bluuebunny/crossref_metadata_2025_split huggingface dataset:
Open design eight‐channel transmit/receive coil for high‐resolution and real‐time ankle imaging at 7 T
Authors: Orzada Stephan , Bitz Andreas K. , Schäfer Lena C. , Ladd Susanne C. , Ladd Mark E. , Maderwald Stefan 
Published: March 2011

Purpose:At 1.5 T, real‐time MRI of joint movement has been shown to be feasible. However, 7 T, provides higher SNR and thus an improved potential for parallel imaging acceleration. The purpose of this work was to build an open, U‐shaped eight‐channel transmit/receive microstrip coil for 7 T MRI to enable high‐resolution and real‐time imaging of the moving ankle joint.Methods:A U‐shaped eight‐channel transmit/receive array for the human ankle was built.‐parameters and ‐factor were measured. SAR calculations of different ankle postures were performed to ensure patient safety. Inhomogeneities in the transmit field consequent to the open design were compensated for by the use of static RF shimming. High‐resolution and real‐time imaging was performed in human volunteers.Results:The presented array showed good performance with regard to patient comfort and image quality. High acceleration factors of up to 4 are feasible without visible acceleration artifacts. Reasonable image homogeneity was achieved with RF shimming.Conclusions:Open, noncylindrical designs for transmit/receive coils are practical at 7 T and real‐time imaging of the moving joint is feasible with the presented coil design.
Dosimetric verification of surface and superficial doses for head and neck IMRT with different PTV shrinkage margins
Authors: Shiau An‐Cheng , Lai Pei‐Ling , Liang Ji‐An , Shueng Pei‐Wei , Chen Wei‐Li , Kuan Wei‐Peng 
Published: March 2011

Purpose:Dosimetric uncertainty in the surface and superficial regions is still a major concern for radiation therapy and becomes more important when using the inverse planning algorithm for IMRT. The purpose of this study was to measure dose distributions and to evaluate the calculation accuracy in the superficial region for different planning target volume (PTV) shrinkage methods for head and neck IMRT plans.Methods:A spherical polystyrene phantom 160 mm in diameter (ball phantom) was used to simulate the shape of the head. Strips of superflab bolus with thicknesses of 3.5 and 7.0 mm were spread on the surface of the ball phantom. Three sets of CT images were acquired for the ball phantom without and with the bolus. The hypothetical clinical target volume (CTV) and critical structures (spinal cord and parotid glands) were outlined on each set of CT images. The PTVs were initially created by expanding an isotropic 3 mm margin from the CTV and then margins of 0, 3, and 5 mm were shrunk from the phantom surface for dosimetric analysis. Seven‐field IMRT plans with a prescribed dose of 180 cGy and same dose constraints were designed using an Eclipse treatment planning system. Superficial doses at depths of 0, 3.5, and 7.0 mm and at seven beam axis positions (gantry angles of 0°, 30°, 60°, 80°, 330°, 300°, and 280°) were measured for each PTV shrinkage margin using 0.1 mm ultrathin thermoluminescent dosimeters. For each plan, the measured doses were compared to the calculated doses.Results:The PTV without shrinkage had the highest intensity and the steepest dose gradient in the superficial region. The mean measured doses for different positions at depths of 0, 3.5, and 7.0 mm were, , and , respectively. For a PTV with 3 mm shrinkage, the mean measured doses were , , and . For a PTV with 5 mm shrinkage, the mean measured doses were , , and . The comparisons indicated that more than 73.3% of the calculated points are with doses lower than the measured points and the difference of the dose becomes more significant in the shallower region. At 7.0 mm depth, the average difference between calculations and measurements was 2.5% (maximum 5.5%).Conclusions:Application of the PTV shrinkage method should take into account the calculation inaccuracy, tumor coverage, and possible skin reaction. When the tumor does not invade the superficial region, an adequate shrinkage margin from the surface is helpful for reducing the skin reaction. As the tumor invades the superficial region, adding a bolus is a method better than only contouring PTV with skin inclusion.
Beam hardening effects in grating‐based x‐ray phase‐contrast imaging
Authors: Chabior Michael , Donath Tilman , David Christian , Bunk Oliver , Schuster Manfred , Schroer Christian , Pfeiffer Franz 
Published: March 2011

