bluuebunny/crossref_metadata_2025 huggingface dataset:
Out-Of-Order Matrix Processor: Implementation and Performance Evaluation
Authors: Soliman Mostafa I. , Al-Junaid Abdulmajid F.
Published: December 2010

Mat-Core is a research processor aiming at exploiting the increasingly number of transistors per IC to improve the performance of a wide range of applications. It extends a general-purpose scalar processor with a matrix unit for processing vector/matrix data, where scalar and vector/matrix instructions are executed out-of-order. To hid memory latency, the extended matrix unit is decoupled into two components: address generation and data computation, which communicate through data queues and executed also out-of-order. Like vector architectures, the data computation unit is organized in parallel lanes. However, on parallel lanes, Mat-Core can execute scalar-matrix, vector-matrix, and matrix-matrix instructions in addition to scalar-vector and vector-vector instructions. By extending the well known scoreboard algorithm, these instructions are executed out-of-order on parallel pipelines. This paper describes the SystemC (system level modeling language) implementation of Mat-Core and evaluates its performance on vector and matrix kernels. On four parallel lanes and matrix registers of size 4×8 or 32 elements each, the performance of Mat-Core with queues size of 10, start up time of 6 clock cycles, and memory latency of 10 clock cycles, is about 1.4, 2.1, 4.2, 2.6, 4.2, and 6.4 FLOPs per clock cycle; achieved on scalar-vector multiplication, SAXPY, Givens, rank-1 update, vector-matrix multiplication, and matrix-matrix multiplication, respectively.
Imprinted quarter wave plate at terahertz frequency
Authors: Saha Shimul C. , Ma Yong , Grant James P. , Khalid A. , Cumming David R. S.
Published: December 2010

The authors have imprinted high aspect ratio artificial dielectric quarter wave plates (QWPs) on polymers for use at 2.6, 3.2, and 3.8 THz. The QWPs are imprinted on high density polyethylene using silicon masters. The grating period for the quarter wave plates is 60 μm. Deep gratings of 330, 280, and 230 μm are used to obtain a π/2 phase retardance between TE and TM polarizations propagating through the QWPs. An inductively coupled plasma etch process was used to create the silicon masters for the imprint. A combination of heat and pressure was used for the imprinting process. Two plates, fixed in a back-to-back configuration, were used for each QWP. A highest aspect ratio (grating height/grating width) of 7 was obtained using the imprint technology.
Nanoimprinting for diffractive light trapping in solar cells
Authors: Weiss Dirk N. , Yuan Hao-Chih , Lee Benjamin G. , Branz Howard M. , Meyers Stephen T. , Grenville Andrew , Keszler Douglas A.
Published: December 2010

The authors investigate the light-trapping efficiency of nanoimprinted ceramic grating reflectors for crystal silicon photovoltaic cells. Using 25 μm silicon wafers as a model system and hemispherical reflection measurements, they demonstrate a 4%–6% increase in AM 1.5 solar-photon absorption for one-dimensional square and sinusoidal gratings compared to flat reflectors. The extrapolated increase in a short-circuit current for a 2 μm thick silicon film cell due to diffractive light trapping is 20%.
Long-range ordered aluminum oxide nanotubes by nanoimprint-assisted aluminum film surface engineering
Authors: Noh Kunbae , Choi Chulmin , Kim Jin-Yeol , Oh Young , Brammer Karla S. , Loya Mariana C. , Jin Sungho
Published: December 2010

The authors present successful fabrications of hexagonally ordered and vertically aligned anodic aluminum oxide (AAO) nanotube array patterns over a large area (at least ∼6×6 mm2) by utilizing nanoimprint-guided anodization on sputter deposited Al thin films. Perfectly periodic nanotube arrays with no domain boundaries are obtained. Nanoindented patterns comprising hexagonal pillar arrays having a periodically absent pillar in the center of each hexagon were pattern transferred onto a poly(methyl methacrylate) coated Al film surface via reactive ion etch (RIE) followed by a subsequent guided anodization to produce long-range ordered vertical pore arrays. Upon further anodization, a self-assembled extra pore was formed in the center of each hexagon in addition to the regular pores formed at the impression location, thus leading to a pattern increase by 50%. Interestingly, it is seen that the resultant AAO structure can be altered via RIE process time duration, i.e., Al surface topographic modification prior to anodization. Similarly, a pattern-tripling phenomenon was observed when a triangular-patterned nanoimprint stamp was used by producing self-assembled central pores in the center of all triangles as well as guided pores at the impressed location, thus increasing the total number of pores by a factor of 3.
Hole mobility enhancement by chain alignment in nanoimprinted poly(3-hexylthiophene) nanogratings for organic electronics
Authors: Zhou Min , Aryal Mukti , Mielczarek Kamil , Zakhidov Anvar , Hu Walter
Published: December 2010

