bluuebunny/crossref_metadata_2025 huggingface dataset:
Slip Factors of Centrifugal Slurry Pumps
Authors: Sheth K. K. , Morrison G. L. , Peng W. W.
Published: October 2009

Experiments have been carried out in order to determine the effects on slip factor due to the various parameters affecting the performance characteristics of a centrifugal slurry pump. The experiments were conducted with water, sand slurry, and a glass bead slurry at three different pump speeds. Measurements of power, flow rate, head developed by the pump and the density of the slurry were made in order to obtain the characteristic curves of the pump. Using Euler’s equation, equations were derived for calculating the slip and friction factors of the flow. The deduced slip factors for centrifugal slurry pump can be correlated well with suggested non dimensional groups. It shows a consistent trend of decreasing slip factor with increasing slurry mixture density and impeller rotation, or with a decreasing through flow rate. The sizes of the sand and glass bead particles are significantly different (0.71 mm versus 0.09 mm), however, the data correlations do not suggest its effect on the slip factors significantly as the other parameters. The slip factors deduced from head-flow rate curves are more reliable than those deduced from power-flow rate curves, since the shut-off power measurements are likely subjected to errors associated with the particles settling, or the transient effect if the measurements are taken momentarily.
Drag Coefficient and Settling Velocity of Particles in Non-Newtonian Suspensions
Authors: Dedegil M. Y.
Published: October 2009

Drag forces on bodies in non-Newtonian fluids which are to be described by using the Reynolds number should only contain forces which are associated with the fluid velocity or particle velocity. Forces due to the yield stress τ0 must be considered separately. According to its physical composition, the Reynolds number must be calculated by means of the fully representative shear stress including the yield stress τ0. Then the drag coefficient cD as a function of the Reynolds number can be traced back to that of Newtonian fluids.
Experimental and Numerical Investigations of Plane Duct Flows With Sudden Contraction
Authors: Durst F. , Schierholz W. F. , Wunderlich A. M.
Published: October 2009

The present paper reports on experimental and numerical studies of laminar, two-dimensional flow through plane ducts with sudden contractions in cross-sectional area. A laser-Doppler anemometer and a flow computational program were complementarity employed to study details of the flow close to the step. The results reveal details of the velocity profile variations in the vicinity of the contraction. Information is also provided on the separated flow region in the front concave corner of the duct and on the separated flow region just downstream of the lip of the step. The dimensions of the front separation region are shown to agree well with existing data. The recirculating flow region just downstream of the lip is much smaller than occasionally assumed. At higher contraction ratios off-axis velocity maxima occur just downstream of the contraction. It is shown that strong elongational flow fields occur. These are concentrated to a very small region close to the step.
Air Flow Resistance of Wire Nettings in Natural Convection
Authors: Ishizuka M.
Published: October 2009

This paper describes some experimental values for flow resistance of wire nettings in low Reynolds number flows, such as natural air convection, providing basic thermal data necessary for designing electronic equipment casings. The experiment was designed to evaluate the wire netting resistance coefficient in natural air convection. As a result, the relationships among the resistance coefficient for wire netting, Reynolds number, and porosity coefficient were obtained in useful form.
Noise and Erosion of Self-Resonating Cavitating Jets
Authors: Chahine G. L. , Courbie`re P.
Published: October 2009

Self-resonating jets have been developed which take advantage of the natural tendency of a jet to organize in large structures. Tests have shown that these jets are both highly erosive and a source of a discrete frequency high level noise. Simultaneous investigations of the noise and erosion of these jets have been conducted and have shown a definite trend toward correlation. For instance, time evolution of volume removal rates of an impacted surface and rms readings of a pressure transducer have been found to be correlated. Similarly, shifts in the relative importance of the various frequencies have followed the advancement of erosion. These results could be of great advantage in the determination of the evolution of a jet cutting operation in progress. In this paper jet noise and erosion correlation tests will be described and the results analyzed.
Erosion Due to Impingement of Cavitating Jet
Authors: Yamaguchi A. , Shimizu S.
Published: October 2009

Cavitation erosion produced by impingent of cavitating jet was experimentally studied with specimens of aluminum alloy in high water base fluid of chemical solution type and tap water. Furthermore, the behavior of impinging cavity clouds was observed through instantaneous photographs.
Laboratory Slurry Erosion Tests and Pump Wear Rate Calculations
Authors: Tuzson J. J.
Published: October 2009

