bluuebunny/crossref_metadata_2025_split huggingface dataset:
Real‐time free‐breathing cardiac imaging with self‐calibrated through‐time radial GRAPPA
Authors: Sayin Ozan , Saybasili Haris , Zviman M. Muz , Griswold Mark , Halperin Henry , Seiberlich Nicole , Herzka Daniel A. 
Published: March 2016

PurposeReal‐time free‐breathing cardiac imaging with highly undersampled radial trajectories has previously been successfully demonstrated using calibrated radial generalized autocalibrating partially parallel acquisition (rGRAPPA). A self‐calibrated approach for rGRAPPA is proposed that removes the need for the calibration prescan.MethodsTo investigate the effect of various parameters on image quality, a comprehensive imaging study on one normal swine was performed. Root mean squared errors (RMSEs) were computed with respect to gold standard acquisitions, and several acquisition/reconstruction strategies were compared. Additionally, the method was tested on 13 human subjects, and RMSEs relative to standard through‐time radial GRAPPA were computed.ResultsReal‐time images with high spatiotemporal resolution were obtained. Image quality was comparable to calibrated through‐time rGRAPPA with endocardial and epicardial borders clearly delineated. In the swine, the average RMSE between self‐calibrated and gold‐standard calibrated images was 5.18 ± 0.84%. In normal human subjects, the average RMSE between self‐calibrated and calibrated through‐time rGRAPPA was 3.79 ± 0.64%. For lower accelerations rates (R = 6‐8) image quality was similar to comparable calibrated scans though RMSE increased for higher degrees of undersampling (R = 12–16).ConclusionHighly accelerated real‐time imaging with undersampled radial trajectories without additional calibration data is feasible. Image quality was acceptable for real‐time cardiac MRI applications demanding high speed. Magn Reson Med 77:250–264, 2017. © 2016 Wiley Periodicals, Inc.
Desynchronization of Cartesian k‐space sampling and periodic motion for improved retrospectively self‐gated 3D lung MRI using quasi‐random numbers
Authors: Weick Stefan , Völker Michael , Hemberger Kathrin , Meyer Cord , Ehses Philipp , Polat Bülent , Breuer Felix A. , Blaimer Martin , Fink Christian , Schad Lothar R. , Sauer Otto A. , Flentje Michael , Jakob Peter M. 
Published: March 2016

PurposeTo demonstrate that desynchronization between Cartesian k‐space sampling and periodic motion in free‐breathing lung MRI improves the robustness and efficiency of retrospective respiratory self‐gating.MethodsDesynchronization was accomplished by reordering the phase (ky) and partition (kz) encoding of a three‐dimensional FLASH sequence according to two‐dimensional, quasi‐random (QR) numbers. For retrospective respiratory self‐gating, the k‐space center signal (DC signal) was acquired separately after each encoded k‐space line. QR sampling results in a uniform distribution of k‐space lines after gating. Missing lines resulting from the gating process were reconstructed using iterative GRAPPA. Volunteer measurements were performed to compare quasi‐random with conventional sampling. Patient measurements were performed to demonstrate the feasibility of QR sampling in a clinical setting.ResultsThe uniformly sampled k‐space after retrospective gating allows for a more stable iterative GRAPPA reconstruction and improved ghost artifact reduction compared with conventional sampling. It is shown that this stability can either be used to reduce the total scan time or to reconstruct artifact‐free data sets in different respiratory phases, both resulting in an improved efficiency of retrospective respiratory self‐gating.ConclusionQR sampling leads to desynchronization between repeated data acquisition and periodic respiratory motion. This results in an improved motion artifact reduction in shorter scan time. Magn Reson Med 77:787–793, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Flexible proton 3DMR spectroscopic imaging of the prostate with low‐power adiabatic pulses for volume selection and spiral readout
Authors: Steinseifer Isabell K. , Philips Bart W.J. , Gagoski Borjan , Weiland Elisabeth , Scheenen Tom W. J. , Heerschap Arend 
Published: March 2016

