bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic resonance angiography of rat spinal cord at 9.4 T: A feasibility study
Authors: Bilgen Mehmet , Al‐Hafez Baraa , He Yong‐Yue , Brooks William M.
Published: May 2005

In this study we investigated the feasibility of performing 3D time‐of‐flight magnetic resonance angiography to remotely image the arteries of rat spinal cord. Using a custom‐designed implantable radiofrequency coil, we acquired angiograms from normal and injured cords. The potential of the approach was evaluated in terms of longitudinally monitoring the vascular reorganization of spinal cord following an injury. Magn Reson Med 53:1459–1461, 2005. © 2005 Wiley‐Liss, Inc.
In vivo detection of cortical GABA turnover from intravenously infused [1‐13C]D‐glucose
Authors: Yang Jehoon , Li Charles Q. , Shen Jun
Published: May 2005

In this study [2‐13C] γ‐aminobutyric acid (GABA) was spectrally resolved in vivo and detected simultaneously with [4‐13C]glutamate (Glu) and [4‐13C]glutamine (Gln) in the proton spectra obtained from a localized 40 μL voxel in rat neocortex with the use of an adiabatic 1H‐observed, 13C‐edited (POCE) spectroscopy method and an 89‐mm‐bore vertical 11.7 Tesla microimager. The time‐resolved kinetics of 13C label incorporation from intravenously infused [1‐13C]glucose into [4‐13C]Glu, [4‐13C]Gln, and [2‐13C]GABA were measured after acute administration of gabaculine, a potent and specific inhibitor of GABA‐transaminase. In contrast to previous observations of a rapid turnover of [2‐13C]GABA from [1‐13C]glucose in intact rat brain, the rate of 13C incorporation from [1‐13C]glucose into [2‐13C]GABA in the gabaculine‐treated rats was found to be significantly reduced as a result of the blockade of the GABA shunt. Magn Reson Med 53:1258–1267, 2005. Published 2005 Wiley‐Liss, Inc.
Radial GRASE: Implementation and applications
Authors: Gmitro Arthur F. , Kono Mitsuko , Theilmann Rebecca J. , Altbach Maria I. , Li Zhiqiang , Trouard Theodore P.
Published: May 2005

RAD‐GRASE is an MRI sequence that combines radial (RAD) k‐space scanning with the gradient and spin‐echo (GRASE) technique. RAD‐GRASE has the advantages of all radial data acquisition methods in that it can reduce motion sensitivity and correct motion‐induced data errors, which can be exploited to achieve high‐resolution diffusion‐weighted imaging (DWI). One can obtain different types of image contrast, including DWI, T1, T2, and T2*, in RAD‐GRASE by controlling the magnetization preparation and sequence timing. Moreover, because there is oversampling of the low spatial frequencies inherent to radial sequences, partial data reconstruction can be used to achieve multiple forms of image contrast from a single acquired data set, and to generate parametric image maps of equilibrium magnetization, T2, and T. The RAD‐GRASE technique can also be used to achieve fat‐suppressed and/or separated fat and water images by choosing the appropriate timing parameters. Magn Reson Med 53:1363–1371, 2005. © 2005 Wiley‐Liss, Inc.
Determination of mouse skeletal muscle architecture using three‐dimensional diffusion tensor imaging
Authors: Heemskerk Anneriet M. , Strijkers Gustav J. , Vilanova Anna , Drost Maarten R. , Nicolay Klaas
Published: May 2005

Muscle architecture is the main determinant of the mechanical behavior of skeletal muscles. This study explored the feasibility of diffusion tensor imaging (DTI) and fiber tracking to noninvasively determine the in vivo three‐dimensional (3D) architecture of skeletal muscle in mouse hind leg. In six mice, the hindlimb was imaged with a diffusion‐weighted (DW) 3D fast spin‐echo (FSE) sequence followed by the acquisition of an exercise‐induced, T2‐enhanced data set. The data showed the expected fiber organization, from which the physiological cross‐sectional area (PCSA), fiber length, and pennation angle for the tibialis anterior (TA) were obtained. The values of these parameters ranged from 5.4–9.1 mm2, 5.8–7.8 mm, and 21–24°, respectively, which is in agreement with values obtained previously with the use of invasive methods. This study shows that 3D DT acquisition and fiber tracking is feasible for the skeletal muscle of mice, and thus enables the quantitative determination of muscle architecture. Magn Reson Med 53:1333–1340, 2005. © 2005 Wiley‐Liss, Inc.
The effect of B1 field inhomogeneity and the nonselective inversion profile on the kinetics of FAIR‐based perfusion MRI
Authors: Schepers Janneke , van Osch Matthias J. P. , Bartels Lambertus W. , Heukels Sean N. , Viergever Max A. , Nicolay Klaas
Published: May 2005

Perfusion imaging with pulsed arterial spin labeling techniques, like flow‐sensitive alternating inversion recovery (FAIR), may suffer from inflow of fresh, i.e., unlabeled, spins. Inflow of fresh spins is caused by the arrival of unlabeled spins in the image slice and can lead to underestimation of the perfusion if not taken into account. In this study it was shown that a decrease in B1 field strength toward the edge of the transmit coil and the consequent reduction in the inversion efficiency leads to a narrowing of the arterial delivery function and a reduction in FAIR signal. Increasing the B1 amplitude of the adiabatic inversion pulse from 2.3 to 5.7 times its minimum amplitude requirement resulted in an observed increase of 40 to 80% in the rat brain FAIR signal at inflow times longer than 0.65 s. For coils with limited dimensions and significant B1 inhomogeneity over the perfusion labeling slab, the application of an excessively large B1 amplitude in combination with adiabatic inversion is recommended to optimize the FAIR perfusion contrast. Magn Reson Med 53:1355–1362, 2005. © 2005 Wiley‐Liss, Inc.
Multiexponential T2‐relaxation analysis in cerebrally damaged rats in the absence and presence of a gadolinium contrast agent
Authors: Lascialfari A. , Zucca I. , Asdente M. , Cimino M. , Guerrini U. , Paoletti R. , Tremoli E. , Lorusso V. , Sironi L.
Published: May 2005

