bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction of Freeform Feature Models With Attachments
Authors: van den Berg Eelco , Bidarra Rafael , Bronsvoort Willem F.
Published: June 2008

In freeform feature modeling, the shape domain of current feature modeling systems is extended with freeform shapes. A challenging task in this context is to develop a method for constructing a feature model in an intuitive, yet unambiguous manner, comparable to the construction methods for regular-shaped feature models. This paper describes a framework in which it is possible to attach a face of a new freeform, volumetric feature instance to a face of a feature instance already in the model. In this framework, features are represented by configurations of freeform definition points, from which the shape is generated. By using geometric constraints on these definition points and other geometric entities within the model, freeform attachments can be realized. Apparent problems that emerge in this context are positioning of the new feature instance on the freeform attach face, fitting the geometry of the new feature instance to the existing model geometry, and maintenance of valid feature model geometry. The framework accommodates for these issues. Two types of attachment, for a freeform extrusion feature respectively a freeform wrap feature, are elaborated. With the attachments presented here, freeform feature models can be constructed in a fully parametrized, constraint-based way, just like regular-shaped feature models.
Finite Element Analysis Template Approach to Support Web Based Customer Centric Design
Authors: Ninan Jiju A. , Siddique Zahed
Published: June 2008

To survive in today’s volatile market, companies are striving to deliver greater quality, more customization and innovative designs by offering user customizable products. Mass customization features products that can be altered or changed by the customer to fit his/her needs. In order to incorporate customer specifications it is necessary to integrate the customer into the design process. Offering customized products while maintaining the reliability and efficiency of mass produced products calls for new tools and strategies in the design and manufacturing process. This paper presents a web based mass customization framework to provide customizable products in real time by integrating the customer into the design process. The approach is based on template(s) to automatically generate CAD models from customer specifications. Structural feasibility of the user specified configurations are then evaluated using automated Finite Element Analysis and communicated back to the user in real time. To achieve automated analysis a Product Family CAD and FEA template is presented. The CAD and FEA product family template generalizes the rules and guidelines for the entire product family to allow users to generate any member product. The template and the framework is implemented using commercial software. The applicability of the system is illustrated for web based customization of bicycle frames.
Boolean Algebra and Analysis Using Approximate Step Functions
Authors: Kumar Ashok V. , Lee Jongho
Published: June 2008

Implicit equations of curves and surfaces have been shown to be useful for constructing solutions for boundary value problems such that the boundary conditions are satisfied exactly. This application has generated interest in constructing solid models where the geometry is represented using implicit equations rather than parametric equations. In this paper we present a method for constructing step functions of solids that have a unit value within the solid and zero outside. A level set of this step function can then be defined as the boundary of the solid. This step function can be used not only to apply boundary conditions but also to compute volume integrals over the solid. Methods for combining step functions of solid primitives using ordinary and regularized Boolean operations to construct step functions of the Boolean result are also presented.
Local Feature Extraction Using Scale-Space Decomposition
Authors: Bespalov Dmitriy , Shokoufandeh Ali , Regli William C. , Sun Wei
Published: June 2008

In our recent work we have introduced a framework for extracting features from solid of mechanical artifacts in polyhedral representation based on scale-space feature decomposition [1]. Our approach used recent developments in efficient hierarchical decomposition of metric data using its spectral properties. In that work, through spectral decomposition, we were able to reduce the problem of matching to that of computing a mapping and distance measure between vertex-labeled rooted trees. This work discusses how Scale-Space decomposition frame-work could be extended to extract features from CAD models in polyhedral representation in terms of surface triangulation. First, we give an overview of the Scale-Space decomposition approach that is used to extract these features. Second, we discuss the performance of the technique used to extract features from CAD data in polyhedral representation. Third, we show the feature extraction process on noisy data — CAD models that were constructed using a 3D scanner. Finally, we conclude with discussion of future work.
Scenario-Based Learning and Multimedia in Improving Engineering Education
Authors: Mariappan Jawaharlal , Shih Angela , Schrader Peter G. , Elmore Robert
Published: June 2008

Use of multimedia and new technologies has become very common in education and the corporate training industry. Unlike text-on-the-screen (page-turner) instructions, multimedia based interactions involve audio, video, animation and rich graphics. These attributes are very appealing to learners, and have become the predominant approach to deliver self-paced learning material. The use of multimedia and computer-based training has improved web-based as well as computer-based training and instructional delivery tremendously. However, providing an authentic learning experience requires much more than multimedia. It requires an active learning approach built on sound principles of instructional design. Scenario Based Learning (SBL) is an effective pedagogical approach which utilizes new technology and provides an excellent framework for active learning. This paper presents a SBL approach and its application to teach engineering. This approach will engage learners, increase their interest, improve knowledge retention, and facilitate understanding of the physical meaning behind abstract concepts.
Textual Annotation in a Head Tracked, Stereoscopic Virtual Design Environment
Authors: Karasuda Eric , McMains Sara
Published: June 2008

