bluuebunny/crossref_metadata_2025 huggingface dataset:
Breed‐specific variation of hematologic and biochemical analytes in healthy adult Bernese Mountain dogs
Authors: Nielsen Lise , Kjelgaard‐Hansen Mads , Jensen Asger Lundorff , Kristensen Annemarie T.
Published: September 2009

Background:Hematology and serum biochemistry reference intervals in dogs may be affected by internal factors, such as breed and age, and external factors, such as the environment, diet, and lifestyle. In humans, it is well established that geographic origin and age may have an impact on reference intervals and, therefore, more specific reference intervals are sought for subpopulations.

Objective:The objective of this study was to validate and transfer standard laboratory reference intervals for healthy Bernese Mountain dogs and to create new intervals for analytes where the established laboratory reference intervals were rejected.

Methods:The procedure was performed using the human Clinical and Laboratory Standards Institute‐approved model modified for veterinary use. Thirty‐two dogs were included in the study using a direct a priori method, as recommended.

Results:While 23 of the standard laboratory reference intervals were readily validated, 7 of the analytes (eosinophils, MCHC, alkaline phosphatase [ALP], γ‐glutamyltransferase, total bilirubin, amylase, and cholesterol) required new reference intervals according to the standard. These were calculated using the robust method. In particular, the new reference range for ALP was wide compared with the established laboratory reference interval. No clinical causes were found for differences in the results of these analytes.

Conclusion:We found significant differences in 7 hematologic and serum biochemical analytes for which a breed‐specific variation appears to be the most plausible explanation. Breed‐specific reference intervals for Bernese Mountain dogs will help avoid misinterpretation of laboratory results in the diagnostic process.
The Securitization of Transnational Labor Migration: The Case of Malaysia and Indonesia
Authors: Arifianto Alexander R.
Published: September 2009

Existing studies on transnational migration in Southeast Asia tend to view it primarily from labor, human rights, or gender perspectives. Few of these studies have viewed labor migration as a security problem between the countries involved. This article attempts to close this gap in the literature by looking at the case study of labor migration from Indonesia and Malaysia from a security perspective and how it affects the relationship between migrants, citizens, and governments of these two countries. The article utilizes securitization theory introduced by the Copenhagen School to explain why, within the last two decades, Malaysian politicians have shifted their treatment of Indonesian migrants from a policy of toleration to one that considers them a security threat against Malaysian society.
Exponential Stabilization of Transverse Vibration and Trajectory Tracking for General In-Plane Motion of an Euler–Bernoulli Beam Via Two-Time Scale and Boundary Control Methods
Authors: Lotfavar Amir , Eghtesad Mohammad
Published: September 2009

In this paper, exponential stabilization of vibration of a flexible beam together with its general in-plane trajectory tracking is presented. Coupled beam dynamics including beam vibration (flexible/fast subsystem) and its rigid in-plane motion (rigid/slow subsystem) takes place in two different time domains. Therefore, to have the beam track a desired trajectory while suppressing its vibration by an exponential rate of decay, a composite control scheme is elaborated by two-time scale (TTS) control theory. This control law has two parts: one is a tracking controller designed for the rigid subsystem based on inverse dynamic law, and the other one is an exponential stabilizing controller for the flexible subsystem based on boundary control (BC) laws. Exponential stabilization is proved by using a metric containing kinetic and potential energies of the fast subsystem and by feedback of the rate of deflection and the slope at one end of the beam. Simulation results show that fast BC is able to remove undesirable vibration of the flexible beam and together with the slow inverse controller is able to provide very good trajectory tracking with acceptable actuating forces/moments. Also, they illustrate that tracking errors and the vibration amplitude are decreased versus time by the fast exponential stabilizing control law compared with an asymptotic stabilizing control law.
Free Vibration States of an Oscillator With a Linear Time-Varying Mass
Authors: Nhleko Sifiso
Published: September 2009

Due to its application in various dynamic systems, the free vibration behavior of a single-degree-of-freedom (SDoF) oscillator system with nonperiodic time-varying parameters has been the subject of recent interest. When dealing with this subject, past investigators have often isolated two special states of free vibration from the governing equation of motion. Naturally, this leads to the examination of solutions to two separate equations making it a tedious process given that each equation is different and equally complicated to solve. This paper presents a single equation that does not discriminate between the two special free vibration cases. The equation allows the description of all possible free vibration states and the two commonly investigated cases become its special cases. The procedure is illustrated by analyzing the free vibration behavior of a SDoF oscillator system subjected to a linear time-varying mass, constant stiffness, and damping. The solution established here highlights the critical role played by negative damping on the instability of the system. Based on this role, a minimum damping criterion that ensures stability is defined in terms of the natural frequency and the rate of change of mass of the principal system. Finally, the solution is used further to develop a numerical procedure for analyzing systems with arbitrary time-varying mass. A numerical example demonstrates that the proposed method converges to the exact solution more rapidly compared with other generic time stepping techniques.
Vibration Mode Analysis of Frames by the Method of Reverberation Ray Matrix
Authors: Miao F. X. , Sun Guojun , Pao Y. H.
Published: September 2009

