bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reperfused myocardial infarctions on T1‐ and susceptibility‐enhanced MRI: Evidence for loss of compartmentalization of contrast media
Authors: Saeed Maythem , Wendland Michael F. , Masui Takayuki , Higgins Charles B. 
Published: March 2007

AbstractThe purpose of this study was to characterize the contrast caused by a susceptibility MRI contrast agents, on spin echo T2‐weighted imaging of reperfused myocardial infarction. Our interest in this model focused on the expected requirement that such agents be compartmentalized in the tissue to cause signal loss on spin echo images, a condition which may not be present in reperfused infarcted myocardium. Accordingly, nine rats were subjected to 2 h of left coronary artery occlusion followed by 3 ± 0.5 h of reperfusion prior to administration of contrast media. Three sets of MR images were acquired: (a) baseline axial images at the midventricle, both T1‐weighted (TR/TE = 300/20) and T2‐weighted (TR/TE = 1500/60); (b) T1‐weighted images after administering a T1‐enhancing agent, Gd‐DTPA‐BMA (0.2 mmol/kg), to document that contrast media is delivered to the reperfused infarction; and (c) T2‐weighted images after administering the susceptibility agent, Dy‐DTPA‐BMA (1.0 mmol/kg). Gadolinium‐enhanced T1 images depicted reperfused infarction as regions with greatly enhanced signal intensity compared with unin‐farcted myocardium, indicating that contrast agent was delivered to the infarcted zone. Dysprosium‐enhanced T1 images depicted the injury as a region of persistent signal intensity relative to depletion of signal in normal myocardium, consistent with failure of the contrast agent to cause signal loss. Similar infarction sizes were observed for unenhanced T2‐weighted images (33 ± 5%), gadolinium‐enhanced T1 weighted images (36 ± 5%) and postmortem staining (30 ± 6%); strong correlations (r > 0.9) were noted in comparisons of these data. Dysprosium‐enhanced images exhibited a smaller region of differential signal presumed to be infarction (20 ± 5%, P < 0.05) and weak correlations (r < 0.75) with the other measurements. We conclude that the smaller infarction depicted on dysprosium‐enhanced images is a subregion of the true infarction in which myocardial necrosis is sufficiently advanced that the agent is homogeneously distributed throughout all tissue compartments, preventing T2*‐dependent phase loss on spin echo images.
Interleaved echo planar imaging on a standard MRI system
Authors: Butts Kim , Riederer Stephen J. , Ehman Richard L. , Thompson Richard M. , Jack Clifford R. 
Published: March 2007

AbstractThis work describes an interleaved echo planar imaging (EPI) method for use on a standard whole body scanner. The data acquisition is divided into two to eight repetitions rather than one to two, as implemented by dedicated EPI systems. Interleaving allows the use of a lower sampling bandwidth with a significant increase in signal‐to‐noise. The method also has the advantages of relative ease of implementation, no need for postprocessing to remove image distortion, and no need for shimming on a case‐by‐case basis. The interleaved EPI method was applied to two applications ideally suited to EPI: breathhold T2‐weighted abdominal imaging and functional imaging. In vivo liver‐lesion contrast as measured in a 35‐patient study showed increased contrast for the Interleaved EPI by an average factor of 1.21 (± 0.34) over conventional spin‐echo imaging. CNR measurements showed the EPI to be comparable with conventional spin echo with a relative factor of 1.00 (± 0.36). Functional imaging with an eight‐shot interleaved EPI sequence provided 128 × 128 images of cerebral activation during bilateral finger tapping.
Detection of brain activation using oxygenation sensitive functional spectroscopy
Authors: Hennig J. , Emst Th. , Speck O. , Deuschl G. , Feifel E. 
Published: March 2007

AbstractA nonwater‐suppressed localized spectroscopy experiment using the PRESS‐sequence has been used to study the signal changes of the water resonance during cortical activation. Significant effects with an effect‐to‐noise ratio up to 50:1 for a single shot experiment have been observed upon photic stimulation. The exceedingly high signal‐to‐noise ratio of the experiment was used to demonstrate signal changes as low as 0.1% after electrical stimulation of the median nerve.
Fructose 3‐phosphate and 5‐phosphoribosyl‐1‐pyrophosphate formation in perhsed human erythrocytes: 31P NMR studies
Authors: Lundberg Peter , Roy Sushmita , Kuchel Philip W. 
Published: March 2007