The authors report that the poly(3-hexylthiophene-2,5-diyl) (P3HT) nanogratings shaped by nanoimprint lithography show enhanced hole mobility and strong anisotropy of conductance due to nanoimprint-induced three-dimensional polymer chain alignment. Field effect transistors were fabricated using these nanogratings and device measurements show a hole mobility of 0.03 cm2/V s along the grating direction, which is about 60 times higher than that of nonoptimized thin film transistors. Organic photovoltaic devices (OPV) were made using the P3HT nanograting with infiltration of [6,6]-phenyl-C61-butyric acid methyl ester. Compared to similar bilayer and bulk heterojunction devices, the nanoimprinted OPV shows improved device performance.
Sub-10-nm half-pitch electron-beam lithography by using poly(methyl methacrylate) as a negative resist
Authors: Duan Huigao , Winston Donald , Yang Joel K. W. , Cord Bryan M. , Manfrinato Vitor R. , Berggren Karl K.
Published: December 2010

Developing high-resolution resists and processes for electron-beam lithography is of great importance for high-density magnetic storage, integrated circuits, and nanoelectronic and nanophotonic devices. Until now, hydrogen silsesquioxane (HSQ) and calixarene were the only two reported negative resists that could approach sub-10-nm half-pitch resolution for electron-beam lithography. Here, the authors report that 10-nm half-pitch dense nanostructures can also be readily fabricated using the well known poly(methyl methacrylate) (PMMA) resist operating in negative tone, even at exposure energies as low as 2 keV. In addition to scanning electron microscopy metrology, transmission electron microscopy metrology was done to confirm the high-resolution capability of negative-tone PMMA. This process was compared to HSQ with salty development and showed similar ultimate resolution, so it could be used as an alternative for applications incompatible with HSQ.
Analysis of surface electromagnetic wave resonant structures for potential application in an array of compact photoelectron sources
Authors: Choi Heon J. , Groves Timothy R.
Published: December 2010

Two different surface electromagnetic wave assisted light concentrators are analyzed that can, in principle, be integrated into an array with each concentrator delivering optical power to a photoelectron emitting metal nanodot. Such arrays could be used as a source for multiple electron-beam lithography and inspection systems. The optical power concentrators, composed of metal structures embedded onto the surface of a quartz substrate, can, in principle, be tuned to any wavelength from UV to IR, capturing and enhancing broad area optical excitation and focusing it to subwavelength dimensions. Results of the finite difference time domain computer simulations of the structures are presented, and the optical power density enhancement factors at the focal spot are calculated to be over an order of magnitude for both structures. General methods for manipulating the spectral response are proposed and analyzed.
Sputtering with an etch-free lift-off in thermal nanoimprint lithography
Authors: Mayer Andre , Bogdanski Nicolas , Möllenbeck Saskia , Dhima Khalid , Papenheim Marc , Scheer Hella-Christin
Published: December 2010

Two low-cost techniques suitable for large area processing are combined to define submicrometer metal structures, thermal nanoimprint lithography, and sputtering. With very low residual layers after thermal nanoimprint, as obtained under partial cavity filling conditions, it is possible to skip the etching step for residual layer removal before sputtering. As imprinted structures typically feature a positive sidewall angle, the authors investigate the morphology of sputtered layers on sloped sidewalls. Independent from inclination, the sputtered layers exhibit a columnar structure with only a slight taper, where the crystallites extend perpendicular to the substrate through the whole layer thickness. This structure allows penetration of the solvent, swelling of the polymer, and lifting of the top layer as long as the adhesion to the substrate within the contact area is sufficiently high, thus enabling successful lift-off.
Impact of molecular size on resist filling process in nanoimprint lithography: Molecular dynamics study
Authors: Taga Akihiro , Yasuda Masaaki , Kawata Hiroaki , Hirai Yoshihiko
Published: December 2010

The molecular size effects on resist filling process in nanoimprint lithography are studied by molecular dynamics simulation. Poly(methyl methacrylate) is selected as a resist model. The press force required to fill the resist into the mold cavity is calculated by the simulation. The press force increases with decreasing mold cavity size. When the cavity size goes below the molecular size of the resist polymer chain, the required press force increases sharply. This polymer size effect is not seen in the continuum mechanics simulation. The mold sidewall roughness effect on required press force also depends on the polymer size in molecular dynamics simulation.
Fabrication of seamless three-dimensional roll mold using direct electron-beam writing on rotating cylindrical substrate
Authors: Taniguchi Jun , Tsuji Shintaro , Aratani Masao
Published: December 2010

A three-dimensional (3D) seamless roll mold is difficult to fabricate because of its cylindrical shape. However, seamless 3D nanoscale patterns are in great demand for optical film applications and printed electronics. The authors have therefore developed a method for producing a 3D seamless roll mold by direct electron-beam (EB) writing onto a layer of resist material coated on a cylindrical substrate that is rotating in a vacuum. In addition, the 3D shape is produced by using the EB dose change method and the controlled-acceleration-voltage electron beam lithography (CAV-EBL) method developed by the authors. In the case of the EB dose change method, hydrogen silsesquioxane (HSQ), which is a negative-type EB resist, was used for the 3D roll mold. In the case of CAV-EBL, spin on glass, which is a positive-type EB resist, was used for the 3D roll mold. As a result, the developed HSQ height can be controlled by changing the EB dose; however, the dose change also causes a line width change. On the other hand, in the CAV-EBL method, the EB dose and acceleration voltage can be used to control the line width and depth independently; therefore, this method can successfully fabricate the coveted 3D roll mold.
Model for nanopillar growth by focused helium ion-beam-induced deposition
Authors: Alkemade Paul F. A. , Chen Ping , van Veldhoven Emile , Maas Diederik
Published: December 2010

