bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensional micro‐MRI analysis of cerebral artery development in mouse embryos
Authors: Berrios‐Otero Cesar A. , Wadghiri Youssef Zaim , Nieman Brian J. , Joyner Alexandra L. , Turnbull Daniel H. 
Published: October 2009

AbstractVascular system development involves a complex, three‐dimensional branching process that is critical for normal embryogenesis. In the brain, the arterial systems appear to develop in a stereotyped fashion, but no detailed quantitative analyses of the mouse embryonic cerebral arteries have been described. In this study, a gadolinium‐based contrast perfusion method was developed to selectively enhance the cerebral arteries in fixed mouse embryos. Three‐dimensional magnetic resonance micro‐imaging (micro‐MRI) data were acquired simultaneously from multiple embryos staged between 10 and 17 days of gestation, and a variety of image analysis methods was used to extract and analyze the cerebral arterial patterns. The results show that the primary arterial branches in the mouse brain are very similar between individuals, with the patterns established early and growth occurring by extension of the segments, while maintaining the underlying vascular geometry. To investigate the utility of this method for mutant mouse phenotype analysis, contrast‐enhanced micro‐MRI data were acquired from Gli2‐/‐ mutant embryos and their wild‐type littermates, showing several previously unreported vascular phenotypes in Gli2−/− embryos, including the complete absence of the basilar artery. These results demonstrate that contrast‐enhanced micro‐MRI provides a powerful tool for analyzing vascular phenotypes in a variety of genetically engineered mice. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Robust GRAPPA‐accelerated diffusion‐weighted readout‐segmented (RS)‐EPI
Authors: Holdsworth Samantha J. , Skare Stefan , Newbould Rexford D. , Bammer Roland 
Published: October 2009

AbstractReadout segmentation (RS‐EPI) has been suggested as a promising variant to echo‐planar imaging (EPI) for high‐resolution imaging, particularly when combined with parallel imaging. This work details some of the technical aspects of diffusion‐weighted (DW)‐RS‐EPI, outlining a set of reconstruction methods and imaging parameters that can both minimize the scan time and afford high‐resolution diffusion imaging with reduced distortions. These methods include an efficient generalized autocalibrating partially parallel acquisition (GRAPPA) calibration for DW‐RS‐EPI data without scan time penalty, together with a variant for the phase correction of partial Fourier RS‐EPI data. In addition, the role of pulsatile and rigid‐body brain motion in DW‐RS‐EPI was assessed. Corrupt DW‐RS‐EPI data arising from pulsatile nonlinear brain motion had a prevalence of ∼7% and were robustly identified via k‐space entropy metrics. For DW‐RS‐EPI data corrupted by rigid‐body motion, we showed that no blind overlap was required. The robustness of RS‐EPI toward phase errors and motion, together with its minimized distortions compared with EPI, enables the acquisition of exquisite 3 T DW images with matrix sizes close to 5122. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
High‐contrast in vivo visualization of microvessels using novel FeCo/GC magnetic nanocrystals
Authors: Lee Jin Hyung , Sherlock Sarah P. , Terashima Masahiro , Kosuge Hisanori , Suzuki Yoriyasu , Goodwin Andrew , Robinson Joshua , Seo Won Seok , Liu Zhuang , Luong Richard , McConnell Michael V. , Nishimura Dwight G. , Dai Hongjie 
Published: October 2009

AbstractFeCo‐graphitic carbon shell nanocrystals are a novel MRI contrast agent with unprecedented high per‐metal‐atom‐basis relaxivity (r1 = 97 mM‐1 sec‐1, r2 = 400 mM‐1 sec‐1) and multifunctional capabilities. While the conventional gadolinium‐based contrast‐enhanced angiographic magnetic MRI has proven useful for diagnosis of vascular diseases, its short circulation time and relatively low sensitivity render high‐resolution MRI of morphologically small vascular structures such as those involved in collateral, arteriogenic, and angiogenic vessel formation challenging. Here, by combining FeCo‐graphitic carbon shell nanocrystals with high‐resolution MRI technique, we demonstrate that such microvessels down to ∼100 μm can be monitored in high contrast and noninvasively using a conventional 1.5‐T clinical MRI system, achieving a diagnostic imaging standard approximating that of the more invasive X‐ray angiography. Preliminary in vitro and in vivo toxicity study results also show no sign of toxicity. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Classification of brain tumor type and grade using MRI texture and shape in a machine learning scheme
Authors: Zacharaki Evangelia I. , Wang Sumei , Chawla Sanjeev , Soo Yoo Dong , Wolf Ronald , Melhem Elias R. , Davatzikos Christos 
Published: October 2009

