bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of water proton relaxation rates by liposomes containing paramagnetic materials
Authors: Bačić G. , Niesman M. R. , Bennett H. F. , Magin R. L. , Swartz H. M. 
Published: March 2007

AbstractLiposomes containing paramagnetic chemicals have significant potential for enhancing the effectiveness and selectivity of contrast agents in magnetic resonance imaging. We have studied the interactions of water, liposomes, and contrast agents using NMR and ESR. We find that the permeability of liposomes to water is of major importance in determining the effects of these systems on water proton relaxation. Key factors include (1) liposome composition, which determines the phospholipid membrane phase behavior as a function of temperature; (2) liposome structure (unilamellar or multilamellar); (3) location of the contrast agent in the liposome (aqueous space or lipid membrane); and (4) binding of contrast agents by liposomes. By appropriate selection of these factors it is possible to obtain effective proton relaxation enhancement in a manner suitable for particular experimental or clinical needs for contrast in MRI. For maximum relaxivity using lipophilic nitroxides, the optimum system appears to be 5‐doxyl stearate in multilamellar vesicles with a membrane composition that gives a phase transition temperature slightly above body temperature. © 1988 Academic Press, Inc.
A new steady‐state imaging sequence for simultaneous acquisition of two MR images with clearly different contrasts
Authors: Bruder H. , Fischer H. , Graumann R. , Deimling M. 
Published: March 2007

AbstractWe present a new steady‐state imaging sequence, which simultaneously allows in a single acquisition the formation of two MR images with clearly different contrasts. The contrast of the first image is FISP‐like, whereas the second image is strongly T2‐weighted. In principle the T2 values in the image can be calculated from the combination of the first and second images. We also show calculated T2 images. © 1988 Academic Press, Inc.
A magnetic resonance imaging study of experimental cerebral edema and its response to dexamethasone
Authors: Barnes D. , McDonald W. I. 
Published: March 2007

AbstractVasogenic edema following cortical freezing, and its response to dexamethasone were studied in cats. The time course of the edema shown by MRI was the same as that observed by invasive techniques. Dexamethasone retards early edema formation and may reduce its total volume, but does not accelerate its disappearance. © 1988 Academic Press, Inc.
Relaxivity and binding of Mn2+ ions in solutions of phosphatidylserine vesicles
Authors: Koenig Seymour H. , Brown Rodney D. , Kurland Robert , Ohkit Shinpei 
Published: March 2007

AbstractWe report the magnetic field dependence (NMRD profiles) of 1/T1, of solvent protons in solutions of unilamellar phosphatidylserine vesicles with added Mn2+ ions, including studies of the variation of the profiles with temperature, extent of coverage of available binding sites by Mn2+ ions, ionic strength, and competition with (nonparamagnetic) Ca2+ ions. In addition, we sketch the theory of screening of the negative surface charges of the vesicles due to both specific binding of Mn2+ ions and nonspecific effects of other mobile solute ions. The major result is that the NMRD profiles, although qualitatively similar, vary systematically as the parameters of the solutions are altered, in a manner consistent with the theory of screening. The profiles of the Mn2+‐vesicle complexes are much like those of Mn2+‐protein complexes that have the ions in an octahedral ligand environment. In addition, we find that the profiles are similar to those reported for Mn2+ ions in packed liver cells and liver tissue, supporting a previous conjecture that available Mn2+ in liver binds to the polar head groups of cell membranes, saturating these sites before binding elsewhere. Again, it is evident that results for in vitro model systems can be extrapolated reliably to tissue behavior. © 1988 Academic Press, Inc.
Averaging error in NMR slice profile measurements
Authors: Selikson Mark , Fearon Thomas 
Published: March 2007

AbstractSlice thickness is a primary operational parameter in the evaluation of the performance of an MRI system with regard to providing accurate imaging of a slice of tissue. Of the various methods that have been utilized to evaluate slice thickness, a continuous high‐signal ramp has gained the most support as the method of choice. However, problems with the accuracy of the measurement method have been associated with the finite thickness of the ramp. This report considers the accuracy of the measurement method as a function of ramp width. © 1988 Academic Press, Inc.
A volume‐localized, two‐dimensional NMR method for the determination of lactate using zero‐quantum coherence created in a stimulated echo pulse sequence
Authors: Sotak Christopher H. 
Published: March 2007

