bluuebunny/crossref_metadata_2025_split huggingface dataset:
Broad‐band angle insensitive frequency‐selective surface with multiple resonant modes
Authors: Zhao Zhen‐Zhen , Li Wei , Chen Xiao‐Ming , Chen Jian‐Zhong , Shi Hong‐Yu , Li Jian‐Xing , Zhu Shi‐Tao , Zhang An‐Xue 
Published: October 2018

AbstractIn this work, a broadband frequency selective surface (FSS), which is insensitive to incident angle is designed. This FSS is composed of three metallic layers and two identical dielectric layers. The top and bottom layers are two identical metal patches, while the middle layer is a slot structure etched in a metal screen. This FSS achieves a broadband pass‐band response from 9.8 to 20.8 GHz by combining different resonant modes at 12.6, 15.2, and 19.2 GHz, respectively. Meanwhile, this FSS can still function properly at up to 60° oblique incidence for TE polarization, which is attributed to the independence of incident angle of the middle slot layer and miniaturization of the whole structure. In addition, two key parameters (that are of great importance in adjusting flatness of the pass‐band) of the FSS element have been studied. A prototype of the FSS was manufactured and measured. Good agreements between measurements and simulations are observed.
Part II: Verification of the TrueBeam head shielding model in Varian VirtuaLinac via out‐of‐field doses
Authors: Wijesooriya Krishni , Liyanage Nilanga K. , Kaluarachchi Maduka , Sawkey Daren 
Published: October 2018

PurposeA good Monte Carlo model with an accurate head shielding model is important in estimating the long‐term risks of unwanted radiation exposure during radiation therapy. The aim of this paper was to validate the Monte Carlo simulation of a TrueBeam linear accelerator (linac) head shielding model. We approach this by evaluating the accuracy of out‐of‐field dose predictions at extended distances which are comprised of scatter from within the patient and treatment head leakage and thus reflect the accuracy of the head shielding model. We quantify the out‐of‐field dose of a TrueBeam linac for low‐energy photons, 6X and 6X‐FFF beams, and compare measurements to Monte Carlo simulations using Varian VirtuaLinac that include a realistic head shielding model, for a variety of jaw sizes and angles up to a distance of 100 cm from the isocenter, in both positive and negative directions. Given the high value and utility of the VirtuaLinac model, it is critical that this model is validated thoroughly and the results be available to the medical physics community.Materials and methodSimulations were done using VirtuaLinac, the GEANT4‐based Monte Carlo model of the TrueBeam treatment head from Varian Medical Systems, and an in‐house GEANT4‐based code. VirtuaLinac included a detailed model of the treatment head shielding and was run on the Amazon Web Services cloud to generate spherical phase space files surrounding the treatment head. These phase space files were imported into the in‐house code, which modeled the measurement setup with a solid water buildup, the carbon fiber couch, and the gantry stand. For each jaw size (2 × 2 cm2, 4 × 4 cm2, 10 × 10 cm2, and 20 × 20 cm2) and angular setting (0°, 90°, 45°, 135°), the dose was calculated at intervals of 5 cm along each measurement direction.ResultsFor the 10 × 10 cm2 jaw size, both 6X and 6X‐FFF showed very good agreement between simulation and measurement in both in‐plane directions, with no apparent systematic bias. The percentage deviations for these settings were as follows: (mean, STDEV, maximum) (8.34, 6.44, 24.84) for 6X and (13.21, 8.93, 35.56) for 6X‐FFF. For all jaw sizes, simulation agreed well in the in‐plane direction going away from the gantry, but, some deviations were observed moving toward the gantry at larger distances. At larger distances, for the jaw sizes smaller than 10 × 10 cm2, the simulation underestimates the dose compared with measurement, while for jaw sizes larger than 10 × 10 cm2, it overestimates dose. For all comparisons between ±50 cm from isocenter, average absolute agreement between simulation and measurement was better than 28%.ConclusionWe have validated the Varian VirtuaLinac's head shielding model via out‐of‐field doses and quantified the differences between TrueBeam head shielding model created out‐of‐field doses and measurements for an extended distance of 100 cm.
Dynamic diffusion‐weighted hyperpolarized 13C imaging based on a slice‐selective double spin echo sequence for measurements of cellular transport
Authors: Zhu Xucheng , Gordon Jeremy W. , Bok Robert A. , Kurhanewicz John , Larson Peder E.Z. 
Published: October 2018