AbstractThe objective of this study is to investigate the use of pattern classification methods for distinguishing different types of brain tumors, such as primary gliomas from metastases, and also for grading of gliomas. The availability of an automated computer analysis tool that is more objective than human readers can potentially lead to more reliable and reproducible brain tumor diagnostic procedures. A computer‐assisted classification method combining conventional MRI and perfusion MRI is developed and used for differential diagnosis. The proposed scheme consists of several steps including region‐of‐interest definition, feature extraction, feature selection, and classification. The extracted features include tumor shape and intensity characteristics, as well as rotation invariant texture features. Feature subset selection is performed using support vector machines with recursive feature elimination. The method was applied on a population of 102 brain tumors histologically diagnosed as metastasis (24), meningiomas (4), gliomas World Health Organization grade II (22), gliomas World Health Organization grade III (18), and glioblastomas (34). The binary support vector machine classification accuracy, sensitivity, and specificity, assessed by leave‐one‐out cross‐validation, were, respectively, 85%, 87%, and 79% for discrimination of metastases from gliomas and 88%, 85%, and 96% for discrimination of high‐grade (grades III and IV) from low‐grade (grade II) neoplasms. Multiclass classification was also performed via a one‐vs‐all voting scheme. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Sodium MRI using a density‐adapted 3D radial acquisition technique
Authors: Nagel Armin M. , Laun Frederik B. , Weber Marc‐André , Matthies Christian , Semmler Wolfhard , Schad Lothar R. 
Published: October 2009

AbstractA density‐adapted three‐dimensional radial projection reconstruction pulse sequence is presented which provides a more efficient k‐space sampling than conventional three‐dimensional projection reconstruction sequences. The gradients of the density‐adapted three‐dimensional radial projection reconstruction pulse sequence are designed such that the averaged sampling density in each spherical shell of k‐space is constant. Due to hardware restrictions, an inner sphere of k‐space is sampled without density adaption. This approach benefits from both the straightforward handling of conventional three‐dimensional projection reconstruction sequence trajectories and an enhanced signal‐to‐noise ratio (SNR) efficiency akin to the commonly used three‐dimensional twisted projection imaging trajectories. Benefits for low SNR applications, when compared to conventional three‐dimensional projection reconstruction sequences, are demonstrated with the example of sodium imaging. In simulations of the point‐spread function, the SNR of small objects is increased by a factor 1.66 for the density‐adapted three‐dimensional radial projection reconstruction pulse sequence sequence. Using analytical and experimental phantoms, it is shown that the density‐adapted three‐dimensional radial projection reconstruction pulse sequence allows higher resolutions and is more robust in the presence of field inhomogeneities. High‐quality in vivo images of the healthy human leg muscle and the healthy human brain are acquired. For equivalent scan times, the SNR is up to a factor of 1.8 higher and anatomic details are better resolved using density‐adapted three‐dimensional radial projection reconstruction pulse sequence. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Disease state prediction from resting state functional connectivity
Authors: Craddock R. Cameron , Holtzheimer Paul E. , Hu Xiaoping P. , Mayberg Helen S. 
Published: October 2009

AbstractThe application of multivoxel pattern analysis methods has attracted increasing attention, particularly for brain state prediction and real‐time functional MRI applications. Support vector classification is the most popular of these techniques, owing to reports that it has better prediction accuracy and is less sensitive to noise. Support vector classification was applied to learn functional connectivity patterns that distinguish patients with depression from healthy volunteers. In addition, two feature selection algorithms were implemented (one filter method, one wrapper method) that incorporate reliability information into the feature selection process. These reliability feature selections methods were compared to two previously proposed feature selection methods. A support vector classifier was trained that reliably distinguishes healthy volunteers from clinically depressed patients. The reliability feature selection methods outperformed previously utilized methods. The proposed framework for applying support vector classification to functional connectivity data is applicable to other disease states beyond major depression. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Tailored RF pulse for magnetization inversion at ultrahigh field
Authors: Hurley Aaron C. , Al‐Radaideh Ali , Bai Li , Aickelin Uwe , Coxon Ron , Glover Paul , Gowland Penny A. 
Published: October 2009

