bluuebunny/crossref_metadata_2025 huggingface dataset:
Short‐Term Evaluation of Dorsal Acetabular Augmentation in 10 Canine Total Hip Replacements
Authors: Pooya Hooman A. , Schulz Kurt S. , Wisner Eric R. , Montavon Pierre , Jackson Josh
Published: March 2003

Objective—To report the use of dorsal acetabular augmentation (DAA) in canine total hip arthroplasty (THA) and to evaluate the clinical and radiographic outcome after a minimum of 1 year follow‐up.

Study Design—Clinical study.

Animals—Nine dogs that had THA.

Methods—Ten hips requiring acetabular augmentation for optimum acetabular cup implantation for THA were evaluated retrospectively. The excised femoral head and neck was used as the corticocancellous bone graft for index THA surgeries, and the dorsal crest of the ipsilateral ilial wing was used as the bone graft in 1 dog that had a revision surgery. Clinical and radiographic follow‐up examinations were performed at approximately 8 weeks and 1 year postoperatively. Long‐term radiographic examinations included use of a standing dorsal acetabular rim (DAR) projection for assessment of graft‐recipient boundary. Functional clinical outcome was assessed using direct patient evaluation and telephone interview.

Results—One dog failed to regain limb function after surgery. Suspected aseptic loosening of the acetabular cup was observed on radiographs approximately 12 weeks postoperatively. Excluding this single explantation, follow‐up physical and radiographic examinations indicated good implant and graft positioning and normal function for all dogs.

Conclusions—Acetabular augmentation permitted implantation of an appropriately sized acetabular cup while maintaining complete DAR coverage of the prosthesis. Nine out of 10 hips had a successful outcome with minimal radiographic and no functional abnormalities. Further follow‐up is necessary to determine the long‐term outcome of DAR augmentation in canine THA.

Clinical Relevance—Acetabular augmentation with an autogenous corticocancellous bone graft constructed from the femoral head and neck can provide complete DAR coverage to permit use of an appropriately sized acetabular cup in THA.
New service design in the NHS: an evaluation of the strategic alignment of NHS Direct
Authors: Silvestro Rhian , Silvestro Claudio
Published: March 2003

Awareness of inconsistencies and variability in the delivery of health services across the UK has heightened in recent years, leading to general acknowledgement that a move away from “health care by post code” is a strategic priority for the National Health Service (NHS). NHS Direct, a call centre service for patients and their carers, is unique in the NHS in that it represents an entirely new service concept, with a rare opportunity to design a single nation‐wide service from scratch, and to manage and co‐ordinate a delivery system consistently throughout the country. Evaluates the strategic alignment of NHS Direct during the first three years of implementation through an analysis of its service concept, its operational objectives, the design of its delivery systems and its volume and variety characteristics. The evaluation reveals an absence of a central design specification which has resulted in wide variation in the call centres’ service portfolios, resource bases, competences, telephony and clinical expert systems. Contends that variation and variability in the design of the call centres has severely compromised NHS Direct's ability to meet its strategic and operational objectives, resulting in strategic misalignment. Also identifies missed opportunities to learn from the growing call centre literature and from service shops in other industries.
Function approximation of total system cost for a continuous manufacturing system
Authors: Nagaraj P. , Selladurai V.
Published: March 2003

This paper presents a case study conducted in a sugar mill. The multi‐level lot‐sizing model suggested by Gunasekaran where the whole manufacturing system modelled as a function of total system cost (TSC) is used for this application. This study deals with minimising the TSC of a multi‐stage, multi‐facility and multi‐product manufacturing system in which the buffer in between the stages is not allowed. The model is applied to find out the TSC and hence the fluctuating purchase prices of raw material. The consequence of implementing different costs that may occur due to change in government policies is analysed. This work has been carried out in an IBM/PC compatible system.
E‐trust: the influence of perceived interactivity on e‐retailing users
Authors: Merrilees Bill , Fry Marie‐Louise
Published: March 2003

E‐retailing has received considerable attention in recent years, especially with the help of consumer behaviour concepts and tools. This particular paper focuses on e‐trust and its antecedents. Special attention is given to the proposition that the more a site is perceived to be interactive, then the greater the trust that users attach to that site. Previous research has demonstrated this relationship with respect to a particular site. The current paper re‐examines this relationship with respect to another site. More importantly, the paper tests whether the nexus between interactivity and e‐trust applies to both pure “click” and “brick and click” e‐retailers.
Fast search algorithms for look‐up tables
Authors: Yoon Sugjoon , Kang Hyunjoo
Published: March 2003

