Purpose: Ultrasound is prevalent in image-guided therapy as a safe, inexpensive, and widely available imaging modality. However, extensive training in interpreting ultrasound images is essential for successful procedures. An open-source ultrasound image simulator was developed to facilitate the training of ultrasound-guided spinal intervention procedures, thereby eliminating the need for an ultrasound machine from the phantom-based training environment. Methods: Anatomical structures and surgical tools are converted to surface meshes for data compression. Anatomical data is converted from segmented volumetric images, while the geometry of surgical tools is available as a surface mesh. The pose of the objects are either constants or live measurements from a pose tracking device. Intersection points between the surface models and the ultrasound scan lines are determined with a binary space partitioning tree. The scan lines are divided into segments and filled with grey values determined by an intensity calculation accounting for material properties, reflection, and attenuation parameters defined in a configuration file. The scan lines are then converted to a regular brightness-mode ultrasound image. Results: The simulator was tested in a tracked ultrasound imaging system, with a mock transducer tracked by an Ascension TrakStar electromagnetic tracker, on a spine phantom. A mesh model of the spine was created from CT. The simulated ultrasound images were generated at a speed of 50 frames per second, and a resolution of 820 x 616 pixels on a PC with a 3.4 GHz processor. A human subject trial was conducted to compare the learning performance of novice trainees with real and simulated ultrasound in the localization of the facet joints of a spine phantom. With 22 participants split into two equal groups and each participant localizing 6 facet joints, there was no statistical difference in the performance of the two groups, indicating that simulated ultrasound could indeed replace the real ultrasound in phantom-based ultrasonography training for spinal interventions. Conclusion: The ultrasound simulator was implemented and integrated into the open-source Public Library for Ultrasound (www.plustoolkit.org) and SlicerIGT (www.SlicerIGT.org) toolkits / Thesis (Master, Computing) -- Queen's University, 2013-07-24 12:28:57.201

Multi-hop wireless mesh networks (WMNs) provide a cost-effective means to enable broadband wireless access (BWA) services to end users. Such WMNs are required to support different classes of traffic where each class requires certain quality of service (QoS) levels. The research direction undertaken in this thesis considers the development of enhanced routing and scheduling algorithms that enable WMNs to support various QoS metrics for the served traffic. A fundamental class of routing problems in WMNs asks whether a given end-to-end flow that requires certain bandwidth, and benefits from routing over a single path (also called non-bifurcated routing), can be routed given that some ongoing flows are being served in the network. In the thesis, we focus on the development of combinatorial algorithms for solving such incremental non-bifurcated problems for two types of WMNs: 1. WMNs where mesh routers use contention-based protocol for medium access control (MAC), and 2. WMNs where mesh routers use time division multiple access (TDMA) for MAC. For WMNs employing contention-based MAC protocols, we present a novel non-bifurcated routing algorithm that employs techniques from the theory of network flows. The main ingredient in our algorithm is a method for computing interference-constrained flow augmenting paths for routing subscriber demands in the network. For WMNs employing TDMA, we develop a number of joint routing and scheduling algorithms, and investigate the use of such algorithms to maximize the number of served flows. In chapter 4, we consider a throughput maximization problem in the well-known class of grid WMNs. We present an iterative algorithm that strives to achieve high throughput by considering routing and scheduling a pair of distinct flows simultaneously to the gateway in each iteration. In chapter 5, we explore joint routing and scheduling in TDMA-based WMNs with arbitrary topologies, and devise an algorithm that can deal with arbitrary interference relations among pairs of transmission links. In particular, our devised algorithm solves a generalized problem where a cost value is associated with using any possible time-slot on any transmission link, and a minimum cost route is sought along which a new flow can be scheduled without perturbing existing slot assignments.

No description available.

Although most work on Wireless Mesh Networks (WMNs) has focused on traffic flowing in and out of the network via gateways, traffic within the WMN may also be significant in many environments. This point-to-point (P2P) traffic between the nodes within WMN can be handled in different ways, particularly in WMNs containing multiple gateways. The approach used affects the performance of both the P2P flows and other traffic in the network. This work studies the impact of handling P2P traffic in the presence of gateways and gateway traffic. Through mathematical analysis of the resulting traffic patterns, along with extensive simulations, the need to route P2P traffic appropriately is demonstrated. While direct routing yields considerable performance improvements in small networks, it can actually decrease capacity in larger networks. Consequently, we extend the Hybrid Wireless Mesh Protocol (HWMP) proposed in IEEE 802.11s by adding two new message types to obtain more information useful for choosing the best route. Through simulations on different networks, HWMP shows better average delivery ratio and end-to-end delay than the original gateway-based and the P2P routing mechanisms in the simulation settings.