The method of reverberation ray matrix (MRRM) has been developed by (Pao et al. 1999, “Dynamic Response and Wave Propagation in Plane Trusses and Frames,” AIAA J., 37(5), pp. 594–603) recently based on the theory of wave propagation for transient analysis of truss or frame structures. In this study, the MRRM is employed to obtain the frequency response function (FRF) of displacement of a frame under the action of a unit impulse load. The natural frequencies of the frame are determined from the FRF, since the curve of FRF has peak when a resonant frequency is approached. The vibration mode is retrieved from the adjoint matrix of the coefficient matrix of the governing equations of MRRM. The MRRM has advantage over numerical methods, such as finite element method (FEM), since in MRRM the frame is treated as an assembly of multiconnected beams, and exact solutions to the beam differential equations are employed to yield the system matrix of the frame. The vibration mode obtained is therefore exact. A planar frame made of 17 aluminum bars is analyzed. The vibration modes, as well as natural frequencies obtained from MRRM, coincide accurately with those obtained from FEM of ANSYS for the first a few modes; however, the difference of the frequencies between the two methods becomes a bit obvious when high order modes are examined.
Parametric Analyses of Multispan Viscoelastic Shear Deformable Beams Under Excitation of a Moving Mass
Authors: Kiani Keivan , Nikkhoo Ali , Mehri Bahman
Published: September 2009

This paper presents a numerical parametric study on design parameters of multispan viscoelastic shear deformable beams subjected to a moving mass via generalized moving least squares method (GMLSM). For utilizing Lagrange’s equations, the unknown parameters of the problem are stated in terms of GMLSM shape functions and the generalized Newmark-β scheme is applied for solving the discrete equations of motion in time domain. The effects of moving mass weight and velocity, material relaxation rate, slenderness, and span number of the beam on the design parameters and possibility of mass separation from the base beam are scrutinized in some detail. The results reveal that for low values of beam slenderness, the Euler–Bernoulli beam theory or even Timoshenko beam theory could not predict the real dynamic behavior of the multispan viscoelastic beam properly. Moreover, higher beam span number would result in higher inertial effects as well as design parameters values. Also, more distinction has been observed between the predicted values of design parameters regarding the shear deformable beams and those of Euler–Bernoulli beams, specifically for high levels of moving mass velocity and low values of material relaxation rate. Furthermore, the possibility of mass separation from the base beam moves to a greater extent as the beam span number increases and the relaxation rate of the beam material decreases, regardless of the assumed beam theory.
Mode Evolution of Cyclic Symmetric Rotors Assembled to Flexible Bearings and Housing
Authors: Kim Hyunchul , Colonnese Nick Theodore Khalid , Shen I. Y.
Published: September 2009

This paper is to study how the vibration modes of a cyclic symmetric rotor evolve when it is assembled to a flexible housing via multiple bearing supports. Prior to assembly, the vibration modes of the rotor are classified as “balanced modes” and “unbalanced modes.” Balanced modes are those modes whose natural frequencies and mode shapes remain unchanged after the rotor is assembled to the housing via bearings. Otherwise, the vibration modes are classified as unbalanced modes. By applying fundamental theorems of continuum mechanics, we conclude that balanced modes will present vanishing inertia forces and moments as they vibrate. Since each vibration mode of a cyclic symmetric rotor can be characterized in terms of a phase index (Chang and Wickert, “Response of Modulated Doublet Modes to Travelling Wave Excitation,” J. Sound Vib., 242, pp. 69–83; Chang and Wickert, 2002, “Measurement and Analysis of Modulated Doublet Mode Response in Mock Bladed Disks,” J. Sound Vib., 250, pp. 379–400; Kim and Shen, 2009, “Ground-Based Vibration Response of a Spinning Cyclic Symmetric Rotor With Gyroscopic and Centrifugal Softening Effects,” ASME J. Vibr. Acoust. (in press)), the criterion of vanishing inertia forces and moments implies that the phase index by itself can uniquely determine whether or not a vibration mode is a balanced mode as follows. Let N be the order of cyclic symmetry of the rotor and n be the phase index of a vibration mode. Vanishing inertia forces and moments indicate that a vibration mode will be a balanced mode if n≠1,N−1,N. When n=N, the vibration mode will be balanced if its leading Fourier coefficient vanishes. To validate the mathematical predictions, modal testing was conducted on a disk with four pairs of brackets mounted on an air-bearing spindle and a fluid-dynamic bearing spindle at various spin speeds. Measured Campbell diagrams agree well with the theoretical predictions.
Effective Tool-Point Acceleration of Serial Chain Mechanisms Based on Basic Geometric Transformations
Authors: Rios Oziel , Tesar Delbert
Published: September 2009

