bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient in vivo 31P magnetization transfer approach for noninvasively determining multiple kinetic parameters and metabolic fluxes of ATP metabolism in the human brain
Authors: Du Fei , Zhu Xiao‐Hong , Qiao Hongyan , Zhang Xiaoliang , Chen Wei 
Published: December 2006

AbstractATP metabolism is controlled mainly by ATP synthase (ATPase) and creatine kinase (CK) reactions that regulate cerebral ATP production, transportation, and utilization. These coupled reactions constitute a chemical exchange metabolic network of PCr↔ATP↔Pi characterized by two forward and two reverse reaction fluxes, which can be studied noninvasively by in vivo 31P MRS combined with magnetization transfer (MT). However, it is still debated whether current MT approaches can precisely determine all of these fluxes. We developed and tested a modified in vivo 31P MT approach based on a multiple single‐site saturation (MSS) technique to study the entire PCr↔ATP↔Pi network in human occipital lobe at 7T. Our results reveal that 1) the MSS MT approach can explicitly determine all four reaction fluxes with a minimal number of 31P spectra; 2) the three‐spin exchange model accurately determines reverse reaction fluxes, resulting in equal forward and reverse fluxes for both CK and ATPase reactions; and 3) the ATP synthesis rate (8.8 ± 1.9 μmol/g/min, N = 11) measured in the human brain reflects cerebral oxidative phosphorylation. The MSS MT approach should provide an important modality for noninvasively studying the essential roles of ATP metabolism in brain bioenergetics, function, and diseases. Magn Reson Med 57:103–114, 2007. © 2006 Wiley‐Liss, Inc.
Quantitative BOLD: Mapping of human cerebral deoxygenated blood volume and oxygen extraction fraction: Default state
Authors: He Xiang , Yablonskiy Dmitriy A. 
Published: December 2006

AbstractSince Ogawa et al. (Proc Natl Acad Sci USA 1990;87:9868–9872) made the fundamental discovery of blood oxygenation level‐dependent (BOLD) contrast in MRI, most efforts have been directed toward the study of dynamic BOLD (i.e., temporal changes in the MRI signal during changes in brain activity). However, very little progress has been made in elucidating the nature of BOLD contrast during the resting or baseline state of the brain, which is important for understanding normal human performance because it accounts for most of the enormous energy budget of the brain. It is also crucial for deciphering the consequences of baseline‐state impairment by cerebral vascular diseases. The objective of this study was to develop a BOLD MR‐based method that allows quantitative evaluation of tissue hemodynamic parameters, such as the blood volume, deoxyhemoglobin concentration, and oxygen extraction fraction (OEF). The proposed method, which we have termed quantitative BOLD (qBOLD), is based on an MR signal model that incorporates prior knowledge about brain tissue composition and considers signals from gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), and blood. A 2D gradient‐echo sampling of spin‐echo (GESSE) pulse sequence is used for the acquisition of the MRI signal. The method is applied to estimate the hemodynamic parameters of the normal human brain in the baseline state. Magn Reson Med 57:115–126, 2007. © 2006 Wiley‐Liss, Inc.
Variance of estimated DTI‐derived parameters via first‐order perturbation methods
Authors: Chang Lin‐Ching , Koay Cheng Guan , Pierpaoli Carlo , Basser Peter J. 
Published: December 2006

AbstractIn typical applications of diffusion tensor imaging (DTI), DT‐derived quantities are used to make a diagnostic, therapeutic, or scientific determination. In such cases it is essential to characterize the variability of these tensor‐derived quantities. Parametric and empirical methods have been proposed to estimate the variance of the estimated DT, and quantities derived from it. However, the former method cannot be generalized since a parametric distribution cannot be found for all DT‐derived quantities. Although powerful empirical methods, such as the bootstrap, are available, they require oversampling of the diffusion‐weighted imaging (DWI) data. Statistical perturbation methods represent a hybrid between parametric and empirical approaches, and can overcome the primary limitations of both methods. In this study we used a first‐order perturbation method to obtain analytic expressions for the variance of DT‐derived quantities, such as the trace, fractional anisotropy (FA), eigenvalues, and eigenvectors, for a given experimental design. We performed Monte Carlo (MC) simulations of DTI experiments to test and validate these formulae, and to determine their range of applicability for different experimental design parameters, including the signal‐to‐noise ratio (SNR), diffusion gradient sampling scheme, and number of DWI acquisitions. This information should be useful for designing DTI studies and assessing the quality of inferences drawn from them. Magn Reson Med 57:141–149, 2007. Published 2006 Wiley‐Liss, Inc.
Automated estimation of tumor probability in prostate magnetic resonance spectroscopic imaging: Pattern recognition vs quantification
Authors: Kelm B. Michael , Menze Bjoern H. , Zechmann Christian M. , Baudendistel Klaus T. , Hamprecht Fred A. 
Published: December 2006