An analysis of the multiexponential relaxation of transverse nuclear magnetization with and without a gadolinium‐based paramagnetic contrast agent in spontaneously hypertensive stroke‐prone rats (SHR‐SP) and in the rat model of ischemia induced by middle cerebral artery occlusion is described. From the multiexponential relaxation, the presence of two T2 relaxation times in the range of 0.03–0.5 s, T2A (shortest) and T2B (longest), with very different relative weights (respectively, A and B), is evidenced. In our models of cerebral damage, the changes in A and B were more evident than those in T2A and T2B. The two T2 values were interpreted as belonging to water molecules in two different compartments; therefore, the difference between the damaged and normal regions revealed by means of standard T2‐weighted images is suggested to be due to a different water distribution in the two compartments, rather than different T2's. The T2 relaxation in the SHR‐SP stroke model is analyzed for the first time using a multiexponential method. The power of a detailed analysis of MRI relaxation times is confirmed by the correspondence between the revealed changes in T2A, T2B, A and B, and the known T2W and DWI results about blood–brain barrier functionality. Magn Reson Med 53:1326–1332, 2005. © 2005 Wiley‐Liss, Inc.
3D MDEFT imaging of the human brain at 4.7 T with reduced sensitivity to radiofrequency inhomogeneity
Authors: Thomas David L. , De Vita Enrico , Deichmann Ralf , Turner Robert , Ordidge Roger J.
Published: May 2005

A modification to the 3D modified driven equilibrium Fourier transform (MDEFT) imaging technique is proposed that reduces its sensitivity to RF inhomogeneity. This is especially important at high field strengths where RF focusing effects exacerbate B1 inhomogeneity, causing significant signal nonuniformity in the images. The adiabatic inversion pulse used during the preparation period of the MDEFT sequence is replaced by a hard (nonadiabatic) pulse with a nominal flip angle of 130°. The spatial inhomogeneity of the hard pulse preparation compensates for the inhomogeneity of the excitation pulses. Uniform signal intensity is obtained for a wide range of B1 amplitudes and the high CNR characteristic of MDEFT is retained. The new approach was validated by numerical simulations and successfully applied to human brain imaging at 4.7 T, resulting in high‐quality T1‐weighted images of the whole human brain at high field strength with uniform signal intensity and contrast, despite the presence of significant RF inhomogeneity. Magn Reson Med 53:1452–1458, 2005. © 2005 Wiley‐Liss, Inc.
Optimizing spatiotemporal sampling for k‐t BLAST and k‐t SENSE: Application to high‐resolution real‐time cardiac steady‐state free precession
Authors: Tsao Jeffrey , Kozerke Sebastian , Boesiger Peter , Pruessmann Klaas P.
Published: May 2005

In k‐t BLAST and k‐t SENSE, data acquisition is accelerated by sparsely sampling k‐space over time. This undersampling in k‐t space causes the object signals to be convolved with a point spread function in x‐f space (x = spatial position, f = temporal frequency). The resulting aliasing is resolved by exploiting spatiotemporal correlations within the data. In general, reconstruction accuracy can be improved by controlling the k‐t sampling pattern to minimize signal overlap in x‐f space. In this work, we describe an approach to obtain generally favorable patterns for typical image series without specific knowledge of the image series itself. These optimized sampling patterns were applied to free‐breathing, untriggered (i.e., real‐time) cardiac imaging with steady‐state free precession (SSFP). Eddy‐current artifacts, which are otherwise increased drastically in SSFP by the undersampling, were minimized using alternating k‐space sweeps. With the synergistic combination of the k‐t approach with optimized sampling and SSFP with alternating k‐space sweeps, it was possible to achieve a high signal‐to‐noise ratio, high contrast, and high spatiotemporal resolutions, while achieving substantial immunity against eddy currents. Cardiac images are shown, demonstrating excellent image quality and an in‐plane resolution of ∼2.0 mm at >25 frames/s, using one or more receiver coils. Magn Reson Med 53:1372–1382, 2005. © 2005 Wiley‐Liss, Inc.
PASTA: Pointwise assessment of streamline tractography attributes
Authors: Jones Derek K. , Travis Adam R. , Eden Greg , Pierpaoli Carlo , Basser Peter J.
Published: May 2005

