bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of severe global ischemia on N‐acetylaspartate and other metabolites in the rat brain
Authors: Higuchi Toshihiro , Graham Steven H. , Fernandez Erik J. , Rooney William D. , Gaspary Heidi L. , Weiner Michael W. , Maudsley Andrew A. 
Published: March 2007

AbstractN‐acetylaspartate (NAA) is found exclusively in neurons and their processes in the adult brain. Since the regional distribution of NAA may be imaged using magnetic resonance spectroscopic imaging (1H‐MRSI), a regional measure of neuronal density may be noninvasively obtained. The technique may be particularly useful in the diagnosis of diseases where neurons are selectively injured, since these diseases do not result in definitive changes on conventional imaging studies. The goal of this study was to determine whether 1H‐MRSI measurement of NAA detects neuronal loss following global ischemia. 1H‐MRSI was performed in rats 24 h after global ischemia was induced by bilateral carotid occlusion plus hypotension. 1H‐MRSI showed that NAA was decreased by 29–74% in vulnerable regions, including the cortex, striatum, hippocampus, and, to a lesser extent, the thalamus. No change was observed in the brain stem or cerebellum. Regions where 1H‐MRSI observed NAA was decreased also had histological evidence of selective neuronal necrosis and showed marked increase of lactate and alanine. These results show that 1H‐MRSI detected loss of NAA in brain regions with selective neuronal loss, suggesting that 1H‐MRSI measurements of NAA could detect neuronal loss in a variety of disease states where there is selective neuronal necrosis.
Improved vessel visualization in MR angiography by nonlinear anisotropic filtering
Authors: Orkisz Maciej M. , Bresson Christine , Magnin Isabelle E. , Champin Olivier , Douek Philippe C. 
Published: March 2007

AbstractThis paper deals with a preprocessing technique of magnetic resonance angiography (MRA) images, applied before maximum‐intensity‐projection (MIP). The purpose was to recover small low‐intensity vessels, visible in individual slices, but lost in MIP images that usually have higher background level than the individual slices. The authors have developed a nonlinear three‐dimensional spatial filtering technique (called HD filter) based on anisotropic smoothing. The filter first searches for the local orientation of the vessel. It then performs a nonlinear smoothing in the vessel's local direction so as to avoid blurring its boundaries. Noise level reduction, contrast enhancement, and improved small vessel visibility achieved by this filter are illustrated on dynamic contrast‐enhanced subtraction MRA images of the lower limbs.
Reduction of geometric and intensity distortions in echo‐planar imaging using a multireference scan
Authors: Wan Xin , Gullberg Grant T. , Parker Dennis L. , Zeng Gengsheng L. 
Published: March 2007

AbstractEcho‐planar imaging (EPI) is very sensitive to patient‐induced field inhomogeneity caused by susceptibility changes between different anatomical regions. This results in geometric and intensity distortions in the image, especially near tissue/ air and tissue/bone interfaces. A new approach is presented to reduce geometric and intensity distortions in EPI. A phaseencoded multireference scan is used to estimate the amplitude and phase errors in the measured signals due to the field inhomogeneity. The EPI data is corrected using both the amplitude and phase of the measured errors. This technique has been evaluated using EPI pulse sequences implemented with conventional gradients and implemented with imaging systems that have special resonating gradients and fast analog to digital converters. The results in both phantom and human studies show that in the absence of object motion the new correction technique can effectively reduce the geometric and intensity distortions.
Catheter tracking using continuous radial MRI
Authors: Rasche Volker , Holz Dietrich , Köhler Jürgen , Proksa Roland , Röschmann Peter 
Published: March 2007

AbstractThe guidance of minimally invasive procedures may become a very important future application of MRI. The guidance of interventions requires images of the anatomy as well as the information of the position of invasive devices used. This paper introduces continuous radial MRI for the simultaneous acquisition of the anatomic MR image and the position of one or more small RF‐coils (μ‐coils), which can be mounted on invasice devices such as catheters or biopsy needles. This approach allows the in‐plane tracking of an invasive device without any prolongation of the overall acquisition time. The extension to three‐dimensional position tracking is described. Phantom studies are presented demonstrating the capability of this technique for real‐time automatic adjustment of the slice position to the current catheter position with a temporal resolution of 100 ms. Simultaneously the in‐plane catheter position is depicted in the actually acquired MR image during continuous scanning.
Integrated RF coil with stabilization for fMRI human cortex
Authors: Fitzsimmons Jeffrey R. , Scott James D. , Peterson David M. , Wolverton Bryan L. , Webster Charles S. , Lang Peter J. 
Published: March 2007