An analytical model for the growth of nanopillars by helium ion-beam-induced deposition is presented and compared to experimental data. This model describes the competition between pillar growth in vertical and lateral directions. It assumes that vertical growth is induced by incident primary ions and type-1 secondary electrons, whereas lateral growth is induced by scattered ions and type-2 secondary ions. An essential element of the model is the notion that depletion of adsorbed precursor molecules occurs only at the pillars’ apex. Depletion impedes vertical growth at the apex, allowing more time for lateral outgrowth of the pillar’s sidewalls. The model describes qualitatively the trends in measured vertical, lateral, and volumetric growth rates of PtC pillars as functions of the ion-beam current. It can be used to design growth experiments and Monte Carlo simulations.
Impact of substrate deformation on demolding force for thermal imprint process
Authors: Kawata H. , Watanabe Y. , Fujikawa N. , Yasuda M. , Hirai Y.
Published: December 2010

The impact of deformation on the demolding force is investigated both experimentally and by simulation for the thermal imprint process. The effects of substrate thickness are the focus of this article. In experiments, one mold is used throughout all experiments in order to exclude any effects of the mold fabrication process. The mold pattern is transferred to a polymethylmethacrylate (PMMA) film by the thermal imprint. The PMMA surface height is measured by a commercial height profiler after the imprint, and it agrees with lateral variations in residual layer thickness. Demolding force increases as substrate thickness increases. Substrate deformation is simulated by simplifying a model to assume the presence of large cavities. Substrate deformation in the simulation agrees with the PMMA surface height profile in the experiment. The normal force to the PMMA side wall by the mold pattern is important for estimating the demolding force. Since the normal force during the pressing process is simulated, the normal force is induced by both the lateral expansion of PMMA resin and substrate deformation. The normal force from substrate deformation is selected based on a detailed analysis of the simulated normal force. The obtained normal force agrees with the demolding force in the experiment.
Performance characterization of negative resists for sub-10-nm electron beam lithography
Authors: Bonam R. , Verhagen P. , Munder A. , Hartley J.
Published: December 2010

As scaling continues, the need for reliable sub-10-nm electron beam lithography is apparent. Throughput is a major drawback and complex test structure fabrication would be constrained by practical limits on writing time. A major challenge for sub-10-nm patterning with electron beam lithography is tool and process efficiency especially for high sensitivity resists. This article presents current work done at the College of Nanoscale Science and Engineering where the authors investigated three different commercially available resist systems, namely, SU-8, NEB-31, and HSQ, which have a range of sensitivity from close to the shot noise limit to slow material with high resolution. The authors present the results obtained from these resists with their respective critical dimension, line edge roughness (LER), and line width roughness (LWR) values that correlate with sensitivity and are consistent with the well known resolution, line edge roughness, sensitivity trade-off. Due to the inability of tools to deliver low doses at step sizes close to grid size limit of the tool, the ultimate resolution limit of SU-8 and NEB-31 with acceptable LER and LWR is yet to be determined.
A statistical, task‐based evaluation method for three‐dimensional x‐ray breast imaging systems using variable‐background phantoms
Authors: Park Subok , Jennings Robert , Liu Haimo , Badano Aldo , Myers Kyle
Published: December 2010

Purpose:

For the last few years, development and optimization of three‐dimensional (3D) x‐ray breast imaging systems, such as digital breast tomosynthesis (DBT) and computed tomography, have drawn much attention from the medical imaging community, either academia or industry. However, there is still much room for understanding how to best optimize and evaluate the devices over a large space of many different system parameters and geometries. Current evaluation methods, which work well for 2D systems, do not incorporate the depth information from the 3D imaging systems. Therefore, it is critical to develop a statistically sound evaluation method to investigate the usefulness of inclusion of depth and background‐variability information into the assessment and optimization of the 3D systems.

Methods:

In this paper, we present a mathematical framework for a statistical assessment of planar and 3D x‐ray breast imaging systems. Our method is based on statistical decision theory, in particular, making use of the ideal linear observer called the Hotelling observer. We also present a physical phantom that consists of spheres of different sizes and materials for producing an ensemble of randomly varying backgrounds to be imaged for a given patient class. Lastly, we demonstrate our evaluation method in comparing laboratory mammography and three‐angle DBT systems for signal detection tasks using the phantom's projection data. We compare the variable phantom case to that of a phantom of the same dimensions filled with water, which we call the uniform phantom, based on the performance of the Hotelling observer as a function of signal size and intensity.

Results:

Detectability trends calculated using the variable and uniform phantom methods are different from each other for both mammography and DBT systems.