In this paper, a method to manage the actuator parameters of a serial chain mechanism composed of revolute joints to achieve improved responsiveness characteristics (acceleration capability) based on the basic geometric parameters of the mechanism is presented. Here, an analytic framework presented by the authors in an earlier work, which exploits the geometric structure of this type of mechanism is extended to address the tool-point mass and acceleration. The manipulator’s geometry is reduced to a set of lengths, which are representative of the mechanical gains associated with the manipulator and they, along with the transmission ratio of the actuators, are used to map the actuator parameters to their effective values at the tool-point where a direct comparison to the task requirements can be made. With this method, minimal computations are required to evaluate the system’s performance since only the forward kinematic computations are required. The effects of the actuator transmission ratio parameter on the effective tool-point force, mass, and acceleration are investigated for a six-DOF serial chain manipulator. Through this case study, it is demonstrated how the transmission ratio is managed to balance the system’s effective tool-point force and mass to obtain an optimal tool-point acceleration. In addition to the investigation of the effects of the actuator parameters, the method is shown to be useful in the solution of the configuration management or modular design problem since the exponential design space can be searched for a globally optimal solution with minimal computations. The goal of the configuration management problem is to quickly configure and/or reconfigure a robotic manipulator from a finite set of actuator modules.
Finite Element Modeling and Analysis of Friction Wedge Damping During Suspension Bounce Modes
Authors: Sun Y. Q. , Cole C.
Published: September 2009

A two-dimensional finite element model (2D FEM) has been developed to improve the modeling and understanding of the friction damping characteristics of freight bogie suspensions. The specific suspension considered utilizes friction dampers with constant preload force as are widely used in three-piece bogie wagons in Australia. Unlike simpler models commonly used in rail vehicle dynamics, the FE model developed can accommodate distributed normal forces across the wedge surfaces. The model was tested in bounce modes and compared with the normal equations used to model wedge friction forces, which treat the forces on the wedge as a static problem. The simulation results using the 2D FEM model showed that the friction damping force is not constant and changes when the suspension is in motion. It was also shown that the force changes magnitude during the loading and unloading situations. The factors, which affect the change in friction force, are the friction characteristics on wedge contact surfaces, the direction and change in tangent force on wedge angular surface, the elastic deformation of the wedge, the wedge relative movement, and the wedge structure arrangement. The FE model assumptions are investigated and insights on wedge friction and creepage discussed.
Mobility Change in Two Types of Metamorphic Parallel Mechanisms
Authors: Gan Dongming , Dai Jian S. , Liao Qizheng
Published: September 2009

This paper presents a new joint coined as the rT joint and proposes two types of metamorphic parallel mechanisms assembled with this rT joint. In the first type, the mechanism changes its topology by turning the rT joints in all limbs into different configurations. This change in mobility is completed by two cases illustrated by a 3(rT)PS metamorphic parallel mechanism having variable mobility from 3 to 6 and a 3(rT)P(rT) parallel mechanism having various configurations including pure translations, pure rotations, and mobility 4. In the second type, a central strut with the rT joint is added in a parallel mechanism. The variable mobility of the mechanism results from the topological change of the central (rT)P(rT) strut. This is illustrated in a 3SPS-1(rT)P(rT) metamorphic parallel mechanism, which changes its mobility from 4 to 5. It is demonstrated in mobility analysis that the change in local mobility of each limb results in the change in the platform mobility that a metamorphic process can be achieved. This particular analysis leads to advancement of improved Grübler–Kutzbach criterion by introducing the local mobility factor in the mobility analysis.
Tomographic image via background subtraction using an x‐ray projection image and a priori computed tomography
Authors: Zhang Jin , Yi Byongyong , Lasio Giovanni , Suntharalingam Mohan , Yu Cedric
Published: September 2009

Kilovoltage x‐ray projection images (kV images for brevity) are increasingly available in image guided radiotherapy (IGRT) for patient positioning. These images are two‐dimensional (2D) projections of a three‐dimensional (3D) object along the x‐ray beam direction. Projecting a 3D object onto a plane may lead to ambiguities in the identification of anatomical structures and to poor contrast in kV images. Therefore, the use of kV images in IGRT is mainly limited to bony landmark alignments. This work proposes a novel subtraction technique that isolates a slice of interest (SOI) from a kV image with the assistance of a priori information from a previous CT scan. The method separates structural information within a preselected SOI by suppressing contributions to the unprocessed projection from out‐of‐SOI‐plane structures. Up to a five‐fold increase in the contrast‐to‐noise ratios (CNRs) was observed in selected regions of the isolated SOI, when compared to the original unprocessed kV image. The tomographic image via background subtraction (TIBS) technique aims to provide a quick snapshot of the slice of interest with greatly enhanced image contrast over conventional kV x‐ray projections for fast and accurate image guidance of radiation therapy. With further refinements, TIBS could, in principle, provide real‐time tumor localization using gantry‐mounted x‐ray imaging systems without the need for implanted markers.
A theoretical study on phase‐contrast mammography with Thomson‐scattering x‐ray sources
Authors: De Caro Liberato , Giannini Cinzia , Bellotti Roberto , Tangaro Sabina
Published: September 2009