AbstractDespite its diagnostic value and technological availability,1H NMR spectroscopic imaging (MRSI) has not found its way into clinical routine yet. Prerequisite for the clinical application is an automated and reliable method for the diagnostic evaluation of MRS images. In the present paper, different approaches to the estimation of tumor probability from MRSI in the prostate are assessed. Two approaches to feature extraction are compared: quantification (VARPRO, AMARES, QUEST) and subspace methods on spectral patterns (principal components, independent components, nonnegative matrix factorization, partial least squares). Linear as well as nonlinear classifiers (support vector machines, Gaussian processes, random forests) are applied and discussed. Quantification‐based approaches are much more sensitive to the choice and parameterization of the quantification algorithm than to the choice of the classifier. Furthermore, linear methods based on magnitude spectra easily achieve equal performance and also allow for biochemical interpretation in combination with subspace methods. Nonlinear methods operating directly on magnitude spectra achieve the best results but are less transparent than the linear methods. Magn Reson Med 57:150–159, 2007. © 2006 Wiley‐Liss, Inc.
Quantitative proton magnetic resonance spectroscopy of the human cervical spinal cord at 3 tesla
Authors: Marliani Anna Federica , Clementi Valeria , Albini‐Riccioli Luca , Agati Raffaele , Leonardi Marco 
Published: December 2006

AbstractCervical spinal cord spectroscopy has the potential to add metabolic information to spinal cord MRI and improve the clinical evaluation and research investigation of spinal cord diseases, such as multiple sclerosis (MS) and intraspinal tumors. However, in vivo proton MR spectroscopy (1H‐MRS) of the spinal cord is difficult to perform due to magnetic field inhomogeneities, physiological movements, and the size of the anatomical region of interest (ROI). For these reasons, few spinal cord 1H‐MRS studies have been undertaken and two preliminary studies on a 3T system were only recently presented as abstracts. In this work we demonstrate the feasibility of cervical spinal cord quantitative 1H‐MRS on a clinical 3T system, propose a study protocol, and report quantification results obtained from healthy volunteers. The main metabolite concentration ratios obtained in 10 healthy subjects, as provided by LCModel, were as follows: total N‐acetyl aspartate/creatine (tNAA/Cr) 1.4 ± 0.3, choline/creatine (Cho/Cr) 0.5 ± 0.1, and myoinositol/creatine (mI/Cr) 1.7 ± 0.2. A significant difference was found between spinal cord tNAA, Cr, Cho, and mI concentration ratios and brainstem concentrations previously acquired on the same system. Magn Reson Med 57:160–163, 2007. © 2006 Wiley‐Liss, Inc.
Serial in vivo MR tracking of magnetically labeled neural spheres transplanted in chronic EAE mice
Authors: Ben‐Hur Tamir , van Heeswijk Ruud B. , Einstein Ofira , Aharonowiz Michal , Xue Rong , Frost Emma E. , Mori Susumu , Reubinoff Benjamin E. , Bulte Jeff W.M. 
Published: December 2006

AbstractNeural stem cell (NSC) transplantation has been shown to attenuate the severity of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Central to the future success of NSC transplantation in MS is the ability of transplanted cells to migrate from the site of transplantation to relevant foci of disease. Using magnetically labeled mouse neurospheres and human embryonic stem cell (hESC)‐derived neurospheres, we applied serial magnetic resonance imaging (MRI) to assess the biodynamics of transplanted cell migration in a chronic mouse EAE model. Magnetic labeling did not affect the in vitro and in vivo characteristics of cells as multipotential precursors. Cell migration occurred along white matter (WM) tracts (especially the corpus callosum (CC), fimbria, and internal capsule), predominantly early in the acute phase of disease, and in an asymmetric manner. The distance of cell migration correlated well with clinical severity of disease and the number of microglia in the WM tracts, supporting the notion that inflammatory signals promote transplanted cell migration. This study shows for the first time that hESC‐derived neural precursors also respond to tissue signals in an MS model, similarly to rodent cells. The results are directly relevant for designing and optimizing cell therapies for MS, and achieving a better understanding of in vivo cell dynamics and cell–tissue interactions. Magn Reson Med 57:164–171, 2007. © 2006 Wiley‐Liss, Inc.
Artifact reduction in moving‐table acquisitions using parallel imaging and multiple averages
Authors: Fautz H.P. , Honal M. , Saueressig U. , Schäfer O. , Kannengiesser S.A.R. 
Published: December 2006

