bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of cerebral blood flow by volume‐selective 19F NMR spectroscopy
Authors: van Zijl Peter C. M. , Ligeti Laszlo , Sinnwell Teresa , Alger Jeffry R. , Chesnick A. Scott , Moonen Chrit T. W. , McLaughlin Alan C. 
Published: March 2007

AbstractA stimulated echo sequence was used to obtain 19F NMR spectra from within a 4‐ml voxel in a cat brain. The time dependence of the 19F NMR signal from an inert gas (CHF3) was used to calculate the blood flow in the voxel. The position of the voxel was selected using a 1H MR image. © 1990 Academic Press, Inc.
RF cavity resonator and split‐resonator designs
Authors: Mansfield P. , McJury M. , Glover P. , Clemence M. 
Published: March 2007

AbstractA simple high‐pass cavity resonator has been constructed for NMR imaging use at 500 MHz. A capacitative circuit arrangement is used to drive the device. A novel split‐coil or half‐resonator design is also introduced for lower‐frequency operation with applications in whole‐body medical imaging. © 1991 Academic Press, Inc.
Flow‐independent magnetic resonance projection angiography
Authors: Wright G. A. , Nishimura D. G. , Macovski A. 
Published: March 2007

AbstractThe performance of current, flow‐based sequences for imaging vasculature using MR is severely restricted in regions with inherently slow flow. We address this problem with a flow‐independent imaging method. Specifically, we generate projection images of blood in the limbs while suppressing signal from all other tissues (primarily skeletal muscle, bone marrow, and subcutaneous fat) using a flow‐compensated, water‐selective, short TI inversion recovery sequence with a long echo time. We experimentally evaluate the effectiveness of this sequence and present in vivo results clearly demonstrating the method's potential. © 1991 Academic Press, Inc.
Surface coil spectroscopic imaging: Time and spatial evolution of lactate production following fluid percussion brain injury
Authors: Cohen Y. , Sanada T. , Pitts L. H. , Chang L.‐H. , Nishimura M. C. , Weinstein P. R. , Litt L. , James T. L. 
Published: March 2007

AbstractDetailed temporal and spatial distributions of lactate production are presented for graded fluid‐percussion brain injury in the rat. A one‐dimensional proton spin‐echo spectroscopic imaging (ID SESI) technique, performed with a surface coil, is presented and evaluated. This technique, which represents a practical compromise, provides spatially localized proton nuclear magnetic resonance (NMR) brain spectra from a series of small voxels (<0.15 cm3) in less than 10 min, thus enabling both spatial and temporal monitoring of lactate production. These high‐resolution lactate maps are correlated with hyperintense regions observed in T2‐weighted images taken 10 h after impact, which, in turn, correlate with histology. The data demonstrate that, following severe trauma there is delayed production and propagation of lactate to regions of the brain that are remote from the trauma site. The extent of lactate production depends on the severity of impact. More significantly, the data show that following severe trauma, local lactate concentrations exceed 15 μmol/ g, the concentration that has been claimed as the threshold for brain injury. Therefore high lactate levels cannot be ruled out a priori as a possible factor in brain injury following severe head trauma. © 1991 Academic Press, Inc.
Multiple‐readout selective inversion recovery angiography
Authors: Wang Samuel J. , Nishimura Dwight G. , Macovski Albert 
Published: March 2007

AbstractWe have developed a variation of selective inversion recovery (SIR) angiography that allows us to obtain a collection of several angiograms within the same acquisition time previously required to obtain a single image. In basic SIR, a single readout is performed after the tagging inversion pulse. In multiple‐readout SIR, a succession of readout pulses is applied following the inversion pulse. By varying the gradients appropriately during the successive readouts, we can obtain a set of multiple projection‐angle angiograms, or, by appropriately spacing the readouts throughout the cardiac cycle, we can obtain a set of time‐resolved angiograms. This technique allows us to obtain additional spatial or temporal information without increasing total scan time. A sequence of increasing flip‐angle read pulses is used to maintain a constant signal level across the images. A trade‐off exists between SNR and the number of images acquired. © 1991 Academic Press, Inc.
Arrays of mutually coupled receiver coils: Theory and application
Authors: Wright Steven M. , Magin Richard L. , Kelton James R. 
Published: March 2007