From order-of-magnitude calculations, the erosion mechanism in slurry pumps for mining applications was found to be a scouring type. Impact erosion was found to be unlikely to occur. The erosion model assumes a “sliding bed” type of flow pattern and neglects the effect of turbulent diffusion of slurry particles. This choice was based on flow regime data from slurry pipeline flow and was not verified experimentally in pumps. A new centrifugal-erosion laboratory testing fixture was designed and fabricated at Allis-Chalmers which reproduces this type of erosion. Since flow conditions were closely controlled, an absolute rate of erosion could be determined. For mild steel (Rockwell C = 10) and aluminum oxide particles, a specific erosion energy of 1.5 × 108 in-lb/in3 (1000 joules/mm3) was measured. Flow pattern and slurry concentrations were calculated in a pump impeller using a quasi-three-dimensional streamline curvature method. These were combined with the above erosion model and the local erosion rate was estimated. Actual operating data had to be estimated for a quarry application of the pump because field test data was not available. The uncertainties of the field test data did not allow an exact numerical verification of the wear rate calculation, but order of magnitude agreement was obtained. The wear rate distribution agreed very well with the wear pattern observed on the impeller used in the quarry and the locations of excessive wear could be identified.
Correlation of Cavitating Centrifugal Pumps
Authors: Zika V. J.
Published: October 2009

The foreknowledge of the minimum NPSH (“net positive suction head”) required for a cavitation-free performance of centrifugal pumps is important for a safe and sound operation of these machines. The required NPSH varies from pump to pump, from fluid to fluid, and from temperature to temperature of the pumped fluid. This is known as the thermodynamic effect. The methods currently used for the correlation and analysis of this condition are not always reliable because of the multi-variable nature of the cavitation process. In this paper, two new methods are proposed which lead to more consistent correlations of the required minimum NPSH; thus they can also be used for more dependable predictions of the net positive suction head for any pump, fluid and temperature. The predictions by the two methods do not coincide, but outline a narrow band of probability, within which the actual test points are invariably located.
Fluctuating Forces on a Rectangular Prism and a Circular Cylinder Placed Vertically in a Turbulent Boundary Layer
Authors: Sakamoto H. , Oiwake S.
Published: October 2009

An experimental study was conducted to investigate the fluctuating force generated by the shedding of vortices from a three-dimensional bluff body placed vertically in a turbulent boundary layer. A conventional strain-gauge balance was modified and used in the experiment. The balance used has a relatively high natural frequency and gives a linear relation between force and strain. Prisms with a square cross section and circular cylinders were selected as three-dimensional bodies varing in aspect ratio and height. The aspect ratio and the ratio of the height to the boundary layer thickness were varied in the measurement of the fluctuating force on a body.
Laser Velocimeter Measurements in Highly Turbulent Recirculating Flows
Authors: Stevenson W. H. , Thompson H. D. , Craig R. R.
Published: October 2009

This paper presents the results of an extensive study of subsonic separated flows using a laser Doppler velocimeter. Both a rectangular rearward facing step and cylindrical (axisymmetric) sudden expansion geometry were studied. The basic objectives were to resolve the question of whether a velocity bias error does, in fact, occur in LDV measurements in highly turbulent flows of this type and, if so, how it may be eliminated; map the velocity field (mean velocity, turbulence intensity, Reynolds stress, etc.) including the entire recirculation zone; and compare experimental results with numerical predictions based on the k-ε turbulence model. Measurements were carried out using a one-dimensional LDV operating in forward scatter with signal processing by means of a commercial counter-type processor. Results obtained show that velocity bias does occur in turbulent flows and that it can be overcome by proper data acquisition procedures. The results also indicate that the important mean velocity and turbulence quantities can be obtained with reasonable accuracy using a one-dimensional LDV system. Although the k-ε turbulence model provides a good qualitative picture of the flow field, it does not yield a completely adequate quantitative description. Results obtained here illustrate the discrepancies to be expected and provide a basis for further model development.
A Guide to Uncertainty Analysis of Hot-Wire Data
Authors: Yavuzkurt S.
Published: October 2009

Uncertainty analysis of hot-wire data in turbulent flows are made for time-averaging and real-time data reduction techniques. Equations of uncertainty are derived in general form for every step of data taking and evaluation. Numerical examples are supplied for two-dimensional flat plate boundary layer data. Results show that the real-time data reduction techniques generally have a lower and much more uniform uncertainty distribution than the time-averaging techniques (whose uncertainties are much higher for the near-wall data).
The Gru¨neisen Parameter in Fluids
Authors: Arp V. , Persichetti J. M. , Chen Guo-bang
Published: October 2009

The Gru¨neisen parameter has long been used in equations of state for solids to relate thermodynamic properties to lattice vibrational spectra [1]. A few papers have extended the concept to studies of liquid structure. Knopoff and Shapiro [2] have evaluated a Gru¨neisen parameter for water and for mercury, attempting to relate its temperature dependence in a limited range to atomic clustering within the liquid. Sharma [3], in a series of papers, has evaluated a pseudo-Gru¨neisen parameter in mercury and liquefied gases and related it to internal pressures, a solubility parameter, and clustering phenomena. In this paper we evaluate the Gru¨neisen parameter for a variety of fluids, and show how it occurs in many problems in compressible fluid hydrodynamics, without reference to concepts of liquid structure. The work extends that reported in an earlier paper for the special case of steady state, single phase flow [4].
Flow Field Due to Free Convection in Dead-End Channels
Authors: Yildirim Y. , Jain S. C.
Published: October 2009

