bluuebunny/crossref_metadata_2025 huggingface dataset:
SAKACIN A‐CONTAINING PULLULAN FILM: AN ACTIVE PACKAGING SYSTEM TO CONTROL EPIDEMIC CLONES OF LISTERIA MONOCYTOGENES IN READY‐TO‐EAT FOODS
Authors: TRINETTA VALENTINA , FLOROS JOHN D. , CUTTER CATHERINE N.
Published: March 2010

The effectiveness of sakacin A, a bacteriocin produced by Lactobacillus sakei DSMZ 6333, was evaluated against epidemic clones of Listeria monocytogenes isolated from foodborne outbreaks; sakacin A activity was determined in ready‐to‐eat (RTE) foods, and a biopolymer was identified to deliver the bacteriocin onto a RTE food. Sakacin A demonstrated antimicrobial activity against epidemic clones of L. monocytogenes in food slurries. When sakacin A (50 mg/mL) was applied directly to experimentally inoculated turkey breast, populations of the most sensitive epidemic clone were reduced more than 2 log10 cfu/g after 3 weeks at 4C. Sakacin A‐containing (1 mg/cm2) pullulan films demonstrated antimicrobial activity in vitro. When experimentally inoculated surfaces of turkey breast were treated with these pullulan films, L. monocytogenes populations were reduced 3 log10 cfu/g after 3 weeks under refrigerated storage. These results demonstrate the possibility of using sakacin A‐containing‐pullulan film to inhibit or reduce L. monocytogenes on the surface of a RTE food.

PRACTICAL APPLICATIONS

Increased use of synthetic packaging films has led to ecological problems due to their nonbiodegradability. Consumers are demanding that food packaging materials be made of biobased materials, and to be easily biodegradable and recyclable. The incorporation and/or slow release of antimicrobial agents in packaging materials may provide a means of extending the bacterial lag phase, reducing microorganism growth rate and extending the shelf life of foods. Bacteriocins are compounds that can be used as a means of biopreservation. In this study, we demonstrated the effectiveness of sakacin A‐containing pullulan films to control Listeria monocytogenes growth and the applicability of active pullulan films as a means of delivering a bacteriocin directly to a food surface. Pullulan films require less antimicrobial, demonstrate longer antimicrobial activity and allow for controlled migration of the molecule from film to the food matrix, as compared with the direct addition of sakacin A to ready‐to‐eat meat products.
INHIBITORY EFFECT OF CLOVE OIL (SYZIUM AROMATICUM) AGAINST LISTERIA MONOCYTOGENES CELLS INCUBATED IN FRESH‐CUT SALMON
Authors: MILADI HANENE , CHAIEB KAMEL , AMMAR EMNA , BAKHROUF AMINA
Published: March 2010

The ability of Listeria monocytogenes to survive and grow at refrigeration temperature in a wide spectrum of foods is a public health concern. Essential oil of clove (Syzium aromaticum) was investigated for its ability to inhibit the growth of this pathogen in food. Three strains of L. monocytogenes (106 cfu/g) were inoculated on fresh‐cut salmon and stored (4C and 25C) for 2 weeks. The effect of clove oil (1% and 2%) on the growth of cells was determined. The results proved that all strains survived and grew at 4C and 25C. In addition, we noted that the growth was inhibited under storage conditions in the presence of clove oil (1% or 2%). Listeria counts in treated samples were 1–4 log10 cfu/g less compared with controls at different intervals during storage. The results revealed the potential of clove oil as a natural preservative in fresh salmon.

PRACTICAL APPLICATIONS

Listeria monocytogenes continues to be a significant threat to the safety of the food supply. It was isolated from a variety of foods and ready‐to‐eat products and generated a serious public health problem. Because of its growth capacity at refrigerating temperatures and its survival in diverse environments, the control of L. monocytogenes is becoming a challenge.

Several agents were used to suppressing contamination by L. monocytogenes, such as the addition of biopreservatives and essential oil. Spices and herbs are commonly used in food preservation because they do not have a strong effect on food quality unlike chemical and synthetic compounds. Clove oil, contains eugenol which when tested on various agar media, has antimicrobial properties, and it was able to restrict the proliferation of L. monocytogenes in food products. For this reason, clove oil has good potential as an antilisterial substance in food preservation as it may be more acceptable to consumers.
Green Spaces of Self‐Interest Within Shared Urban Governance
Authors: Perkins Harold A.
Published: March 2010

Municipal governments in Western Europe and the United States historically built and programmed public, urban park spaces to promote citizenship in accord with middle class values. In many cities these decades‐old green spaces have recently fallen into disrepair as fiscally austere governments cut parks budgets. Shared governance for green space is a new solution to parks disinvestment whereby responsibility for their upkeep is redistributed among corporations, non‐profits, and local residents. Individual citizenship status in this process is not gained by patronizing parks as in the past, but by assuming responsibility for rebuilding and reprogramming them. But while shared governance increases the number of stakeholders in decision making, its democratic potential is often subverted by entrepreneurial growth coalitions that wield disproportionate power to make market‐based, urban environmental decisions. An extension of what counts as governable green space comes with an increase in entrepreneurialism – from the largest waterfront redevelopment projects to the smallest gardens on vacant neighborhood lots. The uneven distribution and quality of green space under market forms of shared governance is intensified as ‘communities of self‐interest’ arise around green spaces in some locations whereas others continue to be disinvested in the absence of direct state support. I provide three examples of green space renovation in Milwaukee, Wisconsin to further demonstrate that shared governance arrangements possess democratic potential despite the injustice of their exclusivity as currently negotiated.
Heterogeneity of archaeal and bacterial ammonia‐oxidizing communities in Lake Taihu, China
Authors: Wu Yucheng , Xiang Yan , Wang Jianjun , Zhong Jicheng , He Jizheng , Wu Qinglong L.
Published: March 2010

