bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of IMRT planning parameters on planning efficiency, delivery efficiency, and plan quality
Authors: Mittauer Kathryn , Lu Bo , Yan Guanghua , Kahler Darren , Gopal Arun , Amdur Robert , Liu Chihray 
Published: May 2013

Purpose: To improve planning and delivery efficiency of head and neck IMRT without compromising planning quality through the evaluation of inverse planning parameters.Methods: Eleven head and neck patients with pre‐existing IMRT treatment plans were selected for this retrospective study. The Pinnacle treatment planning system (TPS) was used to compute new treatment plans for each patient by varying the individual or the combined parameters of dose/fluence grid resolution, minimum MU per segment, and minimum segment area. Forty‐five plans per patient were generated with the following variations: 4 dose/fluence grid resolution plans, 12 minimum segment area plans, 9 minimum MU plans, and 20 combined minimum segment area/minimum MU plans. Each plan was evaluated and compared to others based on dose volume histograms (DVHs) (i.e., plan quality), planning time, and delivery time. To evaluate delivery efficiency, a model was developed that estimated the delivery time of a treatment plan, and validated through measurements on an Elekta Synergy linear accelerator.Results: The uncertainty (i.e., variation) of the dose‐volume index due to dose calculation grid variation was as high as 8.2% (5.5 Gy in absolute dose) for planning target volumes (PTVs) and 13.3% (2.1 Gy in absolute dose) for planning at risk volumes (PRVs). Comparison results of dose distributions indicated that smaller volumes were more susceptible to uncertainties. The grid resolution of a 4 mm dose grid with a 2 mm fluence grid was recommended, since it can reduce the final dose calculation time by 63% compared to the accepted standard (2 mm dose grid with a 2 mm fluence grid resolution) while maintaining a similar level of dose‐volume index variation. Threshold values that maintained adequate plan quality (DVH results of the PTVs and PRVs remained satisfied for their dose objectives) were 5 cm2 for minimum segment area and 5 MU for minimum MU. As the minimum MU parameter was increased, the number of segments and delivery time were decreased. Increasing the minimum segment area parameter decreased the plan MU, but had less of an effect on the number of segments and delivery time. Our delivery time model predicted delivery time to within 1.8%.Conclusions: Increasing the dose grid while maintaining a small fluence grid allows for improved planning efficiency without compromising plan quality. Delivery efficiency can be improved by increasing the minimum MU, but not the minimum segment area. However, increasing the respective minimum MU and/or the minimum segment area to any value greater than 5 MU and 5 cm2 is not recommended because it degrades plan quality.
Optimization of convergent collimators for pixelated SPECT systems
Authors: Capote Ricardo M. , Matela Nuno , Conceição Raquel C. , Almeida Pedro 
Published: May 2013

Purpose:The optimization of the collimator design is essential to obtain the best possible sensitivity in single photon emission computed tomography imaging. The aim of this work is to present a methodology for maximizing the sensitivity of convergent collimators, specifically designed to match the pitch of pixelated detectors, for a fixed spatial resolution value and to present some initial results using this approach.Methods:Given the matched constraint, the optimal collimator design cannot be simply found by allowing the highest level of septal penetration and spatial resolution consistent with the imposed restrictions, as it is done for the optimization of conventional collimators. Therefore, an algorithm that interactively calculates the collimator dimensions, with the maximum sensitivity, which respect the imposed restrictions was developed and used to optimize cone and fan beam collimators with tapered square‐shaped holes for low (60–300 keV) and high energy radiation (300–511 keV). The optimal collimator dimensions were locally calculated based on the premise that each hole and septa of the convergent collimator should locally resemble an appropriate optimal matched parallel collimator.Results:The optimal collimator dimensions, calculated for subcentimeter resolutions (3 and 7.5 mm), common pixel sizes (1.6, 2.1, and 2.5 mm), and acceptable septal penetration at 140 keV, were approximately constant throughout the collimator, despite their different hole incidence angles. By using these input parameters and a less strict septal penetration value of 5%, the optimal collimator dimensions and the corresponding mass per detector area were calculated for 511 keV. It is shown that a low value of focal distance leads to improvements in the average sensitivity at a fixed source‐collimator distance and resolution. The optimal cone beam performance outperformed that of other optimal collimation geometries (fan and parallel beam) in imaging objects close to the collimator surface.Conclusions:These results demonstrate the potential of this kind of optimal convergent collimators for the use in small field of view imaging applications.
Magnetothermoacoustics from magnetic nanoparticles by short bursting or frequency chirped alternating magnetic field: A theoretical feasibility analysis
Authors: Piao Daqing , Towner Rheal A. , Smith Nataliya , Chen Wei R. 
Published: May 2013

