bluuebunny/crossref_metadata_2025 huggingface dataset:
Comprehensive Comparisons Between Evaporation and Pool Boiling on Thin Micro Porous Coated Surfaces
Authors: Li Chen , Peterson G. P.
Published: April 2008

The evaporation and pool boiling on micro porous coated surfaces have been shown to provide among the highest heat transfer rates achievable from any type of surfaces. The heat transfer modes in these surfaces, present a number of interesting similarities and also, some fundamental differences, which are the result of the liquid supply methods to the heated surface. For the evaporation from porous coated surfaces, the liquid return to the heated surface is assisted by the capillary pressure at the liquid-vapor interface; while for pool boiling, gravity is the principal driving force that rewets the surface. In order to better understand the physical phenomena that governs the flow behavior of both the liquid and vapor phases, and the heat transfer process inside the porous media, comprehensive comparisons between these return mechanisms and their respective characteristics, and the performance and the critical heat flux (CHF) for each have been made, based on similar physical situations. These systematic comparisons illustrate that at a lower heat flux, the evaporation and pool boiling curves are almost identical due to the similar heat transfer modes, i.e., convection and nucleate boiling. While with further increases in heat flux, the heat transfer performance of the evaporation on micro porous media is generally superior to pool boiling on an identical surface. This shift is believed to be due to the fact that for evaporation on micro porous media, the heat transfer mode is dominated by the film evaporation, while in pool boiling, it is principally the result of fully developed nucleate boiling. It was also observed that the impact of the effective thermal conductivity of the porous coating on pool boiling performance is larger than for evaporation heat transfer on the identical micro porous coated surfaces. In general, the experimental data indicated that the CHF for evaporation heat transfer is much higher than for pool boiling on the same surfaces. The mechanism of CHF for evaporation on porous coated surfaces is believed to be the capillary limit; while for pool boiling the limit is the result of the hydrodynamic instabilities. This difference in mechanisms is clearly demonstrated by the experimental observations, where initially, the dry out process of the porous coated surfaces during evaporation is gradual, while for pool boiling; the entire surface reaches dry out in a very short time. In addition, the sensitivity of the CHF to the thickness of the porous coatings at a constant volumetric porosity and pore size, as well as the various optimal volumetric porosity of the CHF at a given thickness, are clearly the results of the differences induced by the various CHF mechanisms.
Unsteady Flames in Microcombustion
Authors: Prakash Shaurya , Armijo Adrian D. , Masel Richard I. , Shannon Mark A.
Published: April 2008

Unsteady flames within alumina combustors with one submillimeter dimension are evaluated and discussed in this extended abstract. The flame dynamics within the combustors are characterized by non-stabilized and transient flame structures accompanied by acoustic emissions. These flames are studied experimentally and are discussed here. The experimental observations are carried out via two imaging techniques, high-speed and still-frame imaging. The acoustic emission and external wall temperature measurements are also recorded.
Oscillatory Transient Flow Experiments and Analysis in Circular Microchannels
Authors: Javadi A. , Javadi K. , Kra¨gel J. , Miller R. , Kovalchuk V. I. , Ferri J. K. , Bastani D. , Taeibi-Rahni M.
Published: April 2008

In this research purely oscillation fluid flow in two microtubes 150 and 250 μm (3.5 mm length) is studied using computational fluid dynamic (CFD) approach and utilizing a new experimental setup developed for dynamic interfacial tension measurement (capillary pressure technique) in the frequency range between 0.2 and 80 Hz. The experiments are done with pure water at a mean temperature of about 25 °C. The results of oscillatory conditions for microtubes of 0.5 mm in diameter have been compared with experimental results for several frequencies. The computational approach was validated by comparison with experimental data of the continuous constant flow through microtubes and also with experimental results of an oscillatory flow through the same tubes at up to 25 Hz. For evaluation of the effects of hydrodynamic relaxation time th = R2 / ν on the amplitude of the pressure gradient, CFD simulation of the oscillatory flow through microtubes of 0.3 and 0.5 mm (diameter) with th =0.0225 s and 0.0625 s have been provided to compare with own corresponding maximum continuous flow (CMCF) experimental data for each frequency which occurs at maximum speed of sinusoidal motion of the piezo. The comparison demonstrates that for a microtube of 0.5 mm and th=0.0625 s for frequencies F〈(1/th) ≤ 16 Hz the computational results for amplitude of pressure gradient is in relatively good agreement with own CMCF experimental data, while for microtubes of 0.3 mm in diameter this agreement is observed for frequencies lower than F〈(1/th) ≤ 44 Hz. CFD simulations of the velocity profile of oscillatory flow through these microtube support these findings and show a parabolic velocity profile (like Poiseuille flow) for frequencies ≤ 10 Hz for microtube of 0.5 mm diameter while this situation is observed below 40 Hz for microtubes of 0.3 mm diameter. Although for a smaller microtube size a relatively developed flow occurs in a higher frequency range, turbulence effects can appear sooner due to the higher flow rates and consequently higher Reynolds numbers. The combination of these two opposite effects would have to be considered when comparing the flow field through microtubes of different size.
A Design Model for Bending and Extensional Ionic Polymer Transducers
Authors: Akle Barbar J. , Leo Donald J.
Published: April 2008

