bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lanthanide‐based susceptibility contrast agents: Assessment of the magnetic properties
Authors: Fossheim Sigrid , Johansson Christer , Fahlvik Anne K. , Grace David , Klaveness Jo 
Published: March 2007

AbstractThe T2* contrast efficacy of paramagnetic contrast agents is dependent on their magnetic properties. Vibrating sample magnetometry (VSM) and the Live Chan NMR method have been used to evaluate the influence of ligand structure on the bulk magnetic susceptibility (BMS) of low‐molecular weight (LMW) lanthanide chelates. VSM was also used for the BMS assessment of LMW lanthanide chelates covalentiy attached to cross‐linked starch particles. The ligand structure had no influence on the BMS of the gadolinium (Gd) and dysprosium (Dy) chelates. The mean BMS value of the Dychelates was 1.8 fold higher than that of the Gd‐chelates. The holmium (Ho) OTPA‐BMA chelate had a similar BMS to that of Dy‐DTPA‐BMA while the lowest BMS was found for europium (Eu(lll)) DTPA‐BMA. The covatent attachment of Gd‐DTPA and Dy‐DTPA to a cross‐linked starch particle had no impact on their intrinsic magnetic properties. The BMS data were in good accordance with those obtained for non‐particulate bound LMW Dy‐ and Gd‐chelates. The magnetic susceptibility of the Gd‐OTPA labeled particles was described by the Curie law, indicative of no magnetic interactions between Gd‐DTPA molecules. The magnetic susceptibility of the Dy‐DTPA labeled particles followed the Curie‐Weiss law with a Curie‐Weiss temperature of about ‐2 K, indicating magnetic interactions. The magnetic susceptibility of Dy‐DTPA will, however, not be affected by such magnetic interactions at physiological temperatures.
Multiexponential T2 relaxation in degenerating peripheral nerve
Authors: Does Mark D. , Snyder Richard E. 
Published: March 2007

AbstractThe multiexponential T2 relaxation spectrum of peripheral nerve undergoing Wallerian degeneration has been measured both in vivo and in vitro. Degeneration of the sciatic nerve of the amphibian Xenopus laevis was induced by crush injury, and T2 relaxation spectra of the nerve were measured at several times up to 35 days following injury. Histologic evidence verified that the nerve underwent Wallerian degeneration. Relaxation spectra were observed to undergo measurable changes as degeneration progressed, the most evident being a reduction from three well‐resolved T2 components to one and a decline in the fraction of the spectra associated with the shortest T2 component The former appears to reflect the collapse and loss of myelinated fibers, while the latter a combination of interstitial edema and myelin loss.
Imaging of the active B1 field in vivo
Authors: Stollberger Rudolf , Wach Paul 
Published: March 2007

AbstractThe authors describe a method for accurate In vivo muttislice imaging of the active component of the B1 field which is based on a previously proposed method, which uses the signal intensity ratio of two images measured with different excitation angles, and a repetition time TR≥ 5 T1 The new method essentially reduces repetition and scan time by means of an additional compensating pulse. The suppression of T1 effects by this pulse are verified with simulations and measurements. Further investigations concerned the influence of slice selective excitation and magnetization transfer in multislice imaging to the B1 field determination. The stability and accuracy of the presented method is shown by several phantom and in vivo measurements. With the described method the active B1 field can be determined in vivo in 23 cross‐sections in less than 6 min.
An algorithm for eddy currents symmetrization and compensation
Authors: Zur Yuval , Stokar Saul 
Published: March 2007

AbstractEddy currents, which are induced in the magnet cryostat by pulsed magnetic field gradients in MRI, generate undesired eddy fields within the imaging volume. In this work, an automated and computerized algorithm to compensate these eddy currents is presented. The compensation is done in two steps: (i) Eddy fields are symmetrized electronically with an R‐C filter, (ii) The symmetric eddy fields are compensated by another R‐C filter. The compensation algorithm is iterative; therefore, errors that remain from one iteration are eliminated in the next iteration. Hence, the compensation process is very robust and accurate. It is shown that all the even harmonics of the eddy fields are eliminated by the symmetrization process, but the odd field harmonics remain. The amplitude of these odd harmonics can be significantly reduced if the gradient coils are designed so that the field they generate is spatially similar to the eddy fields.
Single‐shot, B1‐insensitive slice selection with a gradient‐modulated adiabatic pulse, BISS‐8
Authors: de Graaf Robin A. , Nicolay Klaas , Garwood Michael 
Published: March 2007

