bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensional magnetization‐prepared rapid gradient‐echo imaging (3D MP RAGE)
Authors: Mugler John P. , Brookeman James R. 
Published: March 2007

AbstractA new three‐dimensional imaging technique which is applicable for 3D MR imaging throughout the body is introduced. In our preliminary investigations we have acquired high‐quality 3D image sets of the abdomen showing minimal respiratory artifacts in just over 7 min (voxel size 2.7 × 2.7 × 2.7 mm3), and 3D image sets of the head showing excellent gray/white contrast in less than 6 min (voxel size 1.0 × 2.0 × 1.4 mm3). © 1990 Academic Press, Inc.
High‐resolution NMR spectroscopy of cerebral white matter in multiple sclerosis
Authors: Sappey‐Marinier Dominique 
Published: March 2007

AbstractMultiple sclerosis (MS) lesions have been shown by conventional methods to have major alterations in water and myelin lipid contents. To characterize these abnormalities more efficiently, NMR spectroscopy was used to evaluate water content by measuring relaxation times at 0.5 and 2.0 T. Subsequently, cholesterol content was obtained by using 1H NMR spectroscopy, while 31P NMR spectroscopy allowed measurement of the four main phospholipids and the inorganic phosphate concentrations in normal and pathological cerebral white matter samples. The relaxation times were significantly prolonged in MS lesions relative to normal white matter. Measured in different sample types, T 1 and T2 times increased with water content. Moreover, the T2 of normal‐appearing white matter was considerably lengthened. Analysis of white matter lipid composition using this method gave accurate values, which showed a significant decrease in phospholipids and cholesterol content in MS samples. © 1990 Academic Press, Inc.
NMR imaging in the earth's magnetic field
Authors: Stepišnik J. , Eržen V. , Kos M. 
Published: March 2007

AbstractThe most important and very expensive part of a magnetic resonance imaging set‐up is the magnet, which is capable of generating a constant and highly homogeneous magnetic field. Here a new MR imaging technique without the magnet is introduced. This technique uses the earth's magnetic field instead of a magnetic field created by a magnet. This new method has not yet reached the stage of medical application, but the first images obtained by MRIE (magnetic resonance imaging in the earth's field) show that the resolution is close to that expected based on sensitivity estimations. © 1990 Academic Press, Inc.
The effect of cardiopulmonary bypass on brain and heart metabolism: A 31P NMR study
Authors: Swain Julie A. , Robbins Robert C. , Balaban Robert S. , McDonald Thomas J. , Schneider Benjamin , Groom Robert C. 
Published: March 2007

AbstractThe development of a large animal preparation using 31P nuclear magnetic resonance (NMR) spectroscopy for the study of cerebral and myocardial metabolism during cardiopulmonary bypass (CPB) is reported. The effect of normothermic CPB on myocardial and cerebral metabolism was evaluated. Adolescent sheep were used which have low levels of 2,3 ‐diphosphoglycerate, a compound which can interfere with the calculation ofintra‐cellular pH and inorganic phosphate content. CPB was performed using standard procedures modified for the presence of a high magnetic field and limited access to the animal. High quality 31P NMR data were obtained from the brains and hearts of these animals before and during normothermic CPB. These results demonstrate that the initiation of normothermic CPB does not change high energy phosphate levels or intracellular pH. In particular, the decreased myocardial oxygen demand associated with CPB is not associated with improvement in the levels of adenosine triphosphate or phosphocreatine. The measurements of energy metabolism and intracellular pH of the brain and heart during CPB were possible within the constraints of the NMR experiment without compromising the CPB procedure. Combining NMR and CPB techniques permits future studies of cerebral and myocardial metabolism, especially those relating to ischemia. © 1990 Academic Press, Inc.
The role of membrane water permeability in characterization of pathologically altered human stomach tissues: NMR studies
Authors: Srejić Radivoje , Popov Danica V. , Boričić Ivan , Žuvela Marinki 
Published: March 2007

