bluuebunny/crossref_metadata_2025_split huggingface dataset:
BOLD imaging in the mouse brain using a turboCRAZED sequence at high magnetic fields
Authors: Schneider Johannes T. , Faber Cornelius 
Published: September 2008

AbstractFunctional MRI (fMRI) based on the detection of intermolecular double‐quantum coherences (iDQC) has previously been shown to provide pronounced activation signal. For fMRI in small animals at very high magnetic fields, the essential fast gradient echo‐based readout methods become problematic. Here, rapid intermolecular double‐quantum coherence (iDQC) imaging was implemented, combining the iDQC preparation sequence with a Turbo spin echo‐like readout. Four‐step phase cycling and a novel intensity‐ordered k‐space encoding scheme with separate acquisition of odd and even echoes were essential to optimize signal to noise ratio efficiency. Compared with a single echo readout of iDQC signal, acceleration of factor 16 was achieved in phantoms using the novel method at 17.6 Tesla. In vivo, echo trains consisting of 32 echoes were possible and images of the mouse brain were obtained in 30 s. The blood oxygen level dependent (BOLD) effect in the mouse brain upon change of breathing gas was observed as average signal change of (6.3 ± 1.1)% in iDQC images. Signal changes in conventional multi spin echo images were (4.4 ± 2.3)% and (8.3 ± 3.8)% with gradient echo methods. Combination of T2*‐weighting with the fast iDQC sequence may yield higher signal changes than with either method alone, and establish fast iDQC imaging a robust tool for high field fMRI in small animals. Magn Reson Med 60:850–859, 2008. © 2008 Wiley‐Liss, Inc.
Validation of oxygen extraction fraction measurement by qBOLD technique
Authors: He Xiang , Zhu Mingming , Yablonskiy Dmitriy A. 
Published: September 2008

AbstractMeasurement of brain tissue oxygen extraction fraction (OEF) in both baseline and functionally activated states can provide important information on brain functioning in health and disease. The recently proposed quantitative BOLD (qBOLD) technique is MRI‐based and provides a regional in vivo OEF measurement (He and Yablonskiy, MRM 2007, 57:115–126). It is based on a previously developed analytical BOLD model and incorporates prior knowledge about the brain tissue composition including the contributions from grey matter, white matter, cerebrospinal fluid, interstitial fluid and intravascular blood. The qBOLD model also allows for the separation of contributions to the BOLD signal from OEF and the deoxyhemoglobin containing blood volume (DBV). The objective of this study is to validate OEF measurements provided by the qBOLD approach. To this end we use a rat model and compare qBOLD OEF measurements against direct measurements of the blood oxygenation level obtained from venous blood drawn directly from the superior sagittal sinus. The cerebral venous oxygenation level of the rat was manipulated by utilizing different anestheisa methods. The study demonstrates a very good agreement between qBOLD approach and direct measurements. Magn Reson Med 60:882–888, 2008. © 2008 Wiley‐Liss, Inc.
Measurement of myocardial frequency offsets during first pass of a gadolinium‐based contrast agent in perfusion studies
Authors: Ferreira Pedro , Gatehouse Peter , Bucciarelli‐Ducci Chiara , Wage Ricardo , Firmin David 
Published: September 2008

AbstractMRI of myocardial perfusion observed with an extracellular contrast agent has proven valuable for the detection of coronary artery disease. During contrast enhancement transient dark rim artifacts are sometimes visible, complicating diagnosis and quantification. In this work a quantification of the frequency offsets caused solely by the first pass of Gd‐DTPA in a typical perfusion setup was made in vivo and compared with both phantom work and numerical simulations data. The results show that numerically simulated and phantom data agree well with in vivo frequency offsets. During the first pass main field distortion occurs mainly in the subendocardium, and the same pattern is always observed: positive for posterior/anterior regions, negative for septal/lateral regions (from −69 to 85 Hz). The larger myocardial frequency offsets were measured for patients with greater angles between the long axis of the heart and the direction of the main field. From these results it would appear that the frequency offsets are too weak to cause dark rim artifacts due simply to intravoxel dephasing in a typical perfusion sequence. However, when added to other sources of off‐resonance it can cause dark rims in particular regions of the myocardium wall in balanced‐SSFP sequences. Magn Reson Med 60:860–870, 2008. © 2008 Wiley‐Liss, Inc.
Comparison of delayed gadolinium enhanced MRI of cartilage (dGEMRIC) using inversion recovery and fast T1 mapping sequences
Authors: Mamisch Tallal Charles , Dudda Marcel , Hughes Timothy , Burstein Deborah , Kim Young‐Jo 
Published: September 2008