Ammonia‐oxidizing archaea (AOA) and bacteria (AOB) communities within the surface sediments of Lake Taihu, a large eutrophic freshwater lake in China, were investigated using molecular approaches targeting the ammonia monooxygenase subunit A (amoA) gene. Large intra‐lake variability in the composition and the relative abundance of both groups of ammonia‐oxidizing prokaryotes was observed. Archaeal amoA far outnumbered bacterial amoA at most sites except those located in the Eastern Taihu Bay. This bay, which is used for intensive pen aquaculture, harboured the most unique AOA communities but was dominated by AOB in terms of relative abundance. Accumulation of organic substances rather than presence of submersed macrophytes significantly influenced the relative abundance of AOA. In contrast, shifts in the abundance of AOB were not found to be significantly related to the investigated environmental parameters. Phylogenetic analysis showed that all archaeal amoA sequences fell within either the Crenarchaeotal Group (CG) I.1b or the CG I.1a subgroup, and all AOB clustered exclusively with the genus Nitrosomonas. These findings represent the first detailed survey of AOA in eutrophic freshwater lake sediments by demonstrating that AOA dominate the ammonia‐oxidizing communities, and are negatively correlated with the accumulation of organic substances.
Phenotypic variation in Azospirillum brasilense exposed to starvation
Authors: Lerner Anat , Valverde Angel , Castro‐Sowinski Susana , Lerner Hadas , Okon Yaacov , Burdman Saul
Published: March 2010

Bacteria have developed mechanisms that allow them maintaining cell viability during starvation and resuming growth when nutrients become available. Among these mechanisms are adaptive mutations and phase variation, which are often associated with DNA rearrangements. Azospirillum brasilense is a Gram‐negative, nitrogen‐fixing, plant growth‐promoting rhizobacterium. Here we report phenotypic variants of A. brasilense that were collected after exposure to prolonged starvation or after re‐isolation from maize roots. The variants differed in several features from the parental strains, including pigmentation, aggregation ability, EPS amount and composition and LPS structure. One of the phenotypic variants, overproducing EPS and showing an altered LPS structure, was further characterized and showed differential response to several stresses and antibiotics relative to its parental strain. Characterization of the variants by repetitive‐PCR revealed that phenotypic variation was often associated with DNA rearrangements.
Characterization of blood cells in the Leopard Cat (Prionailurus bengalensis)
Authors: Salakij Chaleow , Salakij Jarernsak , Prihirunkit Kreangsak , Narkkong Nual‐Anong , Pitakkingthong Decha
Published: March 2010

Background: The Leopard Cat (Prionailurus bengalensis) is the most frequently encountered wild cat in most of Southeast Asia. Limited hematologic investigation exists for this species.

Objectives: The objectives of this study were to assess routine hematologic measurements and parameters and characterize the morphology, cytochemical staining, and ultrastructural features of blood cells in Leopard Cats.

Methods: Blood samples were collected from 12 adult healthy captive Leopard Cats (7 males and 5 females). Complete blood counts were performed using an automated hematology analyzer and manual differential counts. Cytochemical staining (Sudan black B [SBB], peroxidase [PO], periodic acid‐Schiff [PAS], α‐naphthyl acetate esterase [ANAE], and β‐glucuronidase [BG]) and scanning and transmission electron microscopy were performed using standard methods.

Results: Median (range) hematologic results were as follows: PCV 0.46 L/L (0.30–0.55 L/L), hemoglobin 136.5 g/L (100–183 g/L), WBC 9.0 × 109/L (6.9–15.2 × 109/L), band neutrophils 0.07 × 109/L (0–0.30 × 109/L), segmented neutrophils 2.9 × 109/L (1.2–6.34 × 109/L), lymphocytes 5.3 × 109/L (2.7–8.1 × 109/L), eosinophils 0.14 × 109/L (0–0.73 × 109/L), basophils 0/L (0–0.22 × 109/L), and monocytes 0.08 × 109/L (0–0.30 × 109/L). Neutrophils stained strongly positive for SBB, PO, and PAS; lymphocytes had fine granular positivity for ANAE and BG; monocytes were weakly positive for ANAE and BG; and basophils were strongly positive for BG. Ultrastructurally, eosinophils contained many large rod‐shaped granules with prominent crystalloid core structures, ribosomes, and mitochondria. Basophils contained many round to oval specific granules with homogeneous contents. Low number of basophils contained a few small vacuoles that usually were not detected by light microscopy.