Various parameter values are provided in the form of data tables, where data keys are ordered and unevenly spaced in general, for real‐time simulation of dynamic systems. However, most parameter values required for simulation do not explicitly exist in data tables. Thus, unit intervals, including parameter values, are searched rather than the data keys. Since real‐time constraint enforces use of a fixed step size in integration of system differential equations because of the inherent nature of input from and output to real hardware, the worst case of iterated probes in searching algorithms is the core measure for comparison. The worst case is expressed as Big O. In this study, conventional bisection, interpolation, and fast searches are analyzed and compared in Big O as well as the newly developed searching algorithms: modified fast search and modified regular falsi search. If the criterion is actual execution time required for searching, most numerical tests in this paper show that bisection search is superior to the others. Interpolation search and its variations show better performance in the case of linear or near linear data distribution than bisection search. The numerical tests show that modified regular falsi search is faster than the other interpolation searches in either expected time or worst cases. Given parameter tables should be carefully examined for their data distribution in order to determine the most appropriate searching algorithm for the application.
Elasto‐plastic analysis of three‐dimensional structures
Authors: Rezaiee‐Pajand M. , Nazem M.R.
Published: March 2003

In this paper, quasi‐Tresca yield surfaces are reviewed. In order to do elasto‐plastic analysis, a new yield criterion is presented. The proposed yield surface can be used in nonlinear three‐dimensional analysis of structures. Function of the yield surface is presented in principal stress space and also Cartesian one. A computer program has been developed for nonlinear analysis in C++. Numerical examples have been solved by the proposed yield surface and good results have been obtained.
Mesh tying on curved interfaces in 3D
Authors: Puso Michael A. , Laursen Tod A.
Published: March 2003

In this work, a mortar method is implemented for tying arbitrary dissimilar 3D meshes, i.e. 3D meshes with curved, non‐matching interfaces. The 3D method requires approximations to the surface integrals specified by the projection of the displacement jump across the interface onto the Lagrange multiplier space. The numerical integration scheme is presented and several Lagrange multiplier interpolation schemes are considered. Furthermore, some implementational issues such as how to handle boundary conditions will be described such that stability is retained. Finally, the implementation will be demonstrated in numerical simulations and comparison of different formulations will be made.
Sophisticated HDI flexible substrates for advanced applications
Authors: Stampanoni M.
Published: March 2003

Miniaturization driven PWBs used for implantable medical devices, hearing aids and other medical and scientific applications, as well as for advanced products in the printing and telecommunication industry, ask for finer and finer structures. Via/pad geometries down to 40/100 microns with 20 microns line and spaces are required, for example, in advanced medical ultrasound probes and for detectors in particle accelerators. State‐of‐the‐art image transfer processes allow extremely dense and precise conductor geometries on very thin flexible circuits with one to six or even more copper layers. These modern image transfer processes, together with an optimised plating process and the combination of UV‐YAG laser and microwave plasma drilling for mass microvia formation, result in a very efficient manufacturing technology for highly reliable HDI boards. This HDI manufacturing technology, applied to polyimide materials that can operate over a wide range of temperatures and to new flexible liquid crystalline polymer (LCP) materials with outstanding radio frequency properties, opens up a completely new world of exciting opportunities.
A novel process for the manufacturing of advanced interconnects
Authors: Mosses R. , Brackenridge S.
Published: March 2003

A wide variety of novel processing techniques can be used in conjunction with new polymer technologies to enable the clean, efficient and accurate manufacturing of interconnects that provide new solutions to meet the challenges of future environmental, customer and market demands. This paper discusses work undertaken on the development of a suite of alternative approaches to the conventional interconnect manufacturing routes. These new approaches not only offer distinct advantages for the short batch or prototype market, but more interestingly also offer possibilities for use in the high volume, high density interconnect market that increasingly needs innovative manufacturing approaches for many types of electronics products. A new process using mechanical routing or laser ablation in combination with conductive pastes is described.
The relationship between self‐annealing of plated copper and copper surface treatment
Authors: Nakagawa Toshiko
Published: March 2003

This paper discusses how the grain size of plated copper changes as time passes by observing the copper surface topography after surface treatment with a roughening agent. This paper also discusses how the time until the recrystallization terminates depends on the amount and type of plating additives as well as current density. The results agree with the known mechanism of grain growth. As a result of our experiments, the best process to gain the optimal surface topography is proposed. We firmly believe that this paper will contribute to the improvement in quality control of the copper surface treatment process, which will in turn lead to the fabrication of PCBs and plastic packages with higher reliability.
A three‐dimensional transmission line matrix (TLM) simulation method for thermal effects in high power insulated gate bipolar transistors
Authors: Hocine R. , Lim D. , Pulko S.H. , Boudghene Stambouli M.A. , Saidane A.
Published: March 2003

