bluuebunny/crossref_metadata_2025 huggingface dataset:
Rural Economic Development: A Review of the Literature from Industrialized Economies
Authors: Ryser Laura , Halseth Greg
Published: June 2010

Over the past 30 years, accelerating change has been one of the defining attributes of rural landscapes around the world. In response, there has been an increasing volume of rural economic development research and public/policy interest in that research. The purpose of this review article is not to provide a ‘state of the literature’ summary, but rather to highlight thematic directions, opportunities, and trends in the rural economic development literature over the past decade in industrialized economies. We review many of the longstanding research themes in rural economic development research: social and economic restructuring, barriers and challenges to economic development, community economic development, community capacity, governance, and policies and programs. We also explore a range of research issues that have (re‐) emerged over the past decade focusing on new approaches to understanding rural change and the deployment of development strategies in the context of the new rural economy.
China’s Changing National and Regional Innovation Systems and Regional Distribution of R&D
Authors: Zhang Fangzhu , Wu Fulong , Cooke Philip
Published: June 2010

This article examines the transformation of China’s national and regional innovation systems. We review an emerging literature on innovation research on China, especially geographical studies of innovation, and argue that China’s national innovation system has become more enterprise‐centered since the economic reform started in 1979. This article systematically evaluates the strength and weakness of China’s national innovation system and argues that the new innovation system has a significant regional dimension demonstrated through attempts to establish regional innovation systems. R&Ds are concentrated in high‐tech development zones in China. However, these zones are more manufacturing oriented. In other words, there is more development than research. These regional systems, however, play a role in promoting economic competitiveness in their respective regions.
Modeling the Dynamics of Complex Spatial Systems Using GIS, Cellular Automata and Fuzzy Sets Applied to Invasive Plant Species Propagation
Authors: Dragićević Suzana
Published: June 2010

Geographic processes are embedded within complex spatial systems containing multiple interacting variables. These processes have spatial and temporal dynamics that are difficult to represent and model with the standard tools of geographic information systems (GIS) software. Consequently, representing the dynamics of geographic process and accounting for uncertainties in variable measurements are key considerations when developing realistic spatial models. This article discusses an integrated GIS‐based cellular automata (CA) design that addresses spatial and temporal dynamics representation, and incorporates fuzzy sets for handling input spatial data uncertainties and errors. The integrated approach is demonstrated in the context of modeling the dynamics of invasive plant species in a simulated landscape. Using dynamic models as predictive tools can enable more targeted spatial decision making especially when resources are limited. In the case of invasive species, the GIS‐CA model can be used to predict species locations for improved control and management strategies.
Negotiating GIS and Social Theory in Population Geography
Authors: Walker Kyle E.
Published: June 2010

Population researchers are increasingly giving attention to how geographic information systems (GIS)‐based analytical techniques can answer questions about the spatial aspects of demographic processes. This broader turn toward spatial demography, however, has occurred concurrently with concerns within population geography about the sub‐discipline’s position within human geography as it turns toward critical social theory. These developments create distinct tensions for population geographers who seek to engage with the growing interest in GIS and spatial analysis outside of geography, and remain relevant within an increasingly theoretical human geography. This article evaluates the challenges in incorporating insights from critical social theory into spatial demographic research, with attention to issues such as the social construction of space and scale and the modifiable areal unit problem (MAUP). The article then assesses the potential of qualitative GIS as a methodological resolution to these challenges, and considers the prospects for theoretically informed spatial demographic research in population geography.
Impact of Plants Introduced by People During a Time of Rapid Environmental Change
Authors: Holland Peter , Woodland Dennis W. , Hetherington Jillian
Published: June 2010

Relatively few of the many plant species introduced by people have become naturalized, and only a small fraction of them have had a major impact on native species and ecosystems. The risks they pose are driven by environmental disturbance, but whether or not introduced plants cause extinction of native species remains uncertain, nor can we state with certainty which will become established in new areas and persist there without direct or indirect human assistance. It may take decades for some introduced plants to pose a threat to native species whereas others could do so in a few years, but several researchers have argued that until recently the time dimension has received comparatively little attention. The literature shows that the conservational and ecological problems caused by introduced plants do not simply stem from competition with native plants for space, light, nutrients and water. Rather, they involve spatial and temporal combinations of genetics and growth behaviour as well as differential responses to ecological opportunities, how newcomers fit into the biological and environmental structures of the host ecosystem, and the involvements of people, plants and animals. This article argues for long‐term, integrated programmes of observation and experimentation in the field and laboratory into the risks that introduced plants pose for native species and ecosystems.
Los efectos de la crisis de 2007‐2009 en los fondos de pensiones privados y de la seguridad social: ¿una amenaza para su solidez financiera?
Authors: Pino Ariel , Yermo Juan
Published: June 2010