AbstractComparative NMR studies of normal and pathologically altered human stomach tissues were performed on the basis of proton T1 relaxation time measurements in the presence of high external concentrations of relaxation (contrast) agents manganese ethylenediaminetetraacetic acid (Mn‐EDTA) and gadolinium diethylenetriaminepentaacetic acid (Gd‐DTPA). Diffusion permeability of the cell membrane to water, Pd, was determined by measuring the longest proton T1 component sensitive to the exchange of water molecules through the cell membrane. Pathologically altered tissues showed substantially higher (2 to 10 times) average cell membrane permeabilities to water. © 1990 Academic Press, Inc.
1H MR imaging of anatomical compartments within the finger flexor muscles of the human forearm
Authors: Jeneson J. A. L. , Taylor J. S. , Vigneron D. B. , Willard T. S. , Carvajal L. , Nelson S. J. , Murphy‐Boesch J. , Brown T. R. 
Published: March 2007

AbstractFast T2‐weighted 1H MRI following exercise allows investigation of the location of muscle fiber activity within skeletal muscle. Using this method, we have demonstrated that the finger flexor muscles of the human forearm consist of anatomical compartments, located at various depths, which are involved individually in flexion of the index, middle, or ring and little fingers. The results of this study indicate that the exercise protocol in 31P MRS studies of the finger flexor muscles of the human forearm, in which a small surface coil is used for detection, should be carefully reviewed. © 1990 Academic Press, Inc.
Double EPI sequence with 180° RF pulses
Authors: Hennel F. , Jasinski A. , Tomanek B. 
Published: March 2007

AbstractRapid imaging can be performed in the magnetic field of low homogeneity using 180° RF pulses instead of gradient reversals to form a series of differently phase‐encoded echoes. A modified version of π‐pulsed EPI which samples the data in two complementary shots was designed. Its advantage for objects of short T2 is illustrated by phantom images. © 1990 Academic Press, Inc.
The relation of low frequency restoration methods to the gerchberg‐papoulis algorithm
Authors: Yan Hong , Mao Jintong 
Published: March 2007

AbstractIn magnetic resonance imaging, low frequency components can be allowed to saturate the analog to digital converter to reduce the quantization noise. These components can be estimated using least squares error estimation based low frequency restoration methods or the iterative Gerchberg‐Papoulis algorithm. In this paper, we show the relationship between the closed form estimation methods and the iterative algorithm, propose a method for improving the speed of iteration, and discuss the advantages and disadvantages of two types Of methods. © 1990 Academic Press, Inc.
Viability testing of transplantation donor liver by 1H NMR relaxometry
Authors: Holzmueller P. , Reckendorfer H. , Burgmann H. , Moser E. 
Published: March 2007

AbstractWe present preliminary results of water proton relaxation time measurements on perfused, cold‐stored rat livers as a basis of a simple method for testing the viability of human donor livers in liver transplantation surgery. Proton T1 and T2 data correlated strongly (p < 0.01) with bile flow measurements, indicating that relaxation times reflect organ viability and therefore might be used for rapid testing of donor livers shortly before transplantation. © 1990 Academic Press, Inc.
Flow velocity quantitation using inversion tagging
Authors: Salonerand David , Anderson Charles M. 
Published: March 2007

AbstractA method for quantitating flow velocities is presented. The technique tags multiple boli of magnetization in transit across a thick selection slab using of inversion pulses. Results in phantoms andin vivodemonstrate that the method is robust and can provide velocity determinations in tortuous vessels. © 1990 Academic Press, Inc.
Computer modeling of surface coil sensitivity
Authors: Lawry T. J. , Weiner M. W. , Matson G. B. 
Published: March 2007

AbstractA simple model is presented for the calculation of relative signal‐to‐noise (S/N) ratios of coils of different sizes and configurations when applied to in vivo MRS. Axial symmetry is assumed, which enables rather simple expressions to be used for the calculation of coil loading by the tissue. The model is calibrated to experiments through measurement of the loaded and unloaded coil Q's. Applications of the model demonstrate that for small, superficial regions of interest (ROI), small surface coils can provide a S/N much improved over that of a larger coil. However, for very deep ROIs, larger coils or coils producing S/N. © 1990 Academic Press, Inc.
PC‐based system for retrospective cardiac and respiratory gating of NMR data
Authors: Bohning Daryl E. , Carter Bruce , Liu Shinshang , Pohost Gerald M. 
Published: March 2007