Conclusions:

Our results indicate that measuring the system's detection performance with consideration of background variability may lead to differences in system performance estimates and comparisons. For the assessment of 3D systems, to accurately determine trade offs between image quality and radiation dose, it is critical to incorporate randomness arising from the imaging chain including background variability into system performance calculations.
An iterative method for tomographic x‐ray perfusion estimation in a decomposition model‐based approach
Authors: Neukirchen Christoph , Giordano Marco , Wiesner Steffen
Published: December 2010

Purpose:

X‐ray based tomographic blood perfusion imaging requires recovery of contrast time‐attenuation‐curves from dynamic projection data. When using slowly rotating imaging systems, this task is challenging due to nonsimultaneous projection acquisition. A dynamic reconstruction method is proposed that aims at compensating the lack of simultaneously acquired information by incorporating prior knowledge about the expected temporal contrast dynamics.

Methods:

A decomposition model using temporal basis functions to approximate time‐attenuation‐curves is integrated into an iterative tomographic reconstruction method. The computationally efficient implementation of the proposed approach makes use of standard forward‐projections and backprojections, as well as scalar products in image space. The critical issue of projection noise propagation is tackled by the application of regularization which is realized by the early stopping of iteration cycles and by the proper selection of smooth temporal basis functions. The performance of the proposed dynamic reconstruction approach is evaluated in a simulation study concerning various aspects: Noise propagation and regularization, specification of the temporal model, and type of acquisition mode.

Results:

The evaluation based on dynamic phantom data indicates that tomographic recovery of contrast time‐attenuation‐curves in tissue can be achieved with an average range of accuracy of (with respect to dynamic peak attenuation) under ideal noise‐free conditions. The relative estimation error for arterial time‐attenuation‐curves is in the range of 8%, which is due to faster contrast dynamics in the artery. In general, performance depends on the level of acquired information contained in the projection data, which is mainly influenced by the type of rotational acquisition mode; restrictions in angular range and speed can lead to limited accuracy. The analysis of propagated projection noise in a statistical bias‐variance framework reveals relative noise levels in estimated time‐attenuation‐curves of 3%–4% in tissue regions and below 1% in vessels when using optimized settings for regularization. Here, the effect of noise suppression depends on the interrelation between the number of iteration cycles and the constraints imposed by the temporal decomposition model.

Conclusions:

For usage with slowly rotating imaging systems, the presented model‐based iterative dynamic reconstruction method is capable of recovering contrast time‐attenuation‐curves related to tissue perfusion. The proposed regularization framework is an effective means to limit the impact of projection noise, which is a factor dominating estimation accuracy in tissue regions.
Target tracking using DMLC for volumetric modulated arc therapy: A simulation study
Authors: Sun Baozhou , Rangaraj Dharanipathy , Papiez Lech , Oddiraju Swetha , Yang Deshan , Li H. Harold
Published: December 2010

Purpose:

Target tracking using dynamic multileaf collimator (DMLC) is a promising approach for intrafraction motion management in radiation therapy. The purpose of this work is to develop a DMLC tracking algorithm capable of delivering volumetric‐modulated arc therapy (VMAT) to the targets that experience two‐dimensional (2D) rigid motion in the beam's eye view.

Methods:

The problem of VMAT delivery to moving targets is formulated as a control problem with constraints. The relationships between gantry speed, gantry acceleration, MLC leaf‐velocity, dose rate, and target motion are derived. An iterative search algorithm is developed to find numerical solutions for efficient delivery of a specific VMAT plan to the moving target using 2D DMLC tracking. The delivery of five VMAT lung plans is simulated. The planned and delivered fluence maps in the target‐reference frame are calculated and compared.

Results:

The simulation demonstrates that the 2D tracking algorithm is capable of delivering the VMAT plan to a moving target fast and accurately without violating the machine constraints and the integrity of the treatment plan. The average delivery time is only 29 s longer than that of no‐tracking delivery, 101 versus 72 s, respectively. The fluence maps are normalized to 200 MU and the average root‐mean‐square error between the desired and the delivered fluence is 2.1 MU, compared to 14.8 MU for no‐tracking and 3.6 MU for one‐dimensional tracking.

Conclusions:

A locally optimal MLC tracking algorithm for VMAT delivery is proposed, aiming at shortest delivery time while maintaining treatment plan invariant. The inconsequential increase of treatment time due to DMLC tracking is clinically desirable, which makes VMAT with DMLC tracking attractive in treating moving tumors.
Joint correction of respiratory motion artifact and partial volume effect in lung/thoracic PET/CT imaging
Authors: Chang Guoping , Chang Tingting , Pan Tinsu , Clark John W. , Mawlawi Osama R.
Published: December 2010

Purpose:

Respiratory motion artifacts and partial volume effects (PVEs) are two degrading factors that affect the accuracy of image quantification in PET/CT imaging. In this article, the authors propose a joint motion and PVE correction approach (JMPC) to improve PET quantification by simultaneously correcting for respiratory motion artifacts and PVE in patients with lung/thoracic cancer. The objective of this article is to describe this approach and evaluate its performance using phantom and patient studies.

