bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric Fin Array Optimization for Radial Flux Machines Considering Time Varying Loads
Authors: Semidey S. Andrew , Mayor J. Rhett
Published: March 2011

This work utilizes a novel, generic, thermal model of an electric machine in conjunction with particle swarm optimization to optimize the electric machine’s fin array considering time varying loads. The maximum power rating on radial-flux electrical machines is typically based on the steady state temperature of the windings. This leads to over designs in applications in which only short periods of high power are required. The proposed optimization technique can be used in the design process to reduce the risk of over design therefore leading to reduced material costs for finned frames and increased power density in radial flux machines. Whilst many numerical optimization techniques exist, this paper will consider the application of particle swarm optimization techniques to optimize the fin array parameters. The parameter space to be investigated will consider the fin height (hf), fin width (wf), and fin spacing (sf).
Design of Miniature Liquid Cooler for LED
Authors: So̸rensen Henrik , Bertel So̸ren N.
Published: March 2011

An investigation of the average heat transfer coefficient in a heat exchanger for cooling of light-emitting diodes has been carried out by using CFD. The numerical calculations show good agreements with experimentally obtained data on a full scale model. Both CFD and experiments are carried out for Reynolds numbers in the range of 1000 to 10000, where the resulting average heat transfer coefficient is up to 5 times higher than expected values based on classical analytical expressions for the heat transfer coefficient. The explanation for the significant increase in the average heat transfer coefficient shall be found in a relative short tube length combined with a strong swirling flow inside the heat exchanger.
Scaling Laws for Electrohydrodynamic Air Movers
Authors: Jewell-Larsen Nels E. , Joseph Gustavo G. , Honer Kenneth A.
Published: March 2011

As modern electronic devices become more compact and capable, device cooling has become critical not only for the reliability and stability of the electronic circuitry, but also for the comfort of the user. Forced convection can be effective at removing heat to the ambient environment. However, considerable implementation challenges remain for cooling solution thicknesses below 6mm, where the height of rotary fans is a limiting factor. While scaling laws for fans have been previously reported in the literature, the scaling rules for electrohydrodynamic (EHD) air movers have not been widely studied. This paper explores the impact of thickness, width, and input power on pressure and airflow of EHD air movers using coupled-physics modeling, with experimental validation of the results. Device thicknesses were in the 2 to 6mm range, device widths in the 10 to 100mm range, and input powers between 0.25W and 2.5W.
A Parametric Study on Fluid Flow and Heat Transfer in a Printed Circuit Heat Exchanger
Authors: Lee Sang-Moon , Kim Kwang-Yong
Published: March 2011

Numerical analyses for pressure drop and heat transfer in the flow channels of a printed circuit heat exchanger have been performed numerically. Three-dimensional Reynolds-averaged Navier-Stokes equations have been solved in conjunction with the shear stress transport model as a turbulence closure. The numerical solutions are validated with the available experimental results of the reference shape. The effects of two design parameters, namely, the channel angle and the ellipse aspect ratio of the cold channel, on the heat transfer and the friction performance have been evaluated.
Micro and Extended-Nano Fluidics on Microchip for Chemistry and Biomedical Applications
Authors: Kitamori Takehiko
Published: March 2011

The world first calculator was consisted of 17,000 vacuum tubes and huge in size. But now, a laptop computer is much smaller and superior in performance due to the invention of IC in place of vacuum tubes. The micro chemical chips which integrate the functions of chemical operations on microchips have enabled chemical instruments and chemical plants to be miniaturized. For this purpose, we have brought the same concept of IC into the chemical instruments. In place of resistor, capacitor, and diode in IC, mixing, extraction, phase separation, and other unit operation of chemical processes are integrated onto a glass or plastic microchips (Figure 1). These unit operations in a microchip are named as micro unit operations, MUO. These MUO can be combined each others so freely, and a chemical process can be constructed like a electronic circuit (Figure 2). This micro chemical systems is named as continuous flow chemical processing, CFCP.
Role of Interface Thermal Boundary Resistance, Straining and Morphology in Thermal Conductivity of a Set of Si-Ge Superlattices and Biomimetic Si-Ge Nanocomposites
Authors: Samvedi Vikas , Tomar Vikas
Published: March 2011

Nanoscale engineered materials with tailored thermal properties are desirable for applications such as highly efficient thermoelectric, microelectronic and optoelectronic devices. It has been shown earlier that by judiciously varying interface thermal boundary resistance (TBR) thermal conductivity in nanostructures could be controlled. Two types of nanostructures that have gained significant attention owing to the presence of TBR are superlattices and nanocomposites. A systematic comparison of thermal behavior of superlattices and nanocomposites considering their characteristic structural factors such as periodicity and period length for superlattices, and morphology for nanocomposites, under different extents of straining at a range of temperatures remains to be performed. In this presented work, such analyses are performed for a set of Si-Ge superlattices and Si-Ge biomimetic nanocomposites using non-equilibrium molecular dynamics (NEMD) simulations at three different temperatures (400 K, 600 K, and 800 K) and at strain levels varying between −10% and 10%. The analysis of interface TBR contradicts the usual notion that each interface contributes equally to the heat transfer resistance in a layered structure. The dependence of thermal conductivity of superlattice on the direction of heat flow gives it a characteristic somewhat similar to a thermal diode as found in this study. The comparison of thermal behavior of superlattices and nanocomposites indicate that the nanoscale morphology differences between the superlattices and the nanocomposites lead to a striking contrast in the phonon spectral density, interfacial thermal boundary resistance, and thermal conductivity. Both compressive and tensile strains are observed to be important factors in tailoring the thermal conductivity of the analyzed superlattices, whereas have very insignificant influence on the thermal conductivity of the analyzed nanocomposites.
Thermal Conductivity Affected by Temperature and Particle Size in Al2O3-Water Nanofluids
Authors: Kwek D. , Crivoi A. , Duan Fei
Published: March 2011

