bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative flow measurements on phantoms and on blood vessels with MR
Authors: Meier D. , Maier S. , Bösiger P. 
Published: March 2007

AbstractA broad spectrum of MR methods has been published in the last few years for the visualization and the quantification of flow in human blood vessels. We describe the results of an extended study to measure the flow quantitatively using the MR phase modulation method. A gradient echo sequence which allows short repetition times was synchronized with the ECG. The instantaneous velocity profiles and the integrated flow rate can be determined throughout the cardiac cycle in up to 45 consecutive time intervals. The instantaneous velocity distributions can be displayed as 2D profiles over the lumen of the blood vessel. The technique has been successfully evaluated with a set of phantom experiments. Following this, quantifications of the blood flow rates in vivo were performed on the abdominal aortas of healthy volunteers. The MR flow results were compared to those obtained with conventional Doppler ultrasound examinations. The results of both methods are in good quantitative agreement. © 1988 Academic Press, Inc.
Deuterium NMR cerebral imaging in Situ
Authors: Ewy Coleen S. , Ackerman Joseph J. H. , Balaban Robert S. 
Published: March 2007

AbstractNuclear magnetic resonance imaging of deuterium is demonstrated in cat brain in vivo and in situ at 4.7 T magnetic field strength. Images were acquired at 4–5% deuterium enrichment, using D2O as a nuclear spin label, with as little as 10‐s time resolution. This suggests the potential application of D2O as an exogenous MRI label for quantitative flow imaging or contrast enhancement. The efficient quadrupolar relaxation mechanism of the deuterium nuclide results in a short ca. 250 ms spin–lattice relaxation time (T1). This allows for rapid signal averaging, thus increasing signal‐to‐noise in the deuterium image. Additionally, three widely dispersed deuterium spin–spin relaxation times (T2) are observed of ca. 10, 40, and 400 ms which provide high compartmental image contrast, thus yielding information of physiological as well as anatomical interest. T2‐weighted deuterium cerebral images are presented showing marked tissue relaxation discrimination. © 1988 Academic Press, Inc.
Snapshot head imaging at 0.5 T using the echo planar technique
Authors: Ordidge R. J. , Coxon R. , Howseman A. , Chapman B. , Turner R. , Stehling M. , Mansfield P. 
Published: March 2007

AbstractThe echo planar imaging (EPI) method and related variants of this technique can produce complete two‐dimensional images from the data collected in a single experiment lasting a fraction of a second. EPI methods are used at 0.5 T to produce snapshot images of the human head with a suatial resolution of less than 2 mm. © 1988 Academic Press, Inc.
In vivo localized proton spectroscopic studies of human gastrocnemius muscle
Authors: Narayana P. A. , Jackson E. F. , Hazle J. D. , Fotedar L. K. , Kulkarni M. V. , Flamigs D. P. 
Published: March 2007

AbstractIn vivo proton magnetic resonance spectroscopy studies of gastrocnemius muscle were performed in six normal volunteers. Both spatially resolved spectroscopy (SPARS) and stimulated echo acquisition mode (STEAM) sequences were used for volume localization. A number of water suppression sequences have been combined with these localization schemes. Among the various techniques investigated in these studies, STEAM with an inversion pulse (T1 ‐discriminated spectrum) seems to have the best potential for in vivo localized high‐resolution proton spectroscopy studies of human muscle. © 1988 Academic Press, Inc.
Quantitative NMR measurements of hippocampal atrophy in Alzheimer's disease
Authors: Seab J. P. , Jagust W. J. , Wong S. T. S. , Roos M. S. , Reed B. R. , Budinger T. F. 
Published: March 2007

AbstractNuclear magnetic resonance (NMR) imaging was employed to study 10 patients with Alzheimer's disease (AD) and seven healthy elderly control subjects. Coronal sections were used to make volumetric measurements of the hippocampus, ventricles, subarach‐noid space, and brain parenchyma. The hippocampal volume (normalized relative to the size of the lenticular nucleus) was reduced by 40% in the AD group compared to the controls, with no overlap between the two groups. Overall measures of brain atrophy and ventricular and sulcal enlargement also showed significantly different group means, although with overlap between the two groups. Hippocampal atrophy did not correlate with either overall brain atrophy or dementia severity, although the degree of brain atro‐phy was correlated with dementia severity. These results show that NMR is capable of providing in vivo quantification of diminished hippocampal size in AD which is not cor‐related with overall brain atrophy and which may differentiate AD from normal aging. © 1988 Academic Press, Inc.
Rapid31P NMR test of liver function
Authors: Thoma William J. , Uǧurbil Kâmil 
Published: March 2007

