bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of deoxymyoglobin changes during graded myocardial ischemia: An in Vivo1H NMR spectroscopy study
Authors: Chen Wei , Zhang Jianyi , Eljgelshoven Marcel H. J. , Zhang Yi , Zhu Xiao‐Hong , Wang Chunshen , Cho Yong , Merkle Hellmut , Uĝcurbil Kǎmil 
Published: March 2007

Abstract1H NMR spectroscopy was used to detect the proximal histidyl Nδ, proton signal of deoxymyoglobin from canine hearts in vivo during graded myocardial ischemia. The NMR signal intensity provided an indicator of intracellular oxygenation in myocardium. The relationship between the myocardial blood flow and the deoxymyoglobin concentration was successfully measured during resting, partial, and complete coronary artery occlusion conditions. The results demonstrate the feasibility to detect deoxymyoglobin using a 1H NMR spectroscopy technique in living hearts for the first time and the possibility to use this technique for investigating myocardial oxidative metabolism nondestructively and repetitively.
Highly selective water and fat imaging applying multislice sequences without sensitivity to B1 field inhomogeneities
Authors: Schick Fritz , Forster Jürgen , Machann Jürgen , Huppert Peter , Claussen Claus D. 
Published: March 2007

AbstractImproved selectivity to one chemical shift component was obtained using simultaneous slice‐selective and chemical shift‐selective excitation in sequences with usual spin‐echo refocusing. The new type of sequences can be applied on modern whole‐body units and permits multislice operation. Spatial‐spectral excitation is based on prior research in this field, but the proposed improved version provides off‐center slice excitation by the usual processing of the RF pulse envelopes. In addition, no irregular gradient shapes are necessary. The required B0 homogeneity of the new method is similar to conventional “fat‐sat” techniques. In contrast to fat‐sat methods, selectivity to water is not reduced by unavoidable mis‐adjustments of the transmitter or B1 field inhomogeneities in the newly developed approach. Thus, the reported method has the potential to replace standard frequency selective fat‐sat sequences for most applications.
The distribution of lithium in rat brain and muscle in vivo by 7Li NMR imaging
Authors: Komoroski Richard A. , Pearce John M. , Newton Joseph E. O. 
Published: March 2007

AbstractThe regional distribution of lithium (Li) in vivo was determined on a relative basis in the brain and muscle of rats by 7Li NMR imaging. Both high resolution 7Li NMR spectroscopy and atomic absorption spectrophotometry were performed on extracts of brain and muscle tissue from the same rats. The average in vivo results were generally in good agreement with the corresponding average in vitro results, despite the relatively low signal‐to‐noise ratio of the in vivo images. There was good agreement between the two in vitro methods of analysis, both on average and for individual animals. Significant differences were found in vivo among Li concentration ratios for the various brain regions and muscle by 7Li imaging, as well as by the in vitro methods.
In vivo imaging of a stable paramagnetic probe by pulsed‐radiofrequency electron paramagnetic resonance spectroscopy
Authors: Murugesan Ramachandran , Cook John A. , Devasahayam Nallathamby , Afeworki Mobae , Subramanian Sankaran , Tschudin Rolf , Larsen Janhenrik A. , Mitchell James B. , Russo Angelo , Krishna Murali C. 
Published: March 2007

AbstractImaging of free radicals by electron paramagnetic resonance (EPR) spectroscopy using time domain acquisition as in nuclear magnetic resonance (NMR) has not been attempted because of the short spin‐spin relaxation times, typically under 1 μs, of most biologically relevant paramagnetic species. Recent advances in radiofrequency (RF) electronics have enabled the generation of pulses of the order of 10–50 ns. Such short pulses provide adequate spectral coverage for EPR studies at 300 MHz resonant frequency. Acquisition of free induction decays (FID) of paramagnetic species possessing inhomogenously broadened narrow lines after pulsed excitation is feasible with an appropriate digitizer/averager. This report describes the use of time‐domain RF EPR spectrometry and imaging for in vivo applications. FID responses were collected from a water‐soluble, narrow line width spin probe within phantom samples in solution and also when infused intravenously in an anesthetized mouse. Using static magnetic field gradients and back‐projection methods of image reconstruction, two‐dimensional images of the spin‐probe distribution were obtained in phantom samples as well as in a mouse. The resolution in the images was better than 0.7 mm and devoid of motional artifacts in the in vivo study. Results from this study suggest a potential use for pulsed RF EPR imaging (EPRI) for three‐dimensional spatial and spectral‐spatial imaging applications. In particular, pulsed EPRI may find use in in vivo studies to minimize motional artifacts from cardiac and lung motion that cause significant problems in frequency‐domain spectral acquisition, such as in continuous wave (cw) EPR techniques.
Contour‐based registration technique to differentiate between task‐activated and head motion‐induced signal variations in fMRI
Authors: Biswal Bharat B. , Hyde James S. 
Published: March 2007