AbstractA volume‐localized, two‐dimensional NMR method which unambiguously measures lactate protons in the presence of interfering lipid resonances is presented. This technique employs the stimulated echo method for spatial selection and was used to observe lactic acid levels in a subcutaneously implanted RIF‐1 tumor at a concentration of 9.6 mM.. © 1988 Academic Press, Inc.
Concurrent measurements of cerebral blood flow, sodium, lactate, and high‐energy phosphate metabolism using 19F, 23Na, 1H, and 31P nuclear magnetic resonance spectroscopy
Authors: Eleff Scott M. , Schnall Mitchell D. , Ligetti Laszlo , Osbakken Mary , Subramanian Harihara , Chance Britton , Leigh John S. 
Published: March 2007

AbstractA new NMR technique for nondestructive, noninvasive, nonradioactive concurrent measurements of blood flow and several energy‐dependent metabolites were applied to in situ cat brain during high cerebral blood flow states (seizures) and low flow states (carotid occlusion plus hemorrhagic shock). An inductively coupled, quadruple‐tuned surface coil with a 50‐ohm match at all relevant frequencies was used for both excitation and receiving. A broadband spectometer was used to measure the 31P spectrum (PCr, ATP, Pi, and pH), a water‐suppressed 1H spectrum (lactate), 23Na, and 19F (blood flow via CHF3 washout). Each nucleus was excited at an independently determined rate. Sodium, with a short T1, was excited more frequently than phosphorus. The results qualitatively agreed with other techniques. Blood flow greatly increased during seizures with a 10% decrease in the Na signal, minimal lactate accumulation, no pH shift, and a change in the PCr‐to‐Pi ratio from 3.4 to 1.7. During carotid occlusion plus hypotension blood flow, PCr and ATP decreased to less than 10% of baseline values. Changes in PCr and Pi preceded parallel changes in Na and ATP. These experiments demonstrated the feasibility of concurrent measurements of physiologically induced changes in high‐energy phosphates, lactate, sodium, and blood flow from the same volume of brain, in a nondestructive manner using NMR spectroscopy. © 1988 Academic Press, Inc.
The center‐tapped slotted tube autotransformer resonator: A coil for use with a high‐resolution small animal imaging system
Authors: Martin M. , Lemaire C. , Tatton W. G. , Armstrong R. L. , Struk R. 
Published: March 2007

AbstractA radiofrequency (rf) coil design based on a slotted tube resonator which allows highresolution imaging of the rodent brain with excellent anatomic definition on a standard G.E. CSI II 2.0‐T MR imaging unit with no modification of existing apparatus is described. The coil is easily constructed and permits very rapid tuning to different loading conditions, allowing a high sample throughput. © 1988 Academic Press, Inc.
Stability constants for Gd3+ binding to model DTPA‐conjugates and DTPA‐proteins: Implications for their use as magnetic resonance contrast agents
Authors: Sherry A. Dean , Cacheris William P. , Kuan Kah‐Tiong 
Published: March 2007

AbstractFive DTPA‐amide and ester derivatives have been synthesized and their Gd3+ stability constants have been measured using a simple spectrophotometric method. These results are compared to stability constants measured for Gd3+ binding to two different DTPA‐conjugated proteins. Although the thermodynamic constants for Gd3+ binding to DTPA‐monopropylamide and DTPA‐monopropvlester relative to Gd( DTPA)2− decrease by log K = 2.6 and 3.4, respectively, the blood pH conditional constants differ from Gd( DTPA)2− only by log K = 1.2 and 1.9, respectively. The corresponding diprooylamide and ester conjugates of DTPA show considerably lower thermodynamic and conditional constants. This has important implications in the covalent attachment of chelates to macromolecules for use in magnetic resonance imaging. The measured binding constants for Gd(DTPA)‐IgG and Gd( DTPA)‐BSA suggest that many of the DTPA molecules in these systems, prepared under our experimental conditions, are diconjugated. The model compound results indicate that it is important to use methods in attaching DTPA to macromolecules which preclude diconjugation of the chelate. Otherwise, their affinity for Gd3+ and consequently their usefulness as MRI contrast agents may be severely compromised. © 1988 Academic Press, Inc.
Use of magnetic resonance imaging to identify changes in cerebral blood flow in epilepsia partialis continua
Authors: Fish D. R. , Brooks D. J. , Young I. R. , Bydder G. M. 
Published: March 2007