In this paper we describe the textual annotation system we have implemented in CHaMUE, our Collaborative Haptic Mark-Up Environment software. This head tracked, stereoscopic virtual environment for design review allows remote participants to critique and refine product design ideas in real time, both by drawing on 3D virtual representations of the objects and by placing textual annotations linked to specific object features. Each textual annotation is displayed in a floating note with a 3D line path connecting the note with the point being referenced on the object geometry. The exact note positions and the 3D paths are automatically adjusted on a per-user basis according to each user’s current viewing position, balancing the ease of associating each note with its reference point on the object and the occlusion of both paths and the object under discussion. We discuss evaluation criteria for judging well placed notes and well chosen paths, and address the challenges posed by stereoscopic vision and head tracking to optimal note placement and path generation.
Agent-Based Real-Time Computing and Its Applications in Traffic Detection and Management Systems
Authors: Chen Bo , Cheng Harry H. , Palen Joe
Published: June 2008

This paper studies the generic architecture and coordination mechanism of an FIPA (Foundation for Intelligent Physical Agents) compliant heterogeneous multi-agent system (MAS) in a distributed control scenario. Proposed generic MAS framework has been applied to a real-time traffic detection and management system. The agent-based real-time traffic detection and management system (ABRTTDMS) is designed for the information fusion of different traffic detection systems on highways to optimize real-time traffic detection and management. ABRTTDMS is a multi-level agent system. The lowest level agents are responsible for processing the real-time traffic data and monitoring traffic conditions. The middle level agents coordinate all of the lowest level agents in a subnetwork. The highest-level agent is located in the transportation management center (TMC) to accept human commands and delegate tasks to lower level agents. The re-configurable hybrid control architecture of the system provides the capability of dynamically grouping distributed heterogeneous agents (intelligent control systems) into virtual clusters to accomplish tasks related to different geographical areas and different purposes. A platform independent agent execution engine has been implemented using an embeddable C/C++ interpreter called Ch. The communication between agents that reside on different hosts has been simulated in the Integration Engineering Laboratory at the University of California, Davis. The use of agent technology greatly enhances the distributed computing and cooperation capabilities of traffic detection and management systems.
Grasp Identification and Multi-Finger Haptic Feedback for Virtual Assembly
Authors: Zhu Zhenhua , Gao Shuming , Wan Huagen , Luo Yang , Yang Wenzhen
Published: June 2008

The sense of touch is an important way for humans to feel the world. It is very important to provide realistic haptic feedback in virtual assembly applications as to enhancing immersion experience and improving efficiency. This paper presents a novel approach for grasp identification and multi-finger haptic feedback for virtual assembly. Firstly, the Voxmap-PointShell (VPS) algorithm is adapted and utilized to detect collisions between a dexterous virtual hand and a mechanical component or between two mechanical components, and collision detection results are used to guide the motion of a virtual hand. Then collision forces at collision points are calculated (using Hooke Law), classified and converted. Finally, forces received at fingertips of a virtual hand are used to identify whether or not a virtual hand can grasp a mechanical component, and are mapped to exert forces at user’s fingertips with a CyberGrasp force feedback system. Our approach has been incorporated and verified in a CAVE virtual environment.
VIRAM: A Virtual Reality Environment for the Assembly of Micro Devices
Authors: Cecil J. , Gobinath N. , Deshmukh J. P. , Vasquez D.
Published: June 2008

The physical assembly of micron-sized parts is referred to as micro assembly. This paper discusses the creation of a virtual prototyping environment to study and facilitate the assembly of micro devices. The preliminary environment has been implemented using VRML 2.0 on a windows platform. The physical micro assembly system which was used as the target system to model includes a micro gripper, a linear micro-positioner, an assembly platen, a 3 axis micro positioner, cameras and a fixture mounted for the gripper. A description of the various stages involved in the creation of the virtual reality based environment is also described in this paper.
Critical Capabilities for Successful Distributed Collaborative Product Development
Authors: Gerdes Victor B.
Published: June 2008

Discrete manufacturing companies practicing distributed product development encounter challenges creating digital products, collaborating cross functionally in an organization and throughout the value chain, and controlling and managing product information and product development processes throughout the product’s lifecycle. This paper investigates the critical capabilities of a product development system for distributed product lifecycle management (PLM). A comprehensive product development system consisting of PTC’s Windchill PDMLink (control), Windchill ProjectLink (collaborate), and Pro/ENGINEER Wildfire (create - mechanical computer-aided design - MCAD) is presented in this paper with use cases and examples as a software solution for enabling distributed collaborative product development.
Make the Most of Interoperability Along Product Life Cycle Stages: A Framework Based on Multilevel Integration
Authors: Silva Joa˜o P. M. A. , Jardim-Golcalves Ricardo , Monteiro Anto´nio A. C. , Steiger-Garc¸a˜o Adolfo
Published: June 2008