AbstractData acquired using functional magnetic resonance imaging are often contaminated by head motion. As a result, optimal information regarding task‐induced (or resting‐state) signal changes cannot be extracted. Intensity‐based registration methods, including intensity correlation or minimum intensity variance techniques, are widely used to register two or more images. It is shown here that intensity‐based registration cannot accurately register two or more images in the presence of local intensity changes arising from functional magnetic resonance, fMRI, signals. In this paper, we present a contour‐based technique that can be used not only for a more robust registration, but also to help differentiate between task‐induced and motion‐induced signal changes. Results obtained using both phantom and human brain images demonstrate advantages of this technique compared with a conventional intensity registration technique.
Suppression of physiological eye movement artifacts in functional MRI using slab presaturation
Authors: Chen Wei , Zhu Xiao‐Hong 
Published: March 2007

AbstractReduction of image‐to‐image signal fluctuations and imaging artifacts is important for fMRI studies. The imaging artifacts caused by respiration, cardiac pulsation, and gross head motion and the suppression of these artifacts have been studied for many years. However, the artifacts caused by eye movement and their effects on fMRI mapping are not well known. It is demonstrated in this report that involuntary eye movements during resting conditions can cause substantial signal fluctuations in the phase‐encoding direction even for a fast echo‐planar imaging sequence. An oblique slab presaturation technique is proposed for saturating the magnetization of eyes and suppressing the artifacts from eye movements with minimal signal loss of other brain tissues. The results show that the technique significantly reduces signal fluctuations and improves fMRI reliability for mapping functional activation in the human brain.
Myocardial infarction in a canine model monitored by two‐dimensional 31p chemical shift spectroscopic imaging
Authors: Farrall Andrew J. , Thompson R. Terry , Wisenberg Gerald , Campbell Constance M. , Drost Dick J. 
Published: March 2007

AbstractWe have developed a closed chest animal model that allows noninvasive monitoring of cardiac high energy phosphate metabolism before, during, and for at least 3 weeks after a myocardial infarction. Ten beagles underwent 2 h of coronary occlusion followed by 3 weeks of reperfusion. Myocardial high energy phosphates from 12‐ml voxels were noninvasively tracked using 31P two‐dimensional chemical shift imaging. Gadolinium enhanced 1H MRI identified the zone at risk, and radioactive microspheres assessed regional blood flow and partition coefficients. Occlusion of the left anterior descending coronary artery produced infarcts that were 13.7 ± 8.8% (mean ± SD) of the left ventricular volume. Rapid changes in the phosphocreatine and inorganic phosphate levels were observed during occlusion, whereas adenosine triphosphate levels decreased more slowly. All metabolites recovered to base‐line levels 2 weeks after occluder release. Multiple inorganic phosphate peaks in the infarct voxel spectra indicated that more than one metabolically compromised tissue zone developed during occlusion and reperfusion. Microsphere data indicating three distinct blood flow zones during ischemia and reperfusion (<0.3, 0.3‐0.75, and >0.75 ml/min/g) supported the grouping of pH values into three distinct metabolic distributions.
Magnetic resonance properties of ex vivo breast tissue at 1.5 T
Authors: Graham Simon J. , Ness Sola , Hamilton Bradford S. , Bronskill Michael J. 
Published: March 2007