PurposeCartesian k‐space sampling in three‐dimensional magnetic resonance spectroscopic imaging (MRSI) of the prostate limits the selection of voxel size and acquisition time. Therefore, large prostates are often scanned at reduced spatial resolutions to stay within clinically acceptable measurement times. Here we present a semilocalized adiabatic selective refocusing (sLASER) sequence with gradient‐modulated offset‐independent adiabatic (GOIA) refocusing pulses and spiral k‐space acquisition (GOIA‐sLASER‐Spiral) for fast prostate MRSI with enhanced resolution and extended matrix sizes.MethodsMR was performed at 3 tesla with an endorectal receive coil. GOIA‐sLASER‐Spiral at an echo time (TE) of 90 ms was compared to a point‐resolved spectroscopy sequence (PRESS) with weighted, elliptical phase encoding at an TE of 145 ms using simulations and measurements of phantoms and patients (n = 9).ResultsGOIA‐sLASER‐Spiral acquisition allows prostate MR spectra to be obtained in ∼5 min with a quality comparable to those acquired with a common Cartesian PRESS protocol in ∼9 min, or at an enhanced spatial resolution showing more precise tissue allocation of metabolites. Extended field of views (FOVs) and matrix sizes for large prostates are possible without compromising spatial resolution or measurement time.ConclusionThe flexibility of spiral sampling enables prostate MRSI with a wide range of resolutions and FOVs without undesirable increases in acquisition times, as in Cartesian encoding. This approach is suitable for routine clinical exams of prostate metabolites. Magn Reson Med 77:928–935, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Estimating absolute‐phase maps using ESPIRiT and virtual conjugate coils
Authors: Uecker Martin , Lustig Michael 
Published: March 2016

PurposeTo develop an ESPIRiT‐based method to estimate coil sensitivities with image phase as a building block for efficient and robust image reconstruction with phase constraints.Theory and MethodsESPIRiT is a new framework for calibration of the coil sensitivities and reconstruction in parallel magnetic resonance imaging. Applying ESPIRiT to a combined set of physical and virtual conjugate coils (VCC‐ESPIRiT) implicitly exploits conjugate symmetry in k‐space similar to VCC‐GRAPPA. Based on this method, a new post‐processing step is proposed for the explicit computation of coil sensitivities that include the absolute phase of the image. The accuracy of the computed maps is directly validated using a test based on projection onto fully sampled coil images and also indirectly in phase‐constrained parallel‐imaging reconstructions.ResultsThe proposed method can estimate accurate sensitivities which include low‐resolution image phase. In case of high‐frequency phase variations VCC‐ESPIRiT yields an additional set of maps that indicates the existence of a high‐frequency phase component. Taking this additional set of maps into account can improve the robustness of phase‐constrained parallel imaging.ConclusionThe extended VCC‐ESPIRiT is a useful tool for phase‐constrained imaging. Magn Reson Med 77:1201–1207, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Optimal experimental design for filter exchange imaging: Apparent exchange rate measurements in the healthy brain and in intracranial tumors
Authors: Lampinen Björn , Szczepankiewicz Filip , van Westen Danielle , Englund Elisabet , C Sundgren Pia , Lätt Jimmy , Ståhlberg Freddy , Nilsson Markus 
Published: March 2016

PurposeFilter exchange imaging (FEXI) is sensitive to the rate of diffusional water exchange, which depends, eg, on the cell membrane permeability. The aim was to optimize and analyze the ability of FEXI to infer differences in the apparent exchange rate (AXR) in the brain between two populations.MethodsA FEXI protocol was optimized for minimal measurement variance in the AXR. The AXR variance was investigated by test‐retest acquisitions in six brain regions in 18 healthy volunteers. Preoperative FEXI data and postoperative microphotos were obtained in six meningiomas and five astrocytomas.ResultsProtocol optimization reduced the coefficient of variation of AXR by approximately 40%. Test‐retest AXR values were heterogeneous across normal brain regions, from 0.3 ± 0.2 s−1 in the corpus callosum to 1.8 ± 0.3 s−1 in the frontal white matter. According to analysis of statistical power, in all brain regions except one, group differences of 0.3–0.5 s−1 in the AXR can be inferred using 5 to 10 subjects per group. An AXR difference of this magnitude was observed between meningiomas (0.6 ± 0.1 s−1) and astrocytomas (1.0 ± 0.3 s−1).ConclusionsWith the optimized protocol, FEXI has the ability to infer relevant differences in the AXR between two populations for small group sizes. Magn Reson Med 77:1104–1114, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.
Robust diffusion tensor imaging by spatiotemporal encoding: Principles and in vivo demonstrations
Authors: Solomon Eddy , Liberman Gilad , Nissan Noam , Frydman Lucio 
Published: March 2016

