bluuebunny/crossref_metadata_2025_split huggingface dataset:
Detection of metabolic heterogeneity of human intracranial tumors in vivo by 1h nmr spectroscopic imaging
Authors: Segebarth Christoph M. , Balériaux Danielle F. , Luyten Peter R. , Den Hollander Jan A. 
Published: March 2007

AbstractPatients with intracranial tumors (gliomas) were examined by means of localized water‐suppressed 1H NMR single volume spectroscopy and spectroscopic imaging. The 1H NMR spectra of the tumors exhibit signal intensities of the N‐acetyl aspartate, choline compounds, and creatine plus phosphocreatine resonance lines that are different from the corresponding intensities observed on normal brain tissue. Also, for 6 out of the 10 patients examined so far, lactate resonance lines were detected in the tumor spectra. For one patient, abnormal 1H NMR spectra were obtained of a hemisphere which appeared normal with 1H NMR imaging. Metabolic heterogeneity of the tumorous regions could be demonstrated with 1H NMR spectroscopic imaging, using a spatial resolution in the order of 1 cm. These results suggest a spectrum of metabolic observations that may ultimately provide an important means for characterizing brain tumors.
Comparison of 31p mrs and 1h mri at 1.5 and 2.0 T
Authors: Boska M. D. , Hubesch B. , Meyerhoff D. J. , Twieg D. B. , Karczmar G. S. , Matson G. B. , Weiner M. W. 
Published: March 2007

AbstractThe goals of this study were to compare 31P magnetic resonance spectroscopy (MRS) and 1H magnetic resonance imaging (MRI) of human subjects and phantoms at 1.5 and 2.0 T. The 31P signal‐to‐noise (S/N) ratios in phantom standards and in localized volumes in human brain and liver were compared at 1.5 and 2.0 T. In addition, T1 values for 31P resonances in human brain, 31P linewidths of metabolites in human brain and liver, 1H S/N in a phantom standard, and MR image quality in human head and body were compared at the two field strengths. The results of our study showed that at the higher strength field, (1) in vivo 31P MRS studies benefited from up to 32% improvement in S/N; (2) in vivo 31P MRS studies also benefited from increased spectral dispersion; (3) the quality of MR head images remained comparable; and (4) body images showed some decrease in image quality due to increased chemical shift, and flow and motion artifacts.
Numerical analysis of multislice mr excitation and inversion with multifrequency selective rf pulses
Authors: Hafner Hans‐Peter , Müler Stephan , Seelig Joachim 
Published: March 2007

AbstractMultifrequency selective excitation and inversion were recently described and tested for multislice imaging and multivolume selective spectroscopy (Magn. Reson. Med. 6, 364 (1988), J. Magn. Reson. 76, 155 (1988)). The technique is based on the assumption that a multifrequency rf pulse, a linear superposition of several selective rf pulses with different frequencies, generates a MR signal which can be separated into the spin responses due to each individual frequency. This assumption is investigated theoretically by analyzing the effect of multifrequency selective rf pulses on the magnetization of a homogeneous phantom as a function of slice separation, pulse shape, and rf amplitude using computer simulations of the Bloch equations. It is found that multifrequency selective excitation with sinc pulses–up to eight slices are investigated–and two‐frequency inversion with hyperbolic secant pulses lead to profiles comparable in quality and selectivity to those of conventional single‐frequency pulses.
Triple‐quantum‐coherence‐filtered imaging of sodium ions in vivo at 4.7 tesla
Authors: Griffey Richard H. , Griffey Beatrice V. , Matwiyoff Nicholas A. 
Published: March 2007

AbstractThe tissue distribution of sodium ions which generate triple‐quantum coherence (TQC) in vivo is determined from images. A technique for filtering conventional sodium images, so that signal is obtained only from sodium ions which have a correlation time appropriate for producing TQC, is described. The utility of TQC‐filtered sodium images is demonstrated in a study of tumors implanted in a nude rat model, where the intensity of the TQC signal from sodium ions in the growing margin of the tumor is observed to be 200‐250% greater than that from surrounding tissue.
Quality: quantification improvement by converting lineshapes to the lorentzian type
Authors: De Graaf A. A. , Van Dijk J. E. , BoéE W. M. M. J. 
Published: March 2007