Ionomeric polymer transducers have received considerable attention in the past ten years due to their ability to generate large bending strain (~10%) and moderate stress at low applied voltages (~2V). Bending transducers made of an ionomeric polymer membrane sandwiched between two flexible electrodes deform through the expansion of one electrode and contraction of the opposite electrode due to cation displacement across the transducer. Recently the authors reported extensional actuation in ionic polymer transducers (Akle and Leo 2005). In this study we developed and experimentally supported a model that assumes the electrode as the active area in ionic polymer transducers. The electromechanical coupling is represented by a linear and quadratic terms of the charge accumulated at the electrode. The mechanism of charge accumulation in ionic polymer transducers is an electric double layer type process. This charge is correlated with the conductor-ionomer interfacial surface area. In this study we will model the accumulated charge as a function of electrode architecture. The linear and quadratic coefficients are calibrated experimentally for several types of ionic species, ionic liquid uptake levels, and electrode conductor species. A design model based on the previously developed models will predict the generated free strain and blocked force in bending and extensional ionic polymer transducers for the different design variables. The model is experimentally verified by building transducers using the Direct Assembly Process with variable electrode architectures. The thickness and conductor concentration in the electrode and membrane are varied.
Fundamental Investigation of Direct Contact Heat Exchange for Application in HVAC Systems: A Case Study
Authors: Hensley Joshua L. , Bryan James E.
Published: April 2008

An air conditioning system based on a direct contact heat and mass transfer process between water and air may offer benefits such as increased energy efficiency, temperature and humidity control, and improved indoor air quality. To investigate the feasibility of this type of technology, a numeric model is used to study the heat and mass transfer between a single droplet and moist air to gain fundamental insight into the heat and mass transfer process. Further, preliminary experiments are performed in a low speed temperature and humidity controlled wind tunnel to validate some of the models findings, e.g. the effect of droplet size on heat and mass transfer. A case study is presented to investigate how such a system would operate in a hot, dry climate as well as a hot and humid climate.
Preparation and Characteristics of Calcium Oxide Pellets for UT-3 Thermochemical Cycle
Authors: Lee Man Su , Goswami D. Yogi , Hettinger Ben , Vijayaraghavan Sanjay
Published: April 2008

UT-3 thermochemical cycle for hydrogen production involves four gas-solid reactions. In order to make the cycle feasible, the solid reactant must be chemically reactive and physically stable in cyclic operation. Calcium oxide pellets, with CaO dispersed in the CaTiO3 inert matrix, were prepared and stearic acid, graphite, and corn starch were added as pore forming agents during the process. Experimental studies to improve and evaluate the Ca-pellets through the investigation into thermal decomposition of additives, X-ray diffraction, pore size distribution, conversion and reaction rate were conducted. The pore size distributions of the pellets were found to be strongly influenced by the type of pore forming agents used, and the volume of pores greater than 5μm markedly promoted hydrolysis rate.
Integration of Modern Software Tools for Production Design
Authors: Shetty Devdas , Eppes Tom , Chao Lifeng , Campana Claudio
Published: April 2008

Engineers, irrespective of their disciplines, need effective tools to comprehensively design, model, synthesize and analyze the design a product. This is often closely followed by the need to fabricate a working prototype. Engineers need useful methodologies and tools that can be used in preparation for manufacturing. These tools need to effectively analyze assembly & disassembly since a good assembly design makes a product les expensive to service, repair and maintain. A suite of well-integrated tools assists designers to create, simulate and test in a comprehensive manner. Modern software tools can be used at each stage to create conceptual designs, simulate part geometries, analyze key parameters, and generate motion paths for efficient manufacturing. This paper presents a set of comprehensive procedures and tools that can easily be incorporated into product design and manufacturing from early design through analysis. They consider assembly and disassembly factors up to and including the creation of a working prototype. Due to environmental regulations, designers must think about the product life cycle, recycling and reuse aspects from the very beginning. There is a continuing need for more efficient and rapid design processes which can best be driven by better tools and techniques.
Ride Quality of High-Speed Trains Traveling Over the Corrugated Rails
Authors: Farahpour H. , Younesian D. , Esmailzadeh E.
Published: April 2008

Ride comfort of high-speed trains is studied using Sperling's comfort index. Dynamic model is developed in the frequency domain and the power spectral density (PSD) of the body acceleration is obtained for four classes of tracks. The obtained acceleration PSD is then filtered using Sperling's filter. The effects of the rail roughness and train speed on the comfort indicators are investigated. A parametric study is also carried out to evaluate the effects of the primary and secondary suspension systems on the comfort indicators.
Growth CO2 Consumption, and H2 Production of Anabaena Variabilis ATCC 29413-U Under Different Irradiances and CO2 Concentrations
Authors: Berberoglu Halil , Barra Natasha , Pilon Laurent , Jay Jenny
Published: April 2008