AbstractThe 31P NMR spectrum of perfused rat liver was found to be dependent on the exogenous carbon available to the tissue. When pyruvate was supplied to liver initially perfused with lactate, Pi decreased, phosphoenol pyruvate and phosphomonoesters increased, and nucieotide pools remained the same. It is proposed that these changes can be used to evaluate liver function. © 1988 Academic Press, Inc.
Noise reduction in magnetic resonance imaging
Authors: Brosnan Thomas , Wright Graham , Nishimura Dwight , Cao Qizhi , Macovski Albert , Sommer F. Graham 
Published: March 2007

AbstractThis paper describes a noise‐reduction technique applicable to multiple‐measurement systems. This method, known as measurement‐dependent filtering (or MDF), can be used to advantage in a number of MRI applications. We present the general theory for one of these applications, material‐canceled projection imaging. We discuss and show the results of MDF for material‐canceled images as well as for heavily T2‐weighted spinecho images and computed T2 images. Significant improvements in SNR are demonstrated while spatial resolution is preserved. © 1988 Academic Press, Inc.
Multicompartment analysis of blood flow and tissue perfusion employing D2O as a freely diffusible tracer: A novel deuterium NMR technique demonstrated via application with murine RIF‐1 tumors
Authors: Kim Seong‐Gi , Ackerman Joseph J. H. 
Published: March 2007

AbstractDeuterium NMR is employed in concert with multicompartment kinetic analysis for measurement of tissue blood flow and perfusion through a bolus administration of D2O as a freely diffusible tracer. The traditional single‐compartment and two‐compartment in‐parallel flow models with no tracer recirculation are briefly discussed. The two‐compartment in‐series flow model with recirculation is developed to account for reflow of the stable (slowly excreted) deuterium tracer. With this model a monoexponential tracer washout curve is predicted. The rate ofblood flow and tissue perfusion is readily extracted by three‐parameter monoexponential analysis of the residue decay curve. A three‐compartment model with recirculation, incorporating one compartment in‐series with two compartments in‐parallel, is developed for analysis of biexponential tracer washout curves. With this model the flow rates through the two in‐parallel compartments (i.e., fast and slow) and the volume fractions of these two compartments are obtained by five‐parameter biexponential analysis of the residue decay curve. Application of these multicompartment tracer‐recirculation flow models is demonstrated with in situ determinations of murine RIF‐1 tumor blood flow and tissue perfusion. The blood flow rates determined by deuterium NMR and analyzed by the multicompartment flow models agree well with those determined by others using radiolabels. A companion article (S.‐G. Kim and J. J. H. Ackerman, Cancer Res. 48, 3449‐3453, 1988) discusses in more depth the practical aspects of applying these multicompartment models to tumor blood flow measurement. © 1988 Academic Press, Inc.
A 31P NMR study of the GI tract: Effect of fructose loading and measurement of transverse relaxation times
Authors: Karczmar G. S. , Tavares N. J. , Weiner M. W. 
Published: March 2007

AbstractThe effect of fructose loading on high‐energy phosphates in the jejunum, ileum, and large intestine of rats was studied using 31P NMR. Following fructose loading, an increase in the intensity of the PME resonance was observed in the jejunum, indicating an accumulation of fructose‐1‐phosphate. There were no significant changes in ATP or Pi. This demonstrates that the activity of fructokinase in the jejunum can be monitored by 31P NMR. Fructose loading had no detectable effect on metabolite levels in the ileum and large intestine. Resolution of intestinal spectra was poor due to unusually large linewidths and the presence of broad underlying signals. To study the mechanism of line broadening, the T2's of the phosphorus resonances were measured using a solenoidal coil. The T2's ofthe ATP or Pi, PME. and PCr resonances were much longer than the T2's, suggesting that the linewidths of these resonances are primarily due to susceptibility gradients and/or compartmentation of metabolites. Other signals, particularly in the PDE region, were homogeneously broadened and had very short T2's. Spin echoes obtained with evolution times of 1 to 4 ms suppressed these broad components, with little loss of intensity in the inhomogeneously broadened resonances; as a result, resolution was improved. © 1989 Academic Press, Inc.
Magnetic resonance imaging with adiabatic pulses using a single surface coil for RF transmission and signal detection
Authors: Garwood Michael , Uĉurbil Kǎmil , Rath Alan R. , Bendall M. Robin , Ross Brian D. , Mitchell Steven L. , Merkle Hellmut 
Published: March 2007

