bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of frequency‐modulated radiofrequency pulses in MR imaging experiments
Authors: Kunz D. 
Published: March 2007

AbstractWith increasing field strength for whole‐body MR scanners there is a need for rf pulses of higher bandwidth to perform selective excitation or inversion. AM pulses will have to become shorter thus leading to an enormous requirement for the peak power of the power amplifier. To reduce these requirements the use of frequency modulation is investigated. The effect of pulses based on a linear frequency sweep on the spin system is analyzed by calculation and computer simulation. It turns out that the nonlinear phases induced by those pulses may compensate each other, that therefore spin‐echo experiments as usual in MR imaging may be performed, and that the required peak power may be reduced by up to a factor of 50. © 1986 Academic Press, Inc.
1/T1 NMRD profiles of solutions of Mn2+ and Gd3+ protein‐chelate conjugates
Authors: Lauffer Randall B. , Brady Thomas J. , Brown Rodney D. , Baglin Coral , Koenig Seymour H. 
Published: March 2007

AbstractBovine immunoglobulins (IgG) and bovine serum albumin (BSA) were multiply labeled with multidentate ligands, either ethylenediaminetetraacetic acid (EDTA) or diethylene lriaminepentaacetic acid (DTPA), and metal ions were inserted to form the ternary protein ligand‐ion conjugates. The NMRD profiles (the magnetic field dependence of 1/T1) of solutions of the ternary conjugates differ greatly from those of the corresponding binary ligand‐metal‐ion complexes, both in magnitude and functional form, exhibiting 5‐to 10 fold greater relaxivities and prominent peaks near 20 MHz. The inference is that the protein‐bound chelates are relatively rigidly attached to the macromolecules. The structure and metal ion affinities of these novel conjugates, as well as the relevance to contrast enhancement in NMR imaging, is discussed. © 1986 Academic Press, Inc.
Errors in the measurements of T2 using multiple‐echo MRI techniques. II. Effects of static field inhomogeneity
Authors: Majumdar S. , Orphanoudakis S. C. , Gmitro A. , O'Donnell M. , Gore J. C. 
Published: March 2007

AbstractThe accurate estimation of the spin‐spin relaxation time T2 is an important goal in magnetic resonance imaging particularly because it can be used for quantitative tissue characterization. The spin‐spin relaxation time T2 may be estimated using multiecho pulse sequences, but the accuracy of the estimate is dependent on the fidelity of the spin‐echo amplitudes, which may be severely compromised by rf pulse and static field imper‐fections. In this paper, the effects of static field inhomogeneities are investigated. The propagation of the errors introduced by off‐resonance effects are analyzed through computer simulations and analytical solutions of the Bloch equations. A series of experiments performed on a simple tissue phantom using a whole‐body imaging system operating at 6.35 MHz corroborates the simulation and analytical results. For accurate measurements of T2 using a whole‐body imaging system it is necessary to correct for these inhomogeneities. A correction scheme which would enable a more accurate estimate of T2 is currently under investigation. © 1986 Academic Press, Inc.
Pulse techniques for the suppression of individual components in multiexponential relaxation curves
Authors: Metz Kenneth R. , Stankiewicz Paul J. , Sassani Joseph W. , Briggs Richard W. 
Published: March 2007

AbstractNMR pulse sequences have been investigated which selectively suppress undesired signal components from multiple‐exponential spin‐spin and spin‐lattice relaxation curves. Suppression is achieved by exploiting differences in the relaxation times of sample components. Special attention is devoted to discussion of practical details necessary for implementation of these methods, as well as their relative advantages and disadvantages. The techniques are illustrated using multiple‐compartment aqueous phantoms and are then employed in measurements of proton T1 and T2 values for freshly isolated guinea pig lenses immersed in aqueous buffer solutions to prevent dehydration and maintain viability. These methods obviate many of the difficulties inherent in obtaining accurate relaxation times for minor components of multiple‐exponential curves and should be useful in many applications of NMR to the study of intact tissue, both in vitro and in vitro. © 1986 Academic Press, Inc.
Murine in vivo L‐band ESR spin‐label oximetry with a loop‐gap resonator
Authors: Subczynski Witold K. , Lukiewicz S. , Hyde James S. 
Published: March 2007

AbstractSmall mice (∼20 g) were anesthetized and placed in a loop‐gap resonator of diameter 25 mm resonating at 1.1 GHz. An oxygen‐permeable capsule containing 2.5 × 10−2 M perdeutero 15N TEMPONE (1‐oxyl‐2, 2, 6, 6‐tetramethyl‐4‐piperidone) in light paraffin oil was implanted in the peritoneal cavity. Electron spin resonance (ESR) spectra from the capsule are sensitive to the concentration of dissolved oxygen and calibration curves are given. The oxygen concentration was found to rise from a value close to zero when the animal breathes air to a level of 220 μM when the animal breaths pure oxygen. It is speculated that this surprisingly high level is related to the effect of the anesthetic on the cardiovascular system. Encapsulation provides a barrier to spin‐label reductants and to paramagnetic metal ions that might confound the spin‐label oximetric measurements. © 1986 Academic Press, Inc.
New polyvinyl alcohol gel material for MRI phantoms
Authors: Mano Isamu , Goshima Hitoshi , Nambu Masao , Iio Masahiro 
Published: March 2007

AbstractNambu PVA gel which is produced by repeated freezing and thawing of PVA solution has overcome almost all of the problems which present substances have: (1) It is close to human soft tissue in MRI parameters. (2) MRI parameters (1H density, T1, T2) are adjustable to some extent. (3) It has appropriate physical characteristics. The important problem with PVA gel is long‐term stability. It is assumed that this problem can be solved by its periodic calibration and replacement. © 1986 Academic Press, Inc.
Sodium‐23 NMR relaxation times in body fluids
Authors: Shinar Hadassah , Navon Gil 
Published: March 2007

