Judith E. Terrill

A statistical path loss model for medical implant communication channels

Knowledge of the propagation media is a key step toward a successful transceiver design. Such information is typically gathered by conducting physical experiments, measuring and processing the corresponding data to obtain channel characteristics. In case of medical implants, this could be extremely difficult, if not impossible. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe RF propagation from medical implants inside a human body. This virtual environment allows for more natural interaction between experts with different backgrounds, such as engineering and medical sciences. Here, we show how this platform has been used to determine a statistical path loss model for medical implant communication systems.

A parallel reaction-transport model applied to cement hydration and microstructure development

A recently described stochastic reaction-transport model on three-dimensional lattices is parallelized and is used to simulate the time-dependent structural and chemical evolution in multicomponent reactive systems. The model, called HydratiCA, uses probabilistic rules to simulate the kinetics of diffusion, homogeneous reactions and heterogeneous phenomena such as solid nucleation, growth and dissolution in complex three-dimensional systems. The algorithms require information only from each lattice site and its immediate neighbors, and this localization enables the parallelized model to exhibit near-linear scaling up to several hundred processors. Although applicable to a wide range of material systems, including sedimentary rock beds, reacting colloids and biochemical systems, validation is performed here on two minerals that are commonly found in Portland cement paste, calcium hydroxide and ettringite, by comparing their simulated dissolution or precipitation rates far from equilibrium to standard rate equations, and also by comparing simulated equilibrium states to thermodynamic calculations, as a function of temperature and pH. Finally, we demonstrate how HydratiCA can be used to investigate microstructure characteristics, such as spatial correlations between different condensed phases, in more complex microstructures.

Channel Models for Medical Implant Communication

Information regarding the propagation media is typically gathered by conducting physical experiments, measuring and processing the corresponding data to obtain channel characteristics. When this propagation media is human body, for example in case of medical implants, then this approach might not be practical. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe RF propagation from medical implants inside a human body. This virtual environment allows for more natural interaction between experts with different backgrounds, such as engineering and medical sciences. Here, we show how this platform has been used to determine channel models for medical implant communication systems.

Measurement Tools for the Immersive Visualization Environment: Steps Toward the Virtual Laboratory

This paper describes a set of tools for performing measurements of objects in a virtual reality based immersive visualization environment. These tools enable the use of the immersive environment as an instrument for extracting quantitative information from data representations that hitherto had be used solely for qualitative examination. We provide, within the virtual environment, ways for the user to analyze and interact with the quantitative data generated. We describe results generated by these methods to obtain dimensional descriptors of tissue engineered medical products. We regard this toolbox as our first step in the implementation of a virtual measurement laboratory within an immersive visualization environment.

Correction of Location and Orientation Errors in Electromagnetic Motion Tracking

We describe a method for calibrating an electromagnetic motion tracking device. Algorithms for correcting both location and orientation data are presented. In particular, we use a method for interpolating rotation corrections that has not previously been used in this context. This method, unlike previous methods, is rooted in the geometry of the space of rotations. This interpolation method is used in conjunction with Delaunay tetrahedralization to enable correction based on scattered data samples. We present measurements that support the assumption that neither location nor orientation errors are dependent on sensor orientation. We give results showing large improvements in both location and orientation errors. The methods are shown to impose a minimal computational burden.

Simulation study of body surface RF propagation for UWB wearable medical sensors

Ultra Wide-Band (UWB) is a favorable technology for wearable medical sensors that monitor vital signs and other health-related information. Efficient transceiver design requires in-depth understanding of the propagation media which in this case is the human body surface. The results of the few measurement experiments in recent publications point to varying conclusions in the derived parameters of the channel model. As obtaining large amount of data for many scenarios and use-cases is difficult for this channel, a detailed simulation platform can be extremely beneficial in highlighting the propagation behavior of the body surface and determining the best scenarios for limited physical measurements. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe three-dimensional RF propagation from wearable medical sensors around a human body. We have used this virtual environment to further study UWB channels over the surface of a human body. Parameters of a simple statistical path-loss model and their sensitivity to frequency and the location of the sensors on the body are discussed.

Impact of an aortic valve implant on body surface UWB propagation: A preliminary study

Efficient transceiver design in body area networks requires in-depth understanding of the propagation channel which in this case involves the human body. Several studies have been done to characterize RF propagation on the body surface and determine the parameters of an appropriate model. However, the possible effect of an already existing medical implant on body surface propagation has not been considered until during a recent measurement experiment. There it was discovered that an aortic implant may have an impact on Ultra Wide-Band (UWB) propagation between wearable nodes that are in the vicinity of the implant location. In this paper, we use a 3D immersive visualization environment to study and observe the impact of an aortic implant on body surface propagation. Specifically, we focus on the UWB impulse response of the channel between nodes located around the upper body. The difference in the obtained impulse responses (for scenarios with and without the implant) both in measurement and simulation points to the possible impact that such medical implants could have on body surface RF propagation.

Extending Measurement Science to Interactive Visualisation Environments

We describe three classes of tools to turn visualizations into a visual laboratory to interactively measure and analyze scientific data. We move the nor- mal activities that scientists perform to understand their data into the visualization environment, which becomes our virtual laboratory, combining the qualitative with the quantitative. We use representation, interactive selection, quantification, and display to add quantitative measurement methods, input tools, and output tools. These allow us to obtain numerical information from each visualization. The exact form that the tools take within each of our three categories depends on features present in the data, hence each is manifested differently in different situations. We illustrate the three approaches with a variety of case studies from immersive to desktop environments that demonstrate the methods used to obtain quantitative knowledge interactively from visual objects.

Incorporating D3.js information visualization into immersive virtual environments

We have created an integrated interactive visualization and analysis environment that can be used immersively or on the desktop to study a simulation of microstructure development during hydration or degradation of cement pastes and concrete. Our environment combines traditional 3D scientific data visualization with 2D information visualization using D3.js running in a web browser. By incorporating D3.js, our visualization allowed the scientist to quickly diagnose and debug errors in the parallel implementation of the simulation.

A Critical Comparison of 3D Experiments and Simulations of Tricalcium Silicate Hydration

Advances in nano-computed X-ray tomography (nCT), nano X-ray fluorescence spectrometry (nXRF), and high-performance computing have enabled the first direct comparison between observations of three-dimensional nanoscale microstructure evolution during cement hydration and computer simulations of the same microstructure using HydratiCA. nCT observations of a collection of triclinic tricalcium silicate (Ca3SiO5) particles reacting in a calcium hydroxide solution are reported and compared to simulations that duplicate, as nearly as possible, the thermal and chemical conditions of those experiments. Particular points of comparison are the time dependence of the solid phase volume fractions, spatial distributions, and morphologies. Comparisons made at 7 h of reaction indicate that the simulated and observed volumes of Ca3SiO5 consumed by hydration agree to within the measurement uncertainty. The location of simulated hydration product is qualitatively consistent with the observations, but the outer envelope of hydration product observed by nCT encloses more than twice the volume of hydration product in the simulations at the same time. Simultaneous nXRF measurements of the same observation volume imply calcium and silicon concentrations within the observed hydration product envelope that are consistent with Ca(OH)2 embedded in a sparse network of calcium silicate hydrate (C-S-H) that contains about 70 % occluded porosity in addition to the amount usually accounted as gel porosity. An anomalously large volume of Ca(OH)2 near the particles is observed both in the experiments and in the simulations, and can be explained as originating from the hydration of additional particles outside the field of view. Possible origins of the unusually large amount of observed occluded porosity are discussed.