bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling a Biomass Fluidizing Bed With Side Port Air Injection
Authors: Deza Mirka , Battaglia Francine , Heindel Theodore J.
Published: July 2010

Fluidized beds are used to gasify materials such as coal or biomass in the production of producer gas. Modeling these reactors using computational fluid dynamics is advantageous when performing parametric studies for design and scale-up. While two-dimensional simulations are easier to perform than three-dimensional simulations, they may not capture the proper physics. This paper compares two- and three-dimensional simulations with experiments for a reactor geometry with side port air injection. The side port is located within the bed region so that the injected air can help promote mixing. Of interest in this study is validating the hydrodynamics of fluidizing biomass. Two operating conditions of the fluidized bed are studied for superficial gas velocities of 1.5Umf and 3.0Umf, where Umf is the minimum fluidization velocity. The material used to represent biomass is ground walnut shell because it tends to fluidize uniformly and falls within the Geldart type B classification. The simulations are compared to experimental data of time-averaged local gas holdup values using X-ray computed tomography. Results indicate that for the conditions of this study, two-dimensional simulations overpredict the gas holdup trends when compared to the experiments. However, the three-dimensional simulations compare exceptionally well with the experiments, thus predicting the fluidization hydrodynamics, irrespective of flowrate or complexity due to the side air port. Furthermore, the study demonstrates the importance of using a three-dimensional model for bubbling fluidized beds with complex physics.
A k-ε Model for Particle-Laden Turbulent Flows
Authors: Schwarzkopf J. D. , Crowe C. T. , Dutta P.
Published: July 2010

A dissipation transport equation for the carrier phase of particle-laden turbulent flows was recently developed. This equation shows a new production of dissipation term due to the presence of particles that is related to the velocity difference between the particle and the surrounding fluid. In the development, it was assumed that each coefficient was the sum of the coefficient for single phase flow and a coefficient quantifying the contribution of the particulate phase. The coefficient for the new production term (due to the presence of particles) was found from homogeneous turbulence generation by particles and the coefficient for the dissipation of dissipation term was analyzed using DNS. A numerical model was developed and applied to particles falling in a channel of downward turbulent air flow. Boundary conditions were also developed to ensure that the production of turbulent kinetic energy due to mean velocity gradients and particle surfaces balanced with the turbulent dissipation near the wall. The turbulent kinetic energy is compared with experimental data. The results show attenuation of turbulent kinetic energy with increased particle loading; however the model does under predict the turbulent kinetic energy near the center of the channel. To understand the effect of this additional production of dissipation term (due to particles), the coefficients associated with the production of dissipation due to mean velocity gradients and particle surfaces are varied to assess the effects of the dispersed phase on the carrier phase turbulent kinetic energy across the channel. The results show that this additional term plays a significant role in predicting the turbulent kinetic energy and a reason for under predicting the turbulent kinetic energy near the center of the channel is discussed. It is concluded that the dissipation coefficients play a critical role in predicting the turbulent kinetic energy in particle-laden turbulent flows.
Hyperbolicity of One-Dimensional Two-Fluid Model With Interfacial Area Transport Equations
Authors: Wang Xia , Sun Xiaodong
Published: July 2010

Two-fluid model with an empirical flow regime concept is widely used for two-phase flow analyses but suffers from its static and often non-hyperbolic nature. Recently, an interfacial area transport equation (IATE) has been proposed within the framework of the two-fluid model to dynamically describe the interfacial structure evolution and model the interfacial area concentration with the ultimate goal of modeling flow regime transition dynamically. Studies showed that the two-fluid model with the IATE (termed “two-fluid-IATE model” hereafter) could provide a more accurate prediction of the phase distributions and therefore improve the predictive capability of the two-fluid model. The inclusion of the IATE in the two-fluid model, however, brings about a subject of concern, namely, the well-posedness of the model. The objective of the present study is to investigate the issue of the hyperbolicity of a one-dimensional two-fluid-IATE model by employing momentum flux parameters, which take into account the coupling of the void fraction (volumetric fraction of the dispersed phase) and radial velocity distributions over the cross section of a flow passage. A characteristic analysis of the partial differential equations of the one-dimensional two-fluid model and two-group IATEs for an adiabatic flow was performed to identify a necessary condition for the system to achieve hyperbolicty. A case study was performed for an adiabatic liquid-liquid slug flow and the analysis showed that the hyperbolicty of the two-fluid-IATE model was guaranteed if appropriate correlations of the momentum flux parameters were applied in the two-fluid-IATE model.
An Improved Bounded Gradient Maximization Method for Interface-Capturing VOF Simulations
Authors: Witbeck Brandon , Walters D. Keith
Published: July 2010