PurposeTo develop a pulse sequence to dynamically measure the ADC of hyperpolarized substrates during their perfusion, metabolic conversion, and transport.MethodsWe proposed a slice‐selective double spin echo sequence for dynamic hyperpolarized 13C diffusion‐weighted imaging. The proposed pulse sequence was optimized for a high field preclinical scanner through theoretical analysis and simulation. The performance of the method was compared to non‐slice‐selective double spin echo via in vivo studies. We also validated the sequence for dynamic ADC measurement in both phantom studies and transgenic mouse model of prostate cancer studies.ResultsThe optimized pulse sequence outperforms the traditional sequence with smaller saturation effects on the magnetization of hyperpolarized compounds that allowed more dynamic imaging frames covering a longer imaging time window. In pre‐clinical studies (N = 8), the dynamic hyperpolarized lactate ADC maps of 6 studies in the prostate tumors showed an increase measured ADC over time, which might be related to lactate efflux from the tumor cells.ConclusionsThe proposed sequence was validated and shown to improve dynamic diffusion weighted imaging compared to the traditional double spin echo sequence, providing ADC maps of lactate through time.
Quantitative analysis of vascular properties derived from ultrafast DCE‐MRI to discriminate malignant and benign breast tumors
Authors: Wu Chengyue , Pineda Federico , Hormuth David A. , Karczmar Gregory S. , Yankeelov Thomas E. 
Published: October 2018

PurposeWe propose a novel methodology to integrate morphological and functional information of tumor‐associated vessels to assist in the diagnosis of suspicious breast lesions.Theory and MethodsUltrafast, fast, and high spatial resolution DCE‐MRI data were acquired on 15 patients with suspicious breast lesions. Segmentation of the vasculature from the surrounding tissue was performed by applying a Hessian filter to the enhanced image to generate a map of the probability for each voxel to belong to a vessel. Summary measures were generated for vascular morphology, as well as the inputs and outputs of vessels physically connected to the tumor. The ultrafast DCE‐MRI data was analyzed by a modified Tofts model to estimate the bolus arrival time, Ktrans (volume transfer coefficient), and vp (plasma volume fraction). The measures were compared between malignant and benign lesions via the Wilcoxon test, and then incorporated into a logistic ridge regression model to assess their combined diagnostic ability.ResultsA total of 24 lesions were included in the study (13 malignant and 11 benign). The vessel count, Ktrans, and vp showed significant difference between malignant and benign lesions (P = 0.009, 0.034, and 0.010, area under curve [AUC] = 0.76, 0.63, and 0.70, respectively). The best multivariate logistic regression model for differentiation included the vessel count and bolus arrival time (AUC = 0.91).ConclusionThis study provides preliminary evidence that combining quantitative characterization of morphological and functional features of breast vasculature may provide an accurate means to diagnose breast cancer.
Eddy current nulled constrained optimization of isotropic diffusion encoding gradient waveforms
Authors: Yang Grant , McNab Jennifer A. 
Published: October 2018

PurposeIsotropic diffusion encoding efficiently encodes additional microstructural information in combination with conventional linear diffusion encoding. However, the gradient‐intensive isotropic diffusion waveforms generate significant eddy currents, which cause image distortions. The purpose of this study is to present a method for designing isotropic diffusion encoding waveforms with intrinsic eddy current nulling.MethodsEddy current nulled gradient waveforms were designed using a constrained optimization waveform for a 3T GE Premier MRI system. Encoding waveforms were designed for a variety of eddy current null times and sequence timings to evaluate the achievable b‐value. Waveforms were also tested with both eddy current nulling and concomitant field compensation. Distortion reduction was tested in both phantoms and the in vivo human brain.ResultsThe feasibility of isotropic diffusion encoding with intrinsic correction of eddy current distortion and signal bias from concomitant fields was demonstrated. The constrained optimization algorithm produced gradient waveforms with the specified eddy current null times. The reduction in the achievable diffusion weighting was dependent on the number of eddy current null times. A reduction in the eddy current–induced image distortions was observed in both phantoms and in vivo human subjects.ConclusionThe proposed framework allows the design of isotropic diffusion‐encoding sequences with reduced image distortion.
Accelerated 3D T2 mapping with dictionary‐based matching for prostate imaging
Authors: Roccia Elisa , Vidya Shankar Rohini , Neji Radhouene , Cruz Gastão , Munoz Camila , Botnar René , Goh Vicky , Prieto Claudia , Dregely Isabel 
Published: October 2018