Hydrogen production by cultivation of cyanobacteria in photobioreactors offers a clean and renewable alternative to thermochemical or electrolytic hydrogen production technologies with the added advantage of CO2 mitigation. The objective of this study is to experimentally investigate the CO2 consumption, growth, and H2 production of the cyanobacteria Anabaena variabilis ATCC 29413-U under atmosphere containing argon and CO2. Parameters investigated are irradiance and initial CO2 mole fraction in the gas phase. The CO2 consumption half-time, defined as the time at which the CO2 concentration in the gas phase decreases to half of its initial value, appears to be an appropriate time scale for modeling cyanobacterial CO2 consumption, growth, and H2 production. The half-time depends on both the initial CO2 mole fraction and the irradiance. Also, two regimes of growth have been identified depending on irradiance. Below 5,000 lux, the irradiance and the initial CO2 mole fraction have a coupled effect on cyanobacterial growth. Above 5,000 lux, growth depends only on the initial CO2 mole fraction. Furthermore, the optimum initial CO2 mole fraction around 0.05 has been identified for maximum growth and CO2 consumption rates. The growth and CO2 consumption were not inhibited by irradiance up to about 16,000 lux. Finally, the proposed empirical models can be used in conjunction with mass transfer and light transfer models to design and optimize the operating conditions of a photobioreactor for maximum hydrogen production and/or CO2 consumption.
Experiences From the First Offering of a Stringed Instrument Manufacture and Testing Course
Authors: French Mark
Published: April 2008

It is a constant challenge to present technical course content in a way that is attractive to undergraduate technology students. They tend to be focused on the immediate utility of the information and are often skeptical of abstract subjects. With this in mind, a course has been developed that uses the manufacture of stringed instruments as a means of teaching basic concepts of dynamic structural response, acoustic-structure coupling and manufacturing processes. A group of 12 students recently participated in a senior level engineering technology course in which they designed and built 12 nominally identical instruments. Guided by a faculty member who is also an experienced luthier (a maker of stringed instruments), they made production fixtures, fabricated the individual components, assembled the instruments and tested them. The results were used to tune discrete math models that captured the first two resonant frequencies of coupled-air structure interaction. Since reducing build variation is a primary activity in production environments, one measure of merit for the class was to produce identical instruments. Build variation was characterized by the variation in the measured resonant frequencies of instruments and of the identified mode parameters from the discrete models. The class has generated significant student interest and promises to be a compelling venue for teaching important technical concepts. It is, however, dependent on an initial investment in tools, materials and faculty experience.
Robust Control of a Vessel Using Camera Feedback and Extended Kalman Filter
Authors: Nikkhah Mehdi , Ashrafiuon Hashem
Published: April 2008

This paper presents the implementation of a robust position tracking control law for an underactuated autonomous surface vessel. The robust control law is developed based on the sliding mode approach where a first order sliding surface is defined in terms of surge and a second order one in terms of lateral motion tracking errors. The control law uses a simple three-degree-of-freedom planar vessel model with two actuator inputs. The vessel is a small model boat with two propellers in a small indoor pool. The position and orientation of the boat is measured using a camera and with two infrared diodes attached the front and end of the boat. An Extended Kalman Filter is designed to estimate all the unmeasured states and filter out the measurement noise. A computer with controller board processes the camera image, calculates the control inputs, and sends the control signal to a two channel wireless receiver on the vessel using a wireless transmitter. The relationship between the distorted camera image and the vessel actual position as well as the relation between motor input voltage and propeller force are derived through experimental calibrations. An experiment is performed where the vessel follows a predefined straight-line trajectory.
Phase Field Modeling of Ferroelectric Domain Wall Interactions With Charge Defects
Authors: Landis Chad M.
Published: April 2008

The overall objective of this work is to develop a theoretical model that can track the evolution of the domain structures in ferroelectric crystals, which are responsible for the non-linear electromechanical behavior of these materials. To this end, a continuum thermodynamics framework is devised, and the theory falls into the class of phase-field or diffuse-interface modeling approaches. Here a set of micro-forces and governing balance laws are postulated and applied within the second law of thermodynamics to identify the appropriate material constitutive relationships. The approach is shown to yield the commonly accepted Ginzburg-Landau equation for the evolution of the polarization order parameter. Within the theory a form for the free energy is postulated that can be applied to fit the general elastic, piezoelectric and dielectric properties of a ferroelectric material near its spontaneously polarized state. Thereafter, a principle of virtual work is specified for the theory and is implemented to devise a finite element formulation. The theory and numerical methods are used to investigate the interactions of 180° and 90° domain walls with an array of charge defects and to determine the electromechanical pinning strength of the array on the walls.
The Physical Condition of Water Rested on the Earth
Authors: Tanaka Takaharu
Published: April 2008

