bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Web-Based Process Planning Optimization System
Authors: Li W. D. , Lu W. F.
Published: June 2008

A Web-based prototype system has been setup for users to carry out visualization-based manipulations and process planning of design models to support distributed design and manufacturing analysis. The process planning module, which has been deployed as services in the Internet, includes four intelligent approaches, and a Tabu search-based approach is explained to illustrate the optimization process. The Web-based system has been integrated with a distributed feature-based design system, and the latter can generate design models and re-represent them in an XML representation based on VRML and attributes of features to provide the input of the former. Through effective utilization of the Web and Java technologies, this system is independent of the operating system, scalable and service-oriented, and can be used by a geographically distributed design team to organize concurrent engineering design activities effectively.
The Downstream Digital Mock-Up: A New Concept to Support Virtual Reality Applications in the Aeronautic Industry
Authors: Drieux G. , Le´on J.-C. , Chevassus N. , Guillaume F.
Published: June 2008

The Digital Mock-Up (DMU), which is a comprehensive numerical model describing the final manufactured product, is today widely used in the industry (like the automotive and aeronautic industries) to support the concurrent engineering organizations and processes. On the other hand, simulation helps in the development of a product for design decision making or validation purposes. It allows to determine, with the appropriate level of accuracy, the behavior of the future product under a specific environment or set of exterior actions. Virtual Reality (VR) applications are simulations where the focus is on immersion and interaction with the product. However, there is still lacks in the integration of simulation within the product development phases. In particular the link between the DMU and the numerical models for simulation in the large is often hardly achieved. For some types of simulation, it is even inexistent. In this paper, we propose a new object, the Downstream Digital Mock-Up (DDMU), based on a polyhedral representation, and we show that it can be a support for the integration of a subset of simulation activities within the product development process by making the link between the DMU and these simulations. In the particular case of VR, we show that this object is particularly adapted. One particularity of the DDMU is to be prepared for a specific target application, defined by its objectives and the context in which it is immersed.
Design Rationale Acquisition in Conceptual Design by Hierarchical Integration of Action, Model and Argumentation
Authors: Nomaguchi Yutaka , Ohnuma Atsushi , Fujita Kikuo
Published: June 2008

This paper proposes a framework for acquiring design rationale in the conceptual design. Knowledge management is getting much attention for supporting the early phases of design process. While the research outcomes on design rationale might be useful in the direction, their capabilities are still far from practice. Such outcomes are categorized into model-based, argumentation-based and action-based frameworks. These are complementary when knowledge acquisition facility and explanatory power is considered. This paper introduces the hierarchical model of design rationale for overcoming the shortcomings of individual approaches under three frameworks. It consists of argument level, model operation level and action level. Argument level represents a designer’s decision making process. Model operation level represents a sequence of design operations. A design operation follows and is followed by a design stage, which records a design snapshot over conceptual product model. Action level represents design process as a sequence of operation primitives, which are elementary and atomic operations on the product model. These linkages of three levels enable to automatically acquire design rationale through operation primitives over a design support system.
A Multi-Agent Framework for Collaborative Engineering Design and Optimization
Authors: Hao Qi , Shen Weiming , Zhang Zhan , Park Seong-Whan , Lee Jai-Kyung
Published: June 2008

Agent technology is playing an increasingly important role in developing intelligent, distributed and collaborative applications. The innate difficulties of interoperation between heterogeneous agent communities and rapid construction of multi-agent systems have motivated the emergence of FIPA specifications and the proliferation of multi-agent system platforms or toolkits that implement FIPA specifications. In this paper, a FIPA compliant multi-agent framework called AADE (Autonomous Agent Development Environment) is presented. This framework, originating from the engineering fields, can facilitate the rapid development of collaborative engineering applications (especially in engineering design and manufacturing fields) through the provision of reusable packages of agent-level components and programming tools. An agent oriented engineering project on the development of an e-engineering design and optimization environment is designed and developed based on the facilities provided by the AADE framework.
Dynamic Query Interface for 3D Shape Search
Authors: Hou Suyu , Ramani Karthik
Published: June 2008

Our 3D Engineering Shape Search System (3DESS), which uses the skeletal graph as one of its shape features to represent objects, has revealed the potential of graph-based representation for searching 3D models. In this paper, a dynamic user interface, which allows a user to customize the query by reusing the existing skeletal graph, shows another merit of the skeletal graph representation. This innovative user interface serves two purposes: (i) an iconic object for sketching and visualizing the skeletal abstraction, which is a 3D geometric representation of the skeletal graph, and (ii) a dynamic query interface which enables the user to customize the skeletal abstraction of the retrieved model as a new query. In order to more closely represent the original model and more precisely evaluate the shape similarity during the search process, a method of refining the preliminary skeletal graph is presented and implemented. This process elaborates the skeletal abstraction to be closer to the shape of the model. Thus, the skeletal graph contains both the essential topology and the geometry information of the original model. The results show that the retrieved skeletal abstraction matches the skeleton of the original model effectively, and the search retrieval based on the customized skeletal graph is sensitive to the user’s intention.
Feature-Based Geometric Modeling Approach to Surface Micromachined MEMS
Authors: Gao Feng , Hong Steve Y. , Rosen David W.
Published: June 2008