AbstractSpecialized receiver coils having a small sensitive region can provide an improvement in SNR for MR imaging and spectroscopy, at the expense of limiting the usable field of view. This work presents a technique for designing coil arrays that allows the size and location of the sensitive region to be selected remotely. Only one element of the coil array is directly connected to the receiver, allowing flexibility in system design and implementation. A method is presented for the analysis and design of mutually coupled coil arrays of any number of elements of arbitrary shape. The analysis includes mutual coupling effects between primary coils, to allow multiple primary coils to be used simultaneously. A controller system allows remote selection of the sensitive region and automatically matches the impedance of the array to the preamplifier. Results obtained using a mutually coupled coil array designed for spine imaging are shown. © 1991 Academic Press, Inc.
Effect of oral contraception on water‐suppressed proton NMR spectra of plasma
Authors: Carlier Pierre G. , Vaesen Francis , Gilles Raymond G. , Fradin Elisabeth A. , Rorive Georges L. 
Published: March 2007

AbstractLipid linewidths were measured in the plasma proton spectra of young women. The individuals taking a contraceptive pill associating ethinyloestradiol and levonorgestrel or norethisterone were found with an average linewidth 2.5 Hz narrower than controls. As this drug regimen systematically induces an increase in plasma VLDL and a decrease in HDL/LDL ratio, our observation supports the theory that the Fossel test reflects plasma lipids abnormalities in cancer patients. © 1991 Academic Press, Inc.
An evaluation of MRI contrast in the uterus using synthetic imaging
Authors: Lange Robert C. , Duberg Arthur C. , McCarthy Shirley M. 
Published: March 2007

AbstractUsing a 1.5‐T system, we investigated the contrast in MR images of the uterus using a synthetic imaging program that was capable of producing images with TR values of 20 to 10220 ms and TE values of 1 to 511 ms. Synthetic images were calculated from images obtained on six normal women of reproductive age. The synthesized uterine images were essentially indistinguishable from acquired images with the same TR and TE parameters. Cervical and uterine anatomy could be clearly differentiated in synthetic images with a TE = 80 ms when the TR was as low as 100 ms. We conclude that the zonal anatomy of the uterus can be demonstrated using TR values that are much lower than those usually used for demonstrating uterine anatomy. © 1991 Academic Press, Inc.
On the Transverse relaxation rate enhancement induced by diffusion of spins through inhomogeneous fields
Authors: Hardy Peter , Henkelman R. Mark 
Published: March 2007

AbstractThe design of magnetic particles as a magnetic resonance contrast agent will rely on the prediction of their ability to induce transverse relaxation among the surrounding protons. There exists several divergent predictions of the contribution of these agents to 1 / T2. This article points out a problem, commonly overlooked, in the development of expressions for the relaxation enhancement which has led some workers to the derivation of results inappropriate for large magnetic particles. The size of the magnetic inhomogeneity created by the particle precludes the averaging of the interaction over a single proton unless it experiences an average field in the time T between pulses. Computer simulations following the trajectories of diffusing water molecules in inhomogeneous fields are shown to be the correct approach to dealing with large inhomogeneities. © 1991 Academic Press, Inc.
Measurement of the blood‐brain barrier permeability and leakage space using dynamic MR imaging. 1. Fundamental concepts
Authors: Tofts Paul S. , Kermode Allan G. 
Published: March 2007

AbstractLeakage of Gd‐DTPA through a defective blood‐brain barrier is measured quantitatively using dynamic MRI scanning, in which repeated scans are made after a bolus injection. Image registration artifacts are minimized; a dose of 0.1 mM/kg and an IR sequence enable enhancement to be measured quantitatively. The triexponential enhancement curve is fitted to a theoretical model based on compartmental analysis. The transfer constant, or permeability surface area product per unit volume of tissue (k), and leakage space per unit volume of tissue (y) are measured. Estimates for a quickly enhancing multiple sclerosis lesion are k = 0.050 min−1, v1 = 21%; for a slow one k = 0.013 min−1, v1 = 49%. This implies permeability in the range 4‐17 × 10−6 cm s−1, in broad agreement with other physiological methods. The method is noninvasive and can be used to make serial measurements in patients and in experimental animal models. The time course of pathological aspects of diseases with blood‐brain barrier breakdown, such as multiple sclerosis, tumors, and infections (e.g., HIV) can be studied, along with their response to therapy. The measurements are of physiological variables and are therefore independent of imaging equipment and field. © 1991 Academic Press, Inc.
Applications of nuclear magnetic cross‐relaxation spectroscopy to tissues
Authors: Grad Jonathan , Mendelson Daniel , Hyder Fahmeed , Bryant Robert G. 
Published: March 2007