A new high-resolution spatial discretization scheme is presented for the volume-of-fluid (VOF) method. This scheme is an adaptation of the previously published bounded gradient maximization (BGM) scheme [1]. This scheme resolves the phase interface without any explicit geometrical reconstruction of the interface. A net upwind bias in each cell ensures the stability of the scheme, and face limiting satisfies the boundedness criteria at the cell faces to prevent variable overshoot. In contrast to most existing methods, no method using “switching” between upwind-biased and downwind-biased discretization is employed to gain method stability. This paper presents the initial development and implementation of a time-dependent version of the method. Test cases are performed for a number of 2-D and 3-D two-phase flows on both structured and unstructured meshes. Results indicate that the method performs well in maintaining the resolution of the phase interface.
A POD Study of an Impinging Jet Flowfield
Authors: Hammad Khaled J. , Milanovic Ivana M.
Published: July 2010

Snapshot Proper Orthogonal Decomposition (POD) has been applied to reveal the dominant flow structures of an impinging jet flow field. PIV datasets of 200 snapshots were used for the POD analysis. The planar PIV measurements covered the free jet, stagnation and wall jet regions. The jet issued from a long pipe, 112 diameter, D, which ensured fully developed turbulent flow conditions at the outlet. The Reynolds number based on jet mean exit velocity was 16,000 and the pipe-to-plate separation, H, varied between 1D and 8D. The five most energetic modes were identified and found to contain 19–32% of the total turbulent energy. The energetic low modes were most pronounced for H/D = 8. The spatial topology was investigated by using velocity and vorticity fields of the mean flow and first five POD modes. For H/D = 8, the dominant flow structures were vortex tubes along the periphery of the jet. However, for H/D = 1, vortices along the impingement wall, outside of the stagnation region, were most prominent. The formation of vortices and their interaction with the impingement wall enhances local momentum transfer rates and could explain the secondary Nusselt number peak observed only at low separation distances.
Intelligent Control of Compact Multiphase Separation System (CMSS©)—Part I: Modeling and Simulation
Authors: Sampath V. , Mohan R. , Wang S. , Gomez L. , Shoham O. , Marrelli J.
Published: July 2010

Performance of compact separators depends on implementation of stable and robust control strategies that are suited for specific applications. In this investigation, an intelligent control system has been developed for Compact Multiphase Separation System (CMSS©) which consists of integrated configurations of three compact separators, namely, Gas-Liquid Cylindrical Cyclone (GLCC©), Liquid-Liquid Cylindrical Cyclone (LLCC©) and Liquid-Liquid Hydrocyclone (LLHC). This is a two-part paper, the first part (current paper) deals with the Modeling and Simulation of the CMSS© and the second part deals with Experimental Investigation. The specific objective of this CMSS© configuration is to knock out free water from the upstream fluids. In mature oil fields, water handling poses a huge problem. Thus water knock out at the earliest stage helps in significant cost savings. A novel fuzzy logic control system has been designed and tested for change in set-point of differential pressure ratio in LLHC. Dynamic models have been developed for each of the above mentioned control systems for design of stable PID parameters. A dynamic simulation platform (DSP) has been developed based on these models in Matlab/Simulink™ for predicting the transient performance of the integrated system. Steady state mechanistic models of individual devices are integrated to the Matlab/Simulink™ platform using look up tables to predict the overall response of the CMSS© for different scenarios.
Prediction Meter Factor of Turbine Meter Considering the Effects of Cavitation
Authors: Chen Gang , Cao Guangjun , Zhang Weihua , Fu Suhong , Liu Shuhong , Wu Yulin , Liu Deming
Published: July 2010

Turbine meters are wildly used in many fields for flow measurement with high accuracy and good repeatability, but the curve between meter factor and flow rates is affected by cavitation flow inside the meter. Cavitation is the main physical phenomenon which will have great effects on meter factor of turbine meters, especially at large flow rate. The meter factor will change at different cavitation number and will increase when the cavitation number decreases. In order to study its effects on meter factor, transient unsteady numerical simulation is carried out with RNG turbulence model and UDFs (User Defined Functions) based on torque balance equation in FLUENT software. The condensation/evaporation Cavitation Model is included at the simulation process. The results showed that the meter factor increased with the decrease of the cavitation number, and the meter factor is larger than at non-cavitation condition. Also the dynamic characteristics of the turbine flow meter impeller are obtained for the prediction of its meter factor and pressure distributions are obtained by the unsteady numerical simulation. The bearing friction drag is included in the torque balance equation, which is deduced from the theory of bearing.
Experimental Study of Taylor-Couette Flow With Constant Radial Temperature Gradient
Authors: Liu Dong , Choi Seok-Hwan , Lee Sang-Hyuk , Lee Jung-Ho , Kim Hyoung-Bum
Published: July 2010

The flow between two concentric cylinders with the inner one rotating and with an imposed radial temperature gradient is studied using digital particle image velocimetry (DPIV) method. Four models of the outer cylinder without and with different numbers of slits (6, 9 and 18) are considered, and the radius ratio and aspect ratio of each models were 0.825 and 48, respectively. The flow regime in the Taylor-Couette flow was studied by increasing the Reynolds number. The results showed that smaller number of slits has no obvious effect on the transition process, which only change the shape of the vortex, and the transition to turbulent Taylor vortex is accelerated as the number of slit increases in both isothermal and non-isothermal conditions. It is also shown that the presence of temperature gradient increased the flow instability obviously as the Froude number larger than 0.0045.
Using Toys Effectively in Fluid Mechanics Education
Authors: Shakerin Said , Saviz Camilla
Published: July 2010