The velocity and temperature distributions in a long dead-end channel, where the convective flow is driven by the buoyancy flux across the free surface, were investigated. The longitudinal variations of the temperature and velocity were determined using the similarity profiles for the vertical distribution of the temperature and velocity. The governing partial differential equations were reduced to ordinary differential equations by substituting the expressions for the longitudinal variations of the temperature and velocity. The resulting ordinary differential equations were solved numerically by employing a shooting method and a fourth order Runge-Kutta technique. The sensitivity to the temperature and velocity distributions of the various parameters were studied.
Linearized Two-Dimensional Fluid Transients
Authors: Wylie E. B.
Published: October 2009

A numerical analysis of low-velocity two-dimensional transient fluid flow problems is presented. The method is similar in concept to the one-dimensional method of characteristics, but does not follow the traditional characteristics theory for two spatial dimensions. Distinct paths are defined in the three-dimensional space-time domain along which compatibility equations are integrated. The explicit procedure is explained, and validated by comparisons with analytical solutions.
Prediction of Sudden Expansion Flows Using the Boundary-Layer Equations
Authors: Kwon O. K. , Pletcher R. H. , Lewis J. P.
Published: October 2009

A finite-difference calculation method based on the boundary-layer equations is described for the prediction of laminar, developed channel flow undergoing a symmetric sudden expansion. The scheme requires only a fraction of the computational effort required for the numerical solution of the full Navier-Stokes equations that are usually employed for this flow. Predictions of the method compare very favorably with experimental data and solutions of the full Navier-Stokes equations.
Simulation of Vaporous and Gaseous Cavitation
Authors: Wylie E. Benjamin
Published: October 2009

A discrete free gas model is presented for numerical simulation of transients in liquids containing free gas. The model is also able to simulate vapor column separation during liquid transient flows in pipelines. The latter application may be the most significant attribute of the model.
Some Features of Water Flows With Ventilated Cavities
Authors: Michel J. M.
Published: October 2009

A survey of the main mechanisms of air entrainment in largely developed cavity flow is given, with paticular attention being given to plane, almost horizontal flows. Specific characteristics of dimensional analysis in this case are exhibited. The evolution of flow configuration when the airflow rate changes is described. Special emphasis is placed on cavity pulsation and its physical characteristics. Some aspects of the pulsation mechanisms are discussed, from a qualitative point of view, with a more detailed examination of the phase relations between the quantities involved.
Air Entrainment in Ventilated Cavities: Case of the Fully Developed “Half-Cavity”
Authors: Laali A. R. , Michel J. M.
Published: October 2009

Experimental results are given concerning the behavior of the so called “half-cavity” which is formed by a plane water jet, initially horizontal, projected over a small step at the bottom of a channel. The relation between the air flow rate and the cavity pressure is given particular consideration: the influence of geometrical or dynamic parameters on this relation is studied and it is found that the dominant role is played by the Froude number and the cavitation number. Other results concern cavity pulsation frequency and cavity length. Some theoretical considerations concerning the flow geometry are necessary to identify the gravity effect for the case where the cavity is long compared to the height of the step.
Correlation of Cavitation Erosion and Sound Pressure Level
Authors: Lush P. A. , Angell B.
Published: October 2009

The purpose of this paper is to investigate the existence of a correlation between the cavitation erosion rate of 99 percent pure aluminium and the sound pressure level of the cavitation noise. The data used were obtained recently for a variety of cavitation inducers and specimen locations at both the University of Southampton, Southampton, U.K. and the Admiralty Marine Technology Establishment, Holton Heath. A regression analysis of the logarithm of erosion rate on sound pressure level, expressed in decibels, shows that for each configuration there is a significant correlation, which is independent of fluid velocity and cavitation number, although the likely error is quite large. It is concluded that an absolute relation between erosion and sound pressure cannot be ruled out and that in any case it would be possible to define a relation for a given configuration provided that calibration could be done in advance.
The Hydrodynamic Stability of Rapidly Evaporating Liquids With Time Dependent Base States
Authors: Jacobs J. W. , Catton I. , Plesset M. S.
Published: October 2009

The hydrodynamic stability of a rapidly evaporating liquid surface is examined. The problem is modeled to mimic the case of a superheated liquid in equilibrium with its vapor in which, the pressure above the liquid surface is dropped suddenly. Both the liquid and its vapor are assumed to be inviscid, incompressible and semi-infinite in extent. In addition, the temperature dependence of fluid properties is neglected. A linear stability analysis is applied to this model. This study differs from previous work in that time dependent base states are used. As a result, a system of linear homogeneous differential equations must be integrated in time. This system consists of a partial differential equation for the liquid temperature field and two other linked ordinary differential equations in time. Various types of thermal boundary conditions yielding different base state temperature profiles are considered. The results of this experimentation are contrasted. An attempt is made to compare results of the transient method to experimental data.
Rarefied Gas Flow Through a Circular Orifice and Short Tubes
Authors: Fujimoto Tetsuo , Usami Masaru
Published: October 2009