PurposeEvaluate the usefulness of single‐shot and of interleaved spatiotemporally encoded (SPEN) methods to perform diffusion tensor imaging (DTI) under various preclinical and clinical settings.MethodsA formalism for analyzing SPEN DTI data is presented, tailored to account for the spatially dependent b‐matrix weightings introduced by the sequence's use of swept pulses acting while in the presence of field gradients. Using these b‐matrix calculations, SPEN's ability to deliver DTI measurements was tested on phantoms as well as ex vivo and in vivo. In the latter case, DTI involved scans on mice brains and on human lactating breasts.ResultsFor both ex vivo and in vivo investigations, SPEN data proved less sensitive to distortions arising from Bo field inhomogeneities and from eddy currents, than conventional single‐shot alternatives. Further resolution enhancement could be achieved using referenceless methods for interleaved SPEN data acquisitions.ConclusionThe robustness of SPEN‐based sequences vis‐à‐vis field instabilities and heterogeneities, enables the implementation of DTI experiments with good sensitivity and resolution even in challenging environments in both preclinical and clinical settings. Magn Reson Med 77:1124–1133, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Jacobian weighted temporal total variation for motion compensated compressed sensing reconstruction of dynamic MRI
Authors: Royuela‐del‐Val Javier , Cordero‐Grande Lucilio , Simmross‐Wattenberg Federico , Martín‐Fernández Marcos , Alberola‐López Carlos 
Published: March 2016

PurposeTo eliminate the need of spatial intraframe regularization in a recently reported dynamic MRI compressed‐sensing‐based reconstruction method with motion compensation and to increase its performance.Theory and MethodsWe propose a new regularization metric based on the introduction of a spatial weighting measure given by the Jacobian of the estimated deformations. It shows convenient discretization properties and, as a byproduct, it also provides a theoretical support to a result reported by others based on an intuitive design. The method has been applied to the reconstruction of both short and long axis views of the heart of four healthy volunteers. Quantitative image quality metrics as well as straightforward visual assessment are reported.ResultsShort and long axis reconstructions of cardiac cine MRI sequences have shown superior results than previously reported methods both in terms of quantitative metrics and of visual assessment. Fine details are better preserved due to the lack of additional intraframe regularization, with no significant image artifacts even for an acceleration factor of 12.ConclusionsThe proposed Jacobian Weighted temporal Total Variation results in better reconstructions of highly undersampled cardiac cine MRI than previously proposed methods and sets a theoretical ground for forward and backward predictors used elsewhere. Magn Reson Med 77:1208–1215, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Efficient parallel reconstruction for high resolution multishot spiral diffusion data with low rank constraint
Authors: Liao Congyu , Chen Ying , Cao Xiaozhi , Chen Song , He Hongjian , Mani Merry , Jacob Mathews , Magnotta Vincent , Zhong Jianhui 
Published: March 2016

PurposeTo propose a novel reconstruction method using parallel imaging with low rank constraint to accelerate high resolution multishot spiral diffusion imaging.Theory and MethodsThe undersampled high resolution diffusion data were reconstructed based on a low rank (LR) constraint using similarities between the data of different interleaves from a multishot spiral acquisition. The self‐navigated phase compensation using the low resolution phase data in the center of k‐space was applied to correct shot‐to‐shot phase variations induced by motion artifacts. The low rank reconstruction was combined with sensitivity encoding (SENSE) for further acceleration. The efficiency of the proposed joint reconstruction framework, dubbed LR‐SENSE, was evaluated through error quantifications and compared with
regularized compressed sensing method and conventional iterative SENSE method using the same datasets.ResultsIt was shown that with a same acceleration factor, the proposed LR‐SENSE method had the smallest normalized sum‐of‐squares errors among all the compared methods in all diffusion weighted images and DTI‐derived index maps, when evaluated with different acceleration factors (R = 2, 3, 4) and for all the acquired diffusion directions.ConclusionRobust high resolution diffusion weighted image can be efficiently reconstructed from highly undersampled multishot spiral data with the proposed LR‐SENSE method. Magn Reson Med 77:1359–1366, 2017. © 2016 International Society for Magnetic Resonance in Medicine
Enhancing Multiple Routing Configurations through systematic analysis of topological characteristics
Authors: Cevher Selcuk , Ulutas Mustafa , Hokelek Ibrahim 
Published: March 2016