Abstract31P NMR was used to study the formation of fructose 3‐phos‐phate (F3P) and 5‐phosphoribosyl‐1‐pyrophosphate (PRPP) in perfused human erythrocytes, in the presence of 10 different combinations and concentrations of glucose, inosine, pyru‐vate, fructose, and inorganic phosphate (Pi). (1) The cells were immobilized in alginate‐coated agarose threads and perfused with a medium containing fructose, and the level of F3P increased continuously over more than 10 h. The net rate of F3P formation was independent of the concentration of 2,3‐bis‐phosphoglycerate (2,3‐DPG) present in the cells. (2) PRPP was formed in high concentrations, relative to normal, in immobilized cells when they were perfused with a medium containing Pi at a low pH (6.6). (3) The 2,3‐DPG level decreased simultaneously when the sample was perfused with a medium containing fructose, but without inosine or pyruvate. The measured intracellular pH and free Mg2+ concentration were constant in these experiments. (4) The experiments confirmed the presence of fructose‐3‐phosphokinase (E.C. 2.7.1.‐) and ribose‐phosphate pyrophosphokinase (E.C. 2.7.6.1) activity in the human erythrocytes and that the biosynthetic pathways are active in immobilized cells at 37°C. (5) The rates of accumulation of 2,3‐DPG and phosphomonoesters (PME) appeared to be strongly correlated.
Optimization of parameter values for complex pulse sequences by simulated annealing: Application to 3D MP‐RAGE imaging of the brain
Authors: Epstein Frederick H. , Mugler John P. , Brookeman James R. 
Published: March 2007

AbstractA number of pulse sequence techniques, including magnetization‐prepared gradient echo (MP‐GRE), segmented GRE, and hybrid RARE, employ a relatively large number of variable pulse sequence parameters and acquire the image data during a transient signal evolution. These sequences have recently been proposed and/or used for clinical applications in the brain, spine, liver, and coronary arteries. Thus, the need for a method of deriving optimal pulse sequence parameter values for this class of sequences now exists. Due to the complexity of these sequences, conventional optimization approaches, such as applying differential calculus to signal difference equations, are inadequate. We have developed a general framework for adapting the simulated annealing algorithm to pulse sequence parameter value optimization, and applied this framework to the specific case of optimizing the white matter‐gray matter signal difference for a T1‐weighted variable flip angle 3D MP‐RAGE sequence. Using our algorithm, the values of 35 sequence parameters, including the magnetization‐preparation RF pulse flip angle and delay time, 32 flip angles in the variable flip angle gradient‐echo acquisition sequence, and the magnetization recovery time, were derived. Optimized 3D MP‐RAGE achieved up to a 130% increase in white matter‐gray matter signal difference compared with optimized 3D RF‐spoiled FLASH with the same total acquisition time. The simulated annealing approach was effective at deriving optimal parameter values for a specific 3D MP‐RAGE imaging objective, and may be useful for other imaging objectives and sequences in this general class.
A method for in vivo high resolution MRI of rat spinal cord injury
Authors: Ford John C. , Hackney David B. , Joseph Peter M. , Phelan Megan , Alsop David C. , Tabor Stacy L. , Hand Christopher M. , Markowitz Ronald S. , Black Perry 
Published: March 2007

AbstractWe have developed an implanted radiofrequency coil to obtain high resolution in vivo MR images at 1.9 Tesla of rat spinal cords that have been injured using a standardized weight drop technique. The signal‐to‐noise ratio and motion artifact suppression of these images is superior to that achieved in earlier attempts at this field strength using an external surface coil. The high quality and spatial resolution provided by this technique afford the possibility for longitudinal studies of experimental spinal cord injury before and after treatment, as well as detailed correlation of in vivo MRI contrast, histopathological findings, and functional deficit, in a controlled setting.
Discrimination of fluorinated uridine metabolites in N‐417 small cell lung cancer cell extracts via 19F‐ and 31P‐NMR
Authors: Pederson Nathanael V. , Zanghi James A. , Miller William M. , Knop Richard H. 
Published: March 2007

Abstract31P‐NMR extract spectra of N‐417 Small Cell Lung Cancer (SCLC) cells cultured with fluorouridine (FUrd) reveal new peaks with chemical shifts in the diphosphodiester and nucleoside triphosphate regions. These peaks were identified as FUTP, FUDP, FUDP‐glucose, FUDP‐glucuronate, FUDP‐GlcNAc, and FUDP‐GalNAc via enzymatic conversion and 19F‐and 31P‐NYR analysis. Distinct 19F chemical shifts were assigned for FUTP, FUDP, and the FUDP‐sugars.
Signal targeting with alternating radiofrequency (STAR) sequences: Application to MR angiography
Authors: Edelman Robert R. , Siewert Bettina , Adamis Mary , Gaa Jochen , Laub Gerhard , Wielopolski Piotr 
Published: March 2007