PurposeTo develop a fast and accurate method for 3D T2 mapping of prostate cancer using undersampled acquisition and dictionary‐based fitting.Methods3D high‐resolution T2‐weighted images (0.9 × 0.9 × 3 mm3) were obtained with a multishot T2‐prepared balanced steady‐state free precession (T2‐prep‐bSSFP) acquisition sequence using a 3D variable density undersampled Cartesian trajectory. Each T2‐weighted image was reconstructed using total variation regularized sensitivity encoding. A flexible simulation framework based on extended phase graphs generated a dictionary of magnetization signals, which was customized to the proposed sequence. The dictionary was matched to the acquired T2‐weighted images to retrieve quantitative T2 values, which were then compared to gold‐standard spin echo acquisition values using monoexponential fitting. The proposed approach was validated in simulations and a T1/T2 phantom, and feasibility was tested in 8 healthy subjects.ResultsThe simulation analysis showed that the proposed T2 mapping approach is robust to noise and typically observed T1 variations. T2 values obtained in the phantom with T2prep‐bSSFP and the acquisition‐specific, dictionary‐based matching were highly correlated with the gold‐standard spin echo method (r = 0.99). Furthermore, no differences were observed with the accelerated acquisition compared to the fully sampled acquisition (r = 0.99). T2 values obtained in prostate peripheral zone, central gland, and muscle in healthy subjects (age, 26 ± 6 years) were 97 ± 14, 76 ± 7, and 36 ± 3 ms, respectively.Conclusion3D quantitative T2 mapping of the whole prostate can be achieved in 3 minutes.
PEC‐GRAPPA reconstruction of simultaneous multislice EPI with slice‐dependent 2D Nyquist ghost correction
Authors: Liu Yilong , Lyu Mengye , Barth Markus , Yi Zheyuan , Leong Alex T. L. , Chen Fei , Feng Yanqiu , Wu Ed X. 
Published: October 2018

PurposeTo provide simultaneous multislice (SMS) EPI reconstruction with k‐space implementation and robust Nyquist ghost correction.Methods2D phase error correction SENSE (PEC‐SENSE) was recently developed for Nyquist ghost correction in SMS EPI reconstruction for which virtual coil simultaneous autocalibration and k‐space estimation (VC‐SAKE) was used to remove slice‐dependent Nyquist ghosts and intershot 2D phase variations in multi‐shot EPI reference scan. However, masking coil sensitivity maps to exclude background region in PEC‐SENSE and manually selecting slice‐wise target ranks in VC‐SAKE are cumbersome procedures in practice. To avoid masking, the concept of PEC‐SENSE is extended to k‐space implementation and termed as PEC‐GRAPPA. Furthermore, a singular value shrinkage scheme is incorporated in VC‐SAKE to circumvent the empirical slice‐wise target rank selection. PEC‐GRAPPA was evaluated and compared to PEC‐SENSE with/without masking and 1D linear phase correction GRAPPA.ResultsPEC‐GRAPPA robustly reconstructed SMS EPI images from 7T phantom and human brain data, effectively removing the phase error‐induced artifacts. The resulting residual artifact level and temporal SNR were comparable to those by PEC‐SENSE with careful tuning. PEC‐GRAPPA outperformed PEC‐SENSE without masking and 1D linear phase correction GRAPPA.ConclusionOur proposed PEC‐GRAPPA approach effectively removes the artifacts caused by Nyquist ghosts in SMS EPI without cumbersome tuning. This approach provides a robust and practical implementation of SMS EPI reconstruction in k‐space with slice‐dependent 2D Nyquist ghost correction.
Accurate fatty acid composition estimation of adipose tissue in the abdomen based on bipolar multi‐echo MRI
Authors: Schneider Manuel , Janas Gemini , Lugauer Felix , Hoppe Elisabeth , Nickel Dominik , Dale Brian M. , Kiefer Berthold , Maier Andreas , Bashir Mustafa R. 
Published: October 2018