La reciente crisis financiera ha tenido una repercusión sin precedentes en los fondos de pensiones y de la seguridad social. Estos últimos han registrado importantes pérdidas no realizadas en sus inversiones y se han impugnado sus mecanismos de administración, lo que ha puesto en peligro su solidez financiera y cuestionado su capacidad de proporcionar prestaciones adecuadas. El año 2009 finalizó con la recuperación de los mercados financieros, así como con la reasignación de las carteras y la reformulación de los enfoques tradicionales de gestión de riesgos. Los gobiernos han reaccionado frente a la crisis y han aplicado planes de recuperación que podrían suponer una amenaza para la situación fiscal a medio plazo. Es posible que la presión fiscal posterior a la crisis genere una situación de compromiso entre el restablecimiento de la solidez fiscal y la reducción del gasto social. En el presente artículo se analizan los efectos de la crisis en los fondos de pensiones y de la seguridad social y se abordan las cuestiones antes mencionadas.
El impacto de la crisis financiera global en la protección social de los países en desarrollo
Authors: McCord Anna
Published: June 2010

La crisis financiera global ha tenido un efecto devastador en los niveles de pobreza de los países en desarrollo, y la respuesta de la protección social hasta la fecha, en forma de asistencia social, ha sido limitada y se ha visto constreñida por la debilidad de los sistemas y la baja cobertura de las prestaciones preexistentes. Debido a la reducción de los ingresos, a los países en desarrollo les resulta muy difícil respetar sus compromisos políticos en materia de protección social anteriores a la crisis, apenas existiendo potencial, en este contexto, para extender la cobertura y asistir a quienes se han empobrecido aún más y a los «nuevos pobres». A pesar de que muchos países en desarrollo han adoptado soluciones de expansionismo fiscal, las respuestas políticas a la crisis se han centrado en proteger y estimular el crecimiento. Las soluciones adoptadas no han dado prioridad a la provisión de protección social para ayudar directamente a los pobres. En aquellos casos en los que se han producido intervenciones de protección social, en general, se ha tratado de intervenciones exclusivamente ad hoc y, frecuentemente, han sido intervenciones regresivas — como los subsidios generalizados para alimentos o carburantes — en vez de tratarse de intervenciones más sistémicas y favorables a los pobres. No obstante, existe un cierto margen para el optimismo, puesto que la crisis ha estimulado una serie de iniciativas encaminadas a promover la coordinación de donantes y la compatibilidad de la programación, lo cual puede traducirse en una mejora de la eficacia y el impacto de los futuros programas de protección social.
La seguridad social en tiempos de crisis
Authors: Bonnet Florence , Ehmke Ellen , Hagemejer Krzysztof
Published: June 2010

Para contrarrestar los efectos sociales negativos de la crisis actual, los Estados deben adoptar medidas para proporcionar ayuda a los ingresos y nuevas oportunidades de empleo a los trabajadores afectados y sus familias. En este artículo se examinan las respuestas a la crisis aportadas por algunos países a través de programas de desempleo, que es la rama de la seguridad social más afectada por la desaceleración económica. Se abordan asimismo las situaciones de compromiso a las que los regímenes de seguridad social en su conjunto deben hacer frente durante las crisis económicas, cuando disminuyen los ingresos provenientes de cotizaciones e impuestos destinados a financiar los programas y se incrementa el gasto en prestaciones. También se presta especial atención a las preocupaciones que suscitan las políticas en materia de pensiones. Por último, se aborda la iniciativa propuesta por las Naciones Unidas en favor de un «nivel mínimo de protección social» en el plano mundial destinado a facilitar, al menos, protección social básica a la gran mayoría de la población mundial que carece actualmente de cobertura social y sigue siendo vulnerable a los riesgos económicos y sociales.
Crisis económica y protección social en la Unión Europea: más allá de lo evidente
Authors: Euzéby Alain
Published: June 2010

La crisis económica tiene al menos la virtud de poner de manifiesto que la protección social es a la vez un amortiguador social y un estabilizador económico que limita la gravedad de la recesión. De hecho, los países de la Unión Europea, incluso la misma Unión, en el marco de su plan de recuperación económica, utilizan las prestaciones sociales para ayudar a las personas afectadas por la crisis, estimular el consumo de las familias y, de este modo, respaldar la actividad de las empresas y favorecer el empleo. Por otra parte, la crisis también puede ofrecer a la Unión Europea una oportunidad para reforzar sus sistemas de protección social, inspirándose en los grandes principios del derecho social internacional, afirmando la legitimidad de niveles de protección social altos, favoreciendo la convergencia hacia los sistemas de protección social de mayor cobertura entre los Estados miembros, e incrementando su presupuesto.
Design and Development of a Novel Biostretch Apparatus for Tissue Engineering
Authors: Pang Qiming , Zu Jean W. , Siu Geoffrey M. , Li Ren-Ke
Published: June 2010