AbstractThe delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) technique has shown promising results in pilot clinical studies of early osteoarthritis. Currently, its broader acceptance is limited by the long scan time and the need for postprocessing to calculate the T1 maps. A fast T1 mapping imaging technique based on two spoiled gradient echo images was implemented. In phantom studies, an appropriate flip angle combination optimized for center T1 of 756 to 955 ms yielded excellent agreement with T1 measured using the inversion recovery technique in the range of 200 to 900 ms, of interest in normal and diseased cartilage. In vivo validation was performed by serially imaging 26 hips using the inversion recovery and the Fast 2 angle T1 mapping techniques (center T1 756 ms). Excellent correlation with Pearson correlation coefficient R2 of 0.74 was seen and Bland‐Altman plots demonstrated no systematic bias. Magn Reson Med 60:768–773, 2008. © 2008 Wiley‐Liss, Inc.
Macromolecular dynamic contrast‐enhanced (DCE)‐MRI detects reduced vascular permeability in a prostate cancer bone metastasis model following anti–platelet‐derived growth factor receptor (PDGFR) therapy, indicating a drop in vascular endothelial growth factor receptor (VEGFR) activation
Authors: Dafni Hagit , Kim Sun‐Jin , Bankson James A. , Sankaranarayanapillai Madhuri , Ronen Sabrina M. 
Published: September 2008

AbstractThe antivascular function of the platelet‐derived growth factor receptor (PDGFR) inhibitor imatinib combined with paclitaxel has been demonstrated by invasive immunohistochemistry. The purpose of this study was to 1) noninvasively monitor the response to anti‐PDGFR treatment, and 2) understand the underlying mechanism of this response. Thus, response to treatment was studied in a prostate cancer bone metastasis model using macromolecular (biotin–bovine serum albumin [BSA]–Gd‐diethylene triamine pentaacetic acid [GdDTPA]) dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI). Human prostate cancer (PC‐3MM2) bone metastases that caused osteolysis and grew in neighboring muscle showed a high blood‐volume fraction (fBV) and vascular permeability (PS) at the tumor periphery compared to muscle tissue and intraosseous tumor. Imatinib alone or with paclitaxel significantly reduced PS by 35% (one‐tailed paired t‐test, P = 0.045) and 40% (P = 0.0003), respectively, whereas paclitaxel alone or no treatment had no effect. Based on changes in PS, we hypothesized that imatinib interferes with the signaling pathway of vascular endothelial growth factor (VEGF). This mechanism was verified by immunohistochemistry. It demonstrated reduced activation of both PDGFR‐β and VEGF receptor 2 (VEGFR2) in imatinib‐treated mice. Our study therefore demonstrates that macromolecular DCE‐MRI can be used to detect early vascular effects associated with response to therapy targeted to PDGFR, and provides insight into the role played by VEGF in anti‐PDGFR therapy. Magn Reson Med 60:822–833, 2008. © 2008 Wiley‐Liss, Inc.
Comprehensive quantification of signal‐to‐noise ratio and g‐factor for image‐based and k‐space‐based parallel imaging reconstructions
Authors: Robson Philip M. , Grant Aaron K. , Madhuranthakam Ananth J. , Lattanzi Riccardo , Sodickson Daniel K. , McKenzie Charles A. 
Published: September 2008

AbstractParallel imaging reconstructions result in spatially varying noise amplification characterized by the g‐factor, precluding conventional measurements of noise from the final image. A simple Monte Carlo based method is proposed for all linear image reconstruction algorithms, which allows measurement of signal‐to‐noise ratio and g‐factor and is demonstrated for SENSE and GRAPPA reconstructions for accelerated acquisitions that have not previously been amenable to such assessment. Only a simple “prescan” measurement of noise amplitude and correlation in the phased‐array receiver, and a single accelerated image acquisition are required, allowing robust assessment of signal‐to‐noise ratio and g‐factor. The “pseudo multiple replica” method has been rigorously validated in phantoms and in vivo, showing excellent agreement with true multiple replica and analytical methods. This method is universally applicable to the parallel imaging reconstruction techniques used in clinical applications and will allow pixel‐by‐pixel image noise measurements for all parallel imaging strategies, allowing quantitative comparison between arbitrary k‐space trajectories, image reconstruction, or noise conditioning techniques. Magn Reson Med 60:895–907, 2008. © 2008 Wiley‐Liss, Inc.
Exponential excitation pulses for improved water content mapping in the presence of background gradients
Authors: Preibisch Christine , Volz Steffen , Anti Sandra , Deichmann Ralf 
Published: September 2008