SummaryPrevious studies show that topological characteristics in IP networks significantly influence the performance of networking algorithms, which therefore should be systematically analyzed using diverse topologies prior to their deployments. In this paper, we present an elaborate topological dependency analysis of a multi‐topology routing‐based IP fast re‐route technology, namely, Multiple Routing Configurations (MRC), using a large topology pool with diverse properties. Through an extensive analysis using our automated topological analysis tool, we discover a significant correlation between the performance of MRC and topological characteristics. MRC needs to construct a higher number of virtual topologies to provide full alternate path coverage if a network topology tends to have more hub nodes, whose degree is much higher than the rest of the network. Inspired by our topological analysis results, we propose a new heuristic algorithm enhancing MRC. Numerical experiments demonstrate that our heuristic significantly improves the performance of MRC confirming the effectiveness of the systematic analysis of topological characteristics. Copyright © 2016 John Wiley & Sons, Ltd.
Repeated Blood Cultures in Pediatric Febrile Neutropenia: Would Following the Guidelines Alter the Outcome?
Authors: Petty Lindsay A. , Sokol Elizabeth A. , Bartlett Allison H. , McNeer Jennifer L. , Alexander Kenneth A. , Pisano Jennifer 
Published: March 2016

BackgroundThe Infectious Diseases Society of America (IDSA) guidelines recommend collecting blood cultures for the first 3 days of febrile neutropenia (FN) in the clinically stable oncology patient with persistent fevers. Nonetheless, many physicians send daily blood cultures beyond 3 days, and the impact of that practice is uncertain.ProcedureWe reviewed pediatric FN episodes from July 2009 to May 2014 at University of Chicago Comer Children's Hospital. For each positive culture, we determined if it was a pathogen or a contaminant. We reviewed episode and patient demographics to identify risk factors for subsequent positive blood cultures in the setting of an initially negative culture.ResultsWe identified 381 episodes of FN in 162 patients. Of those, 87 had a positive blood culture on day 1 (21.0% incidence of bacteremia). Of 294 episodes with a negative blood culture on day 1, six (2.04%, 95% confidence interval [CI] 0.42–3.67) had a positive culture after day 3. Of those, three were pathogens (1.02%, 95%CI –0.14 to 2.18), and only one was found in a hemodynamically stable patient (0.34%, 95%CI –0.33 to 1.01) with new mucositis. In the other two patients, Escherichia coli was isolated from blood cultures after day 10 in the setting of significant hemodynamic changes. Risk factor analysis performed in stable patients yielded nonsignificant results.ConclusionsOf 294 FN episodes with an initial negative blood culture, only one episode of bacteremia occurred without hemodynamic changes past day 3, supporting the IDSA guidelines to discontinue blood cultures in stable FN patients after day 3.
Association of BNP, NTproBNP, and early postnatal pulmonary hypertension in very preterm infants
Authors: König Kai , Guy Katelyn J. , Walsh Geraldine , Drew Sandra M. , Barfield Charles P. 
Published: March 2016