Purpose:In this work, the authors investigate how beam hardening affects the image formation in x‐ray phase‐contrast imaging and consecutively develop a correction algorithm based on the results of the analysis.Methods:The authors' approach utilizes a recently developed x‐ray imaging technique using a grating interferometer capable of visualizing the differential phase shift of a wave front traversing an object. An analytical description of beam hardening is given, highlighting differences between attenuation and phase‐contrast imaging. The authors present exemplary beam hardening artifacts for a number of well‐defined samples in measurements at a compact laboratory setup using a polychromatic source.Results:Despite the differences in image formation, the authors show that beam hardening leads to a similar reduction of image quality in phase‐contrast imaging as in conventional attenuation‐contrast imaging. Additionally, the authors demonstrate that for homogeneous objects, beam hardening artifacts can be corrected by a linearization technique, applicable to all kinds of phase‐contrast methods using polychromatic sources.Conclusions:The evaluated correction algorithm is shown to yield good results for a number of simple test objects and can thus be advocated in medical imaging and nondestructive testing.
Study of the response of plastic scintillation detectors in small‐field 6 MV photon beams by Monte Carlo simulations
Authors: Wang Lilie L. W. , Beddar Sam 
Published: March 2011

Purpose:To investigate the response of plastic scintillation detectors (PSDs) in a 6 MV photon beam of various field sizes using Monte Carlo simulations.Methods:Three PSDs were simulated: A BC‐400 and a BCF‐12, each attached to a plastic‐core optical fiber, and a BC‐400 attached to an air‐core optical fiber. PSD response was calculated as the detector dose per unit water dose for field sizes ranging from down to for both perpendicular and parallel orientations of the detectors to an incident beam. Similar calculations were performed for a CC01 compact chamber. The off‐axis dose profiles were calculated in the photon beam and were compared to the dose profile calculated for the CC01 chamber and that calculated in water without any detector. The angular dependence of the PSDs' responses in a small photon beam was studied.Results:In the perpendicular orientation, the response of the BCF‐12 PSD varied by only 0.5% as the field size decreased from to , while the response of BC‐400 PSD attached to a plastic‐core fiber varied by more than 3% at the smallest field size because of its longer sensitive region. In the parallel orientation, the response of both PSDs attached to a plastic‐core fiber varied by less than 0.4% for the same range of field sizes. For the PSD attached to an air‐core fiber, the response varied, at most, by 2% for both orientations.Conclusions:The responses of all the PSDs investigated in this work can have a variation of only 1%–2% irrespective of field size and orientation of the detector if the length of the sensitive region is not more than 2 mm long and the optical fiber stems are prevented from pointing directly to the incident source.
Full‐field 3D photoacoustic imaging based on plane transducer array and spatial phase‐controlled algorithm
Authors: Zhou Qiuzhen , Ji Xuanrong , Xing Da 
Published: March 2011

Purpose:Photoacoustic imaging (PAI) used for noninvasive imaging of biological tissue has been reported in many literature. However, there are still some disadvantages in the novel technique, such as the poor efficiency of imaging. In the current PAI, multiple excitation of laser and multiple acquisition of signal are necessary for image reconstruction. In this case, laser pulses may injure biological tissue due to energy accumulation. To popularize PAI in clinical applications, it is necessary to develop a new imaging approach to increase the efficiency of PAI.Methods:A spatial phase‐controlled algorithm is presented for full‐field three‐dimensional (3D) image reconstruction. By using the algorithm, photoabsorption sources at different depths can be reconstructed using just one set of data acquired in single laser shot. Unfocused plane transducer array and parallel data‐acquisition (PDA) equipment are used for real‐time photoacoustic (PA) signal detection and acquisition.Results:The spatial resolution of the 3D PAI system was analyzed. Two graphite rods at various positions in a simulation model and two bifurcate vessels in the ear of rabbit were imaged. In addition, the motion trace of one particle flowing at constant velocity was captured dynamically. Experimental results showed that spatial phase‐controlled algorithm based on plane transducer array and PDA system was capable of static and dynamic 3D PAI.Conclusions:Spatial phase‐controlled algorithm is introduced for 3D image reconstruction. The PA signals are collected by plane transducer array and PDA system in single pulse excitation. The acquired volumetric data are sufficient for 3D image reconstruction. Therefore, tissue can avoid the long‐term exposure to light source and it is safer than the current PAI forin vivo imaging. With an increase in the repetition rate of laser pulse and speed of image display, the imaging method will realize real‐time 3D imaging, which will be significant in clinical detection and medical diagnosis.
A hybrid approach for rapid, accurate, and direct kilovoltage radiation dose calculations in CT voxel space
Authors: Kouznetsov Alexei , Tambasco Mauro 
Published: March 2011