Purpose:To propose an alternative method of thermoacoustic wave generation based on heating of magnetic nanoparticles (MNPs) using alternating magnetic field (AMF).Methods:The feasibility of thermoacoustic wave generation from MNPs by applying a short‐burst of AMF or a frequency‐modulated AMF is theoretically analyzed. As the relaxation of MNPs is strongly dependent upon the amplitude and frequency of AMF, either an amplitude modulated, fixed frequency AMF (termed time‐domain AMF) or a frequency modulated, constant amplitude AMF (termed frequency‐domain AMF) will result in time‐varying heat dissipation from MNPs, which has the potential to generate thermoacoustic waves. Following Rosensweigˈs model of specific power loss of MNPs in a steady‐state AMF, the time‐resolved heat dissipations of MNPs of superparamagnetic size when exposed to a short bursting of AMF and/or to a linearly frequency chirped AMF are derived, and the resulted acoustic propagation is presented. Based on experimentally measured temperature‐rise characteristics of a superparamagnetic iron‐oxide nanoparticle (SPION) matrix in a steady‐state AMF of various frequencies, the heat dissipations of the SPION under time‐domain and frequency‐domain AMF configurations that could have practical utility for thermoacoustic wave generation are estimated.Results:The initial rates of the temperature‐rise of the SPION matrix were measured at an iron‐weight concentration of 0.8 mg/ml and an AMF frequency of 88.8 kHz to 1.105 MHz. The measured initial rates of temperature‐rise were modeled by Rosensweigˈs theory, and projected to 10 MHz AMF frequency, at which a 1μs bursting corresponding to a 1.55 mm axial resolution of acoustic detection could contain 10 complete cycles of AMF oscillation and the power dissipation is approximately 84 times of that at 1 MHz. Exposing the SPION matrix to a 1 μs bursting of AMF at 10 MHz frequency and 100 Oe field intensity would produce a volumetric heat dissipation of 7.7 μJ/cm3 over the microsecond duration of the AMF burst. If the SPION matrix is exposed to a 1 ms long AMF train at 100 Oe field intensity that chirps linearly from 1 to 10 MHz, the volumetric heat dissipation produced over each 2π phase change of the AMF oscillation is estimated to increase from 0.15 to 1.1 μJ/cm3 within the millisecond duration of the chirping of AMF.Conclusions:The heat dissipations upon SPION (∼1 mg/ml iron‐weight concentration) by a 1μs bursting of 100 Oe AMF at 10 MHz and a 1 ms train of 100 Oe AMF that chirps linearly from 1 to 10 MHz were estimated to determine the potential of thermal‐acoustic wave generation. Although thermoacoustic wave generation from MNPs by time‐ or frequency‐domain AMF applications is predicted, the experimental generation of such a wave remains challenging.
EXACT GROUND STATES OF CORRELATED ELECTRONS ON PENTAGON CHAINS
Authors: GULÁCSI ZSOLT 
Published: May 2013