Conclusion: These findings will facilitate interpretation of hematologic results for future investigative and diagnostic studies of this species.
Gradient Deficient Curved Beam Element Using the Absolute Nodal Coordinate Formulation
Authors: Sugiyama Hiroyuki , Koyama Hirohisa , Yamashita Hiroki
Published: March 2010

In this investigation, a gradient deficient beam element of the absolute nodal coordinate formulation is generalized to a curved beam for the analysis of multibody systems, and the performance of the proposed element is discussed by comparing with the fully parametrized curved beam element and the classical large displacement beam element with incremental solution procedures. Strain components are defined with respect to the initially curved configuration and described by the arc-length coordinate. The Green strain is used for the longitudinal stretch, while the material measure of curvature is used for bending. It is shown that strains of the curved beam can be expressed with respect to those defined in the element coordinate system using the gradient transformation, and the effect of strains at the initially curved configuration is eliminated using one-dimensional Almansi strain. This property can be effectively used with a nonincremental solution procedure employed for the absolute nodal coordinate formulation. Several numerical examples are presented in order to demonstrate the performance of the gradient deficient curved beam element developed in this investigation. It is shown that the use of the proposed element leads to better element convergence as compared with the fully parametrized element and the classical large displacement beam element with incremental solution procedures.
Use of General Nonlinear Material Models in Beam Problems: Application to Belts and Rubber Chains
Authors: Maqueda Luis G. , Mohamed Abdel-Nasser A. , Shabana Ahmed A.
Published: March 2010

Accurate modeling of many engineering systems requires the integration of multibody system and large deformation finite element algorithms that are based on general constitutive models, account for the coupling between the large rotation and deformation, and allow capturing coupled deformation modes that cannot be captured using beam formulations implemented in existing computational algorithms and computer codes. In this investigation, new three-dimensional nonlinear dynamic rubber chains and belt drives models are developed using the finite element absolute nodal coordinate formulation (ANCF) that allows for a straight forward implementation of general linear and nonlinear material models for structural elements such as beams, plates, and shells. Furthermore, this formulation, which is based on a more general kinematic description, can be used to predict the cross section deformation and its coupling with the extension and bending of the belt drives and rubber chains. The ANCF cross section deformation results are validated by comparison with the results obtained using solid finite elements in the case of a simple tension test problem. The effect of the use of different linear and nonlinear constitutive laws in modeling belt drive mechanisms is also examined in this investigation. The finite element formulation presented in this paper is implemented in a general purpose three-dimensional flexible multibody algorithm that allows for developing detailed models of mechanical systems subject to general loading conditions, nonlinear algebraic constraint equations, and arbitrary large displacements that characterize belt drives and tracked vehicle dynamics. The successful integration of large deformation finite element and multibody system algorithms is shown to be necessary in order to be able to study the dynamics of complex tracked vehicles with rubber chains. A computer simulation of a three-dimensional multibody tracked vehicle model that consists of twenty rigid bodies and two flexible rubber chains is used in order to demonstrate the use of the formulations presented in this investigation.
Directions of the Tangential Creep Forces in Railroad Vehicle Dynamics
Authors: Afshari Ali , Shabana Ahmed A.
Published: March 2010

In some of the wheel/rail creep theories used in railroad vehicle simulations, the direction of the tangential creep forces is assumed to be the wheel rolling direction (RD). When the Hertz theory is used, an assumption is made that the rolling direction is the direction of one of the axes of the contact ellipse. In principle, the rolling direction depends on the wheel motion while the direction of the axes of the contact ellipse (CE) are determined using the principal directions, which depend only on the geometry of the wheel and rail surfaces and do not depend on the motion of the wheel. The RD and CE directions can also be different from the direction of the rail longitudinal tangent (LT) at the contact point. In this investigation, the differences between the contact frames that are based on the RD, LT, and CE directions that enter into the calculation of the wheel/rail creep forces and moments are discussed. The choice of the frame in which the contact forces are defined can be determined using one longitudinal vector and the normal to the rail at the contact point. While the normal vector is uniquely defined, different choices can be made for the longitudinal vector including the RD, LT, and CE directions. In the case of pure rolling or when the slipping is small, the RD direction can be defined using the cross product of the angular velocity vector and the vector that defines the location of the contact point. Therefore, this direction does not depend explicitly on the geometry of the wheel and rail surfaces at the contact point. The LT direction is defined as the direction of the longitudinal tangent obtained by differentiation of the rail surface equation with respect to the rail longitudinal parameter (arc length). Such a tangent does not depend explicitly on the direction of the wheel angular velocity nor does it depend on the wheel geometry. The CE direction is defined using the direction of the axes of the contact ellipse used in Hertz theory. In the Hertzian contact theory, the contact ellipse axes are determined using the principal directions associated with the principal curvatures. Therefore, the CE direction differs from the RD and LT directions in the sense that it is function of the geometry of the wheel and rail surfaces. In order to better understand the role of geometry in the formulation of the creep forces, the relationship between the principal curvatures of the rail surface and the curvatures of the rail profile and the rail space curve is discussed in this investigation. Numerical examples are presented in order to examine the differences in the results obtained using the RD, LT and CE contact frames.
Nonlinear Periodic Response of Composite Curved Beam Subjected to Symmetric and Antisymmetric Mode Excitation
Authors: Ibrahim S. M. , Patel B. P. , Nath Y.
Published: March 2010

