bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic field and tissue dependencies of human brain longitudinal 1H2O relaxation in vivo
Authors: Rooney William D. , Johnson Glyn , Li Xin , Cohen Eric R. , Kim Seong‐Gi , Ugurbil Kamil , Springer Charles S. 
Published: January 2007

AbstractBrain water proton (1H2O) longitudinal relaxation time constants (T1) were obtained from three healthy individuals at magnetic field strengths (B0) of 0.2 Tesla (T), 1.0T, 1.5T, 4.0T, and 7.0T. A 5‐mm midventricular axial slice was sampled using a modified Look‐Locker technique with 1.5 mm in‐plane resolution, and 32 time points post‐adiabatic inversion. The results confirmed that for most brain tissues, T1 values increased by more than a factor of 3 between 0.2T and 7T, and over this range were well fitted by T1 (s) = 0.583(B0)0.382, T1(s) = 0.857(B0)0.376, and T1(s) = 1.35(B0)0.340 for white matter (WM), internal GM, and blood 1H2O, respectively. The ventricular cerebrospinal fluid (CSF) 1H2O T1 value did not change with B0, and its average value (standard deviation (SD)) across subjects and magnetic fields was 4.3 (±0.2) s. The tissue 1/T1 values at each field were well correlated with the macromolecular mass fraction, and to a lesser extent tissue iron content. The field‐dependent increases in 1H2O T1 values more than offset the well‐known decrease in typical MRI contrast reagent (CR) relaxivity, and simulations predict that this leads to lower CR concentration detection thresholds with increased magnetic field. Magn Reson Med 57:308–318, 2007. © 2007 Wiley‐Liss, Inc.
MR lymphangiography using dendrimer‐based contrast agents: A comparison at 1.5T and 3.0T
Authors: Hama Yukihiro , Bernardo Marcelino , Regino Celeste A.S. , Koyama Yoshinori , Brechbiel Martin W. , Krishna Murali C. , Choyke Peter L. , Kobayashi Hisataka 
Published: January 2007

AbstractMost macromolecular contrast agents (CAs) show lower r1 and higher r2 relaxivities at 3.0T than at 1.5T. MR lymphangiography in mice using a macromolecular G6 dendrimer‐based CA was serially performed and compared at both 1.5T and 3.0T. The r1 and r2 relaxivities of the G6 CA were 25 and 78/s/mM at 1.5T and 17 and 82/s/mM at 3.0T, respectively. The lymph node (LN)‐to‐fat ratios (LN signal intensity (SI)/fat SI) of T1‐weighted 3D‐fast spoiled gradient‐echo (3D‐FSPGR) were 3.2 ± 0.4 (mean ± standard deviation (SD)) at 1.5T and 2.7 ± 0.3 at 3.0T (P = 0.021), and the LN‐to‐fat ratios of T2/T1‐weighted 3D‐fast imaging employing steady‐state acquisition with phase cycling (3D‐FIESTA‐C) were 1.8 ± 0.2 at 1.5T and 1.2 ± 0.4 at 3.0T (P = 0.003). Although 3D‐FSPGR successfully delineated the LNs at both 1.5T and 3.0T, 3D‐FIESTA‐C at 3.0T failed to visualize the LNs. Magn Reson Med 57:431–436, 2007. © 2007 Wiley‐Liss, Inc.
Direct validation of in vivo localized 13C MRS measurements of brain glycogen
Authors: Lei Hongxia , Morgenthaler Florence , Yue Tianwen , Gruetter Rolf 
Published: January 2007

AbstractWith the use of localized 13C MRS in conjunction with [1‐13C]‐D‐glucose infusion, it is possible to study brain glycogen metabolism in vivo. The purpose of this study was to validate in vivo 13C MRS measurements by comparing them with results from a standard biochemical assay. To increase the [1–13C] glycogen concentration, 11 rats were subjected to an episode of acute hypoglycemia followed by a mild hyperglycemic recovery period during which [1‐13C]‐D‐glucose was infused. The total brain [1‐13C] glycogen of the same animal was determined from the enzymatically determined total brain glycogen content, which was fixed by focused microwave irradiation (4 kW in 1.4 s) immediately after the end of the in vivo NMR measurements. The corresponding isotopic enrichment (IE) of glycogen was measured by in vitro 1H MRS of protons bound to glucose C1‐α. The in vivo [1‐13C] glycogen concentration was strongly correlated to the in vitro [1‐13C] glycogen content determined by biochemical measurement in a linear manner (R = 0.79). The results are consistent with the notion that localized 13C MRS measurements closely reflect 13C glycogen content in the brain. Magn Reson Med 57:243–248, 2007. © 2007 Wiley‐Liss, Inc.
Inability to directly detect magnetic field changes associated with neuronal activity
Authors: Parkes Laura M. , de Lange Floris P. , Fries Pascal , Toni Ivan , Norris David G. 
Published: January 2007