Within the globally scaled economy and markets, the production process is re-emerging as the value-creator activity and the main source of enterprise revenues. The worldwide growing market contributes to the increase of customers’ exigencies, in terms of both quality and delivery times. Therefore, the product itself is becoming more complex as a combination of physical components and services, and the production process conceptualization is changing, starting from market understanding, through product and process design, to operations and distribution management, often exceeding the boundaries of a single organization. According to this scenario, the activities performed along the production process should be effectively coordinated and managed within the organization and with the external partners. To accomplish it, production must converge to a single global integrated process, enabled by seamless interoperability between the already operating tools, methods and computational environments. A challenge now is how to make the most of information and knowledge interoperability along the Product Life Cycle stages. The paper contributes to this aim, proposing a standard-based methodology to re-use data and knowledge incorporated in the product models, to support collaborative engineering through a modular multilevel architecture.
First Steps Towards an All Embracing Relations-Based Modeling
Authors: Rusa´k Zolta´n , Horva´th Imre , van der Vegte Wilfred
Published: June 2008

The focus in computer-aided design is shifting from geometric aspects to functional aspects and from the detail design to a multi-aspect conceptual design. As a consequence, new concepts are emerging and being tested, for instance, for comprehensive geometric and functional modeling in conceptual design. This paper introduces a new approach, which has been called relations-based design. Relations are existential, manifestation and behavioral associations, dependencies and interactions between human, artifacts and environments. Nucleus is introduced as a generic modeling entity, which includes two regions of one or two objects that are interconnected by a system of relations in a particular situation. A design concept (or an artifact) is conceived as a purposeful composition of specific instances of nuclei. The nucleus can be instantiated at multiple levels such as entity, component, subassembly and assembly. A set of relations has been predefined to express qualitative and quantitative associations, dependencies and interactions between objects in a parameterized form on these levels. As a modeling entity, the nucleus offers many advantages in multi-aspect conceptual modeling by integrating incomplete and uncertain geometric, structural, physical and behavioral modeling. The paper introduces the foundational theories, the most important mathematical definitions, and the concept of information management. Finally, it points at some advantages of relations based modeling in the context of application cases comparing it with the physical modeling offered in a commercial system.
Distributed Integration of Knowledge-Based Process Planning With CAM Software
Authors: Sormaz Dusan N. , Neerukonda Narender , Jain Vikesh
Published: June 2008

Seamless integration of manufacturing planning activities, though being imperative for application of advanced technologies, is still not completely developed. Integration between design and manufacturing systems is usually done within tightly implemented suite of CAD/CAM applications. However, there is a need to integrate these applications into a wider framework in which manufacturing knowledge is incorporated into planning tasks, and tasks may be executed in distributed environment. This paper proposes such a framework. The methodology is based on integration of CAM software with rule-based process planning on several levels. The basis for this approach is existence of feature based CAD model that is usually designed in CAD package. The process-planning task can be performed in two modes: traditional mode and distributed mode. In traditional mode, tightly integrated CAM package is used to create necessary tool paths and detailed specification for particular geometry from the design. They are exported into a CAPP package for cost optimization and sequencing for the final NC program. Distributed mode allows utilization of rule base for creation of manufacturing operations. Results are imported into CAM package for tool path generation and NC code post processing. CAD/CAM package exports its feature into rule-based process planning system. For each feature, rules are fired in order to select the most appropriate machining operation, tool, and cutting parameters. Process sequencing can also be performed. In both modes, integration may be carried out between different computers using TCP/IP protocol to enable distributed processing of different tasks. The current results in implementing the prototype, which supports proposed methodology and few test cases of both operating modes, are also described.
CAE Data Management Using Traditional PDM Systems
Authors: Joshi Alhad A.
Published: June 2008

Over the past decade, Computer Aided Engineering (Simulation) has experienced explosive growth being a significant enabler for: 1. Validating product design; 2. Providing low-cost methods for exploring a variety of product design alternatives; 3. Optimizing parts for better service performance; 4. Reducing dependence on physical testing; 5. Reducing warranty costs; 6. Achieving faster time to market. This rapid growth in the number of simulations performed and the amount of data generated in the absence of any significant data and process management initiatives has led to considerable inefficiencies in the CAE domain. Many companies now recognize the need to manage their CAE process and data as well as their desire to leverage their existing PDM systems as the primary repositories of CAE data. Some major issues are: 1. There is a need for a PDM data model to support CAE; 2. The CAE data model can be very complex; 3. There is an immense variety of CAE applications and data types; 4. Many CAE simulations require access to physical test data for input and correlation; 5. Data management discipline is not typically part of the CAE culture today. Despite the unique challenges posed by bringing PDM into the CAE world, the transition could occur faster than it has in the CAD world. This presentation will showcase an approach for managing CAE data in traditional PDM systems. Two working examples of CAE process automation software solutions integrated with CAD and PDM will be discussed. In particular, these applications will show how CAE users can leverage established PDM infrastructure and interact with EDS’ Teamcenter/Enterprise, Teamcenter/Engineering and Dassault Systeme’s SmarTeam through seamless integrations with their CAE systems.
STEP, XML, and UML: Complementary Technologies
Authors: Lubell Joshua , Peak Russell S. , Srinivasan Vijay , Waterbury Stephen C.
Published: June 2008