The periodic response of cross-ply composite curved beams subjected to harmonic excitation with frequency in the neighborhood of symmetric and antisymmetric linear free vibration modes is investigated. The analysis is carried out using higher-order shear deformation theory based finite element method (FEM). The governing equations are integrated using Newmark’s time marching coupled with shooting technique and arc-length continuation. Shooting method is used to solve the second-order differential equations of motion directly without converting them to the first-order differential equations. This approach is computationally efficient as the banded nature of equations is retained. A detailed study revealed that the response of antisymmetrically excited beams has contribution of higher antisymmetric as well as symmetric modes whereas the response of symmetrically excited beams has the significant participation of the higher symmetric modes except for the excitation in the neighborhood of first symmetric mode. The beam excited in the neighborhood of first symmetric mode has an additional branch corresponding to significant participation of first antisymmetric mode due to two-to-one internal resonance. Furthermore, for the beams excited in the neighborhood of higher modes, the peak response amplitude becomes less than that of the beam excited in the neighborhood of first mode but vibration behavior is drastically different due to the presence of subharmonics and higher harmonics. Two-to-one internal resonance between second antisymmetric mode and first symmetric mode is predicted for the first time.
Modeling and Dynamics of a Self-Sustained Electrostatic Microelectromechanical System
Authors: Kitio Kwuimy C. A. , Woafo P.
Published: March 2010

This paper deals with the study of a model of self-sustained electrostatic microelectromechanical system (MEMS). The electrical part contains two nonlinear components: a nonlinear resistance with a negative slope in the current-voltage characteristics, and a capacitor, having a cubic form as the charge-voltage characteristics. The modal approximation and the finite differences numerical scheme are used to analyze the dynamical behavior of the system: Resonant oscillations and bifurcation diagram leading to chaos are observed for some values of the polarization voltage. Hints of applications of the device are given.
Severity of Tip-Out Induced Impacts in Drive Line Systems With Backlash
Authors: Boere S. W. , Shukla A. , Fey R. H. B. , Nijmeijer H.
Published: March 2010

Numerical simulations are used to study the transient behavior of a four degree-of-freedom, rotational piecewise linear system. This study focuses on the impact between bodies in a system with backlash as a result of a sudden step input and the associated transient response. The subsequent single sided impacts and double sided impacts are studied as a function of the amplitude of the step input and the size of the backlash. Transitions have been observed between double sided impact regions and single sided impact regions, which agree with earlier findings. However, in this paper a more complete overview of the boundaries is given. The severity of the impacts is quantified with the peak-to-peak acceleration of the impacting bodies. The increase in the size of step input increases the severity of the impacts. However, the increase in backlash size leads to an extremum in impact severity. This is a possible explanation for seeming contradictions in literature.
Dynamic Modeling and Simulation of Percussive Impact Riveting for Robotic Automation
Authors: Li Yuwen , Xi Fengfeng , Behdinan Kamran
Published: March 2010

Dynamic modeling and simulation of percussive impact riveting are presented for robotic automation. This is an impact induced process to deform rivets, which involves an impact rivet gun driven under pneumatic pressure to pound a rivet against a bucking bar. To model this process, first, a new approach is developed to determine the hammer output speed under input pneumatic pressure. Second, impact dynamics is applied to model the impact acting on the rivet under the hammer hits. Finally, elastoplastic analysis is carried out to derive nonlinear equations for the determination of permanent (plastic) deformations of the rivet when hitting the bucking bar. For simulation, numerical integration algorithms are applied to solve the impact dynamic model and determine the riveting time according to riveting specifications. Riveting tests are carried out for model validation. Agreement between the simulation and experimental results shows the effectiveness of the proposed method.
Electron holography for analysis of deep submicron devices: Present status and challenges
Authors: Ikarashi Nobuyuki , Toda Akio , Uejima Kazuya , Yako Koichi , Yamamoto Toyoji , Hane Masami , Sato Hiroshi
Published: March 2010

A potential distribution analysis of source/drain (SD) regions in sub-30-nm-gate-length metal-oxide-semiconductor field-effect transistors (MOSFETs) is presented as an example of the present status of electron holography analysis. First, the authors describe experimental setups that determine the resolutions of the analysis in practice. They show that specimen preparation artifacts significantly affect the energy resolution and that the artifacts can be reduced by preparing specimens using low-energy back side ion milling. Second, they describe the SD potential analysis in sub-30-nm-gate-length MOSFETs.
Fluorine clustering and diffusion in silicon: Ab initio calculations and kinetic Monte Carlo model
Authors: Vollenweider Kilian , Sahli Beat , Zographos Nikolas , Zechner Christoph
Published: March 2010

The authors performed systematic ab initio calculations of fluorine clustering in silicon. The calculated formation energies were used to implement a new kinetic Monte Carlo (KMC) model. They present the ab initio results, discuss the new KMC model, and compare the resulting simulated profiles to experimental profiles. The calculated formation energies show clear trends with the number of missing silicon atoms and the number of fluorine atoms. The deduced KMC model based on the ab initio energetics is able to reproduce the reduction in boron transient enhanced diffusion in the presence of fluorine.
Medical applications of shortwave FM radar: Remote monitoring of cardiac and respiratory motion
Authors: Mostov K. , Liptsen E. , Boutchko R.
Published: March 2010

Purpose:

This article introduces the use of low power continuous wave frequency modulated radar for medical applications, specifically for remote monitoring of vital signs in patients.