In this paper, thermal analysis for a 1,200 A, 3.3 kV insulated gate bipolar transistor (IGBT) module was investigated and analysed using the three‐dimensional transmission line matrix (3D‐TLM) method. This paper also reviews the present status of the use of various thermal heat spreaders such as AlSiC MMC, Cu‐Mo and graphite‐Cu MMC and compares these with copper based heat spreaders and the use of aluminium nitride (AlN), diamond and BeO as substrates and their effect to dissipate the heat flux in heat sources localised in IGBT module design. The TLM method was found to be a versatile tool which is ideally suited to the modelling of many power electronic devices and which proved very useful in the study of transient thermal effects in a variety of device structures.
Application of the Hoshin Kanri methodology at a higher education establishment in the UK
Authors: Roberts Paul , Tennant Charles
Published: March 2003

Hoshin Kanri has been described as one of the core aspects of Japan’s management system, for integrating the principles of total quality management (TQM) within the organisation’s business strategy. Although most of the published case studies have involved large multinational manufacturers, the authors believe that Hoshin Kanri can be applied in any type or size of organisation. This paper describes how the quality and reliability (Q&R) team of the Warwick Manufacturing Group (WMG) at the University of Warwick has applied Hoshin Kanri to create a deeper understanding of customer requirements, a team vision and strategic goals. Deployment has led to achievement of team consensus and commitment to delivering and reviewing the plan, and has demonstrated that the technique works well in a small team within the service sector.
Where next for ISO 9000 companies?
Authors: Coleman Shirley , Douglas Alex
Published: March 2003

Many organisations take their quality improvement initiatives no further than ISO 9000. Others try to achieve TQM and fail, while others successfully make the transition. This may be because the requirements for TQM are not clear. However, the requirements for implementing the EFQM model criteria are clear and therefore may allow an organisation’s senior management to help drive their company towards excellence, perhaps with some external assistance. This paper investigates what happens with regard to quality management after an organisation has achieved ISO 9000. In particular, the extent of adoption of the EFQM excellence model is examined, as is the use of proven quality improvement tools and techniques such as statistical process control (SPC). Associated with these improvement techniques, the importance and standard of external assistance in implementing them are examined. The paper concludes that training, the use of SPC and working to the EFQM model criteria are all significant factors if an organisation is to be perceived as successful.
The establishment of a TQM system for the health care industry
Authors: Yang Ching‐Chow
Published: March 2003

In recent years, the health care industry in Taiwan has been facing various difficulties, which are primarily from the implementation of National Health Care Insurance policy. The more severe problems, like the increase in operating costs and income reduction, are included with the high cut rate examined by BNHI, and the shortage of physicians. The most critical current issue to hospitals is researching the remedies to resolve the problems. Some hospitals have employed ISO 9000 as the solution; some have chosen HQIC or MQIP. However, it is necessary to implement advanced TQM when the health care institutes want to resolve these problems more effectively. There are some conflicts between the health care professional and the TQM concepts and practices. In this paper, a practically applicable system of TQM is developed for the health care institutes. Several hospitals have utilized this TQM system and have obtained many substantial results, such as upgrading the service quality and customers’ satisfaction, and improving the administration performance, etc. Therefore, for a more efficient operation, the Bureau of National Health Care should eagerly promote the TQM system to hospitals.
Online university learning: cognitive and affective perspectives
Authors: Katz Yaacov J. , Yablon Yaacov B.
Published: March 2003

Online university courses have become popular in many universities and colleges throughout the world. In addition to the relative cost‐effectiveness of online learning, there are studies that indicate that students reach satisfactory achievement levels in these courses. The major aim of the present research was two‐fold: to examine students’ academic performance in a mandatory first‐year university Internet‐based “Introduction to statistics” course and to investigate psycho‐pedagogical variables which contributed to students’ online learning, compared to learning of students who participated in a traditional lecture‐based “Introduction to statistics” course. Results of the study indicate that students who participated in the mandatory online course reached similar academic performance levels to those achieved by students who participated in the traditional lecture‐based course. In addition, the findings indicate that participation in the online course improves psycho‐pedagogical attitudes towards online learning despite the initial misgivings of the participants in the course.
A longitudinal study of the uptake of and confidence in using e‐mail among parks management students
Authors: Spennemann Dirk H.R. , Atkinson John S.
Published: March 2003

This paper details a longitudinal study into the e‐mail habits of first year students at Charles Sturt University. This study is part of ongoing research investigating the factors and barriers that can influence the successfully adoption of technology into the learning environment. The findings from this study illustrate that e‐mail applications are very popular in terms of both useage as well as the high level of confidence that students exhibit. The survey identified two main areas that need to be addressed, namely the disadvantage of rural students in accessing e‐mail and second that male students tend not to be as frequent users of e‐mail compared to their female counterparts.
A model for monitoring and migrating Web resources
Authors: Evans M.P. , Furnell S.M.
Published: March 2003