AbstractTwo‐dimensional (2D) axial continuously‐moving‐table imaging has to deal with artifacts due to gradient nonlinearity and breathing motion, and has to provide the highest scan efficiency. Parallel imaging techniques (e.g., generalized autocalibrating partially parallel acquisition GRAPPA)) are used to reduce such artifacts and avoid ghosting artifacts. The latter occur in T2‐weighted multi‐spin‐echo (SE) acquisitions that omit an additional excitation prior to imaging scans for presaturation purposes. Multiple images are reconstructed from subdivisions of a fully sampled k‐space data set, each of which is acquired in a single SE train. These images are then averaged. GRAPPA coil weights are estimated without additional measurements. Compared to conventional image reconstruction, inconsistencies between different subsets of k‐space induce less artifacts when each k‐space part is reconstructed separately and the multiple images are averaged afterwards. These inconsistencies may lead to inaccurate GRAPPA coil weights using the proposed intrinsic GRAPPA calibration. It is shown that aliasing artifacts in single images are canceled out after averaging. Phantom and in vivo studies demonstrate the benefit of the proposed reconstruction scheme for free‐breathing axial continuously‐moving‐table imaging using fast multi‐SE sequences. Magn Reson Med 57:226–232, 2007. © 2007 Wiley‐Liss, Inc.
Correlation of proton transverse relaxation rates (R2) with iron concentrations in postmortem brain tissue from alzheimer's disease patients
Authors: House Michael J. , St. Pierre Timothy G. , Kowdley Kris V. , Montine Thomas , Connor James , Beard John , Berger Jose , Siddaiah Narendra , Shankland Eric , Jin Lee‐Way 
Published: December 2006

AbstractIron accumulates in the Alzheimer's disease (AD) brain and is directly associated with β‐amyloid pathology. The proton transverse relaxation rate (R2) has a strong linear relationship with iron concentrations in healthy brain tissue; however, an independent test of this relationship has not been extended to AD brain tissue. In this study in vitro single spin‐echo (SE) measurements were made on tissue samples from four human AD brains using a 4.7T MRI research scanner. R2 values were calculated for 14 cortical and subcortical gray matter (GM) and white matter (WM) regions. Atomic absorption spectroscopy was used to measure iron concentrations in the corresponding excised brain regions. Significant positive linear correlations were observed between R2 values and iron concentrations in GM regions assessed across individual tissue samples and data averaged by brain region. With the use of a predictive model for R2, a threshold iron concentration of 55 μg Fe/g wet tissue was determined above which R2 appears to be dominated by the affects of iron in AD brain tissue. High‐field MRI may therefore be a useful research tool for assessing brain iron changes associated with AD. Magn Reson Med 57:172–180, 2007. © 2006 Wiley‐Liss, Inc.
Actual flip‐angle imaging in the pulsed steady state: A method for rapid three‐dimensional mapping of the transmitted radiofrequency field
Authors: Yarnykh Vasily L. 
Published: December 2006

AbstractA new method has been developed for fast image‐based measurements of the transmitted radiofrequency (RF) field. The method employs an actual flip‐angle imaging (AFI) pulse sequence that consists of two identical RF pulses followed by two delays of different duration (TR1 < TR2). After each pulse, a gradient‐echo (GRE) signal is acquired. It has been shown theoretically and experimentally that if delays TR1 and TR2 are sufficiently short and the transverse magnetization is completely spoiled, the ratio r = S2/S1 of signal intensities S1 and S2, acquired at the beginning of the time intervals TR1 and TR2, depends on the flip angle (FA) of applied pulses as r = (1 + n * cos(FA))/(n + cos(FA)), where n = TR2/TR1. The method allows fast 3D implementation and provides accurate B1 measurements that are highly insensitive to T1. The unique feature of the AFI method is that it uses a pulsed steady‐state signal acquisition. This overcomes the limitation of previous methods that required long relaxation delays between sequence repetitions. The method has been shown to be useful for time‐efficient whole‐body B1 mapping and correction of T1 maps obtained using a variable FA technique in the presence of nonuniform RF excitation. Magn Reson Med 57:192–200, 2007. © 2006 Wiley‐Liss, Inc.
Classification of spatiotemporal hemodynamics from brain perfusion MR images using expectation‐maximization estimation with finite mixture of multivariate gaussian distributions
Authors: Wu Yu‐Te , Chou Yen‐Chun , Guo Wan‐Yuo , Yeh Tzu‐Chen , Hsieh Jen‐Chuen 
Published: December 2006

