bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion in compartmental systems. I. A comparison of an analytical model with simulations
Authors: Meier Christian , Dreher Wolfgang , Leibfritz Dieter 
Published: August 2003

AbstractThis article examines the way in which microscopic tissue parameters affect the signal attenuation of diffusion‐weighted MR experiments. The influence of transmembrane water flux on the signal decay is emphasized using the Kärger equations, which are modified with respect to the cellular boundary restrictions for intra‐ and extracellular diffusion. This analytical approach is extensively compared to Monte‐Carlo simulations for a tissue model consisting of two compartments. It is shown that diffusion‐weighted MR methods provide a unique tool for estimation of the intracellular exchange time. Restrictions of applicability to in vivo data are examined. It is shown that the intracellular exchange time strongly depends on the size of a cell, leading to an apparent diffusion time dependence for in vivo data. Hence, an analytical model of a two‐compartment system with an averaged exchange time is inadequate for the interpretation of signal curves measured in vivo over large ranges of b‐values. Furthermore, differences of multiexponential signal curves, as obtained by different methods of diffusion weighting, can be explained by the influence of transmembrane water flux. Magn Reson Med 50:500–509, 2003. © 2003 Wiley‐Liss, Inc.
Diffusion in compartmental systems. II. Diffusion‐weighted measurements of rat brain tissue in vivo and postmortem at very large b‐values
Authors: Meier Christian , Dreher Wolfgang , Leibfritz Dieter 
Published: August 2003

AbstractDiffusion‐weighted single‐voxel 1H spectroscopic measurements were performed on rat brain tissue in vivo and postmortem. Diffusion weighting was achieved by varying the diffusion time from 23 ms to 1.18 sec via the mixing time in a stimulated echo sequence. A series of constant gradient (cg‐) experiments of eight effective gradient strengths q̃2(q̃2 = γ2δ2g2) from 24.2 × 103 to 490.2 × 103 mm−2 was performed, resulting in a maximum attenuation factor of b = 580,000 s/mm2. A fit of three exponential terms was found to be appropriate to represent the attenuation signal over the whole b‐range. The behavior of the slowest decaying component can be fully understood in terms of a long time limit of a modified Kärger formalism for a two‐compartment system. This allowed estimation of the transmembrane water exchange rate: the intracellular exchange time was determined to be 622 ± 29 ms and 578 ± 20 ms in vivo and postmortem, respectively. Magn Reson Med 50:510–514, 2003. © 2003 Wiley‐Liss, Inc.
Arterial transit time imaging with flow encoding arterial spin tagging (FEAST)
Authors: Wang Jiongjiong , Alsop David C. , Song Hee Kwon , Maldjian Joseph A. , Tang Kathy , Salvucci Alana E. , Detre John A. 
Published: August 2003

AbstractArterial spin labeling (ASL) perfusion imaging provides direct and absolute measurement of cerebral blood flow (CBF). Arterial transit time is a related physiological parameter reflecting the duration for the labeled spins to reach the brain region of interest. Most of the existing ASL approaches to assess arterial transit time rely on multiple measurements at various postlabeling delay times, and thus are vulnerable to motion artifact as well as computational error. We describe the use of flow encoding arterial spin tagging (FEAST) technique to measure tissue transit time, which can be derived from the ratio between the ASL signals measured with and without appropriate bipolar gradients. In the present study, we provided a theoretical framework and carried out an experimental validation during steady‐state imaging. The global mean tissue transit time was ∼1100 and 1400 ms for two conditions of bipolar gradients with specific encoding velocity (Venc) of 29 and 8 mm/sec, respectively. The mean tissue transit time measured within cerebral vascular territories was shortest in the deep middle cerebral artery (MCA) territory. Application of the FEAST technique in two patients with cerebrovascular disease demonstrated prolonged tissue transit times in the affected vascular territories which were consistent with results from other MR imaging modalities. Magn Reson Med 50:599–607, 2003. © 2003 Wiley‐Liss, Inc.
Breathhold abdominal and thoracic proton MR spectroscopy at 3T
Authors: Katz‐Brull Rachel , Rofsky Neil M. , Lenkinski Robert E. 
Published: August 2003