AbstractThe magnetic resonance absorption spectrum, T1 and T2 relaxation time distributions, and magnetization transfer properties of ex vivo breast tissue have been characterized at 1.5 T and 37°C. The fraction of fibroglandular tissue within individual tissue samples (n = 31) was inferred from the tissue volumetric water content obtained by integration of resolvable broad‐line fat and water resonances. The spectroscopically estimated water content was strongly correlated with that extracted enzymatically (Pearson correlation coefficient 0.98, P « 0.01), which enabled the assignment of principal relaxation components for fibroglandular tissue (T2 = 0.04 ± 0.01, T1 = 1.33 ± 0.24 s), and for adipose tissue (T2 = 0.13 ± 0.01, T1 = 0.23 ± 0.01 s, and T2 = 0.38 ± 0.03, T1 = 0.62 ± 0.16 s). The relaxation components for fibroglandular tissue exhibited strong magnetization transfer, whereas those for adipose tissue showed little magnetization transfer effect. These results ultimately have applicability to the optimization of clinical magnetic resonance imaging and research investigations of the breast.
Myocardial function in infarcted and remote regions early after infarction in man: Assessment by magnetic resonance tagging and strain analysis
Authors: Marcus J. Tim , Götte Marco J. W. , van Rossum Albert C. , Kuijer Joost P. A. , Heethaar Robert M. , Axel Leon , Visser Cees A. 
Published: March 2007

AbstractEarly after infarction in the perfusion bed of the left anterior descending coronary artery, cine MRI with spatial modulation of magnetization (SPAMM) tagging (7‐mm grid) was used for short‐ and long‐axis cardiac imaging. Two‐dimensional strain analysis of triangular finite elements was performed between end‐diastole and end‐systole. Patients (n = 10) were compared with age‐matched healthy subjects (n = 8). The anteroseptal region at midventricular level was considered representative for “infarcted” and the posterolateral region at basal level was considered “remote”. The left ventricular end‐diastolic volume index was larger in the patients (69 ± 15 ml/m2 versus 56 ± 4 ml/m2, P < 0.05). Short‐axis images showed in the infarcted region a decrease of first principal strain (greatest systolic lengthening: 1.10 ±. 06 versus 1.27 ± 0.04, P < 0.0001), and in the remote region an increase (1.48 ± 0.11 versus 1.36 ± 0.07, P < 0.025). The lateral and inferior ventricular regions at mid‐ and basal levels were found to function normally. Long‐axis images yielded similar results. Early after infarction, regions with dysfunction, normal function, and hyperfunction can be delineated with MR tagging. The compensatory increased contraction in the remote region is possibly triggered by the Frank‐Starling mechanism.
Assessment of quantitative artificial neural network analysis in a metabolically dynamic ex vivo31p NMR pig liver study
Authors: Ala‐Korpela Mika , Changani K. K. , Hiltunen Y. , Bell J. D. , Fuller B. J. , Bryant David J. , Taylor‐Robinson S. D. , Davidson B. R. 
Published: March 2007

AbstractQuantitative artificial neural network analysis for 1550 ex vivo 31P nuclear magnetic resonance spectra from hypothermically reperfused pig livers was assessed. These spectra show wide ranges of metabolite concentrations and have been analyzed using metabolite prior knowledge based lineshape fitting analysis which had proved robust in its biochemical interpretation. This finding provided a good opportunity to assess the performance of artificial neural network analysis in a biochemically complex situation. The results showed high correlations (0.8655 ≤ R ≤ 0.992) between the lineshape fitting and artificial neural network analysis for the metabolite values, and the artificial neural network analysis was able to fully represent the trends in the metabolic fluctuations during the experiments.
Recording of EEG during fMRI experiments: Patient safety
Authors: Lemieux Louis , Allen Philip J. , Franconi Florence , Symms Mark R. , Fish David K. 
Published: March 2007