A uniaxial cyclic stretch apparatus is designed and developed for tissue engineering research. The biostretch apparatus employs noncontact electromagnetic force to uniaxially stretch a rectangular Gelfoam® or RTV silicon scaffold. A reliable controller is implemented to control four stretch parameters independently: extent, frequency, pattern, and duration of the stretch. The noncontact driving force together with the specially designed mount allow researchers to use standard Petri dishes and commercially available CO2 incubators to culture an engineered tissue patch under well-defined mechanical conditions. The culture process is greatly simplified over existing processes. Further, beyond traditional uniaxial stretch apparatuses, which provide stretch by fixing one side of the scaffolds and stretching the other side, the new apparatus can also apply uniaxial stretch from both ends simultaneously. Using the biostretch apparatus, the distributions of the strain on the Gelfoam® and GE RTV 6166 silicon scaffolds are quantitatively analyzed.
The Effect of Knee Model on Estimates of Muscle and Joint Forces in Recumbent Pedaling
Authors: Koehle Michael J. , Hull M. L.
Published: June 2010

The usefulness of forward dynamic simulations to studies of human motion is well known. Although the musculoskeletal models used in these studies are generic, the modeling of specific components, such as the knee joint, may vary. Our two objectives were (1) to investigate the effects of three commonly used knee models on forward dynamic simulation results, and (2) to study the sensitivity of simulation results to variations in kinematics for the most commonly used knee model. To satisfy the first objective, three different tibiofemoral models were incorporated into an existing forward dynamic simulation of recumbent pedaling, and the resulting kinematics, pedal forces, muscle forces, and joint reaction forces were compared. Two of these models replicated the rolling and sliding motion of the tibia on the femur, while the third was a simple pin joint. To satisfy the second objective, variations in the most widely used of the three knee models were created by adjusting the experimental data used in the development of this model. These variations were incorporated into the pedaling simulation, and the resulting data were compared with the unaltered model. Differences between the two rolling-sliding models were smaller than differences between the pin-joint model and the rolling-sliding models. Joint reactions forces, particularly at the knee, were highly sensitive to changes in knee joint model kinematics, as high as 61% root mean squared difference, normalized by the corresponding peak force of the unaltered reference model. Muscle forces were also sensitive, as high as 30% root mean squared difference. Muscle excitations were less sensitive. The observed changes in muscle force and joint reaction forces were caused primarily by changes in the moment arms and musculotendon lengths of the quadriceps. Although some level of inaccuracy in the knee model may be acceptable for calculations of muscle excitation timing, a representative model of knee kinematics is necessary for accurate calculation of muscle and joint reaction forces.
Multi-Objective Optimization of the Heating Rods Layout for Rapid Electrical Heating Cycle Injection Mold
Authors: Zhao Guoqun , Li Xiping , Guan Yanjin
Published: June 2010

Rapid electrical heating cycle injection molding (ERHCM) technology is a promising green manufacturing technology for plastic parts. By using this technology, the defects that usually appear on the surface of conventionally injected parts, such as weld and flow marks, can be avoided effectively. This paper studies rapid electrical heating cycle injection molding technology and its mold structure design techniques. Temperature distribution uniformity and heating efficiency on the mold cavity surface are considered as the major influencing factors on product quality and production efficiency. A multi-objective optimization model for the heating rods layout in the mold cavity plate is formulated to optimize temperature distribution uniformity and heating efficiency with respect to the heating rods layout. An application to a liquid crystal display TV panel is implemented successfully using a genetic algorithm.
Methodical Extensions for Decomposition of Matrix-Based Design Problems
Authors: Li Simon
Published: June 2010

The two-phase method is a matrix-based approach for system decomposition, in which a system is represented by a rectangular matrix to capture dependency relationships of two sets of system elements. While the two-phase method has its own advantages in problem decomposition, this paper focuses on two methodical extensions to improve the method’s capability. The first extension is termed nonbinary dependency analysis, which can handle nonbinary dependency information, in addition to just binary information, of the model. This extension is based on the formal analysis of a resemblance coefficient to quantify the couplings among the model’s elements. The second extension is termed heuristic partitioning analysis, which allows the method to search for a reasonably good decomposition solution with less computing effort. This extension can be viewed as an alternative to the original partitioning approach that uses an enumerative approach to search for an optimal solution. At the end, the relief valve redesign example is applied to illustrate and justify the newly developed method components.
Flowrate Formulation of Deviation Function Based Gerotor Pumps
Authors: Yang Daniel C. H. , Yan Jia , Tong Shih-Hsi
Published: June 2010

This paper derives formulas for evaluating the flowrate of gerotor pumps. The flowrate formulas are based on a deviation function, and the pitch and generating curves can be circular or noncircular. Two dimensionless parameters, the lobe noncircularity and the pitch noncircularity, are introduced so that gerotor performance can be analyzed systematically.
Kinematic Analysis of Planetary Gear Systems Using Block Diagrams
Authors: Tsai Mi-Ching , Huang Cheng-Chi , Lin Bor-Jeng
Published: June 2010