Diffusion tensor MRI tractography aims to reconstruct noninvasively the 3D trajectories of white matter fasciculi within the brain, providing neuroscientists and clinicians with a potentially useful tool for mapping brain architecture. While this technique is widely used to visualize white matter pathways, the associated uncertainty in fiber orientation and artifacts have, to date, not been visualized in conjunction with the trajectory data. In this work, the bootstrap method was used to determine the distributions of diffusion indices such as trace and anisotropy, together with the uncertainty in fiber orientation. A novel visualization scheme was developed to encode this information at each point along reconstructed trajectories. By integrating these schemes into a graphical user interface, a new tool which we call PASTA (Pointwise Assessment of Streamline Tractography Attributes) was created to facilitate identification of artifacts in tractography that would otherwise go undetected. Magn Reson Med 53:1462–1467, 2005. Published 2005 Wiley‐Liss, Inc.
Formalin fixation alters water diffusion coefficient magnitude but not anisotropy in infarcted brain
Authors: Sun Shu‐Wei , Neil Jeffrey J. , Liang Hsiao‐Fang , He Yong Y. , Schmidt Robert E. , Hsu Chung Y. , Song Sheng‐Kwei
Published: May 2005

This study was designed to determine whether formalin fixation alters diffusion parameters in the infarcted brain. Diffusion tensor images were obtained from anesthetized mice 1 hr after middle cerebral artery occlusion and repeated after formalin fixation of brains. In live animals, there was a significant decrease in the trace of the diffusion tensor (Tr(D)) in infarcted cortex and external capsule compared with contralateral brain areas, with no change in relative anisotropy (RA). After formalin fixation, Tr(D) was reduced 30–80%. However, the Tr(D) differential present in vivo between injured and healthy tissues was lost, with Tr(D) reduced to similar values in all tissues except for the edge of the cortical infarction, where it was lower than in surrounding tissues. RA values were unchanged after fixation. This study supports the preservation of diffusion anisotropy for both healthy and injured white matter in fixed mouse brain. However, the sensitivity of water diffusion in detecting tissue injury in vivo is not preserved in fixed tissues. Magn Reson Med 53:1447–1451, 2005. © 2005 Wiley‐Liss, Inc.
Spiral balanced steady‐state free precession cardiac imaging
Authors: Nayak Krishna S. , Hargreaves Brian A. , Hu Bob S. , Nishimura Dwight G. , Pauly John M. , Meyer Craig H.
Published: May 2005

Balanced steady‐state free precession (SSFP) sequences are useful in cardiac imaging because they achieve high signal efficiency and excellent blood–myocardium contrast. Spiral imaging enables the efficient acquisition of cardiac images with reduced flow and motion artifacts. Balanced SSFP has been combined with spiral imaging for real‐time interactive cardiac MRI. New features of this method to enable scanning in a clinical setting include short, first‐moment nulled spiral trajectories and interactive control over the spatial location of banding artifacts (SSFP‐specific signal variations). The feasibility of spiral balanced SSFP cardiac imaging at 1.5 T is demonstrated. In observations from over 40 volunteer and patient studies, spiral balanced SSFP imaging shows significantly improved contrast compared to spiral gradient‐spoiled imaging, producing better visualization of cardiac function, improved localization, and reduced flow artifacts from blood. Magn Reson Med 53:1468–1473, 2005. © 2005 Wiley‐Liss, Inc.
3Parallel magnetic resonance imaging with adaptive radius in k‐space (PARS): Constrained image reconstruction using k‐space locality in radiofrequency coil encoded data
Authors: Yeh Ernest N. , McKenzie Charles A. , Ohliger Michael A. , Sodickson Daniel K.
Published: May 2005

A parallel image reconstruction algorithm is presented that exploits the k‐space locality in radiofrequency (RF) coil encoded data. In RF coil encoding, information relevant to reconstructing an omitted datum rapidly diminishes as a function of k‐space separation between the omitted datum and the acquired signal data. The proposed method, parallel magnetic resonance imaging with adaptive radius in k‐space (PARS), harnesses this physical property of RF coil encoding via a sliding‐kernel approach. Unlike generalized parallel imaging approaches that might typically involve inverting a prohibitively large matrix for arbitrary sampling trajectories, the PARS sliding‐kernel approach creates manageable and distributable independent matrices to be inverted, achieving both computational efficiency and numerical stability. An empirical method designed to measure total error power is described, and the total error power of PARS reconstructions is studied over a range of k‐space radii and accelerations, revealing “minimal‐error” conditions at comparatively modest k‐space radii. PARS reconstructions of undersampled in vivo Cartesian and non‐Cartesian data sets are shown and are compared selectively with traditional SENSE reconstructions. Various characteristics of the PARS k‐space locality constraint (such as the tradeoff between signal‐to‐noise ratio and artifact power and the relationship with iterative parallel conjugate gradient approaches or nonparallel gridding approaches) are discussed. Magn Reson Med 53:1383–1392, 2005. © 2005 Wiley‐Liss, Inc.
Observation of coupled 1H metabolite resonances at long TE
Authors: Soher Brian J. , Pattany Pradip M. , Matson Gerald B. , Maudsley Andrew A.
Published: May 2005

A PRESS localization 1H MRS acquisition sequence with a Carr–Purcell train of refocusing pulses (CP‐PRESS) has been implemented using global refocusing “sandwich” pulses. The CP pulse train minimized the effects of J‐coupled dephasing in metabolites with strongly coupled, multiplet resonance groups as demonstrated in both phantom data and in vivo single‐voxel spectroscopy in normal volunteers. Metabolites with multiplet resonance patterns were maintained with greater signal to noise and a simpler resonance pattern at long echo times. T2 decay times for metabolites with singlet and multiplet resonances were similar to published values, except for the NAA multiplet at 2.5 ppm, which had a significantly shorter T2 value (147 ms) than that typically reported for the singlet at 2.01 ppm. Metabolite‐nulled spectra were acquired in normal volunteers to evaluate the effects of CP‐PRESS on baseline signal contributions from residual water, lipids, and macromolecules. The T2 decay times in four baseline regions in data acquired with the CP‐PRESS sequence showed longer decays than corresponding regions in metabolite‐nulled spectra from a standard PRESS sequence, but were significantly diminished long before the metabolites of interest were gone. The spectral analysis for spectra with longer TE times also showed less variability due the higher metabolite SNR, simpler spectral patterns, and the decreased baseline contributions. Magn Reson Med 53:1283–1287, 2005. © 2005 Wiley‐Liss, Inc.
Partial fourier partially parallel imaging
Authors: Bydder Mark , Robson Matthew D.
Published: May 2005