Purpose
To develop a bipolar multi‐echo MRI method for the accurate estimation of the adipose tissue fatty acid composition (FAC) using clinically relevant protocols at clinical field strength.
Methods
The proposed technique jointly estimates confounding factors (field map, , eddy‐current phase) and triglyceride saturation state parameters by fitting multi‐echo gradient echo acquisitions to a complex signal model. The noise propagation behavior was improved by applying a low‐rank enforcing denoising technique and by addressing eddy‐current‐induced phase discrepancies analytically. The impact of the total echo train duration on the FAC parameter map accuracy was analyzed in an oil phantom at 3T. Accuracy and reproducibility assessment was based on in vitro oil phantom measurements at two field strengths (3T and 1.5T) and with two different protocols. Repeatability was assessed in vivo in patients (n = 8) with suspected fatty liver disease using test–retest acquisitions in the abdominal subcutaneous, perirenal and mesenteric fat depots.
Results
Echo train readout durations of at least five times the conventional in‐phase time were required for accurate FAC estimation in areas of high fat content. In vitro, linear regression and Bland–Altman analyses demonstrated strong (r > 0.94) and significant (P ≪ 0.01) correlations between measured and reference FACs for all acquisitions, with smaller overall intercepts and biases at 3T compared to 1.5T. In vivo, reported mean absolute differences between test and retest were 1.54%, 3.31%, and 2.63% for the saturated, mono‐unsaturated, and poly‐unsaturated fat component, respectively.
Conclusions
Accurate and reproducible MRI‐based FAC quantification within a breath‐hold is possible at clinical field strengths.
Fast and sensitive dynamic oxygen‐enhanced MRI with a cycling gas challenge and independent component analysis
Authors: Moosvi Firas , Baker Jennifer H.E. , Yung Andrew , Kozlowski Piotr , Minchinton Andrew I. , Reinsberg Stefan A. 
Published: October 2018

Purpose
There is a critical need for non‐invasive imaging biomarkers of tumor oxygenation to assist in patient stratification and development of hypoxia targeting therapies. Using a cycling gas challenge and independent component analysis (ICA), we sought to improve the sensitivity and speed of existing oxygen enhanced MRI (OE‐MRI) techniques to detect changes in oxygenation with dynamically acquired T1W signal intensity images (dOE‐MRI).
Methods
Mice were implanted with SCCVII, HCT‐116, BT‐474, or SKOV3 tumors in the dorsal subcutaneous region and imaged at 7T. T1W images were acquired during a respiratory challenge with alternating 2‐minute periods of air and 100% oxygen for three cycles. Data were analyzed with ICA and oxygenation maps were generated and compared to corresponding histology sections stained for hypoxia (pimonidazole) and blood vessels (CD31).
Results
Cycling air‐oxygen‐air gas challenges were well tolerated and ICA permitted extraction of the oxygen‐enhancing component in all imaged tumors from four different models. Comparison with synthetic response functions showed that dOE‐MRI does not require any a‐priori knowledge of the physiological response. The fraction of O2‐negative dOE‐MRI voxels that correlate inversely with the ICA gas‐cycling component correspond well with the histological hypoxic fraction in SCCVII tumors (r = 0.91, p = 0.0016) but did not correlate in HCT‐116 tumors (r = 0.13, p = 0.81).
Conclusions
Using ICA and adding a cycling gas challenge extends the sensitivity of OE‐MRI and allows the oxygenation status of tumors to be assessed in as little as six minutes. These findings support further development of OE‐MRI as a biomarker of tumor oxygenation.
A hybrid finite element‐spectral boundary integral approach: Applications to dynamic rupture modeling in unbounded domains
Authors: Ma Xiao , Hajarolasvadi Setare , Albertini Gabriele , Kammer David S. , Elbanna Ahmed E. 
Published: October 2018