This paper employs control techniques to analyze kinematic relationships via block diagrams for planetary gear systems. The revealed tangent-velocity equations at each contact point of the mechanical gearsets are utilized to plot the block diagrams. Then, the concepts of feedback and feedforward strategies are adopted to illustrate speed-reduction and increasing functions in kinematics with sensitivity analysis. The structural difference between unusual planetary gears and common ones is also explained based on the characteristic equation of feedback strategies for structural constraints in terms of stability conditions. A cam-controlled planetary gear is further illustrated for the constraint and kinematic analysis by using the block diagram technique and characteristic equation, and the computational simulations for the sensitivity and the motion output of this planetary gear are obtained. Through the correspondence between control and kinematics, this paper provides a guide for engineers in various fields to easily understand the function of mechanical design.
A Nonlinear Stiffness Safe Joint Mechanism Design for Human Robot Interaction
Authors: Park Jung-Jun , Song Jae-Bok
Published: June 2010

Service robots used in human environments must be designed to avoid collisions with humans. A safe robot arm can be designed using active or passive compliance methods. A passive compliance system composed of purely mechanical elements often provides faster and more reliable responses for dynamic collision than an active one involving sensors and actuators. Because positioning accuracy and collision safety are equally important, a robot arm should have very low stiffness when subjected to a collision force that could cause human injury but should otherwise maintain very high stiffness. A novel safe joint mechanism (SJM) consisting of linear springs and a double-slider mechanism is proposed to address these requirements. The SJM has variable stiffness that can be achieved with only passive mechanical elements. Analyses and experiments on static and dynamic collisions show high stiffness against an external torque less than a predetermined threshold value and an abrupt drop in stiffness when the external torque exceeds this threshold. The SJM enables the robotic manipulator to guarantee positioning accuracy and collision safety and it is simple to install between an actuator and a robot link without a significant change in the robot’s design.
Characterization of a unit at a secondary standard dosimetry laboratory: Monte Carlo simulations compared to measurements and results from the literature
Authors: Tedgren Åsa Carlsson , de Luelmo Sandro , Grindborg Jan‐Erik
Published: June 2010

Purpose

To compare a Monte Carlo (MC) characterization of a unit at the Swedish Secondary Standard Dosimetry Laboratory (SSDL) with the results of both measurements and literature with the aims of (1) resolving a change in the ratio of air‐kerma free in air and absorbed dose to water in a water phantom noted experimentally after a source exchange in the laboratory and (2) reviewing results from the literature on similar MC simulations. Although their use in radiotherapy is decreasing, the characteristics of beams are of interest since beams are utilized in calibrating ionization chambers for the absolute dosimetry of radiotherapy beams and as reference radiation quality in evaluating the energy dependence of radiation detectors and in studies on radiobiological effectiveness.

Methods

The BEAMnrc MC code was used with a detailed geometrical model of the treatment head and two models of the source representing the sources used before and after source exchange, respectively. The active diameters of the sources were 1.5 cm in pellet form and 2.0 cm in sintered form. Measurements were performed on the actual unit at the Swedish SSDL.

Results

Agreement was obtained between the MC and the measured results within the estimated uncertainties for beam profiles, water depth‐dose curve, relative air‐kerma output factors, and for the ratios of before and after source exchange. The on‐axis energy distribution of the photon fluence free in air for the unit loaded with its present (1.5 cm in diameter) source agreed closely with the results from the literature in which a source of the same make and active diameter, inside a different treatment head, was simulated. The spectrum for the larger (2.0 cm in diameter) source was in close agreement with another published spectrum, also modeling a source with an active diameter of 2.0 cm inside a different treatment head.

Conclusions

The reduction in the value of following source exchange was explained by the spectral differences between the two sources that were larger in the free in‐air geometry used for calibrations than at depth in the water phantom used for calibrations. Literature review revealed differences between published in‐air spectra derived for sources of different active diameters, and investigators in need of an accurately determined in‐air spectrum should be aware of differences due to source active diameter.
A field size specific backscatter correction algorithm for accurate EPID dosimetry
Authors: Berry Sean L. , Polvorosa Cynthia S. , Wuu Cheng‐Shie
Published: June 2010

Purpose

Portal dose images acquired with an amorphous silicon electronic portal imaging device (EPID) suffer from artifacts related to backscattered radiation. The backscatter signal varies as a function of field size (FS) and location on the EPID. Most current portal dosimetry algorithms fail to account for the FS dependence. The ramifications of this omission are investigated and solutions for correcting the measured dose images for FS specific backscatter are proposed.

Methods

A series of open field dose images were obtained for field sizes ranging from to . Each image was analyzed to determine the amount of backscatter present. Two methods to account for the relationship between FS and backscatter are offered. These include the use of discrete FS specific correction matrices and the use of a single generalized equation. The efficacy of each approach was tested on the clinical dosimetric images for ten patients, 49 treatment fields. The fields were evaluated to determine whether there was an improvement in the dosimetric result over the commercial vendor's current algorithm.