One important aspect of product lifecycle management (PLM) is the computer-sensible representation of product information. Over the past fifteen years or so, several languages and technologies have emerged that vary in their emphasis and applicability for such usage. ISO 10303, informally known as the Standard for the Exchange of Product Model Data (STEP), contains the high-quality product information models needed for electronic business solutions based on the Extensible Markup Language (XML). However, traditional STEP-based model information is represented using languages that are unfamiliar to most application developers. This paper discusses efforts underway to make STEP information models available in universal formats familiar to most business application developers: specifically XML and the Unified Modeling Language™ (UML®). We also present a vision and roadmap for future STEP integration with XML and UML to enable enhanced PLM interoperability.
Automation Integration Over the Project Lifecycle for the Pueblo Chemical Agent-Destruction Pilot Plant
Authors: Parsons Brock K. , James John E. , Reuss Mark C.
Published: June 2008

The architecture of an integrated suite of automation tools used to manage all project data for a major engineered facility is described. This paper discusses how these tools are configured to manage and manipulate the generation of design data by geographically dispersed team members; to support engineering, procurement, construction, operation and decommissioning; and to maintain data integrity throughout the project lifecycle. The challenges of team collaboration, knowledge management, cultural integration, and lessons learned are described.
Manufacturing Information Integration in Product Lifecycle Management (PLM)
Authors: Qiao Guixiu , McLean Charles
Published: June 2008

The research on manufacturing information integration in PLM calls for a new fundamental information technology to enable adaptive information representation and exchange between manufacturing applications. Four major problems are studied, including interchangeable common data representation, management of information access, information reuse, and disturbance reflection of information change. An information model for manufacturing simulation is built. Problem about the abstraction of real models to virtual models is also discussed. A neutral model of shop information, developed by NIST based on the eXtensible Markup Language (XML), is detailed in this paper with illustrations from industrial applications.
Distributed Data Access Control for Lean Product Information Sharing in Collaborative Design
Authors: Wang Yan , Ajoku Pamela N. , Nnaji Bart O.
Published: June 2008

Efficient, effective, and trustworthy collaboration in design is vital to maintain organizational competence. Conventional access control methods are too coarse in inter-organizational lean and secure data exchange. In this paper, a Scheduled Role-Based Distributed Data Access Control Model is described to support data security management in a distributed environment. The model allows for fine-grained data access control at both the server and client sides, thus securing different levels of design information dissemination for intellectual property protection purposes. Common interface for heterogeneous data is built based on XML.
Real-Time Architecture for an Electro-Mech-Optical System for Detection of Vehicles on Highway
Authors: Wang Zhaoqing , Cheng Harry H. , Nestinger Stephen S. , Shaw Benjamin D. , Palen Joe
Published: June 2008

A real-time architecture for a highway vehicle detection system is presented in the article. The Laser Based Detection System (LBDS), focused on helping the Intelligent Transportation System (ITS), measures a key quantitative parameter of vehicles moving across a link of highway, namely, travel time. Travel time is based upon the identifying and reidentifying vehicles at various points on the highway. This article provides a method to collect real-time signals from an active laser source in the LBDS and calculate vehicle parameters using a standard computer. A method of message exchange between a real-time kernel process, for real-time data acquisition, and a user space process, for computing and displaying, is given under the RTLinux environment. Experimental results from field tests have shown that the application of the real-time architecture to the LBDS provides speeds deterministically.
Exemplar Networks: Extensions of the Design Exemplar
Authors: Summers Joshua D. , Shah Jami J.
Published: June 2008

The design exemplar has been offered in the literature as a design automation representation structure for embodiment design. Experience with the design exemplar has shown the design exemplar to be tedious to develop. For this reason, an extension to the design exemplar is proposed that offers design automation developers the flexibility of combining atomic design exemplars through exemplar networks. This paper introduces the exemplar networks, providing justifications, algorithms, and demonstrations.
Logical Connectives for a CAD Query Language: Algorithms and Verification
Authors: Divekar Ameya , Summers Joshua D.
Published: June 2008

