Slime mould computes planar shapes

Computing a polygon defining a set of planar points is a classical problem of modern computational geometry. In laboratory experiments we demonstrate that a concave hull, a connected alpha-shape without holes, of a finite planar set is approximated by slime mould Physarum polycephalum. We represent planar points with sources of long-distance attractants and short-distance repellents and inoculate a piece of plasmodium outside the data set. The plasmodium moves towards the data and envelops it by pronounced protoplasmic tubes

Design of testbed and emulation tools

The research summarized was concerned with the design of testbed and emulation tools suitable to assist in projecting, with reasonable accuracy, the expected performance of highly concurrent computing systems on large, complete applications. Such testbed and emulation tools are intended for the eventual use of those exploring new concurrent system architectures and organizations, either as users or as designers of such systems. While a range of alternatives was considered, a software based set of hierarchical tools was chosen to provide maximum flexibility, to ease in moving to new computers as technology improves and to take advantage of the inherent reliability and availability of commercially available computing systems

An architecture for interactive raster graphics

A radical reappraisal of the 3-D Interactive raster graphics pipeline has resulted In an experimental architecture for a workstation which is currently being evaluated at the CW!. The principal features of this architecture are that It: - concentrates exclusively on real-time interactive 3-D graphics (initially for CAD). - uses object space rather than Image space methods where possible. - avoids using a frame buffer. - only uses custom VLSI where commercial products are unlikely to suffice In the near term. Four years Into the project the system design Is complete and the major components have been acquired and the custom VLSI chips hove been packaged and tested. The current experience with the system is based on detailed simulations which gave a fairiy clear Idea on Its strengths and limitations. A complete, but reduced resolution, experimental prototype system is now being assembled

Immersive Visualization for Enhanced Computational Fluid Dynamics Analysis

Modern biomedical computer simulations produce spatiotemporal results that are often viewed at a single point in time on standard 2D displays. An immersive visualization environment (IVE) with 3D stereoscopic capability can mitigate some shortcomings of 2D displays via improved depth cues and active movement to further appreciate the spatial localization of imaging data with temporal computational fluid dynamics (CFD) results. We present a semi-automatic workflow for the import, processing, rendering, and stereoscopic visualization of high resolution, patient-specific imaging data, and CFD results in an IVE. Versatility of the workflow is highlighted with current clinical sequelae known to be influenced by adverse hemodynamics to illustrate potential clinical utility

Fluid structure interaction of patient specific abdominal aortic aneurysms: a comparison with solid stress models

BACKGROUND: Abdominal aortic aneurysm (AAA) is a dilatation of the aortic wall, which can rupture, if left untreated. Previous work has shown that, maximum diameter is not a reliable determinant of AAA rupture. However, it is currently the most widely accepted indicator. Wall stress may be a better indicator and promising patient specific results from structural models using static pressure, have been published. Since flow and pressure inside AAA are non-uniform, the dynamic interaction between the pulsatile flow and wall may influence the predicted wall stress. The purpose of the present study was to compare static and dynamic wall stress analysis of patient specific AAAs. METHOD: Patient-specific AAA models were created from CT scans of three patients. Two simulations were performed on each lumen model, fluid structure interaction (FSI) model and static structural (SS) model. The AAA wall was created by dilating the lumen with a uniform 1.5 mm thickness, and was modeled as a non-linear hyperelastic material. Commercial finite element code Adina 8.2 was used for all simulations. The results were compared between the FSI and SS simulations. RESULTS: Results are presented for the wall stress patterns, wall shear stress patterns, pressure, and velocity fields within the lumen. It is demonstrated that including fluid flow can change local wall stresses slightly. However, as far as the peak wall stress is concerned, this effect is negligible as the difference between SS and FSI models is less than 1%. CONCLUSION: The results suggest that fully coupled FSI simulation, which requires considerable computational power to run, adds little to rupture risk prediction. This justifies the use of SS models in previous studies

Volume-based Estimates of Left Ventricular Blood Pool Volume and Ejection Fraction from Multi-plane 2D Ultrasound Images

Accurate estimations of left ventricular (LV) blood pool volume and left ventricular ejection fraction (LVEF) are crucial for the clinical diagnosis of cardiac disease, patient management, or other therapeutic treatment decisions, especially given a patient’s LVEF often affects his or her candidacy for cardiovascular intervention. Ultrasound (US) imaging is the most common and least expensive imaging modalities used to non-invasively image the heart to estimate the LV blood pool volume and assess LVEF. Despite advances in 3D US imaging, 2D US images are routinely used by cardiologists to image the heart and their interpretation is inherently based on the 2D LV blood pool area information immediately available in the US images, rather than 3D LV blood pool volume information. This work proposes a method to reconstruct the 3D geometry of the LV blood pool from three tri-plane 2D US images to estimate the LV blood pool volume and subsequently the LVEF. This technique uses a statistical shape model (SSM) of the LV blood pool characterized by several anchor points – the mitral valve hinges, apex, and apex-to-mitral valve midpoints – identified from the three multi-plane 2D US images. Given a new patient image dataset, the diastolic and systolic LV blood pool volumes are estimated using the SSM either as a linear combination of the n-closest LV geometries according to the Mahalanobis distance or based on the n-most dominant principal components identified after projecting the new patient into the principal component space defined by the training dataset. The performance of the proposed method was assessed by comparing the estimated LV blood pool volume and LVEF to those measured using the EchoPac PC clinical software on a dataset consisting of 66 patients, and several combinations of 50-16 used for training and validation, respectively. The studies show the proposed method achieves LV volume and LVEF estimates within 5% of those computed using the clinical software. Lastly, this work proposes an approach that requires minimal user interaction to obtain accurate 3D estimates of LV blood pool volume and LVEF using multi-plane 2D US images and confirms its performance similar to the ground truth clinical measurements