Purpose:To develop and validate a fast and accurate method that uses computed tomography (CT) voxel data to estimate absorbed radiation dose at a point of interest (POI) or series of POIs from a kilovoltage (kV) imaging procedure.Methods:The authors developed an approach that computes absorbed radiation dose at a POI by numerically evaluating the linear Boltzmann transport equation (LBTE) using a combination of deterministic and Monte Carlo (MC) techniques. This hybrid approach accounts for material heterogeneity with a level of accuracy comparable to the general MC algorithms. Also, the dose at a POI is computed within seconds using the Intel® Core™ i7 CPU 920 2.67 GHz quad core architecture, and the calculations are performed using CT voxel data, making it flexible and feasible for clinical applications. To validate the method, the authors constructed and acquired a CT scan of a heterogeneous block phantom consisting of a succession of slab densities: Tissue (1.29 cm), bone (2.42 cm), lung (4.84 cm), bone (1.37 cm), and tissue (4.84 cm). Using the hybrid transport method, the authors computed the absorbed doses at a set of points along the central axis and direction of the phantom for an isotropic 125 kVp photon spectral point source located along the central axis 92.7 cm above the phantom surface. The accuracy of the results was compared to those computed with MCNP, which was cross‐validated with EGSnrc, and served as the benchmark for validation.Results:The error in the depth dose ranged from −1.45% to with a mean and standard deviation of −0.12% and 0.66%, respectively. The error in the profile ranged from −1.3% to , with standard deviations of −0.3% and 0.5%, respectively. The number of photons required to achieve these results was .Conclusions:The voxel‐based hybrid method evaluates the LBTE rapidly and accurately to estimate the absorbed x‐ray dose at any POI or series of POIs from a kV imaging procedure.
Confidence limit variation for a single IMRT system following the TG119 protocol
Authors: Gordon J. D. , Krafft S. P. , Jang S. , Smith‐Raymond L. , Stevie M. Y. , Hamilton R. J. 
Published: March 2011

Purpose:To evaluate the robustness of TG119‐based quality assurance metrics for an IMRT system.Methods:Four planners constructed treatment plans for the five IMRT test cases described in TG119. All plans were delivered to a solid water phantom in one treatment session in order to minimize session‐dependent variation from phantom setup, film quality, machine performance, etc. Composite measurements utilized film and an ionization chamber. Per‐field measurements were collected using a diode array device at an effective depth of 5 cm. All data collected were analyzed using the TG119 specifications to determine the confidence limit values for each planner separately and then compared.Results:The mean variance of ion chamber measurements for each planner was within 1.7% of the planned dose. The resulting confidence limits were 3.13%, 1.98%, 3.65%, and 4.39%. Confidence limit values determined by composite film analysis were 8.06%, 13.4%, 9.30%, and 16.5%. Confidence limits from per‐field measurements were 1.55%, 0.00%, 0.00%, and 2.89%.Conclusions:For a single IMRT system, the accuracy assessment provided by TG119‐based quality assurance metrics showed significant variations in the confidence limits between planners across all composite and per‐field evaluations. This observed variation is likely due to the different levels of modulation between each planner's set of plans. Performing the TG119 evaluation using plans produced by a single planner may not provide an adequate estimation of IMRT system accuracy.
A GMM‐based breast cancer risk stratification using a resonance‐frequency electrical impedance spectroscopy
Authors: Lederman Dror , Zheng Bin , Wang Xingwei , Sumkin Jules H. , Gur David 
Published: March 2011