AbstractThe radiofrequency (RF) transmit field is severely inhomogeneous at ultrahigh field due to both RF penetration and RF coil design issues. This particularly impairs image quality for sequences that use inversion pulses such as magnetization prepared rapid acquisition gradient echo and limits the use of quantitative arterial spin labeling sequences such as flow‐attenuated inversion recovery. Here we have used a search algorithm to produce inversion pulses tailored to take into account the heterogeneity of the RF transmit field at 7 T. This created a slice selective inversion pulse that worked well (good slice profile and uniform inversion) over the range of RF amplitudes typically obtained in the head at 7 T while still maintaining an experimentally achievable pulse length and pulse amplitude in the brain at 7 T. The pulses used were based on the frequency offset correction inversion technique, as well as time dilation of functions, but the RF amplitude, frequency sweep, and gradient functions were all generated using a genetic algorithm with an evaluation function that took into account both the desired inversion profile and the transmit field inhomogeneity. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Initial results on in vivo human coronary MR angiography at 7 T
Authors: van Elderen Saska G. C. , Versluis Maarten J. , Webb Andrew G. , Westenberg Jos J. M. , Doornbos Joost , Smith Nadine B. , de Roos Albert , Stuber Matthias 
Published: October 2009

AbstractSeven tesla (T) MR imaging is potentially promising for the morphologic evaluation of coronary arteries because of the increased signal‐to‐noise ratio compared to lower field strengths, in turn allowing improved spatial resolution, improved temporal resolution, or reduced scanning times. However, there are a large number of technical challenges, including the commercial 7 T systems not being equipped with homogeneous body radiofrequency coils, conservative specific absorption rate constraints, and magnified sample‐induced amplitude of radiofrequency field inhomogeneity. In the present study, an initial attempt was made to address these challenges and to implement coronary MR angiography at 7 T. A single‐element radiofrequency transmit and receive coil was designed and a 7 T specific imaging protocol was implemented, including significant changes in scout scanning, contrast generation, and navigator geometry compared to current protocols at 3 T. With this methodology, the first human coronary MR images were successfully obtained at 7 T, with both qualitative and quantitative findings being presented. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Radial k‐t FOCUSS for high‐resolution cardiac cine MRI
Authors: Jung Hong , Park Jaeseok , Yoo Jaeheung , Ye Jong Chul 
Published: October 2009

AbstractA compressed sensing dynamic MR technique called k‐t FOCUSS (k‐t FOCal Underdetermined System Solver) has been recently proposed. It outperforms the conventional k‐t BLAST/SENSE (Broad‐use Linear Acquisition Speed‐up Technique/SENSitivity Encoding) technique by exploiting the sparsity of x‐f signals. This paper applies this idea to radial trajectories for high‐resolution cardiac cine imaging. Radial trajectories are more suitable for high‐resolution dynamic MRI than Cartesian trajectories since there is smaller tradeoff between spatial resolution and number of views if streaking artifacts due to limited views can be resolved. As shown for Cartesian trajectories, k‐t FOCUSS algorithm efficiently removes artifacts while preserving high temporal resolution. k‐t FOCUSS algorithm applied to radial trajectories is expected to enhance dynamic MRI quality. Rather than using an explicit gridding method, which transforms radial k‐space sampling data to Cartesian grid prior to applying k‐t FOCUSS algorithms, we use implicit gridding during FOCUSS iterations to prevent k‐space sampling errors from being propagated. In addition, motion estimation and motion compensation after the first FOCUSS iteration were used to further sparsify the residual image. By applying an additional k‐t FOCUSS step to the residual image, improved resolution was achieved. In vivo experimental results show that this new method can provide high spatiotemporal resolution even from a very limited radial data set. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
Quantitative T2 analysis: The effects of noise, regularization, and multivoxel approaches
Authors: Bjarnason Thorarin A. , McCreary Cheryl R. , Dunn Jeff F. , Mitchell J. Ross 
Published: October 2009