AbstractAn adiabatic pulse has been developed to accomplish uniform slice‐selective excitation with a spatially inhomogeneous B1. This new pulse can generate a uniform, arbitrary flip angle that is determined by four adjustable phase shifts in the pulse. Self‐refocused slice selection is achieved by modulating a Bo gradient in concert with the pulse frequency (or phase) modulation. B1‐compensated, self‐refocused slice selection is demonstrated in computer simulations and phantom experiments using a surface transmitter/receiver coil. This adiabatic pulse can provide optimal performance in multislice MRI and localized spectroscopy when transmitting with an inhomogeneous B1.
Abnormal cerebral metabolism in polydrug abusers during early withdrawal: A 31P MR spectroscopy study
Authors: Christensen James D. , Kaufman Marc J. , Levin Jonathan M. , Mendelson Jack H. , Holman B. Leonard , Cohen Bruce M. , Renshaw Perry F. 
Published: March 2007

AbstractPhosphorus magnetic resonance spectroscopy (31P MRS) at 1.5 T was performed on nine polysubstance abusing men. All nine patients met DSM‐III‐R criteria for concurrent cocaine and heroin dependence, were neurologically normal, were negative for the human immunodeficiency virus, and had normal clinical brain MRI scans. Patients were scanned 2‐7 days after admission to a drug treatment unit. Eleven age‐matched control subjects also were studied. The ISIS localized phosphorus spectra were obtained from a 5‐cm thick axial brain slice and a 100‐cc white matter volume. In the brain slice, the phosphorus metabolite signal expressed as a percentage of total phosphorus signal was 15% higher for phosphomonoesters, 10% lower for nucleotide triphosphates (β‐NTP), and 7% lower for total nucleotide phosphates in polydrug abusers compared with those in controls. Phosphodiesters, inorganic phosphate, phosphocreatine, total phosphorus, pH, and free magnesium concentration were unchanged. None of these parameters correlated with the methadone dose or the number of days abstinence. Single photon emission computed tomographic imaging of a subgroup of the patients revealed abnormal cerebral perfusion in 80% of the patients scanned. These data suggest that cerebral high energy phosphate and phospholipid metabolite changes result from long term drug abuse and/or withdrawal and that these changes can be detected and studied by 31P MRS.
Removal of lipid artifacts in 1H spectroscopic imaging by data extrapolation
Authors: Haupt Christine I. , Schuff Norbert , Weiner Michael W. , Maudsley Andrew A. 
Published: March 2007

AbstractProton MR spectroscopic imaging (MRSI) of human cerebral cortex is complicated by the presence of an intense signal from subcutaneous lipids, which, if not suppressed before Fourier reconstruction, causes ringing and signal contamination throughout the metabolite images as a result of limited k‐space sampling. In this article, an improved reconstruction of the lipid region is obtained using the Papoulis‐Gerchberg algorithm. This procedure makes use of the narrow‐band‐limited nature of the subcutaneous lipid signal to extrapolate to higher k‐space values without alteration of the metabolite signal region. Using computer simulations and in vivo experimental studies, the implementation and performance of this algorithm were examined. This method was found to permit MRSI brain spectra to be obtained without applying any lipid suppression during data acquisition, at echo times of 50 ms and longer. When applied together with optimized acquisition methods, this provides an effective procedure for imaging metabolite distributions in cerebral cortical surface regions.
Improved MR images of arterial specimens by submersion in trichlorotrifluoroethane
Authors: Chu Kenneth C. , Martin Alastair J. , Rutt Brian K. 
Published: March 2007

AbstractMR Images of ex vivo arterial specimens immersed in 1,1,2‐trichloro‐1,2,2‐trifluoroethane (R‐113) have improved signal‐to‐noise ratio and contrast‐to‐noise ratio. R‐113 has no hydrogen atoms, so it yields no proton signal; hence, the contrast between the specimen and its background is maximized. SNR is maximized because (i) R‐113 is nonconductive so that coil loading and inductive noise are minimized, and (ii) the volume susceptibility of R‐113 closely matches that of water and tissue so that T2* effects are minimized. Short‐term submersion of porcine aortas in R‐113 was found to have no significant effect on the artery's hydration level, relaxation time, tensile strength, and structure or quantity of elastin, collagen, or smooth muscle cells.
NMR studies on human, pathologically changed synovial fluids: Role of hypochlorous acid
Authors: Schiller Jürgen , Arnhold Jürgen , Sonntag Kerstin , Arnold Klaus 
Published: March 2007