AbstractThe ability to directly detect neuronal magnetic fields by MRI would help investigators achieve the “holy grail” of neuroimaging, namely both high spatial and temporal resolution. Both positive and negative findings have been reported in the literature, with no clear consensus as to the feasibility of direct detection. The aim of this study was to replicate one of the most promising published in vivo results. A second aim was to investigate the use of steady‐state visual evoked potentials (ssVEPs), which give a large evoked response and offer a well‐controlled approach because the frequency of the neuronal response can be dictated by the experimenter. For both studies we used a general linear model (GLM) that included regressors for both the expected blood oxygen level‐dependent (BOLD) signal and the magnetic source (MS) signal. The results showed no activity that could be attributed to the neuromagnetic signals in either study, and no frequency component corresponding to the frequency of the ssVEPs. This study demonstrates that for the particular stimuli and hardware used, the sensitivity of the magnitude MRI signal to detect evoked neuronal currents is too low to be of practical use. Magn Reson Med 57:411–416, 2007. © 2007 Wiley‐Liss, Inc.
Comparison of a reference region model with direct measurement of an AIF in the analysis of DCE‐MRI data
Authors: Yankeelov Thomas E. , Cron Greg O. , Addison Christina L. , Wallace Julia C. , Wilkins Ruth C. , Pappas Bruce A. , Santyr Giles E. , Gore John C. 
Published: January 2007

AbstractModels have been developed for analyzing dynamic contrast‐enhanced (DCE)‐MRI data that do not require measurements of the arterial input function (AIF). In this study, experimental results obtained from a reference region (RR) analysis are compared with results of an AIF analysis in the same set of five animals (four imaged twice, yielding nine data sets), returning estimates of the volume transfer constant (Ktrans) and the extravascular extracellular volume fraction (ve). Student's t‐test values for comparisons of Ktrans and ve between the two models were 0.14 (P = 0.88) and 0.85 (P > 0.4), respectively (where the high P‐values indicate no significant difference between values derived from the two models). Linear regression analysis indicated there was a correlation between Ktrans extracted by the two methods: r2 = 0.80, P = 0.001 (where the low P‐value indicates a significant linear correlation). For ve there was no such correlation (r2 = 0.02). The mean (absolute) percent difference between the models was 22.0% for Ktrans and 28.1% for ve. However, the RR parameter values were much less precise than the AIF method. The mean SDs for Ktrans and ve for the RR analysis were 0.024 min–1 and 0.06, respectively, vs. 0.002 min–1 and 0.03 for AIF analysis. Magn Reson Med 57:353–361, 2007. © 2007 Wiley‐Liss, Inc.
Single‐shot ADC imaging for fMRI
Authors: Song Allen W. , Guo Hua , Truong Trong‐Kha 
Published: January 2007

AbstractIt has been suggested that apparent diffusion coefficient (ADC) contrast can be sensitive to cerebral blood flow (CBF) changes during brain activation. However, current ADC imaging techniques have an inherently low temporal resolution due to the requirement of multiple acquisitions with different b‐factors, as well as potential confounds from cross talk between the deoxyhemoglobin‐induced background gradients and the externally applied diffusion‐weighting gradients. In this report a new method is proposed and implemented that addresses these two limitations. Specifically, a single‐shot pulse sequence that sequentially acquires one gradient‐echo (GRE) and two diffusion‐weighted spin‐echo (SE) images was developed. In addition, the diffusion‐weighting gradient waveform was numerically optimized to null the cross terms with the deoxyhemoglobin‐induced background gradients to fully isolate the effect of diffusion weighting from that of oxygenation‐level changes. The experimental results show that this new single‐shot method can acquire ADC maps with sufficient signal‐to‐noise ratio (SNR), and establish its practical utility in functional MRI (fMRI) to complement the blood oxygenation level‐dependent (BOLD) technique and provide differential sensitivity for different vasculatures to better localize neural activity originating from the small vessels. Magn Reson Med 57:417–422, 2007. © 2007 Wiley‐Liss, Inc.
Real‐time shimming to compensate for respiration‐induced B0 fluctuations
Authors: van Gelderen P. , de Zwart J.A. , Starewicz P. , Hinks R.S. , Duyn J.H. 
Published: January 2007