AbstractA method and a means for retrospectively clustering NMR k‐space measurement profiles with respect to both cardiac and respiratory phases were developed to explore strategies for (1) reducing cardiovascular and respiratory flow/motion image artifacts and (2) improving T1 and T2 characterization of the heart. The image data are collected at a uniform rate so that echo (TE) and repetition (TR) times are independent of the varying cardiac cycle R‐R interval and/or respiratory motions. Cardiac (C) time, respiratory (R) time or diaphragm position, and NMR data acquisition (A) cycle time are collected by microcomputer in parallel with free running (untriggered) image collection on a standard magnetic resonance imager. After the raw data equivalent of multiple images are collected, the C‐A‐R phase timing data are uploaded from the microcomputer to the scanner's minicomputer for use in a normalized C‐R phase plane clustering of the image raw data. Each profile's position in the C‐R phase plane is determined and then clustered into a new set of data, one image being equivalent for each desired C‐R phase combination. These raw data are then zero‐filled and (optionally) filtered to compensate for the nonuniform k‐space sampling and, finally, reconstructed. Cardiac “cines” made from these retrospectively gated images are comparable to similarly phased triggered images. When high time resolution is required, retrospective gating can be expected to show improvements over triggering, especially toward the critical latter part of the cardiac cycle, where coronary artery filling occurs. The system described can readily be assembled from generally available components. © 1990 Academic Press, Inc.
The importance of phase‐encoding order in ultra‐short TR snapshot MR imaging
Authors: Holsinger Anna E. , Riederer Stephen J. 
Published: March 2007

AbstractWe show the importance of phase‐encoding order in ultra‐short TR (< 10 ms) snapshot MR imaging. Contrast is more heavily dictated by the contrast preparation phase early in the measurement phase than later. When the low spatial frequencies are measured first, the resultant image contrast more closely resembles that established by the preparation phase. The transient nature of the data acquisition causes a k‐space filter to be applied to the data. The effects of this filter can be minimized by appropriate choice of scan parameters. © 1990 Academic Press, Inc.
Passive magnetic screening
Authors: Andrew E. R. 
Published: March 2007

AbstractIt is shown that a passive magnetic shield for a 1,5‐T whole‐body magnet requires about 20 tons of iron. Moreover, to first order, the amount of shielding material is independent of the radius of the shield. The choice between a thick shield fitting tightly round the magnet and a thinner shield of larger radius is determined by considerations of available space and the need for the highest uniformity of field in the bore. Very high permeability materials such as mu‐metal are useful only in special circumstances. Multiple shields are valuable if a high degree of shielding is required, but the spacing between the shields needs careful attention. Although exact reciprocity of internal and external shielding is not found in the general case, the degree of shielding will be of the same order in both cases. The complete behavior of cylindrical shields around superconducting magnets can be determined by analytical solution of Maxwell's equations; for less regular shapes, solutions may be determined numerically by computer. © 1991 Academic Press, Inc.
Saturation effects in phosphorus‐31 magnetic resonance spectra of the human liver
Authors: Cox I. J. , Coutts G. A. , Gadian D. G. , Ghosh P. , Sargentoni J. , Young I. R. 
Published: March 2007

AbstractPhosphorus‐31 liver spectra were recorded from 6 controls and 12 patients with liver disease using TR values of 0.5 and 5 s and a pulse angle of 45°. One of the control subjects was also examined at seven TR values ranging from 0.5 to 20 s. Spectra from one additional patient were collected at TRs of 0.5, 1, and 2 s only. There was a significant increase in the mean ratio of peak areas phosphomonoesters (PME)/β‐ATP in 9 of the 13 patients and a decrease in phosphodiesters (PDE)/β‐ATP in 3 of the patients, compared with controls, at the longer TR values. The saturation factors for PME and PDE were greater than those for Pi and β‐ATP, and spectral abnormalities in disease were often more evident as the TR value was increased from 0.5 to 5 s. Acquisition parameters need to be chosen with a knowledge of the impact that saturation effects have on metabolite quantification and Spectral Contrast. © 1991 Academic Press, Inc.
31P NMR spectroscopy in chronic adriamycin cardiotoxicity
Authors: Bittner Vera , Reeves Russell C. , Digerness Stanley B. , Caulfield James B. , Pohost Gerald M. 
Published: March 2007