Even if the condition of water on the earth seems rest, if we look at the fluid particles condition in molecular level or atomic level, fluid particles might be in the condition rotational vortex motion around themselves or in the condition equivalent to rotational motion around themselves, and they act centrifugal forces or equivalent forces to them on the fluid particles vertical upward (radial outward) and their weight of masses that directs vertical downward (radial inward) is supported vertical upward (radial outward) and balanced everywhere all around at every depth along the radial line on the earth.
Failure of an Impulsively-Loaded Composite Steel/Polymer Plate
Authors: Shim JongMin , Wierzbicki Tomasz
Published: April 2008

The concept of spraying a thick layer of a polymeric material onto a metal plate has recently received considerable interest in many civilian and military applications. There are numerous analytical and numerical solutions for single thin (membrane) plates made of either a steel or an elastomer. However, solutions for a composite plate made of both of the above constituents are lacking. The objective of the present paper is to formulate a model for a composite steel/elastomer plate, derive an analytical solution for the plate subjected to impulsive loading and compare it with a more exact numerical solution. It is assumed that the circular plate is fully clamped around its periphery, and it is loaded by a uniformly distributed transverse pressure of high intensity and short duration. The pressure imparts an initial impulse which is proportional to the initial transverse velocity of the plate. As an example, DH-36 is used for a steel backing plate while polyurea is chosen as a coating. The analytical model is developed where the steel layer is treated as a rigid perfectly-plastic material. The magnitude of flow stress is adjusted iteratively according to the calculated magnitude of average strain. On the other hand, a linear elastic material is assumed for the polyurea with elastic modulus in the tensile range calculated from the Arruda-Boyce model. The magnitude of the average strain rate was relatively low, about 100 sec-1; therefore, the effect of strain rate is not considered in this paper. A comprehensive parametric study was performed by varying several material and structural parameters in the model. A closed-form analytical solution was compared with the results of detailed FE simulations of composite plates, and good correlation is obtained. It was found that the polyurea coating could improve the failure resistance of the composite plate by 20 % provided that the thickness of the coating is 5 – 10 times larger than the plate.
Analysis of Heat Conduction in Silicon Using Molecular Dynamics Simulations
Authors: Henry Asegun S. , Chen Gang
Published: April 2008

Silicon's material properties, have been studied extensively because of its technological significance in a variety of industries, including microelectronics. Yet, questions surrounding the phonon relaxation times in silicon continue to linger.1,2 Previous theoretical works3-5 have generated qualitative expressions for phonon relaxation times, however these approaches require fitting parameters that cannot be determined reliably. This paper first discusses implementation issues associated with using the Green-Kubo method in molecular dynamics (MD) simulations. We compare various techniques used in similar works and discusses several implementation issues that have arisen in the literature. We then describe an alternative procedure for analyzing the normal modes of a crystal to extract phonon relaxation times. As an example material we study bulk crystalline silicon using equilibrium MD simulations and lattice dynamics. The environment dependent interatomic potential6 is used to model the interactions and frequency dependent phonon properties are extracted from the MD simulations.
On-Line Fuzzy Logic Temperature Control of a Concentric-Tubes Heat Exchanger Facility
Authors: Ruiz-Mercado Claudia , Pacheco-Vega Arturo , Peters Kevin
Published: April 2008

We develop a fuzzy rule based controller to perform on-line temperature control of a concentric-tubes heat exchanger facility. The rules were derived from dynamical values of the mass flow rates and fluid temperatures in the heat exchanger. The controller was embedded in a closed-loop single-input single-output system to control the outlet temperature of the cold fluid. The controller was constructed in two stages, the difference between them being the amount of information provided to the controller. To validate the fuzzy controller two sets of tests were carried out for maintaining a constant value of the outlet temperature under different perturbations. Results from this analysis demonstrate that the fuzzy-based controller is able to achieve control of the system, and that the information about the system provided to it is important in terms of accuracy and efficiency.
Combustion Performance Improved by Atomization for a Gas Turbine Engine Burning Diesel
Authors: Gan Xiaohua , Su Zhonggao , Wang Hongming , Dong Yan
Published: April 2008

In this paper, an emission control technology for a gas turbine engine is studied. When an aero gas turbine engine WJ5A is modified to drive ground electrical generator, some pollutant emission problems, such as black smoke and excessive NOx, have arisen from the substitution of diesel fuel for aero fuel. In order to reduce these emissions, the original pressure-swirl atomizers are replaced by the air-assist atomizers, which can enhance the atomization quality, to expand the combusting zone, and to improve air to fuel ratio in primary zone of the combustor. Experimental studies on the atomization, combustion and the engine tests with the atomizers are conducted. The experiments show that the pollutant emission decreases significantly through the air-assist atomizers.
Experimental Methods to Determine the Constitutive Properties of Fabric Inflatable Structures
Authors: Turner Adam W. , Davids William G. , Peterson Michael L.
Published: April 2008