Web resource usage statistics enable server owners to monitor how their users use their Web sites. However, such statistics are only compiled for individual servers. If resource usage was monitored across the whole Web, the changing interests of society would be revealed, and deep insights made into the changing nature of the Web. However, capturing the information required for such a service, and providing acceptable system performance, presents significant challenges. As such, we have developed a model, called WebRUM, which offers a scalable system‐wide solution through the extension of a resource migration mechanism that we have previously designed. The paper describes the mechanism, and shows how it can be extended to monitor Web‐wide resource usage. The information stored by the model is defined, and the performance of a prototype mechanism is presented to demonstrate the effectiveness of the design.
Polylogue as a platform for governance: integrating people, the planet, profit and posterity
Authors: Kakabadse Nada K. , Kakabadse Andrew
Published: March 2003

Although the current wave of globalization is the result of unprecedented scientific and technological advances, through history, movements of an international nature have been, to a large extent, about the spread of political and economic ideas across borders. “Geopolitical realism is based on the interests of the state”. Scientific and technological advances, together with the opening of markets to the free passage of goods, services and finance, has led to a huge growth in world trade. However, such positive developments have also their downside. The findings of the United Nations Human Development Programme Report highlight that global inequalities in income and living standards have reached grotesque proportions. Further, such disparities are linked to ever‐intensified environmental degradation and the extinction of some 11,046 species. Such circumstances have witnessed the growth of community‐based local currencies, the emergence of a social movement advocating corporate social reasonability (CSR) and a growing literature critical of the Anglo‐American corporate governance model, where shareholder wealth maximization is the driving force. Yet, the philosophy and practice of shareholder wealth maximization persists. This paper explores the effects of free‐market economics, globalization and western capitalist practices in terms of their consequences for the planet, people, profit and posterity (the four Ps). A case is made outlining the need for an advanced corporate governance model that integrates the four Ps. In so doing, the paper seeks inspiration from the ancient philosophy of Buddhism and, in conclusion, examines the role of the Business School in developing future, reflexive practitioners, equipped to effectively provide the necessary balance between shareholder expectations and stakeholder needs within a new paradigm of a balanced society.
Chicanery in the corporate culture: WorldCom or world con?
Authors: Boyd David P.
Published: March 2003

Repercussions from the failure of WorldCom have profoundly affected all the company’s stakeholders. As evidence of malfeasance escalates, the company may prove to have been a mere mirage without substance or soul. This paper addresses one particular facet of the company’s dramatic and devastating demise. By authorizing personal loans to Bernie Ebbers, the board ultimately compromised the effectiveness and credibility of its own CEO. Moreover, its actions maligned the very shareholders that it was seeking to protect. The sequence of events at WorldCom raises red flags for any board that might be considering sweetheart loans to its CEO or fellow directors.
Automated analysis of multiple performance characteristics in magnetic resonance imaging systems
Authors: Covell Michelle M. , Hearshen David O. , Carson Paul L. , Chenevert Thomas P. , Shreve Paul , Aisen Alex M. , Bookstein Fred L. , Murphy Brian W. , Martel William
Published: March 2003

As with other digital imaging systems in heavy medical use, it is desirable with magnetic resonance imaging (MRI) to obtain extensive, rigorous system performance measures from a small set of images of one or two relatively simple test objects. Digital analysis of the parallel square rod (PSR) test object introduces digital image system self‐evaluation to MRI and extends automated image evaluation to include rigorous measures throughout the imaging volume rather than just average measures over the image. Precise comparisons with theory and between systems can be performed as well as quality control and corrections for nonuniformities. The PSR test object consists of an 18×18×36 cm rectangular acrylic container enclosing 60 parallel square acrylic rods running the entire length. The inter‐rod space is filled with a liquid or gel that produces strong, tissuelike signals in MRI and high contrast relative to the rods for computed tomography (CT). For profiles of slice thickness and separation, the rods are tilted in the test object to intersect the image plane at a 45° angle when the test object sides are parallel and perpendicular to the image plane. The test object itself is rotated 6–12° about its major axis so that the sides of the rods make a small angle to the rows and columns of pixels. This allows digital sampling at finer spacing than the pixels for determination of edge response functions. Over the 25–49 blocks in each slice of the imaged volume, maxima, minima, mean values, variances, and ratios currently are reported for the following variables: signal‐to‐noise ratio and sensitivity, linear and nonlinear image distortion, full width at half maximum (FWHM) resolution of the point spread function (PSF), slice separation, and slice thickness. These performance values at each rod or edge are displayed as gray scale functional images. Individual rod values are recorded and plotted as histograms and profiles. Results of the automated analysis for MRI system examples are in good agreement with expectations from theory and more manual tests.
A logit model for the modulation transfer function of screen–film systems
Authors: Bencomo J. A. , Fallone B. G.
Published: March 2003

An empirically derived logit function is proposed to describe the modulation transfer function of x‐ray screen–film systems. Simple and exact weighted linear regression analyses are performed to characterize the function and to describe the data within experimental accuracy. Calculations comparing the proposed function and the complementary error function (probit) representations of the modulation transfer function are given and discussed.
Completely implantable hyperthermia applicator with externalized temperature monitoring: Tests in conductive gel
Authors: Doss James D. , McCabe Charles W.
Published: March 2003