AbstractWe describe a time of flight subtraction method for cine MR angiography that provides nearly perfect suppression of background signal intensity with excellent flow contrast. The method consists of a preparation phase, during which the longitudinal magnetization of the target tissue is inverted on alternate acquisitions and the background tissue is presaturated, followed by a readout phase using a cine segmented turboFLASH sequence with a shared echo modification to improve temporal resolution. With appropriate alternation of the phases of the radiofrequency excitation pulses, there is cancellation of the background signal intensity but flow signal is optimized. By using a thick section (up to 25 mm), substantial portions of the vascular territory are encompassed in a single plane. This permits rapid, dynamic assessment of flow patterns in areas such as the circle of Willis, carotid bifurcation, or renal arteries. Applications of the method for bright and dark blood cine MR angiography are demonstrated.
Determination of proton magnetization transfer rate constants in heterogeneous biological systems
Authors: Brooks Douglas , Kuwata Kazuo , Schleich Thomas 
Published: March 2007

AbstractTwo procedures are currently in use for the determination of proton magnetization transfer rate constants between macro‐molecular tissue components and water. The first method assumes that there are only two spin baths (macromolecular plus solvent) and that during off‐resonance irradiation complete saturation of the “immobile” proton spin bath occurs (S. H. Koenig, R. D. Brown, 111, R. Ugolini, Magn. Reson. Med. 29, 311 (1993)). This approach neglects the possibility of incomplete saturation and polydispersity, and yields an apparent magnetization transfer rate constant, Kapp. The second approach utilizes a formalism which can account for polydispersity and incomplete saturation of the immobile spin bath (K. Kuwata, D. Brooks, H. Yang, T. Schleich, J. Magn. Reson., in press). In this work magnetization transfer rate constants derived by the use of both methods for two systems, ocular lens tissue and cross‐linked bovine serum albumin (BSA) were compared. For both samples Kapp was dependent on B2, off‐resonance irradiation frequency and power when the first method was used. The second method provided values of the magnetization transfer rate constant that were similar to the values obtained by the first method, as the limit of complete saturation was approached.
Further observations on the measurement of tissue T1 to monitor temperature in vivo by MRI
Authors: Young I. R. , Hand J. W. , Oatridge A. , Prior M. V. , Forse G. R. 
Published: March 2007

AbstractPrevious results for the measurement of T1 as a means of monitoring temperature have demonstrated a linear calibration with a coefficient of the order of 1.5%C. We have studied the changes in T1, further, and observe that changes in tissue perfusion are substantial contributors to the effects observed, and that the model of what is happening is complex and may not permit a simple temperature calibration.
Water and fat MR imaging with chemical shift selective 3D steady state methods
Authors: Sun L. , Aletras A. H. , Schmalbrock P. , Skinner T. E. , Chakeres D. , Irsik R. , Robitaille Pierre‐Marie 
Published: March 2007

AbstractA new 3D acquisition regimen that enables the collection of conventional, water‐suppressed, and fat‐suppressed images with no increase in scan times compared with currently implemented 3D sequences is presented. The method is based on conventional 3D steady state with interleaved selective excitation of the fat resonance resulting in acquisition of a fat‐based image during the TR period experienced by the water spins. This new sequence is relatively tolerant to susceptibility artifacts and results in excellent water‐based images. Because the idea, which we propose, is independent of the type of steady‐state imaging protocol utilized, it can be easily applied with regimens that are specifically tailored to enhance contrast.
Automated single‐voxel proton MRS: Technical development and multisite verification
Authors: Webb Peter G. , Sailasuta Napapon , Kohler Susan J. , Raidy Tom , Moats Rex A. , Hurd Ralph 
Published: March 2007