Methods:

The proposed joint correction approach incorporates a model of motion blurring, PVE, and object size/shape. A motion blurring kernel (MBK) is then estimated from the deconvolution of the joint model, while the activity concentration (AC) of the tumor is estimated from the normalization of the derived MBK. To evaluate the performance of this approach, two phantom studies and eight patient studies were performed. In the phantom studies, two motion waveforms—a linear sinusoidal and a circular motion—were used to control the motion of a sphere, while in the patient studies, all participants were instructed to breathe regularly. For the phantom studies, the resultant MBK was compared to the true MBK by measuring a correlation coefficient between the two kernels. The measured sphere AC derived from the proposed method was compared to the true AC as well as the ACs in images exhibiting PVE only and images exhibiting both PVE and motion blurring. For the patient studies, the resultant MBK was compared to the motion extent derived from a 4D‐CT study, while the measured tumor AC was compared to the AC in images exhibiting both PVE and motion blurring.

Results:

For the phantom studies, the estimated MBK approximated the true MBK with an average correlation coefficient of 0.91. The tumor ACs following the joint correction technique were similar to the true AC with an average difference of 2%. Furthermore, the tumor ACs on the PVE only images and images with both motion blur and PVE effects were, on average, 75% and 47.5% (10%) of the true AC, respectively, for the linear (circular) motion phantom study. For the patient studies, the maximum and mean AC/SUV on the PET images following the joint correction are, on average, increased by 125.9% and 371.6%, respectively, when compared to the PET images with both PVE and motion. The motion extents measured from the derived MBK and 4D‐CT exhibited an average difference of 1.9 mm.

Conclusions:

The proposed joint correction approach can improve the accuracy of PET quantification by simultaneously compensating for the respiratory motion artifacts and PVE in lung/thoracic PET/CT imaging.
A comprehensive study of the Gafchromic EBT2 radiochromic film. A comparison with EBT
Authors: Andrés C. , del Castillo A. , Tortosa R. , Alonso D. , Barquero R.
Published: December 2010

Purpose:

Radiochromic film has become an important tool to assess complex dose distributions. In particular, EBT was accepted by the scientific community as a reference two‐dimensional detector. Recently, Gafchromic EBT2 has replaced old film, providing new improvements in both accuracy and handling.

Methods:

This work presents a dosimetric study of the new Gafchromic EBT2 using an Epson 10000XL flatbed scanner, also comparing the results with EBT film as reference when necessary. The most important film characteristics have been studied, such as ambient light sensitivity, different possibilities of the three RGB color channels, postirradiation development, high dose behavior, exposition at temperatures similar to the human body, and dependence on orientation during the scanning process.

Results:

The results obtained confirm a considerably lower sensitivity to ambient light of EBT2, as well as a fast stabilization of the film within 2 h. It has also been found that the green channel has a better behavior at high dose levels up to 35 Gy, in addition to good behavior of the red channel at doses below 10 Gy. Other features, such as temperature independence and scanning orientation dependence, have also been shown.

Conclusions:

Gafchromic EBT2 can be used for clinical practice in the same way as the old EBT film. However, a much easier handling as the result of all new enhancements improves film behavior, expanding in this way the potential applications of radiochromic film dosimetry.
The role of x‐ray Swank factor in energy‐resolving photon‐counting imaging
Authors: Tanguay Jesse , Kim Ho Kyung , Cunningham Ian. A.
Published: December 2010

Purpose:

Energy‐resolved x‐ray imaging has the potential to improve contrast‐to‐noise ratio by measuring the energy of each interacting photon and applying optimal weighting factors. The success of energy‐resolving photon‐counting (EPC) detectors relies on the ability of an x‐ray detector to accurately measure the energy of each interacting photon. However, the escape of characteristic emissions and Compton scatter degrades spectral information. This article makes the theoretical connection between accuracy and imprecision in energy measurements with the x‐ray Swank factor for, Si, CdZnTe, and ‐based detectors.

Methods:

For a detector that implements adaptive binning to sum all elements in which x‐ray energy is deposited for a single interaction, energy imprecision is shown to depend on the Swank factor for a large element with x rays incident at the center. The response function for each converter material is determined using Monte Carlo methods and used to determine energy accuracy, Swank factor, and relative energy imprecision in photon‐energy measurements.

Results:

For each material, at energies below the respective K edges, accuracy is close to unity and imprecision is only a few percent. Above the K‐edge energies, characteristic emission results in a drop in accuracy and precision that depends on escape probability. In Si, and to some extent, Compton‐scatter escape also degrades energy precision with increasing energy. The influence of converter thickness on energy accuracy and imprecision is modest for low‐Z materials but becomes important when using high‐Z materials at energies greater than the K‐edge energies.

Conclusions:

Accuracy and precision in energy measurements by EPC detectors are determined largely by the energy‐dependent x‐ray Swank factor. Modest decreases in the Swank factor (5%–15%) result in large increases in relative imprecision (30%–40%).
Multiscale entropy of laser Doppler flowmetry signals in healthy human subjects
Authors: Humeau Anne , Buard Benjamin , Mahé Guillaume , Rousseau David , Chapeau‐Blondeau François , Abraham Pierre
Published: December 2010

Purpose:

The cardiovascular system (CVS) regulation can be studied from a central viewpoint, through heart rate variability (HRV) data, and from a peripheral viewpoint, through laser Doppler flowmetry (LDF) signals. Both the central and peripheral CVSs are regulated by several interacting mechanisms, each having its own temporal scale. The central CVS has been the subject of many multiscale studies. By contrast, these studies at the level of the peripheral CVS are very recent. Among the multiscale studies performed on the central CVS data, multiscale entropy has been proven to give interesting physiological information for diagnostic purposes. However, no multiscale entropy analysis has been performed on LDF signals. The authors' goal is therefore to propose a first multiscale entropy study of LDF data recorded in healthy subjects.