Purpose:

The x‐ray transmitted beam from any material/tissue depends on the complex refractive index, where is responsible for the phase shift and is for the beam attenuation. Although for human tissues, the cross section is about 1000 times greater than the ones in the x‐ray energy range from 10 to 150 keV, the gain in breast tumor visualization of phase‐contrast mammography (PCM) with respect to absorption contact imaging (AI) is limited by the maximum dose that can be delivered to the patient. Moreover, in‐line PC imaging (PCI) is the simplest experimental mode among all available x‐ray PCI techniques since no optics are needed. The latter is a fundamental requirement in order to transfer the results of laboratory research into hospitals. Alternative to synchrotron radiation sources, the implementation of relativistic Thomson‐scattering (TS) x‐ray sources is particularly suitable for hospital use because of their high peak brightness within a relatively compact and affordable system. In this work, the possibility to realize PCM using a TS source in a hospital environment is studied, accounting for the effect of a finite deliverable dose on the PC visibility enhancement with respect to AI.

Methods:

The contrast‐to‐noise ratio of tumor‐tissue lesions in PCM has been studied on the bases of a recent theoretical model, describing image contrast formation by means of both wave‐optical theory and the mutual coherence formalism. The latter is used to describe the evolution, during wave propagation, of the coherence of the wave field emitted by a TS source. The contrast‐to‐noise ratio for both PCI and AI has been analyzed in terms of tumor size, beam energy, detector, and source distances, studying optimal conditions for performing PCM. Regarding other relevant factors which could influence “tumor” visibility, the authors have assumed simplified conditions such as a spherical shape description of the tumor inclusion, a constant surrounding background, ideal conditions for the calculus of the contrast‐to‐noise ratio.

Results:

The results show the possibility to enhance with PCI the signal‐to‐noise ratio for features in the submillimeter scale. This finding could give PCM a great advantage with respect to AI, opening the possibility to decrease the number of wrong diagnoses before histological exams. The results agree with experimental evidences obtained by Dreossi et al. [D. Dreossi et al., “The mammography project at the SYRMEP beamline,” Eur. J. Radiol. 68, S58–S62 (2008)] with real PCM using synchrotron radiation.

Conclusions:

The challenging characteristics of TS sources, suitable for PCM, should be fluxes of at least emitted by very small sources of about , together with moderate energy spreads (less than 10%) in order to realize both sufficient spatial coherence and enough fluence on the patient, collecting images in reasonable exposure times. These fluxes will be achieved by next generation TS sources which are already under development.
Replacement correction factors for cylindrical ion chambers in electron beams
Authors: Wang L. L. W. , Rogers D. W. O.
Published: September 2009

Purpose:

In the TG‐21 dosimetry protocol, for cylindrical chambers in electron beams the replacement correction factor (or the product in the IAEA's notation), was conceptually separated into two components: the gradient correction accounting for the effective point of measurement and the fluence correction dealing with the change in the electron fluence spectrum. At the depth of maximum dose , is taken as 1. There are experimental data available at for the values of (or ). In the TG‐51 dosimetry protocol, the calibration is at the reference depth where is required for cylindrical chambers and is unknown and so the measured values at are used with the corresponding mean electron energy at . Monte Carlo simulations are employed in this study to investigate the replacement correction factors for cylindrical chambers in electron beams.

Methods:

Using previously established Monte Carlo calculation methods, the values of and are calculated with high statistical precision for cylindrical cavities of a variety of diameters and lengths in a water phantom irradiated by various electron beams. The values of as defined in the TG‐51 dosimetry protocol are also calculated.

Results:

The calculated values of the fluence correction factors are in good agreement with the measured values when the wall correction factors are taken into account for the plane‐parallel chambers used in the measurements. An empirical formula for for cylindrical chambers at in electron beams is derived as a function of the chamber radius and the beam quality specifier .

Conclusions:

The mean electron energy at depth is a good beam quality specifier for. Thus TG‐51's adoption of at with the same mean electron energy for use at is proven to be accurate. The values of for a Farmer‐type chamber as defined in the TG‐51 dosimetry protocol may be wrong by 0.3% for high‐energy electron beams and by more than 1% for low‐energy electron beams.
Investigation of a source for intra‐ocular treatment of wet age‐related macular degeneration
Authors: Holmes Shannon M. , Micka John A. , DeWerd Larry A.
Published: September 2009

Purpose:

The purpose of this study is to perform an extensive investigation of an approximately long source designed for treating wet age‐related macular degeneration.

Methods:

As part of this investigation, a NIST‐traceable absorbed dose to water calibration technique was established, and a source deployment verification test was developed. The influence of treatment cannula construction tolerance on the measurements as well as the dose delivered to the patient was investigated using the Monte Carlo code MCNP5. Variation between production cannulae was quantified experimentally using a well‐type ionization chamber, and additional measurements along with Monte Carlo calculations of the collimating insert used for source deployment verification were performed to validate the model.