We construct a class of exact ground states for correlated electrons on pentagon chains in the high density region and discuss their physical properties. In this procedure the Hamiltonian is first cast in a positive semidefinite form using composite operators as a linear combination of creation operators acting on the sites of finite blocks. In the same step, the interaction is also transformed to obtain terms which require for their minimum eigenvalue zero at least one electron on each site. The transformed Hamiltonian matches the original Hamiltonian through a nonlinear system of equations whose solutions place the deduced ground states in restricted regions of the parameter space. In the second step, nonlocal product wave functions in position space are constructed. They are proven to be unique ground states which describe non-saturated ferromagnetic and correlated half metallic states. These solutions emerge when the strength of the Hubbard interaction Ui is site-dependent inside the unit cell. In the deduced phases, the interactions tune the bare dispersive band structure such to develop an effective upper flat band. We show that this band flattening effect emerges for a broader class of chains and is not restricted to pentagon chains. For the characterization of the deduced solutions, uniqueness proofs, exact ground state expectation values for long-range hopping amplitudes and correlation functions are also calculated. The study of physical reasons which lead to the appearance of ferromagnetism has revealed a new mechanism for the emergence of an ordered phase, described here in detail. This works as follows: starting from a completely dispersive bare band structure, the interactions quench the kinetic energy, hence the ordered phase is obtained solely by a drastic decrease of the interaction energy. Since Ui are site dependent, this determinative decrease is obtained by a redistribution of the double occupancy di such to attain small di where the on-site Coulomb repulsion Ui is high, and vice versa. The kinetic energy quench leads to the upper effective flat band, whose role is to enhance by its degeneracy the switching to the ordered phase dictated and stabilized by the interactions present. It is shown that for this phenomenon to occur, a given degree of complexity is needed for the chain, and the mechanism becomes inactive when the Ui interactions are homogeneous, or are missing from the ground state wave function.
Effects of Synoptic-Scale Wind under the Typical Summer Pressure Pattern on the Mesoscale High-Temperature Events in the Osaka and Kyoto Urban Areas by the WRF Model
Authors: Takane Yuya , Ohashi Yukitaka , Kusaka Hiroyuki , Shigeta Yoshinori , Kikegawa Yukihiro 
Published: May 2013

AbstractThe actual conditions of mesoscale summer high temperatures (HTs) recorded in the Osaka–Kyoto urban area of Japan were investigated using an observation network. The daytime temperatures observed on 10 HT events in this area were the highest in the southern area of Kyoto [area with no Automated Meteorological Data Acquisition System (AMeDAS) observation sites]. To quantitatively evaluate the formation mechanisms of HT events, a heat budget analysis on an atmospheric column was conducted using the Weather Research and Forecasting (WRF) model. The results showed that over the HT area the daytime column temperature increased as a result of sensible-heat diffusion generated from the urban surface at the contribution rate of 54% and as a result of the sensible-heat advection and diffusion supplied from the sides and at the top of the column at the rate of 46% of all sensible heat supplied. To clarify previously unreported effects of synoptic-scale winds under typical summer pressure patterns on the HT events, a sensitivity experiment with no surface heat fluxes, backward trajectory analysis, and Euler forward tracer analysis was performed. These analyses yielded the following findings: 1) sensible heat at the synoptic scale and/or mesoscale was transported from the tropics by circulation patterns along the edge of the Pacific high as well as from tropical cyclones that were present in the vicinity of Japan and 2) airflow over the Kii Mountains also contributes to the HT events.
Solutions for Improving the Radar Refractivity Measurement by Taking Operational Constraints into Account
Authors: Besson Lucas , Parent du Châtelet Jacques 
Published: May 2013

Abstract
Atmospheric refractivity depends on meteorological parameters such as temperature, water vapor pressure, and air pressure and can be measured using weather radar. This could be useful for convection prediction through the assimilation by numerical forecasting models in the boundary layer, particularly in prestorm conditions. However, this measurement is highly sensitive to phase ambiguities, induced by signal undersampling during rapid atmospheric fluctuations because of strong turbulent fluxes in the boundary layer or during extreme events. The refractivity measurement has been recently implemented on some radars of the French Application Radar à la Météorologie Infra-Synoptique (ARAMIS) network, which is composed of three different frequencies (S, C, and X bands). In view of operational applications, investigations are performed to improve the measurement and limit the phase ambiguity rate. The first recommendation is to decrease the time interval between two measurements by increasing the antenna speed rotation or by the use of a higher elevation angle. These methods lead to decreased sensitivity of the refractivity to the phase aliasing. The second recommendation is to improve the information from ground target by combining the two polarization radar returns and using shorter pulse width. These two different approaches, based on the radar capacity and the description of the target, are complementary and noticeably improve the quality of the refractivity retrieval.
Extracolonic findings (ECF) on CT colonography (CTC) in patients presenting with colorectal symptoms
Authors: Badiani Sarit , Tomas-Hernandez Silvia , Karandikar Sharad , Roy-Choudhury Shuvro 
Published: May 2013