In an effort to reduce deployment cost and time, the military is taking a closer look at how to more efficiently deploy and construct their shelters. In support of this effort, one current research topic is lightweight inflatable structures used for maintenance and shelter. While inflatable fabric structures are not new, recent developments have vastly improved the load-carrying capability and durability of these structures, allowing them to replace traditional framed tent structures. This is due in large part to the development of inflated structural members called airbeams, which are essentially pressurized fabric tubes with an impermeable internal bladder. The working pressures of the structural airbeams are upwards of 592 kPa. There are two major types of airbeams; woven and braided. The woven beams generally operate at lower pressures (69-296 kPa), while the more recently developed braided beams operate at much higher pressures (296-592 kPa). Since the technology of airbeams is relatively new, there are few standard material tests for determining the fabric constitutive properties necessary for airbeam design. This represents a significant barrier to their efficient implementation. This paper will present the current state of the art in relevant areas of textile testing and describe test practices useful for identifying the constitutive properties of the airbeam fabrics. In addition, preliminary testing of inflated airbeams will also be presented, and the results discussed.
Finite Element Analysis of Pressurized Fabric Beams With Material Nonlinearity
Authors: Zhang Hui , Davids William G. , Peterson Michael L. , Turner Adam , Malm Christopher
Published: April 2008

This paper presents a finite element analysis of inflated fabric beams that considers nonlinear material response and shear deformations. Applying the principle of virtual work, we obtain the FEM formulation for inflated fabric beams with material nonlinearity. Comparisons between 4-point bend tests of inflated woven fabric beams and finite element results indicate that the finite element analysis provides good estimates of deflections, and that it is important to incorporate the effects of shear deformation and pressure when predicting inflated fabric beam response.
Quantifying the accuracy of automated structure segmentation in 4D CT images using a deformable image registration algorithm
Authors: Wijesooriya Krishni , Weiss E. , Dill V. , Dong L. , Mohan R. , Joshi S. , Keall P. J.
Published: April 2008

Four‐dimensional (4D) radiotherapy is the explicit inclusion of the temporal changes in anatomy during the imaging, planning, and delivery of radiotherapy. One key component of 4D radiotherapy planning is the ability to automatically (“auto”) create contours on all of the respiratory phase computed tomography (CT) datasets comprising a 4D CT scan, based on contours manually drawn on one CT image set from one phase. A tool that can be used to automatically propagate manually drawn contours to CT scans of other respiratory phases is deformable image registration. The purpose of the current study was to geometrically quantify the difference between automatically generated contours with manually drawn contours. Four‐DCT data sets of 13 patients consisting of ten three‐dimensional CT image sets acquired at different respiratory phases were used for this study. Tumor and normal tissue structures [gross tumor volume (GTV), esophagus, right lung, left lung, heart and cord] were manually drawn on each respiratory phase of each patient. Large deformable diffeomorphic image registration was performed to map each CT set from the peak‐inhale respiration phase to the CT image sets corresponding with subsequent respiration phases. The calculated displacement vector fields were used to deform contours automatically drawn on the inhale phase to the other respiratory phase CT image sets. The code was interfaced to a treatment planning system to view the resulting images and to obtain the volumetric, displacement, and surface congruence information; 692 automatically generated structures were compared with 692 manually drawn structures. The auto‐ and manual methods showed similar trends, with a smaller difference observed between the GTVs than other structures. The auto‐contoured structures agree with the manually drawn structures, especially in the case of the GTV, to within published inter‐observer variations. For the GTV, fractional volumes agree to within , center of mass displacements agree to within , and agreement of surface congruence is . The surface congruence between automatic and manual contours for the GTV, heart, left lung, right lung and esophagus was less than in 99%, 94%, 94%, 91% and 89%, respectively. Careful assessment of the performance of automatic algorithms is needed in the presence of 4D CT artifacts.
Respiratory motion effects on whole breast helical tomotherapy
Authors: Moeckly Steven R. , Lamba Michael , Elson Howard R.
Published: April 2008