The techniques of partial Fourier (PF) and partially parallel imaging have been combined using a constrained reconstruction technique. The benefits compared with the individual techniques are reduced imaging time and/or an increase in signal‐to‐noise ratio. Low‐resolution phase maps and coil sensitivities may be obtained using autocalibration or from a prescan followed by additional processing. Minor phase artifacts that are introduced by relying on conjugate symmetry can be reduced using a novel regularization scheme to vary the degree to which PF is used in the reconstruction. A nonrectilinear reconstruction algorithm is presented and the potential for motion artifact reduction is investigated using robust reconstruction. Magn Reson Med 53:1393–1401, 2005. © 2005 Wiley‐Liss, Inc.
Isotropic diffusion weighting in radial fast spin‐echo magnetic resonance imaging
Authors: Sarlls Joelle E. , Newbould Rexford D. , Altbach Maria I. , Gmitro Arthur F. , Seeger Joachim , Trouard Theodore P.
Published: May 2005

Radial fast spin‐echo (radial‐FSE) methods enable multishot diffusion‐weighted MRI (DWMRI) to be carried out without significant artifacts due to motion and/or susceptibility and can be used to generate DWMRI images with high spatial resolution. In this work, a novel method that allows isotropic diffusion weighting to be obtained in a single radial k‐space data set is presented. This is accomplished by altering the direction of diffusion weighting gradients between groups of TR periods, which yield sets of radial lines that possess diffusion weighting sensitive to motion in different directions. By altering the diffusion weighting directions and controlling the view ordering appropriately within the sequence, an effectively isotropic diffusion‐weighted image can be obtained within one radial‐FSE scan. The order in which radial lines are acquired can also be controlled to yield data sets without significant artifacts due to motion, T2 decay, and/or diffusion anisotropy. Magn Reson Med 53:1347–1354, 2005. © 2005 Wiley‐Liss, Inc.
X‐ray compatible radiofrequency coil for magnetic resonance imaging
Authors: Rieke Viola , Ganguly Arundhuti , Daniel Bruce L. , Scott Greig , Pauly John M. , Fahrig Rebecca , Pelc Norbert J. , Butts Kim
Published: May 2005

The range of RF coils that can be used in combined X‐ray/MR (XMR) systems is limited because many conventional coils contain highly X‐ray attenuating materials that are visible in the X‐ray images and potentially obscure patient anatomy. In this study, an X‐ray compatible coil design that has minimal X‐ray attenuation in the field of view (FOV) of the X‐ray image is presented. In this design, aluminum is used for the loop conductor and discrete elements of the coil are eliminated from the X‐ray FOV. A surface coil and an abdominal phased array coil were built using the X‐ray compatible design. X‐ray attenuation and MR imaging properties of the coils were evaluated and compared to conventional coils. The X‐ray compatible phased array coil was used to image patients during two interventional procedures in the XMR system. The X‐ray compatible coils allowed for fluoroscopic X‐ray image acquisition, without degradation by the coil, while maintaining excellent MR imaging qualities. Magn Reson Med 53:1409–1414, 2005. © 2005 Wiley‐Liss, Inc.
Fast oxygen‐enhanced multislice imaging of the lung using parallel acquisition techniques
Authors: Dietrich Olaf , Losert Christoph , Attenberger Ulrike , Fasol Ulrike , Peller Michael , Nikolaou Konstantin , Reiser Maximilian F. , Schoenberg Stefan O.
Published: May 2005

The purpose of this study was to evaluate an optimized multislice acquisition technique for oxygen‐enhanced MRI of the lung using slice‐selective inversion and refocusing pulses in combination with parallel imaging. An inversion recovery HASTE sequence was implemented with respiratory triggering to perform imaging in end‐expiration and with ECG triggering to avoid image acquisition during the systolic phase. Inversion pulses and the readout of echo trains could be interleaved to decrease acquisition time. The sequence was evaluated in 15 healthy volunteers, comparing three acquisition schemes: (1) acquisition of four slices without parallel imaging; (2) acquisition of four slices with parallel imaging; (3) acquisition of six slices with parallel imaging. These multislice acquisitions were repeated 80 times with alternating inhalation of room air and oxygen. The oxygen‐induced signal increase showed no significant difference with and without parallel imaging. However, only with parallel imaging did the interleaved acquisition of six or more slices become possible, thus enabling a more complete anatomic coverage of the lung. The average required end‐expiration time per repetition to acquire six slices could be significantly reduced from 4112 ms without to 2727 ms with parallel imaging. Total acquisition time varied between 8 and 13 min depending on the respiratory frequency. Magn Reson Med 53:1317–1325, 2005. © 2005 Wiley‐Liss, Inc.
Comparison of [3,4‐13C2]glucose to [6,6‐2H2]glucose as a tracer for glucose turnover by nuclear magnetic resonance
Authors: Jin Eunsook S. , Jones John G. , Burgess Shawn C. , Merritt Matthew E. , Dean Sherry A. , Malloy Craig R.
Published: May 2005