AbstractTypical quantitative T2 (qT2) analysis involves creating T2 distributions using a regularized algorithm from region‐of‐interest averaged decay data. This study uses qT2 analysis of simulated and experimental decay signals to determine how (a) noise‐type, (b) regularization, and (c) region‐of‐interest versus multivoxel analyses affect T2 distributions. Our simulations indicate that regularization causes myelin water fraction and intra/extracellular water geometric mean T2 underestimation that worsens as the signal‐to‐noise ratio decreases. The underestimation was greater for intra/extracellular water geometric mean T2 measures using Rician noise. Simulations showed significant differences between myelin water fractions determined using region‐of‐interest and multivoxel approaches compared to the true value. The nonregularized voxel‐based approach gave the most accurate measure of myelin water fraction and intra/extracellular water geometric mean T2 for a given signal‐to‐noise ratio and noise type. Additionally, multivoxel analysis provides important information about the variability of the analysis. Results obtained from in vivo rat data were similar to our simulation results. In each case, a nonregularized, multivoxel analysis provided myelin water fractions significantly different from the regularized approaches and obtained the largest myelin water fraction. We conclude that quantitative T2 analysis is best performed using a nonregularized, multivoxel approach. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
Robust water/fat separation in the presence of large field inhomogeneities using a graph cut algorithm
Authors: Hernando Diego , Kellman P. , Haldar J. P. , Liang Z.‐P. 
Published: October 2009

AbstractWater/fat separation is a classical problem for in vivo proton MRI. Although many methods have been proposed to address this problem, robust water/fat separation remains a challenge, especially in the presence of large amplitude of static field inhomogeneities. This problem is challenging because of the nonuniqueness of the solution for an isolated voxel. This paper tackles the problem using a statistically motivated formulation that jointly estimates the complete field map and the entire water/fat images. This formulation results in a difficult optimization problem that is solved effectively using a novel graph cut algorithm, based on an iterative process where all voxels are updated simultaneously. The proposed method has good theoretical properties, as well as an efficient implementation. Simulations and in vivo results are shown to highlight the properties of the proposed method and compare it to previous approaches. Twenty‐five cardiac datasets acquired on a short, wide‐bore scanner with different slice orientations were used to test the proposed method, which produced robust water/fat separation for these challenging datasets. This paper also shows example applications of the proposed method, such as the characterization of intramyocardial fat. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
T2 measurement in articular cartilage: Impact of the fitting method on accuracy and precision at low SNR
Authors: Raya José G. , Dietrich Olaf , Horng Annie , Weber Jürgen , Reiser Maximilian F. , Glaser Christian 
Published: October 2009

AbstractT2 relaxation time is a promising MRI parameter for the detection of cartilage degeneration in osteoarthritis. However, the accuracy and precision of the measured T2 may be substantially impaired by the low signal‐to‐noise ratio of images available from clinical examinations. The purpose of this work was to assess the accuracy and precision of the traditional fit methods (linear least‐squares regression and nonlinear fit to an exponential) and two new noise‐corrected fit methods: fit to a noise‐corrected exponential and fit of the noise‐corrected squared signal intensity to an exponential. Accuracy and precision have been analyzed in simulations, in phantom measurements, and in seven repetitive acquisitions of the patellar cartilage in six healthy volunteers. Traditional fit methods lead to a poor accuracy for low T2, with overestimations of the exact T2 up to 500%. The noise‐corrected fit methods demonstrate a very good accuracy for all T2 values and signal‐to‐noise ratio. Even more, the fit to a noise‐corrected exponential results in precisions comparable to the best achievable precisions (Cramér‐Rao lower bound). For in vivo images, the traditional fit methods considerably overestimate T2 near the bone‐cartilage interface. Therefore, using an adequate fit method may substantially improve the sensitivity of T2 to detect pathology in cartilage and change in T2 follow‐up examinations. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
Optimization ofk‐space trajectories for compressed sensing by Bayesian experimental design
Authors: Seeger Matthias , Nickisch Hannes , Pohmann Rolf , Schölkopf Bernhard 
Published: October 2009