AbstractThe clinical utility of proton MR spectroscopy (1H‐MRS) has been well demonstrated in the brain, prostate, and breast. The aims of this work were to investigate 1) the feasibility of abdominal and thoracic 1H‐MRS at 3T, 2) the benefits of breathholding to MRS in these regions, and 3) the utility of multiple breathhold averaging for MRS. Breathholding either eliminated or markedly reduced phase and frequency shifts and outer voxel contamination that were associated with the motion of the abdomen and the thorax during breathing. Breathholding was found to be essential to spectroscopic investigation of the thorax. Spectra of renal cell carcinoma metastases in the abdomen and thorax were obtained utilizing multiple breathhold averaging. These spectra exhibited a resonance at 3.2 ppm attributed to the trimethylamine moiety of choline metabolites. The results of this study suggest a practical strategy for implementation of 1H‐MRS in the body. Magn Reson Med 50:461–467, 2003. © 2003 Wiley‐Liss, Inc.
Removing spikes caused by quantization noise from high‐resolution histograms
Authors: Tozer Daniel J. , Tofts Paul S. 
Published: August 2003

AbstractA novel method is presented for the removal of spikes, caused by the division of two series of integers, from high‐resolution histograms. When two series of integers are divided the results take the form of a nonuniform distribution. Such a division is often used in medical imaging, due to the storage of most images as integers. An example of this is the division of the saturated and unsaturated signal intensities to obtain a magnetization transfer ratio. Histograms produced using these methods often contain spikes relating to the nonuniform distribution mentioned above. These spikes can have serious implications for certain histogram characteristics. Most commonly, peak height and location can be seriously distorted by these spikes, which have predictable locations. These spikes can be removed by the addition of uniformly distributed noise to the integer signal intensities before division. Magn Reson Med 50:649–653, 2003. © 2003 Wiley‐Liss, Inc.
High‐resolution magic angle spinning proton NMR analysis of human prostate tissue with slow spinning rates
Authors: Taylor Jennifer L. , Wu Chin‐Lee , Cory David , Gonzalez R. Gilberto , Bielecki Anthony , Cheng Leo L. 
Published: August 2003

AbstractThe development of high‐resolution magic angle spinning (HR‐MAS) NMR spectroscopy for intact tissue analysis and the correlations between the measured tissue metabolites and disease pathologies have inspired investigations of slow‐spinning methodologies to maximize the protection of tissue pathology structures from HR‐MAS centrifuging damage. Spinning sidebands produced by slow‐rate spinning must be suppressed to prevent their complicating the spectral region of metabolites. Twenty‐two human prostatectomy samples were analyzed on a 14.1T spectrometer, with HR‐MAS spinning rates of 600 Hz, 700 Hz, and 3.0 kHz, a repetition time of 5 sec, and employing various rotor‐synchronized suppression methods, including DANTE, WATERGATE, TOSS, and PASS pulse sequences. Among them, DANTE, as the simplest scheme, has shown the most potential in suppression of tissue water signals and spinning sidebands, as well as in quantifying metabolic concentrations. Magn Reson Med 50:627–632, 2003. © 2003 Wiley‐Liss, Inc.
Time‐resolved flow measurement in the isolated rat heart: Characterization of left coronary artery stenosis
Authors: Köhler Sascha , Hiller Karl‐Heinz , Jakob Peter M. , Bauer Wolfgang R. , Haase Axel 
Published: August 2003

AbstractThe investigation of flow behavior in coronary arteries is of great importance for an understanding of heart failure and heart regulation mechanisms. The purpose of the present study was to demonstrate that flow velocity can be quantified in the coronary arteries of the isolated rat heart with high‐resolution phase contrast MRI. A phase contrast cine‐FLASH imaging sequence was used for flow quantification with an in‐plane resolution of 70 μm and a slice thickness of 500 μm. With time‐resolved measurements, coronary flow over the heart cycle was analyzed. Furthermore, the flow behavior in coronary stenosis was investigated and the degree of stenosis was quantified with MR phase contrast imaging. To achieve the required spatial resolution and a satisfactory signal‐to‐noise ratio, the experiments were performed at 11.75 T. Magn Reson Med 50:449–452, 2003. © 2003 Wiley‐Liss, Inc.
Magnetization transfer effect on the creatine methyl resonance studied by CW off‐resonance irradiation in human skeletal muscle on a clinical MR system
Authors: Renema W. Klaas Jan , Klomp Dennis W.J. , Philippens Mariëlle E.P. , van den Bergh Adrianus J. , Wieringa Bé , Heerschap Arend 
Published: August 2003