AbstractFunctional brain imaging of the human cortex is limited by poor contrast to noise ratio (CNR) and image degradation due to subject motion during the acquisition period. The work described here combines the use of closely coupled phased array receiver coils with a stabilization system to address these needs. Several phased array designs are evaluated and compared with the conventional “birdcage” design. Coil performance is reported in terms of relative SNR and fMRI results. Relative improvements of up to 360% are obtained for the occipital region and 180% in the temporal region. More modest gains of 10–30% were obtained for a “dome”‐shaped birdcage volume coil covering the entire cortex.
MRI and NMR spectroscopy of the lipids of atherosclerotic plaque in rabbits and humans
Authors: Trouard Theodore P. , Altbach Maria I. , Hunter Glenn C. , Eskelson Cleamond D. , Gmitro Arthur F. 
Published: March 2007

AbstractThe early stages of atherosclerosis are characterized by the deposition of cholesteryl esters and triglycerides into the arterial wall. In the excised human atherosclerotic plaque these lipids are in a liquid‐like state at body temperature and observable via MRI and NMR spectroscopy. To assess the ability of MRI to quantitatively image the lipids of atherosclerotic plaque in vivo, we have investigated eight New Zealand White rabbits fed atherogenic diets (2 weight (wt)% cholesterol, 1 wt% cholesterol + 6 wt% peanut oil, and 1 wt% cholesterol + 6 wt% corn oil). Postmortem examination indicated that all rabbits developed atherosclerosis in the aorta. Except for one animal, magnetic resonance angiography showed no noticeable obstruction in the aorta. MRI was carried out in an attempt to image atherosclerotic plaque lipids directly, but no signal was detected in vivo. However, a plaque lipid signal was observed from excised tissue using a small diameter RF coil. 1H NMR spectroscopy of the atherosclerotic plaque from excised aortas indicated that the major fraction of plaque lipids in rabbits is not in a liquid state at physiological temperature and are only marginally MRI‐visible compared to human plaque lipid. The differences in the MRI characteristics of rabbit and human plaque are due to differences in the fatty acid profile of the cholesteryl esters, chiefly a decrease of linoleic acid in rabbit lesions.
Acceleration mapping by fourier acceleration‐encoding: in vitro study and initial results in the great thoracic vessels
Authors: Tasu Jean‐Pierre , Jolivet Odile , Mousseaux Elie , Delouche Annie , Diebold BenoǐT , Bittoun Jacques 
Published: March 2007

AbstractAcceleration mapping can be conducted by replacing the bipolar gradient pulse of a velocity mapping sequence by a tripolar pulse. However, since the acceleration encoding pulse is longer, the image quality is altered by the requirement of a long echo time. Since Fourier encoding velocity imaging has been shown to be robust, this velocity mapping method was transformed into an acceleration mapping method. Four steps of the tripolar acceleration encoding gradient pulse were applied successively; acceleration was then obtained by Fourier transform after zero‐filling. The accuracy of the method was assessed with a phantom giving a pulsatile flow. Acceleration maps of the ascending aorta and pulmonary artery were obtained in 10 healthy volunteers. The acceleration values measured were in the range of known physiologic values. The feasibility of Fourier encoding acceleration imaging was also demonstrated in four patients.
Catheter visualization using locally induced, actively controlled field inhomogeneities
Authors: Glowinski Arndt , Adam Gerhard , Bücker Arno , Neuerburg Jörg , van Vaals Joop J. , Günther Rolf W. 
Published: March 2007