Methods:

The LDF signals recorded in the forearm of seven healthy subjects are processed. Their period sampling is, and coarse‐graining scales from to are studied. Also, for validation, the algorithm is first tested on synthetic signals of known theoretical multiscale entropy.

Results:

The results reveal nonmonotonic evolution of the multiscale entropy of LDF signals, with a maximum at small scales around and a minimum at longer scales around , singling out in this way two distinctive scales where the LDF signals undergo specific changes from high to low complexity. This also marks a strong contrast with the HRV signals that usually display a monotonic increase in the evolution of the multiscale entropy.

Conclusions:

Multiscale entropy of LDF signals in healthy subjects shows variation with scales. Moreover, as the variation pattern observed appears similar for all the tested signals, multiscale entropy could potentially be a useful stationary signature for LDF signals, which otherwise are probe‐position and subject dependent. Further work could now be conducted to evaluate possible diagnostic purposes of the multiscale entropy of LDF signals.
A comparison of the respiratory signals acquired by different respiratory monitoring systems used in respiratory gated radiotherapy
Authors: Otani Yuki , Fukuda Ichirou , Tsukamoto Nobuhiro , Kumazaki Yu , Sekine Hiroshi , Imabayashi Etsuko , Kawaguchi Osamu , Nose Takayuki , Teshima Teruki , Dokiya Takushi
Published: December 2010

Purpose:

Respiratory monitoring systems are used to detect the respiratory phase of patients during the planning and administration of respiratory gated radiotherapy by using four‐dimensional computed tomography (4DCT) or 4D positron‐emission tomography/CT (4DPET/CT) and the linear accelerator (linac), respectively. Generally, identical respiratory monitoring systems are used for 4DCT, 4DPET/CT, and linac. However, different systems are sometimes used in combination because the accessibility of the respiratory monitoring systems may differ by manufacturer. The combined use of different respiratory monitoring systems in phase‐based gating is of concern because the differences in the timing of tags (end‐respiration signals algorithmically determined by the respiratory monitoring system), defined by the two systems, may result in phase differences. The purpose of this study is to estimate this difference and evaluate its effect on 4DCT data.

Methods:

Ten patients (seven men and three women) with a median age of 75 yr (range: 57–84 yr) were treated by gated stereotactic body radiation therapy between April and December 2009. Two types of respiratory monitoring systems—RPM (Varian Medical Systems) and AZ‐733V (Anzai MEDICAL)—were placed on the abdominal surface of the patients, and the respiratory signals were acquired by both systems. The relationship between the amplitude peak and the tag obtained by each respiratory system was analyzed for each patient. Further, the 4DCT images were reconstructed by using the signals obtained from both the RPM and the AZ‐733V systems, and the tumor volumes and the tumor centroid positions in the craniocaudal plane were analyzed for each patient.

Results:

The correlation factor between the respiratory signals from the RPM system and AZ‐733V system was 0.990 (range: 0.940–0.994). The amplitude peak of the RPM system corresponded well with that of the AZ‐733V system. The deviation of the phase difference for all the patients ranged from to . In the case of some patients, differences were noted between the two systems in the estimation of the tumor centroid position and tumor shape.

Conclusions:

The estimation of the position of the tumor centroid and tumor shape may vary with the use of different respiratory monitoring systems. This implies that it is preferable to use the same respiratory monitoring system with 4DCT, 4DPET‐CT, and linac.
Reconstruction of a cone‐beam CT image via forward iterative projection matching
Authors: Brock R. Scott , Docef Alen , Murphy Martin J.
Published: December 2010

Purpose:

To demonstrate the feasibility of reconstructing a cone‐beam CT (CBCT) image by deformably altering a prior fan‐beam CT (FBCT) image such that it matches the anatomy portrayed in the CBCT projection data set.

Methods:

A prior FBCT image of the patient is assumed to be available as a source image. A CBCT projection data set is obtained and used as a target image set. A parametrized deformation model is applied to the source FBCT image, digitally reconstructed radiographs (DRRs) that emulate the CBCT projection image geometry are calculated and compared to the target CBCT projection data, and the deformation model parameters are adjusted iteratively until the DRRs optimally match the CBCT projection data set. The resulting deformed FBCT image is hypothesized to be an accurate representation of the patient's anatomy imaged by the CBCT system. The process is demonstrated via numerical simulation. A known deformation is applied to a prior FBCT image and used to create a synthetic set of CBCT target projections. The iterative projection matching process is then applied to reconstruct the deformation represented in the synthetic target projections; the reconstructed deformation is then compared to the known deformation. The sensitivity of the process to the number of projections and the DRR/CBCT projection mismatch is explored by systematically adding noise to and perturbing the contrast of the target projections relative to the iterated source DRRs and by reducing the number of projections.