Background Computed tomographic colonography (CTC) is now an established method for imaging the colon and rectum in the screening and symptomatic setting. Additional benefit of CTC is the ability to assess for extracolonic findings especially in patients presenting with colorectal symptoms. Purpose To determine prevalence of extracolonic findings (ECF) in symptomatic patients undergoing CTC and determine accuracy of CTC for exclusion of significant abdominal disease and extracolonic malignancy (ECM). Material and Methods A total of 1359 unenhanced prone and postcontrast supine CTC studies were performed between March 2002 and December 2007. ECF were retrospectively classified according to C-RADS criteria into E1 to E4 findings. For ECM, a gold standard of clinical and/or radiological follow-up supplemented with data from the regional cancer registry with a median follow-up of 42 months was created. Sensitivity and negative predictive values for ECM was calculated. Results Following exclusions, 1177 CTCs were analyzed. Of 1423 extracolonic findings reported, 328/1423 (23%) E3 and 100/1423 (7%) E4 (including six eventual FP studies) findings were identified. Thirty-two ECMs were confirmed following further investigations. Seven further small ECMs were detected during the entire follow-up, of which two were potentially visible in retrospect (false-negative studies). Additional tests were generated from 55/1177 (4.7%) studies. Sensitivity and negative predictive value for ECM was 94.1% (95% CI 78.9–98.9%) and 99.8% (95% CI 99.3–99.9%), respectively. Conclusion One in 37 patients were found to have an ECM. Two potentially detectable cancers were missed. Only a small proportion of patients underwent additional work-up.
Utility of high-definition FDG-PET image reconstruction for lung cancer staging
Authors: Ozawa Yoshiyuki , Hara Masaki , Shibamoto Yuta , Tamaki Tsuneo , Nishio Masami , Omi Kumiko 
Published: May 2013

Background High-definition (HD) positron emission tomography (PET) image reconstruction is a new image reconstruction method based on the point spread function system, which improves the spatial resolution of the images. Purpose To compare the utility of HD reconstruction of PET images for staging lung cancer with that of conventional 2D ordered subset expectation maximization + Fourier rebinning (2D) reconstruction. Material and Methods Thirty-five lung cancer patients (24 men, 11 women; median age, 66 years) who underwent surgery after 18F-2-deoxy-fluoro-D-glucose (FDG)-PET-CT were studied. Their PET data were reconstructed with 2D and HD PET reconstruction algorithms. Two radiologists individually TNM staged both sets of images. They also evaluated the quality of the images and the diagnostic confidence that the images afforded them using 5-point scales. Results T, N, and M stages were correctly diagnosed on both the 2D and HD reconstructed images in 23 (66%), 25 (71%), and 30 (86%) of 35 cases, respectively. Overall TNM stage was correctly diagnosed on both types of reconstructed images in 23 cases (66%), underestimated in three (9%), and overestimated in nine (26%). No significant difference in T, N, or M stage or overall TNM stage was observed between the two reconstruction methods. However, the HD reconstructed images afforded a significantly higher level of diagnostic confidence during TNM staging than the 2D reconstructed images and were also of higher quality than the 2D reconstructed images. Conclusion Although HD reconstruction of FDG-PET images did not improve the diagnostic accuracy of lung cancer staging compared with 2D reconstruction, the quality of the HD reconstructed images and the diagnostic confidence level they afforded the radiologists were higher than those of the conventional 2D reconstructed images.
Pearls and pitfalls: Neuroimaging in headache
Authors: May Arne 
Published: May 2013