AbstractA new technique for visualization of interventional devices using MR is presented. A prototype catheter was equipped with a thin copper wire loop, leading from the proximal end to the tip and back. A small current (10‐150 mA) through these two parts of a wire induces a local magnetic field along the catheter. Introduction of this catheter into the main magnetic field of the MR imager locally disturbs the homogeneity of the magnetic field. Image locations within the locally induced fields appear dark due to signal loss, and the extent of this effect can be varied during the procedure by simply adjusting the current. Different dedicated wire configurations allow visualization of the catheter in its whole length or in parts, i.e., with markers for balloons. Fast gradient echo sequences that provide a bright signal from inflowing blood are used for rapid imaging.
Triple quantum sodium imaging of articular cartilage
Authors: Reddy Ravinder , Insko Erik K. , Leigh John S. 
Published: March 2007

AbstractTriple quantum (TQ) sodium imaging of bovine articular cartilage is presented. True triple quantum imaging sequence was modified to incorporate asymmetric echo acquisition. Triple quantum signal expression in the presence of residual quadrupolar interaction is presented. The filtering capability of the sequence is first demonstrated on an agarose phantom. Both single and triple quantum images of articular cartilage are compared. The TQ image shows non‐zero signal intensity solely from cartilage, indicating complete suppression of signals from bone marrow and saline. The advantages of TQ imaging of articular cartilage, its feasibility in in vivo situations and further improvements in SNR are described.
Reduction of carcinogenic chromium(vi) on the skin of living rats
Authors: Liu Ke Jian , Mäder Karsten , Shi Xianglin , Swartz Harold M. 
Published: March 2007

AbstractThe reduction of chromate (Cr(VI)) on the skin of living rats was investigated using the technique of in vivo electron paramagnetic resonance (EPR) spectroscopy with a surface coil resonator. Topical application of aqueous solution of Cr(VI) on the skin of rats generated the transient species, Cr(V). Partial removal of the stratum corneum increased the rates of formation and decay of Cr(V), as well as Cr(V) signal intensity. The results demonstrate that skin represents one route for chromium to enter into animals and humans. The generation of reactive Cr(V) species in the reduction of Cr(VI) by the skin may play an important role in the mechanism of Cr(VI)‐induced skin cancer. These findings indicate the potential for in vivo EPR spectroscopy for studying the metabolism of paramagnetic reactive species in chemical and biochemical reactions occurring in/on the skin of both small and large animals, and possibly humans.
A multinuclear MR study of Gd‐EOB‐DTPA: Comprehensive preclinical characterization of an organ specific MRI contrast agent
Authors: Elst Luce Vander , Maton Frédéric , Laurent Sophie , Seghi Frédéric , Chapelle Florence , Muller Robert N. 
Published: March 2007

AbstractThe characterization of the hepatobiliary contrast agent Gd‐EOB‐DTPA (gadolinium 3, 6, 9‐triaza‐3, 6, 9‐tris(carboxymethyl)‐4‐(4‐ethoxybenzyl)‐undecandicarboxylic acid) in various media (water solution, protein containing solution, phosphorylated metabolites solution, and excised and perfused liver) was performed using different NMR approaches: water 1H nuclear magnetic relaxation dispersion profiles, 2H NMR longitudinal and transverse relaxation rates of labeled complex, water 17O transverse relaxation rates and chemical shifts, 31P relaxation rates and peak area of phosphorylated metabolites. The higher proton relaxivity of Gd‐EOB‐DTPA in water compared with Gd‐DTPA is related to a shorter distance (r) between the water proton and the gadolinium ion and to a longer rotational correlation time (TR) of the hydrated complex. Although the thermodynamic stability of Gd‐EOB‐DTPA is identical to the one of Gd‐DTPA, its kinetic stability in solutions containing phosphorylated metabolites (ATP, phosphocreatine, and inorganic phosphate) as measured by 31P relaxation rates analysis is higher than for the parent compound. Gd‐EOB‐DTPA binds noncovalently to serum proteins. Its interaction with human serum albumin is characterized by a dissociation constant of 1‐4.1 mM as calculated from proton and deuterium relaxation rates and equilibrium dialysis. This noncovalent interaction involves the subdomain IIA of human serum albumin. 31P spectroscopy of the excised and perfused rat livers was used to monitor the uptake of Gd‐EOB‐DTPA by the hepatocytes where it enhances the nuclear relaxation of the intracellular metabolites without impairing the adenosine triphosphate metabolism of the cells.
Improved activation maps via the elimination of motion effects through time‐domain mixing of data in conventional gradient echo functional MRI
Authors: Constable R. Todd 
Published: March 2007