AbstractTo improve clinical utility, an integrated method has been developed to automatically acquire and process single‐voxel in vivo proton spectra on a 1.5 T clinical scanner. This method includes automated adjustment of linear shims using a very rapid modified simplex method, automated water suppression, and applies a water referencing scheme to correct for phase and residual eddy current effects. No operator intervention is required for the acquisition and processing of these pure‐absorption spectra. This method was tested in a preliminary multisite trial to determine intersite and intrasite variability of metabolite ratio measurements. In a sample of over 100 examinations, the standard deviation of the ratios NAA:Cr, Cho:Cr, and ml:Cr were found to be under 15% when using this method, a substantially narrower range than has been found In studies relying on manual adjustment of the instrument and/or manual processing. This result indicates that automated setting of acquisition and processing parameters is of critical importance in the clinical application of in vivo spectroscopy.
Stability assessment of gadolinium complexes by P‐31 and H‐1 relaxometry
Authors: Elst Luce Vander , van Haverbeke Yves , Goudemant Jean‐François , Muller Robert N. 
Published: March 2007

AbstractLongitudinal P‐31 relaxation rate enhancements of phosphate groups have been measured at pH 7–7.2 and 310°K on aqueous solutions containing adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pl) and some lanthanide complexes (Gd‐DOTA, Gd‐HPDO3A, Gd‐DO3A, Gd‐DTPA, Gd‐DTPA‐BMA). The macrocyclic complexes induce linear enhancements of the relaxation rates of all phosphorus nuclei. For Gd‐DOTA and Gd‐HPDO3A, the mechanism of the interaction with the P‐31 nuclei seems to be of the outer sphere type and a better efficiency is noted for the “neutral” Gd‐HPDO3A. A short‐lived ternary complex between Gd‐DO3A and the phosphorylated metabolites appears to be formed enabling an inner sphere interaction. In solutions containing the open chain complexes, Gd‐DTPA and Gd‐DTPA‐BMA, P‐31 relaxation rates of ATP exhibit significant and nonlinear enhancements that are much larger than those observed for PCr and Pi. A ternary complex involving the lanthanide Ion, its original chelator, and the ATP molecule is precluded by various experiments which confirm that the lanthanide ion shifts from the original complexes to the ATP phosphate groups.
Torque free asymmetric gradient coils for echo planar imaging
Authors: Abduljalil A. M. , Aletras A. H. , Robitaille Pierre‐Marie 
Published: March 2007

AbstractIn this work, we present a new torque‐free asymmetric gradient coil that is capable of generating high quality axial, sagittal, and coronal echo planar images of the human head. This gradient set was calculated using the Biot‐Savart law and least square approaches to optimize the field in the region of interest and to minimize net torques. The resulting structure has excellent shoulder‐to‐coil clearance and, as such, has the advantage of providing good patient access to the linear portion of the gradient while minimizing patient discomfort from claustrophobia.
In vivo and in vitro31P magnetic resonance spectroscopic studies of the hepatic response of healthy rats and rats with acute hepatic damage to fructose loading
Authors: Lu Wuhua , Locke Steven J. , Brauer Manfred 
Published: March 2007

AbstractThe hepatic response to a fructose challenge for control rats, and rats subjected to an acute sublethal dose of carbon tetrachloride (CCI4) or bromobenzene (BB), was compared using dynamic in vivo 31P MRS. Fructose loading conditions were used in which control rats showed only a modest increase in hepatic phosphomonoester (PME), and a small decrease in ATP, Pi, and intracellular pH after fructose administration. Both CCI4, and BB‐treated rats showed a much greater fructose‐induced accumulation of PME than did controls. Trolox C, a free radical scavenger, prevented most of this PME increase. BB‐treated rats, given sufficient time to recover from the hepa‐totoxic insult, responded to the fructose load similarly to controls. Liver aldolase activities of control, toxicant‐treated rats, and toxicant plus Trolox C‐treated rats correlated inversely with PME accumulation after fructose loading (correlation coefficient: −0.834, P < 0.05). Perchloric acid extracts of rat livers studied by in vitro 31P MRS confirmed that the PME accumulation after fructose loading is mainly due to an increase in fructose 1‐phosphate. These studies are consistent with the aldolase‐catalyzed cleavage of fructose 1‐phosphate being rate‐limiting in hepatic fructose metabolism, and that the CCI, and BB treatment modify and inactivate the aldolase enzyme.
The application of breath hold phase velocity mapping techniques to the measurement of coronary artery blood flow velocity: Phantom data and initial in vivo results
Authors: Keegan Jennifer , Firmin David , Gatehouse Peter , Longmore Donald 
Published: March 2007