Results:

Maximum variation in the integrated target dose was seen when the source was shifted laterally within the treatment cannula. For the well chamber measurements, the observed standard deviation in ionization current for a single source placed in different reference cannulae was, with a maximum observed range of less than . Clinical cannulae in the collimating insert showed an average of of the reference signal when sources were fully deployed compared to 18.5% predicted by Monte Carlo calculations. This discrepancy has been attributed primarily to construction of the collimator since the collimation gap was observed to be approximately smaller than specified. Construction tolerance of the well chamber insert as well as position tolerance of the cannula tip were both investigated, and their influence on the predicted signal was quantified. Additional measurements along with Monte Carlo based calculations of the collimating insert with polyethylene spacers added to the setup were performed to validate the Monte Carlo model. The shimmed Monte Carlo and measured data agree to within 1%, which is a magnitude difference of approximately 0.1% of the reference signal.

Conclusions:

This investigation confirms that the signal for an acceptably deployed source in the collimating insert is between 17.5% and 21.5% of the reference signal, as calculated using Monte Carlo models. Clinical cannulae for which the source deployment verification measurement falls outside the acceptable range should not be used to treat patients.
Is radiography justified for the evaluation of patients presenting with cervical spine trauma?
Authors: Theocharopoulos Nicholas , Chatzakis Georgios , Damilakis John
Published: September 2009

Conventional radiography has been for decades the standard method of evaluation for cervical spine trauma patients. However, currently available helical multidetector CT scanners allow multiplanar reconstruction of images, leading to increased diagnostic accuracy. The purpose of this study was to determine the relative benefit/risk ratio between cervical spine CT and cervical spine radiography and between cervical spine CT and cervical spine radiography, followed by CT as an adjunct for positive findings. A decision analysis model for the determination of the optimum imaging technique was developed. The sensitivity and specificity of CT and radiography were obtained by dedicated meta‐analysis. Lifetime attributable risk of mortal cancer from CT and radiography was calculated using updated organ‐specific risk coefficients and organ‐absorbed doses. Patient organ doses from radiography were calculated using Monte Carlo techniques, simulated exposures performed on an anthropomorphic phantom, and thermoluminescence dosimetry. A prospective patient study was performed regarding helical CT scans of the cervical spine. Patient doses were calculated based on the dose‐length‐product values and Monte Carlo‐based CT dosimetry software program. Three groups of patient risk for cervical spine fracture were incorporated in the decision model on the basis of hypothetical trauma mechanism and clinical findings. Radiation effects were assessed separately for males and females for four age groups (20, 40, 60, and 80 yr old). Effective dose from radiography amounts to 0.050 mSv and from a typical CT scan to 3.8 mSv. The use of CT in a hypothetical cohort of patients prevents approximately 130 incidents of paralysis in the low risk group (a priori fracture probability of 0.5%), 500 in the moderate risk group (a priori fracture probability of 2%), and 5100 in the high risk group (a priori fracture probability of 20%). The expense of this CT‐based prevention is 15–32 additional radiogenic lethal cancer incidents. According to the decision model calculations, the use of CT is more favorable over the use of radiography alone or radiography with CT by a factor of 13, for low risk 20 yr old patients, to a factor of 23, for high risk patients younger than 80 yr old. The radiography/CT imaging strategy slightly outperforms plain radiography for high and moderate risk patients. Regardless of the patient age, sex, and fracture risk, the higher diagnostic accuracy obtained by the CT examination counterbalances the increase in dose compared to plain radiography or radiography followed by CT only for positive radiographs and renders CT utilization justified and the radiographic screening redundant.
Monte Carlo evaluations of the absorbed dose and quality dependence of in radiotherapy photon beams
Authors: Chen Shao Wen , Wang Xue Tao , Chen Li Xin , Tang Qiang , Liu Xiao Wei
Published: September 2009

Purpose:

The purpose of this work was to evaluate the absorbed dose to dosimeter at various depths of water phantom in radiotherapy photon beams by Monte Carlo simulation and evaluate the beam quality dependence.

Methods:

The simulations were done using EGSnrc. The cylindrical dosimeter was placed at the central axis of the water phantom at depths between 0.5 and 8 cm. The incident beams included monoenergetic photon beams ranging from 1 to 18 MeV, beams, Varian 6 MV beams using phase space files based on a full simulation of the linac, and Varian beams between 4 and 24 MV using Mohan's spectra. The absorbed dose to the dosimeter and the water at the corresponding position in the absence of the dosimeter, as well as absorbed dose ratio factor , was calculated.

Results:

The results show that depends obviously on the photon energy at the shallow depths. However, as the depth increases, the change in becomes small, beyond the buildup region, the maximum discrepancy of to the average value is not more than 1%.