AbstractIn order to overcome the problems that arise from nonuniform B1, fields, there has been interest in developing pulses that are insensitive to large variations in RF power. Pulses derived from adiabatic passage principles that can execute spin inversion, excitation, and 90°and 180° plane rotations in the presence of B1, inhomogeneities have recently been described. When driven with optimized modulation functions, these pulses can execute uniform excitation, refocusing, and slice‐selective inversion over a 10‐fold or greater variation in B1 magnitude. This insensitivity to B1 strength enables the execution of T and/or T weighted spin‐echo imaging experiments using coils, such as the surface coil, with extremely inhomogeneous B1 profiles. We have successfully acquired images with these pulses at 200 MHz using a single surface coil as the transmitter and receiver. Images of the slice definition, the region over which the excitation and refocusing pulses operate with a surface coil, and brain images obtained with slice planes perpendicular to the plane of the surface coil are presented. Results demonstrate that these pulses can be transmitted with a surface coil to yield high‐quality T and/or T weighted images without B1, artifacts. © 1989 Academic Press, Inc.
In Vivo functioning of creatine phosphokinase in human forearm muscle, studied by 31P NMR saturation transfer
Authors: Rees Deborah , Smith Michael B. , Harley Judith , Radda George K. 
Published: March 2007

Abstract31P nuclear magnetic resonance (NMR) saturation transfer has been used to measure enzymatic flux through the creatine phosphokinase reaction in the direction of ATP synthesis in the human forearm muscle flexor digitorum superficialis. Modification of the ratio method for measurement of spin‐lattice relaxation (R. Freeman, H. D. W. Hill, and R. Kaptein, J. Mags. Reson. 7, 82 (1972) was tested and used to appreciably shorten the duration of the measurement. Under conditions of steady state work intracellular pH decreased slightly by 0.06 units and the spin‐lattice relaxation time of phosphocreatine in muscle was unchanged, while flux from phosphocreatine to ATP was 64 ± 10% of the resting value. This is contrary to the increase in flux of 155% predicted from previous saturation transfer studies carried out in vitro on rabbit skeletal muscle creatine phosphokinase using metabolite concentrations to mimic those in vivo (E. A. Shoubridge, J. L. Bland, and G. K. Radda, Biochim. Biophys. Acta 805, 72 (1984). This discrepancy could be accounted for by an underestimation of the ADP concentrations to which the enzyme is exposed due to inaccurate assumptions about the total metabolite concentrations, or possibly by compartmentation of creatine phosphokinase and its reactants. © 1989 Academic Press, Inc.
Water suppression with B0 field gradient homospoil pulses in high‐resolution NMR spectroscopy
Authors: Brereton I. M. , Field J. , Moxon L. N. , Irving M. G. , Doddrell D. M. 
Published: March 2007

AbstractThe combination of a frequency nonselective excitation suppression method (1331 sequence) with selective excitation followed by gradient‐induced dephasing of water transverse magnetization yielded suppression ratios of greater than 10,000:1. The need for gradient preemphasis and correction of Bo field shifts is discussed. The suppression efficiency of this method compared favorably to results obtained using the CPMG spin‐ echo technique to observe metabolite resonances in a urine sample. © 1989 Academic Press, Inc.
Determination of halothane distribution in the rat head using 19F NMR technique
Authors: Wyrwicz A. M. , Conboy C. B. 
Published: March 2007

AbstractThe distribution of halothane in the rat head was examined with 19F NMR rotatingframe zuegmatography and 2DFT 19F NMR imaging. The rotating frame experiments were conducted at varying times following anesthesia to assess the time dependence of the halothane distribution. The results of these experiments demonstrate that halothane and halothane metabolite are unequally partitioned through the rat tissues examined. 19F spin‐echo imaging experiments were conducted immediately following anesthesia. The results of these experiments are compared with those of the spectroscopic technique. © 1989 Academic Press, Inc.
Single‐scan volume‐selective spectral editing by homonuclear polarization transfer
Authors: Knüttel A. , Kimmich R. 
Published: March 2007