AbstractThe use of a phase mapping technique for detection of brain perfusion is described. The method was used in a patient with epilepsia partialis continua and displayed an area of abnormal perfusion in the frontal lobe during the ictal phase. Following improved treatment the perfusion pattern was near normal 12 weeks later. © 1988 Academic Press, Inc.
Spin probe reduction in cells and tissues
Authors: Kveder Marina , Sentjurc Marjeta , Schara Milan 
Published: March 2007

AbstractThe reduction rates of different nitroxides in rat lung tissue were measured by electron paramagnetic resonance. We confirmed that the reduction rate of nitroxide spin probe molecules is coupled with their structure and transport characteristics. Oxygen was found to slow down the reduction rate of nitroxides in rat lung tissues. On the basis of these findings it can be concluded that most nitroxide properties described for homogeneous systems—cells and tissue homogenates—are also valid for heterogeneous systems, which is important for the application of nitroxides as metabolically active NMR contrast agents. © 1988 Academic Press, Inc.
Simultaneous multislice acquisition of MR images
Authors: Weaver John B. 
Published: March 2007

AbstractThe simultaneous multislice technique is a method of imaging multiple parallel slices with the number of echoes normally used to image a single slice. Images of 16 slices have been obtained from a single 128‐echo acquisition. The distance between the slices can be decreased to approximately 15% of the field of view in the readout direction with the cost of significant image blurring. The image blurring is negligible when the distance between the slices approaches the field of view in the readout direction. The trade‐offs are de‐ scribed, and equations and images are presented. © 1988 Academic Press, Inc.
Gastrointestinal contrast agents: A diamagnetic approach
Authors: Listinsky Jay J. , Bryant Robert G. 
Published: March 2007

AbstractThe clay minerals kaolin and bentonite are demonstrated as gastrointestinal contrast agents for MRI. Weak field dependence of the relaxation efficiency assures effectiveness of these agents at all field strengths in clinical use. These agents eliminate signals from their immediate environment and are not toxic. © 1988 Academic Press, Inc.
SLIM: Spectral localization by imaging
Authors: Hu Xiaoping , Levin David N. , Lauterbur Paul C. , Spraggins Thomas 
Published: March 2007

AbstractNonspectroscopic magnetic resonance (MR) imaging often shows that a slice is composed of several compartments, each of which can be assumed to have a spatially homogeneous magnetic resonance spectrum, e.g., a limb composed of fat, muscle, bone marrow, and tumor. We show how to use structural information from such a nonspectroscopic image in order to increase the efficiency of subsequent localized spectroscopic measurements. Specifically, knowledge of the boundaries of N compartments makes it possible to reconstruct compartmental spectra from spectroscopic signals from an entire cross section with N or more different degrees of phase encoding. Experimental studies of a two‐compartment phantom show that this method (SLIM) can be used to derive regional hydrogen spectra of a single slice from signals with as few as 2 phase‐encoding steps, although Fourier transform chemical‐shift imaging requires 64 steps to achieve a result of comparable accuracy. SLIM required only 16 phase‐encoding steps to obtain accurate regional single slice spectra in a human limb with three compartments. Spectra of similar quality, obtained by Fourier transform chemical‐shift imaging, required 256 to 1024 Steps. © 1988 Academic Press, Inc.
Maximum Entropy and 2DFT NMR images
Authors: De Simone B. C. , De Luca F. , Maraviglia B. 
Published: March 2007