Design engineers create models of design artifacts with commercial Computer Aided Design (CAD) solid modeling systems. These systems stop short of providing support for querying and retrieving data from within the CAD data files. The design exemplar has been proposed as an approach to developing a CAD query language based upon an analysis of the design exemplar components, vocabulary, and extensions to support logical connectives. The implementation of the required extensions is offered in this paper. Algorithms are developed to implement the NOT and OR logical connectives. These algorithms are discussed as they relate to the generic exemplar algorithm. The verification of the algorithms is performed using test cases and comparing the expected results with those found using the software. The design exemplar, supported with the AND, NOT, and OR logical connectives, provides for complex and precise query expression and geometric information retrieval.
Enabling “Self-Service” Data Management: Distributed Product Data Management Architecture
Authors: Raj Ajoy R. , Ramani Karthik
Published: June 2008

Distributed Product Data Management (DPDM) is a framework which links disparate data sources together to create a hybrid network of resources that can be exchanged in real-time by different organizations. Current product management systems optimize intra-organizational processes by centralizing data management while maintaining distinct original system configurations. DPDM can manage disparate data sources without creating additional resource management databases. In addition, it eases intra-organizational management by normalizing interaction between various tiers. The architecture contains a hybrid server for controlling the application and managing client details. Distributed agents are used to link the system to different client data sources. DPDM provides deployment tools to integrate new clients into the system and programmable modules to extend the architecture programmatically for implementing additional features. Multitiered implementation of the framework enables transparent extraction and exchange of data across the network. A prototype is built using the architecture to demonstrate the flexibility, affordability, extendibility and interoperability of the framework. A distributed architecture is used with project-product oriented data modeling and illustrates various aspects of framework. DPDM being an extendable interface can be deployed in domains that require distributed data exchange. Implementations can be developed in a “self-service” and low cost manner to suit specific organizational requirements.
Vibration Analysis of Axially Loaded Beams Including Rotary Inertia: An Exact Dynamic Finite Element
Authors: Hashemi Seyed M.
Published: June 2008

An ‘exact’ basis function Dynamic Finite Element (DFE) for the free vibrational analysis of axially loaded beams and assemblages composed of beams is presented. The shear deformation is neglected but the Rotary Inertia (RI) effects are taken into consideration. The dynamic trigonometric shape functions for bending vibrations of an axially loaded uniform beam element are first derived in an exact sense. Then, exploiting the Principle of Virtual Work together with the nodal approximations of variables based on these dynamic shape functions, leads to a single frequency dependent Dynamic Stiffness Matrix (DSM) that represents both mass and stiffness properties. A Wittrick-Williams algorithm, based on a Sturm sequence root counting technique, is then used as the solution method. The application of the theory is demonstrated by an illustrative example of cantilever beam where the influence of Rotary Inertia (RI) effect and different axial loads on the natural frequencies of the system is demonstrated by numerical results.
Knowledge Management and Support Environment in Early Phases of Design Process
Authors: Fischer X. , Merlo C. , Legardeur J. , Zimmer L. , Anglada A.
Published: June 2008

Most of the time, starting new design projects based on innovative product concepts is a strategic but complicated process. Individual initiatives and the development of new ideas take place within conflicting contexts combining technical, economical and social aspects. During theses phases actors have to formalize new ideas, to exchange them and to collaborate to promote them. Traditional tools do not support such activities. We propose in this paper a new approach dedicated to the product development process from the early phases to the embodiment design phases. Metamodeling techniques and new tools (ID2 - Innovation Development and Diffusion - and CE - Constraint Explorer -) are proposed in order to support those phases ensuring the collaboration and the interaction between design actors, the knowledge and information management, the development of innovative ideas, and the improvement of embodiment design solutions. More over we propose to link our tools to a PLM environment to improve the sharing and the management of information, documents and design solutions in order to foster collaboration. The main objective of our implementation is to foster innovation during design process by improving sharing and reuse of innovative ideas and allowing the organization to identify rapidly best consensus for design solutions.
Accessing the Performance of Model-Based Control in a Distributed Machine Tool Control Environment
Authors: Michaloski John L. , Soons Johannes A. , Proctor Frederick M.
Published: June 2008

Although Computerized Numerical Controller (CNC) machine tools have greatly improved precision, quality and productivity, there are still many areas where inaccuracies and inefficiencies remain. Model-Based Control (MBC) is a technique to advance machine tool accuracy and part quality by compensating for machine and process errors. Nominal Differential Expansion (NDE) thermal compensation is one MBC approach which we have integrated into a CNC turning machine testbed. To allow portability and redeployment of the CNC technology, the MBC testbed was implemented as a component-based system using a distributed programming infrastructure. This paper looks at software and performance issues related to distributed MBC architecture, which is slower due to increased overhead from network communication. We look at the requirements of distributed infrastructure as implemented by the Distributed Component Object Model (DCOM), and assess the performance of various DCOM configurations matching the MBC requirements. Results from our analysis of the distributed performance using MBC-based DCOM configurations are presented.
A semi‐automatic technique for measurement of arterial wall from black blood MRI
Authors: Ladak Hanif M. , Thomas Jonathan B. , Mitchell J. Ross , Rutt Brian K. , Steinman David A.
Published: June 2008