Conclusions:

These simulation results confirm the use of dosimeter in radiotherapy photon beams and clearly indicate that more attention should be paid when using such a dosimeter in the buildup region of high‐energy radiotherapy photon beams.
Detectability of motions in AAA with ECG‐gated CTA: A quantitative study
Authors: Klein Almar , Oostveen Luuk J. , Greuter Marcel J. W. , Hoogeveen Yvonne , Schultze Kool Leo J. , Slump Cornelis H. , Klaas Jan Renema W.
Published: September 2009

Purpose: ECG‐gated CT enables the visualization of motions caused by the beating of the heart. Although ECG gating is frequently used in cardiac CT imaging, this technique is also very promising for evaluating vessel wall motion of the aortic artery and the motions of (stent grafts inside) abdominal aortic aneurysms (AAA). Late stent graft failure is a serious complication in endovascular repair of aortic aneurysms. Better understanding of the motion characteristics of stent grafts will be beneficial for designing future devices. In addition, these data can be valuable in predicting stent graft failure in patients. To be able to reliably quantify the motion, however, it is of importance to know the performance and limitations of ECG gating, especially when the motions are small, as is the case in AAA. Since the details of the reconstruction algorithms are proprietary information on the CT manufacturers and not in the public domain, empirical experiments are required. The goal of this study is to investigate as to what extent the motions in AAA can be measured using ECG‐gated CT. The authors quantitatively investigate four aspects of motion in ECG‐gated CT: The detectability of the motion of objects at different amplitudes and different periodic motions, the temporal resolution, and the volume gaps that occur as a function of heart rate.

Methods: They designed an experiment on a standard static phantom to empirically determine temporal resolution. To investigate motion amplitude and frequency, as well as patient heart rate, they designed dynamic experiments in which a home‐made phantom driven by a motion unit moves in a predetermined pattern.

Results: The duration of each ECG‐gated phase was found to be , which corresponds to half of the rotation time and is thus in accordance with half scan reconstruction applied by the scanner. By using subpixel localization, motions become detectable from amplitudes of as small as in the direction and in the direction. With the rotation time used in this study, motions up to can be reliably detected. The reconstruction algorithm fills volume gaps with noisy data using interpolation, but objects within these gaps remain hidden.

Conclusions: This study gives insight into the possibilities and limitations for measuring small motions using ECG‐gated CT. Application of the experimental method is not restricted to the CT scanner of a single manufacturer. From the results, they conclude that ECG‐gated CTA is a suitable technique for studying the expected motions of the stent graft and vessel wall in AAA.
Quantitative image‐based spectral reconstruction for computed tomography
Authors: Heismann B. , Balda M.
Published: September 2009

Computed tomography (CT) devices are routinely employed to obtain three‐dimensional images of the human body. The reconstructed CT numbers represent weighted x‐ray attenuation coefficients. Their spectral weighting is influenced by the selected x‐ray source spectrum, the detector characteristics, and the attenuating object itself. The quantitative ground truth of the scanned object is given by the spectral attenuation coefficient. It is not directly measurable in standard CT. For spectral CT measurements, algorithms like the basis material decomposition yield parametrized representations of the spectral mass attenuation coefficient. In practical applications, image‐based formulations are commonly used. They are affected by both the CT system characteristics and the object self‐attenuation effects. In this article the authors introduce an image‐based spectral CT method. It expresses measured CT data as a spectral integration of the spectral attenuation coefficient multiplied by a local weighting function (LWF). The LWF represents the local energy weighting in the image domain, taking into account the system and reconstruction properties and the object self‐attenuation. A generalized image‐based formulation of spectral CT algorithms is obtained, with no need for additional corrections of, e.g., beam hardening. The iterative procedure called local spectral reconstruction yields both the mass attenuation coefficients of the object and a representation of the LWF. The quantitative accuracy and precision of the method are investigated in several applications: First, beam hardening corrections to various target energy weightings and attenuation correction maps for SPECT/CT and PET/CT are calculated. Second, an iodine density evaluation is performed. Finally, a direct identification of spectral attenuation functions using the LWF result is demonstrated. In all applications, the ground truth of the objects is reproduced with a quantitative accuracy in the subpercent to 2% range. An exponential convergence behavior of the iterative procedure is observed, with one to two iteration steps as a good compromise between quantitative accuracy and precision. The authors conclude that the method can be used to perform image‐based spectral CT reconstructions with quantitative accuracy. Existing algorithms benefit from the intrinsic treatment of beam hardening and system properties. Novel algorithms are enabled to directly compare material model functions to spectral measurement data.
Evaluation of scatter effects on image quality for breast tomosynthesis
Authors: Wu Gang , Mainprize James G. , Boone John M. , Yaffe Martin J.
Published: September 2009