Results

It was found that backscatter manifests itself as an asymmetry in the measured signal primarily in the inplane direction. The maximum error is approximately 3.6% for and field sizes. The asymmetry decreased with increasing FS to approximately 0.6% for fields larger than . The dosimetric comparison between the measured and predicted dose images was significantly improved when a FS specific backscatter correction was applied. The average percentage of points passing a 2%, 2 mm gamma criteria increased from 90.6% to between 96.7% and 97.2% after the proposed methods were employed.

Conclusions

The error observed in a measured portal dose image depends on how much its FS differs from the calibration conditions. The proposed methods for correcting for FS specific backscatter effectively improved the ability of the EPID to perform dosimetric measurements. Correcting for FS specific backscatter is important for accurate EPID dosimetry and can be carried out using the methods presented within this investigation.
A method for MRI guidance of intercostal high intensity focused ultrasound ablation in the liver
Authors: Quesson Bruno , Merle Mathilde , Köhler Max O. , Mougenot Charles , Roujol Sebastien , de Senneville Baudouin Denis , Moonen Chrit T.
Published: June 2010

Purpose

High intensity focused ultrasound (HIFU) is a promising method for the noninvasive treatment of liver tumors. However, the presence of ribs in the HIFU beam path remains problematic since it may lead to adverse effects (skin burns) by absorption and reflection of the incident beam at or near the bone surface. This article presents a method based on magnetic resonance (MR) imaging for identification of the ribs in the HIFU beam, and for selection of the transducer elements to deactivate.

Methods

The ribs are visualized on anatomical images acquired prior to heating and manually segmented. The resulting regions of interest surrounding the ribs are projected onto the transducer surface by ray tracing from the focal point. The transducer elements in the “shadow” of the ribs are then deactivated. The method was validatedex vivo and in vivo in pig liver during breathing under multislice real‐time MR thermometry, using the proton resonance frequency shift method.

Results

Ex vivo and in vivo temperature data showed that the temperature increase near the ribs was substantial when HIFU sonications were performed with all elements active, whereas the temperature was reduced with deactivation of the transducer elements located in front of the ribs. The temperature at the focal point was similar with and without deactivation of the transducer elements, indicative of no loss of heat efficiency with the proposed technique.

Conclusions

This method is simple, rapid, and reliable, and enables intercostal HIFU ablation while sparing ribs and their surrounding tissues.
Uncertainties in IMRT dosimetry
Authors: Li Jin Sheng , Lin Teh , Chen Lili , Price Robert A. , Ma Chang‐Ming
Published: June 2010

Purpose

The purpose of this study is to investigate some characteristics of the beam delivery system and their effects on the dose distribution of intensity‐modulated radiation therapy (IMRT) and the results of patient‐specific IMRT quality assurance (QA). These characteristics include the accelerator source distribution and multileaf collimator (MLC) geometry.

Methods

Monte Carlo dose calculations based on intensity maps that were built from the actual deliverable IMRT leaf sequences with and without considering the characteristics of the beam delivery system were performed in this study using in‐house Monte Carlo software. The effect of the resolution of the intensity maps on the dose distribution was investigated first. The mean dose of the treatment target and the voxel doses in the high dose region of seven IMRT plans generated by different treatment planning systems for Varian 21EX and Siemens Primus linear accelerators were used for comparison and evaluation.

Results

The results show that a or smaller pixel size is needed for the intensity maps for accurate IMRT dose calculation. The extrafocal source, MLC leaf thickness, leakage, tongue‐and‐groove structure, and the effective leaf offset can affect the mean dose by up to 1.5%, 4.5%, 5.6%, 5.3%, and 7.8%, respectively, when these factors are considered separately. They also cause significant uncertainties to the voxel dose with standard deviations up to 2.5%, 0.7%, 2.1%, 1.3%, and 5%, respectively. The overall effect on the mean dose is up to 8% and the standard deviation of the voxel dose uncertainty is up to 6.4% when all the effects are included. The maximum standard deviation is reduced to 4.6% if the voxel size of the dose calculation matrix is increased from 0.04 to to make it comparable with the sensitive volume of the ionization chamber used for IMRT QA measurements.

Conclusions

It can be concluded that the characteristics of the beam delivery system are the major contributors to the uncertainty of measurement‐based IMRT QA because most of them are not fully considered in the currently available treatment planning systems.
A quality assurance tool for high‐dose‐rate brachytherapy
Authors: Rickey Daniel W. , Sasaki David , Bews Jeff
Published: June 2010

Purpose: The purpose of this work was to develop a quality assurance (QA) tool for high‐dose‐rate (HDR) brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times).

Methods: The authors constructed a QA tool that combined radiochromic film to verify position with four photodiode detectors to verify dwell times. To characterize the temporal accuracy of the tool, a function generator powered four red light‐emitting diodes that were optically coupled to the four photodiode detectors. The QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one‐dimensional optical camera that acquired 1000 lines/s.

Results: The temporal accuracy of the QA tool was found to be about 1 ms. For visual assessment, the source position could be located within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, the authors found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. They found that the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined within about 0.2 mm.