AbstractTo date, most functional imaging centers have relied on ultra‐fast imaging approaches such as echo‐planar imaging (EPI) techniques for acquiring functional brain activation data. These methods require specialized hardware and are not yet installed widely on clinical MR imagers, thus limiting the application of functional MR imaging at many sites. EPI is used to limit motion artifacts and to collect multiple images under different task paradigms in order to distinguish reliably true signal changes from noise. However, it suffers from poor signal to noise ratio because of the high sampling bandwidth employed. This work presents an approach for increasing the efficiency of functional studies that use conventional gradient echo imaging. In this approach, small numbers of image data sets are acquired and recombined to generate composite datasets with minimized motion artifacts. The technique is introduced, and several algorithms for combining the data are explored. A receiver operator characteristic analysis and in vivo studies are performed to examine the efficacy of this approach for improving functional MR imaging studies.
High relaxivity linear Gd(DTPA)‐polymer conjugates: The role of hydrophobic interactions
Authors: Kellar Kenneth E. , Henrichs P. Mark , Hollister Robert , Koenig Seymour H. , Eck Jennifer , Wei Donna 
Published: March 2007

AbstractA series of linear copolymers of DTPA‐class Gd3+ conjugates, linked by α,ω‐alkyldiamides with a varying number (n) of methylenes separating the amide function, were synthesized. Surprisingly, their relaxivities at all fields increased with increasing n. At MRI fields and 35°C, the relaxivities of the n = 10 and n = 12 polymers were unexpectedly high, similar to those of rigid dendrimer‐based Gd3+ chelates. The magnetic field dependence of solvent proton 1/T1 was measured for aqueous urea‐free and urea‐containing polymer solutions. The results for urea‐free solutions imply an increase of rigidity (required for high relaxivities) with increasing n, arising from hydrophobic interactions of the methylene groups with solvent. This hypothesis is supported by a large decrease in the relaxivities upon addition of urea, which is known to weaken hydrophobic interactions. The relaxivities are also independent of polymer concentration, indicating that the hydrophobic interactions are intramolecular.
MR microimaging of the lung using volume projection encoding
Authors: Shattuck Mark D. , Gewalt Sally L. , Glover Gary H. , Hedlund Laurence W. , Johnson G. Allan 
Published: March 2007

AbstractRadial acquisition (RA) techniques have been extended to produce isotropic, three‐dimensional images of lung in live laboratory animals at spatial resolution down to 0.013 mm3 with a signal‐to‐noise ratio of 30:1. The pulse sequence and reconstruction algorithm have been adapted to allow acquisition of image matrices of up to 2563 in less than 15 min. Scan‐synchronous ventilation has been incorporated to limit breathing motion artifacts. The imaging sequence permits randomizing and/or discarding selected views to minimize the consequences of breathing motion. The signal in lung parenchyma was measured as a function of flip angle (α) for different repetition times and found to follow the predictions for which there is an optimum excitation (Ernst) angle. A single T1, relaxation value of 780 ± 54 ms fits all data from six guinea pigs at 2.0 T. This T1, value parameterizes the signal and allows for a priori optimization, such as calculation of the Ernst angle appropriate for lung imaging.
Phase alignment of multiple surface coil data for reduced bandwidth and reconstruction requirements
Authors: Debbins Josef P. , Felmlee Joel P. , Riederer Stephen J. 
Published: March 2007

AbstractMultiple element surface coils are often used in clinical MRI to increase the image signal‐to‐noise ratio (S/N). Use of multicoils typically requires increased net sampling bandwidth and data processing for each coil element. A phase‐alignment technique is described which combines the signals from all coil elements before image reconstruction, greatly relaxing the technical requirements of the standard multicoil methods. Hardware and software implementations allow reduction of the reconstruction requirement to that of a single coil. The hardware implementation additionally allows a significant reduction in the net sampling bandwidth. The method is applicable to high speed MRI techniques, as demonstrated in phantoms and volunteers.
MR microscopy of lung airways with hyperpolarized 3He
Authors: Chen X. Josette , Chawla Mark S. , Hedlund Laurence W. , Möller Harald E. , Macfall James R. , Johnson G. Allan , G. Elaine 
Published: March 2007