The effective thermal conductivity of Al2O3-water nanofluids has been measured using a transient hot wire method. Experimental results demonstrate that the thermal conductivity of Al2O3 nanofluids increases linearly with increasing nanoparticle concentration. Adding 5 vol % of Al2O3 nanoparticles in water increases the effective thermal conductivity of the nanofluids by 20%. Thermal conductivity of Al2O3 nanofluids increases with an increase of temperature. The enhancement is around 1.7% at 15 °C in comparison with around 16% at 55 °C in a 1 vol % nanofluid. The particle size is another important parameter for the effective thermal conductivity. The increase of thermal conductivity reduces from 30% to 10% as the particle sizes increase from 10 nm to 35 nm. The increase of the effective thermal conductivity starts as the particle size increases above 35 nm, reaching about 27.5% in the nanofluid with the particle size at 150 nm.
Development of a Compact Micro Pulsating Heat Pipe
Authors: Youn Young Jik , Kim Sung Jin
Published: March 2011

A compact micro pulsating heat pipe was developed and tested to investigate thermal performance. Micro Flat Plate Pulsating Heat Pipe (FP-PHP) was fabricated using DRIE MEMS technique. A total of 10 parallel interconnected rectangular channels forming a meandering closed loop are engraved on the silicon wafer with a thickness of 1 mm. The top of the silicon wafer was covered by a transparent glass plate (#7740PyrexTM) with a thickness of 0.5 mm to allow visualization of the internal thermo-hydrodynamic behavior in the PHP. The overall FP-PHP has length of 50 mm, width of 15.5 mm, and thickness of 1.5 mm, respectively. The width and height of the engraved rectangular channel is 1 mm and 0.6 mm and the hydraulic diameter is 0.75 mm. The ethanol is used for working fluid. The results show that the FP-PHP without working fluid has thermal resistance of 17 °C/W and the FP-PHP with working fluid of filling ratio of 50% has thermal resistance of 4 °C/W. In other words, the FP-PHP has effective thermal conductivity of 650 W/mK which is about 1.6 times as much as of that of the Copper (keff = 400 W/mK). Therefore the developed FP-PHP can be used as compact high performance electronic cooling system.
Characterization of a Dual Chambered Two Phase Separator
Authors: Klein Casey , Kurwitz Cable , Best Frederick
Published: March 2011

Fuel cells have been used as a power source in the space shuttle for decades and are expected to be used in future higher power, larger systems. A new, passive gas/liquid phase separator for use in such large fuel cell space applications has been invented. It is a vortex separator designed to accommodate gas driven two phase flows. The work presented here is a first of a kind study of this newly invented separator examining the minimum inlet gas flow rate necessary for a stable vortex inside the separator as a function of separator size. A dimensional scaling analysis was done to predict this minimum inlet gas flow rate. Experiments were performed on the ground and in conjunction with the NASA microgravity simulating aircraft to validate modeling. The results of the experiments and scaling analysis are compared.
Dosimetry tools and techniques for IMRT
Authors: Low Daniel A. , Moran Jean M. , Dempsey James F. , Dong Lei , Oldham Mark
Published: March 2011

Intensity modulated radiation therapy (IMRT) poses a number of challenges for properly measuring commissioning data and quality assurance (QA) radiation dose distributions. This report provides a comprehensive overview of how dosimeters, phantoms, and dose distribution analysis techniques should be used to support the commissioning and quality assurance requirements of an IMRT program. The proper applications of each dosimeter are described along with the limitations of each system. Point detectors, arrays, film, and electronic portal imagers are discussed with respect to their proper use, along with potential applications of 3D dosimetry. Regardless of the IMRT technique utilized, some situations require the use of multiple detectors for the acquisition of accurate commissioning data. The overall goal of this task group report is to provide a document that aids the physicist in the proper selection and use of the dosimetry tools available for IMRT QA and to provide a resource for physicists that describes dosimetry measurement techniques for purposes of IMRT commissioning and measurement‐based characterization or verification of IMRT treatment plans. This report is not intended to provide a comprehensive review of commissioning and QA procedures for IMRT. Instead, this report focuses on the aspects of metrology, particularly the practical aspects of measurements that are unique to IMRT. The metrology of IMRT concerns the application of measurement instruments and their suitability, calibration, and quality control of measurements. Each of the dosimetry measurement tools has limitations that need to be considered when incorporating them into a commissioning process or a comprehensive QA program. For example, routine quality assurance procedures require the use of robust field dosimetry systems. These often exhibit limitations with respect to spatial resolution or energy response and need to themselves be commissioned against more established dosimeters. A chain of dosimeters, from secondary standards to field instruments, is established to assure the quantitative nature of the tests. This report is intended to describe the characteristics of the components of these systems; dosimeters, phantoms, and dose evaluation algorithms. This work is the report of AAPM Task Group 120.
The neutron dose equivalent evaluation and shielding at the maze entrance of a Varian Clinac 23EX treatment room
Authors: Wang Xudong , Esquivel Carlos , Nes Elena , Shi Chengyu , Papanikolaou Nikos , Charlton Michael
Published: March 2011