Many inexpensive and readily available toys can offer benefits in support of technical education in addition to their primary function as tools for fun and entertainment. These toys can help facilitate learning at all levels from K-12 to university. In this paper, a short review of the use of toys in physics and engineering education is provided, followed by an introduction to several categories of toys that use principles of fluid mechanics. Several examples of beautiful and fun toys that demonstrate properties of density and viscosity and their effects on fluid behavior and motion are described. Features of each toy are explained and the relevant engineering/scientific concepts demonstrated by the toy are discussed. Furthermore, suggestions are made as to how the toys could be used as part of a curriculum, and assignments based on these toys are suggested as challenges for students.
Practical Methods for Calculation of Supercavitation on Axisymmetric Bodies for High Speed Motion in Water
Authors: Serebryakov Vladimir V.
Published: July 2010

The system of the simple dependencies for practical calculations of axisymmeric supecavitation flows are presented based on modern theoretical and experimental research. Main attention is paid to asymptotic dependencies on the basis of Slender Body Theory and heuristic models. The calculations examples of steady and unsteady cavities for motion under gravity, acceleration, oscillation of pressure are given.
Electrokinetic Mixing in Microplates and its Applications to Kinase and ELISA-Assay Type Reactions
Authors: Mader Maud-Alix , Bottausci Frederic , Mezic Igor
Published: July 2010

While 384 well-plate format is still commonly used by the Biomolecular community, miniaturized formats (1536 and 3456 well-plates) are gaining in popularity, due to promise of higher throughput and lower reagent consumption. However, decrease in reagent volume in such miniaturized formats leads to issues of accuracy and sensitivity caused by incomplete mixing and the mechanical stirring methods satisfactory used for 384 well-plate formats, give poor mixing with lower volumes. Here we present results obtained in 1536-well and 3456-well plates equipped with electrodes where we induced fluid flow by the action of electromagnetic fields. Improvement in two types of reactions are obtained, related to ELISA-type assays and kinase-based assays. For example, in the kinase reaction, we show that, when using the electrode-enabled mixing technology, an 8 minutes protocol in 1536-well plate format is equivalent in accuracy to a 90 minutes protocol in standard 96-well plate format mixed using an orbital shaker. This mixing technology is scalable, due to modern developments in electrode manufacturing and can be used in super-high throughput screening formats, such as 10000-well or droplets.
Linear Instability Analysis of an Annular Liquid Sheet With Inner and Outer Gas Flow
Authors: Ommi Fathollah , Mahdavi Seid Askari , Hosseinalipour S. Mostafa , Movahednejad Ehsan
Published: July 2010

A linear instability analysis of an inviscid annular liquid sheet emanating from an atomizer subjected to inner and outer swirling air streams has been carried out. The dimensionless dispersion equation that governs the instability is derived. The dispersion equation solved by Numerical method to investigate the effects of the liquid-gas swirl orientation on the maximum growth rate and its corresponding unstable wave number that it produces the finest droplets. To understand the effect of air swirl orientation with respect to liquid swirl direction, four possible combinations with both swirling air streams with respect to the liquid swirl direction have been considered. Results show that at low liquid swirl Weber number a combination of co-inner air stream and counter-outer air stream has the largest most unstable wave number and shortest breakup length. The combination of inner and the outer air stream co-rotating with the liquid has the highest growth rate.
Influence of Longitudinal Fluctuation in Long Corridor Surge Tank on Hydraulic Transients
Authors: Zhang Jian , Lu Weihua , Yu Xiaodong , Zheng Yu
Published: July 2010

Since the length-width ratio of large long corridor surge tank is big, longitudinal flow appears obviously, which influences the safety of water diversion system. Based on the water conveyance system of hydropower station with long corridor surge tank, influence of longitudinal fluctuation on hydraulic transients is analyzed, which is contrasted with the results without consideration of longitudinal fluctuation, and corresponding model test is also carried out. It is shown that numerical simulation results, without consideration of longitudinal fluctuation, are more dangerous and those considering longitudinal fluctuation relatively conform to reality. Further more, influence factors on longitudinal fluctuation are studied, the bigger the length-width ratio of surge tank and the lower the operation water level, the severer the longitudinal fluctuation. In order to decrease longitudinal fluctuation, surge tank with small length-width ratio should be designed, and station should be operated on high water level as much as possible.
Transient Filling of Sacrificially Etched Nanochannels by Capillarity
Authors: Hamblin M. , Murray D. , Maynes D. , Hawkins A.
Published: July 2010