Results:

When there is no noise or contrast mismatch in the CBCT projection images, a set of 64 projections allows the known deformed CT image to be reconstructed to within a nRMS error of 1% and the known deformation to within a nRMS error of 7%. A CT image nRMS error of less than 4% is maintained at noise levels up to 3% of the mean projection intensity, at which the deformation error is 13%. At 1% noise level, the number of projections can be reduced to 8 while maintaining CT image and deformation errors of less than 4% and 13%, respectively. The method is sensitive to contrast mismatch between the simulated projections and the target projections when the soft‐tissue contrast in the projections is low.

Conclusions:

By using prior knowledge available in a FBCT image, the authors show that a CBCT image can be iteratively reconstructed from a comparatively small number of projection images, thus saving acquisition time and reducing imaging dose. This will enable more frequent daily imaging during radiation therapy. Because the process preserves the CT numbers of the FBCT image, the resulting 3D image intensities will be more accurate than a CBCT image reconstructed via conventional backprojection methods. Reconstruction errors are insensitive to noise at levels beyond what would typically be found in CBCT projection data, but are sensitive to contrast mismatch errors between the CBCT projection data and the DRRs.
Estimation and correction of cardiac respiratory motion in SPECT in the presence of limited‐angle effects due to irregular respiration
Authors: Dey Joyoni , Segars William P. , Pretorius P. Hendrik , Walvick Ronn P. , Bruyant Philippe P. , Dahlberg Seth , King Michael A.
Published: December 2010

Purpose:

One issue with amplitude binning list‐mode studies in SPECT for respiratory motion correction is that variation in the patient's respiratory pattern will result in binned motion states with little or no counts at various projection angles. The reduced counts result in limited‐angle reconstruction artifacts which can impact the accuracy of the necessary motion estimation needed to correct the images. In this work, the authors investigate a method to overcome the effect of limited‐angle reconstruction artifacts in SPECT when estimating respiratory motion.

Methods:

In the first pass of the reconstruction method, only the projection angles with significant counts in common between the binned respiratory states are used in order to better estimate the motion between them. After motion estimation, the estimates are used to correct for motion within iterative reconstruction using all of the acquired projection data.

Results:

Using simulated SPECT studies based on the NCAT phantom, the authors demonstrate the problem caused by having data available for only a limited number of angles when estimating motion and the utility of the proposed method in diminishing this error. For NCAT data sets with a clinically appropriate level of Poisson noise, the average registration error for motion with the proposed method was always less with the use of their algorithm, the reduction being statistically significant in the majority of cases. The authors illustrate the ability of their method to correct the degradations caused by respiratory motion in short‐axis slices and polar maps of the NCAT phantom for cases with 1 and 2 cm amplitudes of respiratory motion. In four cardiac‐perfusion patients acquired on the same day, the authors demonstrate the large variability of the number of counts in the amplitude‐binned projections. Finally, the authors demonstrate a visual improvement in the slices and polar maps of patient studies with the algorithm for respiratory motion correction.

Conclusions:

The authors' method shows promise in reducing errors in respiratory motion estimation despite the presence of limited‐angle reconstruction effects due to irregularity in respiration. Improvements in image quality were observed in both simulated and clinical studies.
An Innate Itch?
Authors: Adler Elizabeth M.
Published: December 2010

TLR7 may provide a target for antipruritic therapy.
The Role of JNK Proteins in Metabolism
Authors: Vallerie Sara N. , Hotamisligil Gökhan S.
Published: December 2010

To combat metabolic diseases, therapeutic c-Jun N-terminal kinase (JNK) inhibitors must target multiple cell types.
Solving Cystic Fibrosis One Swine at a Time
Authors: Ahmad Shama
Published: December 2010

Dysfunction of the cystic fibrosis transmembrane conductance regulator leads to tracheal abnormalities in CF.
Tracing the Fate of an Essential Element
Authors: Buettner Christoph
Published: December 2010

Mutations in the SBP2 protein result in reduced synthesis of selenoproteins and a multisystem disorder.
Synthesis of alkenylphosphonium salts from tributyl[(trimethylsilyl)methylene]phosphorane and enolisable aldehydes
Authors: Majewski Piotr , Łukaszewicz Ewa
Published: December 2010

Efficient synthesis of alkenylphosphonium salts via treatment of enolizable aliphatic aldehydes with tributyl[(trimethylsilyl)methylene]phosphorane has been described. The simple way for preparation of tributyl[(trimethylsilyl)methylene]phosphorane is also presented.
Electrochemical study of glimepiride and its complexation with β-cyclodextrin
Authors: Radi Abd-Elgawad M. , Eissa Shimaa H.
Published: December 2010