Development is underway on a hyperthermia applicator intended for complete implantation and long‐term use. Radio frequency energy is transmitted from an external antenna to a closely coupled subdermal antenna. This internal antenna is connected via a transmission line to deeply implanted electrodes. Changes in temperature at the electrodes result in a change in tissue resistivity which modifies the complex impedance seen at the external antenna terminals. This variation in antenna impedance (magnitude and/or phase angle) can, in principle, be utilized to indirectly monitor and regulate tissue temperature at the electrode location. Test results from conductive‐gel tissue phantom experiments are presented.
A “natural” volume–dose histogram for brachytherapy
Authors: Anderson Lowell L.
Published: March 2003

The most useful formulation of the volume–dose histogram for brachytherapy is one which suppresses inverse square law effects while preserving proportionality between volume and the area under the curve. These objectives are met by plotting the distribution of volume per unit −3/2 power of dose rate versus the −3/2 power of dose rate; such a distribution is constant for a single point source. Adding sources results in the formation of a peak, which provides a graphical indication of dose rate uniformity. Evaluation of other peak parameters such as width, position, and contained volume, in relation to treatment dose rate, permits a quantitative and clinically relevant volume–dose assessment of interstitial implants.
A new description of the photon beam peak‐depth profile as a function of field size
Authors: van de Geijn J. , Miller R. W.
Published: March 2003

The dose profile at peak depth in water is described as the product of an apparatus function and a source function. In principle, the source function is the circularly symmetric profile which would be measured at peak depth without any collimation. In practice, the peak‐depth profile in the diagonal plane, measured for the largest collimator setting, is used for this purpose. The apparatus function represents the collimator acting upon the source function, and is referred to as the collimator function. The collimator function for any field size can be developed from the ratio of the peak‐depth profile for a single medium‐sized field and the source function. The method has been tested for a set of irregularly flattened 4‐MV x‐ray beams as well as for practically flat 15‐MV x‐ray beams. The model requires as basic data only three peak‐depth profiles: one in each principal plane of a medium‐sized square field and the peak‐depth profile in the diagonal plane for the largest field. It replaces the peak‐depth transformation in the projective beam model.
Development of radiographic chest phantoms
Authors: Constantinou Chris , Cameron John , DeWerd Larry , Liss Margaret
Published: March 2003

Diagnostic imaging studies, particularly in chest radiography, require adequate phantoms. Two such phantoms have been made and used; one is a semianthropomorphic phantom and the other is a geometric phantom with embedded test objects. These phantoms, constructed of epoxy resin‐based solid water, are described in detail and compared to a common commercial phantom.
Extension of Fourier methods to the calculation of effective depths in heterogeneous media of arbitrary contour
Authors: Starkschall George
Published: March 2003

The description of patient contours and internal structures by means of truncated Fourier series can be extended to continuous contours of arbitrary shape and location by expressing the x and z Cartesian coordinates of the contour as independent Fourier series in a parameter t. An analytic equation for the intersection of the contour and a ray line is then written as an equation in the parameter t. The equation can be solved using numerical methods yielding the Cartesian coordinates of the intersection point directly.
The effect of lead attenuators on dose in homogeneous phantoms
Authors: El‐Khatib Ellen E. , Podgorsak Ervin B. , Pla Conrado
Published: March 2003

In radiotherapy, the radiation beam is sometimes shaped so as to deliver different doses to different organs or give a homogeneous dose to structures of different densities. This objective is achieved by the use of attenuating materials introduced into the beam. These attenuators alter the primary as well as the scattered radiation components of the beam. There is at present no accurate method of dose calculation for these situations. Most calculations are performed considering only the effect of the attenuators on the primary radiation beam and can produce large errors in dosimetry. In the present study, the broad beam attenuation is investigated in homogeneous phantoms for various radiation field sizes, photon beam energies, and depths in phantom. A calculational method taking account of primary as well as first scatter radiation is developed. This method predicts reasonably well the transmission through lead attenuators for the various experimental conditions investigated.
Dosimetry of asymmetric x‐ray collimators
Authors: Khan Faiz M. , Gerbi Bruce J. , Deibel Firmin C.
Published: March 2003

We have studied the dosimetry of an independent jaw system (provided with the Varian Clinac 2500) using ionometric measurements performed both in air and in a water phantom. Our study shows that the effect of the independent jaw on the dose distribution is similar to that of secondary blocking except for changes produced in the collimator scatter. A system of dose calculation was developed which takes into account the changes in the collimator scatter as well as in the isodose distribution. A method is described to correctly generate isodose curves for fields shaped by an independent jaw using a modified AECL TP11 treatment planning system. The primary modification in the program consists of correcting the zero‐area tissue–maximum ratios for the off‐axis variation in beam quality.
Determination of the source position for the electron beams from a high‐energy linear accelerator
Authors: Jamshidi Abolghassem , Kuchnir Franca T. , Reft Chester S.
Published: March 2003