AbstractSeveral water content mapping techniques are based on the acquisition of multiple gradient echoes (GE) with different echo times (TE). However, in the presence of linear magnetic field gradients Gsusc the signal decay is no longer exponential but in the case of a rectangular slice profile weighted by a sinc function, giving rise to erroneous initial amplitudes S0 in monoexponential fitting. Generally, it can be shown that the signal decay is weighted by the time profile of the excitation pulse. Thus, for an excitation pulse with an exponential time profile, i.e., a Lorentzian slice profile, the signal decay remains exponential and exponential fitting still yields the correct amplitude S0. Multiecho GE images of a gel phantom and five human volunteers were acquired at 3 T using a sinc‐shaped and an exponential excitation pulse. In addition, simulations were performed to investigate the influence of saturation effects due to distortion of the ideal Lorentzian slice profile. A considerable overestimation of S0 when using a sinc‐shaped excitation pulse was observed. Errors were greatly reduced with an exponential excitation pulse. We thus propose the use of excitation pulses with exponential time profile to obtain accurate estimates for S0 from exponential fitting. Magn Reson Med 60:908–916, 2008. © 2008 Wiley‐Liss, Inc.
Predictive modeling in glioma grading from MR perfusion images using support vector machines
Authors: Emblem Kyrre E. , Zoellner Frank G. , Tennoe Bjorn , Nedregaard Baard , Nome Terje , Due‐Tonnessen Paulina , Hald John K. , Scheie David , Bjornerud Atle 
Published: September 2008

AbstractThe advantages of predictive modeling in glioma grading from MR perfusion images have not yet been explored. The aim of the current study was to implement a predictive model based on support vector machines (SVM) for glioma grading using tumor blood volume histogram signatures derived from MR perfusion images and to assess the diagnostic accuracy of the model and the sensitivity to sample size. A total of 86 patients with histologically‐confirmed gliomas were imaged using dynamic susceptibility contrast (DSC) MRI at 1.5T. Histogram signatures from 53 of the 86 patients were analyzed independently by four neuroradiologists and used as a basis for the predictive SVM model. The resulting SVM model was tested on the remaining 33 patients and analyzed by a fifth neuroradiologist. At optimal SVM parameters, the true positive rate (TPR) and true negative rate (TNR) of the SVM model on the 33 patients was 0.76 and 0.82, respectively. The interobserver agreement and the TPR increased significantly when the SVM model was based on an increasing sample size (P< 0.001). This result suggests that a predictive SVM model can aid in the diagnosis of glioma grade from MR perfusion images and that the model improves with increasing sample size. Magn Reson Med 60:945–952, 2008. © 2008 Wiley‐Liss, Inc.
Advantage of sampling density weighted apodization over postacquisition filtering apodization for sodium MRI of the human brain
Authors: Stobbe Robert , Beaulieu Christian 
Published: September 2008

AbstractFor sodium imaging of the human brain, Gibbs' ringing can degrade image appearance and confound image analysis; k‐space filtering is generally required. In this work, the signal to noise ratio (SNR) advantage of sampling density weighted apodization (SDWA) over uniform k‐space sampling with postacquisition filtering apodization (UPFA) is quantified for sodium three‐dimensional (3D) twisted projection imaging (TPI) of the human brain. A direct comparison was conducted with the creation of two TPI projection data sets (each with an equal number of projections of equal length): one generating uniform sampling density, and the other a “generalized Hamming” sampling density that conformed to 3D‐TPI constraints for full k‐space sampling. In this work it is shown theoretically, and then experimentally with sodium imaging of the human brain, that an SNR advantage of 17% is associated with the use of SDWA over UPFA for the filter presented, along with a significant noise‐coloring benefit. Magn Reson Med 60:981–986, 2008. © 2008 Wiley‐Liss, Inc.
Gibbs tracking: A novel approach for the reconstruction of neuronal pathways
Authors: Kreher B.W. , Mader I. , Kiselev V.G. 
Published: September 2008