AbstractIn MRI of human brain, the respiratory cycle can induce B0‐field fluctuations through motion of the chest and fluctuations in local oxygen concentration. The associated NMR frequency changes can affect the MRI data in various ways and lead to temporal signal fluctuations, and image artifacts such as ghosting and blurring. Since the size of the effect scales with magnetic field strength, artifacts become particularly problematic at fields above 3.0T. Furthermore, the spatial dependence of the B0‐field fluctuations complicates their correction. In this work, a new method is presented that allows compensation of field fluctuations by modulating the B0 shims in real time. In this method, a reference scan is acquired to measure the spatial distribution of the B0 effect related to chest motion. During the actual scan, this information is then used, together with chest motion data, to apply compensating B0 shims in real time. The method can be combined with any type of scan without modifications to the pulse sequence. Real‐time B0 shimming is demonstrated to substantially improve the phase stability of EPI data and the image quality of multishot gradient‐echo (GRE) MRI at 7T. Magn Reson Med 57:362–368, 2007. © 2007 Wiley‐Liss, Inc.
Proposed radiofrequency phased‐array excitation scheme for homogenous and localized 7‐Tesla whole‐body imaging based on full‐wave numerical simulations
Authors: Abraham Roney , Ibrahim Tamer S. 
Published: January 2007

AbstractIn this article, a radiofrequency (RF) excitation scheme for 7‐Tesla (T) whole‐body applications is derived and analyzed using the finite difference time domain (FDTD) method. Important features of the proposed excitation scheme and coil (a potential 7T whole‐body transverse electromagnetic [TEM] resonator design), from both operational and electromagnetic perspectives, are discussed. The choice of the coil's operational mode is unconventional; instead of the typical “homogenous mode,” we use a mode that provides a null field in the center of the coil at low‐field applications. Using a 3D FDTD implementation of Maxwell's equations, we demonstrate that the whole‐body 7T TEM coil (tuned to the aforementioned unconventional mode and excited in an optimized near‐field, phased‐array fashion) can potentially provide 1) homogenous whole‐slice (demonstrated in three axial, sagittal, and coronal slices) and 2) 3D localized (demonstrated in the heart) excitations. As RF power was not considered as a part of the optimization in several cases, the significant improvements achieved by whole‐slice RF excitation came at the cost of considerable increases in RF power requirements. Magn Reson Med 57:235–242, 2007. © 2007 Wiley‐Liss, Inc.
Quantitative magnetization transfer imaging via selective inversion recovery with short repetition times
Authors: Gochberg Daniel F. , Gore John C. 
Published: January 2007

AbstractQuantitative magnetization transfer imaging (qMTI) methods are able to estimate fundamental sample parameters, such as the relative size of the solid‐like macromolecular proton pool and the spin exchange rate between this pool and the directly measured free water protons. One such method is selective inversion recovery (SIR), in which the free water protons are selectively inverted and the signal is fit to a biexponential function of the inversion time (TI). SIR uses only low‐power pulses and requires no separate RF (B1) or static field (B0) field maps, and the analysis is largely independent of the macromolecular pool lineshape. These are all advantages over steady‐state off‐resonance saturation qMTI methods. However, up to now, SIR has been implemented only with repetition times TR ≫ T1. This paper describes a modification of SIR with smaller TR values and a greater signal‐to‐noise ratio (SNR) efficiency. Magn Reson Med 57:437–441, 2007. © 2007 Wiley‐Liss, Inc.
Impact of coil design on the contrast‐to‐noise ratio, precision, and consistency of quantitative cartilage morphometry at 3 Tesla: A pilot study for the osteoarthritis initiative
Authors: Eckstein Felix , Kunz Manuela , Hudelmaier Martin , Jackson Rebecca , Yu Joseph , Eaton Charles B. , Schneider Erika 
Published: January 2007

AbstractPhased‐array (PA) coils generally provide higher signal‐to‐noise ratios (SNRs) than quadrature knee coils. In this pilot study for the Osteoarthritis Initiative (OAI) we compared these two types of coils in terms of contrast‐to‐noise ratio (CNR), precision, and consistency of quantitative femorotibial cartilage measurements. Test‐retest measurements were acquired using coronal fast low‐angle shot with water excitation (FLASHwe) and coronal multiplanar reconstruction (MPR) of sagittal double‐echo steady state with water excitation (DESSwe) at 3T. The precision errors for cartilage volume and thickness were ≤2.6% for the quadrature coil and ≤2.3% for the PA coil with FLASHwe, and ≤2.3%/≤2.5% with DESSwe. The precision for aggregate medial and lateral cartilage measures was significantly higher than that for single plates, independently of coil and sequence. The PA coil measurements did not always fully agree with the quadrature coil measurements, and some differences were significant. The higher CNR of the PA coil did not translate directly into improved precision of cartilage measurement; however, summing up cartilage plates within the medial and lateral compartment reduced precision errors. Magn Reson Med 57:448–454, 2007. © 2007 Wiley‐Liss, Inc.
Novel strategy for cerebral 13C MRS using very low RF power for proton decoupling
Authors: Li Shizhe , Yang Jehoon , Shen Jun 
Published: January 2007