We have investigated the energy and field‐size dependence of the source position of the electron beams from a Varian Clinac‐2500 accelerator. Three independent experimental methods were used: (1) multipinhole camera (MPC), (2) back projection of the full width at half maximum (FWHM), and (3) the inverse square law (ISL). The positions of the virtual and effective sources were calculated using the multiple Coulomb scattering (MCS) formalism. The results obtained from the MPC agree, within the experimental uncertainties, with the calculated values for the virtual source position. Similarly, the results from the FWHM method agree with the calculations with the exception of those for small field sizes at the lower energies. This is consistent with the fact that both kinds of measurements are not very sensitive to scattering in the photon and electron collimators. In contrast, the source position determined by the ISL method shows strong dependence on field size and energy, and does not agree with the values predicted by the MCS formalism. This is due to contamination from electrons scattered in the x ray and electron collimation system. The techniques and results reported here should be generally applicable to other scatter foil linear accelerators.
Reconstruction of diagnostic x‐ray spectra by numerical analysis of transmission data
Authors: Huang Pin‐Hua , Chen Tao‐Seng , Kase Kenneth R.
Published: March 2003

Numerical reconstruction of x‐ray spectra from narrow‐beam transmission data was tested with published spectra in the range from 45 to 100 kVp. Transmission curves were calculated from the spectra to simulate measured data. Spectra were reconstructed from these transmission curves with use of an iterative numerical analysis. Comparison of the calculated spectra with the original spectra shows good agreement, including the tungsten characteristic x rays. This demonstrates the potential usefulness of measured transmission data for deducing x‐ray spectra in the diagnostic energy range.
Digital background subtraction for fluorescence imaging
Authors: Profio A. Edward , Balchum Oscar J. , Carstens Felix
Published: March 2003

A method of enhancing contrast in fluorescence imaging has been devised, based on real‐time digital subtraction of a background video image from a signal‐plus‐background video image. Color filters are used to differentiate signal from background. The technique has been applied to detection of small tumors labeled with the tumor specific fluorescent drug hematoporphyrin derivative.
Analytic evaluation of heterogeneity locations for external beam treatment planning
Authors: Starkschall George
Published: March 2003

A method has been developed to calculate depths of calculation points analytically in patient contours containing internal heterogeneities. In this method, each contour is approximated by a Fourier series comprising five to ten terms. Using this approximation, the intersections of a ray line with each contour are found as the solution of a transcendental equation. Once these intersections have been located, effective depths used in heterogeneity calculations can readily be calculated.
The neutron dose and energy spectrum outside a 20‐MV accelerator treatment room
Authors: Muller‐Runkel R. , Ovadia J. , Culbert H. , Cooke R. H. , Dolecek E. H.
Published: March 2003

A maze design is discussed for a Therac 20 linear accelerator (manufactured by Atomic Energy of Canada, Ltd.) which reduces the flux of neutrons at the door to permissible levels in controlled areas. The L‐shaped design allows for a relatively light door at the end of the maze, consisting of 5.08‐cm (2‐in.) borated polyethylene and 2‐mm lead. A comparison is made between the neutron dose equivalent (DE) calculated by various methods and the DE measured with a variety of portable neutron survey meters. In addition, the neutron energy spectrum outside the maze at 1 m from the door, measured with a polyethylene multisphere LiI system, is reported.
Clarification of the AAPM Task Group 21 protocol
Authors: Schulz R. J. , Almond P. R. , Kutcher G. , Loevinger R. , Nath R. , Rogers D. W. O. , Suntharalingam N. , Wright K. A. , Kahn Faiz M.
Published: March 2003

In light of recent questions and comments from the physics community, a review is made of the AAPM protocol for high‐energy x‐ray and electron beam dosimetry.
Suppression of respiratory motion artifacts in magnetic resonance imaging
Authors: Wood Michael L. , Henkelman R. Mark
Published: March 2003

Anatomical structures that are displaced periodically during respiration are repeated as ghosts in magnetic resonance (MR) images. These ghosts can be suppressed in many ways: the averaging of multiple sets of data, respiratory gating, deliberate positioning of ghosts, and respiratory ordering of phase encoding. Each method has a unique mechanism, which is described in detail. A theoretical investigation has been conducted into the effects that the methods have on the point spread function of a moving point. Data acquired in Fourier imaging are actually in the spatial frequency domain, so that respiratory motion can be regarded as a function of spatial frequency. The four methods above modify this functional dependence in different ways, allowing a unified comparison. Motion artifact suppression imposes additional constraints on image acquisition, which can prolong the imaging time. A technique has been developed that keeps the imaging time short by using the configuration of the subject to regulate the timing of image acquisition.
A general method for optimizing tissue discrimination in magnetic resonance imaging
Authors: Fox R. A. , Henson P. W.
Published: March 2003