Methods:

Gigahertz frequency radar measures the electromagnetic wave signal reflected from the surface of a human body and from tissue boundaries. Time series analysis of the measured signal provides simultaneous information on range, size, and reflective properties of multiple targets in the field of view of the radar. This information is used to extract the respiratory and cardiac rates of the patient in real time.

Results:

The results from several preliminary human subject experiments are provided. The heart and respiration rate frequencies extracted from the radar signal match those measured independently for all the experiments, including a case when additional targets are simultaneously resolved in the field of view and a case when only the patient's extremity is visible to the radar antennas.

Conclusions:

Micropower continuous wave FM radar is a reliable, robust, inexpensive, and harmless tool for real‐time monitoring of the cardiac and respiratory rates. Additionally, it opens a range of new and exciting opportunities in diagnostic and critical care medicine. Differences between the presented approach and other types of radars used for biomedical applications are discussed.
A technique optimization protocol and the potential for dose reduction in digital mammography
Authors: Ranger Nicole T. , Lo Joseph Y. , Samei Ehsan
Published: March 2010

Digital mammography requires revisiting techniques that have been optimized for prior screen/film mammography systems. The objective of the study was to determine optimized radiographic technique for a digital mammography system and demonstrate the potential for dose reduction in comparison to the clinically established techniques based on screen‐ film. An objective figure of merit (FOM) was employed to evaluate a direct‐conversion amorphous selenium FFDM system (Siemens Mammomat , Siemens AG Medical Solutions, Erlangen, Germany) and was derived from the quotient of the squared signal‐difference‐to‐noise ratio to mean glandular dose, for various combinations of technique factors and breast phantom configurations including kilovoltage settings , target/filter combinations (Mo–Mo and W–Rh), breast‐equivalent plastic in various thicknesses and densities (100% adipose, 50% adipose/50% glandular, and 100% glandular), and simulated mass and calcification lesions. When using a W–Rh spectrum, the optimized FOM results for the simulated mass and calcification lesions showed highly consistent trends with kVp for each combination of breast density and thickness. The optimized kVp ranged from for 100% adipose breasts to for 100% glandular breasts. The use of the optimized W–Rh technique compared to standard Mo–Mo techniques provided dose savings ranging from 9% for thick, 100% adipose breasts, to 63% for thick, 100% glandular breasts, and for breasts with a 50% adipose/50% glandular composition, from 12% for thick breasts up to 57% for thick breasts.
Ultrasound B‐scan image simulation, segmentation, and analysis of the equine tendon
Authors: Meghoufel Ali , Cloutier Guy , Crevier‐Denoix Nathalie , de Guise Jacques A.
Published: March 2010

Purpose:

The hypothesis is that an imaging technique based on decompression and segmentation of B‐scan images with morphological operators can provide a measurement of the integrity of equine tendons.

Methods:

Two complementary approaches were used: (i) Simulation of B‐scan images to better understand the relationship between image properties and their underlying biological structural contents and (ii) extraction and quantification from B‐scan images of tendon structures identified in step (i) to diagnose the status of the superficial digital flexor tendon (SDFT) by using the proposed imaging technique.

Results:

The simulation results revealed that the interfascicular spaces surrounding fiber fascicle bundles were the source of ultrasound reflection and scattering. By extracting these fascicle bundles with the proposed imaging technique, quantitative results from clinical B‐scan images of eight normal and five injured SDFTs revealed significant differences in fiber bundle number and areas: mean values were 50 (±11) andfor the normal SDFT data set. Different values were observed for injured SDFTs where the intact mean fiber bundle number decreased to 40 (±7); inversely, mean fiber bundle areas increased to, which indicate disruption of the thinnest interfascicular spaces and of their corresponding fiber fascicle bundles where lesions occurred.

Conclusions:

To conclude, this technique may provide a tool for the rapid assessment and characterization of tendon structures to enable clinical identification of the integrity of the SDFT.
Radiation protection measurements around a 12 MeV mobile dedicated IORT accelerator
Authors: Soriani Antonella , Felici Giuseppe , Fantini Mario , Paolucci Massimiliano , Borla Oscar , Evangelisti Giovanna , Benassi Marcello , Strigari Lidia
Published: March 2010

Purpose:

The aim of this study is to investigate radioprotection issues that must be addressed when dedicated accelerators for intraoperative radiotherapy (IORT) are used in operating rooms. Recently, a new version of a mobile IORT accelerator (LIAC™ Sordina SpA, Italy) with 12 MeV electron beam has been implemented. This energy is necessary in some specific pathology treatments to allow a better coverage of thick lesions. At an electron energy of 10 MeV, leakage and scattered x‐ray radiation (stray radiation) coming from the accelerator device and patient must be considered. If the energy is greater than 10 MeV, the x‐ray component will increase; however, the most meaningful change should be the addition of neutron background. Therefore, radiation exposure of personnel during the IORT procedure needs to be carefully evaluated.