AbstractA method of time domain deconvolution, QUALITY, is described for general use in quantitative NMR spectroscopy. By division of the experimental NMR time domain signal by a reference signal, which may be obtained either in a separate experiment or via inverse Fourier transformation of an isolated single resonance in the experimental spectrum, perfect Lorentzian lineshapes can be obtained regardless of the magnetic field inhomogeneity. Experiments, both in vivo using a surface coil and in vitro using a surface coil and a HR NMR probe, show excellent performance of the method.
Switched array coils
Authors: Requardt H. , Offermann J. , Erhard P. 
Published: March 2007

AbstractSwitched array coils (SACs) are a useful tool in local coil imaging since they allow in a user‐friendly manner one to make the best choice in the trade‐off between field of view and signal‐to‐noise ratio. This is done by selecting the current path within a conductor array equipped with suitable switches. Since the switching can be controlled by the system, this allows changing of the coil dimensions within multislice sequences. Thus image quality can be improved due to smaller coil dimensions for a given slice and a larger area can be covered by electronically shifting this sensitive area. The principle can be applied to surface–as Well as volume–coil designs. © 1990 Academic Press, Inc.
In situ assessment of tumor vascularity using fluorine nmr imaging
Authors: Ceckler Toni L. , Gibson Scott L. , Hilf Russell , Bryant Robert G. 
Published: March 2007

AbstractIn situ fluorine NMR imaging has been used to measure vascularity in subcutancously implanted mammary tumors. Oxyferol, a perfluorinated blood substitute comprised of an emulsion of 25% w/v perfluorotributylamine, was used as a tracer. Following iv administration, this perfluorocarbon emulsion remains primarily in the vasculature during the image acquisition period. The distribution of the PFTA in the 19F NMR image gives a map of tissue regions with intact vascularity. This technique has been used to demonstrate decreased blood flow in necrotic regions of R3230AC mammary tumors in which vasculature had been damaged either as a result of spontaneous necrosis or by photodynamic therapy (PDT). Damage to tumor vascularity following PDT was observed prior to the development of necrosis.
Multinuclear nmr investigations of probe construction materials at 4.7 t
Authors: Babcock E. E. , Vaughan J. T. , Lesan And B. , , Nunnally R. L. 
Published: March 2007

AbstractSince background signal from NMR probes can overwhelm the signal from a sample, the NMR analysis of plastics or machinable ceramics is a prerequisite to their use in probe implementations. The contributions from a variety of materials to proton, fluorine, and carbon NMR spectra are presented.
Signal loss induced by superparamagnetic iron oxide particle in NMR spin‐echo images: The role of diffusion
Authors: Rozenman Yoseph , Zou Xueming , Kantor Howard L. 
Published: March 2007

AbstractMR contrast agents are used to improve the detectability of pathologic conditions. In this study we clarify the mechanism of action of a newly developed superparamagnetic agent (AMI‐25, Advanced Magnetics Inc., Cambridge, MA). Transverse relaxation rates were measured from segments of rat brain, heart, and liver using a CPMG pulse sequence. Relaxation rates varied with the time interval between the refocusing pulses in the sequence ( τ)The diffusion effect on signal intensity was quantitated from the variation of T2with τ. We find that diffusion in the presence of microscopic field gradients reduces T2 and that this effect differs in magnitude among tissues. Superparamagnetic iron oxide particles enhance this T2reduction. The dependence of T2upon τ suggests a model of restricted diffusion. Tissue image contrast induced by superparamagnetic iron oxide in spin‐echo NMR studies is the result of a combination of diffusion‐dependent and diffusion‐independent differences in transverse relaxation. © 1990 Academic Press, Inc.
Perfusion imaging with NMR contrast agents
Authors: Rosen Bruce R. , Belliveau John W. , Vevea James M. , Brady Thomas J. 
Published: March 2007