SummaryObjectiveB‐type natriuretic peptide (BNP) has been shown to correlate with pulmonary hypertension (PH) in term neonates with persistent pulmonary hypertension of the newborn or congenital diaphragmatic hernia, and in very preterm infants with bronchopulmonary dysplasia. This study investigated the potential association of BNP and N‐terminal‐pro‐BNP (NTproBNP) and PH within the first 72 hr of life in very preterm infants.MethodsPreterm infants <32 weeks gestational age who received an echocardiogram within the first 72 hr of life were eligible. BNP and NTproBNP were sampled at the time of the echocardiogram. Right ventricular systolic pressure (RVSP) was calculated as a surrogate marker of PH. Simple and multiple linear regression analysis was performed to examine associations and potential confounding factors.ResultsSixty‐one infants were included with a median (IQR) birth weight of 983 g (826–1,167) and a median (IQR) gestational age of 272 weeks (262–286). There was no difference between BNP or NTproBNP levels for infants with or without measurable RVSP. There was no significant correlation of BNP and RVSP in multiple linear regression analysis (regression coefficient −0.0035 (95%CI: −0.020 to 0.013), P = 0.67). Also, NTproBNP and RVSP were not significantly correlated in multiple linear regression analysis (regression coefficient 0.0071 (95%CI: −0.019 to 0.033), P = 0.58).ConclusionB‐type natriuretic peptides did not correlate with RVSP in the early postnatal period of very preterm infants. Pediatr Pulmonol. 2016;51:820–824. © 2016 Wiley Periodicals, Inc.
Thermal conductivity of bulk boron nitride nanotube sheets and their epoxy‐impregnated composites
Authors: Jakubinek Michael B. , Niven John F. , Johnson Michel B. , Ashrafi Behnam , Kim Keun Su , Simard Benoit , White Mary Anne 
Published: March 2016

The thermal conductivity of bulk, self‐supporting boron nitride nanotube (BNNT) sheets composed of nominally 100% BNNTs oriented randomly in‐plane was measured by a steady‐state, parallel thermal conductance method. The sheets were either collected directly during synthesis or produced by dispersion and filtration. Differences between the effective thermal conductivities of filtration‐produced BNNT buckypaper (∼1.5 W m−1 K−1) and lower‐density as‐synthesized sheets (∼0.75 W m−1 K−1), which are both porous materials, were primarily due to their density. The measured results indicate similar thermal conductivity, in the range of 7–12 W m−1 K−1, for the BNNT network in these sheets. High BNNT‐content composites (∼30 wt.% BNNTs) produced by epoxy impregnation of the porous BNNT network gave 2–3 W m−1 K−1, more than 10× the baseline epoxy. The combination of manufacturability, thermal conductivity, and electrical insulation offers exciting potential for electrically insulating, thermally conductive coatings and packaging.Thermal conductivity of free‐standing BNNT buckypaper, buckypaper composites, and related materials at room temperature.
Searchable symmetric encryption capable of searching for an arbitrary string
Authors: Uchide Yoshinao , Kunihiro Noboru 
Published: March 2016

AbstractA booming cloud service has made it possible to consider a third‐party server as private storage. When storage is used as a document archive, it is useful to provide functionality that allows users to find documents containing a specified string as a substring. The current method for providing such functionality while keeping the contents of the documents secret, either has linear complexity in the total size of the documents or needs to extract keywords when the documents are stored. Therefore, no method exists for efficiently searching for an arbitrary string that has not been extracted as a keyword. We propose the first encryption scheme that enables efficient searching for an arbitrary string. Although our scheme leaks some information for the sake of efficiency, all information leaked is derived from the precise leakage profile we have defined. © 2016 The Authors Security and Communication Networks Published by John Wiley & Sons Ltd
A secure chaotic maps‐based privacy‐protection scheme for multi‐server environments
Authors: Li Chun‐Ta 
Published: March 2016

AbstractA multi‐server environment helps the users to register at the registration center once and can gain numerous network services and resources provided by remote application servers. In order to protect sensitive data from unauthorized disclosure, to authenticate the identities of network participants, and to preserve user anonymity, many chaotic maps‐based multi‐server authenticated key agreement schemes with user anonymity were proposed. Recently, Zhu proposed a provable privacy‐protection system towards multi‐server architecture, and the main contributions of their proposed system are achieving mutual authentication between network participants and ensuring the anonymity or hiding identities for the login users. However, we analyze the security of Zhu's scheme and show that it is vulnerable to privileged‐insider attack and does not protect user anonymity. We also demonstrate that Zhu's scheme fails to provide mutual authentication between login user and application server and has a design flaw in anonymous authentication. To withstand these security drawbacks, we further design an improved chaotic maps‐based privacy‐protection scheme for multi‐server environments. In comparison with the existing chaotic maps‐based privacy‐protection schemes, our proposed scheme is more secure with acceptable computation costs for multi‐server environments. Copyright © 2016 John Wiley & Sons, Ltd.