Methods:

In this study, stray x‐ray radiation was measured and characterized in a series of spherical projections by means of an ion chamber survey meter. To simulate the patient during all measurements, a polymethylmethacrylate (PMMA) slab phantom with volume and density was used. The PMMA phantom was placed along the central axis of the beam in order to absorb the electron beams and the tenth value layer (TVL) and half value layer (HVL) of scattered radiation (at 0°, 90°, and 180° scattering angles) were also measured at 1 m of distance from the phantom center. Neutron measurements were performed using passive bubble dosimeters and a neutron probe, specially designed to evaluate ambient dose equivalent .

Results:

The x‐ray equivalent dose measured at 1 m along the beam axis at 12 MeV was . The value measured at 1 m at 90° scattering angle was . The HVL and TVL values were 1.1 and 3.5 cm of lead at 0°, and 0.4 and 1 cm at 90°, respectively. The highest equivalent dose of fast neutrons was found to be at the surface of the phantom on the central beam axis , while a lower value was observed below the phantom . The neutron dose equivalent at 90° scattering angle and on the floor plane on the beam axis below the beam stopper was negligible.

Conclusions:

Our data confirm that neutron exposure levels around the new dedicated IORT accelerator are very low. Mobile shielding panels can be used to reduce x‐ray levels to below regulatory levels without necessarily providing permanent shielding in the operating room.
Electrode displacement strain imaging of thermally‐ablated liver tissue in an in vivo animal model
Authors: Rubert N. , Bharat S. , DeWall R. J. , Andreano A. , Brace C. , Jiang J. , Sampson L. , Varghese T.
Published: March 2010

Purpose:

Percutaneous thermal ablation is increasingly being used to destroy hepatic tumors in situ. The success of ablative techniques is highly dependent on adequate ablation zone monitoring, and ultrasound‐based strain imaging could become a convenient and cost‐effective means to delineate ablation zone boundaries. This study investigates in vivo electrode displacement‐based strain imaging for monitoring hepatic ablation procedures that are difficult to perform with conventional elastography.

Methods:

In our method, minute displacements (less than a millimeter) are applied to the unconstrained end of the ablation electrode, resulting in localized tissue deformation within the ablation zone that provides the mechanical stimuli required for strain imaging. This article presents electrode displacement strain images of radiofrequency ablation zones created in porcine liverin vivo .

Results:

Cross‐sectional area measurements from strain images of these ablation zones were obtained using manual and automated segmentation. Area measurements from strain images were highly correlated with areas measured on histopathology images, quantitated using linear regression (, and , , respectively).

Conclusions:

This study further demonstrates that electrode displacement elastography is capable of providing high‐contrast images using widely available commercial ultrasound systems which may potentially be used to assess the extent of thermal ablation zones.
Analysis of deformable image registration accuracy using computational modeling
Authors: Zhong Hualiang , Kim Jinkoo , Chetty Indrin J.
Published: March 2010

Computer aided modeling of anatomic deformation, allowing various techniques and protocols in radiation therapy to be systematically verified and studied, has become increasingly attractive. In this study the potential issues in deformable image registration (DIR) were analyzed based on two numerical phantoms: One, a synthesized, low intensity gradient prostate image, and the other a lung patient's CT image data set. Each phantom was modeled with region‐specific material parameters with its deformation solved using a finite element method. The resultant displacements were used to construct a benchmark to quantify the displacement errors of the Demons and B‐Spline‐based registrations. The results show that the accuracy of these registration algorithms depends on the chosen parameters, the selection of which is closely associated with the intensity gradients of the underlying images. For the Demons algorithm, both single resolution (SR) and multiresolution (MR) registrations required approximately 300 iterations to reach an accuracy of 1.4 mm mean error in the lung patient's CT image (and 0.7 mm mean error averaged in the lung only). For the low gradient prostate phantom, these algorithms (both SR and MR) required at least 1600 iterations to reduce their mean errors to 2 mm. For the B‐Spline algorithms, best performance (mean errors of 1.9 mm for SR and 1.6 mm for MR, respectively) on the low gradient prostate was achieved using five grid nodes in each direction. Adding more grid nodes resulted in larger errors. For the lung patient's CT data set, the B‐Spline registrations required ten grid nodes in each direction for highest accuracy (1.4 mm for SR and 1.5 mm for MR). The numbers of iterations or grid nodes required for optimal registrations depended on the intensity gradients of the underlying images. In summary, the performance of the Demons and B‐Spline registrations have been quantitatively evaluated using numerical phantoms. The results show that parameter selection for optimal accuracy is closely related to the intensity gradients of the underlying images. Also, the result that the DIR algorithms produce much lower errors in heterogeneous lung regions relative to homogeneous (low intensity gradient) regions, suggests that feature‐based evaluation of deformable image registration accuracy must be viewed cautiously.
Dose convolution filter: Incorporating spatial dose information into tissue response modeling
Authors: Huang Yimei , Joiner Michael , Zhao Bo , Liao Yixiang , Burmeister Jay
Published: March 2010

Purpose:

A model is introduced to integrate biological factors such as cell migration and bystander effects into physical dose distributions, and to incorporate spatial dose information in plan analysis and optimization.