Rarefied gas flow through a circular orifice and short tubes has been investigated experimentally, and the conductance of the aperture has been calculated for Knudsen number between 2 × 10−4 and 50. The unsteady approach was adopted, in which the decay of pressure in an upstream chamber was measured as a function of time. For flow with high pressure ratio, empirical equations of the conductance are proposed as a function of Reynolds number, or Knudsen number, and length-to-diameter ratio of the apertures.
An Analysis of Jet Stripping of Liquid Coatings
Authors: Ellen C. H. , Tu C. V.
Published: October 2009

This paper presents a new analysis of the jet stripping process, as used to control coating thicknesses in the paper, photographic and galvanizing industries, and demonstrates that the inclusion of a surface shear stress term, acting in conjunction with the pressure gradient on the coating, gives theoretical predictions of coating behavior quite different from those based on stripping which allows only for pressure gradient effect. An illustration is given of how jets operating close to, and further from, the strip during hot dip galvanizing have different effects on the molten coating even though the final coating mass might be the same. Measurements of coating mass, taken from galvanizing line trials, have shown good agreement with the revised theory.
Some Effects of Upstream Turbulence on the Unsteady Lift Forces Imposed on Prismatic Two Dimensional Bodies
Authors: Gartshore I. S.
Published: October 2009

Measurements of fluctuating lift are reported from four fixed rectangular prisms and a fixed circular cylinder, for various intensities of turbulence in the oncoming stream. Variations of unsteady lift with intensity of small scale turbulence are similar to present (and previous) measured variations of mean drag or base pressure. Reasons are suggested for these trends. Observations are also reported of the maximum (resonant) RMS amplitude of two cylinders, one square and the other circular in cross section, free to move in the cross stream direction. Small scale free stream turbulence provided by the wake of a small upstream rod increased the resonant amplitude of motion in both cases, the greater increase (and subsequent decrease) occurring for the square section. Two possible explanations for these observations are advanced.
An Acoustic Detection Method of Cloud Cavitation
Authors: Arai C.
Published: October 2009

This paper deals with an investigation of a method which detects the generation of cloud cavitation by the measurement of cavitation noise. Cavitation noise consists of a pulse train with approximately 1 μs rise time and 10 μs duration and has almost ultrasonic characteristics. By utilizing these chracteristics, the pulses of cavitation noise were measured, and a chart of cumulative pulseheight frequency was obtained. On this chart, the noise pattern due to cloud cavitation on a propeller working in nonuniform flow was clearly distinguished from other cavitation patterns.
Visualization Techniques for Unsteady Flows: An Overview
Authors: Gad-el-Hak Mohamed
Published: October 2009

The purpose of this article is to review some of the novel flow visualization techniques that are particularly suited for studying unsteady flows. While many of these techniques are equally conducive for steady flow fields, the present paper will emphasize applications to time-dependent flows. Possible pitfalls in interpreting the visualization results are elaborated. The flow visualization methods presented include those that make use of scattered light from small particles or other foreign additives as well as those that make use of changes in the index of refraction.
Consistent Boundary Conditions for Reduced Navier-Stokes (RNS) Scheme Applied to Three-Dimensional Viscous Flows
Authors: Reddy D. R. , Rubin S. G.
Published: October 2009

A consistent and efficient set of boundary conditions are developed for the multi-sweep space marching pressure-elliptic Reduced Navier-Stokes (RNS) scheme as applied for three-dimensional internal viscous flow problems. No-slip boundary conditions are directly imposed on the solid walls. There is no iteration procedure required in the cross plane to ensure mass conservation across each marching plane. The finite difference equations forming the coefficient matrix are ordered such that the surface normal velocity is specified on all the solid walls; unlike external flows, a pressure boundary condition in the cross plane is not required. Since continuity is directly satisfied at all points in the flow domain, the first order momentum equations can be solved directly for the pressure without the need for a Poisson pressure correction equation. The procedure developed herein can also be applied with periodic boundary conditions. The analysis is given for general compressible flows. Incompressible flow solutions are obtained, for straight and curved ducts of square cross section, to validate the procedure. The solutions of these test cases are used to demonstrate the applicability of the RNS scheme, with the improved boundary conditions, for internal flows with strong interaction as would be encountered in ducts and turbomachinery geometries.
An Optical Method for Determining Bubble Size Distributions—Part I:Theory
Authors: Meernik P. R. , Yuen M. C.
Published: October 2009