AbstractKnowledge of regional hemodynamics has widespread application for both physiological research and clinical assessment. Here we review the use of MR contrast agents to measure tissue perfusion. Two primary mechanisms of image contrast are discussed: relaxivity and susceptibility effects. Relaxivity effects result from dipolar enhancement of T1 and T2 rates. Because tissue T1 rates are intrinsically smaller, the dominant effect is shortening of T1 relaxation times. The second mechanism of image contrast is the variation in tissue magnetic field produced by heterogeneous distribution of high magnetic susceptibility agents. Quantitation of tissue perfusion requires a detailed understanding of the relation between contrast agent concentration and associated MR signal changes. Studies to date show a linear relationship between contrast agent concentration and rate change in most organs. The exact nature of this relationship in the dynamic setting of rapid contrast agent passage through the microcirculatory bed is less well established. If this relationship is known, tracer kinetic modeling can be used to calculate regional blood flow and blood volume. Data are presented which indicate that this approach is feasible, and suggest the potential of contrast‐enhanced NMR for high resolution in vivo mapping of both physiology and anatomy. © 1990 Academic Press, Inc.
A 1‐year time course study of the relaxation times and histology for irradiated rat lungs
Authors: Shioya Sumie , Haida T Munetaka , Fukuzaki Minoru , Ono Yoshiaki , Tsuda Masayuki , Ohta Yasuyo , Yamabayashi Hajime 
Published: March 2007

AbstractTo investigate the NMR relaxation times for irradiated rat lung tissue, we measured T1, and T2 at 11 different times during the injury's 1‐year time course. A biexponential analysis of T2 was used to determine T2 fast (T2f) and T2 slow (T2s). In addition, we measured water content and correlated changes in the relaxation times with pathological changes. The correlation indicates the following: (1) Shortly after irradiation, the biexponential T2 decay for 1/3 of the samples became monoexponential and there were no noticeable pathological changes observed using light microscopy. (2) During radiation pneumonitis, T2f and T2s were prolonged. This accompanied acute edematous changes and inflammatory cell infiltration. (3) Finally, during radiation fibrosis T1 shortened and collagen increased. We observed no significant correlation between relaxation time changes and water content changes throughout the 1‐year time course. © 1990 Academic Press, Inc.
Magnetic resonance imaging of experimental demyelinating lesions
Authors: Ford Corey C. , Ceckler Toni L. , Karp Juliana , Herndon Robert M. 
Published: March 2007

AbstractAn animal model of central nervous system demyelination was created by injecting rat internal capsules with lysophosphatidylcholine (LPC). The resulting chemically induced demyelinating lesions were readily visible in T1 ‐weighted spin‐echo, T2 weighted spin‐echo, and inversion‐recovery magnetic resonance imaging (MRI) sequences. Changes in lesions were followed over 8 weeks and correlated with histopathology. Histologically, lesions were characterized initially by an acute, inflammatory phase with edema and blood‐brain barrier breakdown, followed by macrophage‐mediated removal of myelin debris and finally by remyelination after 3 to 4 weeks. MRI can differentiate lesion stages in the LPC model and may be useful in investigating mechanistic aspects of the demyelinating process. In addition the well‐localized lesions may be amenable to study by techniques of volume‐localized NMR Spectroscopy. © 1990 Academic Press, Inc.
Hydrogen ultrathin phase‐encoded spectroscopy (HUPSPEC)
Authors: Listerud John , Lenkinski Robert E. , Axel Leon , Roberts Michael 
Published: March 2007

AbstractThis paper describes a new clinical spectroscopy pulse program, hydrogen ultrathin phase‐encoded spectroscopy. This sequence combines high spatial resolution with magnitude hydrogen spectroscopy. A linear volume is spatially frequency encoded with a conventional readout gradient and phase encoded spectrally by incrementing the timing of acquisition. The pulse sequence is implemented on a whole‐body MRI scanner and supports several standard scanner options, including autoprescanning, offset of the center of field of view in the frequency‐encoding direction, and oblique imaging. Some preliminary experimental experience is reported, demonstrating the possibility of observing the spectral line widths of fat and water in marrow, and of observing the spectral line widths of fat and water in marrow, and of observing multiline spectra. Combination of the technique with water suppression methods in a sequence called WASHUP is also discussed © 1990 Academic Press, Inc.
Enzyme kinetics and relaxation measurements with surface coils
Authors: Clarke Geoffrey D. , Rehr Roger B. 
Published: March 2007

AbstractA pulse sequence which produces the inversion of magnetization at a selected chemical shift for in vivo surface coil spectroscopy is proposed. The sequence uses a shaped, complex sech inversion pulse and “depth pulse” phase alternation. The sequence can be used for both in vivo inversion transfer and inversion recovery experiments. © 1990 Academic Press, Inc.
Metabolic response to exercise in malignant hyperthermia‐sensitive patients measured by 31P magnetic resonance spectroscopy
Authors: Webster D. W. , Thompson T. , Gravelle D. R. , Laschuk M. J. , Driedger A. A. 
Published: March 2007