The effects of intrafraction respiratory motion on nonhelical intensity‐modulated radiotherapy have been well addressed in the literature, both theoretically and experimentally. However, the consequences of respiratory motion on helical tomotherapy, for patient‐specific treatment plans, are less well known. Parameters specific to this treatment modality such as pitch, gantry speed, and degree of modulation may play prominent roles in radiation delivery with respect to intrafraction respiratory motion. This phantom‐based study specifically addressed the effects of intrafraction respiratory motion on whole breast helical tomotherapy. A device capable of driving an acrylic phantom with reproducible, one‐dimensional, anterior‐posterior motion resembling a sinusoid of 4.6 mm crest‐trough amplitude was developed. A plan to irradiate the corner of an acrylic phantom using parameters typical of a whole breast helical tomotherapy technique was developed using the TomoTherapy Hi‐Art‐II System®. The treatment was delivered to the phantom, with Kodak EDR2 film in the axial plane, for each of the following conditions: (i) phantom at initial sinusoidal phase and 12 cycles/min motion, (ii) phantom at initial sinusoidal phase and 18 cycles/min motion, and (iii)–(v) phantom at 18 cycles/min motion with , , and initial sinusoidal phases. A measure of technique reproducibility was also performed for several irradiations with the phantom static at initial sinusoidal phase. Films were processed using a Kodak MIN‐R mammography film processor, scanned with a Vidar NXR‐16 Dosimetry Pro scanner and analyzed with RIT113 v.4.2 software. Films were compared to a reference film irradiated under the conditions of no motion and sinusoidal phase. For all comparisons, dose difference threshold, dose difference and 2 mm distance‐to‐agreement gamma analysis, and isodose plots were generated. The results of this study show a small area of greater than decrease in dose at the phantom's anterior surface and a posterior‐medial shift of isodose lines in the penumbral and apex regions of the PTV. Frequency and phase effects are apparent within the PTV where dose varies with high spatial frequency. As the reference film was produced by delivering the treatment plan to the phantom static and in the position corresponding to maximum expiration, results are representative of extreme deviations between planned and delivered dose with respect to sinusoidal motion of clinically relevant magnitudes and frequencies.
MRI‐compatible transurethral ultrasound system for the treatment of localized prostate cancer using rotational control
Authors: Chopra Rajiv , Baker Nicole , Choy Vanessa , Boyes Aaron , Tang Kee , Bradwell David , Bronskill Michael J.
Published: April 2008

Magnetic resonance imaging (MRI)‐guided transurethral ultrasound therapy is a potential minimally invasive treatment for localized prostate cancer offering precise targeting of tissue within the gland, short treatment times, and the capability to quantify the spatial heating pattern delivered during therapy. A significant challenge in MRI‐guided ultrasound therapy is the design and construction of MRI‐compatible equipment capable of operation in a closed‐bore MR imager. We describe a prototype system developed for MRI‐guided transurethral ultrasound therapy and characterize the performance of the different components including the heating applicator design, rotational motor, and radio frequency electronics. The ultrasound heating applicator described in this study incorporates a planar transducer and is capable of producing high intensity ultrasound energy in a localized region of tissue. Results demonstrated that the heating applicator exhibits excellent MRI‐compatibility, enabling precise MR temperature measurements to be acquired as close as 6 mm from the device. Simultaneous imaging and rotational motion was also possible during treatment using a motor based on piezoelectric actuators. Heating experiments performed in both phantoms and in a canine model with the prototype system verified the capability to perform simultaneous MR imaging and therapy delivery with this system. Real‐time control over therapy using MR temperature measurements acquired during heating can be implemented to achieve precise patterns of thermal damage within the prostate gland. The technical feasibility of using the system developed in this study for MRI‐guided transurethral ultrasound therapy in a closed‐bore MR imager has been demonstrated.
Radiotherapy dosimetry using a commercial OSL system
Authors: Viamonte A. , da Rosa L. A. R. , Buckley L. A. , Cherpak A. , Cygler J. E.
Published: April 2008

A commercial optically stimulated luminescence (OSL) system developed for radiation protection dosimetry by Landauer, Inc., the InLight™ microStar reader, was tested for dosimetry procedures in radiotherapy. The system uses carbon‐doped aluminum oxide, , as a radiation detector material. Using this OSL system, a percent depth dose curve for gamma radiation was measured in solid water. Field size and SSD dependences of the detector response were also evaluated. The dose response relationship was investigated between 25 and 400 cGy. The decay of the response with time following irradiation and the energy dependence of the OSL detectors were also measured. The results obtained using OSL dosimeters show good agreement with ionization chamber and diode measurements carried out under the same conditions. Reproducibility studies show that the response of the OSL system to repeated exposures is (1sd), indicating a real possibility of applying the Landauer OSL commercial system for radiotherapy dosimetric procedures.
Dosimetric characterization of model Cs‐1 Rev2 cesium‐131 brachytherapy source in water phantoms and human tissues with MCNP5 Monte Carlo simulation
Authors: Wang Jianhua , Zhang Hualin
Published: April 2008

A recently developed alternative brachytherapy seed, Cs‐1 Rev2 cesium‐131, has begun to be used in clinical practice. The dosimetric characteristics of this source in various media, particularly in human tissues, have not been fully evaluated. The aim of this study was to calculate the dosimetric parameters for the Cs‐1 Rev2 cesium‐131 seed following the recommendations of the AAPM TG‐43U1 report [Rivard et al., Med. Phys. 31, 633–674 (2004)] for new sources in brachytherapy applications. Dose rate constants, radial dose functions, and anisotropy functions of the source in water, Virtual Water™, and relevant human soft tissues were calculated using MCNP5 Monte Carlo simulations following the TG‐43U1 formalism. The results yielded dose rate constants of 1.048, 1.024, 1.041, and in water, Virtual Water™, muscle, and prostate tissue, respectively. The conversion factor for this new source between water and Virtual Water™ was 1.02, between muscle and water was 1.006, and between prostate and water was 1.004. The authors’ calculation of anisotropy functions in a Virtual Water™ phantom agreed closely with Murphy's measurements [Murphy et al., Med. Phys. 31, 1529–1538 (2004)]. Our calculations of the radial dose function in water and Virtual Water™ have good agreement with those in previous experimental and Monte Carlo studies. The TG‐43U1 parameters for clinical applications in water, muscle, and prostate tissue are presented in this work.
A registration based approach for 4D cardiac micro‐CT using combined prospective and retrospective gating
Authors: Badea Cristian T. , Schreibmann Eduard , Fox Tim
Published: April 2008