Geometric modeling is an important aspect of MEMS design. It not only creates geometric models for visual evaluation, but also supplies input for device performance analysis. This paper focuses on developing a feature-based geometric design methodology that enables designers to create fabrication-ready 3D models of MEMS devices without concerning the mask layout. Compared with the present geometric design routine, which builds 3D device models through simulating the fabrication process from the photolithography masks, the function-oriented geometric design method allows designers to establish 3D models by using a set of pre-defined volumetric primitives associated with geometric constraints. The fabrication information is derived from the corresponding function-oriented data specified by designers. Hence, designers are released from the down-stream fabrication planning, and can focus on creative design. This research is the application of feature modeling and constraint-based design to the micro world. The workbench of this system is developed on the geometric model kernel ACIS.
A Statistical Approach to Causality Analysis in a Distributed Design Framework
Authors: Kim Jaehyun , Wallace David
Published: June 2008

Numerous collaborative design tools have been developed to accelerate the product development, and recently environments for building distributed simulations have been proposed. For example, a simulation framework called DOME (Distributed Object-oriented Modeling and Evaluation) has been developed in MIT CADLAB. DOME is unique in its decentralized structure that allows heterogeneous simulations to be stitched together while allowing proprietary information an simulation models to remain secure with each participant. While such an approach offers many advantages, it also hides causality and sensitivity information, making it difficult for designers to understand problem structure and verify solutions. The purpose of this research is to analyze the relationships between design parameters (causality) and the strength of the relationships (sensitivity) in decentralized web-based design simulation. Algorithms and implementations for the causality and sensitivity analysis are introduced. Causality is determined using Granger’s definition of causality, which is to distinguish causation from association using conditional variance of the suspected output variable. Sensitivity is estimated by linear regression analysis and a perturbation method, which transfers the problem into a frequency domain by generating periodic perturbations. Varying Internet latency and disturbances are problematic issues with these methods. Thus, new algorithms are developed and tested to overcome these problems.
Virtual Engineering: A Vision of the Next-Generation Product Realization Using Virtual Reality Technologies
Authors: Xiao Angran , Bryden Kenneth Mark
Published: June 2008

The dynamic and changing nature of the modern marketplace requires product development engineers to quickly perceive and understand the developed product, including its geometric features and physical characteristics. Virtual reality (VR) technology is capable of constructing a user-centered, three-dimensional environment in which abstract and complex information is visualized in an intuitive and realistic manner, hence becoming an efficacious tool for product realization. However, in most current applications, VR is only used as a visualization tool for showing geometry shapes and engineering analysis results. In this paper, we discuss virtual engineering, which expands the application scope of VR to the integration of virtual product model with analysis, simulation, decision making and other engineering tools into a virtual product realization environment that facilitates multidisciplinary and collaborative product realization among distributed engineers. In this paper, we present the implementation framework of a virtual engineering system and introduce our current work at developing this system. That is, we introduce VE-Suite, an extensible, cross-platform, open source library of tools that enable product realization in a virtual environment. Its functions and capabilities are demonstrated using a virtual fermentation tank used in biotechnology industry. Finally we raise a set of key research questions as a guideline for the further research and realization of virtual engineering.
An Approach to Supporting Synchronized Collaborative Design Within Heterogeneous CAD Systems
Authors: Li Min , Gao Shuming , Li Jie , Yang Youdong
Published: June 2008

This paper presents an approach to building up a synchronized collaborative design platform upon heterogeneous CAD systems. In the approach, Neutral Modeling Commands are used to achieve the real-time exchange of modeling operations between heterogeneous CAD systems. For the Neutral Modeling Commands, an object oriented representation is given and employed to support the translation between System Modeling Operations (SMO) and Neutral Modeling Commands (NMC). Moreover, two kinds of translators, SMO-to-NMC and NMC-to-SMO, are established, which can deal with modification/deletion operations and composite features and user-defined features besides common creation operations. The preliminary test results show that the proposed approach is promising.
Collaborative Product Development and Customization: A Platform-Based Strategy and Implementation
Authors: Zha Xuan F. , Sriram Ram D.
Published: June 2008