AbstractAbnormal cardiac energy metabolism has been postulated as a mechanism for adriamycin induced cardiotoxicity. This study was designed to determine high energy phosphate stores at rest and with hemodynamic stress in perfused rat hearts after animals had been chronically exposed to adriamycin (2 mg/kg weekly for 14 weeks). Morphologic and hemodynamic changes were mild in this model. Phosphorus‐31 NMR determined intracellular pH and levels of inorganic phosphate (Pi) and ATP were comparable in treated and control hearts. Phosphocreatine (PCr) levels were markedly decreased in treated hearts (0.89 ± 0.07 units/g versus 1.7 ± 0.13 units/g, p < 0.001). The PCr/Pi ratio decreased in both groups during hemodynamic stress. It recovered earlier in controls and there was a marked overshoot after cessation of rapid pacing in this group which was not present in adriamycin treated hearts. These results suggest that metabolic regulation in response to hemodynamic stress is impaired after chronic adriamycin exposure. PCr depletion and delayed metabolic recovery after hemodynamic stress appear to be potentially useful markers for the effect of adriamycin on the heart. © 1991 Academic Press, Inc.
Site‐specific water proton relaxation enhancement of iron (III) chelates noncovalently bound to human serum albumin
Authors: Jenkins Bruce G. , Armstrong Eileen , Lauffer Randall B. 
Published: March 2007

AbstractBinding of potential blood pool and hepatobiliary paramagnetic iron(III) contrast agents, rac‐ and Meso‐Fe(5‐Br‐EHPG)− (iron(III) N,N′‐ethylenebis[(5‐bromo‐2‐hydroxyphenyl)glycinate]) and Fe(5‐Br‐HBED)− (iron(III) N,N′‐bis‐(5‐bromo‐2‐hydroxybenzyl)ethylenediaminediacetic acid) to human serum albumin (HSA) has been studied using the proton relaxation enhancement (PRE) effect on solvent protons. These chelates bind avidly to multiple sites on HSA with binding constants on the order of 104 to 105 M−1. Interestingly, binding results in a decrease in the diamagnetic component of the water relaxivity due to HSA, while the expected enhancement of the paramagnetic component of water proton relaxation rates occurs due to the increase in the rotational correlation times of the protein‐bound agents. These relaxation enhancements are variable, depending upon the site on the protein to which these chelates are bound, and can be as high as ∼7 mM−1 s−1 at 5°C and ∼5 mM−1 s−1 at 37°C at 20 MHz (enhancements of ∼2−5). Change of temperature from 5 to 37°C also appears to switch the relative affinities of these chelates for their primary and secondary binding sites. It is found that the important HSA binding site for the heme breakdown product, bilirubin‐IXα, is a target for these agents and is the site of highest relaxivity for all the agents. © 1991 Academic Press, Inc.
GdDTPA‐enhanced magnetic resonance imaging of the aqueous flow in the rabbit eye
Authors: Cheng Hong‐Ming , Kwong Kenneth K. , Xiong Jing , Chang Chen 
Published: March 2007

AbstractMagnetic resonance imaging with gadolinium‐diethylenetriaminepentaacetic acid complex (GdDTPA) as the contrast agent was used to image the aqueous chamber of the eye. This method, in addition to providing spatial information, permits quantitative study of the aqueous flow. GdDTPA solution was applied either topically or intravenously, entering the anterior chamber via different pathways. The wash‐in and wash‐out of GdDTPA follow a two‐compartment model which enables determination of the aqueous flow rate by multiplying the aqueous chamber volume by the wash‐out rate constant. Rabbit eyes showed a flow rate of 1.5−2 μ1/min which was retarded by the systemic administration of acetazolamide ( Diamox ). © 1991 Academic Press, Inc.
NMR determination of myocardial pH in vivu: Separation of tissue inorganic phosphate from blood 2, 3‐DPG
Authors: Zahler Raphael , Majumdar S. , Frederick Blaise , Laughlin Maren , Barrett Eugene , Gore John C. 
Published: March 2007

AbstractPhosphorus NMR can measure myocardial tissue pH from the chemical shift of inorganic phosphate (Pi) in isolated buffer‐perfused hearts, but in vivo the Pi peak originating from the myocardium is obscured by the resonance of 2, 3‐diphosphoglycerate (DPG) in the blood, making pH difficult to determine. Taking advantage of the fact that most of the interfering DPG is within the cardiac chambers and is rapidly flowing out of the sensitive volume of our coil, we developed a pulse sequence which would separate myocardial Pi signal from interfering DPG. We tested this method on a flow phantom and in living rat heart, using exogenous glycerol phosphate as a blood‐pool marker. The results indicated that signal from moving and nonmoving substances could be separated, and derived values for myocardial pH and PCr/Pi ratio were consistent with previous estimates. This method should be useful for studying myocardial acid‐base physiology with NMR. © 1991 Academic Press, Inc.
Fast MR cardiac profiling with two‐dimensional selective pulses
Authors: Cline Harvey E. , Hardy Christopher J. , Pearlman Justin D. 
Published: March 2007

