Joachim Georgii - Profile on Academia.edu (original) (raw)

Papers by Joachim Georgii

Fast Numerical Simulation of Focused Ultrasound Treatments During Respiratory Motion With Discontinuous Motion Boundaries

IEEE transactions on bio-medical engineering, 2017

Focused ultrasound (FUS) is rapidly gaining clinical acceptance for several target tissues in the... more Focused ultrasound (FUS) is rapidly gaining clinical acceptance for several target tissues in the human body. Yet, treating liver targets is not clinically applied due to a high complexity of the procedure (noninvasiveness, target motion, complex anatomy, blood cooling effects, shielding by ribs, and limited image-based monitoring). To reduce the complexity, numerical FUS simulations can be utilized for both treatment planning and execution. These use-cases demand highly accurate and computationally efficient simulations. We propose a numerical method for the simulation of abdominal FUS treatments during respiratory motion of the organs and target. Especially, a novel approach is proposed to simulate the heating during motion by solving Pennes' bioheat equation in a computational reference space, i.e., the equation is mathematically transformed to the reference. The approach allows for motion discontinuities, e.g., the sliding of the liver along the abdominal wall. Implementing ...

Segmentation of hepatic artery in multi-phase liver CT using directional dilation and connectivity analysis

Medical Imaging 2016: Computer-Aided Diagnosis, 2016

Simulation and Visualization to Support Breast Surgery Planning

Lecture Notes in Computer Science, 2016

Integration of Focused Ultrasound with Radiotherapy: the benefit of the hyperthermia field

ABSTRACT Conformal External Beam Radiotherapy (EBRT) and High Intensity Focused Ultrasound (HIFU)... more ABSTRACT Conformal External Beam Radiotherapy (EBRT) and High Intensity Focused Ultrasound (HIFU) are important weapons in oncology, but both suffer from inherent limitations. Their combination (FUS/RT) can overcome these difficulties and, possibly, be more effective than the simple addition of the two techniques. This is a first attempt to simulate the HIFU-Hyperthermia field around an ablated region and evaluate the potential enhancement effect on EBRT.

Vmv, 2009

We present a novel real-time method for geometric displacement mapping on arbitrary 2-manifold tr... more We present a novel real-time method for geometric displacement mapping on arbitrary 2-manifold triangle meshes. It is independent of the surface resolution and allows very fine geometric details to be added. We first compute a local surface parameterization using barycentric particle tracing and a constrained mass-spring system. This system satisfies the hard constraint of keeping all mass points on the surface. We propose a novel, entangled spring topology that is regularly 6-connected and has a chromatic number of 2. Therefore, the system can be efficiently solved on the GPU using a Gauss-Seidel solver. To render the displaced surface, we introduce a new GPU technique to cut out a surface patch at sub-pixel precision. The displacement mesh is then smoothly blended into the resulting opening. We show that our method overcomes common problems of displacement mapping such as limited resolution of the base surface and the need for a low-distortion global parameterization.

System and method for on-the-fly segmentations for image deformations

In this paper, we present a multigrid framework for constructing implicit, yet interactive solver... more In this paper, we present a multigrid framework for constructing implicit, yet interactive solvers for the governing equations of motion of deformable volumetric bodies. We have integrated linearized, corotational linearized and non-linear Green strain into this framework. Based on a 3D finite element hierarchy, this approach enables realistic simulation of objects exhibiting an elastic modulus with a dynamic range of several orders of magnitude. Using the linearized strain measure, we can simulate 50 thousand tetrahedral elements with 20 fps on a single processor CPU. By using corotational linearized and non-linear Green strain, we can still simulate five thousand and two thousand elements, respectively, at the same rates.

Tissue Stiffness Assignment

Image deformation using physical models

Advanced Volume Rendering for Surgical Training Environments

International Journal of Computer Assisted Radiology and Surgery

Real-Time Simulation and Visualization of Deformable Objects

... 200,000 el-ements can be simulated at a rate of 10 time steps per second. ... Al-though many ... more ... 200,000 el-ements can be simulated at a rate of 10 time steps per second. ... Al-though many papers have been published in this area, a large majority of ... Framework for Real-Time Simulation ofDeformable Volumes [GW05a,GW06a] Interactive GPU-based Collision Detection ...

Fast and reliable methods for predicting and monitoring in-vivo bone strength are of great import... more Fast and reliable methods for predicting and monitoring in-vivo bone strength are of great importance for hip joint replacement. To avoid adaptive remodeling with cortical thinning and increased porosity of the bone due to stress shielding, in a preoperative planning process the optimal implant design, size, and position has to be determined. This process involves interactive implant positioning within the bone as well as simulation and visualization of the stress within bone and implant due to exerting forces. In this paper, we present a prototype of such a visual analysis tool, which, to our best knowledge, provides the first computational steering environment for optimal implant selection and positioning. This prototype considers patient-specific biomechanical properties of the bone to select the optimal implant design, size, and position according to the prediction of individual load transfer from the implant to the bone. We have developed a fast and stable multigrid finite-element solver for hexahedral elements, which enables interactive simulation of the stress distribution within the bone and the implant. By utilizing a real-time GPU-method to detect elements that are covered by the moving implant, we can automatically generate computational models from patient-specific CT scans in real-time, and we can instantly feed these models into the simulation process. Hardware-accelerated volume ray-casting, which is extended by a new method to accurately visualize sub-hexahedron implant boundaries, provides a new quality of orthopedic surgery planning.