AbstractAn RF and field gradient pulse sequence is presented permitting the single‐scan volume‐selective spectral editing of the signals of coupled spins. The attribute “single scan” means that the editing of resonance lines is performed in each accumulation or phase cycling scan rather than by subtraction of independently acquired signals. As an example the methyl line of lactate has been investigated. The method is considered to be a useful tool in biomedical research using lactate as an ischemic parameter. The basic principles applied are the VOSY pulse scheme for volume selection and the INEPT sequence for homonuclear polarization transfer from the CH to the CH3 groups. As an intrinsically single‐scan editing method (“homonuclear single‐scan VOSING procedure”), the pulse train is expected to provide results that are more reliable than the two‐scan subtraction methods previously reported. © 1989 Academic Press, Inc.
23Na NMR measurement of the maximal rate of active sodium efflux from human red blood cells
Authors: Knubovets T. L. , Revazov A. V. , Sibeldina L. A. , Eichhoff U. 
Published: March 2007

AbstractThe method for 23Na NMR measurement of the maximal rate of active Na+ efflux from human red blood cells (RBC) is proposed. The nonpenetrating paramagnetic shift reagent (SR) bis(tripolyphosphate)dysprosium(III) complex is used to distinguish extracellular Na+ ions from intracellular. RBC are proved to retain their physiological activity in the presence of SR. Intracellular Na+ is shown to be 100% NMR visible. The levels of intracellular and extracellular Na+ and K+ ions are changed to decrease their concentration gradients across the erythrocyte membrane to make active Na+ efflux the only 23Na NMR measurable process; so the integrated areas of intra‐and extracellular Na+ peaks remain invariant throughout the incubation period in the presence of 0.25 mM ouabain, a specific inhibitor of Na+, K+‐ATPase. The accuracy of the proposed technique is evaluated to be 10%. The maximal Na+ efflux is determined to be 10.1 ± 1.0 mM/h/liter of Cells. © 1989 Academic Press, Inc.
Determination of triacylglycerol lipase activity using carbon‐13‐labeled triacylglycerols and nuclear magnetic resonance spectroscopy: Evidence that hepatic lipase hydrolyzes medium‐chain triacylglycerols
Authors: Dimand R. J. , Bradbury E. M. , Cox K. L. 
Published: March 2007

AbstractTriacylglycerol lipse activity was studied using glycerol [1‐13C] trioctanoate mixed with postheparin rat plasma. 13C NMR spectroscopy demonstrated triacylglycerol hydrolysis into free fatty acids with no difference at the 1,3 or 2 glycerol positions. There was no inhibition by high sodium concentration, consistent with lipase of hepatic origin. © 1989 Academic Press, Inc.
Addendum to “Rapid Local Rectangular Views and Magnifications: Reduced Phase Encoding of Orthogonally Excited Spin Echoes”
Authors: Conturo Thomas E. , Price Ronald R. , Beth Albert H. 
Published: March 2007

AbstractAttention is called to a previous work of Feinberg et al. on inner volume MRI, a work which was not known to the present authors when preparing a recent similar manuscript on imaging local fields of view. The rationale is discussed for tandemly offsetting the reconstruction window and excited volume. © 1989 Academic Press, Inc.
In vivo pharmacokinetics by electron magnetic resonance spectroscopy
Authors: Berliner Lawrence J. , Wan Xiaoming 
Published: March 2007

AbstractLow‐field in vivo electron spin resonance (ESR) has been used to follow the course of metabolism and distribution of a paramagnetic spin probe, 3‐carboxamido‐2,2,5,5‐tetramethylpyrrolidine‐1‐oxyl. Sprague‐Dawley rats (250‐300 g) were catheterized in the jugular vein and given serial doses ofthe nitroxide spin probe above. The decrease in the tail blood nitroxide ESR spectrum with the time was followed. This reflects both normal distribution/excretion and a significant metabolic step–reversible reduction of the nitroxide group to its hydroxylamine. The studies serve as important and useful comparisons to the nitroxide reduction kinetics in vitro while offering the important advantage of avoiding those non‐steady‐state artifacts frequently expected in ex vivo procedures. This study represents the first report of systematic in vivo phannacokinetics of a paramagnetic probe. © 1989 Academic Press, Inc.
The uncommon longitudinal relaxation dispersion of human brain white matter
Authors: Fischer Helmut W. , Van Haverbeke Yves , Schmitz‐Feuerhake Inge , Muller Robert N. 
Published: March 2007

AbstractHuman brain white matter exhibits an uncommonly strong dispersion of 1/T1 at high fields. An additional relaxation pathway via the myelin lipids, which are not directly visible to medical NMR due to their fast T2 decay, is proposed. Relaxation dispersion data are successfully analyzed on the basis of this model. © 1989 Academic Press, Inc.
Fluid shear and spin‐echo images
Authors: Kuethe Dean O. , Herfkens Robert J. 
Published: March 2007