AbstractThe ability to cluster different perfusion compartments in the brain is critical for analyzing brain perfusion. This study presents a method based on a mixture of multivariate Gaussians (MoMG) and the expectation‐maximization (EM) algorithm to dissect various perfusion compartments from dynamic susceptibility contrast (DSC) MR images so that each compartment comprises pixels of similar signal‐time curves. This EM‐based method provides an objective way to 1) delineate an area to serve as the in‐plane arterial input function (AIF) of the feeding artery for adjacent tissues to better quantify the relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), and mean transit time (MTT); 2) demarcate regions with abnormal perfusion derangement to facilitate diagnosis; and 3) obtain parametric maps with supplementary information, such as temporal scenarios and recirculation of contrast agent. Results from normal subjects show that perfusion cascade manifests (in order of appearance) the arteries, gray matter (GM), white matter (WM), veins and sinuses, and choroid plexus mixed with cerebrospinal fluid (CSF). The averaged rCBV, rCBF, and MTT ratios between GM and WM are in good agreement with those in the literature. Results from a patient with cerebral arteriovenous malformation (CAVM) showed distinct spatiotemporal characteristics between perfusion patterns, which allowed differentiation between pathological and nonpathological areas. Magn Reson Med 57:181–191, 2007. © 2006 Wiley‐Liss, Inc.
Compensation for spin‐lock artifacts using an off‐resonance rotary echo in T1ρoff‐weighted imaging
Authors: Witschey Walter R.T. , Borthakur Arijitt , Elliott Mark A. , Mellon Eric , Niyogi Sampreet , Wang Chenyang , Reddy Ravinder 
Published: December 2006

AbstractThe origin of image artifacts in an off‐resonance spin‐locking experiment is shown to be imperfections in the excitation flip angle. A pulse sequence for off‐resonance spin locking is implemented that compensates for imperfections in the excitation flip angle through an off‐resonance rotary echo. The off‐resonance rotary echo alternates the frequency offset and phase of the RF transmitter during two spin‐locking pulses of equal duration. The underlying theory is detailed, and MR images demonstrate the effectiveness of the technique in agarose gel phantoms and in in vivo human brain at 3T. Magn Reson Med 57:2–7, 2007. © 2006 Wiley‐Liss, Inc.
Impact of decision‐making in a multidisciplinary perinatal team
Authors: Bijma Hilmar H. , Van der Heide Agnes , Wildschut Hajo I. J. , Van der Maas Paul J. , Wladimiroff Juriy W. 
Published: December 2006

AbstractObjectives
To describe the characteristics of decision‐making about management of unborn infants with serious anomalies by a multidisciplinary perinatal team.
To evaluate the impact of multidisciplinary team discussions on the degree to which decisions about the management of unborn infants with serious anomalies are supported.
To evaluate the impact of the team discussions on the arguments used by physicians for their preferences concerning management.
MethodsProspective analysis of 78 cases discussed within the multidisciplinary perinatal team of a tertiary centre by means of an anonymous one‐page questionnaire with structured questions pertaining to the opinion of the responder on medical management of each case.ResultsWe did not find systematic differences between specialties prior to the discussion of cases. However, discussion with the multidisciplinary perinatal team improved decision‐making about management of unborn infants with serious anomalies by enhancing the degree of support for the decisions taken. The discussions of the team did not change the physicians' arguments mentioned for their preferences.ConclusionMultidisciplinary team discussions improve decision‐making about management of unborn infants with serious congenital anomalies. Copyright © 2006 John Wiley & Sons, Ltd.
Prenatal diagnosis for a novel homozygous mutation in PKLR gene in an Indian family
Authors: Gupta Neerja , Bianchi Paola , Fermo Elisa , Kabra Madhulika , Warang Prashant , Kedar Prabhakar , Gupta Nomeeta , Colah Roshan 
Published: December 2006