Mass customization and global economic collaboration drive the product development and management beyond internal enterprise to cover the whole product value chain. This paper presents a platform-based strategy and approach for collaborative product development and customization. The implementation of this strategy takes 1) the product platform as the core, 2) the view/search engine and rule-based control as the data access and navigation mechanism, and 3) the internet-enabled web-based integration and collaboration bus as an enabler to allow participants involved in the product lifecycle to access into both internal and external enterprise resources, applications, and services. In the paper, a generic collaborative platform design and development process model is presented for product family design and mass customization. Based on this model, a module-based integrated & distributed collaborative framework for product family design and mass customization is developed with knowledge intensive support for customer or task requirements’ modeling, product architecture modeling, product platform establishment, product family generation, and product variant assessment for customization. The issues related to the high-level information & knowledge modeling and the development of knowledge-intensive collaborative support framework are addressed. Finally, a case study for collaborative design of families of modular robotic systems is given.
Design System for Composite Transmission Error Prediction for Automatic Transmissions
Authors: Gudal Sameer , Pan Yong , Liou Shuh-Yuan , Sundararajan V. , Antonetti Daniel , Wright Paul K.
Published: June 2008

Noise in vehicular automatic transmissions is a complex phenomenon involving several interacting factors. One of the contributing factors to noise for a single pair of meshing gears has been shown to be the transmission error. The transmission error (TE) is defined in terms of deviation of the speed ratio from the ideal speed ratio. It has since been hypothesized that the composite transmission error in a planetary system would be the key contributor to noise in automatic transmissions. This composite error would have to include the contributions from individual meshes and account for the configuration of the transmission system. This paper describes a design system that enables engineers to predict and study effects of parameter variation on the composite transmission error. The designer first specifies the configuration of the transmission using canonical graphs. The graph contains the elements such as gears, clutches and brakes of the transmission system as its nodes and the relationship among them for the edges. The design system uses the graph to solve for the speeds and torques. The transmission errors for the individual meshes are computed and then combined into the composite transmission error using a simple average.
Metamodel Defined Multidimensional Embedded Sequential Sampling Criteria
Authors: Turner Cameron J. , Campbell Matthew I. , Crawford Richard H.
Published: June 2008

Collecting data to characterize an unknown space presents a series of challenges. Where in the space should data be collected? What regions are more valuable than others to sample? When have sufficient samples been acquired to characterize the space with some level of confidence? Sequential sampling techniques offer an approach to answering these questions by intelligently sampling an unknown space. Sampling decisions are made with criteria intended to preferentially search the space for desirable features. However, N-dimensional applications need efficient and effective criteria. This paper discusses the evolution of several such criteria based on an understanding of the behaviors of existing criteria, and desired criteria properties. The resulting criteria are evaluated with a variety of planar functions, and preliminary results for higher dimensional applications are also presented. In addition, a set of convergence criteria, intended to evaluate the effectiveness of further sampling are implemented. Using these sampling criteria, an effective metamodel representation of the unknown space can be generated at reasonable sampling costs. Furthermore, the use of convergence criteria allows conclusions to be drawn about the level of confidence in the metamodel, and forms the basis for evaluating the adequacy of the original sampling budget.
Effect of Pillow Block Deformation on Ball Bearing Load Distribution
Authors: Tibbits Patrick A.
Published: June 2008

Support structure deflection distorts bearing rings, redistributes loads over bearing balls, and affects bearing life. In this study, solid finite elements modeled a shaft, bearing inner ring, outer ring, and pillow block. A nonlinear spring element represented each of the bearing balls. The force-versus-deflection curve of the spring element modeled the variable stiffness of the ball/raceway Hertzian contact. The curve also incorporated the diametrical clearance of the bearing to determine if each ball contacted the raceways. Further modification of the curve compensated for the compliance of the nodes of solid elements that modeled raceways. This construct avoided computationally expensive surface-to-surface contact calculations. Program output included deflection of the pillow block and a listing of spring element forces, which characterized the ball loads. The maximum ball load decreased for a bearing installed in a pillow block, and life increased. Material or geometric changes that reduced pillow block stiffness further improved life.
Study of Supersonic Flowfield With Secondary Injection
Authors: Sun D. , Amano R. S.
Published: June 2008

Two and three-dimensional steady flowfields generated by transverse secondary injection into a supersonic flow, was simulated by solving the Favre-averaged Navier-Stokes equations using the weighted essentially nonoscillatory (WENO) schemes. Both the two-dimensional and three-dimensional results are given. Some parameters affecting the penetration height and separation length of the interactive flowfield, including the total pressure ratio of the jet to the freestream, the boundary layer thickness, slot width, the Mach number of the freestream and injection, the jet angle, and the shape of the injection orifice in the 3D flowfield, were calculated in more detail.
On System Identification and Model Verification of Differential Hysteresis
Authors: Ng C. H. , Ma F.
Published: June 2008