AbstractReconstruction of neuronal fibers using diffusion‐weighted (DW) MRI is an emerging method in biomedical research. Existing fiber‐tracking algorithms are commonly based on the “walker principle.” Fibers are reconstructed as trajectories of “walkers,” which are guided according to local diffusion properties. In this study, a new method of fiber tracking is proposed that does not engage any “walking” algorithm. It resolves a number of inherent problems of the “walking” approach, in particular the reconstruction of crossing and spreading fibers. In the proposed method, the fibers are built with small line elements. Each line element contributes an anisotropic term to the simulated DW signal, which is adjusted to the measured signal. This method demonstrates good results for simulated fibers. A single in vivo result demonstrates the successful reconstruction of the dominant neuronal pathways. A comparison with the diffusion tensor imaging (DTI)‐based fiber assignment with continuous tracking (FACT) method and the probabilistic index of connectivity (PICo) method based on a multitensor model is performed for the callosal fibers. The result shows a strong increase in the number of reconstructed fibers. These almost fill the total white matter (WM) volume and connect a large area of the cortex. The method is very computationally expensive. Possible ways to address this problem are discussed. Magn Reson Med 60:953–963, 2008. © 2008 Wiley‐Liss, Inc.
Anesthetic effects on regional CBF, BOLD, and the coupling between task‐induced changes in CBF and BOLD: An fMRI study in normal human subjects
Authors: Qiu Maolin , Ramani Ramachandran , Swetye Michael , Rajeevan Nallakkandi , Constable R. Todd 
Published: September 2008

AbstractFunctional MR imaging was performed in sixteen healthy human subjects measuring both regional cerebral blood flow (CBF) and blood oxygen level dependent (BOLD) signal when visual and auditory stimuli were presented to subjects in the presence or absence of anesthesia. During anesthesia, 0.25 mean alveolar concentration (MAC) sevoflurane was administrated. We found that low‐dose sevoflurane decreased the task‐induced changes in both BOLD and CBF. Within the visual and auditory regions of interest inspected, both baseline CBF and the task‐induced changes in CBF decreased significantly during anesthesia. Low‐dose sevoflurane significantly altered the task‐induced CBF‐BOLD coupling; for a unit change of CBF, a larger change in BOLD was observed in the anesthesia condition than in the anesthesia‐free condition. Low‐dose sevoflurane was also found to have significant impact on the spatial nonuniformity of the task‐induced coupling. The alteration of task‐induced CBF‐BOLD coupling by low‐dose sevoflurane introduces ambiguity to the direct interpretation of functional MRI (fMRI) data based on only one of the indirect measures—CBF or BOLD. Our observations also indicate that the manipulation of the brain with an anesthetic agent complicates the model‐based quantitative interpretation of fMRI data, in which the relative task‐induced changes in oxidative metabolism are calculated by means of a calibrated model given the relative changes in the indirect vascular measures, usually CBF and BOLD. Magn Reson Med 60:987–996, 2008. © 2008 Wiley‐Liss, Inc.
Three‐dimensional high‐resolution magnetic resonance spectroscopic imaging for absolute quantification of 31P metabolites in human liver
Authors: Chmelík M. , Schmid A. I. , Gruber S. , Szendroedi J. , Krššák M. , Trattnig S. , Moser E. , Roden M. 
Published: September 2008

AbstractLiver dysfunction correlates with alterations of intracellular concentrations of 31P metabolites. Localization and absolute quantification should help to trace regional hepatic metabolism. An improved protocol for the absolute quantification of 31P metabolites in vivo in human liver was developed by employing three‐dimensional (3D) k‐space weighted spectroscopic imaging (MRSI) with B1‐insensitive adiabatic excitation. The protocol allowed for high spatial resolution of 17.8 ± 0.22 cm3 in 34 min at 3 T. No pulse adjustment prior to MRSI measurement was necessary due to adiabatic excitation. The protocol geometry was identical for all measurements so that one calibration data set, acquired from phantom replacement measurement, was applied for all quantifications. The protocol was tested in 10 young, healthy volunteers, for whom 57 ± 7 spectra were quantified. Concentrations per liter of liver volume (reproducibilities) were 2.24 ± 0.10 mmol/L (1.8%) for phosphomonoesters (PME), 1.37 ± 0.07 mmol/L (7.9%) for inorganic phosphate (Pi), 11.40 ± 0.96 mmol/L (2.9%) for phosphodiesters (PDE), and 2.14 ± 0.10 mmol/L (1.6%) for adenosine triphosphate (ATP), respectively. Taken together, this approach provides fast, simple, and reproducible high‐resolution absolute quantification and detailed mapping of the spatial distribution of hepatic 31P metabolites. This method allows for examination of regional deviations of energy metabolism in human liver diseases. Magn Reson Med 60:796–802, 2008. © 2008 Wiley‐Liss, Inc.
Design and use of tailored hard‐pulse trains for uniformed saturation of myocardium at 3 Tesla
Authors: Sung Kyunghyun , Nayak Krishna S. 
Published: September 2008