Digital breast tomosynthesis uses a limited number (typically 10–20) of low‐dose x‐ray projections to produce a pseudo‐three‐dimensional volume tomographic reconstruction of the breast. The purpose of this investigation was to characterize and evaluate the effect of scattered radiation on the image quality for breast tomosynthesis. In a simulation, scatter point spread functions generated by a Monte Carlo simulation method were convolved over the breast projection to estimate the distribution of scatter for each angle of tomosynthesis projection. The results demonstrate that in the absence of scatter reduction techniques, images will be affected by cupping artifacts, and there will be reduced accuracy of attenuation values inferred from the reconstructed images. The effect of x‐ray scatter on the contrast, noise, and lesion signal‐difference‐to‐noise ratio (SDNR) in tomosynthesis reconstruction was measured as a function of the tumor size. When a with‐scatter reconstruction was compared to one without scatter for a 5 cm compressed breast, the following results were observed. The contrast in the reconstructed central slice image of a tumorlike mass (14 mm in diameter) was reduced by 30%, the voxel value (inferred attenuation coefficient) was reduced by 28%, and the SDNR fell by 60%. The authors have quantified the degree to which scatter degrades the image quality over a wide range of parameters relevant to breast tomosynthesis, including x‐ray beam energy, breast thickness, breast diameter, and breast composition. They also demonstrate, though, that even without a scatter rejection device, the contrast and SDNR in the reconstructed tomosynthesis slice are higher than those of conventional mammographic projection images acquired with a grid at an equivalent total exposure.
Sliding characteristic and material compressibility of human lung: Parametric study and verification
Authors: Al‐Mayah A. , Moseley J. , Velec M. , Brock K. K.
Published: September 2009

Purpose:

To find and verify the optimum sliding characteristics and material compressibility that provide the minimum error in deformable image registration of the lungs.

Methods:

A deformable image registration study has been conducted on a total of 16 lung cancer patients. Patient specific three dimensional finite element models have been developed to model left and right lungs, chest (body), and tumor based on 4D CT images. Contact surfaces have been applied to lung‐chest cavity interfaces. Experimental test data are used to model nonlinear material properties of lungs. A parametric study is carried out on seven patients, 20 conditions for each, to investigate the sliding behavior and the tissue compressibility of lungs. Three values of coefficient of friction of 0, 0.1, and 0.2 are investigated to model lubrication and sliding restriction on the lung‐chest cavity interface. The effect of material compressibility of lungs is studied using Poisson's ratios of 0.35, 0.4, 0.45, and 0.499. The model accuracy is examined by calculating the difference between the image‐based displacement of bronchial bifurcation points identified in the lung images and the calculated corresponding model‐based displacement. Furthermore, additional bifurcation points around the tumor and its center of mass are used to examine the effect of the mentioned parameters on the tumor localization.

Results:

The frictionless contact model with 0.4 Poisson's ratio provides the smallest residual errors of, , and in the LR, AP, and SI directions, respectively. Similarly, this optimum model provides the most accurate location of the tumor with residual errors of , , and in all three directions. The accuracy of this model is verified on an additional nine patients with average errors of , , and in the LR, AP, and SI directions, respectively.

Conclusions:

The optimum biomechanical model with the smallest registration error is when frictionless contact model and 0.4 Poisson's ratio are applied. The overall accuracies of all bifurcation points in all 16 patients including tumor points are, , and in the LR, AP, and SI directions, respectively.
Assessment of three dead detector correction methods for cone‐beam computed tomography
Authors: Nelms David W. , Shukla Hemant I. , Nixon Earl , Bayouth John E. , Flynn Ryan T.
Published: September 2009

Purpose:

Dead detectors due to manufacturing defects or radiation damage in the electronic portal imaging devices (EPIDs) used for cone‐beam computed tomography (CBCT) can lead to image degradation and ring artifacts. In this work three dead detector correction methods were assessed using megavoltage CBCT (MVCBCT) as a test system, with the goals of assessing the relative effectiveness of the three methods and establishing the conditions for which they fail.

Methods:

MVCBCT projections acquired with four linacs at 8 and 60 MU (monitor units) were degraded with varying percentages (2%–95%) of randomly distributed dead single detectors (RDSs), randomly distributed dead detector clusters (RDCs) of 2 mm diameter, and nonrandomly distributed dead detector disks (NRDDs) of varying diameter (4–16 mm). Correction algorithms were bidirectional linear interpolation (BLI), quad‐directional linear interpolation (QLI), and a Laplacian solution (LS) method. Correction method failure was defined to occur if ring artifacts were present in the reconstructed phantom images from any linac or if the modulation transfer function (MTF) for any linac dropped below baseline with a value, calculated with the two sample test, of less than 0.01.

Results:

All correction methods failed at the same or lower RDC/RDS percentages and NRDD diameters for the 60 MU as for the 8 MU cases. The LS method tended to outperform or match the BLI and QLI methods. If ring artifacts anywhere in the images were considered unacceptable, the LS method failed for 60 MU at RDS, RDC, and NRDD. If ring artifacts within 4 mm longitudinally of the phantom section interfaces were considered acceptable, the LS method failed for 60 MU at RDS, RDC, and NRDD. LS failed due to MTF drop for 60 MU at RDS, RDC, and NRDD.