AbstractThe acquisition of electroencephalograms (EEG) during functional magnetic resonance imaging (fMRI) experiments raises important practical issues of patient safety. The presence of electrical wires connected to the patient in rapidly changing magnetic fields results in currents flowing through the patient due to induced electromotive forces (EMF), by three possible mechanisms: fixed loop in rapidly changing gradient fields; fixed loop in a RF electromagnetic field; moving loop in the static magnetic field. RF‐induced EMFs were identified as the most important potential hazard. We calculated the minimum value of current‐limiting resistance to be fitted in each EEG electrode lead for a representative worst case loop, and measured RF magnetic field intensity and heating in a specific type of current‐limiting resistors. The results show that electrode resistance should be ≥13 kΩ for our setup. The methodology presented is general and can be useful for other centers.
Measurements of human cerebral GABA at 4.1 T using numerically optimized editing pulses
Authors: Hetherington Hoby P. , Newcomer Bradley R. , Pan Jullie W. 
Published: March 2007

AbstractThe goal of this work was to develop and evaluate a numerically optimized inversion pulse to be used with a homonuclear editing sequence to measure human cerebral GABA 117 vivo at 4.1 T in the occipital lobe. The optimized pulse was constructed using pallindromic symmetry with 30 pulses and 29 delays. The optimized pulse provided greater selectivity than the equivalent bandwidth matched DANTE pulse and sine shaped DANTE. The improved selectivity reduced the co‐editing of the macromolecule resonance, permitting the GABA edited doublet to be resolved in vivo. Using cerebral creatine as a reference, 7.1 mM, the measured GABA level was 1.15 ± 0.13 mM in the occipital lobe.
Differentiation of metabolic concentrations between gray matter and white matter of human brain by in vivo1H magnetic resonance spectroscopy
Authors: Wang Yonker , Li Shi‐Jiang 
Published: March 2007

AbstractDifferentiation of absolute metabolite concentrations between gray and white matter in the occipital region of normal human brain was performed by in vivo localized single‐voxel 1H magnetic resonance spectroscopy at 1.5 Testa with long echo time (136 ms). With the combination of image segmentation between white and gray matter and cerebrospinal fluid, signal compensation of T, and T2 effects, tissue water signal as the internal concentration reference, as well as compensation by different water contents in gray and white matters, it was determined that the levels of N‐acetylaspartate (NAA), creatine and/or phosphocreatine (Cr), and choline‐containing compounds (Cho) in gray matter were significantly higher than in white matter. The averaged NAA, Cr, and Cho concentrations in gray matter were 11.0, 9.7, and 1.9 mM/liter, respectively, in comparison with 7.5, 5.2, and 1.6 mM/liter in white matter. These results suggest that precise composition of white and gray matter and cerebrospinal fluid is necessary to avoid partial voluming effect in a single voxel and to accurately quantify the metabolite concentrations.
A new silent magnetic resonance imaging using a rotating DC gradient
Authors: Cho Z. H. , Chung S. T. , Chung J. Y. , Park S. H. , Kim J. S. , Moon C. H. , Hong I. K. 
Published: March 2007

AbstractA new approach to silent MR imaging using a rotating DC gradient has been explored and experimentally studied. Acoustic or sound noise has been one of the problems in examining patients, mainly due to the fast gradient pulsings in interaction with the main magnetic field. The sound noise has been noted to be proportionately louder as the magnetic field strength becomes larger. In this report, we describe a new imaging technique using a mechanically rotating DC gradient coil. The rotating DC gradient coil can effectively replace both phase encoding as well as readout gradient pulsings, and data obtained in this manner can provide a set of projection data that later can be used for projection reconstruction. With some interpolation techniques one can also perform conventional two‐dimensional fast Fourier transform image reconstruction. The sound noise intensity compared with the conventional imaging technique, such as the spin‐echo sequence, has been reduced down to about −20.7 dB or 117.5 times with this new technique. The experimental pulse sequence and its principle are described and images obtained by the new silent MR imaging technique are reported.
Sodium TQF NMR and intracellular sodium in isolated crystalloid perfused rat heart
Authors: Schepkin Victor D. , Choy I. Oojin , Budinger Thomas F. , Obayashi Derek Y. , Taylor Scott E. , Decampli William M. , Amartur Sundar C. , Young J. Nilas 
Published: March 2007