AbstractMagnetization transfer (MT) between the mobile (MR‐visible) spin pool and immobile (MR‐invisible) spin pool of creatine (Cr) was studied on a clinical 1.5 T MR scanner in human skeletal muscle using continuous wave (CW) pre‐irradiation as the saturation method for the immobile pool. For this purpose, only slight modifications to the MR system were made. A specially designed electronic circuit was used to couple a CW amplifier to the RF channel of the scanner. The CW pulse power (γB2/2π) and pulse length were determined to be approximately 550 Hz and 3 s, respectively, for optimal signal attenuation of the Cr methyl signal. The bound Cr fraction in human gastrocnemius muscle was determined to be 0.4–1.3% using a two‐pool exchange model function to describe the MT effect. Magn Reson Med 50:468–473, 2003. © 2003 Wiley‐Liss, Inc.
Equilibrium water exchange between the intra‐ and extracellular spaces of mammalian brain
Authors: Quirk James D. , Bretthorst G. Larry , Duong Timothy Q. , Snyder Avi Z. , Springer Charles S. , Ackerman Joseph J.H. , Neil Jeffrey J. 
Published: August 2003

AbstractThis report describes the measurement of water preexchange lifetimes and intra/extracellular content in intact, functioning mammalian brain. Intra‐ and extracellular water magnetic resonance (MR) signals from rat brain in vivo were quantitatively resolved in the longitudinal relaxation domain following administration of an MR relaxation agent into the extracellular space. The estimated intracellular water content fraction was 81% ± 8%, and the intra‐ to extracellular exchange rate constant was 1.81 ± 0.89 s–1 (mean ± SD, N = 9), corresponding to an intracellular water preexchange lifetime of ∼550 ms. These results provide a temporal framework for anticipating the water exchange regime (fast, intermediate, or slow) underlying a variety of compartment‐sensitive measurements. The method also supplies a means by which to evaluate membrane water permeability and intra/extracellular water content serially in intact tissue. The data are obtained in an imaging mode that permits detection of regional variations in these parameters. Magn Reson Med 50:493–499, 2003. © 2003 Wiley‐Liss, Inc.
In vivo qualitative assessments of articular cartilage in the rabbit knee with high‐resolution MRI at 3 T
Authors: Laurent Didier , Wasvary James , O'Byrne Elizabeth , Rudin Markus 
Published: August 2003

AbstractProteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high‐resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One‐millimeter thick coronal images were obtained at 3 T with a 97 × 97 μm2 pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an ∼2‐fold greater Gd(DTPA)2‐‐induced decrease in T1 relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two‐point method was tested as an alternative to the more time‐consuming multipoint method typically used to measure T1 changes. Kinetics of Gd(DTPA)2‐ uptake were observed with a 10‐min time resolution. The diffusive transport of Gd(DTPA)2‐ was characterized by a T1 decrease ∼2‐fold faster in papain‐treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T1 variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA)2‐‐MRI may help in identifying new active compounds during efficacy studies on cartilage protection. Magn Reson Med 50:541–549, 2003. © 2003 Wiley‐Liss, Inc.
Model of the human vasculature for studying the influence of contrast injection speed on cerebral perfusion MRI
Authors: van Osch Matthias J.P. , Vonken Evert‐jan P.A. , Wu Ona , Viergever Max A. , van der Grond Jeroen , Bakker Chris J.G. 
Published: August 2003

AbstractSimulations of dynamic susceptibility contrast (DSC) MRI are frequently performed by assuming a certain shape for the input function and the microvascular response function. However, to investigate the influence of parameters that will affect the shape of the input function, a more complex model of the human vasculature is required. In this study, a model of the human vasculature is proposed that consists of a network of vascular operators based on physiological data typical of a 35‐year‐old male subject. The simulated contrast passage curves were found to be within the range of observed contrast passage curves in a population of patients without vascular disease. The model was used to predict the effect of different injection speeds of the contrast agent on the accuracy of the perfusion experiment. It was found that injection speeds of <3 ml/s lead to an underestimation of the observed cerebral blood flow (CBF). Additionally, it was determined that decreasing the temporal resolution of the acquisition results in an underestimation of the CBF values, and an increase of the standard deviation (SD) of CBF measurements. Magn Reson Med 50:614–622, 2003. © 2003 Wiley‐Liss, Inc.
In vivo study of microcirculation in canine myocardium using the IVIM method†
Authors: Callot Virginie , Bennett Eric , Decking Ulrich K.M. , Balaban Robert S. , Wen Han 
Published: August 2003