A recently introduced tracer, [3,4‐13C2]glucose, was compared to the widely used tracer, [6,6‐2H2]glucose, for measurement of whole‐body glucose turnover. The rate of glucose production (GP) was measured in rats after primed infusions of [3,4‐13C2]glucose, [6,6‐2H2]glucose, or both tracers simultaneously followed by a constant infusion of tracer(s) over 90 min. Blood glucose was purified and converted into monoacetone glucose for analysis by 13C NMR (for [3,4‐13C2]glucose) or 1H and 2H NMR (for [6,6‐2H2]glucose). The values of GP measured during infusion of each single tracer were not significantly different. In rats infused with both tracers simultaneously, GP was identical as reported by each tracer, 42 ± 4 μmol/kg/min. Since 2H and 13C enrichment in glucose is typically much less than 2% for in vivo studies, [3,4‐13C2]glucose does not interfere with measurements of 13C or 2H enrichment patterns and therefore is valuable when multiple metabolic pathways are being evaluated simultaneously. Magn Reson Med 53:1479–1483, 2005. © 2005 Wiley‐Liss, Inc.
Improving the reliability of obtaining tumor hemodynamic parameters in the presence of contrast agent extravasation
Authors: Quarles C. C. , Ward B. D. , Schmainda K. M.
Published: May 2005

A new approach to improve the reliability of dynamic susceptibility contrast MRI for the evaluation of brain tumor hemodynamics in the presence of contrast agent extravasation is described. This model‐based technique simultaneously estimates the voxel‐wise tumor residue function and the temporal extravascular T1 changes following contrast agent leakage. With these estimates the model corrects the measured MRI signal, which is then used to calculate tumor hemodynamic parameters. The feasibility of this technique is demonstrated with computer simulations that cover a wide range of hemodynamic conditions and by application to eight tumor‐bearing rats. The simulations demonstrate that the corrected hemodynamic parameters precisely matched the actual values with a maximum percentage error of 4.2% compared to 68.6% for the uncorrected parameters. The corrected parameters are also essentially independent of the tumor hemodynamic state and degree of contrast extravasation. Consistent with these improvements, significant differences between corrected and uncorrected parameters, calculated from a gradient‐echo sequence, are shown in a rat 9L gliosarcoma model. This method combined with the hemodynamic parameters derived from GE and SE sequences shows promise as a new tool to evaluate tumor angiogenesis and its therapy. Magn Reson Med 53:1307–1316, 2005. © 2005 Wiley‐Liss, Inc.
Quantitative magnetic resonance spectroscopy: Semi‐parametric modeling and determination of uncertainties
Authors: Elster Clemens , Schubert Florian , Link Alfred , Walzel Monika , Seifert Frank , Rinneberg Herbert
Published: May 2005

A semi‐parametric approach for the quantitative analysis of magnetic resonance (MR) spectra is proposed and an uncertainty analysis is given. Single resonances are described by parametric models or by parametrized in vitro spectra and the baseline is determined nonparametrically by regularization. By viewing baseline estimation in a reproducing kernel Hilbert space, an explicit parametric solution for the baseline is derived. A Bayesian point of view is adopted to derive uncertainties, and the many parameters associated with the baseline solution are treated as nuisance parameters. The derived uncertainties formally reduce to Cramér–Rao lower bounds for the parametric part of the model in the case of a vanishing baseline.

The proposed uncertainty calculation was applied to simulated and measured MR spectra and the results were compared to Cramér–Rao lower bounds derived after the nonparametrically estimated baselines were subtracted from the spectra. In particular, for high SNR and strong baseline contributions the proposed procedure yields a more appropriate characterization of the accuracy of parameter estimates than Cramér–Rao lower bounds, which tend to overestimate accuracy. Magn Reson Med 53:1288–1296, 2005. © 2005 Wiley‐Liss, Inc.
Correlation between insulin resistance and intramyocellular lipid levels in rats
Authors: Kuhlmann J. , Neumann‐Haefelin C. , Belz U. , Kramer W. , Juretschke H.‐P. , Herling A. W.
Published: May 2005

Increased intramyocellular lipid (IMCL) content has been proposed as biomarker for insulin resistance (IR). An inverse correlation between IMCL and insulin sensitivity (IS) was found in nonathletic humans, whereas in animal models only a few validation studies have been performed. The aim of this study was to investigate the interrelation between IS indices determined by the glucose clamp technique (glucose disposal (GD), exogenous glucose infusion rates (GIR)) and IMCL content in the tibialis (TIB) and the soleus (SOL) muscle obtained by magnetic resonance spectroscopy in different rat models of IR. Diet‐induced insulin‐resistant Wistar rats as well as genetic disease models (ZDF rats) were used. In both muscles, elevated IMCL correlated with an impaired IS in all models of IR. The correlation of IMCL with both parameters for IS was comparable in TIB and SOL. The best fit between IMCL and IS was obtained using TIB and GIR data (r = −0.69, P < 0.001). Diabetic male ZDF rats exhibited comparatively low IMCL levels due to their catabolic state: exclusion of this group improved r. In summary, IMCL, especially in TIB, is a valid biomarker for IS in various rat models of IR with the advantage of a fast repeatable noninvasive measurement in individual animals. Magn Reson Med 53:1275–1282, 2005. © 2005 Wiley‐Liss, Inc.
Cross‐subject comparison of principal diffusion direction maps
Authors: Schwartzman Armin , Dougherty Robert F. , Taylor Jonathan E.
Published: May 2005