AbstractMagnetic cross‐relaxation in aqueous heterogeneous systems is a long established phenomenon that makes the observable decay constants for the system mixtures of more fundamental relaxation times which characterize the relaxation of the coupled components. By exploiting the magnetic relaxation coupling between the water spins and the immobilized spins in a tissue, the water‐proton‐signal intensity may be used to map indirectly a frequency response that is directly related to the 1H NMR spectrum of the immobilized components of the tissue. This method is applied to a number of rat tissues to determine whether there are significant differences among tissues that might be exploited in applications of this experiment to diagnostic magnetic imaging. Significant differences are found among nine rat tissues studied, which suggests that the experimental approach may be used to superimpose fundamentally new information, the dynamic character of the usually unobservable immobilized macromolecular components of the tissue, on a magnetic image. © 1991 Academic Press, Inc.
In vivo Quantitative characterization of trabecular bone by NMR
Authors: Ford John C. , Wehrli Felix W. 
Published: March 2007

AbstractIn trabecular bone the NMR linewidth is found to be governed by the magnetic field inhomogeneity arising from the difference in magnetic permeability between bone and marrow. T21 was measured in vivo in the distal femur by interferometry and localized spectroscopy. Both methods showed T21 to be inversely related to trabecular plate density. © 1991 Academic Press, Inc.
Real‐time flow measurements using echo‐planar imaging
Authors: Guilfoyle D. N. , Gibbs P. , Ordidge R. J. , Manwield P. 
Published: March 2007

AbstractThe ultra‐high‐speed echo‐planar imaging (EPI) method is combined with velocity encoding prior to EPI read‐out, thereby allowing real‐time measurement of flow. Results of EPI flow measurement experiments are presented on phantoms and human volunteers. © 1991 Academic Press. Inc.
Volume rendering and connectivity algorithms for MR angiography
Authors: Cline Harvey E. , Dumoulin Charles L. , Lorensen William E. , Souza Steven P. , Adams William J. 
Published: March 2007

AbstractSeveral display algorithms for three‐dimensional angiographic data are evaluated. The mathematical analysis assumes additive Gaussian noise to predict the background distribution function for maximum intensity projection, sum projection, and connectivity display methods. In the maximum intensity projection method the mean noise level increases with the number of voxels in the ray, while in the sum projection the noise distribution width increases with the projection thickness, but the mean level remains constant. Comparisons of maximum intensity projection, sum projection, and connectivity algorithms applied to an MR angiogram of the circle of Willis are made. Measurements of the noise distribution are in agreement with the analysis. Algorithms combining connectivity with maximum intensity and sum projection are also evaluated. In these methods, a projection image is created using only the voxels marked by connectivity, typically with a 6% threshold of the data. Fine vessels are resolved and background noise is reduced in agreement with the analysis. © 1991 Academic Press. Inc.
Sodium MRI with coated magnetite: Measurement of extravascular lung water in rats
Authors: Lancaster Luke , Bogdan Andrew R. , Kundel Harold L. , McAffee Bethanne 
Published: March 2007

AbstractThis study was done to see if signal intensity in sodium images of edematous rat lungs made after iv administration of a negative intravascular contrast agent could serve as a measure of the edema fluid present. First, a method to produce a stable condition of hydrostatic pulmonary edema was developed and verified by CT. Second, dose‐response curves for coated magnetite preparations were constructed by giving edematous rats vaned doses of these preparations and measuring signal intensity changes of various organs by sodium MRI in a 31‐cm‐bore 1.9‐T magnet. Third, rats were given varied levels of pulmonary edema followed by a constant dose of coated magnetite to eliminate the plasma sodium signal. Finally, coated magnetite particles of two sizes were administered to rats, and the differences in effects on signal from various organs were measured. Signal intensity of the lungs after magnetite correlated (r = 0.86) with extravascular lung water measured gravimetrically, suggesting that sodium MRI may be useful for measuring pulmonary edema fluid. Smaller particles appear to remain in the blood longer than larger particles. © 1991 Academic Press, Inc.
Proton chemical‐shift imaging with magnetically and electrically inhomogeneous objects
Authors: Nozokido Tatsuo , Yamamoto Etsuji , Kohno Hideki , Yamamoto Shinji 
Published: March 2007