AbstractThe intravoxel incoherent motion (IVIM) method was implemented in closed‐chest dogs to obtain measurements on microcirculation in the left ventricular wall in vivo. Specifically, it enabled us to measure the mean microflow velocity (400 ± 40 μm/s) and the vascular volume fraction (VVF) (11.1% ± 2.2%), and observe the directional preference of capillary orientation. The apparent diffusion coefficients (ADCs) of water along and perpendicular to myofibers were also measured. With vasodilatation by adenosine infusion, a 25% increase in the VVF and a 7% increase in the mean microflow velocity were observed, while no change in the ADC was detected. A 28.5% decrease of the ADC was observed postmortem. Magn Reson Med 50:531–540, 2003. Published 2003 Wiley‐Liss, Inc.
Isotropic susceptibility shift under MAS: The origin of the split water resonances in 1H MAS NMR spectra of cell suspensions
Authors: Chen Jin‐Hong , Enloe Brian M. , Xiao Yong , Cory D.G. , Singer Samuel 
Published: August 2003

AbstractBulk susceptibility variations in a multiphase system such as cultured cells and tissue have two manifestations: a dipolar field component outside the regular heterogenous region which introduces linebroadening, and an isotropic field part which results in a frequency shift. Previous NMR studies have emphasized the utility of magic angle spinning for averaging the dipolar component, particularly if the spins of interest are limited to one phase of a multiphase system such as a sample of liquid with air pockets or glass beads. However, in analyzing spectra from complex multiphase systems, such as cell suspensions and tissues, etc., the isotropic part is often neglected, leading to questionable interpretation of experimental results. The present study demonstrates that under magic angle spinning, the water resonance in NMR experiments of cell suspensions is split into two resolved peaks due to the isotropic susceptibility shift. These two peaks are assigned to a central core of cell free water and an outer cylindrical ring of tightly packed cells in close association with water. A comprehensive theory for this splitting is provided based on a coaxis cylinder model with different susceptibilities. The frequency difference is shown to be dependent on the susceptibility difference and also on the angle of the rotor in the magnetic field. The splitting distance of the two water peaks can be used to measure the susceptibility difference of water in these two phases. The susceptibility difference was measured for three different cell types: 3T3 F442A preadipocyte cells, mouse embryonic stem cells, and human red blood cells. Magn Reson Med 50:515–521, 2003. © 2003 Wiley‐Liss, Inc.
Block regional off‐resonance correction (BRORC): A fast and effective deblurring method for spiral imaging
Authors: Moriguchi Hisamoto , Dale Brian M. , Lewin Jonathan S. , Duerk Jeffrey L. 
Published: August 2003

AbstractOne primary disadvantage of spiral imaging is blurring artifact due to off‐resonance effects. The conventional frequency segmented off‐resonance correction method that is performed over the entire image is computationally intense due to the large number of fast Fourier transforms (FFTs) required. Here, a new fast off‐resonance correction method, block regional off‐resonance correction (BRORC), is presented. In this method, off‐resonance correction proceeds block‐by‐block through the reconstructed image with FFTs performed on matrices that are smaller than the full image matrix. The BRORC algorithm is typically several times more computationally efficient than the conventional off‐resonance correction algorithm. Additional computational reductions can be expected for the BRORC if only specific image regions require deblurring. The newly proposed off‐resonance correction method offers significant speed advantages and equivalent image quality when compared to conventional off‐resonance correction methods. Magn Reson Med 50:643–648, 2003. © 2003 Wiley‐Liss, Inc.
Effect of vascular crushing on FAIR perfusion kinetics, using a BIR‐4 pulse in a magnetization prepared FLASH sequence
Authors: Schepers Janneke , van Osch Matthias J.P. , Nicolay Klaas 
Published: August 2003