AbstractBecause clinical studies have indicated that shear in fluids may be one of the major causes of magnetic resonance image artifacts, we imaged an apparatus that would separate the effects of shear from the plethora of other motion artifacts. The apparatus contained fluid between two concentric cylinders. To produce shear, we turned the outer cylinder. To produce motion without shear, we turned both cylinders as one. Shear rates near 200 s−1 (similar to those in large arteries) can cause pixel intensities either to increase 40% or decrease to background levels. Increases can occur when the velocities are nearly parallel to the phase‐encoding gradient. Decreases can occur when velocities are in the direction of the frequency gradient. The decreases are similar to those predicted from phase dispersion within a “voxel” so long as the voxel's phase warp does not exceed 2π. © 1989 Academic Press. Inc.
A model of acute regional myocardial ischemia and reperfusion in the rat
Authors: Sievers R. E. , Schmiedl U. , Wolfe C. L. , Moseley M. E. , Parmley W. W. , Brasch R. C. , Lipton M. J. 
Published: March 2007

AbstractStudies were conducted in 76 rats to describe and validate a new closed‐chest in vivo model for acute ischemia and reperfusion of the left coronary artery. Radiolabeled microsphere distribution in six rat hearts confirmed a significant reduction in arteriolar flow at the center of the ischemic zone (93% reduction of total myocardial counts compared to nonischemic region, P < 0.01) after 7 min of occlusion. Arteriolar flow returned to control values upon reperfusion. While hemodynamic parameters in 10 ratsduring 7 min of occlusion and 7 min of reperfusion were monitored, end diastolic pressures increased significantly (P < 0.01) during occlusion. Finally, the utility of this rat model was demonstrated in a study of contrast enhanced magnetic resonance imaging (N=4). Normal myocardium could not be differentiated from acutely ischemic myocardium on noncontrast‐enhanced MR images. After 5 min of myocardial ischemia and following contrast administration (albumin‐Gd‐DTPA), the ischemic zone appeared less enhanced than normal myocardium. Upon release ofthe occluder the left ventricular free wall once again yielded a homogeneous signal similar to that of the normal myocardium. © 1989 Academic Press, Inc.
Snapshot imaging at 0.5 t using echo‐planar techniques
Authors: Ordidge R. J. , Howseman A. , Coxon R. , Turner R. , Chapman B. , Glover P. , Stehling M. , Mansfield P. 
Published: March 2007

AbstractEcho‐planar imaging using a magnetic field strength of 0.5 T has resulted in an improvement in image quality compared with recent images published at 0.1 T. The sensitivity of the technique to main magnetic field inhomogeneity and transient eddy currents has necessitated innovations in gradient and radiofrequency coil design. These improvements are described, and new variations in the echo‐planar pulse sequence which provide better contrast and allow separate imaging of water and fat distributions are presented. © 1989 Academic Press, Inc.
Magnetic field modulation of receptor binding
Authors: Chiles Catherine , Hawrot Edward , Gore John , Byck Robert 
Published: March 2007

AbstractAlthough it is widely held that the magnetic fields encountered during magnetic resonance imaging (MRI) and other procedures have no discernible effect on biological systems, we find that at early times of incubation, the amount of binding of the neurotoxin, α‐bungarotoxin, to nicotinic acetylcholine receptor is significantly reduced in a constant 2.0‐T magnetic field. This finding suggests that steady magnetic fields can directly affect the functional activity of biologically important macromolecules, in this particular case a neurotransmitter receptor. © 1989 Academic press, Inc.
High field localized proton spectroscopy in small volumes: greatly improved localization and shimming using shielded strong gradients
Authors: van Zijl Peter C. M. , Moonen Chrit T. W. , Alger Jeffry R. , Cohen Jack S. , Chesnick Scott A. 
Published: March 2007

AbstractThe availability of shielded gradients facilitates accurate single‐voxel localized spectroscopy. Exact localization (90−99%) of volumes as small as 2 × 2 × 2 mm is demonstrated using a modified stimulated echo sequence. Strong gradient pulses (up to 200 mT/m) are employed to clear the stimulated echo of unwanted magnetization, enabling superior (single‐scan) shimming of the selected volume. In vivo and in vitro proton NMR results at 4.7 T are presented. © 1989 Academic Press, Inc.