The electrochemical behavior of a hypoglycemic drug, glimepiride (GM), was studied at glassy carbon (GCE) and carbon paste (CPE) electrodes in phosphate buffer over the pH range of 2.7–11.7 using cyclic and differential pulse voltammetry. Oxidation of the drug was shown to be an irreversible and diffusion-controlled process. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric peak in phosphate buffer pH 6.4 at +1.16 V and pH 7.0 at +1.07 V (vs Ag|AgCl) on glassy carbon and carbon paste electrodes, respectively. This process could be used to determine glimepiride concentrations in the range from 1.0 × 10–5 to 3.2 × 10–5 mol l–1 with a detection limit of 2.0 × 10–6 mol l–1 in case of the glassy carbon electrode and in the range of 2.0 × 10–6 to 1.5 × 10–5 mol l–1 with a detection limit of 7.5 × 10–7 mol l–1 in case of the carbon paste electrode. The method was successfully applied to the determination of the drug in a tablet dosage form. Next, the formation of an inclusion complex of glimepiride with β-cyclodextrin (β-CD) in phosphate buffer (pH 7.0):methanol (90:10 (v/v)) has been investigated by differential pulse voltammetry as well as UV spectrophotometry and its stability constant was determined by both methods to be 202.0 and 197.9 l mol–1, respectively.
Reference assays forClostridium difficileinfection: one or two gold standards?
Authors: Planche Timothy , Wilcox Mark
Published: December 2010

Accurate diagnosis ofClostridium difficileinfection (CDI) is essential for optimal treatment, prevention and control. There are two reference assays for CDI diagnosis: the cell cytotoxicity assay (CCTA) and toxigenic culture (TC). Importantly, these tests actually detect different targets: CCTA detects the presence ofC difficiletoxins (primarily toxin B, but also toxin A), whereas TC detects the presence in the stool ofC difficilewith the potential to produce toxin. Not surprisingly studies comparing the results of these assays show imperfect agreement. Thus, a faecal sample may be CCTA negative but TC positive, and this raises the crucial question about the clinical significance of the presence ofC difficilewith the capacity to produce toxin but no actual detectable free toxin. A positive TC result indicates that a patient with diarrhoea is potentially infectious. TC also has the advantage that the cultured isolate is available for typing and for susceptibility testing. In general, however, CCTA has been shown to be a better test for the laboratory confirmation of CDI, although additional culture may be needed to optimise sensitivity. Crucially, when these reference assays are used to determine the accuracy of alternative diagnostic tests, care should be taken to compare methods with their appropriate standard (ie, compare tests that target equivalent end-points). Such issues have contributed to the variable and often suboptimal performance of rapid diagnostic tests for CDI. Further research is urgently needed to improve knowledge of the utility of routine diagnostic tests in CDI and the factors that influence their performance.
Non-smoking worksites in the residential construction sector: using an online forum to study perspectives and practices
Authors: Bondy Susan J , Bercovitz Kim L
Published: December 2010

Objectives

Blue-collar workers are a recognised priority for tobacco control. Construction workers have very high smoking rates and are difficult to study and reach with interventions promoting smoke-free workplaces and cessation. The objectives of this study were to explore the smoking-related social climate in the North American residential construction sector and to identify potential barriers and facilitators to creating smokefree worksites.

Methods

The data source used was a popular internet forum on home building. Participants included a broad and unselected population of employers, employees and freelance tradespersons working in residential construction. The forum archive contained 10 years of discourse on the subjects of smoking, workplace secondhand smoke and smoking restrictions on construction sites. Qualitative data analysis methods were used to describe major and minor discussion themes relevant to workplace smoking culture and policies in this sector.

Results

Participants described considerable tension between smoking and non-smoking tradespersons, but there was also much interpersonal support for cessation and support for non-smokers' rights. Employers and employees described efforts to make construction sites smoke free, and a movement towards preferential hiring of non-smoking tradespersons was discussed. Board participants wanted detailed scientific evidence on secondhand smoke exposure levels and risk thresholds, particularly in open-air workplaces.

Conclusions

Experience with success of smoking bans in other challenging workplaces can be applied to the construction sector. Potential movement of smokers out of the workforce represents a challenge for public health systems to ensure equitable access to cessation supports and services.
FRACTAL PROPERTIES OF SURFACE ELECTROMYOGRAM FOR CLASSIFICATION OF LOW-LEVEL HAND MOVEMENTS FROM SINGLE-CHANNEL FOREARM MUSCLE ACTIVITY
Authors: ARJUNAN SRIDHAR P. , KUMAR DINESH K.
Published: December 2010

Surface electromyogram (sEMG) has been used in the identification of various hand movements which can lead to a number of rehabilitation, medical, and human computer interface applications. These applications are currently in need of higher accuracy and become challenging because of its unreliability in the classification of sEMG when the level of muscle contraction is low and when there are multiple active muscles. The presence of noise and cross-talk from closely located and simultaneously active muscles is exaggerated when muscles are weakly active such as during sustained wrist and finger flexion. This study reports the use of fractal properties of sEMG to identify the small changes in strength of muscle contraction and the location of the active muscles. It is observed that the fractal dimension (FD) of the signal is related to the complexity of the muscle contraction while maximum fractal length (MFL) is related to the strength of contraction of the associated muscle. The results show that the MFL and FD of a single-channel sEMG from the forearm can be used to accurately identify a set of finger-and-wrist flexion-based actions even when the muscle activity is very weak. It is proposed that such a system could be used to control a prosthetic hand or for a human computer interface.