AbstractProton chemical‐shift imaging with the elimination of three kinds of artifacts caused by main magnetic field inhomogeneities, susceptibility distributions of imaging objects, and the electromagnetic properties of radiofrequency (RF) fields is presented in this paper. In addition, the last of these artifacts, which is dependent upon the conductivity distributions of objects, especially in high‐tesla imaging, is also demonstrated experimentally. The method proposed here enables the reconstruction of artifact‐free water/fat separation images by using simple image data manipulations without the complicated phase‐unwrap process, even with main magnetic field inhomogeneities larger than the chemical‐shift difference between water and fat magnetizations. © 1991 Academic Press, Inc.
A technique of double‐resonant operation of 19F and 1H quadrature birdcage coils
Authors: Lu Dongfeng , Joseph Peter M. 
Published: March 2007

AbstractA technique was developed to change the resonant frequency of a rotating field birdcage coil from 19F resonance (76.14 MHz) to 1H resonance (80.92 MHz). This was done by inserting an additional shield with a smaller radius on the coil which resonates at 19F. It was shown that the inhomogeneity introduced by reducing the shield radius is not significant. A working coil built with this technique produced both 19F and 1H images satisfactorily. © 1991 Academic Press, Inc.
Hybrid MR angiography and Fourier velocity imaging using two echo 3D acquisition
Authors: Hou Ping , Parker Dennis L. , Blatter Duane D. , Robison Ronald O. 
Published: March 2007

AbstractFourier velocity imaging can be accomplished without cardiac gating from the second echo of a standard 3D MR angiography sequence. The stepped bipolar velocity encoding gradient is obtained by adding a gradient pulse opposite in area to the spatial phase encoding gradient. In this technique, Fourier images of three spatial coordinates are obtained from the first echo and images of two spatial coordinates and one velocity component are obtained from the second echo. © 1991 Academic Press, Inc.
Functional variations in parenchymal microvascular systems within the brain
Authors: Fenstermacher Joseph , Nakata Hiroyuki , Tajima Atsushi , Lin Shinn‐Zong , Otsuka Tadahiro , Acuff Virgil , Wei Ling , Bereczki Daniel 
Published: March 2007

AbstractVariations in microvascular system functions were observed among a number of brain areas. The rates of local blood flow varied 18‐fold among areas and were extremely high in neuroendocrine structures. Marked differences in blood flow were also found within some brain structures. The volume of radiolabeled blood in perfused parenchymal micro‐vessels ranged from 5 to 70 μl/g and correlated closely with local cerebral blood flow. The hematocrits within parenchymal microvessels were 45–75% of the arterial hematocrit, which indicates that red cells more rapidly traverse brain microvessels than do plasma proteins. The mean transit times of blood through parenchymal microvessels were extremely short and ranged from 0.3 to 0.6 s. © 1991 Academic Press, Inc.
Diffusion imaging using stimulated echoes
Authors: Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Frahm Jens 
Published: March 2007

AbstractThe application of stimulated echo acquisition mode (STEAM) sequences for NMR imaging of diffusion is especially suited for spins with T1 ≫ T2 as, e.g., encountered in proton NMR studies of biological systems. Molecular self‐diffusion coefficients may be calculated from a set of diffusion‐weighted images acquired with different gradient strengths. A variation of the diffusion time allows the determination of restricted and/or anisotropic diffusion in cellular systems ranging from plants to humans. Problems associated with the presence of unavoidable macroscopic motions in vivo are demonstrated in diffusion studies of human brain. Motion ghosting in diffusion‐weighted images may be overcome by means of a high‐speed STEAM sequence yielding single‐shot images within subsecond acquisition times. © 1991 Academic Press, Inc.
Magnetic resonance diffusion/perfusion phantom experiments
Authors: Lorenz Christine H. , Pickens David R. , Puffer Donald B. , Price Ronald R. 
Published: March 2007