A graphical preprocessor for Spectral Element Method (SEM) is developed with an emphasis on user friendly graphical interface and instructive element construction. The interface of the preprocessor helps users with every step during mesh generation, aiding their understanding of SEM. This preprocessor's Graphical User Interface (GUI) and help system are comparable to other commercial tools. Moreover, this preprocessor is designed for educational purposes, and prior knowledge of Spectral Element formulation is not required to use this tool. The information window in the preprocessor shows stepby- step instructions for the user. The preprocessor provides a graphical interface which enables visualization while the mesh is being constructed, so that the entire domain can be discretized easily. In addition, by following informative steps during the mesh construction, the user can gain knowledge about the intricate details of computational fluid dynamics. This preprocessor provides a convenient way to implement h/p type nonconforming interfaces between elements. This aids the user in learning advanced numerical discretization techniques, such as the h/p nonconforming SEM. Using the preprocessor facilitates enhanced understanding of SEM, isoparametric mapping, h and p type nonconforming interfaces, and spectral convergence. For advanced users, this preprocessor provides a proficient and convenient graphical interface independent of the solvers. Any spectral element solver can utilize this preprocessor, by reading the format of the output file from the preprocessor. Given these features, this preprocessor is useful both for novice and advanced users.

Internet of Things (IoT) is a scenario that theorizes objects and people as potential nodes in an ever-growing wireless network. This idea pushes the development of low-cost wireless technologies that can run on portable power sources for months, or even years. One candidate technique that has shown promising results in this area thru the last years is BluetoothLow Energy (BLE). This thesis studies various techniques to enable and maintain large scale mesh networks over BLE communication. The initial study puts focus on an existing flooding based BLE mesh protocol. The thesis later presents an improved protocol that reduces power consumption with respect to the packet delivery ratio. Other enhancements which are added to the improved protocol are a self-adapting procedure and a packet routing algorithm. Simulations show that the improved protocol can save up to 50 % of the power consumption for a device, compared to the original protocol. / Sakernas Internet (IoT) är ett scenario som skisserar objekt och människor som potentiella noder i ett ständigt växande trådlöst nätverk. Denna vision driver utvecklingen av trådlösa lågkostnadsteknologier som kan köras på portabla strömkällor i flera månader. En kandiderande teknik som har visat goda resultat inom detta område är Bluetooth Low Energy (BLE). Detta uppsatsarbete studerar flera tekniker för att möjliggöra och upprätthålla storskaliga meshnätverk över BLE-kommunikation. Den inledande studien granskar ett existerande översvämningsbaserat meshprotokoll för BLE. Uppsatsarbetet presenterar därefter ett förbättrat protokoll som reducerar strömförbrukningen med avseende på kvoten mellan antalet mottagna paket genom antalet skickade paket. Ytterliggare upprustningar som tillkommer i det förbättrade protokollet är en procedur för självanpassning, samt en algorithm för dirigering av paket. Simuleringar visar att det förbättrade protokollet kan spara upp till 50 % av strömkonsumptionen för en enhet, jämfört med originalprotokollet.

Although most work on Wireless Mesh Networks (WMNs) has focused on traffic flowing in and out of the network via gateways, traffic within the WMN may also be significant in many environments. This point-to-point (P2P) traffic between the nodes within WMN can be handled in different ways, particularly in WMNs containing multiple gateways. The approach used affects the performance of both the P2P flows and other traffic in the network. This work studies the impact of handling P2P traffic in the presence of gateways and gateway traffic. Through mathematical analysis of the resulting traffic patterns, along with extensive simulations, the need to route P2P traffic appropriately is demonstrated. While direct routing yields considerable performance improvements in small networks, it can actually decrease capacity in larger networks. Consequently, we extend the Hybrid Wireless Mesh Protocol (HWMP) proposed in IEEE 802.11s by adding two new message types to obtain more information useful for choosing the best route. Through simulations on different networks, HWMP shows better average delivery ratio and end-to-end delay than the original gateway-based and the P2P routing mechanisms in the simulation settings.

No description available.

No description available.

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