Conclusions:

The LS method is superior to the BLI and QLI methods, and correction algorithm effectiveness decreases as imaging dose increases. All correction methods failed first due to ring artifacts and second due to MTF drop. If ring artifacts in axial slices within a 4 mm longitudinal distance from phantom section interfaces are acceptable, statistically significant loss in spatial resolution does not occur until over 25% of the EPID is covered in randomly distributed dead detectors, or NRDDs of 4 mm diameter are present.
An iterative technique to segment PET lesions using a Monte Carlo based mathematical model
Authors: Nehmeh S. A. , El‐Zeftawy H. , Greco C. , Schwartz J. , Erdi Y. E. , Kirov A. , Schmidtlein C. R. , Gyau A. B. , Larson S. M. , Humm J. L.
Published: September 2009

Purpose:

The need for an accurate lesion segmentation tool in PET is a prerequisite for the estimation of lesion response to therapy, for radionuclide dosimetry, and for the application of PET to radiotherapy planning. In this work, the authors have developed an iterative method based on a mathematical fit deduced from Monte Carlo simulations to estimate tumor segmentation thresholds.

Methods:

The GATE software, a GEANT4 based Monte Carlo tool, was used to model the GE Advance PET scanner geometry. Spheres ranging between 1 and in diameters were simulated in a high and in diameter cylinder. The spheres were filled with water‐equivalent density and simulated in both water and lung equivalent background. The simulations were performed with an infinite, , and target‐to‐background ratio (T/B). A mathematical fit describing the correlation between the lesion volume and the corresponding optimum threshold value was then deduced through analysis of the reconstructed images. An iterative method, based on this mathematical fit, was developed to determine the optimum threshold value. The effects of the lesion volume and T/B on the threshold value were investigated. This method was evaluated experimentally using the NEMA NU2‐2001 IEC phantom, the ACNP cardiac phantom, a randomly deformed aluminum can, and a spheroidal shape phantom implemented artificially in the lung, liver, and brain of patient PET images. Clinically, the algorithm was evaluated in six lesions from five patients. Clinical results were compared to CT volumes.

Results:

This mathematical fit predicts an existing relationship between the PET lesion size and the percent of maximum activity concentration within the target volume (or threshold). It also showed a dependence of the threshold value on the T/B, which could be eliminated by background subtraction. In the phantom studies, the volumes of the segmented PET targets in the PET images were within 10% of the nominal ones. Clinically, the PET target volumes were also within 10% of those measured from CT images.

Conclusions:

This iterative algorithm enabled accurately segment PET lesions, independently of their contrast value.
TG‐43 U1 based dosimetric characterization of model 67‐6520 Cs‐137 brachytherapy source
Authors: Meigooni Ali S. , Wright Clarissa , Koona Rafiq A. , Awan Shahid B. , Granero Domingo , Perez‐Calatayud Jose , Ballester Facundo
Published: September 2009

Purpose:

Brachytherapy treatment has been a cornerstone for management of various cancer sites, particularly for the treatment of gynecological malignancies. In low dose rate brachytherapy treatments, sources have been used for several decades. A new source design has been introduced (model 67‐6520, source B3‐561) by Isotope Products Laboratories (IPL) for clinical application. The goal of the present work is to implement the TG‐43 U1 protocol in the characterization of the aforementioned source.

Methods:

The dosimetric characteristics of the IPL source are measured using LiF thermoluminescent dosimeters in a Solid Water™ phantom material and calculated using Monte Carlo simulations with the GEANT4 code in Solid Water™ and liquid water. The dose rate constant, radial dose function, and two‐dimensional anisotropy function of this source model were obtained following the TG‐43 U1 recommendations. In addition, the primary and scatter dose separation(PSS) formalism that could be used in convolution/superposition methods to calculate dose distributions around brachytherapy sources in heterogeneous media was studied.

Results:

The measured and calculated dose rate constants of the IPL source in Solid Water™ were found to be and , respectively. The agreement between these two methods was within our experimental uncertainties. The Monte Carlo calculated value in liquid water of the dose rate constant was . Similarly, the agreement between measured and calculated radial dose functions and the anisotropy functions was found to be within ±5%. In addition, the tabulated data that are required to characterize the source using the PSS formalism were derived.

Conclusions:

In this article the complete dosimetry of the newly designed IPL source following the AAPM TG‐43 U1 dosimetric protocol and the PSS formalism is provided.
Optical Coherence Tomography Technology and Applications
Authors: Gueye Paul
Published: September 2009

Optical Coherence Tomography Technology and Applications Drexel Wolfgang and Fujimoto James G. Springer‐Verlag, Berlin, Heidelberg, Germany, 2008. $199.00. ISBN: 9783540775492. Hardcover 1346pp.
Radiation Damage in Biomolecular Systems: Proceedings of the Fifth International Conference (RADAM 2008), Debrecen, Hungary, 13–15 June 2008
Authors: Gueye Paul
Published: September 2009

Radiation Damage in Biomolecular Systems: Proceedings of the Fifth International Conference (RADAM 2008), Debrecen, Hungary, 13–15 June 2008 Tőkési Károly and Sulik Béla AIP Conference Proceedings, NY, 2008. Hardcover 232 pp. Price: $154.00. ISBN: 9780735406117.