AbstractThe currently favored theory of pathogenesis of malignant hyperthermia (MH) implicates an abnormality in skeletal muscle calcium ion transport. During a MH crisis a profound lactic acidosis occurs and in MH‐sensitive individuals a delayed recovery of venous lactate has been previously noted postexercise. We have used 31P magnetic resonance spectroscopy to follow noninvasively in vivo changes in muscle of intracellular pH and high‐energy phosphate metabolites during rest, exercise, and recovery of MH‐sensitive subjects. Eleven biopsy‐positive MH‐sensitive patients have been studied and compared to 26 normal subjects. The MH‐sensitive subjects as a group prematurely dropped their intracellular pH during mild aerobic exercise and they demonstrated a marked delay before the recovery of pH after maximal exercise. PCr/(PCr + Pi) ratios also dropped early during exercise but recovered normally. The observed changes in pH and PCr/(PCr + Pi) are consistent with a myopathy in MH‐susceptible individuals. © 1990 Academic Press, Inc.
Two‐dimensional spectra of intact tissue: Homonuclear Hartmann‐Hahn spectroscopy provides increased sensitivity and information content as compared to COSY
Authors: Alonso Juli , Arüs Carles , Westler William M. , Markley John L. 
Published: March 2007

AbstractHartmann‐Hahn (HOH AHA) spectroscopy led to good definition of proton spin systems of metabolites such as lactate, (phospho) creatine, and carnosine from a 3‐g sample of excised frog gastrocnemius muscle in a 17‐min experiment. The sign of the HOHAHA cross‐peak intensity appears to provide additional information about interactions between metabolites and their protein binding sites. © 1990 Academic Press, Inc.
Optimization of magnetization transfer measurements: Statistical analysis by stochastic simulation. Application to creatine kinase kinetics
Authors: Rydzy Marek , Deslauriers Roxanne , Smithand Ian C. P. , Saunders John K. 
Published: March 2007

AbstractA systematic study was performed to optimize the accuracy of kinetic parameters derived from magnetization transfer measurements. Three techniques were investigated: time‐dependent saturation transfer (TDST), saturation recovery (SRS), and inversion recovery (IRS). In the last two methods, one of the resonances undergoing exchange is saturated throughout the experiment. The three techniques were compared with respect to the accuracy of the kinetic parameters derived from experiments performed in a given, fixed, amount of time. Stochastic simulation of magnetization transfer experiments was performed to optimize experimental design. General formulas for the relative accuracies of the unidirectional rate constant (k) were derived for each of the three experimental methods. It was calculated that for k values between 0.1 and 1.0 s−1, T, values between 1 and 10 s, and relaxation delays appropriate for the creatine kinase reaction, the SRS method yields more accurate values of k than does the IRS method. The TDST method is more accurate than the SRS method for reactions where T1 is long and k is large, within the range of k and T1 values examined. Experimental verification of the method was carried out on a solution in which the forward (PCr → ATP) rate constant (k) of the creatine kinase reaction was measured. © 1990 Academic Press, Inc.
Improved quantification of in vivo1H NMR spectra by optimization of signal acquisition and processing and by incorporation of prior knowledge into the spectral fitting
Authors: De Graaf A. A. , Bovée W. M. M. J. 
Published: March 2007

AbstractQuantification of localized in vivo brain 1H spectra is in general very difficult due to excessive spectral overlap. In addition, intensity distortions may result from the effects of the NMR pulse sequence on the spins. This paper describes an approach to solving these problems. It comprises optimization of the pulse sequence; correction of the experimental lineshape; determination of intensity distortions, of relative line positions, and of linewidths using model solutions; and incorporation of the thus obtained prior knowledge into a nonlinear least‐squares spectral fitting procedure. This approach resulted in greatly improved accuracy, precision, and reliability of the quantitation of our in vivo spectra of rat brain, and enabled us to estimate absolute metabolite concentrations. © 1990 Academic Press, Inc.
Localized 1H in vivo NMR spectroscopy of small‐volume elements in human brain at 1.5 T
Authors: Jung Wulf‐Ingo , Grodd Wolfgang , Lutz Otto , Petersen Dirk 
Published: March 2007