AbstractFlow‐sensitive alternating inversion recovery (FAIR) perfusion imaging suffers from high vascular signal, resulting in artifacts and overestimation of perfusion. With TurboFLASH acquisition, crushing of vascular signal by bipolar gradients after each excitation is difficult due to the requirement of an ultrashort repetition time. Therefore, insertion of a preparation phase in the FAIR sequence, after labeling and prior to TurboFLASH acquisition, is proposed. A segmented adiabatic BIR‐4 pulse, interleaved with crusher gradients, was used for flow crushing. The effect of the crusher preparation is shown as a function of crusher strength for a flow phantom and in rat brain. Influence of crusher strength on the time‐dependent FAIR signal from rat brain was also measured. Signal from flowing spins in a flow phantom and from arterial spins in rat brain was significantly suppressed. Image quality was improved and the overestimation of perfusion at short inflow times was eliminated. Magn Reson Med 50:608–613, 2003. © 2003 Wiley‐Liss, Inc.
Magnetic resonance spectroscopic imaging reconstruction with deformable shape‐intensity models
Authors: Zhu Xiao‐Ping , Du An‐Tao , Jahng Geon‐Ho , Soher Brian J. , Maudsley Andrew A. , Weiner Michael W. , Schuff Norbert 
Published: August 2003

AbstractA new method, based on a deformable shape‐intensity model (DSM), was developed to improve the signal‐to‐noise ratio (SNR) of multidimensional magnetic resonance spectroscopic imaging (MRSI) data sets without affecting spectral lineshapes and linewidths. Improvements with DSM, compared to digital filters using conventional signal apodization, were demonstrated on both simulated and experimental in vivo1H MRS images from 22 cognitively normal (CN) elderly subjects and 25 patients with Alzheimer's disease (AD). Simulated MRSI data showed that DSM achieved superior noise suppression compared to a matched apodization filter. Experimental MRSI data showed that SNR could be increased 2.1‐fold with DSM without distorting spectral resolution, thus maintaining all spectral features of the raw, unfiltered data. In conclusion, DSM should be used to achieve high SNR in reconstructing MRSI data. Magn Reson Med 50:474–482, 2003. © 2003 Wiley‐Liss, Inc.
Mapping of periodic waveforms using the ghost reconstructed alternating current estimation (GRACE) magnetic resonance imaging technique
Authors: Yang Hua , Cook Greg G. , Paley Martyn N.J. 
Published: August 2003

AbstractA new method of estimating alternating currents using ghost images created when the magnetic field from a fluctuating current modulates the phase of the magnetic resonance (MR) signal between successive phase‐encode views is described. The method, known as ghost reconstructed alternating current estimation (GRACE), may be useful for directly mapping fields, and hence current impulses produced by neuronal firing events when synchronized periodic modulation can be induced. Images were acquired on a 1.5 T MR system with small oil capsule phantoms and a single wire with an applied alternating current, placed perpendicular to the main field direction. Computer simulations of these experiments yielded ghost images that agreed with experimental results. A simulated ghost image resulting from an evoked neuronal waveform is also discussed. Weak magnetic fields were detected from both sinusoidal and square wave modulations. Magn Reson Med 50:633–637, 2003. © 2003 Wiley‐Liss, Inc.
Statistical motor unit number estimation: From theory to practice
Authors: Lomen‐Hoerth Catherine , Slawnych Michael P. 
Published: August 2003

AbstractStatistical motor unit number estimation (MUNE) is one of several experimental techniques used to estimate the number of lower motor neurons innervating a given muscle. All are fairly reproducible and have been applied successfully in monitoring neurogenic disease progression. Quantitating the number of lower motor neurons is important, since the compound muscle action potential (CMAP) and strength may not change as rapidly over time due to the confounding effect of reinnervation. MUNE techniques differ in the way they obtain samples of surface‐recorded motor unit potentials (SMUP). Statistical MUNE is based on Poisson statistics, uses surface stimulation, and is useful in testing distal, superficial nerves. This review focuses on the theory behind the development of the technique, critiques the publications resulting from applying the technique in control and disease subjects, and discusses the future developments needed for clinical utility. Muscle Nerve 28: 263–272, 2003