Purpose:

To evaluate the neutron and photon dose equivalent rate ( and ) at the outer maze entrance and the adjacent treatment console area after the installation of a Varian Clinac 23EX accelerator with a higher beam energy than its predecessor. The evaluation was based on measurements and comparison with several empirical calculations. The effectiveness of borated polyethylene (BPE) boards, as a maze wall lining material, on neutron dose and photon dose reduction is also reported.

Methods:

A single energy Varian 6 MV photon linear accelerator (linac) was replaced with a Varian Clinac 23EX accelerator capable of producing 18 MV photons in a vault originally designed for the former accelerator. In order to evaluate and redesign the shielding of the vault, the neutron dose equivalent was measured using an Andersson–Braun neutron Rem meter and the photon dose equivalent was measured using a Geiger Müller and an ion chamber ‐ray survey meter at the outer maze entrance. The measurement data were compared to semiempirical calculations such as the Kersey method, the modified Kersey method, and a newly proposed method by Falcão et al. Additional measurements were taken after BPE boards were installed on the maze walls as a neutron absorption lining material.

Results:

With the gantry head tilted close to the inner maze entrance and with the jaws closed, both neutron dose equivalent and photon dose equivalent reached their maximum. Compared to the measurement results, the Kersey method overestimates the neutron dose equivalent by about two to four times (calculation/measurement ). Falcão's method largely overestimates the (calculation/measurement ). The modified Kersey method has a calculation to measurement ratio about 0.6–0.9. The photon dose equivalent calculation including McGinley's capture gamma dose equivalent equation estimates about 77%–98% of the measurement. After applying BPE boards as a lining material on the inner corner of the maze wall, the and the at maze entrance were decreased by 41% and 59%, respectively.

Conclusions:

This work indicates that the Kersey method overestimates the neutron dose equivalent for a Varian Clinac 23EX accelerator. The Falcão method overestimates the partially due to the discrepancy in the International Commission on Radiological Protection (ICRP) conversion factors caused by the uncertainties of the estimated average neutron energy. The modified Kersey method gives the closest estimation of a Varian Clinac 23EX accelerator operated at 18 MV photon mode in a maze with a similar design as in the authors' study. However, it should be used with caution because of its tendency to underestimate the . A borated polyethylene lining can provide a cost effective method to reduce neutron and photon dose equivalent at the maze door for an existing linac vault, following the installation of a higher energy linac.
Validation of SPAMM tagged MRI based measurement of 3D soft tissue deformation
Authors: Moerman Kevin M. , Sprengers Andre M. J. , Simms Ciaran K. , Lamerichs Rolf M. , Stoker Jaap , Nederveen Aart J.
Published: March 2011

Purpose:

This study presents and validates a novel (non‐ECG‐triggered) MRI sequence based on spatial modulation of the magnetization (SPAMM) to noninvasively measure 3D (quasistatic) soft tissue deformations using only six acquisitions (three static and three indentations). In the current SPAMM tagged MRI approaches, data are typically constructed from many repeated motion cycles. This has so far restricted its application to the measurement of highly repeatable and periodic movements (e.g., cardiac deformation). In biomechanical applications where soft tissue deformation is artificially induced, often by indentation, significant repeatability constraints exist, and for clinical applications, discomfort and health issues generally preclude a large number of repetitions.

Methods:

A novel (non‐ECG‐triggered) SPAMM tagged MRI sequence is presented, whereby a single 1‐1 (first order) SPAMM set is acquired following a 3D transient field echo acquisition. Full 3D deformation measurement is achieved through the combination of only six acquisitions (three static and three motion cycles). The 3D deformation measurements were validated using quasistatic indentation tests and marker tracking in a silicone gel soft tissue phantom. In addition, the technique's ability to measure 3D soft tissue deformationin vivo was evaluated using indentation of the biceps region of the upper arm in a volunteer.

Results:

Following comparison to marker tracking in the silicone gel phantom, the SPAMM tagged MRI based displacement measurement demonstrated subvoxel accuracy with a mean displacement difference of and a standard deviation of . In addition, precision of displacement magnitude was evaluated for both the phantom and the volunteer data. The standard deviations of the displacement magnitude with respect to the average displacement magnitude were 75 and for the phantom and volunteer data, respectively.