Premise One of the most exciting developments in modern neuroscience was the development of imaging techniques providing a non-invasive technique for detection of structure-function relationships characteristic of pain and headache. There is no question that neuroimaging has provided us with a better understanding of how the aura in migraine develops, and it has served as a bridge between neurophysiological studies and clinical findings, although doubtless several questions remain. Pearls Neuroimaging drew attention toward central mechanisms in idiopathic headache syndromes. Outstanding functional studies have reinforced the crucial role of the brainstem in acute and chronic migraine and the hypothalamic area in trigemino-autonomic headaches. Several morphometric studies suggest a decreased gray matter in pain-transmitting areas in headache patients; however, those have to be seen in the light of a wealth of pain studies and studies on exercise-dependent plasticity. Goal This review focuses on neuroimaging as a scientific tool and highlights the recent advances made in studying primary headache syndromes using functional and structural neuroimaging techniques. It will also point toward open questions and gives recommendations for future studies.
Ethical considerations in biomedical research: A personal view
Authors: Dahlöf Carl 
Published: May 2013

Premise Ethical considerations are made when an experiment is planned and take a regulatory system of moral principles into account. Discussion Ethical considerations should first and foremost be made in order to protect the individual subject/animal from being exposed to any unethical and perhaps even illegal intervention and to ensure that the experimental conditions used are appropriate. Summary The main role of research ethics committees is to assess the scientific and ethical aspects of submitted protocols and follow up the trial until its closure.
Pearls and pitfalls in neural CGRP immunohistochemistry
Authors: Warfvinge Karin , Edvinsson Lars 
Published: May 2013

This review outlines the pearls and pitfalls of calcitonin-gene related protein (CGRP) immunohistochemistry of the brain. Pearls In 1985, CGRP was first described in cerebral arteries using immunohistochemistry. Since then, cerebral CGRP (and, using novel antibodies, its receptor components) has been widely scrutinized. Here, we describe the distribution of cerebral CGRP and pay special attention to the surprising reliability of results over time. Pitfalls Pitfalls might include a fixation procedure, antibody clone and dilution, and interpretation of results. Standardization of staining protocols and true quantitative methods are lacking. The use of computerized image analysis has led us to believe that our examination is objective. However, in the steps of performing such an analysis, we make subjective choices. By pointing out these pitfalls, we aim to further improve immunohistochemical quality. Recommendations Having a clear picture of the tissue/cell morphology is a necessity. A primary morphological evaluation with, for example, hematoxylin-eosin, helps to ensure that small changes are not missed and that background and artifactual changes, which may include vacuoles, pigments, and dark neurons, are not over-interpreted as compound-related changes. The antigen-antibody reaction appears simple and clear in theory, but many steps might go wrong. Remember that methods including the antigen-antibody complex rely on handling/fixation of tissues or cells, antibody shipping/storing issues, antibody titration, temperature/duration of antibody incubation, visualization of the antibody and interpretation of the results. Optimize staining protocols to the material you are using.
Pearls and pitfalls in experimental in vivo models of headache: Conscious behavioral research
Authors: Romero-Reyes Marcela , Ye Yi 
Published: May 2013

Background Physiological studies have been determinant for the understanding of migraine pathophysiology and the screening of novel therapeutics. At present, there is no animal model that translates fully the clinical symptoms of migraine, and generally these studies are conducted on anesthetized animals. Methodology Pain as well as non-painful symptoms such as photophobia, need to have a conscious individual to be experienced; therefore, the new development and adaptation of behavioral assays assessing pain and other non-painful symptomatology in conscious animals represents a great opportunity for headache research and it is exciting that more and more researchers are using behavioral paradigms. Summary This review will describe the different behavioral models for the study of headache that are performed in non-anesthetized conscious animals. The pearls and challenges for measuring hypersensitivity in rodents such as the common tests for measuring mechanical allodynia and thermal hyperalgesia have been the landmark for the development of assays that measure hypersensitivity in the craniofacial region. Here we describe the different behavioral assays that measure hypersensitivity in the craniofacial region as well as the established behavioral models of trigeminovascular nociception and non-nociceptive migrainous symptoms.