AbstractThe optimization ofk‐space sampling for nonlinear sparse MRI reconstruction is phrased as a Bayesian experimental design problem. Bayesian inference is approximated by a novel relaxation to standard signal processing primitives, resulting in an efficient optimization algorithm for Cartesian and spiral trajectories. On clinical resolution brain image data from a Siemens 3T scanner, automatically optimized trajectories lead to significantly improved images, compared to standard low‐pass, equispaced, or variable density randomized designs. Insights into the nonlinear design optimization problem for MRI are given. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
3D steady‐state diffusion‐weighted imaging with trajectory using radially batched internal navigator echoes (TURBINE)
Authors: McNab Jennifer A. , Gallichan Daniel , Miller Karla L. 
Published: October 2009

AbstractWhile most diffusion‐weighted imaging (DWI) is acquired using single‐shot diffusion‐weighted spin‐echo echo‐planar imaging, steady‐state DWI is an alternative method with the potential to achieve higher‐resolution images with less distortion. Steady‐state DWI is, however, best suited to a segmented three‐dimensional acquisition and thus requires three‐dimensional navigation to fully correct for motion artifacts. In this paper, a method for three‐dimensional motion‐corrected steady‐state DWI is presented. The method uses a unique acquisition and reconstruction scheme named trajectory using radially batched internal navigator echoes (TURBINE). Steady‐state DWI with TURBINE uses slab‐selection and a short echo‐planar imaging (EPI) readout each pulse repetition time. Successive EPI readouts are rotated about the phase‐encode axis. For image reconstruction, batches of cardiac‐synchronized readouts are used to form three‐dimensional navigators from a fully sampled central k‐space cylinder. In vivo steady‐state DWI with TURBINE is demonstrated in human brain. Motion artifacts are corrected using refocusing reconstruction and TURBINE images prove less distorted compared to two‐dimensional single‐shot diffusion‐weighted‐spin‐EPI. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
IIR GRAPPA for parallel MR image reconstruction
Authors: Chen Zhaolin , Zhang Jingxin , Yang Ran , Kellman Peter , Johnston Leigh A. , Egan Gary F. 
Published: October 2009

AbstractAccelerated parallel MRI has advantage in imaging speed, and its image quality has been improved continuously in recent years. This paper introduces a two‐dimensional infinite impulse response model of inverse filter to replace the finite impulse response model currently used in generalized autocalibrating partially parallel acquisitions class image reconstruction methods. The infinite impulse response model better characterizes the correlation of k‐space data points and better approximates the perfect inversion of parallel imaging process, resulting in a novel generalized image reconstruction method for accelerated parallel MRI. This k‐space‐based reconstruction method includes the conventional generalized autocalibrating partially parallel acquisitions class methods as special cases and has a new infinite impulse response data estimation mechanism for effective improvement of image quality. The experiments on in vivo MRI data show that the proposed method significantly reduces reconstruction errors compared with the conventional two‐dimensional generalized autocalibrating partially parallel acquisitions method, particularly at the high acceleration rates. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.
A discrete thermodynamic approach for anisotropic plastic–damage modeling of cohesive‐frictional geomaterials
Authors: Zhu Q. Z. , Zhou C. B. , Shao J. F. , Kondo D. 
Published: October 2009

AbstractA discrete plastic–damage model is developed for cohesive‐frictional geomaterials subjected to compression‐dominated stresses. Macroscopic plastic strains of material are physically generated by frictional sliding along weakness planes. The evolution of damage is related to the evolution of weakness planes physically in connection with the propagation of microcracks. A discrete approach is used to account for anisotropic plastic flow and damage evolution, by introducing two stress invariants and one plastic hardening variable for each family of sliding weakness planes. Plastic flow in each family is coupled with damage evolution. The proposed model is applied to typical geomaterials and comparisons between numerical predictions and experimental data are presented. Copyright © 2009 John Wiley & Sons, Ltd.
General resolution of a convergence question of L. Krukier
Authors: Johnson Charles , Krukier Lev 
Published: October 2009

AbstractIt was shown that there exists a matrix norm N such that N(A−1B)<1 if A, B∈Mn(𝒞), 0∉F(A), and g(A, B)<1 where g(A, B)=max|z|, z∈G(A, B),

Copyright © 2009 John Wiley & Sons, Ltd.