Conclusions:

The subvoxel accuracy and precision demonstrated in the phantom in combination with the precision comparison between the phantom and the volunteer data provide confidence in the methods presented for measurement of soft tissue deformationin vivo. To the author's knowledge, since only six acquisitions are required, the presented methodology is the fastest SPAMM tagged MRI method currently available for the noninvasive measurement of quasistatic 3D soft tissue deformation.
Accurate Monte Carlo modeling and performance assessment of the X‐PET™ subsystem of the FLEX Triumph™ preclinical PET/CT scanner
Authors: Zeraatkar N. , Ay M. R. , Kamali‐Asl A. R. , Zaidi H.
Published: March 2011

Purpose:

X‐PET™ is a commercial small animal PET scanner incorporating several innovative designs to achieve improved performance. It is employed as a PET subsystem in the FLEX Triumph™ preclinical PET/CT scanner, the first commercial small animal PET/CT scanner worldwide. The authors report on a novel Monte Carlo (MC) model designed for the evaluation of performance parameters of the X‐PET™.

Methods:

The Geant4 Application for Tomographic Emission (GATE) MC code was used as a simulation tool. The authors implemented more accurate modeling of the geometry of detector blocks and associated electronic chains, including dead‐time and time‐independent parameters, compared to previously presented MC models of the X‐PET™ scanner. Validation of the MC model involved comparison between simulated and measured performance parameters of the X‐PET™, including spatial resolution, sensitivity, and noise equivalent count rate (NECR). Thereafter, various simulations were performed to assess scanner performance parameters according to NEMA NU 4‐2008 standards with the aim to present a reliable Monte Carlo platform for small animal PET scanner design optimization.

Results:

The average differences between simulated and measured results were 11.2%, 33.3%, and 9.1% for spatial resolution, sensitivity, and NECR, respectively. The average system absolute sensitivity was 2.7%. Furthermore, the peak true count rate, peak NECR, and scatter fraction were 2050 kcps, 1520 kcps, and 4.7%, respectively, for a mouse phantom and 1017 kcps, 469 kcps, and 18.2%, respectively, for a rat phantom. Spatial resolution was also measured in ten different positions at two axial locations. The radial, tangential, and axial FWHM ranged from 1.31 to 1.96 mm, 1.17 to 2.11 mm, and 1.77 to 2.44 mm, respectively, as the radial position varied from 0 to 25 mm at the centre of the axial field‐of‐view.

Conclusions:

The developed MC simulation platform provides a reliable tool for performance evaluation of small animal PET scanners and has the potential to be used in other applications such as detector design optimization, correction of image degrading factors such as randoms, scatter, intercrystal scatter, parallax error, and partial volume effect.
Low‐dose 4DCT reconstruction via temporal nonlocal means
Authors: Tian Zhen , Jia Xun , Dong Bin , Lou Yifei , Jiang Steve B.
Published: March 2011

Purpose:

Four‐dimensional computed tomography (4DCT) has been widely used in cancer radiotherapy for accurate target delineation and motion measurement for tumors in the thorax and upper abdomen areas. However, its prolonged scanning duration causes a considerable increase of radiation dose compared to conventional CT, which is a major concern in its clinical application. This work is to develop a new algorithm to reconstruct 4DCT images from undersampled projections acquired at low mA s levels in order to reduce the imaging dose.

Methods:

Conventionally, each phase of 4DCT is reconstructed independently using the filtered backprojection (FBP) algorithm. The basic idea of the authors' new algorithm is that by utilizing the common information among different phases, the input information required to reconstruct the image of high quality, and thus the imaging dose, can be reduced. The authors proposed a temporal nonlocal means (TNLM) method to explore the interphase similarity. All phases of the 4DCT images are reconstructed simultaneously by minimizing a cost function consisting of a data fidelity term and a TNLM regularization term. The authors utilized a modified forward‐backward splitting algorithm and a Gauss–Jacobi iteration method to efficiently solve the minimization problem. The algorithm was also implemented on a graphics processing unit (GPU) to improve the computational speed. The authors' reconstruction algorithm has been tested on a digital NCAT thorax phantom in three low dose scenarios: All projections with low mA s level, undersampled projections with high mA s level, and undersampled projections with low mA s level.

Results:

In all three low dose scenarios, the new algorithm generates visually much better CT images containing less image noise and streaking artifacts compared to the standard FBP algorithm. Quantitative analysis shows that by comparing the authors' TNLM algorithm to the standard FBP algorithm, the contrast‐to‐noise ratio has been improved by a factor of 3.9–10.2 and the signal‐to‐noise ratio has been improved by a factor of 2.1–5.9, depending on the cases. In the situation of undersampled projection data, the majority of the streaks in the images reconstructed by FBP can be suppressed using the authors' algorithm. The total reconstruction time for all ten phases of a slice ranges from 40 to 90 s on an NVIDIA Tesla C1060 GPU card.