AbstractA segmented k‐space breath hold phase velocity mapping technique has been developed for the study of coronary artery blood flow velocity. In vitro validation has been performed using a number of pulsatile flow phantoms and the accuracy of the technique for determining the velocity increase at the site of a stenosis demonstrated in several phantom models. Examples of both in‐plane and through‐plane velocity maps of the left anterior descending and right coronary arteries of normal subjects in early diastole are presented. In one subject, through‐plane velocity maps were obtained in the right and left anterior descending arteries throughout the cardiac cycle in order to generate flow velocity time curves. The problems associated with coronary artery velocity mapping are discussed.
Automated processing for proton spectroscopic imaging using water reference deconvolution
Authors: Maudsley Andrew A. , Wu Zhe , Meyerhoff Dieter J. , Weiner Michael W. 
Published: March 2007

AbstractAutomated formation of MR spectroscopic images (MRSI) is necessary before routine application of these methods is possible for in vivo studies; however, this task is complicated by the presence of spatially dependent instrumental distortions and the complex nature of the MR spectrum. A data processing method is presented for completely automated formation of in vivo proton spectroscopic images, and applied for analysis of human brain metabolites. This procedure uses the water reference deconvolution method (G. A. Morris, J. Magn. Reson. 80,547(1988)) to correct for line shape distortions caused by instrumental and sample characteristics, followed by parametric spectral analysis. Results for automated image formation were found to compare favorably with operator dependent spectral integration methods. While the water reference deconvolution processing was found to provide good correction of spatially dependent resonance frequency shifts, it was found to be susceptible to errors for correction of line shape distortions. These occur due to differences between the water reference and the metabolite distributions.
Experimental confirmation of phase encoding of instantaneous derivatives of position
Authors: Duerk Jeffrey L. , Simonetti Orlando P. , Hurst Gregory C. , Finelli Daniel A. 
Published: March 2007

AbstractPrevious theoretical reports described the dependence of interpretation of the observed phase of the NMR signal on the time origin(s) of moment calculations and position's Taylor series expansion. This work provides experimental confirmation of predictions derived from that theory. For accelerative motion, experimental phase‐encoded velocity measurements give instantaneous values at a time corresponding to the origin used for waveform momemt calculations. For laminar flow, experimental intensity profiles agree well with theoretical simulations; new findings extend amplitude and spatial distributions of oblique flow profiles beyond previous descriptions. Experiments using sequences with controlled position of the time origins for phase and read axes show that displacement and motion artifacts are reduced when they're coincident (pulsed flow, nongated acquisitions), and virtually eliminated when combined with gating. Potentially significant clinical consequences of coincident and noncoincident time origins are demonstrated in human head MIP MRA images. These results have fundamental implications in waveform design.
Rapid tissue oxygen tension mapping using 19F inversion‐recovery echo‐planar imaging of P erfluoro‐15 ‐crown‐5‐ether
Authors: Dardzinski Bernard J. , Sotak Christopher H. 
Published: March 2007

AbstractFluorine‐19 inversion‐recovery, echo‐planar imaging (IR‐EPI) wais used in conjunction with a new PFC emulsion, perfluoro‐15‐crown‐5‐ether, to map the spatial distribution of oxygen tension in murine liver, spleen and radiation induced fibrosarcoma (RIF‐1) tumors. Intravenously administered PFC emulsions were allowed to sequester in the liver, spleen, and tumor 3 to 7 days prior to imaging experiments. Seven, 64 × 64 IR‐EPls were acquired with successively increasing inversion times (TI). A nonlinear least‐squares regression algorithm was used to fit the seven two‐dimensional matrices, on a pixel‐by‐pixel basis, to solve for the relaxation rate, R1, of the sequestered PFC. From in vitro calibration curves, the oxygen tension (pO2,) was calculated from the measured R1. Oxygen tension maps were then murine liver and spleen were produced (in 2.5 min) to demonstrate the technique and changes in tissue oxygenation as a function of breathing gas (air and carbogen (95% O2 ‐ 5% CO2)) are presented. Tissue pO2 maps from RIF‐1 tumors (n = 5) were obtained in less than 10 min and changes in tumor pO2 were studied when the breathing gals was switched from air to carbogen. The results from tumor pO2 maps were compared with 19F MR spectroscopy measurements to check for consistency. Histogram analysis yielded an average liver and spleen pO2 of 43 torr and 26 torr for RIF‐1 tumors when the animals were breathing air. Statistically significant changes in tumor oxygenation as a function of breathing gas were obtained from both pO2 maps (6 ± 2 torr, P < 0.05) and 19F MR spectroscopy (13 ± 3 torr, P < 0.01) as evaluated using the Student's paired t test.