The generalized Bouc-Wen differential model is a widely used empirical model of hysteresis for structures under cyclic loadings. In this paper, system identification based upon the simplex algorithm is used to estimate the thirteen parameters of the differential model. It is then experimentally verified that the identified models of hysteresis possess predictive capabilities. Through identification and verification, it is demonstrated that the response of a structure may be predicted well beyond its linear range.
Design of an Electric Motor Failure Testbed
Authors: Turner Cameron J. , Crawford Richard H.
Published: June 2008

Component failures in hazardous and unfamiliar design environments can be critical. One needs to look no further than at the results of component failures in the Mars probe Spirit to see how significant a simple failure may become. However, similarly unusual environments can be found on Earth, such as within the materials processing lines at Los Alamos National Laboratory. In these lines, radioactive materials must be handled with extreme care. Not only do these materials present a radiological hazard, but also they often they represent toxic and corrosive hazards. To limit human contact with these materials, automation systems are desirable, but unlike humans, automation systems do not provide warning of impending failures. Developing the capabilities for automation systems to warn operators of developing incipient failures is crucial to the continued introduction of automation systems into this unusual terrestrial environment. This paper describes the design, fabrication and integration of a testbed intended to develop our knowledge of how failures occur within simple mechanical component systems typically deployed within this environment. The preliminary results suggest that incipient failures are detectable, and that with this knowledge, it may be possible to develop automation technologies that can provide warning of impending failures before the continued operation of the system is jeopardized.
Handling Imprecise and Uncertain Engineering Information in IDEF1X and Relational Data Models
Authors: Ma Z. M.
Published: June 2008

Database modeling of engineering information is crucial for constructing manufacturing systems because current manufacturing industries are typically information-based enterprises and information systems have become their nervous center. Engineering information can be modeled at two levels: conceptual data model and logical database model. Generally a conceptual data model is designed and then the designed conceptual data model will be transformed into the chosen logical database schema. Imprecise and uncertain information, however, is generally involved in many engineering activities and imprecise and uncertain engineering information are represented by fuzzy sets. Nowadays relational databases are still the most useful database product and IDEF1X is most useful for logical database design of relational databases in engineering. So in this paper, we focus on fuzzy data modeling in IDEF1X and relational databases. The formal approaches to mapping fuzzy IDEF1X models to fuzzy relational database schemes are hereby developed.
A Knowledge Repository for Behavioral Models in Engineering Design
Authors: Mocko Gregory , Malak Richard , Paredis Christiaan , Peak Russell
Published: June 2008

Computer simulations and behavioral modeling are becoming increasingly important in product development processes. Simulations can result in better decisions in less time by providing the designers with greater understanding of the product’s behavior. However, behavior model creators (i.e. analysts) and behavior model users (i.e. designers) often do not have the same level of understanding of the model, thus limiting the reuse of a model. Our goal in this research is to develop a clean interface that reduces the knowledge gap between engineering design and analysis by facilitating reuse of behavioral models. To achieve a higher level of reuse in the product design process, we propose a meta-data representation for formally characterizing behavioral models. The meta-data representation captures the assumptions, limitations, accuracy, and context of engineering behavioral models. Based on this knowledge representation, a proof-of-concept repository is implemented for archiving and exchanging reusable behavioral models. The knowledge representation and implementation is illustrated with a simple cantilever beam example.
Improving the Engineering Processes With Text Mining
Authors: Kasravi Kas
Published: June 2008

The engineering process relies on extensive sources of knowledge in textual form, such as books, conference papers, product catalogs, and web pages. Leveraging the full value of the knowledge in textual data is difficult due to the length of time required to read and comprehend the documents. Text mining untaps the vast amounts of information buried in textual data. Text mining can process the content of large numbers of documents, semantically analyze and organize the content, and extract the useful information for downstream applications. Once analyzed, the informational content of documents can be indexed and accessed in multiple formats, such as summaries, key concepts, events, relationships, and visual representations. Applications of text mining in engineering are diverse and include predictive warranty analysis, quality improvements, patent analysis, competitive assessments, FMEA, and product searches.
Backscatter dose from metallic materials due to obliquely incident high‐energy photon beams
Authors: Nadrowitz Roger , Feyerabend Thomas
Published: June 2008