AbstractOne of the major difficulties of in vivo 13C MRS is the need to decouple the large, one‐bond, 1H‐13C scalar couplings in order to obtain useful signal‐to‐noise ratios (SNRs) and spectral resolution at magnetic field strengths that are accessible to clinical studies. In this report a new strategy for in vivo cerebral 13C MRS is proposed. We realized that the turnover kinetics of glutamate (Glu) C5 from exogenous [2‐13C]glucose (Glc) is identical to that of Glu C4 from exogenous [1‐13C]Glc. The carboxylic/amide carbons are only coupled to protons via very weak long‐range 1H‐13C scalar couplings. As such, they can be effectively decoupled at very low RF power. Therefore, decoupling of the large 1H‐13C scalar couplings can be avoided by the use of [2‐13C]Glc. An additional advantage of this strategy is the lack of contamination from subcutaneous lipids because there are no overlapping fat signals in the vicinity of the Glu C5 and glutamine (Gln) C5 peaks. The feasibility of this strategy was demonstrated using 13C MRS on rhesus monkey brains at 4.7T. Magn Reson Med 57:265–271, 2007. © 2007 Wiley‐Liss, Inc.
Reducing susceptibility artifacts in fMRI using volume‐selective z‐shim compensation
Authors: Du Yiping P. , Dalwani Manish , Wylie Korey , Claus Eric , Tregellas Jason R. 
Published: January 2007

AbstractSusceptibility‐induced magnetic field gradients (SFGs) can result in severe signal loss in the orbitofrontal cortex (OFC) in gradient‐echo‐based functional MRI (fMRI) studies. Although conventional z‐shim techniques can effectively recover the MRI signal in this region, the substantial penalty in imaging time hampers their use in routine fMRI studies. A modified z‐shim technique with high imaging efficiency is presented in this study. In this technique, z‐shim compensations are applied only to a selective volume where the susceptibility artifact is severe. The results of an fMRI study (N = 6) demonstrate the feasibility of detecting the OFC activation with z‐shim in whole‐brain fMRI studies at a temporal resolution of 2 s. Magn Reson Med 57:396–404, 2007. © 2007 Wiley‐Liss, Inc.
Simplified quantitative description of amide proton transfer (APT) imaging during acute ischemia
Authors: Sun Phillip Zhe , Zhou Jinyuan , Huang Judy , van Zijl Peter 
Published: January 2007

AbstractAmide proton transfer (APT) imaging employs the chemical exchange saturation transfer (CEST) mechanism to detect mobile endogenous proteins and peptides. It can be used to detect pH reduction during acute ischemia and thus provide complementary information to perfusion‐weighted (PWI) and diffusion‐weighted (DWI) imaging. However, the APT contrast depends strongly on the choice of imaging parameters, especially the radiofrequency (RF) saturation time and strength, which need to be optimized. In this work it is shown that even though at least three proton pools are present, the description of the APT process during acute ischemia can be greatly simplified by means of a dual two‐pool model analysis. With this approach, the experimentally measured RF irradiation power dependence of the effect in the rat brain was well predicted. The results showed an optimal RF strength of 0.75 μT for our particular coil setup, and a maximally obtainable APT ratio difference of 2.9% ± 0.3% between ischemic and normal brain regions. Magn Reson Med 57:405–410, 2007. © 2007 Wiley‐Liss, Inc.
Transceive surface coil array for MRI of the human prostate at 4T
Authors: Pinkerton Robert G. , Near James P. , Barberi Enzo A. , Menon Ravi S. , Bartha Robert 
Published: January 2007