Conclusions: For pretreatment QA, the authors found that this tool allowed verification of dwell positions and dwell times in about 6 min.
Real‐time volumetric image reconstruction and 3D tumor localization based on a single x‐ray projection image for lung cancer radiotherapy
Authors: Li Ruijiang , Jia Xun , Lewis John H. , Gu Xuejun , Folkerts Michael , Men Chunhua , Jiang Steve B.
Published: June 2010

Purpose

To develop an algorithm for real‐time volumetric image reconstruction and 3D tumor localization based on a single x‐ray projection image for lung cancer radiotherapy.

Methods

Given a set of volumetric images of a patient at breathing phases as the training data, deformable image registration was performed between a reference phase and the other phases, resulting in deformation vector fields (DVFs). These DVFs can be represented efficiently by a few eigenvectors and coefficients obtained from principal component analysis (PCA). By varying the PCA coefficients, new DVFs can be generated, which, when applied on the reference image, lead to new volumetric images. A volumetric image can then be reconstructed from a single projection image by optimizing the PCA coefficients such that its computed projection matches the measured one. The 3D location of the tumor can be derived by applying the inverted DVF on its position in the reference image. The algorithm was implemented on graphics processing units (GPUs) to achieve real‐time efficiency. The training data were generated using a realistic and dynamic mathematical phantom with ten breathing phases. The testing data were 360 cone beam projections corresponding to one gantry rotation, simulated using the same phantom with a 50% increase in breathing amplitude.

Results

The average relative image intensity error of the reconstructed volumetric images is . The average 3D tumor localization error is . On an NVIDIA Tesla C1060 GPU card, the average computation time for reconstructing a volumetric image from each projection is 0.24 s (range: 0.17 and 0.35 s).

Conclusions

The authors have shown the feasibility of reconstructing volumetric images and localizing tumor positions in 3D in near real‐time from a single x‐ray image.
A radiobiological investigation on dose and dose rate for permanent implant brachytherapy of breast using or sources
Authors: Baltas Dimos , Lymperopoulou Georgia , Löffler Edgar , Mavroidis Panayiotis
Published: June 2010

Purpose

The present report addresses the question of what could be the appropriate dose and dose rate for and permanent seed implants for breast cancer as monotherapy for early stage breast cancer. This is addressed by employing a radiobiological methodology, which is based on the linear quadratic model, to identify a biologically effective dose (BED) to the prescription point of the brachytherapy implant, which would produce equivalent cell killing (or same cell survival) when compared to a specified external radiotherapy scheme.

Methods

In the present analysis, the tumor and normal tissue BED ratios of brachytherapy and external radiotherapy are examined for different combinations of tumor proliferation constant , ratios, initial dose rate , and reference external radiotherapy scheme (50 or 60 Gy in 2 Gy per fraction). The results of the radiobiological analysis are compared against other reports and clinical protocols in order to examine possible opportunities of improvement.

Results

The analysis indicates that physical doses of approximately 100–110 Gy delivered with an initial dose rate of around and 78–80 Gy delivered at for and permanent implants, respectively, are equivalent to 50 Gy external beam radiotherapy (EBRT) in 2 Gy per fraction. Similarly, for physical doses of approximately 115–127 Gy delivered with an initial dose rate of around and 92 Gy delivered at for and , respectively, are equivalent to 60 Gy EBRT in 2 Gy per fraction. It is shown that the initial dose rate required to produce isoeffective tumor response with 50 or 60 Gy EBRT in 2 Gy per fraction increases as the repopulation factor increases, even though repopulation is also considered in EBRT. Also, the initial dose rate increases as the value of the ratio decreases. The impact of the different ratios on the ratio of the tumor BEDs is significantly large for both the and implants with the deviation between the ratios and those using the 4.0 and 3.5 Gy values ranging between 18% and 22% in most of the cases.

Conclusions

For the cases of and , the equivalent physical doses to 50 Gy EBRT in 2 Gy per fraction are associated with an overdosage of the involved normal tissue in the range of 4%–16% and an underdosage by 10%–15% for a BED for normal tissue, using an value of 3.0 Gy of 100 Gy. These values are lower by 10%–20% than the published value of 124 Gy for and by about 13% when compared to the published isoeffective dose of 90 Gy for . Similarly, the equivalent physical doses to 60 Gy EBRT in 2 Gy per fraction are associated with an overdosage of the involved normal tissue by 10%–20% and an underdosage by 4%–10% for of 110 Gy.
Dynamic contrast enhanced–MRI in head and neck cancer patients: Variability of the precontrast longitudinal relaxation time
Authors: Craciunescu Oana , Brizel David , Cleland Esi , Yoo David , Muradyan Naira , Carroll Madeline , Barboriak Daniel , MacFall James
Published: June 2010

Purpose: Calculation of the precontrast longitudinal relaxation times is an integral part of the Tofts‐based pharmacokinetic (PK) analysis of dynamic contrast enhanced–magnetic resonance images. The purpose of this study was to investigate the interpatient and over time variability of in head and neck primary tumors and involved nodes and to determine the median for primary and nodes . The authors also looked at the implication of using voxel‐based values versus region of interest (ROI)‐based on the calculated values for vascular permeability and extracellular volume fraction .