If metallic material is exposed to ionizing radiation of sufficient high energy, an increase in dose due to backscatter radiation occurs in front of this material. Our purpose in this study was to quantify these doses at variable distances between scattering materials and the detector at axial beam angles between (zero angle in beams eye view) and Copper, silver and lead sheets embedded in a phantom of perspex were exposed to 10 MV‐bremsstrahlung. The detector we developed is based on the fluorescence property of pyromellitic acid (1,2,4,5 benzenetetracarboxylic acid) after exposure to ionizing radiation. Our results show that the additional doses and the corresponding dose distribution in front of the scattering materials depend quantitatively and qualitatively on the beam angle. The backscatter dose increases with varying beam angle from to up to a maximum at for copper and silver. At angles of and the integral backscatter doses over a tissue‐equivalent depth of 2 mm are 11.2% and 21.6% for copper and 24% and 28% for silver, respectively. In contrast, in front of lead there are no obvious differences of the measured backscatter doses at angles between and With a further increase of the beam angle from to the backscatter dose decreases steeply for all three materials. In front of copper a markedly lower penetrating depth of the backscattered electrons was found for an angle of compared to This dependence from the beam angle was less pronounced in front of silver and not detectable in front of lead. In conclusion, the dependence of the backscatter dose from the angle between axial beam and scattering material must be considered, as higher scattering doses have to be considered than previously expected. This may have a clinical impact since the surface of metallic implants is usually curved.
Monte Carlo calculation of output factors for circular, rectangular, and square fields of electron accelerators (6–20 MeV)
Authors: Verhaegen F. , Mubata C. , Pettingell J. , Bidmead A. M. , Rosenberg I. , Mockridge D. , Nahum A. E.
Published: June 2008

Monte Carlo (MC) techniques can be used to build a simulation model of an electron accelerator to calculate output factors for electron fields. This can be useful during commissioning of electron beams from a linac and in clinical practice where irregular fields are also encountered. The Monte Carlo code BEAM/EGS4 was used to model electron beams (6–20 MeV) from a Varian 2100C linear accelerator. After optimization of the Monte Carlo simulation model, agreement within 1% to 2% was obtained between calculated and measured (with a Si diode) lateral and depth dose distributions or within 1 mm in the penumbral regions. Output factors for square, rectangular, and circular fields were measured using two different plane‐parallel ion chambers (Markus and NACP) and compared to MC simulations. The agreement was usually within 1% to 2%. This study was not primarily concerned with minimizing the simulation time required to obtain output factors but some considerations with respect to this are presented. It would be particularly useful if the MC model could also be used to calculate output factors for other, similar linacs. To see if this was possible, the primary electron energies in the MC model were retuned to model a recently commissioned similar linac. Good agreement between calculated and measured output factors was obtained for most field sizes for this second accelerator.
An automated patient recognition method based on an image‐matching technique using previous chest radiographs in the picture archiving and communication system environment
Authors: Morishita Junji , Katsuragawa Shigehiko , Kondo Keisuke , Doi Kunio
Published: June 2008

An automated patient recognition method for correcting “wrong” chest radiographs being stored in a picture archiving and communication system (PACS) environment has been developed. The method is based on an image‐matching technique that uses previous chest radiographs. For identification of a “wrong” patient, the correlation value was determined for a previous image of a patient and a new, current image of the presumed corresponding patient. The current image was shifted horizontally and vertically and rotated, so that we could determine the best match between the two images. The results indicated that the correlation values between the current and previous images for the same, “correct” patients were generally greater than those for different, “wrong” patients. Although the two histograms for the same patient and for different patients overlapped at correlation values greater than 0.80, most parts of the histograms were separated. The correlation value was compared with a threshold value that was determined based on an analysis of the histograms of correlation values obtained for the same patient and for different patients. If the current image is considered potentially to belong to a “wrong” patient, then a warning sign with the probability for a “wrong” patient is provided to alert radiology personnel. Our results indicate that at least half of the “wrong” images in our database can be identified correctly with the method described in this study. The overall performance in terms of a receiver operating characteristic curve showed a high performance of the system. The results also indicate that some readings of “wrong” images for a given patient in the PACS environment can be prevented by use of the method we developed. Therefore an automated warning system for patient recognition would be useful in correcting “wrong” images being stored in the PACS environment.
Acceleration of dose calculations for intensity‐modulated radiotherapy
Authors: Siebers Jeffrey V. , Tong Shidong , Lauterbach Marc , Wu Qiuwen , Mohan Radhe
Published: June 2008