In this paper we present results of an experimental investigation that explores the transient filling of nanochannels due to capillarity. The nanochannels explored here were fabricated using sacrificial metal cores and were designed to mimic the parallel-plate channel geometry. Channels of heights ranging from 41 to 91 nm were utilized in the experimental program and both aluminum and chromium were utilized as the sacrificial metal from which the channels were formed. The filling dynamics of channels that were closed on one end were also explored. The data reveal that the channels fabricated with aluminum as the sacrificial core yield marked departure from expected behavior, with the apparent frictional constant significantly elevated above classical values. Potential reasons for the departure are discussed. Channels fabricated with chromium cores result in behavior that yields much less deviation from anticipated Stokes flow behavior. However, for these channels the meniscus speed is observed to vary markedly across the channels transverse width. Channels that are closed on one end yield behavior that is significantly different from the open-ended channel results. Here the meniscus becomes destabilized as it approaches the capped channel end and the trapped air becomes entrained by the liquid and dispersed without evidence of bubble existence.
High-Temperature Self-Healing Metallic Coating: Concepts and First Results
Authors: Kutelia E. R. , Bakhtiyarov S. I. , Tsurtsumia O. O. , Bakhtiyarov A. S. , Eristavi B. P.
Published: July 2010

This work presents the possibility to realize the self healing mechanisms for heterogeneous architectured metal/ceramic high temperature sandwich thermal barrier coating systems on the surfaces refractory metals by analogy of wound healing in the skin.
Examination of the Bi-Directional Velocity Probe Used in Flames
Authors: Hogan Brian C. , Bocanegra Humberto , Alarcon Ramiro Chavez , Yilmaz Nadir , Donaldson A. Burl , Gill Walt
Published: July 2010

The bidirectional probe has been used in combustion environments to measure localized flame velocities. The device measures the pressure difference between a closed forward-facing cavity, and a closed rearward-facing cavity. Each device must be experimentally calibrated to determine the “amplification factor,” which is unity if the measured differential pressures match Bernoulli’s equation. It is hypothesized that the probe design disrupts the flow, creating turbulence and irreversibilities, resulting in measured pressure differences. This study uses computational fluid dynamics, particle image velocimetry, and flow visualization techniques to examine the flow field around the probe, as well as an experimental study exploring the impact of minor changes in probe design on differential pressure measurements for velocity calculations.
Modeling Cavitating Flow in High Temperature Water
Authors: Ji Bin , Luo Xianwu , Wu Yulin , Zhang Yao , Liu Shuhong , Xu Hongyuan , Nishi Michihiro
Published: July 2010

Thermal effects substantially impact the cavitation dynamics of high temperature water. This paper strives towards developing an effective computational strategy to simulate thermal cavitation. A transport equation based on mass transfer has been proposed by considering thermodynamic effect. The cavitating flow over a foil at the temperature of 293K and 373K has been calculated to evaluate the feasibility of the proposed model. The result comparison of the proposed model as well as the full cavitation model with the experiment data indicates that the proposed model is suitable for modeling cavitating flow in high temperature water.
Natural Convection in Inclined Two Dimensional Rectangular Cavities
Authors: Khezzar Lyes , Siginer Dennis
Published: July 2010

Steady two-dimensional natural convection in fluid filled cavities has been investigated numerically. The conservation equations of mass, momentum and energy governing the motion of a Newtonian Boussinesq fluid have been numerically solved using the finite volume technique. The computations were performed for three cavity height based Rayleigh numbers 104, 105 and 106. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for several aspect ratios. For the case of the square cavity the calculated values are in excellent agreement with previously published benchmark results. The effects of the inclination of the cavity to the horizontal, with the angle varying from 0 to 180° and the initial start up conditions were investigated in turn for each aspect ratio. The inclination and the “initial” assumed conditions have a significant effect on the flow patterns, temperature distributions and the heat transfer rates. In particular it is found that the average Nusselt number exhibits discontinuities for rectangular cavities and that the occurrence of the discontinuity with angle of inclination is strongly influenced by the assumed start up field in the steady calculations in much the same way as the hysteresis effect that was identified by other workers.
Permeability Measurement of Orthotropic Fibers Under an Acoustic Force Field
Authors: Sharma Sanjay , Siginer Dennis
Published: July 2010

Using the validated acoustic method of determining physical properties of porous materials, acoustical properties of the orthotropic medium is used to predict longitudinal and transverse permeability. Measurement of samples in the impedance tube is conducted using ASTM E 1050 for a frequency range of 50 Hz to 6.4 KHz. The acoustical method is shown to compute longitudinal and transverse permeability for various porosity levels. The method describes permeability prediction for carbon, glass and hybrid lay ups. Longitudinal permeability calculated from the absorption coefficient of sized and unsized fibers is found to be the same in contrast to the flow methods.
Means for Improving Pump Efficiency
Authors: Karvinen R. , Koivikko M. , Virtanen S.
Published: July 2010