AbstractA technique using hyperpolarized (HP) 3He to image the small airways of the lung by using moderate flip angles and a short scanning period during early inspiration is demonstrated. Flip angles (α) ranging from 10–90° were used in guinea pig experiments with scanning during the entire inspiration period. A second series acquired data throughout a short window of the ventilatory cycle with α= 45°. The success of the animal studies has motivated implementation of similar imaging techniques in the clinical arena. Human studies involved imaging over the total inspiration period with α ≈︁ 10°. The first series of guinea pig experiments demonstrated that larger flip angles (50‐90°) destroy the magnetization before it reaches the smaller airways. At moderate flip angles (20‐40°), airway branching down to the fourth generation was apparent. Fifth‐order branchings were seen in the images of the second series. The trachea down to fourth generation pulmonary airway branching, along with some distal air spaces, was seen in the human lung images.
Automatic probe tuning and matching
Authors: Hwang F. , Hoult D. I. 
Published: March 2007

AbstractThe problem of automatically tuning and matching a probe is considered, and attention is drawn to the main cause of difficulty: the interaction of tuning and matching mechanisms. The use of a doubly resonant, inductively coupled probe is therefore advocated, for to first order, tuning, and matching are then orthogonal for small perturbations. It is shown that when such a probe is equipped with negative feedback control of tuning and matching elements, driven by error signals derived from a bridge and the NMR spectrometer, stable and rapid automatic tuning and matching are achieved. The importance of approximately correct phasing of the error signals is emphasized, but the restriction of having to have specific cable lengths to achieve this task is removed. The effects of small errors of phasing are then considered and shown to be unimportant for the chosen probe, in contrast to the situation for other, nonorthogonal probe types. Suggestions for orthogonalization of two common capacitively coupled probe designs are made, and a practical instrument design is then given that, with the addition of external components, can also be used if the NMR receiver cannot be pressed into service.
Tissue‐independent MR tracking of invasive devices with an internal signal source
Authors: Erhart Peter , Ladd Mark E. , Steiner Paul , Heske Norbert , Dumoulin Charles L. , Debatin Jöorg F. 
Published: March 2007

AbstractAn improved MR tracking coil design is described that provides more robust tracking performance. It is shown theoretically and experimentally that a coil equipped with an internal spin source increases the signal‐to‐noise ratio in comparison to a coil system without internal source. The tracking behavior is stable even in air, which is important for laparoscopic work, in which the device has to be placed inside the inflated abdomen. Two types of coil windings were tested: one with the windings perpendicular to the coil axis and the other one with the windings tilted relative to this axis. The experiments showed no significant effect on the signal‐to‐noise ratio between the two types. The improved MR‐tracking coil design with internal source was successfully used in cholecystosto‐mies and in laparoscopic interventions; both procedures were performed on swine.
Effects of the acoustic noise of the gradient systems on fMRI: A study on auditory, motor, and visual cortices
Authors: Cho Zang‐Hee , Chung Soon‐Chul , Lim Dae‐Woon , Wong Edward K. 
Published: March 2007

AbstractMR acoustic, or sound, noise due to gradient pulsing has been one of the problems in MRI, both in patient scanning as well as in many areas of psychiatric and neuroscience research, such as brain fMRI. Especially in brain fMRI, sound noise is one of the serious noise sources that obscures the small signals obtainable from the subtle changes occurring in oxygenation status in the cortex and blood capillaries. Therefore, we have studied the effects of acoustic, or sound, noise arising in fMR imaging of the auditory, motor, and visual cortices. The results show that the effects of acoustic noise on motor and visual responses are opposite. That is, for motor activity, there is an increased total motor activation, whereas for visual stimulation, the corresponding (visual) cortical activity is diminished substantially when the subject is exposed to a loud acoustic sound. Although the current observations are preliminary and require more experimental confirmation, it seems that the observed acoustic‐noise effects on brain functions, such as in the motor and visual cortices, are new observations and could have significant consequences in data observation and interpretation in future fMRI studies.