The requirements and trade‐offs between accuracy and speed for radiotherapy dose computations have been discussed for decades. Inverse planning used for intensity‐modulated radiotherapy (IMRT) optimization imposes additional demands on dose calculation since it is an iterative process in which dose calculations might be repeated many (10's to 1000's) of times. This work discusses the accuracy and speed issues as related to IMRT dose calculations. A hybrid dose calculation method which accelerates the optimization process is proposed and applied in which a fast‐pencil beam (PB) model is used for initial optimization iterations, followed by superposition/convolution (SC) calculations. Optimization dose results are compared for pure PB optimization, pure SC optimization, and PB optimization followed by SC optimization. Plans were evaluated in terms of isodose coverage, dose‐volume histograms, and total dose calculation time for five head and neck cases with diverse locations, sizes, and shapes for tumors and critical structures. Patient plans were designed for nine equispaced beams. For one patient, an additional five‐beam configuration was tested. We found that gross features of intensity distributions resulting from all schemes were similar, however there were differences in the fine detail. Differences were small between composite dose distributions optimized with PB and SC methods, yet differences in individual beam dose distributions were quite significant. When the SC method was used to compute dose following optimization with PB method, dose differences were reduced significantly both for composite plans and for individual beams. Substantial overall timesavings were observed, allowing IMRT dose planning to become a more interactive activity.
A measured data set for evaluating electron‐beam dose algorithms
Authors: Boyd Robert A. , Hogstrom Kenneth R. , Antolak John A. , Shiu Almon S.
Published: June 2008

The purpose of this work was to develop an electron‐beam dose algorithm verification data set of high precision and accuracy. Phantom geometries and treatment‐beam configurations used in this study were similar to those in a subset of the verification data set produced by the Electron Collaborative Working Group (ECWG). Measurement techniques and quality‐control measures were utilized in developing the data set to minimize systematic errors inherent in the ECWG data set. All measurements were made in water with p‐type diode detectors and using a Wellhöfer dosimetry system. The 9 and 20 MeV, beams from a single linear accelerator composed the treatment beams. Measurements were made in water at 100 and 110 cm source‐to‐surface distances. Irregular surface measurements included a “stepped surface” and a “nose‐shaped surface.” Internal heterogeneity measurements were made for bone and air cavities in differing orientations. Confidence in the accuracy of the measured data set was reinforced by a comparison with Monte Carlo (MC)‐calculated dose distributions. The MC‐calculated dose distributions were generated using the OMEGA/BEAM code to explicitly model the accelerator and phantom geometries of the measured data set. The precision of the measured data, estimated from multiple measurements, was better than 0.5% in regions of low‐dose gradients. In general, the agreement between the measured data and the MC‐calculated data was within 2%. The quality of the data set was superior to that of the ECWG data set, and should allow for a more accurate evaluation of an electron beam dose algorithm. The data set will be made publicly available from the Department of Radiation Physics at The University of Texas M. D. Anderson Cancer Center.
Regional improvement of signal‐to‐noise and contrast‐to‐noise ratios in dual‐screen CR chest imaging—a phantom study
Authors: Liu Xinming , Shaw Chris C.
Published: June 2008

The improvement of signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) in dual‐screen computed radiography (CR) has been investigated for various regions in images of an anthropomorphic chest phantom. With the dual‐screen CR technique, two image plates are placed in a cassette and exposed together during imaging. The exposed plates are separately scanned to form a front image and a back image, which are then registered and superimposed to form a composite image with improved SNRs and CNRs. The improvement can be optimized by applying specifically selected weighting factors during superimposition. In this study, dual‐screen CR images of an anthropomorphic chest phantom were acquired and formed with four different combinations of standard resolution (ST) and high‐resolution (HR) screens: ST–ST, ST–HR, HR–ST, and HR–HR. SNRs and their improvements were measured and compared over twelve representative regions‐of‐interest (ROIs) in these images. A 19.1%–45.7% increase of the SNR was observed, depending on the ROI and screen combination used. The optimal weighting factors were found to vary by only 4.5%–12.4%. Largest improvement was found in the lung field for all screen combinations. Improvement of CNRs was investigated over two ROIs in the lung field using the rib bones as the contrast objects and a 29.2%–43.9% improvement of the CNR was observed. Among the four screen combinations, ST–ST resulted in the most SNR and CNR improvement, followed in order by HR–ST, HR–HR, and ST–HR. The HR–ST combination yielded the lowest spatial variation of the optimal weighting factors with improved SNRs and CNRs close to those of the ST–ST combination.
A theoretical model for event statistics in microdosimetry. I: Uniform distribution of heavy ion tracks
Authors: Cruz G. A. Santa , Palmer M. R. , Matatagui E. , Zamenhof R. G.
Published: June 2008