AbstractLocalized in vivo proton NMR spectra of volume elements of minimal size (13 × 13 × 13 mm3) were obtained in human brain with a whole‐body imager working at 1.5‐T field strength. By use of an optimized version of the 90°‐180°‐180° volume selection method, well‐resolved proton spectra were acquired within 9 min and a comparison of spectra with different echo times (135 and 270 ms) was possible within 20 min. © 1990 Academic Press, Inc.
Velocity imaging of slow coherent flows using stimulated echoes
Authors: Caprihan A. , Griffey R. H. , Fukushima E. 
Published: March 2007

AbstractWe measure the velocity distribution of slow fluid flow in model systems using stimulated echoes and velocity phase encoding. We show velocity images of slow coherent flow with velocities of the order of 0.1 mm/s which is slower than can be obtained by the bolus‐tracking method. The eddy current errors were compensated by phase Correction. © 1990 Academic Press, Inc.
Aortoiliac and femoropopliteal phase‐based NMR angiography: A comparison between FLAG and RSE
Authors: Lanzer P. , Bohning D. , Groen J. , Gross G. , Nanda N. , Pohost G. 
Published: March 2007

AbstractTo assess the performance of FLAG and RSE NMR angiography 22 aortoiliac (A1) and 22 femoropopliteal (FP) angiograms in 11 healthy males, mean age 38 ± 7.6 years, were acquired. The image quality was graded in a blinded fashion by two independent readers. The readers grades were not statistically different (K = 0.5696). The representation of diagnostic images was 6/ 11 FLAG and 8/ 11 RSE A1 as well as 8/ 11 FLAG and 8/ 11 RSE FP. On back‐to‐back comparison six RSE A1 and seven RSE FP were graded bettcr than their FLAG counterparts. Although these differences did not achieve a statistical significance RSE NMR angiography provided consistently better images and appears preferable for imaging of the peripheral vascular system in normal subjects. © 1990 Academic Press, Inc.
Application of reverse‐DEPT polarization transfer pulse sequence to study the metabolism of carbon‐13‐labeled substrates in perfused organs by 1H NMR Spectroscopy
Authors: Desmoulin F. , Confort‐Gouny S. , Masson S. , Bernard M. , Doddrell D. M. , Cozzone P. J. 
Published: March 2007

AbstractMetabolism of 13C‐enriched metabolites can be advantageously studied by reverse‐polarization transfer methods. In this work an improved reverse‐DEPT sequence has been applied for the first time on perfused organs in a 20‐mm probe. The metabolic fate of 99% enriched [ 2‐13C] acetate perfused in excised rat liver and heart has been documented. © 1990 Academic Press, Inc.
High‐speed line scan MR angiography
Authors: Brown Donna G. , Riederer Stephen J. , Wright Ronald C. , Liu Yu , Farzaneh Farhad 
Published: March 2007

AbstractWe describe a system which forms MR angiographic images at high speed. Multiple axial sections are imaged sequentially using a 2DFT GRASS sequence with TR/TE 50/15 ms, 64 phase encodings per image. Reconstruction and projection of each image are performed immediately (within 220 ms) after data for that image are acquired. The projection angiogram is constructed line by line as the scan progresses, thereby totally eliminating any additional time required for reconstruction and projection. © 1990 Academic Press, Inc.
Magnetic resonance imaging of blood vessels at high fields: In vivo and in vitro measurements and image simulation
Authors: Ogawa Seiji , Lee Tso‐Ming 
Published: March 2007

AbstractUnusually high image contrast in vivo magnetic resonance imaging of the brain becomes observable at high magnetic fields when the blood oxygenation level is lowered. The cause of the contrast has been attributed to a magnetic susceptibility effect induced by paramagnetic deoxyhemoglobin in red cells. When the cylinder axis of a blood vessel is not parallel to the main magnetic field, the susceptibility difference produces varying local fields around the blood vessel. In gradient‐echo images, not in spin‐echo images, these local fields cause intravoxel dephasing of the water signal of the surrounding tissue. This description of the contrast enhancement has been confirmed by a series of in vitro blood sample experiments and image simulations. A predicted contrast change has been demonstrated in brain images of a mouse placed at two different orientations in the magnet. From the simulated images, the dependence of the contrast on the field strength has been estimated. © 1990 Academic Press, Inc.