AbstractRecently, it has been reported that hypochlorous acid (HOCl), a special product of neutrophil myeloperoxidase, degrades N‐acetyl groups of N‐acetylglucosamine, chondroitin sulfate, hyaluronic acid, and minced articular cartilage via a transient product to acetate. This work concerns 1H NMR investigations of synovia! fluids of patients with rheumatoid arthritis (RA). Synovial fluids of patients with severe forms of this disease are characterized by enhanced 1H NMR signals for N‐acetyl groups (˜2.0 ppm) and acetate (1.90 ppm) and the appearance of a broad but less intense signal at 2.35 ppm. It is likely that this signal corresponds to the transient, chlorinated product of degradation of N‐acetyl groups by hypochlorous acid. Moreover, 1H NMR signal intensities of N‐acetyl groups and acetate strongly correlate with the myeloperoxidase activities in synovial fluids from patients with rheumatoid arthritis. These results have been confirmed by treatment of native sheep synovial fluid with sodium hypochlorite, resulting in the formation of the same resonances as observed in pathologically changed synovial fluids from humans. Thus, it is concluded that HOCI plays an important role for the cartilage degradation during rheumatoid arthritis.
Multislice interleaved excitation cycles (MUSIC): An efficient gradient‐echo technique for functional MRI
Authors: Loenneker Thomas , Hennel Franciszek , Hennig Jürgen 
Published: March 2007

AbstractA method providing improved slice efficiency for gradient‐echo imaging requiring long echo times, such as in functional neuromagnetic resonance imaging, is presented. To enhance the volume coverage while maintaining the short imaging time of a conventional single‐slice gradient‐echo technique, an interleaved muttislice excitation is performed during the echo time. This technique allows detection of susceptibility changes, e.g., the acquisition of stimulated human cortical activation maps, on clinical MR instruments at multiple planes within total imaging times of a few seconds. The efficiency of the technique is demonstrated in the detection of temporary changes in T2* in functional MRI experiments of the human visual cortex at magnetic field strengths of 2 Tesla and 3 Tesla. Fourteen 128 × 128 slices can be acquired in 13 s to cover a large volume‐of‐interest in the same time that would be required for single‐slice acquisition using the conventional technique.
Improvement of measurement precision in absorption spectra by apodization
Authors: Wang Zhiyue 
Published: March 2007

AbstractIn in vivo MR spectroscopy studies, it is desirable to determine metabolite peak parameters with good precision and to estimate the uncertainties. How to achieve optimal precision for an apodized MR spectrum by using a weighted least squares estimator is discussed and demonstrated. Analytic methods for calculating the uncertainties of all parameters obtained from least squares estimators are described. The time domain apodization before Fourier transformation can substantially decrease the minimum variance bound in parameters obtained from the frequency domain absorption spectrum. A weighted least squares estimation is needed to reach the Cramer‐Rao lower bound. When an unweighted least squares estimation is performed, the time domain apodization also leads to improvement in precision.
Decay characteristics of bone marrow in the presence of a trabecular bone network: In vitro and in vivo studies showing a departure from monoexponential behavior
Authors: Newitt David C. , Majumdar Sharmila , Jergas Michael D. , Genant Harry K. 
Published: March 2007

AbstractIn this study, we examine MRI T2′ decay characteristics for bone marrow in trabecular bone networks, using an asymmetric spin‐echo sequence to isolate the inhomogeneous decay due to susceptibility variations between bone and marrow or water. In in vitro measurements on trabecular bone specimens from human vertebral bodies, tibia, and radii, we find significant deviations from a monoexponential signal decay. The initial decay is seen to have a Gaussian decay character, switching to a primarily exponential decay at later decay times. A similar trend is observed in in vivo measurements in the distal radius. Unlike an exponential decay, which may be characterized by a single decay rate, this is indicative of a significant variation in the decay rate with time. The deviations from exponential decay are seen to be orientation dependent, being most significant when the primary trabecular orientation is perpendicular to the static magnetic field.
Observation of resolved glucose signals in 1H NMR spectra of the human brain at 4 Tesla
Authors: Gruetter Rolf , Garwood Michael , Uǧurbil Kǎmil , Seaquist Elizabeth R. 
Published: March 2007