A new optical technique is developed to determine the size distribution of bubbles in a two-phase flow. Implementation involves passing a narrow beam of light through the bubbly flow and monitoring the transmitted light intensity. The basic units of data are the rate at which each bubble blocks off the beam and the duration of blockage. Adding the hypothesis that the distance of closest approach between a bubble’s center and the beam axis is randomly distributed, a statistical analysis yields the bubble size distribution.
Measurement and Prediction of Rough Wall Effects on Friction Factor—Uniform Roughness Results
Authors: Scaggs W. F. , Taylor R. P. , Coleman H. W.
Published: October 2009

The results of an experimental investigation of the effects of surface roughness on turbulent pipe flow friction factors are presented and compared with predictions from a previously published discrete element roughness model. Friction factor data were acquired over a pipe Reynolds number range from 10,000 to 600,000 for nine different uniformly rough surfaces. These surfaces covered a range of roughness element sizes, spacings and shapes. Predictions from the discrete element roughness model were in very good agreement with the data.
Potential Core of a Submerged Laminar Jet
Authors: Akaike Shiro , Nemoto Mitsumasa
Published: October 2009

This study is intended to clarify the flow pattern in the flow developing region of an axisymmetric laminar water jet issuing into the surrounding calm water. The jet, initially having a potential core region of some extent at the nozzle exit, was studied. The numerical solution of the Navier-Stokes equations in the developing region was obtained using a finite-difference approximation. The velocity profile was measured using a miniature cone-type hot probe. Flow visualization by the hydrogen bubble method was also performed. Experiments were carried out for the jet Reynolds number ranging from 100 to 600. The flow pattern in the developing region was made clear. The experimental results were compared with the numerical solution.
Predictions of the Laminarization Phenomena in an Axially Rotating Pipe Flow
Authors: Hirai Shuichiro , Takagi Toshimi , Matsumoto Masaharu
Published: October 2009

Numerical predictions are compared with the experiments of swirling turbulent flows in a pipe where the swirl is driven by the pipe wall rotating around the pipe axis. The laminarization phenomena, that is, the deformation of the axial velocity profile into a shape similar to the laminar one and the decrease of the friction factor, caused by the pipe rotation can be predicted by the calculations applying the stress equation turbulence model. However, calculations applying two types of the k-ε two-equation models with and without the modification by the Richardson number, cannot predict the laminarization phenomena and the characteristic behaviors due to the swirl. The interpretations of the laminarization phenomena and the applicability of the turbulence models are presented.
A high spatial resolution in vivo 1H magnetic resonance spectroscopic imaging technique for the human breast at
Authors: Hu Jiani , Feng Wenzheng , Hua Jia , Jiang Quan , Xuan Yang , Li Tao , Haacke E. Mark
Published: October 2009

Purpose:

The technical challenges that have prevented routine proton magnetic resonance spectroscopic imaging (1H MRSI) examinations of the breast include insufficient spatial resolution, increased difficulties in shimming compared to the brain, and strong lipid contamination at short echo time (TE) at. The authors investigated the feasibility of high spatial resolution 1H MRSI of human breast cancer in a clinical setting at .

Methods:

Ten patient studies (eight cancers and two benign lesions) were performed in a whole‐body clinical imager using a pulse sequence consisting of optional outer volume presaturation, optional CHESS pulse for lipid suppression, CHESS pulse for water suppression, and standard 2D/3D PRESS pulse sequence with an elliptical weighted ‐space sampling scheme.

Results:

All ten studies were technically successful. The spectral quality was acceptable for all cases even the one with a width of water peak at half height. Choline (Cho) signals were clearly visible in malignant lesion areas, while there was no detectable Cho in normal appearing breast or in benign lesions. It was also observed that the distribution of Cho signal can be nonuniform across MRI demonstrated lesions.

Conclusions:

To the author's knowledge, this is the first 2D/3D MRSI study of human breast cancer with short TE (less than) at and the highest spatial resolution (up to ) to date. In conclusion, the authors have presented a robust technique for high spatial resolution in vivo 1H MRSI of human breast cancer that uses the combined advantages of high field, short TE, multivoxel, and high spatial resolution itself to overcome the major technical challenges and illustrated its potential for routine clinical examination as well as advantages over single‐voxel techniques in studying metabolite heterogeneity.
Development and testing of texture discriminators for the analysis of trabecular bone in proximal femur radiographs
Authors: Huber M. B. , Carballido‐Gamio J. , Fritscher K. , Schubert R. , Haenni M. , Hengg C. , Majumdar S. , Link T. M.
Published: October 2009

Purpose:

Texture analysis of femur radiographs may serve as a potential low cost technique to predict osteoporotic fracture risk and has received considerable attention in the past years. A further application of this technique may be the measurement of the quality of specific bone compartments to provide useful information for treatment of bone fractures. Two challenges of texture analysis are the selection of the best suitable texture measure and reproducible placement of regions of interest (ROIs). The goal of this in vitro study was to automatically place ROIs in radiographs of proximal femur specimens and to calculate correlations between various different texture analysis methods and the femurs’ anchorage strength.