The design of pumps has been mainly based on results obtained from experiments. Because there has been no detailed information concerning very complicated flow fields inside pumps, only by accident have some new ideas been found. At present, numerical modeling of the flow offers an opportunity to understand basic phenomena which make it possible to find new connections between hydraulic and geometric parameters. With the help of numerical modeling in a long-term project, new design instructions have been successfully developed. It seems that some existing ideas on how different factors affect pump performance should be re-evaluated. An important finding is that the effect of specific speed on efficiency is quite small. Also the efficiencies of existing pumps can be clearly improved with proper design.
Simulation study of the in-plane-type triode carbon nanotube emitter
Authors: Furuta Hiroshi , Ishii Kazuhisa , Okada Kouji , Furuta Mamoru , Hirao Takashi
Published: July 2010

The field emissions of the in-plane-type triode carbon nanotube emitters for the field emission backlight lamps were investigated in simulation by the finite element method in order to indicate ideal high efficient field emission fluorescent lamps (FELs). The anode current are commonly controlled by the gate bias voltages for the FEL triode emitters. The simulation of the in-plane-type triode emitter indicated that the ON/OFF ratio of the anode current density for the gate bias voltage of 0 V/−100 V was increased by decreasing the cathode to gate spacing, by decreasing the cathode and gate electrode width, and by using the lower ratio of the cathode to the gate electrode width.
Fabrication of submicron-sized features in InP/InGaAsP/AlGaInAs quantum well heterostructures by optimized inductively coupled plasma etching with Cl2/Ar/N2 chemistry
Authors: Dylewicz R. , De La Rue R. M. , Wasielewski R. , Mazur P. , Mezősi G. , Bryce A. C.
Published: July 2010

Inductively coupled plasma dry etching for the fabrication of fine-pitch patterns in a wide range of InP-based materials has been developed. The effect of plasma chemistry (the N2 content in the total Cl2/Ar/N2 gas mixture) on the degree of undercut in the sidewall profile and surface morphology has been studied. Optimization of the etch process conditions produces strong passivation effects on the sidewalls, together with a highly anisotropic process, while still maintaining a good etch rate (560–730 nm/min). Single-step etching using hydrogen silsesquioxane as a resist/hard-mask resulted in high aspect ratio features being obtained (up to 30:1). Low plasma excitation power (inductively coupled plasma machine operating power of 400 W) and moderate ion energy (rf power of 120 W) were utilized to minimize etch-induced damage and provide low scattering losses. Low-loss (<0.3 dB/mm) optical ridge waveguides and high reflectivity and high-wavelength selectivity (Δλ=2 nm) results with 236 nm period sidewall gratings were demonstrated experimentally.
Precision of dosimetry‐related measurements obtained on current multidetector computed tomography scanners
Authors: Mathieu Kelsey B. , McNitt‐Gray Michael F. , Zhang Di , Kim Hyun J. , Cody Dianna D.
Published: July 2010

Purpose:

Computed tomography (CT) intrascanner and interscanner variability has not been well characterized. Thus, the purpose of this study was to examine the within‐run, between‐run, and between‐scanner precision of physical dosimetry‐related measurements collected over the course of 1 yr on three different makes and models of multidetector row CT (MDCT) scanners.

Methods:

Physical measurements were collected using nine CT scanners (three scanners each of GE VCT, GE LightSpeed 16, and Siemens Sensation 64 CT). Measurements were made using various combinations of technical factors, including kVp, type of bowtie filter, and x‐ray beam collimation, for several dosimetry‐related quantities, including (a) free‐in‐air CT dose index; (b) calculated half‐value layers and quarter‐value layers; and (c) weighted CT dose index calculated from exposure measurements collected in both a 16 and 32 cm diameter CTDI phantom. Data collection was repeated at several different time intervals, ranging from seconds (for values) to weekly for 3 weeks and then quarterly or triannually for 1 yr. Precision of the data was quantified by the percent coefficient of variation (%CV).

Results:

The maximum relative precision error (maximum %CV value) across all dosimetry metrics, time periods, and scanners included in this study was 4.33%. The median observed %CV values for ranged from 0.05% to 0.19% over several seconds, 0.12%–0.52% over 1 week, and 0.58%–2.31% over 3–4 months. For for a 16 and 32 cm CTDI phantom, respectively, the range of median %CVs was 0.38%–1.14% and 0.62%–1.23% in data gathered weekly for 3 weeks and 1.32%–2.79% and 0.84%–2.47% in data gathered quarterly or triannually for 1 yr.

Conclusions:

From a dosimetry perspective, the MDCT scanners tested in this study demonstrated a high degree of within‐run, between‐run, and between‐scanner precision (with relative precision errors typically well under 5%).
Design and optimization of large area thin‐film CdTe detector for radiation therapy imaging applications
Authors: Parsai E. Ishmael , Shvydka Diana , Kang Jun
Published: July 2010

Purpose:

The authors investigate performance of thin‐film cadmium telluride (CdTe) in detecting high‐energy (6 MV) x rays. The utilization of this material has become technologically feasible only in recent years due to significant development in large area photovoltaic applications.