Black blood magnetic resonance imaging (MRI) has become a popular technique for imaging the artery wall in vivo. Its noninvasiveness and high resolution make it ideal for studying the progression of early atherosclerosis in normal volunteers or asymptomatic patients with mild disease. However, the operator variability inherent in the manual measurement of vessel wall area from MR images hinders the reliable detection of relatively small changes in the artery wall over time. In this paper we present a semi‐automatic method for segmenting the inner and outer boundary of the artery wall, and evaluate its operator variability using analysis of variance (ANOVA). In our approach, a discrete dynamic contour is approximately initialized by an operator, deformed to the inner boundary, dilated, and then deformed to the outer boundary. A group of four operators performed repeated measurements on 12 images from normal human subjects using both our semi‐automatic technique and a manual approach. Results from the ANOVA indicate that the inter‐operator standard error of measurement (SEM) of total wall area decreased from 3.254 mm2 (manual) to 1.293 mm2 (semi‐automatic), and the intra‐operator SEM decreased from 3.005 mm2 to 0.958 mm2. Operator reliability coefficients increased from less than 69% to more than 91% (inter‐operator) and 95% (intra‐operator). The minimum detectable change in wall area improved from more than 8.32 mm2 (intra‐operator, manual) to less than 3.59 mm2 (inter‐operator, semi‐automatic), suggesting that it is better to have multiple operators measure wall area with our semi‐automatic technique than to have a single operator make repeated measurements manually. Similar improvements in wall thickness and lumen radius measurements were also recorded. Since the semi‐automatic technique has effectively ruled out the effect of the operator on these measurements, it may be possible to use such techniques to expand prospective studies of atherogenesis to multiple centers so as to increase access to real patient data without sacrificing reliability.
Validation of a two‐ to three‐dimensional registration algorithm for aligning preoperative CT images and intraoperative fluoroscopy images
Authors: Penney Graeme P. , Batchelor Philipp G. , Hill Derek L. G. , Hawkes David J. , Weese Juergen
Published: June 2008

We present a validation of an intensity based two‐ to three‐dimensional image registration algorithm. The algorithm can register a CT volume to a single‐plane fluoroscopy image. Four routinely acquired clinical data sets from patients who underwent endovascular treatment for an abdominal aortic aneurysm were used. Each data set was comprised of two intraoperative fluoroscopy images and a preoperative CT image. Regions of interest (ROI) were drawn around each vertebra in the CT and fluoroscopy images. Each CT image ROI was individually registered to the corresponding ROI in the fluoroscopy images. A cross validation approach was used to obtain a measure of registration consistency. Spinal movement between the preoperative and intraoperative scene was accounted for by using two fluoroscopy images. The consistency and robustness of the algorithm when using two similarity measures, pattern intensity and gradient difference, was investigated. Both similarity measures produced similar results. The consistency values were rotational errors below 0.74° and in‐plane translational errors below 0.90 mm. These errors approximately relate to a two‐dimensional projection error of 1.3 mm. The failure rate was less than 8.3% for three of the four data sets. However, for one of the data sets a much larger failure rate (28.5%) occurred.
Wavelength dependence of the precision of noninvasive optical measurement of oxy‐, deoxy‐, and total‐hemoglobin concentration
Authors: Yamashita Yuichi , Maki Atsushi , Koizumi Hideaki
Published: June 2008

The precision of noninvasive optical measurement of the concentration changes in oxy‐, deoxy‐, and total‐hemoglobin depends on wavelength. For estimating the precision, we calculated the noise level of the concentration changes as the uncertainty in measurements using several wavelength pairs of light. Seven laser diodes (664–848 nm) were used simultaneously for spectroscopic measurement of brain activity during finger motor stimulation. We also used the analysis of error propagation from the uncertainty in direct measurements of absorbance changes to estimate indirectly the uncertainty of concentration changes. The measurement of the concentration changes made using an 830/664‐nm pair are two times (oxy‐Hb) and six times (deoxy‐Hb) more precise than those made using an 830/782‐nm pair.
Leaf sequencing with secondary beam blocking under leaf positioning constraints for continuously modulated radiotherapy beams
Authors: Kuterdem H. Görkem , Cho Paul S.
Published: June 2008