Diffusion tensor imaging (DTI) data differ fundamentally from most brain imaging data in that values at each voxel are not scalars but 3 × 3 positive definite matrices also called diffusion tensors. Frequently, investigators simplify the data analysis by reducing the tensor to a scalar, such as fractional anisotropy (FA). New statistical methods are needed for analyzing vector and tensor valued imaging data. A statistical model is proposed for the principal eigenvector of the diffusion tensor based on the bipolar Watson distribution. Methods are presented for computing mean direction and dispersion of a sample of directions and for testing whether two samples of directions (e.g., same voxel across two groups of subjects) have the same mean. False discovery rate theory is used to identify voxels for which the two‐sample test is significant. These methods are illustrated in a DTI data set collected to study reading ability. It is shown that comparison of directions reveals differences in gross anatomic structure that are invisible to FA. Magn Reson Med 53:1423–1431, 2005. © 2005 Wiley‐Liss, Inc.
Noninvasive mapping of regional response to segmental allergen challenge using magnetic resonance imaging and [F‐18]fluorodeoxyglucose positron emission tomography
Authors: Holmes James H. , Sorkness Ronald L. , Meibom Sara K. , Sundaram Senthil K. , Perlman Scott B. , Converse Alexander K. , Pyzalski Robert W. , Hahn Andrew D. , Korosec Frank R. , Grist Thomas M. , Fain Sean B.
Published: May 2005

Magnetic resonance (MR) and positron emission tomography (PET) imaging techniques were coregistered to demonstrate regional ventilation and inflammation in the lung for in vivo, noninvasive evaluation of regional lung function associated with allergic inflammation. Four Brown Norway rats were imaged pre‐ and post segmental allergen challenge using respiratory‐gated He‐3 magnetic resonance imaging (MRI) to visualize ventilation, T1‐weighted proton MRI to depict inflammatory infiltrate, and [F‐18]fluorodeoxyglucose‐PET to detect regional glucose metabolism by inflammatory cells. Segmental allergen challenges were delivered and the pre‐ and postchallenge lung as well as the contralateral lung were compared. Coregistration of the imaging results demonstrated that regions of ventilation defects, inflammatory infiltrate, and increased glucose metabolism correlated well with the site of allergen challenge delivery and inflammatory cell recruitment, as confirmed by histology. This method demonstrates that fusion of functional and anatomic PET and MRI image data may be useful to elucidate the functional correlates of inflammatory processes in the lungs. Magn Reson Med 53:1243–1250, 2005. © 2005 Wiley‐Liss, Inc.
Focused, eight‐element transceive phased array coil for parallel magnetic resonance imaging of the chest—Theoretical considerations
Authors: Keong Li Bing , Liu Feng , Crozier Stuart
Published: May 2005

A new transceive system for chest imaging for MRI applications is presented. A focused, eight‐element transceive torso phased array coil is designed to investigate transmitting a focused radiofrequency field deep within the torso and to enhance signal homogeneity in the heart region. The system is used in conjunction with the SENSE reconstruction technique to enable focused parallel imaging. A hybrid finite‐difference‐time‐domain/method‐of‐moments method is used to accurately predict the radiofrequency behavior inside the human torso. The simulation results reported herein demonstrate the feasibility of the design concept, which shows that radiofrequency field focusing with SENSE reconstruction is theoretically achievable. Magn Reson Med 53:1251–1257, 2005. © 2005 Wiley‐Liss, Inc.
Functional magnetic resonance imaging with intermolecular double‐quantum coherences at 3 T
Authors: Schäfer Andreas , Jochimsen Thies H. , Möller Harald E.
Published: May 2005

Functional magnetic resonance imaging (fMRI) based on the selection of intermolecular double‐quantum coherences (iDQC) was performed with a standard birdcage coil at 3 T in a group of normal human volunteers. Suppression of spurious signal contributions from unwanted coherence‐transfer pathways was achieved by combining a two‐step phase cycle and a long repetition time of 5 s. A gradient‐recalled echo iDQC sequence (echo time, TE = 80 ms) yielded robust activation with a visual paradigm. Maximum z‐scores were about half of those observed with conventional blood‐oxygen level dependent fMRI, whereas the functional signal change increased by more than a factor of 5. No activation was obtained with a spin‐echo iDQC sequence (TE = 160 ms), in which dephasing accumulated during the evolution period was fully rephased by an appropriate delay time. It is hypothesized that substantial inherent diffusion weighting of the iDQC technique efficiently suppresses intravascular contributions to the functional contrast. A consistent quantitative explanation of the observed amount of signal change currently remains speculative. Magn Reson Med 53:1402–1408, 2005. © 2005 Wiley‐Liss, Inc.
Theoretical and experimental evaluation of broadband decoupling techniques for in vivo nuclear magnetic resonance spectroscopy
Authors: de Graaf Robin A.
Published: May 2005