Purpose:The authors developed and tested a multiprobe‐based resonance‐frequency‐based electrical impedance spectroscopy (REIS) system. The purpose of this study was to preliminarily assess the performance of this system in classifying younger women into two groups, those ultimately recommended for biopsy during imaging‐based diagnostic workups that followed screening and those rated as negative during mammography.Methods:A seven probe‐based REIS system was designed, assembled, and is currently being tested in the breast imaging facility. During an examination, contact is made with the nipple and six concentric points on the breast skin. For each measurement channel between the center probe and one of the six external probes, a set of electrical impedance spectroscopy (EIS) signal sweeps is performed and signal outputs ranging from 200 to 800 kHz at 5 kHz interval are recorded. An initial subset of 174 examinations from an ongoing prospective clinical study was selected for this preliminary analysis. An initial set of 35 features, 33 of which represented the corresponding EIS signal differences between the left and right breasts, was established. A Gaussian mixture model (GMM) classifier was developed to differentiate between “positive” (biopsy recommended) cases and “negative” (nonbiopsy) cases. Selecting an optimal feature set was performed using genetic algorithms with an area under a receiver operating characteristic curve (AUC) as the fitness criterion.Results:The recorded EIS signal sweeps showed that, in general, negative (nonbiopsy) examinations have a higher level of electrical impedance symmetry between the two breasts than positive (biopsy) examinations. Fourteen features were selected by genetic algorithm and used in the optimized GMM classifier. Using a leave‐one‐case‐out test, the GMM classifier yielded a performance level of, which compared favorably to other three widely used classifiers including support vector machine, classification tree, and linear discriminant analysis. These results also suggest that the REIS signal based GMM classifier could be used as a prescreening tool to correctly identify a fraction of younger women at higher risk of developing breast cancer (i.e., 47% sensitivity at 90% specificity).Conclusions:The study confirms that asymmetry in electrical impedance characteristics between two breasts provides valuable information regarding the presence of a developing breast abnormality; hence, REIS data may be useful in classifying younger women into two groups of “average” and “significantly higher than average” risk of having or developing a breast abnormality that would ultimately result in a later imaging‐based recommendation for biopsy.
The influence of the field setup on the dosimetry of abutted fields in single‐isocenter half‐beam techniques
Authors: Hernandez V. , Sempau J. 
Published: March 2011

Purpose:To study the influence of the field setup on the dosimetry at the junction in single‐isocenter half‐beam techniques.Methods:The dosimetry at the junction for a two‐field setup with the gantry at zero was first evaluated with radiochromic films. A three‐field setup, with an anterior field and two opposed lateral fields, was also analyzed for two different relative positions of the fields involved. In all cases, the dose increase at the central axis, called the junction dose, was measured.Results:Junction doses varied greatly with the setup. For the three‐field setup, the junction dose differed from that obtained with the two‐field setup, and it greatly depended on the relative position of the fields. When the anterior field was closer to the gantry than the lateral fields, a field gap occurred and the junction dose was negative. When the anterior field was farther from the gantry than the lateral fields, a field overlap was obtained and the junction dose was positive. The difference in the junction dose between the three‐field setups was around 18% for the three accelerators evaluated.Conclusions:Having a uniform dose distribution for two fields at gantry 0° does not guarantee a uniform distribution at other gantry angles. Junction doses are largely affected by the relative position of the radiation fields, which may have an impact in clinical practice. Therefore, any method aiming to assess or to optimize the dose homogeneity at the junction should take this effect into account.
Effect of an Asparagine-to-Serine Mutation at Position 294 in Neuraminidase on the Pathogenicity of Highly Pathogenic H5N1 Influenza A Virus
Authors: Kiso Maki , Ozawa Makoto , Le Mai thi Quynh , Imai Hirotaka , Takahashi Kei , Kakugawa Satoshi , Noda Takeshi , Horimoto Taisuke , Kawaoka Yoshihiro 
Published: March 2011