Methods: Twenty head and neck cancer patients receiving concurrent chemoradiation and molecularly targeted agents on a prospective trial comprised the study population. Voxel‐based 's were generated using a gradient echo sequence on a 1.5 T MR scanner using the variable flip angle method with two flip angles [J. A. Brookes et al., “Measurement of spin‐lattice relaxation times with FLASH for dynamic MRI of the breast,” Br. J. Radiol. 69, 206–214 (1996)]. The voxel‐based , , and were calculated using iCAD's® (Nashua, NH) software. The mean 's in muscle and fat ROIs were calculated . To assess reliability of ROI drawing, values from ROIs delineated by 2 users (A and B) were calculated as the average of the 's for 14 patients. For a subset of three patients, the variability from baseline to end of treatment was also investigated. The and from primary and node ROIs were calculated using voxel‐based values and and differences reported.

Results: The calculated values for fat and muscle are within the range of values reported in literature for 1.5 T, i.e., and . The average over 14 patients of the 's based on drawings by users A and B were , , , and . The absolute percentage difference between and calculated with voxel‐based versus ranged from 6% to 81% and from 2% to 24%, respectively.

Conclusions: There is a certain amount of variability in the median values between patients, but the differences are not significant. There were also no statistically significant differences between the values for primary and nodes at baseline and the subsequent time points ( Friedman test). Voxel‐based calculations are essential when quantitative Tofts‐based PK analysis in heterogeneous tumors is needed. In the absence of mapping capability, when a relative, qualitative analysis is deemed sufficient, a value of can be used as an estimate for for both the primary tumor and the affected nodes in head and neck cancers at all the time points considered.
On the feasibility of MRI‐guided navigation to demarcate breast cancer for breast‐conserving surgery
Authors: Alderliesten Tanja , Loo Claudette , Paape Anita , Muller Sara , Rutgers Emiel , Peeters Marie‐Jeanne Vrancken , Gilhuijs Kenneth
Published: June 2010

Purpose

The aim of this study was to investigate the feasibility of image‐guided navigation approaches to demarcate breast cancer on the basis of preacquired magnetic resonance (MR) imaging in supine patient orientation.

Methods

Strategies were examined to minimize the uncertainty in the instrument‐tip position, based on the hypothesis that the release of instrument pressure returns the breast tissue to its predeformed state. For this purpose, four sources of uncertainty were taken into account: (1) : Uncertainty in the reproducibility of the internal mammary gland geometry during repeat patient setup in supine orientation; (2) : Residual uncertainty in registration of the breast after compensation for breathing motion using an external marker; (3) : Uncertainty in the reconstructed location of the tip of the needle using an optical image‐navigation system (phantom experiments, ); and (4) : Uncertainty in displacement of breast tumors due to needle‐induced tissue deformations (patients, ). A Monte Carlo study was performed to establish the 95% confidence interval (CI) of the combined uncertainties. This region of uncertainty was subsequently visualized around the reconstructed needle tip as an additional navigational aid in the preacquired MR images. Validation of the system was performed in five healthy volunteers (localization of skin markers only) and in two patients. In the patients, the navigation system was used to monitor ultrasound‐guided radioactive seed localization of breast cancer. Nearest distances between the needle tip and the tumor boundary in the ultrasound images were compared to those in the concurrently reconstructed MR images.

Results

Both and were normally distributed with and , respectively. Taking prior estimates for and into account, the combined impact resulted in 3.9 mm uncertainty in the position of the needle tip (95% CI) after release of pressure. The volunteer study showed a targeting accuracy comparable to that in the phantom experiments: versus , respectively. In the patient feasibility study, the deviations were within the 3.9 mm CI.

Conclusions

Image‐guided navigation to demarcate breast cancer on the basis of preacquired MR images in supine orientation appears feasible if patient breathing is tracked during the navigation procedure, positional uncertainty is visualized and pressure on the localization instrument is released prior to verification of its position.
The effect of limited MR field of view in MR/PET attenuation correction
Authors: Delso Gaspar , Martinez‐Möller Axel , Bundschuh Ralph A. , Nekolla Stephan G. , Ziegler Sibylle I.
Published: June 2010

Purpose

A critical question in the development of combined MR/PET scanners is whether MR can provide the tissue attenuation data required for PET reconstruction. Unfortunately, MR images are often unable to encompass the entire patient. The resulting truncation in the transverse plane leads to incomplete attenuation maps, causing artifacts in the reconstructed PET image. This article describes the experiments performed to quantify these artifacts. A method to compensate the missing data was evaluated to determine whether software correction is possible or whether additional transmission hardware has to be included in the scanner.