A theoretical and experimental evaluation of existing broadband decoupling methods with respect to their utility for in vivo 1H‐13C NMR spectroscopy is presented. Simulations are based on a modified product operator formalism, while an experimental evaluation is performed on in vitro samples and human leg and rat brain in vivo. The performance of broadband decoupling methods was evaluated with respect to the required peak and average RF powers, decoupling bandwidth, decoupling side bands, heteronuclear scalar coupling constant, and sensitivity toward B2 inhomogeneity. In human applications only the WALTZ and MLEV decoupling methods provide adequate decoupling performance at RF power levels that satisfy the FDA guidelines on local tissue heating. For very low RF power levels (B2max < 300 Hz) one should verify empirically whether the experiment will benefit from broadband decoupling. At higher RF power levels acceptable for animal studies additional decoupling techniques become available and provide superior performance. Since the average RF power of adiabatic RF pulses is almost always significantly lower than the peak RF power, it can be stated that for average RF powers suitable for animal studies it is always possible to design an adiabatic decoupling scheme that outperforms all other schemes. B2 inhomogeneity degrades the decoupling performance of all methods, but the decoupling bandwidths for WALTZ‐16 and especially adiabatic methods are still satisfactory for useful in vivo decoupling with a surface coil. Magn Reson Med 53:1297–1306, 2005. © 2005 Wiley‐Liss, Inc.
Diffusional kurtosis imaging: The quantification of non‐gaussian water diffusion by means of magnetic resonance imaging
Authors: Jensen Jens H. , Helpern Joseph A. , Ramani Anita , Lu Hanzhang , Kaczynski Kyle
Published: May 2005

A magnetic resonance imaging method is presented for quantifying the degree to which water diffusion in biologic tissues is non‐Gaussian. Since tissue structure is responsible for the deviation of water diffusion from the Gaussian behavior typically observed in homogeneous solutions, this method provides a specific measure of tissue structure, such as cellular compartments and membranes. The method is an extension of conventional diffusion‐weighted imaging that requires the use of somewhat higher b values and a modified image postprocessing procedure. In addition to the diffusion coefficient, the method provides an estimate for the excess kurtosis of the diffusion displacement probability distribution, which is a dimensionless metric of the departure from a Gaussian form. From the study of six healthy adult subjects, the excess diffusional kurtosis is found to be significantly higher in white matter than in gray matter, reflecting the structural differences between these two types of cerebral tissues. Diffusional kurtosis imaging is related to q‐space imaging methods, but is less demanding in terms of imaging time, hardware requirements, and postprocessing effort. It may be useful for assessing tissue structure abnormalities associated with a variety of neuropathologies. Magn Reson Med 53:1432–1440, 2005. © 2005 Wiley‐Liss, Inc.
Quantification of glycine and taurine conjugated bile acids in human bile using 1H NMR spectroscopy
Authors: Ijare Omkar B. , Somashekar B. S. , Gowda G. A. Nagana , Sharma Ajay , Kapoor V. K. , Khetrapal C. L.
Published: May 2005

A simple method for quantification of conjugated bile acids in human bile using 1H NMR spectroscopy is presented. Bile acids in human bile are essentially conjugated with either glycine or taurine. The amide NH resonances from the conjugated bile acids are invariably devoid of interfering signals in 1H NMR spectra. Under physiologic conditions of human bile (pH ∼7.0 to 7.7), amide signal intensities are attenuated due to the chemical exchange and hence quantitative estimation is precluded. In the present study, the quantity of total glycine and taurine conjugated bile acids could be obtained accurately by suppressing the amide exchange by reducing the pH slightly lower than physiologic value (6.0 ± 0.5). Further, the quantity of glycine conjugated bile acids can be calculated accurately by subtracting the quantity of taurine conjugated bile acids from the total conjugated bile acids as determined from the present method. Magn Reson Med 53:1441–1446, 2005. © 2005 Wiley‐Liss, Inc.
Quantitative assessment of emphysema using hyperpolarized 3He magnetic resonance imaging
Authors: Spector Z. Z. , Emami K. , Fischer M. C. , Zhu J. , Ishii M. , Vahdat V. , Yu J. , Kadlecek S. , Driehuys B. , Lipson D. A. , Gefter W. , Shrager J. , Rizi R. R.
Published: May 2005

In this experiment, Sprague–Dawley rats with elastase‐induced emphysema were imaged using hyperpolarized 3He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash‐in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague–Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. With this information, we can use data on fractional ventilation to regionally distinguish between healthy and emphysematous portions of the lung. The successful implementation of such a technique on a rat model could lead to work toward the future implementation of this technique in human patients. Magn Reson Med 53:1341–1346, 2005. © 2005 Wiley‐Liss, Inc.
Enhanced viability imaging: Improved contrast in myocardial delayed enhancement using dual inversion time subtraction
Authors: Foo Thomas K. F. , Wolff Steven D. , Gupta Sandeep N. , Kraitchman Dara L.
Published: May 2005

In delayed contrast‐enhanced MRI for the assessment of myocardial viability, the TI time in a gated inversion‐recovery segmented gradient echo sequence is usually selected to null signal from normal myocardium. Although this TI time generates good contrast between the enhancing infarcted tissue and normal myocardium, there is usually less contrast between the infarct and the blood pool. A subtractive technique utilizing two acquisitions at a long and short TI time is proposed to improve the delineation between infarct‐blood and infarct‐myocardium. The concept was demonstrated in six mongrel dogs with reperfused myocardial infarction. Infarct‐normal myocardium contrast (signal difference) using the proposed enhanced viability imaging (ENVI) technique was 142 ± 50% (P < 0.001) that of standard magnitude inversion recovery (IR), while at the same TI time for the primary image, infarct‐blood contrast, was 247 ± 136% (P < 0.002) that of magnitude IR. Accounting for increased noise due to the subtraction, signal difference‐to‐noise ratios (SDNR) did not show a significant change for infarct‐myocardium but infarct‐blood SDNR for ENVI was 174 ± 105% that of magnitude‐IR (P < 0.03). Thus, marked improvement in the delineation of the infarcted zone was noted over a range of TI times. Magn Reson Med 53:1484–1489, 2005. © 2005 Wiley‐Liss, Inc.
Minimal feedback vertex sets in directed split‐stars
Authors: Wang Fu‐Hsing , Hsu Cheng‐Ju , Tsai Jen‐Chih
Published: May 2005