If two closed polygonal objects with outfacing normals intersect each other there exist one or mo... more If two closed polygonal objects with outfacing normals intersect each other there exist one or more lines that intersect these objects at at least two consecutive front or back facing object points. In this work we present a method to efficiently detect these lines using depth-peeling and simple fragment operations. Of all polygons only those having an intersection with any of these lines are potentially colliding. Polygons not intersected by the same line do not intersect each other. We describe how to find all potentially colliding polygons and the potentially colliding pairs using a mipmap hierarchy that represents line bundles at ever increasing width. To download only potentially colliding polygons to the CPU for polygon-polygon intersection testing, we have developed a general method to convert a sparse texture into a packed texture of reduced size. Our method exploits the intrinsic strength of GPUs to scan convert large sets of polygons and to shade billions of fragments at interactive rates. It neither requires a bounding volume hierarchy nor a pre-processing stage, so it can efficiently deal with very large and deforming polygonal models. The particular design makes the method suitable for applications where geometry is modified or even created on the GPU.

Real-time Breast Deformation using Non-linear Tissue Properties

We present an interactive technique for the registration of captured images of elastic and rigid ... more We present an interactive technique for the registration of captured images of elastic and rigid body parts in which the user is given flexible control over material specific deformation properties. Our method can effectively handle arbitrary stiffness distributions and it achieves an accurate matching without sacrificing the physical correctness of the simulated deformations. The algorithm consists of three steps, which are performed iteratively until an optimal spatial mapping is determined: First, the optical flow is used to predict an initial image transformation. Second, a priori knowledge of the deformation model is used to refine the predicted field. A physics-based filter operation generates a transformation that is consistent with the model of linear elasticity. Third, the process is repeated using the displaced template image. To achieve accurate image deformations we employ implicit multigrid solvers using finite differences (optical flow) and finite elements (linear elasticity). The robustness and accuracy of our method is validated using synthetic and real clinical data composed of heterogeneous materials exhibiting different stiffness characteristics.

Electronic transactions on numerical analysis ETNA

In this paper, we present a numerical algorithm for computing products of the form R KR T , where... more In this paper, we present a numerical algorithm for computing products of the form R KR T , where R, R T and K are sparse matrices. By reformulating the problem into the simultaneous processing of a sequential data and control stream, cache miss penalties are significantly reduced. Even though the algorithm increases memory requirements, it accelerates sparse matrix products on recent processor architectures by a factor of up to 4 compared to previous approaches. We apply the algorithm to compute consistent system matrices at different resolution levels in a dynamic multigrid elasticity simulation, and we show its efficiency for nested and non-nested mesh hierarchies.

Journal of Therapeutic Ultrasound, 2014

Real-Time Approaches for Model-Based PIV and Visual Fluid Analysis

Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2009

Automatic Real-time Position Correlation for Multi-view Tomosynthesis Images to Facilitate the Breast Reading Workflow

PURPOSE/AIM Due to the 3D nature of tomosynthesis, manual position correlation between different ... more PURPOSE/AIM Due to the 3D nature of tomosynthesis, manual position correlation between different acquisitions is time expensive and requires complex thinking. We show how our automatic real-time position correlation method can facilitate comparison between different tomosnythesis images as well as mammograms. CONTENT ORGANIZATION Our workstation features sets of two tomosynthesis images of the same patient acquired at different angles. The user can view both 3D images without our method being active to illustrate the difficulties of manually correlating finding positions between views. If our method is active, the users selected position in one view will automatically and in real-time be correlated to a position in the other view. Additionally, the correlation from one tomosynthesis image to the same patients mammograms (acquired with different compressions or at different angles) is also supported and shown. SUMMARY The presented workstation will show the difficulties of manual cor...

Supporting the Multi-modal Breast Reading Workflow by an Automatic Position Correlation Method for Tomosynthesis and Breast Volume Ultrasound Images

PURPOSE/AIM Tomosynthesis in combination with the 3D breast ultrasound modality ABVS (automated b... more PURPOSE/AIM Tomosynthesis in combination with the 3D breast ultrasound modality ABVS (automated breast volume scanner) has the potential to increase the diagnostic accuracy of breast cancer detection and diagnosis by correlating findings in both modalities. However, the manual position correlation between these differently and highly deformed 3D images is time-expensive and requires complex thinking. We will show how our automatic real-time position correlation method can support the simultaneous navigation of these different datasets. CONTENT ORGANIZATION The presented workstation will simultaneously show a patients tomosynthesis and 3D ultrasound image. When the user navigates through one of the images with a cursor position, our method will automatically show the correlated cursor position in the other view. Additionally, the user has the option to deactivate the automatic method, which will illustrate the difficulties of manually correlatig corrsponding positions in these images...