In this work we describe a novel approach to solving microdosimetry problems using conditional probabilities and geometric concepts. The intersection of a convex site with a field of randomly oriented straight track segments is formulated in terms of the relative overlap between the chord associated with the action line of the track and the track itself. This results in a general formulation that predicts the contribution of crossers, stoppers, starters, and insiders in terms of two separate functions: the chord length distribution (characteristic of the site geometry and the type of randomness) and an independent set of conditional probabilities. A Monte Carlo code was written in order to validate the proposed approach. The code can represent the intersection between an isotropic field of charged particle tracks and a general ellipsoid of unrestricted geometry. This code was used to calculate the event distribution for a sphere as well as the expected mean value and variance of the track length distribution and to compare these against the deterministic calculations. The observed agreement was shown to be very good, within the precision of the Monte Carlo approach. The formulation is used to calculate the event frequency, lineal energy, and frequency mean specific energy for several monoenergetic and isotropic proton fields in a spherical site, as a function of the site diameter, proton energy, and the event type.
A cone beam filtered backprojection (CB‐FBP) reconstruction algorithm for a circle‐plus‐two‐arc orbit
Authors: Tang Xiangyang , Ning Ruola
Published: June 2008

The circle‐plus‐arc orbit possesses advantages over other “circle‐plus” orbits for the application of x‐ray cone beam (CB) volume CT in image‐guided interventional procedures requiring intraoperative imaging, in which movement of the patient table is to be avoided. A CB circle‐plus‐two‐arc orbit satisfying the data sufficiency condition and a filtered backprojection (FBP) algorithm to reconstruct longitudinally unbounded objects is presented here. In the circle suborbit, the algorithm employs Feldkamp's formula and another FBP implementation. In the arc suborbits, an FBP solution is obtained originating from Grangeat's formula, and the reconstruction computation is significantly reduced using a window function to exclude redundancy in Radon domain. The performance of the algorithm has been thoroughly evaluated through computer‐simulated phantoms and preliminarily evaluated through experimental data, revealing that the algorithm can regionally reconstruct longitudinally unbounded objects exactly and efficiently, is insensitive to the variation of the angle sampling interval along the arc suborbits, and is robust over practical x‐ray quantum noise. The algorithm's merits include: only 1D filtering is implemented even in a 3D reconstruction, only separable 2D interpolation is required to accomplish the CB backprojection, and the algorithm structure is appropriate for parallel computation.
Computerized image analysis: Estimation of breast density on mammograms
Authors: Zhou Chuan , Chan Heang‐Ping , Petrick Nicholas , Helvie Mark A. , Goodsitt Mitchell M. , Sahiner Berkman , Hadjiiski Lubomir M.
Published: June 2008

An automated image analysis tool is being developed for the estimation of mammographic breast density. This tool may be useful for risk estimation or for monitoring breast density change in prevention or intervention programs. In this preliminary study, a data set of 4‐view mammograms from 65 patients was used to evaluate our approach. Breast density analysis was performed on the digitized mammograms in three stages. First, the breast region was segmented from the surrounding background by an automated breast boundary‐tracking algorithm. Second, an adaptive dynamic range compression technique was applied to the breast image to reduce the range of the gray level distribution in the low frequency background and to enhance the differences in the characteristic features of the gray level histogram for breasts of different densities. Third, rule‐based classification was used to classify the breast images into four classes according to the characteristic features of their gray level histogram. For each image, a gray level threshold was automatically determined to segment the dense tissue from the breast region. The area of segmented dense tissue as a percentage of the breast area was then estimated. To evaluate the performance of the algorithm, the computer segmentation results were compared to manual segmentation with interactive thresholding by five radiologists. A “true” percent dense area for each mammogram was obtained by averaging the manually segmented areas of the radiologists. We found that the histograms of 6% (8 CC and 8 MLO views) of the breast regions were misclassified by the computer, resulting in poor segmentation of the dense region. For the images with correct classification, the correlation between the computer‐estimated percent dense area and the “truth” was 0.94 and 0.91, respectively, for CC and MLO views, with a mean bias of less than 2%. The mean biases of the five radiologists' visual estimates for the same images ranged from 0.1% to 11%. The results demonstrate the feasibility of estimating mammographic breast density using computer vision techniques and its potential to improve the accuracy and reproducibility of breast density estimation in comparison with the subjective visual assessment by radiologists.
Fast algorithm for iterative image reconstruction with a small animal positron emission tomograph YAP‐PET (in English)
Authors: Motta Alfonso
Published: June 2008