AbstractThe feasibility of monitoring intracellular sodium changes using Na triple quantum filtered NMR without a chemical shift reagent (SR) was investigated in an isolated rat heart during a variety of interventions for Ma, loading. Perfusion with 1 mM ouabain or without K+ present in the perfusate for 30 min produced a rise of the Na TQF signal with a plateau of ‐190% and ˜228% relative to the preintervention level, respectively. Stop‐flow ischemia for 30 min resulted in a TQF signal growth of ˜147%. The maximal Na TQF signal increase of 460% was achieved by perfusion without K+/Ca2+, corresponding to an elimination of the Na transmembrane gradient. The observed values of Na NMR TQF growth in the physiological and pathological ranges are in agreement with reported data by other methods and have a linear correlation with intracellular sodium content as determined in this study by Co‐EDTA method and by sucrose‐histidine washout of the extracellular space. Our data indicate that the increase in Na TQF NMR signal is determined by the growth of Nai, and the extracellular Na contribution to the total TQF signal is unchanged at ˜64%. In conclusion, Na TQF NMR without using SR offers a unique and noninvasive opportunity to monitor alterations of intracellular sodium. It may provide valuable insights for developing car‐dioprotective strategies and for observing the effects of pharmaceutical treatments on sodium homeostasis.
Effects of gradient anisotropy in MRI
Authors: Aldefeld Bernd , Börnert Peter 
Published: March 2007

AbstractA gradient system is anisotropic if the impulse responses of at least two of the gradient channels, x, y, or z, differ from each other. Such an undesired condition may arise, for example, from differences between the gradient channels with respect to eddy currents or from unbalanced time delays in the electronic components. Depending on the degree of anisotropy, the actual gradient then deviates from the nominal, desired gradient under certain oblique orientations during the transient periods of gradient switching. The adverse consequence is degradation of image quality, such as distortion, ghosting, and blurring. In this paper, a theoretical analysis is given of the basic effects. Furthermore, the implications for the MRI process and possible correction methods are described. The effects of anisotropy are shown experimentally for echo‐planar imaging and two‐dimensional selective RF excitation with spiral gradient pulses.
Asymmetric sampling along kslice‐select in two‐dimensional multislice MRI
Authors: Pipe James G. 
Published: March 2007

AbstractReduction of the slice‐select refocusing gradient in two‐dimensional multislice imaging results in asymmetry of the k‐space representation of collected data along the slice‐select direction. Standard methods of partial Fourier reconstruction developed for other methods of asymmetric k‐space sampling can be used to reconstruct these data with final through‐plane resolution smaller than the collected slice thickness. This method can be used for reducing scan time in the same manner as asymmetric sampling in the phase‐encoded direction. In addition, the reduced refocusing gradient reduces minimum TE and motion artifacts in the same manner as for asymmetric sampling in the frequency‐encoded direction (fractional echoes). Results using a resolution phantom and a flow phantom illustrate these concepts.
A new multiple quantum filter design procedure for use on strongly coupled spin systems found in vivo: Its application to glutamate
Authors: Thompson Richard B. , Allen Peter S. 
Published: March 2007

AbstractA numerical procedure is outlined that is appropriate for the design of multiple quantum filter sequences targeted for the strongly coupled, multiple spin systems that occur in metabolites present in brain. The procedure uses numerical methods of solution of the density matrix equations, first, to establish the most appropriate resonance to target with the filter; second, to provide contour plots of a performance index of the filter in terms of critical sequence parameters; and third, to produce the response signals of the target and the background metabolites to the optimized filter. The procedure is exemplified for the AMNPQ spin system of the amino acid glutamate at a field strength of 3 T. The 2.3 ppm peak of the PQ multiplet of glutamate was identified as the target resonance, and the performance of the filter so derived was evaluated experimentally on phantom solutions and in human brain. These experiments clearly demonstrate that a linewidth of £4 Hz is required for full resolution of glutamate from glutamine at 3 T using this double quantum filter. Nevertheless, even at a linewidth of ˜7 Hz in vivo, the 2.3 ppm peak of glutamate dominates the filter response and thereby removes a significant cause of uncertainty in measuring changes in glutamate by eliminating most of the background observed in unedited spectra obtained using PRESS or STEAM.