The basic partial differential formulation for small differences has been applied to the equations for the inversion recovery and saturation recovery sequences with spin‐echo rephase pulses and the spin‐echo sequence itself. The result is a generalized expression which is proportional to tissue discrimination expressed as the signal‐difference‐to‐noise ratio for a pair of tissues. The expression is a function of the fractional differences in the tissue relaxation times and proton densities, T1, T2, and n, respectively, and the sequence parameters TR and TI, or TE. From it can be derived the conditions which lead to optimum tissue discrimination for a given pulse sequence. It is also possible to predict the optimum pulse sequence to use for any pair of tissues of interest. The method requires a knowledge of the fractional differences in T1, T2, and n for both tissues.
Reduction of aliasing in modulation transfer function measurements
Authors: Ehrhardt James C.
Published: March 2003

The images formed by many radiological systems are difficult to sample at spatial intervals small enough to avoid aliasing in the calculation of the system's modulation transfer function. However, if a system's response can be assumed to be symmetrical, this assumption can be used to effectively double the sampling density and to double the frequency limit before aliasing occurs. To accomplish this, a more complex algorithm is required. In this work, the formula for the calculation of the modulation transfer function from a symmetrical, one‐dimensional line spread function is derived and a similar result for a symmetrical, two‐dimensional point spread function is presented. The effect of noisy data and errors in the estimation of the offset of the center of the line spread function from a sampling point are investigated by simulation studies. For low noise (relative standard deviation of 1%) and an offset error of no more than 2% or 3% of a sampling interval, reasonable precision is obtained. These conditions appear to be achievable, especially when the noise is Poisson distributed.
Absolute kVp calibration using characteristic x‐ray yields
Authors: Anderson D. W. , Moore G. J. , Lester P. D.
Published: March 2003

A spectrometer with a high‐resolution room‐temperature silicon detector was used to obtain spectra including characteristic x‐ray peaks produced after fluoroscopic beams were incident on W, Pb, and Th absorbers. Characteristic x‐ray yield points were obtained from spectra taken at several generator kVp settings which produced x rays with energy above the K‐shell absorption edge for each element. A line drawn through the yield points when projected to zero yield served to locate the console setting corresponding to the actual K‐absorption edge energy for each absorber. The technique is useful for precision measurement of generator kVp and absolute calibration of indirect kVp measuring devices under operational conditions.
Ngas determination for a parallel‐plate ion chamber
Authors: Krithivas G. , Rao S. N.
Published: March 2003

A parallel‐plate ion chamber has been investigated with a view to determining Ngas, the cavity‐gas calibration factor, introduced by the Task Group 21 protocol for dose determination. In‐air and in‐phantom irradiation of a Memorial Hospital parallel‐plate ion chamber in a 60Co beam led to the determination of ion collecting volume and a calibration factor for the chamber. When these quantities were used to deduce Ngas factors for the chamber, an agreement within 1% was found. An average of the cavity‐gas factors obtained from 60Co data agreed to within 0.5% with the factor determined through force fitting the doses received by the parallel‐plate chamber and a cylindrical chamber in a 22‐MeV (nominal) electron beam. Additionally, the parallel‐plate chamber was utilized to study the effectiveness, in electron beam dosimetry, of the electron fluence perturbation correction factors introduced when the phantom material is replaced by a cylindrical ion chamber.
The backprojection method applied to classical tomography
Authors: Kampp Thomas D.
Published: March 2003

A method based upon backprojection of projection images which allows six degrees of freedom in the selection of the plane to be tomosynthesized is described. Data can be collected with any type of classical tomographic apparatus, including linear, circular, or other complex motion unit, which has been modified by the addition of a digital imaging chain. A set of projection images can be acquired in a single sweep, although, in principle, they could be acquired simultaneously. In addition, C‐arms can also be used with no limitations of the selection of tomosynthesized planes.
A precise method for correcting count‐rate losses in scintillation cameras
Authors: Madsen Mark T. , Nickles R. Jerome
Published: March 2003

Quantitative studies performed with scintillation detectors often require corrections for lost data because of the finite resolving time of the detector. Methods that monitor losses by means of a reference source or pulser have unacceptably large statistical fluctuations associated with their correction factors. Analytic methods that model the detector as a paralyzable system require an accurate estimate of the system resolving time. Because the apparent resolving time depends on many variables, including the window setting, source distribution, and the amount of scattering material, significant errors can be introduced by relying on a resolving time obtained from phantom measurements. These problems can be overcome by curve‐fitting the data from a reference source to a paralyzable model in which the true total count rate in the selected window is estimated from the observed total rate. The resolving time becomes a free parameter in this method which is optimized to provide the best fit to the observed reference data. The fitted curve has the inherent accuracy of the reference source method with the precision associated with the observed total image count rate. Correction factors can be simply calculated from the ratio of the true reference source rate and the fitted curve. As a result, the statistical uncertainty of the data corrected by this method is not significantly increased.
The effect of coupling materials on specific absorption rate distributions at 915 MHz
Authors: Waterman Frank M. , Nerlinger Rudolph E.
Published: March 2003