Methods:

The CdTe film is combined with a metal plate, facilitating conversion of incoming photons into secondary electrons. The system modeling is based on the Monte Carlo simulations performed to determine the optimized CdTe layer thickness in combination with various converter materials.

Results:

The authors establish a range of optimal parameters producing the highest DQE due to energy absorption, as well as signal and noise spatial spreading. The authors also analyze the influence of the patient scatter on image formation for a set of detector configurations. The results of absorbed energy simulation are used in device operation modeling to predict the detector output signal. Finally, the authors verify modeling results experimentally for the lowest considered device thickness.

Conclusions:

The proposed CdTe‐based large area thin‐film detector has a potential of becoming an efficient low‐cost electronic portal imaging device for radiation therapy applications.
A method for optimizing LINAC treatment geometry for volumetric modulated arc therapy of multiple brain metastases
Authors: Kang Jun , Ford Eric C. , Smith Koren , Wong John , McNutt Todd R.
Published: July 2010

Purpose:

Volumetric modulated arc therapy (VMAT) is a rotational delivery technique in which MLC shapes, dose rate, and gantry rotation speed are optimized to produce conformal dose distributions. The aim of this work is to develop a beam projection method for deriving the optimal table and collimator angles for multilesion treatment planning.

Methods:

The method consists of four steps. The first step is to define the vector of beam‐eye‐view (BEV)‐‐axis in the treatment planning CT coordinates. The second step is to project each target onto the BEV‐‐axis vector. In the third step, the best table and collimator angle are found with a brute‐force optimization technique that minimizes MLC leaf sharing between lesions. The fourth step is to generate an optimized VMAT plan with appropriate table/collimator angles and evaluate the plan quality.

Results:

The authors tested the method on three example cases with targets of various locations in the brain and sizes ranging from 1.18 to. Applying the optimized geometric parameter to generate VMAT plan, a reduction of the 12 Gy volume was more than 6.1% for all cases; the plan homogeneity was improved from to vs a VMAT plan with the manufacturer recommended table and collimator angles.

Conclusions:

The authors conclude that the use of the projection method minimizes the sharing of MLC leaves between lesions and improves the plan quality for multilesion VMAT delivery.
An improved Bayesian tensor regularization and sampling algorithm to track neuronal fiber pathways in the language circuit
Authors: Mishra Arabinda , Anderson Adam W. , Wu Xi , Gore John C. , Ding Zhaohua
Published: July 2010

Purpose:

The purpose of this work is to design a neuronal fiber tracking algorithm, which will be more suitable for reconstruction of fibers associated with functionally important regions in the human brain. The functional activations in the brain normally occur in the gray matter regions. Hence the fibers bordering these regions are weakly myelinated, resulting in poor performance of conventional tractography methods to trace the fiber links between them. A lower fractional anisotropy in this region makes it even difficult to track the fibers in the presence of noise. In this work, the authors focused on a stochastic approach to reconstruct these fiber pathways based on a Bayesian regularization framework.

Methods:

To estimate the true fiber direction (propagation vector), thea priori and conditional probability density functions are calculated in advance and are modeled as multivariate normal. The variance of the estimated tensor element vector is associated with the uncertainty due to noise and partial volume averaging (PVA). An adaptive and multiple sampling of the estimated tensor element vector, which is a function of the pre‐estimated variance, overcomes the effect of noise and PVA in this work.

Results:

The algorithm has been rigorously tested using a variety of synthetic data sets. The quantitative comparison of the results to standard algorithms motivated the authors to implement it forin vivo DTI data analysis. The algorithm has been implemented to delineate fibers in two major language pathways (Broca's to SMA and Broca's to Wernicke's) across 12 healthy subjects. Though the mean of standard deviation was marginally bigger than conventional (Euler's) approach [P. J. Basser et al., “In vivo fiber tractography using DT‐MRI data,” Magn. Reson. Med. 44(4), 625–632 (2000)], the number of extracted fibers in this approach was significantly higher. The authors also compared the performance of the proposed method to Lu's method [Y. Lu et al., “Improved fiber tractography with Bayesian tensor regularization,” Neuroimage 31(3), 1061–1074 (2006)] and Friman's stochastic approach [O. Friman et al., “A Bayesian approach for stochastic white matter tractography,” IEEE Trans. Med. Imaging 25(8), 965–978 (2006)]. Overall performance of the approach is found to be superior to above two methods, particularly when the signal‐to‐noise ratio was low.

Conclusions:

The authors observed that an adaptive sampling of the tensor element vectors, estimated as a function of the variance in a Bayesian framework, can effectively delineate neuronal fibers to analyze the structure‐function relationship in human brain. The simulated andin vivo results are in good agreement with the theoretical aspects of the algorithm.
Dosimetric effects of an air cavity for the SAVI™ partial breast irradiation applicator
Authors: Richardson Susan L. , Pino Ramiro
Published: July 2010

Purpose:

To investigate the dosimetric effect of the air inside the SAVI™ partial breast irradiation device.