AbstractA comparison between contrast and signal‐to‐noise ratio (SNR), as obtained by both maximum entropy (ME) and 2DFT reconstruction, is reported for NMR images. Our results show that in the ME elaboration the contrast and SNR are generally increased with respect to the 2DFT elaboration. The magnitude of such an increase depends on the ME statistical parameter and also, quite strongly, on the values of contrast and SNR of the 2DFT image. © 1988 Academic Press, Inc.
Fat suppression in the time domain in fast MR imaging
Authors: Szumowsiu J. , Plewes D. B. 
Published: March 2007

AbstractTwo gradient‐recalled lipid suppression sequences are proposed. A two‐excitation sequence cycles the TE interval between excitations to alter the lipid phase which is fol‐lowed by complex subtraction. A four‐excitation variant which improves the extent of lipid suppression by partially compensating for errors resulting from spin‐spin relaxation and Bo inhomogeneities is outlined. © 1988 Academic Press, Inc.
Calibrated uncoupling of tightly coupled concentric surface coils for in vivo NMR
Authors: Bendall M. Robin 
Published: March 2007

AbstractThree known active methods of detuning rf coils have been tested by determining the efficiency of uncoupling two concentric transmit surface coils in a double‐coil probe. In a comparison at 80 MHz, the method based on the use of δ/4 cables was found to have advantages. These methods utilize the introduction of an additional resonance at the frequency of interest to completely detune a coil. By offsetting the detuning of the coil (by offsetting the additional resonance) a calibrated fraction of the rf field of the detuned coil can be added to or substracted from the rf field of the neighboring coil. © 1988 Academic Press, Inc.
Nuclear magnetic relaxation studies of the compartmentalized water in crosslinked polymer gels
Authors: Murase Norio , Watanabe Tokuko 
Published: March 2007

AbstractNuclear magnetic relaxation measurements of water in gels made of crosslinked dextran or polyacrylamide (water content, 30‐60 wt%) were carried out using broad‐line proton‐pulsed NMR. Both T1 and T2 values showed inflection against pore size, i.e., the size of the compartment made by crosslinks of the polymer gels. T2 (or T1) values obtained for gels with compartments smaller than the critical size remained low within the range of the water content used in this experiment. Those values of gels with larger compartments, on the other hand, became higher with increasing size. When the size of the compartment was larger than the critical size, T1 and T2 values also became higher with increasing water content. The inflection point can be considered to correspond to the critical compartment size below which the motion of compartmentalized water in gels is more or less restricted. When the compartment is small, however, not only the effect of the molecular motion of water but also that of the proton exchange between compartmentalized water and gel matrix or hydration water should be taken into consideration for the interpretation of the short relaxation times observed, especially by T2. The results obtained in this investigation might provide useful information in the explanation and evaluation of the relaxation values in tissue. © 1989 Academic Press, Inc.
Localized high‐resolution proton NMR spectroscopy using stimulated echoes: Initial applications to human brain in vivo
Authors: Frahm J. , Bruhn H. , Gyngell M. L. , Merboldt K. D. , Hänicke W. , Sauter R. 
Published: March 2007

AbstractWater‐suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brain in vivo. The STEAM spectroscopy sequence allows single‐step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical‐shift‐selective (CHESS) rf pulses. High‐resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). Volumes‐of‐interest (VOI) of 64 ml(4 × 4 × 4 cm3) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from I s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate, N‐acetyl aspartate, γ‐amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mM when assuming N‐acetyl aspartate in white matter to be 6 mM. © 1989 Academic Press, Inc.
Cerebral metabolism in man after acute stroke: New observations using localized proton NMR spectroscopy
Authors: Bruhn H. , Frahm J. , Gyngell M. L. , Merboldt K. D. , Hänicke W. , Sauter R. 
Published: March 2007

AbstractLocalized proton NMR spectroscopy at 1.5 T using stimulated echoes has been applied to study metabolic alterations in the postischemic phase of patients with acute cerebral infarction. A complete depletion of N‐acetyl aspartate in the area of infarction has been observed in a patient studied 4 days after stroke. This finding was paralleled by a dramatic increase in the concentration of lactic acid to about 16 mM within the lesion, indicating continued anaerobic glycolysis. The diluting effect of the edema has been estimated to reduce average metabolite concentrations by about a factor of 3. © 1989 Academic Press, Inc.
A model of the temperature rise in the head due to magnetic resonance imaging procedures
Authors: Athey T. Whit 
Published: March 2007