Recent advances in murine cardiac studies with three‐dimensional cone beam micro‐computed tomography (CT) have used either prospective or retrospective gating technique. While prospective gating ensures the best image quality and the highest resolution, it involves longer sampling times and higher radiation dose. Sampling is faster and the radiation dose can be reduced with retrospective gating but the image quality is affected by the limited number of projections with an irregular angular distribution which complicate the reconstruction process, causing significant streaking artifacts. This work involves both prospective and retrospective gating in sampling. Deformable registration is used between a high quality image set acquired with prospective gating with the multiple data sets during the cardiac cycle obtained using retrospective gating. Tests were conducted on a four‐dimensional (4D) cardiac mouse phantom and after optimization, the method was applied to in vivo cardiac micro‐CT data. Results indicate that, by using our method, the sampling time can be reduced by a factor of 2.5 and the radiation dose can be reduced compared to the prospective sampling while the image quality can be maintained. In conclusion, we proposed a novel solution to 4D cine cardiac micro‐CT based on a combined prospective with retrospective gating in sampling and deformable registration post reconstruction that mixed the advantages of both strategies.
A comparative contrast‐detail study of five medical displaysa)
Authors: Samei Ehsan , Ranger Nicole T. , Delong David M.
Published: April 2008

The objective of this study was to compare the contrast‐detail performance of five different commercial liquid crystal displays (LCDs) to other LCD and cathode‐ray tube (CRT) displays for medical applications. A contrast‐detail phantom, supplemented with 5 in. of acrylic, was imaged on a commercial digital radiographic system using techniques comparable to chest radiography. The phantom design enabled observer evaluation by a four‐alternative forced choice paradigm. The acquired images were independently scored by five observers on five medical display devices: a 5 megapixel monochrome LCD, a 3 megapixel monochrome LCD, a 9 megapixel color LCD, a 5 megapixel monochrome CRT, and a mammographic‐grade monochrome CRT. The data were analyzed using the method suggested by the manufacturer based on a nearest neighbor correction technique. They were further analyzed using a logistic regression response model with a natural threshold using an overall chi‐square test for display type followed by pairwise comparisons for individual display performance. The differences between the display devices were small. The standard analysis of the results based on the manufacturer‐recommended method did not yield any statistically discernible trend among displays. The logistic regression analysis, however, indicated that the 5 megapixel monochrome LCD was statistically significantly superior to the others, followed by the 3 megapixel monochrome LCD . The three other displays exhibited lower but generally similar performance characteristics. The findings suggest that 5 and 3 megapixel monochrome LCDs provide comparable but subtly superior contrast detectability than other tested displays, with the former performing slightly better in the detection of subtle and fine details.
Photon energy spectrum emitted by a novel polymer‐encapsulated source and its effect on the dose rate constant
Authors: Khan Sabrina , Chen Zhe Jay , Nath Ravinder
Published: April 2008

Two independent groups have published intrinsic dosimetry parameters for the recently introduced interstitial brachytherapy source which contains encapsulated by a novel polymer shell. The dose rate constant reported by the two groups, however, differed by more than and there is currently no AAPM recommended consensus value for this source in clinical dosimetry. The aim of this work was to perform an independent determination of for the source using a recently developed photon spectrometry technique. Three sources (model 1032P) with known air‐kerma strength were used in this study. The photon energy spectrum emitted along the radial direction on the source's bisector was measured in air using a high‐resolution intrinsic germanium spectrometer designed and established for low‐energy brachytherapy source spectrometry. The dose rate constant of each source was determined from its emitted energy spectrum and the spatial distribution of radioactivity in the source. Unlike other sources made with traditional titanium encapsulation, the photons emitted by the sources exhibited only slight spectral hardening, yielding a relative energy spectrum closer to that emitted by bare . The dose rate constant determined by the photon spectrometry technique for water was . This value agreed, within experimental uncertainties, with the Monte Carlo‐calculated value of and the TLD‐measured value (with a Monte Carlo‐calculated solid‐phantom‐to‐water conversion factor) of reported by Wang and Hertel [Appl. Radiat. Isot. 63, 311–321 (2005)]. However, it differed by from the of reported by Bernard and Vynckier [Phys. Med. Biol. 50, 1493–1504 (2005)]. The results obtained in this work provide additional information needed for establishing a consensus value for the dose rate constant for the source. It suggests that an eventual consensus value of for the source is likely to be closer to a value of rather than as initially recommended by the source manufacturer based on the two previously published results.
A mathematical model platform for optimizing a multiprojection breast imaging system
Authors: Chawla Amarpreet S. , Samei Ehsan , Saunders Robert S. , Lo Joseph Y. , Baker Jay A.
Published: April 2008