Methods:

The authors have investigated how the air inside the SAVI™ partial breast irradiation device changes the delivered dose from the homogeneously calculated dose. Measurements were made with the device filled with air and water to allow comparison to a homogenous dose calculation done by the treatment planning system. Measurements were made with an ion chamber, TLDs, and film. Monte Carlo (MC) simulations of the experiment were done using the EGSnrc suite. The MC model was validated by comparing the water‐filled calculations to those from a commercial treatment planning system.

Results:

The magnitude of the dosimetric effect depends on the size of the cavity, the arrangement of sources, and the relative dwell times. For a simple case using only the central catheter of the largest device, MC results indicate that the dose at the prescription point 1 cm away from the air‐water boundary is about 9% higher than the homogeneous calculation. Independent measurements in a water phantom with a similar air cavity gave comparable results. MC simulation of a realistic multidwell position plan showed discrepancies of about 5% on average at the prescription point for the largest device.

Conclusions:

The dosimetric effect of the air cavity is in the range of 3%–9%. Unless a heterogeneous dose calculation algorithm is used, users should be aware of the possibility of small treatment planning dose errors for this device and make modifications to the treatment delivery, if necessary.
Advantage in image fidelity and additional computing time of JPEG2000 3D in comparison to JPEG2000 in compressing abdomen CT image datasets of different section thicknesses
Authors: Lee Hyunna , Lee Kyoung Ho , Kim Kil Joong , Park Seongjin , Seo Jinwook , Shin Yeong‐Gil , Kim Bohyoung
Published: July 2010

Purpose:

This study aimed to assess the advantage of the Joint Photographic Experts Group 2000 (JPEG2000) 3D (part 2) over JPEG2000 in compressing abdomen computed tomography (CT) image data sets of different section thicknesses (STs).

Methods:

Twenty CT scans were reconstructed with six STs (0.67, 1, 2, 3, 4, and 5 mm) and were then compressed to seven compression ratios (CRs) (reversible, 6:1, 8:1, 10:1, 12:1, 14:1, and 16:1) using JPEG2000 and JPEG2000 3D algorithms. Computing (encoding and decoding) times were measured. The image fidelity of the compressed images was quantitatively measured with two computerized image fidelity metrics, peak signal‐to‐noise ratio (PSNR) and multiscale structural similarity (MS‐SSIM). For 120 selected case‐relevant images , five radiologists independently compared original and compressed images and assessed the fidelity of the compressed images on a four‐grade scale. Wilcoxon signed‐rank tests and Friedman tests with post hoc Dunn tests were used for the comparisons between the two compressions and among the six STs, respectively.

Results:

For each combination of the ST and irreversible CR, JPEG2000 3D showed higher image fidelity than JPEG2000 in terms of PSNR, MS‐SSIM , and five radiologists’ grading (‐values ranged from to 0.003). At each CR, the advantage of JPEG2000 3D in image fidelity, measured as the differences in the two computerized image fidelity metrics (PSNR and MS‐SSIM), significantly increased as the ST increased from 0.67 to 2 mm, and then slowly decreased as the ST increased from 2 to 5 mm. Similar trends were observed in visual analyses of 120 selected images by five radiologists. At each CR, the 3D‐to‐2D encoding‐time ratio significantly decreased as the ST increased from 0.67 to 2 mm, and then slowly increased as the ST increased from 2 to 5 mm. The 3D‐to‐2D decoding‐time ratio at each CR did not show a notable biphasic trend across the ST.

Conclusions:

In compressing abdomen CT image data sets of different STs, the advantage of JPEG2000 3D over JPEG2000 increases as the ST increases from 0.67 to 2 mm, and then slowly decreases as the ST increases from 2 to 5 mm. The practical advantage of JPEG2000 3D is limited for a submillimeter ST due to its greater computing time with only a marginal improvement in image fidelity.
Measurement of absorbed dose, quality factor, and dose equivalent in water phantom outside of the irradiation field in passive carbon‐ion and proton radiotherapies
Authors: Yonai Shunsuke , Kase Yuki , Matsufuji Naruhiro , Kanai Tatsuaki , Nishio Teiji , Namba Masao , Yamashita Wataru
Published: July 2010

Purpose:

Successful results in carbon‐ion and proton radiotherapies can extend patients’ lives and thus present a treatment option for younger patients; however, the undesired exposure to normal tissues outside the treatment volume is a concern. Organ‐specific information on the absorbed dose and the biological effectiveness in the patient is essential for assessing the risk, but experimental dose assessment has seldom been done. In this study, absorbed doses, quality factors, and dose equivalents in water phantom outside of the irradiation field were determined based on lineal energy distributions measured with a commercial tissue equivalent proportional counter (TEPC) at passive carbon‐ion and proton radiotherapy facilities.

Methods:

Measurements at eight positions in the water phantom were carried out at the Heavy‐Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences for 400 and 290 MeV/u carbon beams and at the National Cancer Center Hospital East for a 235 MeV proton beam.