A fast deconvolutive expectation maximization algorithm for iterative image reconstruction was developed for use with a small animal positron emission tomograph YAP‐PET built by the Medical Physics Group at Ferrara University. It has a FOV of 4 cm diam×4 cm axially. In PET modality, the tomograph has a sensitivity of 640 cps/μCi at its center and a spatial resolution of 1.8 mm FWHM. In SPECT, the sensitivity is 2.1 cps/μCi for each detector head, with a spatial resolution of 3.5 mm FWHM. The 3D‐FBP algorithm, usually used for image reconstruction, has a limited angle due to the geometry of the tomograph, which causes a serious loss in sensitivity. We developed an iterative method using the symmetries and the sparse properties of the “probability matrix,” which correlates the emission from each voxel to the detector within a coincidence tube, which we calculated before the reconstruction. We stored only a fraction of matrix elements on disk, thus avoiding on‐line computation, that needs to be performed for the projection and the backprojection steps. This reduces the required storage space by a factor of and the time per iteration from hours to minutes or tens of minutes. A deconvolutive model differentiates the voxels according to their depth in a coincidence tube. This algorithm is used for both PET and SPECT data. It improves the signal‐to‐noise ratio and the spatial resolution. Additionally it allows quantitative data to be available on images in the SPECT mode for cardiac perfusion and uptake studies using 99m‐Tc labeled radiopharmaceuticals.
Modeling the impact of two forms of hypoxia on novel radiotherapy approaches (in English)
Authors: Daşu Alexandru
Published: June 2008

Theoretical modeling of the biological response is considered for inclusion into treatment planning algorithms. However, the results are model sensitive and therefore the choice of the model is very important. In this thesis we aimed to compare the predictions in the clinical dose range for the linear quadratic (LQ) model and the linear quadratic model with inducible repair (LQ/IR) and to determine the possible therapeutic gain of different treatment strategies, taking into consideration the microenvironmental conditions known to exist in tumors. The main focus was on the availability of oxygen and other nutrients to tumor cells, knowing that tumor vasculature is very poor compared to that in normal tissues. The brief interruption of oxygen supply to the acutely hypoxic cells determines an increased radioresistance, while the lack of oxygen and other nutrients in starved hypoxic cells results in a radiosensitization due to the reduction of cellular energy charge. It is the first time this latter aspect of tumor sensitivity was considered for a theoretical model. The modeling showed that there are some important differences in the clinical dose range between the predicted responses with the two models. Some of these differences provide an alternative explanation to the success of hyperfractionation and also explain some unusual results reported in the literature with respect to hypoxic protection. The analysis of the complex relationship between the induction of repair and the intrinsic radioresistance indicates the possible therapeutic gain that can be expected from more extreme fractionation. The existence of starved chronically hypoxic cells in tumors, with their incapacity to activate repair provides a better understanding of the tumor response to radiation treatments.
The challenge of “sperm ships”: the need for the global regulation of medical technology
Authors: Hunter D , Oultram S
Published: June 2008

This paper discusses the notion of using international shipping legislation to provide healthcare technologies to inhabitants of a country on a ship in international waters based just outside the country’s border. This allows technologies that would otherwise be unavailable, regulated or banned to the citizens of a particular nation to be available, just offshore. This is because in international waters ships are governed by the laws of their home nation not those they are nearby. We focus on the example suggested recently in the UK of “sperm ships”, flying Danish flags to circumvent IVF regulation in the UK. While we acknowledge that this general strategy could be used to do good by providing healthcare where it would not be otherwise available, it also provides a significant challenge to the effective sovereignty of the state and its ability to regulate healthcare technologies for the benefit of its citizens. We discuss this challenge to the regulation of healthcare and suggest a few tentative solutions.
A qualified endorsement of embryonic stem cell research, based on two widely shared beliefs about the brain-diseased patients such research might benefit
Authors: DiSilvestro R
Published: June 2008

Are there persuasive approaches to embryonic stem cell (ESC) research that appeal, not just to those fellow-citizens in one’s own ideological camp, nor just to those undecided citizens in the middle, but to those citizens on the other side of the issue? I believe that there are such arguments and in this short paper I try to develop one of them. In particular, I argue that certain beliefs shared by some proponents and some opponents of ESC research—beliefs about the personal identity and moral status of those who are victims of terrible brain diseases—are beliefs that should lead us to adopt a qualified endorsement of ESC research.
Public healthcare resource allocation and the Rule of Rescue
Authors: Cookson R , McCabe C , Tsuchiya A
Published: June 2008

In healthcare, a tension sometimes arises between the injunction to do as much good as possible with scarce resources and the injunction to rescue identifiable individuals in immediate peril, regardless of cost (the “Rule of Rescue”). This tension can generate serious ethical and political difficulties for public policy makers faced with making explicit decisions about the public funding of controversial health technologies, such as costly new cancer drugs. In this paper we explore the appropriate role of the Rule of Rescue in public resource allocation decisions by health technology funding advisory bodies such as the National Institute for Health and Clinical Excellence. We consider practical approaches to operationalising the Rule of Rescue from Australia and the UK before examining the relevance of individual moral imperatives to public policy making. We conclude that that whilst public policy makers in a humane society should facilitate exceptional departures from a cost effectiveness norm in clinical decisions about identified individuals, it is not so obvious that they should, as a matter of national public policy, exempt any one group of unidentified individuals within society from the rules of opportunity cost at the expense of all others.