AbstractMeasurement of the resonances of glucose between 3.2 and 3.9 ppm in 1H NMR spectra from the human brain is difficult due to spectral overlap with peaks from more concentrated metabolites. The H1 resonance of α‐D‐glucose at 5.23 ppm is resolved from other metabolite peaks, but potentially overlaps with the intense water signal at 4.72 ppm. This paper demonstrates that the increased resolution at 4 Tesla permits to suppress the water signal sufficiently to reliably detect glucose directly at 5.23 ppm by 1H MRS and the estimated peak intensity is consistent with previous 13C NMR quantification.
Quantitative 1H spectroscopic imaging of human brain at 4.1 T using image segmentation
Authors: Hetherington Hoby P. , Pan Jullie W. , Mason Graeme F. , Adams Dorothy , Vaughn Michael J. , Twieg Donald B. , Pohost Gerald M. 
Published: March 2007

AbstractMetabolic differences in the content of N‐acetylaspartate (NAA), creatine (CR), and choline (CH) in cerebral gray and white matter can complicate the interpretation of 1H spectroscopic images. To account for these variations, the gray‐and white‐matter content of each voxel must be known. To provide these data, a T1‐based image segmentation scheme was implemented at 4.1 T. The tissue composition of each voxel was determined using the point‐spread function of the spectroscopic imaging acquisition and the segmented anatomical image. Pure gray‐ and white‐matter values for CR/NAA and CH/NAA, and the content of CR, CH, and NAA, were determined using a linear‐regression analysis of 984 voxels acquired from 10 subjects using white‐matter CR as an internal standard. This information was used to establish means and confidence intervals for CR/NAA and CH/NAA from a voxel of arbitrary tissue composition. Using a single‐tailed t test, the extent and locations of the metabolic abnormalities (P < 0.05) in a patient with multiple sclerosis were identified.
Dynamic changes in water ADC, energy metabolism, extracellular space volume, and tortuosity in neonatal rat brain during global ischemia
Authors: van der Toorn Annette , Syková Eva , Dijkhuizen Rick M. , Vořišek Ivan , Vargová Lydia , Škobisová Evan , van Lookeren Campagne Menno , Reese Torsten , Nicolay Klaas 
Published: March 2007

AbstractTo obtain a better understanding of the mechanisms underlying early changes in the brain water apparent diffusion coefficient (ADC) observed in cerebral ischemia, dynamic changes in the ADC of water and in the energy status were measured at postnatal day 8 or 9 in neonatal rat brains after cardiac arrest using 1H MRS/MRI and 31P MRS, respectively. The time courses of the MR parameters were compared with changes in the extracellular space (ECS) volume fraction (α) and tortuosity (λ), determined from concentration‐time profiles of tetramethylammonium applied by iontophoresis. The data show a decrease of the ADC of tissue water after induction of global ischemia of which the time course strongly correlates with the time course of the decrease in the ECS volume fraction and the increase in ECS tortuosity. This indicates that cell swelling is an important cause for the ADC decrease of water.
A 31P NMR study of preconditioned isolated perfused rat heart exposed to intermittent ischemia
Authors: Sharoni Ram , Olivson Abira , Chandra Mukul , Merin Gideon , Uretzky Gideon , Borman Joseph B. , Chisin Roland , Schwalb Herzl , Berman Elisha 
Published: March 2007

AbstractExposure to a short ischemic period (ischemic preconditioning, IP) will protect the heart from damage following a subsequent longer ischemic episode. The aim of the study was to test whether IP is cardioprotective in the setting of repeated ischemia‐reperfusion cycles. Thus, Langendorff‐perfused hearts, exposed to IP, were subjected to three consecutive ischemia‐reperfusion (10/15 min) cycles. Myocardial energetics, manifested by 31P NMR spectroscopy, was correlated with hemodynamics. ATP recovery was significantly higher for the IP group compared with control (P < 0.02) during reperfusions. However, there was no significant difference in ATP recovery during the three ischemic intervals. The supernormal recovery of phosphocreatine recorded during reperfusion was lower for the IP group (∼120%) compared with control (∼135%, P < 0.065). Better recovery of the left ventriculardeveloped pressure was noted during reperfusions for the IP group and became significant only during the last reperfusion (86% versus 68%, P < 0.025). In conclusion, the above results support prolonged IP cardioprotection.
Estimation of brain iron in vivo by means of the interecho time dependence of image contrast
Authors: Ye Frank Q. , Martin W. R. Wayne , Allen Peter S. 
Published: March 2007