Results:

The dose equivalent per treatment absorbed dose at the center of the range‐modulated region decreased as the position became farther from the beam axis and farther from the phantom surface. The values of ranged from 6.7 to 0.16 mSv/Gy for the 400 MeV/u carbon beam, from 1.3 to 0.055 mSv/Gy for the 290 MeV/u carbon beam, and from 4.7 to 0.24 mSv/Gy for the 235 MeV proton beam. The values of the dose‐averaged quality factor ranged from 2.4 to 4.6 for the 400 MeV/u beam, from 2.8 to 5.3 for the 290 MeV/u beam, and from 5.1 to 8.2 for the proton beam. The authors also observed differences in the distributions of and between the carbon and proton beams.

Conclusions:

The authors experimentally obtained absorbed doses, dose‐averaged quality factors, and dose equivalents in water phantom outside of the irradiation field in passive carbon‐ion and proton radiotherapies with TEPC. These data are very useful for estimating the risk of secondary cancer after receiving passive radiotherapies and for verifying Monte Carlo calculations.
Two‐stage multishape segmentation of brain structures using image intensity, tissue type, and location informationa)
Authors: Akhondi‐Asl Alireza , Soltanian‐Zadeh Hamid
Published: July 2010

Purpose:

The authors propose a fast, robust, nonparametric, entropy‐based, coupled, multishape approach to segment subcortical brain structures from magnetic resonance images (MRIs).

Methods:

The proposed method uses three types of information: Image intensity, tissue types, and locations of structures. The image intensity information is captured by estimating the probability density function (pdf) of the image intensities in each structure. The tissue type information is captured by applying an unsupervised tissue segmentation method to the image and estimating a probability mass function (pmf) for the tissue type of each structure. The location information is captured by estimating pdf of the location of each structure from the training datasets. The resulting pmf's and pdf's are used to define an entropy function whose minimum corresponds to a desirable segmentation of the structures. The authors propose a three‐step optimization strategy for the segmentation method. In the first step, a powerful automatic initialization method is developed based on tissue type and location information of the structures. In the second step, a quasi‐Newton method is used to optimize the parameters of the energy function. To speed up the iterations, derivatives of the energy function with respect to its parameters are analytically derived and used in the optimization process. In the last step, the limitations related to the prior shape model are removed and a level‐set method is applied for the fine tuning of the segmentation results.

Results:

The proposed method is applied to two different datasets and the results are compared to those of previous methods in literature. Experimental results are presented for lateral ventricles, caudate, thalamus, putamen, pallidum, hippocampus, and amygdala.

Conclusions:

The results illustrate superior performance of the proposed segmentation method compared to other methods in literature. The execution time of the algorithm is a few minutes, suitable for a variety of applications.
Evaluating the extent of cell death in 3D high frequency ultrasound by registration with whole‐mount tumor histopathologya)
Authors: Vlad Roxana M. , Kolios Michael C. , Moseley Joanne L. , Czarnota Gregory J. , Brock Kristy K.
Published: July 2010

Purpose:High frequency ultrasound imaging, 10–30 MHz, has the capability to assess tumor response to radiotherapy in mouse tumors as early as 24 h after treatment administration. The advantage of this technique is that the image contrast is generated by changes in the physical properties of dying cells. Therefore, a subject can be imaged before and multiple times during the treatment without the requirement of injecting specialized contrast agents. This study is motivated by a need to provide metrics of comparison between the volume and localization of cell death, assessed from histology, with the volume and localization of cell death surrogate, assessed as regions with increased echogeneity from ultrasound images.

Methods:The mice were exposed to radiation doses of 2, 4, and 8 Gy. Ultrasound images were collected from each tumor before and 24 h after exposure to radiation using a broadband 25 MHz center frequency transducer. After radiotherapy, tumors exhibited hyperechoic regions in ultrasound images that corresponded to areas of cell death in histology. The ultrasound and histological images were rigidly registered. The tumors and regions of cell death were manually outlined on histological images. Similarly, the tumors and hyperechoic regions were outlined on the ultrasound images. Each set of contours was converted to a volumetric mesh in order to compare the volumes and the localization of cell death in histological and ultrasound images.

Results:A shrinkage factor ofwas calculated from the difference in the tumor volumes evaluated from histological and ultrasound images. This was used to correct the tumor and cell death volumes assessed from histology. After this correction, the average absolute difference between the volume of cell death assessed from ultrasound and histological images wasand the volume overlap was.

Conclusions:The method provided metrics of comparison between the volume of cell death assessed from histology and that assessed from ultrasound images. It was applied here to evaluate the capability of ultrasound imaging to assess early tumor response to radiotherapy in mouse tumors. Similarly, it can be applied in the future to evaluate the capability of ultrasound imaging to assess early tumor response to other modalities of cancer treatment. The study contributes to an understanding of the capabilities and limitation of ultrasound imaging at noninvasively detecting cell death. This provides a foundation for future developments regarding the use of ultrasound in preclinical and clinical applications to adapt treatments based on tumor response to cancer therapy.