AbstractObjectiveTo provide prenatal diagnosis of pyruvate kinase deficiency by direct DNA analysis in an Indian family.Materials and MethodThis case report describes diagnosis of a novel homozygous mutation in PKLR gene that subsequently helped the family in the next pregnancy.ResultsAdvancement in molecular genetics has resulted in the prenatal diagnosis of relatively uncommon genetic disorders like pyruvate kinase deficiency.ConclusionThis case reiterates the importance of application of molecular genetics in clinical practice and prenatal diagnosis especially for rare, incurable genetic disorders. Copyright © 2006 John Wiley & Sons, Ltd.
Pregnancy and postnatal outcome of mosaic isochromosome 20q
Authors: Robinson W. P. , McGillivray B. , Friedman J. M. 
Published: December 2006

AbstractPrenatally diagnosed mosaicism for isochromosome 20q is generally reported in association with a normal outcome at birth and is rarely confirmed postnatally. However, the origin of these abnormal cells is unclear and there are few reports of long‐term outcomes. We present an additional case of prenatally detected isochromosome 20q, with normal outcome up to age 3.6 years. The abnormal cells, while present at high levels in the amniotic fluid, could not be confirmed in placenta or fetal blood. Nonetheless, based on a review of the literature, the level of isochromosome 20q cells found is associated with risk of abnormal outcome, suggesting a possible effect in some cases. Copyright © 2006 John Wiley & Sons, Ltd.
Free fetal DNA is not increased before 20 weeks in intrauterine growth restriction or pre‐eclampsia
Authors: Crowley A. , Martin C. , Fitzpatrick P. , Sheils O. , O'Herlihy C. , O'Leary J. J. , Byrne B. M. 
Published: December 2006

AbstractBackgroundThe aim of this study was to quantify maternal plasma fetal DNA and total DNA in early pregnancy in intrauterine growth restriction (IUGR) or pre‐eclampsia (PET).MethodsA nested case control study was carried out in a University Teaching Hospital. Plasma samples were obtained from 1993 women before 20 weeks of gestation. Pregnancies complicated by IUGR or PET were identified and compared to controls. DNA was extracted and real‐time quantitative PCR applied for the SRY and β‐actin genes. IUGR or PET groups were compared to controls using the χ2 and Wilcoxon rank sum tests.ResultsSRY was detected in 86% of IUGR (31/36), 94% of PET (15/16) and 78% of controls (56/72). The median SRY was similar in women with IUGR (28 GE/mL) or PET (30.5 GE/mL) and controls (27.5 GE/mL). β‐actin was increased in the IUGR group (3975 GE/mL) compared to controls (1835 GE/mL) (p = 0.045). Cigarette consumption was greater in the IUGR group compared to controls (p = 0.004).ConclusionsFetal DNA quantitation in maternal plasma before 20 weeks is not a useful predictor of IUGR or PET. β‐actin levels were elevated before 20 weeks in women with IUGR and may be a marker of maternal susceptibility to this condition. Copyright © 2006 John Wiley & Sons, Ltd.
Two‐ or three‐dimensional ultrasonography to predict pulmonary hypoplasia in pregnancies complicated by preterm premature rupture of the membranes
Authors: Gerards Franca A. , Twisk Jos W. R. , Fetter Willem P. F. , Wijnaendts Liliane C. D. , Van Vugt John M. G. 
Published: December 2006

AbstractObjectivesThe purpose of this study was to compare 3D lung volume measurements with 2D biometric parameters in predicting pulmonary hypoplasia in pregnancies complicated by preterm premature rupture of the membranes (PPROM).MethodsIn this prospective study, 18 pregnancies complicated by PPROMs at a mean 21 weeks' gestation (range 14–32 weeks) were examined. The 3D lung volume measurements and the following 2D biometric parameters were measured: thoracic circumference (TC) versus gestational age or femur length (FL), the TC/abdominal circumference (AC) ratio and the thoracic area/heart area (TA/HA) ratio. The sensitivity, specificity, positive and negative predictive value of each measurement to diagnose pulmonary hypoplasia were compared. Pulmonary hypoplasia was diagnosed on the basis of clinical, radiological and/or pathologic criteria.ResultsThe incidence of pulmonary hypoplasia was 33.3%. The best diagnostic accuracy for predicting pulmonary hypoplasia was achieved using the 3D lung volume measurements versus gestational age (sensitivity 83%, specificity 100%, positive predictive value 100% and negative predictive value 92%).ConclusionsThree‐dimensional lung volume measurements seem to be promising in predicting pulmonary hypoplasia prenatally in pregnancies complicated by PPROM. Copyright © 2006 John Wiley & Sons, Ltd.