Methods:

The model consists of a dose convolution filter (DCF) with single parameter . Tissue response is calculated by an existing NTCP model with DCF‐applied dose distribution as input. The authors determined of rat spinal cord from published data. The authors also simulated the GRID technique, in which an open field is collimated into many pencil beams.

Results:

After applying the DCF, the NTCP model successfully fits the rat spinal cord data with a predicted value of , consistent with 2 mm migration distances of remyelinating cells. Moreover, it enables the appropriate prediction of a high relative seriality for spinal cord. The model also predicts the sparing of normal tissues by the GRID technique when the size of each pencil beam becomes comparable to .

Conclusions:

The DCF model incorporates spatial dose information and offers an improved way to estimate tissue response from complex radiotherapy dose distributions. It does not alter the prediction of tissue response in large homogenous fields, but successfully predicts increased tissue tolerance in small or highly nonuniform fields.
Evaluation of delivered monitor unit accuracy of gated step‐and‐shoot IMRT using a two‐dimensional detector array
Authors: Cheong Kwang‐Ho , Kang Sei‐Kwon , Lee MeYeon , Kim Su SSan , Park SoAh , Hwang Tae‐Jin , Kim Kyoung Ju , Oh Do Hoon , Bae Hoonsik , Suh Tae‐Suk
Published: March 2010

Purpose: To overcome the problem of organ motion in intensity‐modulated radiation therapy (IMRT), gated IMRT is often used for the treatment of lung cancer. In this study, the authors investigated the accuracy of the delivered monitor units (MUs) from each segment during gated IMRT using a two‐dimensional detector array for user‐specific verification purpose.

Methods: The authors planned a 6 MV photon, seven‐port step‐and‐shoot lung IMRT delivery. The respiration signals for gated IMRT delivery were obtained from the one‐dimensional moving phantom using the real‐time position management (RPM) system (Varian Medical Systems, Palo Alto, CA). The beams were delivered using a Clinac iX (Varian Medical Systems, Palo Alto, CA) with the Millennium 120 MLC. The MatriXX (IBA Dosimetry GmbH, Germany) was validated through consistency and reproducibility tests as well as comparison with measurements from a Farmer‐type ion chamber. The authors delivered beams with varying dose rates and duty cycles and analyzed the MatriXX data to evaluate MU delivery accuracy.

Results: There was quite good agreement between the planned segment MUs and the MUs computed from the MatriXX within ±2% error. The beam‐on times computed from the MatriXX data were almost identical for all cases, and they matched well with the RPM beam‐on and beam‐off signals. A slight difference was observed between them, but it was less than 40 ms. The gated IMRT delivery demonstrated an MU delivery accuracy that was equivalent to ungated IMRT, and the delivered MUs with a gating signal agreed with the planned MUs within ±0.5 MU regardless of dose rate and duty cycle.

Conclusions: The authors can conclude that gated IMRT is able to deliver an accurate dose to a patient during a procedure. The authors believe that the methodology and results can be transferred to other vendors’ devices, particularly those that do not provide MLC log data for a verification purpose.
4DCT‐based measurement of changes in pulmonary function following a course of radiation therapy
Authors: Ding Kai , Bayouth John E. , Buatti John M. , Christensen Gary E. , Reinhardt Joseph M.
Published: March 2010

Purpose:

Radiation therapy (RT) for lung cancer is commonly limited to subtherapeutic doses due to unintended toxicity to normal lung tissue. Reducing the frequency of occurrence and magnitude of normal lung function loss may benefit from treatment plans that incorporate the regional lung and radiation dose information. In this article, the authors propose a method that quantitatively measures the regional changes in lung tissue function following a course of radiation therapy by using 4DCT and image registration techniques.

Methods:

4DCT data sets before and after RT from two subjects are used in this study. Nonlinear 3D image registration is applied to register an image acquired near end inspiration to an image acquired near end expiration to estimate the pulmonary function. The Jacobian of the image registration transformation, indicating local lung expansion or contraction, serves as an index of regional pulmonary function. Approximately 120 annotated vascular bifurcation points are used as landmarks to evaluate registration accuracy. The authors compare regional pulmonary function before and after RT to the planned radiation dose at different locations of the lung.

Results:

In all registration pairs, the average landmark distances after registration are on the order of 1 mm. The pulmonary function change as indicated by the Jacobian change ranges from −0.15 to 0.1 in the contralateral lung and −0.22 to 0.23 in the ipsilateral lung for subject A, and ranges from −0.4 to 0.39 in the contralateral lung and −0.25 to 0.5 in the ipsilateral lung for subject B. Both of the subjects show larger range of the increase in the pulmonary function in the ipsilateral lung than the contralateral lung. For lung tissue regions receiving a radiation dose larger than 24 Gy, a decrease in pulmonary function was observed. For regions receiving a radiation dose smaller than 24 Gy, either an increase or a decrease in pulmonary function was observed. The relationship between the pulmonary function change and the radiation dose varies at different locations.