Deionized water is commonly used to couple microwave applicators to the patient surface in the administration of local hyperthermia. Profiles of the specific absorption rate (SAR) at 1‐cm depth show that deionized water coupling significantly distorts the SAR distributions of the Clini‐Therm 915‐MHz 10×10 and 15×15 cm2 applicators. Maxima and minima that are discernible in the SAR profiles obtained by direct applicator load contact are amplified producing unexpected hot and cold regions in the heating pattern. An exception is coupling achieved by use of the Clini‐Therm cooling pad, oriented such that the direction of deionized water flow is perpendicular to the electric field. The distortion in the SAR distribution can also be eliminated by replacing deionized water with mineral oil, a material having a much lower dielectric constant (ε=2). The SAR profiles for mineral oil coupling are comparable to those obtained for direct contact; however, the efficiency of power transfer is slightly less (70%) and the level of microwave leakage is approximately four times greater.
An agar phantom for hyperthermia
Authors: Kato Hirokazu , Hiraoka Masahiro , Ishida Tetsuya
Published: March 2003

An agar phantom with wide application in rf heating was developed. The phantom consists of 4 wt./wt. % agar powder, 0.1 wt./wt. % NaN3, 0–0.6 wt./wt. % NaCl, and 95.9–95.3 wt./wt. % water. The conductivity σ (S/m) of the phantom was independent of frequency at 1–40 MHz, being σ=1.74x+0.207 at 23.5±1 °C, where x is the concentration of NaCl (wt./wt. %). The permittivity was nearly equal to 81 in the range of 5–40 MHz and 0–0.6 wt./wt. % of NaCl. The density and the heat capacity of the phantom were 1.02×103 kg/m3 and 1.00 kcal/kg °C, respectively. The phantom had sufficient mechanical strength to permit construction of a torso 60 cm high. With the addition of a preservative, the phantom could be used for experiments on heating, without degeneration, for over one year.
Film dosimetry of small electron beams for routine radiotherapy planning
Authors: Niroomand‐Rad Azam , Gillin Michael T. , Kline Robert W. , Grimm Daniel F.
Published: March 2003

The characteristics of very small fields, 1×1 and 2×2 cm, of electron beams of nominal energies, 5, 7, 10, 12, 15, and 18 MeV have been studied and compared to a 10×10 cm field. A parallel‐plate ion chamber and film have been used to obtain various dose parameters. The central axis depth dose measurements, field flatness, uniformity index, and relative output factors are presented. It was found that satisfactory results for determining the relative output factor can be obtained from film data using a scanning densitometer. It is our conclusion that film dosimetry is acceptable in determining the necessary clinical parameters needed to treat patients with fields as small as 2×2 cm. For the 1×1 cm field size and for the electron energies greater than 10 MeV, there was substantial disagreement between the ion chamber and film data in the buildup region as well as the regions beyond the depth of maximum dose to the depth of 90% dose.
Interface effects in the Monte Carlo simulation of electron tracks
Authors: Smyth Vere G.
Published: March 2003

An analog of Fano's theorem for ionization in cavities is shown to hold for the stepwise representation of electron paths used in Monte Carlo computer models of electron transport. This brings to light an error in the distribution of electron paths and hence energy deposition which is induced by interrupting steps which cross the interface between media of different densities. The magnitude of the error depends on the shape of the cavity and its size relative to the electron path length in the cavity gas. In a typical calculation of a cylindrical chamber exposed to 60Co radiation, if the electron step size is taken as 10% of the remaining path, then a 3% energy deficit in the cavity results. An algorithm for crossing an interface is described which does not produce this error.
A prototype epithermal neutron beam for boron neutron capture therapy
Authors: Noonan D. J. , Russell J. L. , Brugger R. M.
Published: March 2003

An epithermal neutron beam has been designed and tested at the Georgia Insitute of Technology's 5‐MW Research Reactor. The prototype facility consists of aluminum and sulfur disks in a tangential beam port for fast neutron filtration. A cadmium sheet at the port exit removes the thermal neutrons from the transmitted beam, leaving an intensely epithermal neutron beam spanning five energy decades, each contributing to the flux demanded by boron neutron capture therapy. The thermal neutron flux generated by the incident epithermal neutrons in a polyethylene head phantom peaks at a depth of 3 cm and remains above the incident thermal flux to a 7‐cm depth. The beam thus provides the penetration required for treating deep‐seated gliomas. Photon contamination in the prototype facility is high, and a number of basic modifications are proposed for reducing it to safer levels.