Multiprojection imaging is a technique in which a plurality of digital radiographic images of the same patient are acquired within a short interval of time from slightly different angles. Information from each image is combined to determine the final diagnosis. Projection data are either reconstructed into slices as in the case of tomosynthesis or analyzed directly as in the case of multiprojection correlation imaging technique, thereby avoiding reconstruction artifacts. In this study, the authors investigated the optimum geometry of acquisitions of a multiprojection breast correlation imaging system in terms of the number of projections and their total angular span that yield maximum performance in a task that models clinical decision. Twenty‐five angular projections of each breast from 82 human subjects in our breast tomosynthesis database were each supplemented with a simulated 3 mm mass. An approach based on Laguerre–Gauss channelized Hotelling observer was developed to assess the detectability of the mass in terms of receiver operating characteristic (ROC) curves. Two methodologies were developed to integrate results from individual projections into one combined ROC curve as the overall figure of merit. To optimize the acquisition geometry, different components of acquisitions were changed to investigate which one of the many possible configurations maximized the area under the combined ROC curve. Optimization was investigated under two acquisition dose conditions corresponding to a fixed total dose delivered to the patient and a variable dose condition, based on the number of projections used. In either case, the detectability was dependent on the number of projections used, the total angular span of those projections, and the acquisition dose level. In the first case, the detectability approximately followed a bell curve as a function of the number of projections with the maximum between 8 and 16 projections spanning angular arcs of about , respectively. In the second case, the detectability increased with the number of projections approaching an asymptote at 11–17 projections for an angular span of about . These results indicate the inherent information content of the multiprojection image data reflecting the relative role of quantum and anatomical noise in multiprojection breast imaging. The optimization scheme presented here may be applied to any multiprojection imaging modalities and may be extended by including reconstruction in the case of digital breast tomosynthesis and breast computed tomography.
The impact of MLC transmitted radiation on EPID dosimetry for dynamic MLC beams
Authors: Vial Philip , Greer Peter B. , Hunt Peter , Oliver Lyn , Baldock Clive
Published: April 2008

The purpose of this study was to experimentally quantify the change in response of an amorphous silicon electronic portal imaging device (EPID) to dynamic multileaf collimator (dMLC) beams with varying MLC‐transmitted dose components and incorporate the response into a commercial treatment planning system (TPS) EPID prediction model. A combination of uniform intensity dMLC beams and static beams were designed to quantify the effect of MLC transmission on EPID response at the central axis of beams, at off‐axis positions using wide dMLC beam profiles, and at different field sizes. The EPID response to MLC transmitted radiation was of the response to open beam radiation at the central axis of a field. The EPID response to MLC transmitted radiation was further reduced relative to the open beam response with off‐axis distance. The EPID response was more sensitive to field size changes for MLC transmitted radiation compared to open beam radiation by a factor of up to 1.17 at large field sizes. The results were used to create EPID response correction factors as a function of the fraction of MLC transmitted radiation, off‐axis distance, and field size. Software was developed to apply the correction factors to each pixel in the TPS predicted EPID image. The corrected images agreed more closely with the measured EPID images in areas of intensity modulated fields with a large fraction of MLC transmission and, as a result the accuracy of portal dosimetry with EPIDs can be improved. Further investigation into the detector response function and the radiation source model are required to achieve improvements in accuracy for the general case.
Study of direct and indirect parametric estimation methods of linear models in dynamic positron emission tomography
Authors: Tsoumpas Charalampos , Turkheimer Federico E. , Thielemans Kris
Published: April 2008

In dynamic positron emission tomography (PET) studies, the time changing activity of the radiotracer is measured through multiple consecutive frames. Subsequent pixel‐by‐pixel application of the appropriate kinetic model provides quantitative information in terms of images of the distribution of the physiological parameter of interest. In this context, iterative reconstruction methods may be used to reconstruct for each time frame a static image of appreciable higher quality than the analytical algorithms, especially in low‐count cases. Furthermore, if the reconstruction algorithm also models the kinetics of the measured counts, the parametric image is expected to be of even higher quality. In this work, we investigate the methodology to directly reconstruct parametric images in three‐dimensional PET when the kinetic model is linear in its parameters (Patlak plot) and compare with indirectly estimated parametric maps, where the radioactivity distribution was estimated by the filtered back projection and ordered subsets expectation maximization algorithms. Both real and simulated data for tracers with irreversible kinetics in brain studies are included. The results demonstrate appreciable smaller standard deviation and mean squared error characteristics for the direct reconstruction. However, some regions may converge slowly. The FBP and ordered subsets expectation maximization (OSEM) indirect estimations have a similar level of bias after matching their resolutions, but OSEM has smaller standard deviation.