SummaryThe finite element method (FEM) and the spectral boundary integral method (SBI) have both been widely used in the study of dynamic rupture simulations along a weak interface. In this paper, we present a hybrid method that combines FEM and SBI through the consistent exchange of displacement and traction boundary conditions, thereby benefiting from the flexibility of FEM in handling problems with nonlinearities or small‐scale heterogeneities and from the superior performance and accuracy of SBI. We validate the hybrid method using a benchmark problem from the Southern California Earthquake Center's dynamic rupture simulation validation exercises.We further demonstrate the capability and computational efficiency of the hybrid scheme for resolving off‐fault heterogeneities by studying a 2D in‐plane shear crack in two different settings: one where the crack is embedded in a high‐velocity zone and another where it is embedded in a low‐velocity zone. Finally, we discuss the potential of the hybrid method for addressing a wide range of problems in geophysics and engineering.
Human White Adipose Tissue Metabolome: Current Perspective
Authors: Kučera Jan , Spáčil Zdeněk , Friedecký David , Novák Jan , Pekař Matěj , Bienertová‐Vašků Julie 
Published: October 2018

ObjectiveInterest in metabolites produced by adipose tissue has increased substantially in the past several decades. Previously regarded as an inert energy storage depot, adipose tissue is now viewed as a complex metabolically active organ with considerable impact on human health. The emerging field of mass spectrometry‐based metabolomics presents a powerful tool for the study of processes in complex biological matrices including adipose tissue.ResultsA large number of structurally distinct metabolites can be analyzed to facilitate the investigation of differences between physiological and pathophysiological metabolic profiles associated with adipose tissue. Understanding the molecular basis of adipose tissue regulation can thereby provide insight into the monitoring of obesity‐related metabolic disorders and lead to the development of novel diagnostic and prognostic biomarkers.ConclusionsThis review provides the current state of knowledge, recent progress, and critical evaluation of metabolomics approaches in the context of white adipose tissue and obesity. An overview of basic principles and resources describing individual groups of metabolites analyzed in white adipose tissue and biological fluids is given. The focus is on metabolites that can serve as reliable biomarkers indicative of metabolic alterations associated with obesity.
Predicting photovoltaic soiling losses using environmental parameters: An update
Authors: Micheli Leonardo , Deceglie Michael G. , Muller Matthew 
Published: October 2018

AbstractThis study presents an investigation on the correlations between soiling losses and environmental parameters at 41 locations in the United States, with the aim of analyzing the possibility of predicting soiling losses at a site even when soiling data are not available. The results of this work, which considers the largest pool of soiling data points systematically investigated so far, confirm that a single‐variable regression based on particulate matter concentration returns the best correlations with soiling, with adjusted coefficients of determination up to 70%, corresponding to RMSE as low as 0.9%. Among the various particulate matter datasets investigated, a gridded Environment Protection Agency dataset is for the first time found to return correlations similar to those obtained by interpolating particulate matter monitoring station data. We discuss in detail the different interpolation techniques used to process the particulate matter concentrations because they can greatly impact the correlations. Specifically, the correlation coefficients between soiling and particulate matter range between 70% and less than 20%, depending on the interpolation methods and monitoring distance. Spatial interpolation methods based on inverse distance weighting are found to return better correlations than a nearest neighbor or a simple average approach, especially when large distances are considered. Similarly, the effects of different rain thresholds used to calculate the length of the dry periods are examined. An enhanced two‐variable regression is found to achieve higher‐quality correlations, with adjusted R2 of 90% (RMSE = 0.55%), also suggesting that high and low soiling locations might be differentiated depending on fixed particulate matter or rainfall thresholds.
School psychologists’ beliefs and practices about treatment integrity in 2008 and 2017
Authors: Cochrane Wendy S. , Sanetti Lisa M. H. , Minster Molly C. 
Published: October 2018

AbstractA random sample of 1,000 Nationally Certified School Psychologists were mailed a 17‐item survey about treatment integrity. A total of 132 responded and answered questions about the importance of treatment integrity data for tiered interventions and the frequency and methods used to measure treatment integrity in one‐to‐one and problem‐solving team consultation. Ninety‐eight percent agreed that treatment integrity data were critical for tiered interventions. However, only 7% in one‐to‐one consultation and 0% in team consultation reported it was “always” collected. Respondents identified barriers of time, workload, system factors, and staff knowledge as explanations for why there was a gap between belief and practice. The participant responses were compared to those from a 2008 survey and found to be almost unchanged. Issues associated with decision‐making when treatment integrity data are lacking and recommendations for improving the assessment and reporting of treatment integrity are discussed.