AbstractA simple model of power deposition in the head is presented in which the temperature increase in the head in general and, in particular, in a small spherical region of unperfused tissue contained within the head is calculated. The result of the calculation provides a limit on the SAR needed to ensure that a 1°C temperature rise is not exceeded for unperfused spheres of different sizes, imaging sessions of different lengths of time, and different blood flow rates to the head. The model assumes that the rest of the body during a head imaging session can act as a perfect heat sink at 37°C. The model suggests that current practices in MRI imaging will not cause a temperature rise in the center of small unperfused regions such as the eye of more than 1°C. © 1989 Academic Press, Inc.
An analysis of magnetic cross‐relaxation between water and methylene protons in a model system
Authors: Gore J. C. , Brown M. S. , Armitage I. M. 
Published: March 2007

AbstractExperiments have been performed to demonstrate and quantify cross‐relaxation between water and methylene resonances in a simple model system. Inversion recovery experiments on aqueous solutions of polyethylene glycol produce a transient nuclear Overhauser effect that alters the recovery of the methylene resonance. The relevant equations and parameters that describe this effect are identified and their values are explicitly quantified by analyzing the experimental results. It is shown that cross‐relaxation is measurable and significant in this system even though there are no strong hydrophilic interactions available to immobilize water. In studies of dog bile, the water and lipid resonances behave in a qualitatively similar fashion, lending support to the contention that cross‐relaxation cannot be neglected in solutions of biological macromolecules. © 1989 Academic Press, Inc.
Reversibility of chronic alcohol cardiac depression: 31P magnetic resonance spectroscopy in hamsters
Authors: Auffermann Wolfgang , Wu Shao , Parmley William W. , Higgins Charles B. , Wikman‐Coffelt Joan 
Published: March 2007

AbstractIn order to investigate the reversibility of chronic alcohol cardiac depression, hamsters were fed with 50% ethanol for 3 1/2 months, reaching serum alcohol levels of 0.13 ± 0.11 g/dl (mean ± SD). Alcohol was then withdrawn for 2 days. Isolated hearts were perfused according to a modified Langendorff method. Energy metabolites were studied using 31P magnetic resonance spectroscopy of isolated perfused hearts standardized by HPLC analysis of freeze‐clamped tissue. Total intracellular calcium [Ca2+]i, was measured with atomic absorption spectrophotometry, marking the extracellular space in vivo with K(CoEDTA). In alcohol‐treated hamster hearts developed pressure was significantly depressed compared to controls. End‐diastolic pressure was significantly increased. Coronary flow was not changed, whereas oxygen consumption and high‐energy phosphate levels were significantly depressed. Intracellular pH was significantly decreased. [Ca2+]i, was significantly increased. Heart weights were significantly lower. After alcohol withdrawal ventricular function, high‐energy phosphate levels, and [Ca2+]i were not significantly different from control. The results indicate that chronic alcohol consumption depresses ventricular function and energy levels and also leads to myocardial acidosis. The increase in intracellular calcium likely causes mitochondrial dysfunction. Withdrawal of alcohol is associated with reversibility of functional and energetic cardiac depression. © 1989 Academic Press, Inc.
MRI of “diffusion” in the human brain: New results using a modified CE‐FAST sequence
Authors: Merboldt Klaus‐Dietmar , Bruhn Harald , Frahm Jens , Gyngell Michael L. , Hänicke Wolfgang , Deimling Michael 
Published: March 2007

Abstract“Diffusion‐weighted” MRI in the normal human brain and in a patient with a cerebral metastasis is demonstrated. The method employed was a modified CE‐FAST sequence with imaging times of only 6‐10 s using a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). As with previous phantom and animal studies, the use of strong gradients together with macroscopic motions in vivo causes unavoidable artifacts in diffusion‐weighted images of the human brain. While these artifacts are shown to be considerably reduced by averaging of 8‐16 images, the resulting diffusion contrast is compromised by unknown signal losses due to motion. © 1989 Academic press, Inc.