AbstractAn imaging protocol for a quantitative estimation of disease‐induced variations in brain iron is proposed and then validated, first, on a phantom and second, on a group of 11 healthy volunteers. The relative estimate of brain iron is achieved from a rate difference image that measures the enhancement, δR2app, of the transverse relaxation rate of water protons brought about by the heterogeneous accumulation of iron in the glial cells. At 1.5 T, the phantom study demonstrates, over the range 0‐6 A/m, a linear dependence of δR2app on the magnetization difference between micro‐spheres and a paramagnetic gel, with a sensitivity of ∼2 s−1 A−1 m. In the group of healthy volunteers (mean age 33 ± 7 years) devoid of disease‐related or appreciable age‐related accumulations of iron, the precision of δR2app was still sufficient to distinguish the globus pallidus and the putamen from all of the other iron‐containing brain structures in a manner that was significant at the 99% confidence level.
Artifact reduction in EPI with phase‐encoded reference scan
Authors: Hu Xiaoping , Le Tuong Huu 
Published: March 2007

AbstractEcho‐planar imaging is becoming widely used for various applications. However, because of inherent limitations, images obtained with EPI are often degraded by artifacts arising from the inconsistency between the odd and even echoes in the acquired data. Several correction techniques, including those based on reference measurement, have been previously reported. In this paper, a correction method based on phase‐encoded reference measurement is described. This technique is demonstrated with experimental data obtained at 4 Tesla and compared with techniques that use nonphase‐encoded reference scan. Results from experimental studies indicate that the present approach reduces the ghost intensity by a factor of 2‐3.
Some new observations on pulse sequence dependent diffusion related edge enhancement in MR microscopy
Authors: Cho Zang‐Hee , Hong In‐Ki , Ro Yong‐Man 
Published: March 2007

AbstractSelf‐diffusion of nuclear spins has been suggested to cause edge enhancement in images especially on a microscopic scale. According to previously published work, theory suggests that edge enhancement is caused by motional narrowing due to the boundaries and spin self‐diffusion during the data acquisition period. More careful examination reveals that edge enhancement due to motional narrowing develops only under a few specific conditions. This lack of generality of motional narrowing theory, as well as experimental observations, indicate that edge enhancement due to effects other than motional narrowing alone can exist. It is found that edge enhancement depends greatly on the data acquisition mode; therefore, the images obtained are different depending on the pulse sequence employed. For example, excessive attenuation of DC components due to diffusion can result in edge enhancement in the spin echo signal. However, in the case of FID‐like signals, DC components are preserved while positive high frequency parts are attenuated, thereby degrading resolution. The new phenomenon observed has been termed selective spectral suppression since the observed edge enhancement results from the selective attenuation of certain frequency components in the nuclear signals due to diffusion‐dependent signal attenuation for a given pulse sequence.
Measurement of spin‐lattice relaxation times and kinetic rate constants in rat muscle using progressive partial saturation and steady‐state saturation transfer
Authors: Horská Alena , Spencer Richard G. S. 
Published: March 2007

Abstract31P spin‐lattice relaxation times (T1) of metabolites in rat calf muscle at 1.9 Tesla and the forward rate through the creatine kinase (CK) reaction have been measured using a new method based on modeling progressive saturation explicitly incorporating the effect of chemical exchange. In a separate series of experiments, we compared our method with inversion recovery both in vitro and in vivo, finding agreement between the techniques. We found that the T1 values of phosphocreatine (PCr) (6.6 ± 0.3 s), γ‐ATP (2.6 ± 0.6 s), α‐ATP (2.4 ± 0.4 s) and β‐ATP (2.2 ± 0.2 s) are unchanged by stimulation of sufficient intensity to induce a 32% drop in PCr level. The errors in T1 values which arise when chemical exchange is neglected are calculated. These are found to be on the order of 20% for PCr and 30–50% for γ‐ATP under typical conditions. Use of longer repetition times results in larger errors in measured values of T1. This source of error can be effectively eliminated by use of sufficiently short repetition times. We found that the rate constant of the forward CK reaction was increased 60% by stimulation, from 0.20 ± 0.03 s−1 to 0.32 ± 0.03 s−1, but that the phosphorus flux did not change.