ABSTRACT

Like the histidine-to-tyrosine substitution at position 274 in neuraminidase (NA H274Y), an asparagine-to-serine mutation at position 294 in this protein (NA N294S) confers oseltamivir resistance to highly pathogenic H5N1 influenza A viruses. However, unlike viruses with the NA H274Y mutation, the properties of viruses possessing NA N294S are not well understood. Here, we assessed the effect of the NA N294S substitution on the replication and pathogenicity of human H5N1 viruses and on the efficacy of the NA inhibitors oseltamivir and zanamivir in mouse and ferret models. Although NA N294S-possessing H5N1 viruses were attenuated in mice and ferrets compared to their oseltamivir-sensitive counterparts, one of the infected ferrets died from systemic infection, demonstrating the potential lethality in ferrets of oseltamivir-resistant H5N1 viruses with the NA N294S substitution. The efficacy of oseltamivir, but not that of zanamivir, against an NA N294S-possessing virus was substantially impaired both in ferrets and
in vitro
. These results demonstrate the considerable pathogenicity of NA N294S substitution-possessing H5N1 viruses and underscore the importance of monitoring the emergence of the NA N294S mutation in circulating H5N1 viruses.
Contact Transmission of Tobacco Mosaic Virus: a Quantitative Analysis of Parameters Relevant for Virus Evolution
Authors: Sacristán Soledad , Díaz Maira , Fraile Aurora , García-Arenal Fernando 
Published: March 2011

ABSTRACT

Transmission between hosts is required for the maintenance of parasites in the host population and determines their ultimate evolutionary success. The transmission ability of parasites conditions their evolution in two ways: on one side, it affects the genetic structure of founded populations in new hosts. On the other side, parasite traits that increase transmission efficiency will be selected for. Therefore, knowledge of the factors and parameters that determine transmission efficiency is critical to predict the evolution of parasites. For plant viruses, little is known about the parameters of contact transmission, a major way of transmission of important virus genera and species. Here, we analyze the factors determining the efficiency of contact transmission of
Tobacco mosaic virus
(TMV) that may affect virus evolution. As it has been reported for other modes of transmission, the rate of TMV transmission by contact depended on the contact opportunities between an infected and a noninfected host. However, TMV contact transmission differed from other modes of transmission, in that a positive correlation between the virus titer in the source leaf and the rate of transmission was not found within the range of our experimental conditions. Other factors associated with the nature of the source leaf, such as leaf age and the way in which it was infected, had an effect on the rate of transmission. Importantly, contact transmission resulted in severe bottlenecks, which did not depend on the host susceptibility to infection. Interestingly, the effective number of founders initiating the infection of a new host was highly similar to that reported for aphid-transmitted plant viruses, suggesting that this trait has evolved to an optimum value.
Chaperone Role for Proteins p618 and p892 in the Extracellular Tail Development of Acidianus Two-Tailed Virus
Authors: Scheele Urte , Erdmann Susanne , Ungewickell Ernst J. , Felisberto-Rodrigues Catarina , Ortiz-Lombardía Miguel , Garrett Roger A. 
Published: March 2011

ABSTRACT

The crenarchaeal
Acidianus
two-tailed virus (ATV) undergoes a remarkable morphological development, extracellularly and independently of host cells, by growing long tails at each end of a spindle-shaped virus particle. Initial work suggested that an intermediate filament-like protein, p800, is involved in this process. We propose that an additional chaperone system is required, consisting of a MoxR-type AAA ATPase (p618) and a von Willebrand domain A (VWA)-containing cochaperone, p892. Both proteins are absent from the other known bicaudavirus, STSV1, which develops a single tail intracellularly. p618 exhibits ATPase activity and forms a hexameric ring complex that closely resembles the oligomeric complex of the MoxR-like protein RavA (YieN). ATV proteins p387, p653, p800, and p892 interact with p618, and with the exception of p800, all bind to DNA. A model is proposed to rationalize the interactions observed between the different protein and DNA components and to explain their possible structural and functional roles in extracellular tail development.