The creation of arbitrary photon fluence patterns for intensity modulated radiotherapy is addressed. The proposed method is intended for a class of multileaf collimators with a requirement for minimum leaf separation. Unlike the solution of Convery and Webb in which discrete beam intensity modulation was assumed, the present method deals with continuous modulation or that consisting of infinitely small bixels. The method begins with the time‐optimal solution of Spirou–Stein–Svensson disregarding the minimum gap requirement. Subsequently, the gaps are restored by mobilizing the secondary beam blocking devices to prevent overexposure resulting from the leaf separation process. The secondary beam blocking is provided by means of two orthogonal backup diaphragms that are computer controlled. The results indicate that the method can be used to accurately deliver the desired modulation while satisfying the leaf positioning constraints. Furthermore, an example is presented which illustrates the efficacy of using the horizontal backup diaphragms (moving in perpendicular direction of the leaves) in addition to the vertical backup diaphragms (moving in the parallel direction of the leaves) to generate zero fluence regions.
Accuracy limits in the determination of absolute optical properties using time‐resolved NIR spectroscopy
Authors: Ntziachristos Vasilis , Chance Britton
Published: June 2008

We assess typical systematic experimental errors involved in a time‐resolved measurement as applied to NIR diffuse optical spectroscopy and investigate their effect on the quantification accuracy of the absorption and the reduced scattering coefficient. We demonstrate that common systematic experimental uncertainties may lead to quantification errors of 10% or more, even when excellent signal to noise ratio conditions exist and accurate photon propagation models are employed. We further demonstrate that the accuracy of the calculation depends nonlinearly on the optical properties of the medium measured. High scattering and low absorbing media can be quantified more accurately than media with low scattering or high absorption using measurements of the same signal to noise ratio. We further discuss curve‐shape fitting schemes that aid in improving the quantification accuracy in the presence of experimental errors. Finally, we identify uncertainties that set quantification accuracy limits and we find temporal resolution as the ultimate limiting factor in the quantification accuracy achieved. Our findings suggest that temporal resolution of the order of 10 ps is necessary for quantifying the absorption and reduced scattering coefficient of diffuse media with accuracy better than 5% using curve fitting methods. In that sense this analysis can be used in time‐resolved system design and in predicting the expected errors given the technology selected for time‐resolved measurements.
Advanced single‐slice rebinning for tilted spiral cone‐beam CT
Authors: Kachelrieß Marc , Fuchs Theo , Schaller Stefan , Kalender Willi A.
Published: June 2008

Future medical CT scanners and today's micro CT scanners demand cone‐beam reconstruction algorithms that are capable of reconstructing data acquired from a tilted spiral trajectory where the vector of rotation is not necessarily parallel to the vector of table increment. For the medical CT scanner this case of nonparallel object motion is met for nonzero gantry tilt: the table moves into a direction that is not perpendicular to the plane of rotation. Since this is not a special application of medical CT but rather a daily routine in head exams, there is a strong need for corresponding reconstruction algorithms. In contrast to medical CT, where the special case of nonperpendicular motion is used on purpose, micro CT scanners cannot avoid aberrations of the rotational axis and the table increment vector due to alignment problems. Especially for those micro CT scanners that have the lifting stage mounted on the rotation table (in contrast to setups where the lifting stage holds the rotation table), this kind of misalignment is equivalent to a gantry tilt. We therefore generalize the advanced single‐slice rebinning algorithm (ASSR), which is considered a very promising approach for medical cone‐beam reconstruction due to its high image quality and its high reconstruction speed [Med. Phys.27, 754–772 (2000)], to the case of tilted gantries. We evaluate this extended ASSR approach (which we will denote asfor convenience) in comparison to the original ASSR algorithm using simulated phantom data for reconstruction. For the case of nonparallel object motionshows significant improvements over ASSR, however, its computational complexity is slightly increased due to the broken symmetry of the spiral trajectory.
Dosimetric investigation and portal dose image prediction using an amorphous silicon electronic portal imaging device
Authors: McCurdy B. M. C. , Luchka K. , Pistorius S.
Published: June 2008

A two step algorithm to predict portal dose images in arbitrary detector systems has been developed recently. The current work provides a validation of this algorithm on a clinically available, amorphous silicon flat panel imager. The high‐atomic number, indirect amorphous silicon detector incorporates a gadolinium oxysulfide phosphor scintillating screen to convert deposited radiation energy to optical photons which form the portal image. A water equivalent solid slab phantom and an anthropomorphic phantom were examined at beam energies of 6 and 18 MV and over a range of air gaps (∼20–50 cm). In the many examples presented here, portal dose images in the phosphor were predicted to within 5% in low‐dose gradient regions, and to within 5 mm (isodose line shift) in high‐dose gradient regions. Other basic dosimetric characteristics of the amorphous silicon detector were investigated, such as linearity with dose rate (±0.5%), repeatability (±2%), and response with variations in gantry rotation and source to detector distance. The latter investigation revealed a significant contribution to the image from optical photon spread in the phosphor layer of the detector. This phenomenon is generally known as “glare,” and has been characterized and modeled here as a radially symmetric blurring kernel. This kernel is applied to the calculated dose images as a convolution, and is successfully demonstrated to account for the optical photon spread. This work demonstrates the flexibility and accuracy of the two step algorithm for a high‐atomic number detector. The algorithm may be applied to improve performance of dosimetric treatment verification applications, such as direct image comparison, backprojected patient dose calculation, and scatter correction in megavoltage computed tomography. The algorithm allows for dosimetric applications of the new, flat panel portal imager technology in the indirect configuration, taking advantage of a greater than tenfold increase in detector sensitivity over a direct configuration.
A model for the time dependent three‐dimensional thermal distribution within iceballs surrounding multiple cryoprobes
Authors: Rewcastle John C. , Sandison George A. , Muldrew Ken , Saliken John C. , Donnelly Bryan J.
Published: June 2008