In a graph G = (V,E), a subset F ⊂ V(G) is a feedback vertex set of G if the subgraph induced by V(G)\F is acyclic. In this article, we propose an algorithm for finding minimal feedback vertex sets of directed split‐stars. Indeed, our algorithm can derive an upper bound on the size of the minimum feedback vertex set in directed split‐stars. Moreover, a simple distributed algorithm is presented for obtaining such sets. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 218–223 2005
Optimal broadcasting with universal lists based on competitive analysis*
Authors: Kim Jae‐Hoon , Chwa Kyung‐Yong
Published: May 2005

In this article we study a variant of broadcasting: each node has a predetermined ordered list of neighbors regardless of the node, called the source, from which the originating message is transmitted to all nodes in a network. Each node transmits a received message to its neighbors in order of the list. We propose a new measure of the efficiency of a Broadcasting scheme, which is obtained from competitive analysis, and we design new broadcasting schemes for lines, completek‐ary trees, grids, complete graphs, and hypercubes. In particular, we provide optimal broadcasting schemes for lines and grids. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 224–231 2005
Lowering eccentricity of a tree by node upgrading
Authors: Ibaraki Toshihide , Vaxès Yann , Yang Xiao‐guang
Published: May 2005

The eccentricity lowering problem is to reduce the eccentricity of a network by upgrading some nodes (that is, shrinking the lengths of the edges incident to such nodes). We consider two types of node‐upgrading strategies, that is, a continuous upgrading strategy and a discrete upgrading strategy, where the improvement under the first strategy is a continuous variable, and the improvement under the second strategy is a fixed amount. These problems are hard even to approximate, for general graphs. Therefore, we restrict our attention to graphs with simple structures. Assuming that the graph G = (V,E) is a tree, we show that the eccentricity lowering problem under the continuous node‐upgrading strategy can be reduced to the eccentricity lowering problem under the continuous edge‐upgrading strategy, and can be solved by an O(|V| log |V|) time algorithm. We also show that the problem for a tree is NP‐hard under the discrete upgrading strategy, but admits a fully polynomial approximation scheme, if the graph is a line. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 232–239 2005
Up‐regulation of gene expression by hypoxia is mediated predominantly by hypoxia‐inducible factor 1 (HIF‐1)
Authors: Greijer AE , van der Groep P , Kemming D , Shvarts A , Semenza GL , Meijer GA , van de Wiel MA , Belien JAM , van Diest PJ , van der Wall E
Published: May 2005

The hypoxia‐inducible factor 1 (HIF‐1) plays a critical role in cellular responses to hypoxia. The aim of the present study was to evaluate which genes are induced by hypoxia, and whether this induction is mediated by HIF‐1, by expression microarray analysis of wt and HIF‐1α null mouse fibroblasts. Forty‐five genes were up‐regulated by hypoxia and 40 (89%) of these were regulated by HIF‐1. Of the 114 genes down‐regulated by hypoxia, 19 (17%) were HIF‐1‐dependent. All glycolytic enzymes were strongly up‐regulated by hypoxia in a HIF‐1‐dependent manner. Genes already known to be related to hypoxia, such as glucose transporter 1, BNIP3, and hypoxia‐induced gene 1, were induced. In addition, multiple new HIF‐1‐regulated genes were identified, including genes involved in metabolism (adenylate kinase 4, galactokinase), apoptosis (galectin‐3 and gelsolin), and invasion (RhoA). Genes down‐regulated by hypoxia were involved in cytoskeleton maintenance (Rho kinase), mRNA processing (heterogeneous nuclear ribonucleoprotein H1 and splicing factor), and DNA repair (REV3). Furthermore, seven cDNAs from genes with unknown function or expressed sequence tags (ESTs) were up‐regulated and 27 such cDNAs were down‐regulated. In conclusion, hypoxia causes down‐ rather than up‐regulation of gene expression and HIF‐1 seems to play a major role in the regulation of hypoxia‐induced genes. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Effect of dissociation of iron–boron pairs in crystalline silicon on solar cell properties
Authors: Schmidt Jan
Published: May 2005

The effect of dissociation of interstitial iron‐substitutional boron (FeiBs) pairs, as it occurs under illumination in iron‐contaminated silicon solar cells, on the solar cell properties has been studied on the basis of numerical device simulations using reported recombination parameters for Fei and FeiBs. Most cell parameters are found to degrade during FeiBs dissociation. However, the open‐circuit voltage can also increase within certain ranges of the iron concentration. Critical iron concentrations are determined, giving the threshold contamination level above which a significant degradation in the corresponding cell parameter can be observed. The threshold iron contamination level of the open‐circuit voltage degradation is found to be up to two orders of magnitude larger than the threshold iron level of the short‐circuit current degradation. As the behaviour of the cell parameters under illumination is specific to the dissociation of FeiBs pairs, the characteristic changes in the cell parameters due to illumination may be used as a simple way of identifying iron contamination problems in silicon solar cells. Copyright © 2005 John Wiley & Sons, Ltd.