Conclusions:

With the use of 4DCT and image registration techniques, the pulmonary function prior to and following a course of radiation therapy can be measured. In the preliminary application of this approach for two subjects, changes in pulmonary function were observed with a weak correlation between the dose and pulmonary function change. In certain sections of the lung, detected locally compromised pulmonary function may have resulted from radiation injury.
Radiation dose reduction using a CdZnTe‐based computed tomography system: Comparison to flat‐panel detectors
Authors: Le Huy Q. , Ducote Justin L. , Molloi Sabee
Published: March 2010

Purpose:

Although x‐ray projection mammography has been very effective in early detection of breast cancer, its utility is reduced in the detection of small lesions that are occult or in dense breasts. One drawback is that the inherent superposition of parenchymal structures makes visualization of small lesions difficult. Breast computed tomography using flat‐panel detectors has been developed to address this limitation by producing three‐dimensional data while at the same time providing more comfort to the patients by eliminating breast compression. Flat panels are charge integrating detectors and therefore lack energy resolution capability. Recent advances in solid state semiconductor x‐ray detector materials and associated electronics allow the investigation of x‐ray imaging systems that use a photon counting and energy discriminating detector, which is the subject of this article.

Methods:

A small field‐of‐view computed tomography (CT) system that uses CdZnTe (CZT) photon counting detector was compared to one that uses a flat‐panel detector for different imaging tasks in breast imaging. The benefits afforded by the CZT detector in the energy weighting modes were investigated. Two types of energy weighting methods were studied: Projection based and image based. Simulation and phantom studies were performed with a 2.5 cm polymethyl methacrylate (PMMA) cylinder filled with iodine and calcium contrast objects. Simulation was also performed on a 10 cm breast specimen.

Results:

The contrast‐to‐noise ratio improvements as compared to flat‐panel detectors were 1.30 and 1.28 (projection based) and 1.35 and 1.25 (image based) for iodine over PMMA and hydroxylapatite over PMMA, respectively. Corresponding simulation values were 1.81 and 1.48 (projection based) and 1.85 and 1.48 (image based). Dose reductions using the CZT detector were 52.05% and 49.45% for iodine and hydroxyapatite imaging, respectively. Image‐based weighting was also found to have the least beam hardening effect.

Conclusions:

The results showed that a CT system using an energy resolving detector reduces the dose to the patient while maintaining image quality for various breast imaging tasks.
Zero‐shift thimble ionization chamber
Authors: Tessier Frédéric , Hooten Brian D. , McEwen Malcolm R.
Published: March 2010

Purpose:

Verify experimentally the theoretical prediction of F. Tessier and I. Kawrakow [Med. Phys. 37, 96–107 (2010)] that it is possible to design a thimble ionization chamber with no shift in its effective point of measurement (EPOM), i.e., a chamber that provides a measure of the dose to the medium at the location of its central axis.

Methods:

Measure dose from a 25 MV photon beam incident on water with an Exradin A1SL ionization chamber inside a thin sleeve (as a means of effectively increasing the thimble wall thickness). The depth‐dose curve is compared to that obtained using a well‐characterized PTW Roos parallel‐plate chamber.

Results:

With an appropriate increase in thimble wall thickness, the EPOM shift of the Exradin A1SL vanishes. Further increase of the wall thickness yields a chamber with a positive (downstream) shift in its point of measurement.

Conclusions:

It is possible to design a thimble ionization chamber with a zero EPOM shift by adjusting the wall thickness.
Analysis of dose to patient, spouse/caretaker, and staff, from an implanted trackable radioactive fiducial for use in the radiation treatment of prostate cancera)
Authors: Neustadter David , Barnea Gideon , Stokar Saul , Corn Ben
Published: March 2010

Purpose:

A fiducial tracking system based on a novel radioactive tracking technology is being developed for real‐time target tracking in radiation therapy. In this study, the authors calculate the radiation dose to the patient, the spouse/caretaker, and the medical staff that would result from a Ir192 radioactive fiducial marker permanently implanted in the prostate of a radiation therapy patient.

Methods:

Local tissue dose was calculated by Monte Carlo simulation. The patient's whole body effective dose equivalent was calculated by summing the doses to the sensitive organs. Exposure of the spouse/caretaker was calculated from the NRC guidelines. Exposure of the medical staff was based on estimates of proximity to and time spent with the patient.

Results:

The local dose is below 40 Gy at 5 mm from the marker and below 10 Gy at 10 mm from the marker. The whole body effective dose equivalent to the patient is 64 mSv. The dose to the spouse/caretaker is 0.25 mSv. The annual exposures of the medical staff are 0.2 mSv for a doctor performing implantations and 0.34 mSv for a radiation therapist positioning patients for therapy.

Conclusions:

The local dose is not expected to have any clinically significant effect on the surrounding tissue which is irradiated during therapy. The dose to the patient is small in comparison to the whole body dose received from the therapy itself. The exposure of all other people is well below the recommended limits. The authors conclude that there is no radiation exposure related contraindication for use of this technology in the radiation treatment of prostate cancer.