A time dependent three‐dimensional finite difference model of iceball formation about multiple cryoprobes has been developed and compared to experimental data. Realistic three‐dimensional probe geometry is specified and the number of cryoprobes, the cryoprobe cooling rates, and the locations of the probes are arbitrary inputs by the user. The simulation accounts for observed longitudinal thermal gradients along the cryoprobe tips. Thermal histories for several points around commercially available cryoprobes have been predicted within experimental error for one, three, and five probe configurations. The simulation can be used to generate isotherms within the iceball at arbitrary times. Volumes enclosed by the iceball and any isotherms may also be computed to give the ablative ratio, a measure of the iceball's killing efficiency. This ratio was calculated as the volume enclosed by a critical isotherm divided by the total volume of the iceball for assumed critical temperatures of −20 and −40 °C. The ablative ratio for a single probe is a continuously decreasing function of time but when multiple probe configurations are used the ablative ratio increases to a maximum and then essentially plateaus. Maximum values of 0.44 and 0.55 were observed for three and five probe configurations, respectively, with an assumed critical temperature of −20 °C. Assuming a critical temperature of −40 °C, maximum ablative ratios of 0.21 and 0.3 for three and five probe configurations, respectively, were observed.
AAPM protocol for 40–300 kV x‐ray beam dosimetry in radiotherapy and radiobiology
Authors: Ma C.‐M. , Coffey C. W. , DeWerd L. A. , Liu C. , Nath R. , Seltzer S. M. , Seuntjens J. P.
Published: June 2008

The American Association of Physicists in Medicine (AAPM) presents a new protocol, developed by the Radiation Therapy Committee Task Group 61, for reference dosimetry of low‐ and medium‐energy x rays for radiotherapy and radiobiology It is based on ionization chambers calibrated in air in terms of air kerma. If the point of interest is at or close to the surface, one unified approach over the entire energy range shall be used to determine absorbed dose to water at the surface of a water phantom based on an in‐air measurement (the “in‐air” method). If the point of interest is at a depth, an in‐water measurement at a depth of 2 cm shall be used for tube potentials ⩾100 kV (the “in‐phantom” method). The in‐phantom method is not recommended for tube potentials <100 kV. Guidelines are provided to determine the dose at other points in water and the dose at the surface of other biological materials of interest. The protocol is based on an up‐to‐date data set of basic dosimetry parameters, which produce consistent dose values for the two methods recommended. Estimates of uncertainties on the final dose values are also presented.
Automated registration of breast lesions in temporal pairs of mammograms for interval change analysis—local affine transformation for improved localization
Authors: Hadjiiski Lubomir , Chan Heang‐Ping , Sahiner Berkman , Petrick Nicholas , Helvie Mark A.
Published: June 2008

Analysis of interval change is important for mammographic interpretation. The aim of this study is to evaluate the use of an automated registration technique for computer‐aided interval change analysis in mammography. Previously we developed a regional registration technique for identifying masses on temporal pairs of mammograms. In the current study, we improved lesion registration by including a local alignment step. Initially, the lesion position on the prior mammogram was estimated based on the breast geometry. An initial fan‐shaped search region was then defined on the prior mammogram. In the second stage, the location of the fan‐shaped region on the prior mammogram was refined by warping, based on an affine transformation and simplex optimization in a local region. In the third stage, a search for the best match between the lesion template from the current mammogram and a structure on the prior mammogram was carried out within the search region. This technique was evaluated on 124 temporal pairs of mammograms containing biopsy‐proven masses. Eighty‐seven percent of the estimated lesion locations resulted in an area overlap of at least 50% with the true lesion locations and an average distance of 2.4±2.1 mm between their centroids. The average distance between the estimated and the true centroid of the lesions on the prior mammogram over all 124 temporal pairs was 4.2±5.7 mm. The registration accuracy was improved in comparison with our previous study that used a data set of 74 temporal pairs of mammograms. This improvement in accuracy resulted from the improved geometry estimation and the local affine transformation.