Methods:

Radiographs were obtained from 14 femoral specimens and bone mineral density (BMD) was measured in the femoral neck. Biomechanical testing was performed to assess the anchorage strength in terms of failure load, breakaway torque, and number of cycles. Images were segmented using a framework that is based on the usage of level sets and statistical in‐shape models. Five ROIs were automatically placed in the head, upper and lower neck, trochanteric, and shaft compartment in an atlas subject. All other subjects were registered rigidly, affinely, and nonlinearly, and the resulting transformation was used to map the five ROIs onto the individual femora.

Results:

In each ROI, texture features were extracted using gray level co‐occurence matrices (GLCM), third‐order GLCM, morphological gradients (MGs), Minkowski dimensions (MDs), Minkowski functionals (MFs), Gaussian Markov random fields, and scaling index method (SIM). Coefficients of determination for each texture feature with parameters of anchorage strength were computed. In a stepwise multiregression analysis, the most predictive parameters were identified in different models. Texture features were highly correlated with anchorage strength estimated by the failure load of up to (MF and MG features, ) and were partially independent of BMD. The correlations were dependent on the choice of the ROI and the texture measure. The best predictive multiregression model for failure load included a set of recently developed texture methods (MF and SIM) but excluded bone mineral density and commonly used texture measures.

Conclusions:

The results suggest that texture information contained in trabecular bone structure visualized on radiographs may predict whether an implant anchorage can be used and may determine the local bone quality from preoperative radiographs.
Quantitative blood flow measurements in the small animal cardiopulmonary system using digital subtraction angiography
Authors: Lin MingDe , Marshall Craig T. , Qi Yi , Johnston Samuel M. , Badea Cristian T. , Piantadosi Claude A. , Johnson G. Allan
Published: October 2009

Purpose:

The use of preclinical rodent models of disease continues to grow because these models help elucidate pathogenic mechanisms and provide robust test beds for drug development. Among the major anatomic and physiologic indicators of disease progression and genetic or drug modification of responses are measurements of blood vessel caliber and flow. Moreover, cardiopulmonary blood flow is a critical indicator of gas exchange. Current methods of measuring cardiopulmonary blood flow suffer from some or all of the following limitations—they produce relative values, are limited to global measurements, do not provide vasculature visualization, are not able to measure acute changes, are invasive, or require euthanasia.

Methods:

In this study, high‐spatial and high‐temporal resolution x‐ray digital subtraction angiography (DSA) was used to obtain vasculature visualization, quantitative blood flow in absolute metrics (ml/min instead of arbitrary units or velocity), and relative blood volume dynamics from discrete regions of interest on a pixel‐by‐pixel basis .

Results:

A series of calibrations linked the DSA flow measurements to standard physiological measurement using thermodilution and Fick's method for cardiac output (CO), which in eight anesthetized Fischer‐344 rats was found to be. Phantom experiments were conducted to calibrate the radiographic density to vessel thickness, allowing a link of DSA cardiac output measurements to cardiopulmonary blood flow measurements in discrete regions of interest. The scaling factor linking relative DSA cardiac output measurements to the Fick's absolute measurements was found to be .

Conclusions:

This calibrated DSA approach allows repeated simultaneous visualization of vasculature and measurement of blood flow dynamics on a regional level in the living rat.
Accelerating Monte Carlo simulations of photon transport in a voxelized geometry using a massively parallel graphics processing unit
Authors: Badal Andreu , Badano Aldo
Published: October 2009

Purpose:

It is a known fact that Monte Carlo simulations of radiation transport are computationally intensive and may require long computing times. The authors introduce a new paradigm for the acceleration of Monte Carlo simulations: The use of a graphics processing unit (GPU) as the main computing device instead of a central processing unit (CPU).

Methods:

A GPU‐based Monte Carlo code that simulates photon transport in a voxelized geometry with the accurate physics models from PENELOPE has been developed using the CUDA™ programming model (NVIDIA Corporation, Santa Clara, CA).

Results:

An outline of the new code and a sample x‐ray imaging simulation with an anthropomorphic phantom are presented. A remarkable 27‐fold speed up factor was obtained using a GPU compared to a single core CPU.

Conclusions:

The reported results show that GPUs are currently a good alternative to CPUs for the simulation of radiation transport. Since the performance of GPUs is currently increasing at a faster pace than that of CPUs, the advantages of GPU‐based software are likely to be more pronounced in the future.
GAFCHROMIC® EBT photospectral dose response dependence on temperature and implications for flat bed scanning
Authors: Buchauer Konrad , Hillbrand Elmar , de Vries Alexander
Published: October 2009

Purpose:

Various forms of GAFCHROMIC® film have been used for several years as radiographic media for measuring dose distributions. GAFCHROMIC® EBT (GC‐EBT) film is particularly useful for clinical dose ranges. This thin film dosimeter develops a blue color ( approximately 635 nm) when irradiated with ionizing radiation.