Conclusions:

The experimental results indicate that the authors' new algorithm outperforms the conventional FBP algorithm in effectively reducing the image artifacts due to undersampling and suppressing the image noise due to the low mA s level.
Dynamic estimation of three‐dimensional cerebrovascular deformation from rotational angiography
Authors: Zhang Chong , Villa‐Uriol Maria‐Cruz , De Craene Mathieu , Pozo José María , Macho Juan M. , Frangi Alejandro F.
Published: March 2011

Purpose:

The objective of this study is to investigate the feasibility of detecting and quantifying 3D cerebrovascular wall motion from a single 3D rotational x‐ray angiography (3DRA) acquisition within a clinically acceptable time and computing from the estimated motion field for the further biomechanical modeling of the cerebrovascular wall.

Methods:

The whole motion cycle of the cerebral vasculature is modeled using a 4D‐spline transformation, which is estimated from a 4D to image registration framework. The registration is performed by optimizing a single similarity metric between the entire measured projection sequence and the corresponding forward projections of the deformed volume at their exact time instants. The joint use of two acceleration strategies, together with their implementation on graphics processing units, is also proposed so as to reach computation times close to clinical requirements. For further characterizing vessel wall properties, an approximation of the wall thickness changes is obtained through a strain calculation.

Results:

Evaluation onin silico and in vitro pulsating phantom aneurysms demonstrated an accurate estimation of wall motion curves. In general, the error was below 10% of the maximum pulsation, even in the situation when substantial inhomogeneous intensity pattern was present. Experiments on in vivo data provided realistic aneurysm and vessel wall motion estimates, whereas in regions where motion was neither visible nor anatomically possible, no motion was detected. The use of the acceleration strategies enabled completing the estimation process for one entire cycle in 5–10 min without degrading the overall performance. The strain map extracted from our motion estimation provided a realistic deformation measure of the vessel wall.

Conclusions:

The authors' technique has demonstrated that it can provide accurate and robust 4D estimates of cerebrovascular wall motion within a clinically acceptable time, although it has to be applied to a larger patient population prior to possible wide application to routine endovascular procedures. In particular, for the first time, this feasibility study has shown thatin vivo cerebrovascular motion can be obtained intraprocedurally from a 3DRA acquisition. Results have also shown the potential of performing strain analysis using this imaging modality, thus making possible for the future modeling of biomechanical properties of the vascular wall.
Real‐time verification of multileaf collimator‐driven radiotherapy using a novel optical attenuation‐based fluence monitor
Authors: Goulet Mathieu , Gingras Luc , Beaulieu Luc
Published: March 2011

Purpose:

Multileaf collimator (MLC)‐driven conformal radiotherapy modalities [e.g., such as intensity‐modulated radiotherapy (IMRT), intensity‐modulated arc therapy, and stereotactic body radiotherapy] are more subject to delivery errors and dose calculation inaccuracies than standard modalities. Fluence monitoring during treatment delivery could reduce such errors by allowing an independent interface to quantify and assess measured difference between the delivered and planned treatment administration. We developed an optical attenuation‐based detector to monitor fluence for the on‐line quality control of radiotherapy delivery. The purpose of the current study was to develop the theoretical background of the invention and to evaluate the detector's performance both statistically and in clinical situations.

Methods:

We aligned 60 27‐cm scintillating fibers coupled to a photodetector via clear optical fibers in the direction of motion of each of the 60 leaf pairs of a 120 leaves Millenium MLC on a Varian Clinac iX. We developed a theoretical model to predict the intensity of light collected on each side of the scintillating fibers when placed under radiation fields of varying sizes, intensities, and positions. The model showed that both the central position of the radiation field on the fiber and the integral fluence passing through the fiber could be assessed independently in a single measurement. We evaluated the performance of the prototype by (1) measuring the intrinsic variation of the measured values of and , (2) measuring the impact on the measured values of and of random leaf positioning errors introduced into IMRT fields, and (3) comparing the predicted values of and calculated with the treatment planning software to the measured values of and in order to assess the predictive effectiveness of the developed theoretical model.

Results:

We observed a very low intrinsic dispersion, dominated by Poisson statistics, for both (standard deviations of less than 1 mm) and (standard deviations of less than 0.20%). When confronted with random leaf positioning errors from IMRT segments, was highly sensitive to single leaf positioning errors as small as 1 mm at isocenter, while was sensitive to leaf pair translation errors of at least 2 mm at isocenter. Owing to the uncertainties in the doses calculated in regions of high perpendicular dose gradients, the measured values of and deviated from the predicted values of and by a mean of 1.3 mm and 2.6%, respectively.

Conclusion:

Our study showed that an optical attenuation‐based detector can be used to effectively monitor integral fluence during radiotherapy delivery. The performance of such a system would enable real‐time quality control of the incident fluence in current MLC‐driven treatments such as IMRT and future adaptive radiotherapy procedures where new treatment plans will have to be delivered without passing thru the current standard quality control chain.
Experimental validation of a method characterizing bow tie filters in CT scanners using a real‐time dose probe
Authors: McKenney Sarah E. , Nosratieh Anita , Gelskey Dale , Yang Kai , Huang Shin‐ying , Chen Lin , Boone John M.
Published: March 2011

Purpose:

Beam‐shaping or “bow tie” (BT) filters are used to spatially modulate the x‐ray beam in a CT scanner, but the conventional method of step‐and‐shoot measurement to characterize a beam's profile is tedious and time‐consuming. The theory for characterization of bow tie relative attenuation (COBRA) method, which relies on a real‐time dosimeter to address the issues of conventional measurement techniques, was previously demonstrated using computer simulations. In this study, the feasibility of the COBRA theory is further validated experimentally through the employment of a prototype real‐time radiation meter and a known BT filter.