AbstractComplete and uniform saturation of myocardium is essential for quantitative myocardial perfusion imaging using the first pass of a contrast agent. At 3 T, inhomogeneities of both the static (B0) and radiofrequency (B1) magnetic fields have led to the use of adiabatic B1‐insensitive rotation type 4 (BIR‐4) pulses, which in practice are constrained by radiofrequency (RF) heating. In this study, we propose the use of trains of weighted hard pulses that are optimized for the measured variation of B0 and B1 fields in the myocardium. These pulses are simple to design, and require substantially lower RF power when compared with BIR‐4 pulses. In volunteers, at 3 T, we demonstrated that the proposed saturation pulse with three subpulses results in lower peak and lower average residual longitudinal magnetization over the heart, as compared with 8‐msec BIR‐4 pulses and conventional hard pulse trains (P < 0.05). Magn Reson Med 60:997–1002, 2008. © 2008 Wiley‐Liss, Inc.
Transport phenomena in kaolinite clay: Molecular simulation, homogenization analysis and similitude law
Authors: Choi Jung Hae , Anwar A. H. M. Faisal , Kawamura Katsuyuki , Ichikawa Yasuaki 
Published: September 2008

AbstractKaolinite is a common clay mineral. It is a nanomaterial with a platelet crystalline structure. In order to analyze the behavior of kaolinite, its microscopic structure and material properties must be specified correctly. A molecular dynamics (MD) simulation is used for determining the microscale properties of hydrated kaolinite, and these properties are introduced into a multiscale homogenization analysis (HA). We previously developed such an MD/HA technique to investigate seepage, diffusion, sorption and consolidation in bentonite clay (Proceedings of the Science Basis for Nuclear Waste Management, Davos, Switzerland, vol. XXI. Material Research Society: Warrendale, PA, 1997; 359–366; Eng. Geol. 1999; 54:21–31; Eng. Geol. 2001; 60:127–138; Coupled Thermo‐Hydro‐Mechanical‐Chemical Processes in Geo‐systems. Elsevier: Amsterdam, 2005; 457–464). We here apply the method to kaolinite clay to investigate the permeability, diffusion and related similitude law. The obtained results are supported by existing experimental data. Copyright © 2008 John Wiley & Sons, Ltd.
Severe deficiency of coagulation Factor VII results in spontaneous cardiac fibrosis in mice
Authors: Xu H , Noria F , Sandoval‐Cooper MJ , Menchen H , Donahue DL , Ploplis VA , Castellino FJ 
Published: September 2008

AbstractMice genetically modified to produce low levels (∼1% of wild‐type) of coagulation FVII presented with echocardiographic evidence of heart abnormalities. Decreases in ventricular size and reductions in systolic and diastolic functions were found, suggestive of a restrictive cardiomyopathy and consistent with an infiltrative myopathic process. Microscopic analysis of mouse hearts showed severe patchy fibrosis in the low‐FVII mice. Haemosiderin deposition was discovered in hearts of these mice, along with increases in inflammatory cell number, ultimately resulting in widespread collagen deposition. Significant increases in mRNA levels of TGFβ, TNFα and several matrix metalloproteinases in low‐FVII mice, beginning at early ages, supported a state of cardiac remodelling associated with the fibrotic pathology. Mechanistic time‐course studies suggested that cardiac fibrosis in low‐FVII mice originated from bleeding in heart tissue, resulting in the recruitment of leukocytes, which released inflammatory mediators and induced collagen synthesis and secretion. These events led to necrosis of cardiomyocytes and collagen deposition, characteristics of cardiac fibrosis. The results of this study demonstrated that haemorrhagic and inflammatory responses to a severe FVII deficiency resulted in the development of cardiac fibrosis, observed echocardiographically as a restrictive cardiomyopathy, with compromised ventricular diastolic and systolic functions. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.