Methods:

Temperature controlled photospectrometry was used to assess temperature related readout changes in GC‐EBT type film dosimetry. For observing clinical impact of findings, multiple scan studies with rising flat bed scanner temperature were performed.

Results:

The whole optical spectrum in the observed wavelength range of 450–700 nm shows a distinct spectrum shift linear with temperature toward lower wavelengths when readout temperature is increased. In addition, absorption decreases in maximum regions and increases in minimum regions of the absorbance spectrum. The most pronounced wavelength dependent readout differences occur in the slopes of the spectrum curves. Absorption readout differences of −1%/°C for a 2.7 Gy irradiated film piece at a readout wavelength of approximately 650 nm can be found. The readout difference is strongly dependent on readout light spectral characteristic, irradiation dose, and temperature. Readout difference can be positive or negative. Characteristic temperature behavior patterns are present for each color channel of a flat bed scanner. All described effects are reversible within the measurement accuracy of this study.

Conclusions:

When using unsuitable readout light, careful control of the readout temperature is necessary in order to obtain consistent and accurate results. Adapted GC‐EBT type film dosimetry guidelines are presented. Temperature dependent readout differences on a flat bed scanner can be avoided when using scanner bed temperature as a fixed dosimetry parameter.
Discrete beta dose kernel matrices for nuclides applied in targeted radionuclide therapy (TRT) calculated with MCNP5
Authors: Reiner Dora , Blaickner Matthias , Rattay Frank
Published: October 2009

Purpose:

Radiopharmaceuticals administered in targeted radionuclide therapy (TRT) rely to a great extent not only on beta‐emitting nuclides but also on emitters of monoenergetic electrons. Recent advances like combined PET/CT devices, the consequential coregistration of both data, the concept of using beta couples for diagnosis and therapy, respectively, as well as the development of voxel models offer a great potential for developing TRT dose calculation systems similar to those available for external beam treatment planning. The deterministic algorithms in question for this task are based on the convolution of three‐dimensional matrices, one representing the activity distribution and the other the dose point kernel. This study aims to report on three‐dimensional kernel matrices for various nuclides used in TRT.

Methods:

The Monte Carlo code MCNP5 was used to calculate discrete dose kernels of beta particles including the contributions from their respective secondary radiation in soft tissue for the following nuclides: , , , , , , , , , and . For each nuclide a kernel cube of was calculated, the dimensions of a voxel being . Additional kernels with voxel sizes of were simulated.

Results:

Comparison with the‐value data regarding , , , and of the MIRD committee which were calculated with the EGS4 code showed a very good agreement, the secondary particle transport of being the only exception. Documented analytical kernels on the other side show deviations very close and very far to the source.

Conclusions:

The good accordance with the only discrete dose kernels published up to date justifies the method chosen. Together with the additional six nuclides, this report provides a considerable database for three‐dimensional kernel matrices with regard to beta radionuclides applied in TRT. In contrast to analytical dose point kernels, the discrete kernels elude the problem of overestimation near the source and take energy depositions into account, which occur beyond the range of the continuous‐slowing‐down approximation (csda range). Recalculation of the kernels to other dose kernels with varying voxel dimensions, cubic or noncubic, is shown to be easily manageable and thereby provides a resolution‐independent system of dose calculation.
X‐ray energy optimization in minibeam radiation therapy
Authors: Prezado Y. , Thengumpallil S. , Renier M. , Bravin A.
Published: October 2009

Purpose:

The purpose of this work is to assess which energy in minibeam radiation therapy provides the best compromise between the deposited dose in the tumor and the sparing of the healthy tissues.

Methods:

Monte Carlo simulations (PENELOPE 2006) have been used as a method to calculate the ratio of the peak‐to‐valley doses (PVDR) in the healthy tissues and in the tumor for different beam energies. The maximization of the ratio of PVDR in the healthy tissues and in the tumor has been used as a criterion.

Results:

The main result of this work is that, for the parameters being used in preclinical trials (minibeam sizes of and center‐to‐center separation), the optimum beam energy is 375 keV.

Conclusions:

The conclusion is that this is the energy of minibeams that should be used in the preclinical studies.
IMRT commissioning: Multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119
Authors: Ezzell Gary A. , Burmeister Jay W. , Dogan Nesrin , LoSasso Thomas J. , Mechalakos James G. , Mihailidis Dimitris , Molineu Andrea , Palta Jatinder R. , Ramsey Chester R. , Salter Bill J. , Shi Jie , Xia Ping , Yue Ning J. , Xiao Ying
Published: October 2009