Methods:

The COBRA method consisted of four basic steps: (1) The probe was placed at the edge of a scanner's field of view; (2) a real‐time signal train was collected as the scanner's gantry rotated with the x‐ray beam on; (3) the signal train, without a BT filter, was modeled using peak values measured in the signal train of step 2; and (4) the relative attenuation of the BT filter was estimated from filtered and unfiltered data sets. The prototype probe was first verified to have an isotropic and linear response to incident x‐rays. The COBRA method was then tested on a dedicated breast CT scanner with a custom‐designed BT filter and compared to the conventional step‐and‐shoot characterization of the BT filter. Using basis decomposition of dual energy signal data, the thickness of the filter was estimated and compared to the BT filter's manufacturing specifications. The COBRA method was also demonstrated with a clinical whole body CT scanner using the body BT filter. The relative attenuation was calculated at four discrete x‐ray tube potentials and used to estimate the thickness of the BT filter.

Results:

The prototype probe was found to have a linear and isotropic response to x‐rays. The relative attenuation produced from the COBRA method fell within the error of the relative attenuation measured with the step‐and‐shoot method. The BT filter thickness estimates resulting from the dual energy scans on the breast CT system were equivalent to the manufacturing specifications. The clinical CT evaluation produced data conceptually similar to previous computer simulations and plausible relative attenuation profiles were observed.

Conclusions:

The COBRA method is a fast and accurate method for BT filter characterization, which requires a simple experimental setup in a clinical environment. Because of the ease of data acquisition, multienergy scans can be acquired which allow characterization of the BT filter thickness.
Direct intratumoral infusion of liposome encapsulated rhenium radionuclides for cancer therapy: Effects of nonuniform intratumoral dose distribution
Authors: Hrycushko Brian A. , Li Shihong , Goins Beth , Otto Randal A. , Bao Ande
Published: March 2011

Purpose:

Focused radiation therapy by direct intratumoral infusion of lipid nanoparticle (liposome)‐carried beta‐emitting radionuclides has shown promising results in animal model studies; however, little is known about the impact the intratumoral liposomal radionuclide distribution may have on tumor control. The primary objective of this work was to investigate the effects the intratumoral absorbed dose distributions from this cancer therapy modality have on tumor control and treatment planning by combining dosimetric and radiobiological modeling within vivo imaging data.

Methods:

‐encapsulated liposomes were intratumorally infused with a single injection location to human head and neck squamous cell carcinoma xenografts in nude rats. High resolution in vivo planar imaging was performed at various time points for quantifying intratumoral retention following infusion. The intratumoral liposomal radioactivity distribution was obtained from 1 mm resolution pinhole collimator SPECT imaging coregistered with CT imaging of excised tumors at 20 h postinfusion. Coregistered images were used for intratumoral dosimetric and radiobiological modeling at a voxel level following extrapolation to the therapeutic analogs, liposomes. Effective uniform dose (EUD) and tumor control probability (TCP) were used to assess therapy effectiveness and possible methods of improving upon tumor control with this radiation therapy modality.

Results:

Dosimetric analysis showed that average tumor absorbed doses of 8.6 Gy/MBq (318.2 Gy/mCi) and 5.7 Gy/MBq (209.1 Gy/mCi) could be delivered with this protocol of radiation delivery for liposomes, respectively, and 37–92 MBq (1–2.5 mCi)/g tumor administered activity; however, large intratumoral absorbed dose heterogeneity, as seen in dose‐volume histograms, resulted in insignificant values of EUD and TCP for achieving tumor control. It is indicated that the use of liposomes encapsulating radionuclides with higher energy beta emissions, dose escalation through increased specific activity, and increasing the number of direct tumor infusion sites improve tumor control. For larger tumors, the use of multiple infusion locations was modeled to be much more efficient, in terms of activity usage, at improving EUD and TCP to achieve a tumoricidal effect.

Conclusions:

Direct intratumoral infusion of beta‐emitting radionuclide encapsulated liposomes shows promise for cancer therapy by achieving large focally delivered tumor doses. However, the results of this work also indicate that average tumor dose may underestimate tumoricidal effect due to substantial heterogeneity in intratumoral liposomal radionuclide distributions. The resulting intratumoral distribution of liposomes following infusion should be taken into account in treatment planning and evaluation in a clinical setting for an optimal cancer therapy.
Using an EPID for patient‐specific VMAT quality assurance
Authors: Bakhtiari M. , Kumaraswamy L. , Bailey D. W. , de Boer S. , Malhotra H. K. , Podgorsak M. B.
Published: March 2011

Purpose:

A patient‐specific quality assurance (QA) method was developed to verify gantry‐specific individual multileaf collimator (MLC) apertures (control points) in volumetric modulated arc therapy (VMAT) plans using an electronic portal imaging device (EPID).

