replacement by suggesting implant positions optimized for longevity of bone implants. The aim is to pre-operatively assess stress distribution in bone and to determine an optimal implant position with respect to natural function and stress distribution to prevent loosening, early migration, stress shielding, undesired bone remodeling, and fracture. Increasing the longevity of implants will help to enhance quality of life and reduce the cost of health care in aging societies. Focus of the research is the development of efficient optimization algorithms by adaptive quadrature of the high-dimensional space of daily motions and appropriate choice of tolerances for the underlying dynamic contact solver.
  
  http://www.zib.de/projects/adaptive-algorithms-optimization-hip-implant-positioning

• CH-AP11

  Wear Simulation of Knee Implants and Shape Optimization for Patient-group specific Wear Minimization

  Prof. Dr. Ralf Kornhuber / Dr. Martin Weiser

  Project heads: Prof. Dr. Ralf Kornhuber / Dr. Martin Weiser
  Project members: -
  Duration: 01.07.2013 - 30.12.2016
  Status: completed
  Located at: Konrad-Zuse-Zentrum für Informationstechnik Berlin
  

  Description

  For the market admittance of joint implants, a standardized wear test has to be performed. During the design phase, similar tests are necessary as well. Those tests are very cost and time expensive. The project aims at the development of simulation and optimization methods for substituting some of the design phase tests by simulations. Additionally, the design process shall be accelerated by shape optimization, and the offered implants be tailored to the patient population by taking different patient groups into account.
  
  Focus of the work at ZIB is the long-time integration of wear trajectories. The implant geometry is modified due to wear, which in turn changes the wear rate. The evolution is determined by the wear of one load cycle, the simulation of which is computationally expensive. We develop adaptive methods for controlling tolerance, order, and time step for an efficient simulation of many load cycles.
  
  http://www.zib.de/projects/wear-simulation-knee-implants-and-shape-optimization-patient-group-specific-wear-minimization

• GV-AP8

  In vivo and in silico analyses in humans: Cartilage loading of patients' individual knees - the role of soft tissue structures

  Hon.-Prof. Hans-Christian Hege / Dr. Martin Weiser

  Project heads: Hon.-Prof. Hans-Christian Hege / Dr. Martin Weiser
  Project members: -
  Duration: 01.10.2014 - 31.01.2019
  Status: completed
  Located at: Konrad-Zuse-Zentrum für Informationstechnik Berlin
  

  Description

  While a relationship between knee joint laxity and osteoarthritis is often assumed, the exact mechanism is not yet fully understood. It is not clear how stabilization by either the cross ligaments or muscle forces affect the local cartilage stress and strain. We develop a comprehensive analysis tool for individual patients. On one hand, we couple a dynamic multibody model to a quasistatic contact solver for the cartilage and validate it against in vivo measurement data from patient groups at Charite. On the other hand, we develop visualization and statistical analysis tools that allow to understand the impact of anatomical variation and cross ligament loss on the mechanical loading of cartilage and correlate this to osteoarthritis progression.
  
  http://www.zib.de/projects/vivo-and-silico-analyses-humans-cartilage-loading-patients%E2%80%99-individual-knees-%E2%80%93-role-soft-tissue