AbstractA novel torso transceive surface coil array for prostate magnetic resonance imaging (MRI) and spectroscopy (MRS) at 4T is presented. It is shown that with the use of a conformal transceive surface coil array with 50 Ω transmitter amplifiers and receiver preamplifiers, one can perform whole‐volume torso imaging while maintaining the high signal‐to‐noise ratio (SNR) inherent to surface coil designs. Recent theoretical considerations have shown that by focusing the infringing radiofrequency (RF) electromagnetic field, one can achieve increased penetration and signal homogeneity compared to a conventional circularly polarized driving scheme. A variation of this driving scheme particular to the proposed coil design resulted in a twofold increase in SNR in the prostate compared to that achieved with a conventional circularly polarized driving scheme. The novel transceive surface coil array presented is capable of full‐volume imaging of the human torso at 4T while maintaining signal penetration in the deep region of the prostate gland. Magn Reson Med 57:455–458, 2007. © 2007 Wiley‐Liss, Inc.
Minimizing macrovessel signal in cerebral perfusion imaging using independent component analysis
Authors: Reishofer G. , Fazekas F. , Keeling S. , Enzinger C. , Payer F. , Simbrunner J. , Stollberger R. 
Published: January 2007

AbstractThe pronounced susceptibility effect of macrovessels in MR bolus‐tracking studies induces spots of artificially high blood flow and volume in perfusion parameter images. These high‐intensity regions impede the detection of perfusion changes and lead to elevated perfusion parameters in adjacent tissues. The purpose of this work was to explore postprocessing methods to reduce the influence of macrovessel signal in dynamic MRI. After data reduction was performed with the use of a principal component analysis (PCA), an independent component analysis (ICA) was applied to separate signal components of different compartments. Based on this decomposition, the dynamic time series were reconstructed with minimized contributions of macrovessel signal and noise. The influence of the temporal resolution and signal‐to‐noise ratio (SNR) of the source data were investigated by means of a simulation study. A region‐of‐interest (ROI)‐based analysis of corrected and uncorrected in vivo data demonstrated that the influence of arteries and veins was reduced at least by 50%, while gray matter (GM) and white matter (WM) tissues were nearly unaffected by the correction process. Hemodynamic parameter images of the cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) were calculated from corrected and uncorrected scans. The corrected parameter images showed a clearly reduced macrovessel signal and an improved perceptibility of microvascular perfusion changes compared to the uncorrected ones. Magn Reson Med 57:278–288, 2007. © 2007 Wiley‐Liss, Inc.
Tunneling time of electronic wave packet through a parabolic quantum well with double barrier
Authors: Gong J. , Liang X. X. , Ban S. L. 
Published: January 2007

AbstractThe tunneling time of electrons through a parabolic quantum well structure has been investigated. A time‐dependent Schrödinger equation has been numerically solved using the transfer‐matrix method and wave packet dynamic theory. The results show that the probability density of the electron inside the parabolic well first builds up to a maximum and then decays exponentially with time. Furthermore, the dependence of the build‐up time on the structure parameters of the system is weak, but the resonant tunneling lifetime decreases rapidly with the increase of the well width and barrier thickness. It can also be seen from our results that the build‐up time may be longer than the resonant tunneling lifetime for a narrow well. By comparing the parabolic well with a rectangular well, it is also found that the resonant tunneling lifetime through the parabolic quantum well is longer than that through the rectangular one in the case of a wide well with thin barriers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of cubic nonlinearity on laser radiation transmission in a photonic crystal with spatially modified media properties
Authors: Vetrov S. Ya. , Timofeev I. V. , Shabanov A. V. 
Published: January 2007

AbstractThe transfer matrix method was modified to explore the Kerr nonlinearity influence on laser radiation propagation in a one‐dimensional photonic crystal. The suggested spatial distribution of the refractive index allows to remove minibands and to make the transmission curve much steeper. Plain and steep photonic band gap edges are effective in creation of transmission anisotropy of powerful laser radiation. The investigated photonic crystal has a strong anisotropic optical transmission and acts as an optical analog of the electronic diode. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Desegregated learning: An innovative framework for programs of study
Authors: Fuentes Arturo A. , Freeman Robert , Crown Stephen , Kypuros Javier , Mahdi Hashim 
Published: January 2007

AbstractThis chapter presents an innovative framework for a mechanical engineering program of study termed desegregated learning. The goal is not desegregation but rather to promote a higher level of learning and to look for opportunities where desegregating the learning environment yields optimal results with reasonable costs and complexity.
Teaching writing in a laboratory‐based engineering course with a “How People Learn” framework
Authors: Yalvac Bugrahan , Smith H. David , Hirsch Penny L. , Birol Gülnor 
Published: January 2007

AbstractThis chapter discusses the effectiveness of an HPL framework used in a laboratory‐based, tissue‐engineering module designed in part to improve students' written communication skills. It illustrates a successful implementation of written communication instruction that does not compromise content knowledge instruction.