Methods:

VMAT treatment plans were generated in an Eclipse treatment planning system (TPS). DICOM images from a Varian EPID (aS1000) acquired in continuous acquisition mode were used for pretreatment QA. Each cine image file contains the grayscale image of the MLC aperture related to its specific control point and the corresponding gantry angle information. The TPS MLC file of this RapidArc plan contains the leaf positions for all 177 control points (gantry angles). In‐house software was developed that interpolates the measured images based on the gantry angle and overlays them with the MLC pattern for all control points. The 38% isointensity line was used to define the edge of the MLC leaves on the portal images. The software generates graphs and tables that provide analysis for the number of mismatched leaf positions for a chosen distance to agreement at each control point and the frequency in which each particular leaf mismatches for the entire arc.

Results:

Seven patients plans were analyzed using this method. The leaves with the highest mismatched rate were found to be treatment plan dependent.

Conclusions:

This in‐house software can be used to automatically verify the MLC leaf positions for all control points of VMAT plans using cine images acquired by an EPID.
Validation for 2D/3D registration I: A new gold standard data set
Authors: Pawiro S. A. , Markelj P. , Pernuš F. , Gendrin C. , Figl M. , Weber C. , Kainberger F. , Nöbauer‐Huhmann I. , Bergmeister H. , Stock M. , Georg D. , Bergmann H. , Birkfellner W.
Published: March 2011

Purpose:

In this article, the authors propose a new gold standard data set for the validation of two‐dimensional/three‐dimensional (2D/3D) and 3D/3D image registration algorithms.

Methods:

A gold standard data set was produced using a fresh cadaver pig head with attached fiducial markers. The authors used several imaging modalities common in diagnostic imaging or radiotherapy, which include 64‐slice computed tomography (CT), magnetic resonance imaging using Tl, T2, and proton density sequences, and cone beam CT imaging data. Radiographic data were acquired using kilovoltage and megavoltage imaging techniques. The image information reflects both anatomy and reliable fiducial marker information and improves over existing data sets by the level of anatomical detail, image data quality, and soft‐tissue content. The markers on the 3D and 2D image data were segmented usingANALYZE 10.0 (AnalyzeDirect, Inc., Kansas City, KN) and an in‐house software.

Results:

The projection distance errors and the expected target registration errors over all the image data sets were found to be less than 2.71 and 1.88 mm, respectively.

Conclusions:

The gold standard data set, obtained with state‐of‐the‐art imaging technology, has the potential to improve the validation of 2D/3D and 3D/3D registration algorithms for image guided therapy.
Calibration of helical tomotherapy machine using EPR/alanine dosimetry
Authors: Perichon Nicolas , Garcia Tristan , François Pascal , Lourenço Valérie , Lesven Caroline , Bordy Jean‐Marc
Published: March 2011

Purpose:

Current codes of practice for clinical reference dosimetry of high‐energy photon beams in conventional radiotherapy recommend using a square field, with the detector at a reference depth of 10 cm in water and 100 cm source to surface distance (SSD) (AAPM TG‐51) or 100 cm source‐to‐axis distance (SAD) (IAEA TRS‐398). However, the maximum field size of a helical tomotherapy (HT) machine is defined at 85 cm SAD. These nonstandard conditions prevent a direct implementation of these protocols. The purpose of this study is twofold: To check the absorbed dose in water and dose rate calibration of a tomotherapy unit as well as the accuracy of the tomotherapy treatment planning system (TPS) calculations for a specific test case.

Method:

Both topics are based on the use of electron paramagnetic resonance (EPR) using alanine as transfer dosimeter between the Laboratoire National Henri Becquerel (LNHB) reference beam and the Institut Curie's HT beam. Irradiations performed in the LNHB reference beam allowed setting up the calibration method, which was then implemented and tested at the LNHB 6 MV linac x‐ray beam, resulting in a deviation of 1.6% (at a 1% standard uncertainty) relative to the reference value determined with the standard IAEA TRS‐398 protocol.

Results:

HT beam dose rate estimation shows a difference of 2% with the value stated by the manufacturer at a 2% standard uncertainty. A 4% deviation between measured dose and the calculation from the tomotherapy TPS was found. The latter was originated by an inadequate representation of the phantom CT‐scan values and, consequently, mass densities within the phantom. This difference has been explained by the mass density values given by the CT‐scan and used by the TPS which were not the true ones. Once corrected using Monte Carlo N‐Particle simulations to validate the accuracy of this process, the difference between corrected TPS calculations and alanine measured dose values was then found to be around 2% (with 2% standard uncertainty on TPS doses and 1.5% standard uncertainty on EPR measurements).

Conclusion:

Beam dose rate estimation results were found to be in good agreement with the reference value given by the manufacturer at 2% standard uncertainty. Moreover, the dose determination method was set up with a deviation around 2% (at a 2% standard uncertainty).
Optimizing magnetite nanoparticles for mass sensitivity in magnetic particle imaging
Authors: Ferguson R. Matthew , Minard Kevin R. , Khandhar Amit P. , Krishnan Kannan M.
Published: March 2011

Purpose:

Magnetic particle imaging (MPI), using magnetite nanoparticles (MNPs) as tracer material, shows great promise as a platform for fast tomographic imaging. To date, the magnetic properties of MNPs used in imaging have not been optimized. As nanoparticle magnetism shows strong size dependence, the authors explore how varying MNP size impacts imaging performance in order to determine optimal MNP characteristics for MPI at any driving field frequency.