Abstract A rapid‐profiling NMR pulse sequence has been designed to provide an interactive, real‐time cardiac probe analogous to M‐mode ultrasound. The pulse sequence employs a two‐dimensional (2D) selective NMR pulse to excite a narrow (nominally 1 ‐cm‐diameter) cylinder of magnetization intersecting the heart. This procedure is followed by a readout gradient applied along the length of the cylinder, or “beam,” to yield an M‐mode type profile with a one‐dimensional Fourier transform reconstruction. k‐space techniques were used to design 2D pulses which excite cylinders characterized by either Gaussian or square radial excitation profiles. Images of phantoms acquired at 1.5 T confirm the predictions of the k‐space analysis. The cylinder can be displaced interactively by modulating the rf excitation and the beam axis can be reoriented to any oblique direction by changing the relative mixing of the gradient waveforms. Flow compensation using bipolar gradient waveforms inverts the contrast of flowing blood and suppresses flow artifacts. A gated cardiac image is acquired as a reference to locate the excitation axis. A series of cardiac experiments was performed on several healthy volunteers. As the beam is moved and rotated to probe the myocardium, the profile plots resemble an M‐mode echocardiogram. Unlike in M‐mode echocardiography, however, the axis of interrogation is not limited to specific windows, and there is distinct flexibility of contrast. However, the temporal resolution is currently less than that achieved by ultrasound. NMR M‐mode profiling provides a direct, fast method of measuring heart motion to assess cardiac function as part of an MR cardiac exam. © 1991 Academic Press, Inc.
A study of nephrotoxin‐induced acute tubular necrosis with 31P magnetic resonance spectroscopy
Authors: Schutz Thomas , González‐Méndez Ricardo , Nabseth Donald C. , Tune Bruce M. , Jardetzky Oleg , Stevenson David K. 
Published: March 2007

AbstractPhosphorus magnetic resonance spectroscopy (31P MRS) was used to obtain in vivo spectra from rat kidneys undergoing acute tubular necrosis induced by a nephrotoxic dose of cephaloridine (CLD). Spectra were obtained 0, 24, and 48 h after injection of CLD (experimental group, n = 6) or saline vehicle (control group, n = 6). The nephrotoxicity of CLD was demonstrated by severely increased serum creatinine levels and the development of extensive proximal tubular necrosis in the CLD‐injected rats, and the lack of such changes in the controls. 31P MRS showed an increase in the inorganic phosphate region signal (P1, p = 0.004) and a decrease in the phosphodiester region signal (PDE, p = 0.01) in the experimental group by 48 h, whereas these parameters did not vary significantly in the control group during the experiment. Significant correlations were found between serum creatinine and the same two 31P MRS parameters. In summary, rat kidneys which have developed severe CLDinduced proximal tubular necrosis exhibit changes in the 31P spectrum 48 h after administration of the drug. The causes of these changes were not determined. © 1991 Academic Press. Inc.
The phenomenon of separate intra‐ and extracellular resonances of difluorophosphate in 31P and 19F NMR spectra of erythrocytes
Authors: Xu Arron S.‐L. , Potts Jennifer R. , Kuchel Philip W. 
Published: March 2007

AbstractTrifluoroacetate and trifluoroacetamide, when added to a suspension of human red blood cells, give rise to separate 19F NMR signals from the intra‐ and extracellular species. This phenomenon has recently been exploited for measuring the membrane potential of erythrocytes. However, the separation of the peaks was incorrectly ascribed to a difference in magnetic susceptibility between the intra‐ and extracellular environments. Previously, we have reported well‐resolved resonances in 31P NMR spectra for the intra‐ and extracellular populations of some phosphoryl compounds; in these cases, however, the intracellular peak is shifted to low frequency which is the opposite to the situation with the fluorinated compounds. By using difluorophosphate, which rapidly equilibrates across the membrane of human erythrocytes and which has both the phosphoryl and fluorine functional groups, we observed the separate intra‐ and extracellular resonances. But, the intracellular resonance was shifted to high frequency of the extracellular resonance in the 19F spectra and to low frequency in the 31P spectra. The basis for the phenomenon in both cases is thought to be the reduced hydrogen bonding inside the cells between the solvent water and the phosphoryl oxygen or fluorine atoms. © 1991 Academic Press. Inc.