Methods

Three studies were made. First, simulated PET data were used to quantify the bias due to an incomplete attenuation map. A set of spherical lesions was simulated in the lungs and mediastinum of a patient. The data were reconstructed with complete and partial attenuation maps and the uptake differences were evaluated. Second, clinical data from PET/CT oncology patients were used. To reproduce the expected conditions in an MR/PET scanner, only patients scanned with the arms resting along the body were considered. These scans were then used to create maps of the reconstruction bias due to field of view (FOV) limitations. Lastly, a PET reconstruction with incomplete attenuation data was evaluated as a means to obtain attenuation information beyond the MR FOV. The patient outline was automatically segmented with a three‐dimensional snake algorithm and used to fill the truncated data in the attenuation map.

Results

Average bias up to 15% and local biases up to 50% were estimated when PET data were reconstructed with incomplete attenuation information. Completing the attenuation map with data extracted from a PET prereconstruction globally reduced these biases to below 10%. This correction proved to be tolerant to inaccuracies in positioning and attenuation values. However, local artifacts up to 20% could still be found near the edges of the MR FOV.

Conclusions

MR FOV restrictions can indeed make the reconstructed PET data unacceptable for diagnostic purposes. Biases can be globally compensated by automatic preprocessing of the attenuation map. However, inaccuracies in the correction will result in small artifacts near the periphery of the image that could lead to false‐positive findings.
Regression error estimation significantly improves the region‐of‐interest statistics of noisy MR images
Authors: Juras Vladimir , Zbýň Štefan , Szomolanyi Pavol , Trattnig Siegfried
Published: June 2010

Purpose

The region‐of‐interest (ROI) selection and evaluation is one of the key factors in the successful evaluation of radiological images. However, the presence of noise in images may lead to incorrect diagnosis. The aim of this study was to test the hypothesis that the weighting by error estimation in ROI assessment might significantly improve the validity of the results.

Methods

As a model, the data maps of the transverse relaxation time constants from patients who underwent a matrix‐associated chondrocyte transplantation procedure on the femoral condyle were analyzed. Artificial noise with a Rician density probability distribution was added to each TE image. ROIs were processed either as a regular arithmetic mean or as a weighted mean, in which weighted coefficients were calculated with regard to fitting error estimates [coefficient of determination (); root mean squared error (RMSE), mean absolute error (MSE), mean squared error (MAE), and chi‐squared error ()].

Results

The global values in repair tissue (, ; range 51–70 ms) and in healthy cartilage (, ; range 40–60 ms) were significantly different . With a 45% or greater decrease from the original SNR value (corresponding to a noise level of 35% of random value), the statistical significance was lost ; however, the use of the coefficient of determination as a correction factor was able to maintain the p‐value of up to a 56% decrease from the original SNR value.

Conclusions

The results of this study can prospectively be applied in a wide range of radiological imaging techniques in cases when error estimation is possible. Our analysis on MR images with artificially added noise showed that utilization of the correlation of determination as a weighting parameter in ROI evaluation may significantly improve the differentiation between native and transplanted cartilage tissue in noisy images. This could be an added benefit in the non‐invasive monitoring of the post‐operative status of patients with cartilage transplants if the MR images are not ideal (e.g., lower field strength or lower SNR).
Lung cancer and exposure to quartz and diesel exhaust in Swedish iron ore miners with concurrent exposure to radon
Authors: Bergdahl Ingvar A , Jonsson Håkan , Eriksson Kåre , Damber Lena , Järvholm Bengt
Published: June 2010

Objectives

Studies of underground miners have documented an increased risk of lung cancer mainly linked to radon exposure but possibly influenced by other concurrent exposures.

Methods

A cohort study was carried out in 8321 iron ore miners with low exposure to radon, employed in 1923–1998 and followed up for lung cancer in 1958–2000. Historical exposures to radon, crystalline silica and diesel exhaust were assessed. Data including exposure to radon, quartz and diesel exhaust from another mine with higher exposure to radon were reanalysed.

Results

Miners had increased risk for lung cancer (SIR 1.48 (95% CI 1.22 to 1.78), based on 112 cases during 227 000 person-years). The increased risk could not be explained by exposure to radon or diesel exhaust but was associated with exposure to crystalline silica: SIR 0.96 (0.53 to 1.62), 1.45 (1.10 to 1.87), 1.99 (1.31 to 2.90) and 1.77 (0.92 to 3.10) in groups with exposure to 0, 0–2, 2–5 and >5 mg years/m3, respectively. Reanalysis of data from the other mine indicated that quartz was a possible confounder in the analysis of relationship between radon and lung cancer. In the highest radon exposed group, the point estimate for the RR decreased from 5.65 to 3.90 when adjusting for concurrent exposure to quartz.

Conclusions

Crystalline silica, a known carcinogen, probably affects lung cancer risk in iron ore miners. The main implication of the results is for interpretation of the dose–response curve for radon and lung cancer in underground iron ore miners. Since exposure to radon and quartz is often correlated, quartz exposure can be an important confounder.