Methods:

Monodisperse MNPs of varying size were synthesized and their magnetic properties characterized. Their MPI response was measured experimentally using a custom‐built MPI transceiver designed to detect the third harmonic of MNP magnetization. The driving field amplitude and frequency were chosen to be suitable for imaging small animals. Experimental results were interpreted using a model of dynamic MNP magnetization that is based on the Langevin theory of superparamagnetism and accounts for sample size distribution and size‐dependent magnetic relaxation.

Results:

The experimental results show a clear variation in the MPI signal intensity as a function of MNP diameter that is in agreement with simulated results. A maximum in the plot of MPI signal vs MNP size indicates there is a particular size that is optimal for the chosen.

Conclusions:

The authors observed that MNPs 15 nm in diameter generate maximum signal amplitude in MPI experiments at 250 kHz. The authors expect the physical basis for this result, the change in magnetic relaxation with MNP size, will impact MPI under other experimental conditions.
Novel detector design for reducing intercell x‐ray cross‐talk in the variable resolution x‐ray CT scanner: A Monte Carlo study
Authors: Arabi Hosein , Asl Ali Reza Kamali , Ay Mohammad Reza , Zaidi Habib
Published: March 2011

Purpose:

The variable resolution x‐ray (VRX) CT scanner provides substantial improvement in the spatial resolution by matching the scanner's field of view (FOV) to the size of the object being imaged. Intercell x‐ray cross‐talk is one of the most important factors limiting the spatial resolution of the VRX detector. In this work, a new cell arrangement in the VRX detector is suggested to decrease the intercell x‐ray cross‐talk. The idea is to orient the detector cells toward the opening end of the detector.

Methods:

Monte Carlo simulations were used for performance assessment of the oriented cell detector design. Previously published design parameters and simulation results of x‐ray cross‐talk for the VRX detector were used for model validation using theGATE Monte Carlo package. In the first step, the intercell x‐ray cross‐talk of the actual VRX detector model was calculated as a function of the FOV. The obtained results indicated an optimum cell orientation angle of 28° to minimize the x‐ray cross‐talk in the VRX detector. Thereafter, the intercell x‐ray cross‐talk in the oriented cell detector was modeled and quantified.

Results:

The intercell x‐ray cross‐talk in the actual detector model was considerably high, reaching up to 12% at FOVs from 24 to 38 cm. The x‐ray cross‐talk in the oriented cell detector was less than 5% for all possible FOVs, except 40 cm (maximum FOV). The oriented cell detector could provide considerable decrease in the intercell x‐ray cross‐talk for the VRX detector, thus leading to significant improvement in the spatial resolution and reduction in the spatial resolution nonuniformity across the detector length.

Conclusions:

The proposed oriented cell detector is the first dedicated detector design for the VRX CT scanners. Application of this concept to multislice and flat‐panel VRX detectors would also result in higher spatial resolution.
Epp: A C++ EGSnrc user code for x‐ray imaging and scattering simulations
Authors: Lippuner Jonas , Elbakri Idris A. , Cui Congwu , Ingleby Harry R.
Published: March 2011

Purpose:

Easy particle propagation (Epp) is a user code for the EGSnrc code package based on theC++ class library egspp. A main feature of egspp (and Epp) is the ability to use analytical objects to construct simulation geometries. The authors developed Epp to facilitate the simulation of x‐ray imaging geometries, especially in the case of scatter studies. While direct use of egspp requires knowledge of C++, Epp requires no programming experience.

Methods:

Epp's features include calculation of dose deposited in a voxelized phantom and photon propagation to a user‐defined imaging plane. Projection images of primary, single Rayleigh scattered, single Compton scattered, and multiple scattered photons may be generated. Epp input files can be nested, allowing for the construction of complex simulation geometries from more basic components. To demonstrate the imaging features of Epp, the authors simulate 38 keV x rays from a point source propagating through a water cylinder 12 cm in diameter, using both analytical and voxelized representations of the cylinder. The simulation generates projection images of primary and scattered photons at a user‐defined imaging plane. The authors also simulate dose scoring in the voxelized version of the phantom in both Epp and DOSXYZnrc and examine the accuracy of Epp using the Kawrakow–Fippel test.

Results:

The results of the imaging simulations with Epp using voxelized and analytical descriptions of the water cylinder agree within 1%. The results of the Kawrakow–Fippel test suggest good agreement between Epp and DOSXYZnrc.

Conclusions:

Epp provides the user with useful features, including the ability to build complex geometries from simpler ones and the ability to generate images of scattered and primary photons. There is no inherent computational time saving arising from Epp, except for those arising from egspp's ability to use analytical representations of simulation geometries. Epp agrees with DOSXYZnrc in dose calculation, since they are both based on the well‐validated standard EGSnrc radiation transport physics model.