AbstractRecently, several models for determining microcirculatory parameters using magnetic resonance imaging have been proposed. These include the intravoxel incoherent motion (IVIM) model, the intravoxel coherent motion (IVCM) model, and various tracer models. In order to evaluate these models before extension into physiological systems, phantom studies were used to assess model assumptions, measurement uncertainties, and sensitivity to changes in perfusion. Emphasis is placed on the IVIM model, but the techniques discussed could be extended to evaluation of other models as well. An overview of considerations in pulse sequence development, phantom design, and data interpretation is presented for a variety of phantoms ranging in complexity from stationary volumes of fluid and mechanically pumped phantoms to isolated animal kidneys and finally to an in vivo animal model. © 1991 Academic Press, Inc.
Contrast agents and cerebral hemodynamics
Authors: Rosen Bruce R. , Belliveau John W. , Buchbinder Bradley R. , McKinstry Robert C. , Porkka Leena M. , Kennedy David N. , Neuder Michelle S. , Fisel C. Richard , Aronen Hannu J. , Kwong Kenneth K. , Weisskoff Robert M. , Cohen Mark S. , Brady Thomas J. 
Published: March 2007

AbstractContrast‐enhanced magnetic resonance imaging of regional cerebral hemodynamics is discussed. Techniques for measuring cerebral blood volume (CBV) have been validated in animal models and have recently been applied to human studies. Factors affecting CBV measurement in pathologic tissue are addressed. Extension of these techniques to the measurement of cerebral blood flow is presented. © 1991 Academic Press, Inc.
The validation of freely diffusible tracer methods with NMR detection for measurement of blood flow
Authors: Neil Jeffrey J. 
Published: March 2007

AbstractWhile the general theory of measuring organ perfusion using exogenously administered freely diffusible tracers was originally formulated over 40 years ago, the application of NMR techniques for tracer detection is a recent development. A brief theoretical review and discussion of the literature validating the use of deuterium and fluorine as NMR‐detectable tracers is provided. © 1991 Academic Press, Inc.
The visibility of the 1H NMR signal of ethanol in the dog brain
Authors: Moxon Leith N. , Rose Stephen E. , Haseler Luke J. , Galloway Graham J. , Brereton Ian M. , Bore Peter , Doddrell David M. 
Published: March 2007

AbstractIn Vivo, high‐resolution, volume‐selected 1H NMR spectroscopy was used to monitor the concentration of ethanol in the dog brain following intravenous injection of ethanol. Equilibration of ethanol in the body water should result in approximately equivalent concentrations of ethanol in the blood and brain. However, the mean equilibrium brain ethanol concentration determined using N‐acetylaspartate as an internal standard was only 23 ± 5% of the blood ethanol concentration. The disparity between blood and brain ethanol concentrations was attributed to underestimation of the ethanol concentration due to overlapping resonances with NAA and to T2 attenuation or possible nondetection of the 1H signal from ethanol bound at the surface of cell membranes and partitioned into the hydrophobic core of membrane lipids. © 1991 Academic Press, Inc.
Gadolinium‐labeled liposomes containing various amphiphilic Gd‐DTPA derivatives: Targeted MRI contrast enhancement agents for the liver
Authors: Kabalka G. W. , Davis M. A. , Moss T. H. , Buonocore E. , Hubner K. , Holmberg E. , Maruyama K. , Huang L. 
Published: March 2007

AbstractUnique paramagnetic liposomal contrast agents were synthesized and utilized for selective augmentation of T1 MR imaging of the livers of normal Balb/c mice. A series of amphipathic gadolinium complexes, which mimic phospholipids, was incorporated into the lamella of small unilamellar liposomes such that they become an integral part of its surface. The amphipathic complexing agents consisted of DTPA reagents in which two stearyl chains are attached via amide, ester, and thioester linkages. The in vitro stability and the in vivo lifetimes of the new amphipathic agents were dependent on the method used to attach the long‐chain alkyl groups. © 1991 Academic Press, Inc.
31P NMR spectroscopy of 9L cell line in culture: Differential effects of high temperature on anchored cells and spheroids
Authors: Suzuki Nobuyuki , Kwee Ingrid L. , Tamas Laszlo B. , Nakada Tsutomu 
Published: March 2007

AbstractThe differential effects of high temperature on 9L rat gliosarcoma cells cultured in two distinctive forms, namely, anchored monolayer cells and multicellular spheroids, were investigated using 31P nuclear magnetic resonance spectroscopy. The critical temperatures resulting in irreversible changes in cellular energetics were found to be significantly different: 45°C for anchored cells and 43°C for multicellular spheroids, respectively. Phosphonionoester levels in multicellular spheroids were found to be consistently higher than those in anchored monolayer cells regardless of the temperature to which they were exposed. The study demonstrates that tissue derived from a single cell line may exhibit different metabolic properties depending on its growth pattern. © 1991 Academic Press, Inc.