AAPM Task Group 119 has produced quantitative confidence limits as baseline expectation values for IMRT commissioning. A set of test cases was developed to assess the overall accuracy of planning and delivery of IMRT treatments. Each test uses contours of targets and avoidance structures drawn within rectangular phantoms. These tests were planned, delivered, measured, and analyzed by nine facilities using a variety of IMRT planning and delivery systems. Each facility had passed the Radiological Physics Center credentialing tests for IMRT. The agreement between the planned and measured doses was determined using ion chamber dosimetry in high and low dose regions, film dosimetry on coronal planes in the phantom with all fields delivered, and planar dosimetry for each field measured perpendicular to the central axis. The planar dose distributions were assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop confidence limits for the test results using the concept . Other facilities can use the test protocol and results as a basis for comparison to this group. Locally derived confidence limits that substantially exceed these baseline values may indicate the need for improved IMRT commissioning.
Comparing the accuracy of four‐dimensional photon dose calculations with three‐dimensional calculations using moving and deforming phantoms
Authors: Vinogradskiy Yevgeniy Y. , Balter Peter , Followill David S. , Alvarez Paola E. , White R. Allen , Starkschall George
Published: October 2009

Purpose:

Four‐dimensional (4D) dose calculation algorithms, which explicitly incorporate respiratory motion in the calculation of doses, have the potential to improve the accuracy of dose calculations in thoracic treatment planning; however, they generally require greater computing power and resources than currently used for three‐dimensional (3D) dose calculations. The purpose of this work was to quantify the increase in accuracy of 4D dose calculations versus 3D dose calculations.

Methods:

The accuracy of each dose calculation algorithm was assessed using measurements made with two phantoms. Specifically, the authors used a rigid moving anthropomorphic thoracic phantom and an anthropomorphic thoracic phantom with a deformable lung insert. To incorporate a clinically relevant range of scenarios, they programed the phantoms to move and deform with two motion patterns: A sinusoidal motion pattern and an irregular motion pattern that was extracted from an actual patient's breathing profile. For each combination of phantom and motion pattern, three plans were created: A single‐beam plan, a multiple‐beam plan, and an intensity‐modulated radiation therapy plan. Doses were calculated using 4D dose calculation methods as well as conventional 3D dose calculation methods. The rigid moving and deforming phantoms were irradiated according to the three treatment plans and doses were measured using thermoluminescent dosimeters (TLDs) and radiochromic film. The accuracy of each dose calculation algorithm was assessed using measured‐to‐calculated TLD doses and a analysis.

Results:

No significant differences were observed between the measured‐to‐calculated TLD ratios among 4D and 3D dose calculations. The results revealed that 4D dose calculations had significantly greater percentage of pixels passing the criteria than 3D dose calculations.

Conclusions:

These results indicate no significant differences in the accuracy between the 4D and the 3D dose calculation methods inside the gross tumor volume. On the other hand, the film results demonstrated that the 4D dose calculations provided greater accuracy than 3D dose calculations in heterogeneous dose regions. The increase in accuracy of the 4D dose calculations was evident throughout the planning target volume.
Skeletal dosimetry for external exposures to photons based on images of spongiosa: Consideration of voxel resolution, cluster size, and medullary bone surfaces
Authors: Kramer R. , Khoury H. J. , Vieira J. W. , Brown K. A. Robson
Published: October 2009

Skeletal dosimetry based onimages of trabecular bone has recently been introduced to calculate the red bone marrow (RBM) and the bone surface cell (BSC) equivalent doses in human phantoms for external exposure to photons. In order to use theimages for skeletal dosimetry, spongiosa voxels in the skeletons were replaced at run time by so‐called micromatrices, which have exactly the size of a spongiosa voxel and contain segmented trabecular bone and marrow microvoxels. A clusterofmicromatrices was used systematically and periodically throughout the spongiosa volume during the radiation transport calculation. Systematic means that when a particle leaves a spongiosa voxel to enter into a neighboring spongiosa voxel, then the next micromatrix in the cluster will be used. Periodical means that if the particle travels through more than two spongiosa voxels in a row, then the cluster will be repeated. Based on the bone samples available at the time, clusters of up tomicromatrices were studied. While for a given trabecular bone volume fraction the whole‐body RBM equivalent dose showed converging results for cluster sizes between 8 and 27 micromatrices, this was not the case for the BSC equivalent dose. The BSC equivalent dose seemed to be very sensitive to the number, form, and thickness of the trabeculae. In addition, the cluster size and/or the microvoxel resolution were considered to be possible causes for the differences observed. In order to resolve this problem, this study used a bone sample large enough to extract clusters containing up tomicromatrices and which was scanned with two different voxel resolutions. Taking into account a recent proposal, this investigation also calculated the BSC equivalent dose on medullary surfaces of cortical bone in the arm and leg bones. The results showed (1) that different voxel resolutions have no effect on the RBM equivalent dose but do influence the BSC equivalent dose due to voxel effects by up to 5% for incident photon energies up to 200 keV, (2) that the whole‐body BSC equivalent dose calculated with a cluster withmicromatrices is consistent with results received with clusters of up tomicromatrices, and (3) that for external whole‐body exposure the inclusion of the BSC on medullary surfaces of cortical bone has a negligible effect on the whole‐body BSC equivalent dose.