Abstract23Na longitudinal and transverse NMR relaxation times were measured in human serum, plasma, cerebrospinal fluid (CSF), and solutions of plasma proteins. The magnetization decay curves could not be resolved into two exponentials. A procedure to extract quantitative information from the measured relaxation rates in such a case was developed. The relaxation times of 23Na in serum and plasma were analyzed in terms of the different contributions from free Na+, Na+ bound to small molecules, and Na+ bound to various protein fractions in these body fluids. While T1 is essentially that of free Na+ in a solution which is slightly more viscous than salt solution, T2 is influenced by binding to proteins with the largest contribution from serum albumin. The effect of binding to small molecules on T1 and T2 is negligible. From measurements of the relaxation times at several magnetic field strengths a rotational correlation time of Na+ bound to serum albumin of 16 ± 6 ns was obtained. The fraction of bound Na+ in serum and plasma was roughly estimated as 0.02% of the total sodium. The relaxation times in cerebrospinal fluid are very similar to those of NaCl solution. © 1986 Academic Press, Inc.
Errors in T2 estimation using multislice multiple‐echo imaging
Authors: Crawley A. P. , Henkelman R. M. 
Published: March 2007

AbstractAccurate T2 images calculated from multiple‐echo sequences are difficult to obtain over a number of contiguous slices due to the presence of unwanted echoes that are generated at the slice edges. This problem is similar to problems encountered in single‐slice imaging in the presence of rf pulse imperfections. In this paper, we use computer simulations to show that all unwanted echoes can be eliminated by defocusing them using additions to the slice‐selection gradients. Accurate T2 images may then be calculated from the remaining echoes. We also present a method of experimentally displaying the slice shapes of unwanted echoes generated by a multislice imaging sequence. © 1987 Academic Press, Inc.
Effects of nitroxides on the magnetic field and temperature dependence of 1/T1 of solvent water protons
Authors: Bennett H. F. , Brown R. D. , Koenig S. H. , Swartz H. M. 
Published: March 2007

AbstractWe report a study of the longitudinal NMRD profiles (proton longitudinal relaxation rates as a function of field strength) over a broad range of magnetic field (0.01 to 50 MHz proton Larmor frequency) and temperature (−9.6 to 37°C) for aqueous solutions of (i) a fatty acid‐nitroxide/albumin complex and (ii) 10 low molecular weight nitroxides. Analysis of the NMRD profile for the fatty acid‐nitroxide/albumin complex provides a lower bound estimate for the rotational correlation time of the complex, which permits the calculation of an upper bound on the inner sphere contribution to relaxation of the uncomplexed nitroxides. Inner sphere processes, ostensibly due to water molecules hydrogen bonded to the nitroxide moiety, dominate the relaxation effects of the slowly rotating macromolecular nitroxide/albumin complex. By extrapolation, the contribution of these inner sphere processes are negligible for rapidly tumbling nitroxides free in solution, which affect solvent proton relaxation almost entirely through outer sphere processes (i.e., translational diffusion). A comparison of the relaxation data for aqueous solutions of the uncomplexed nitroxides with the theory of outer sphere relaxation of J. H. Freed (J. Chem. Phys. 68, 4034 (1978)) yields values for the distance of closest approach of the water and nitroxide molecules, as well as for their relative diffusion constants, at five different temperatures. Our results indicate that the rather modest relaxivities of aqueous solutions of nitroxides increase substantially with increased solvent viscosity and with protein binding, supporting the potential utility of nitroxides for enhancement of contrast in nuclear magnetic resonance images. © 1987 Academic PRS, Inc.
Fluorine‐19 NMR studies of tumor‐bearing rats treated with difluoromethylornithine
Authors: Joseph Andrew , Davenport Clark , Kwock Lester , Burt C. Tyler , London Robert E. 
Published: March 2007

AbstractCopenhagen rats with implanted metastatic prostate carcinomas have been treated with the drug α‐difluoromethylornithine (DFMO), an inhibitor of the enzyme ornithine decarboxylase. In vivo and in vitro 19F NMR observations were then carried out on a variety of organs and tissues. The distribution of the drug strongly favored tumor over surrounding muscle. DFMO, which gives a spectrum similar to that of the pH indicator difluoromethylalanine, has potential for determination of in vivo pH. However, in contrast to the alanine analog, DFMO exhibits a considerably smaller shift dependence in response to pH changes. © 1987 Academic Press, Inc.
In vivo31P nuclear magnetic resonance studies of T1 and T2 relaxation times in rat brain and in rat brain tumors implanted to nude mice
Authors: Remy C. , Albrand J. P. , Benabid A. L. , Decorps M. , Jacrot M. , Riondel J. , Foray M. F. 
Published: March 2007

Abstract31P NMR spin‐lattice (T1) and spin‐spin (T2) relaxation times of phosphocreatine, ATP, inorganic phosphate, and phosphomonoesters have been measured in vivo at 4.7 T in rat brain and rat brain tumors implanted on nude mice. The relaxation data were acquired using a phase‐cycled saturation‐recovery spin‐echo sequence. The problems associated with the phase modulation of the ATP lines by the homonuclear coupling constants were overcome by using selective refocusing pulses for the T2 measurements. In all the metabolites, large differences (1 to 2 orders of magnitude) are observed between the two relaxation times. T1 values in rat brain tumors are 30 to 90% longer than their counterparts in normal rat brain. T2 values follow the same trend with smaller variations except for phosphocreatine values which seem much less sensitive to the metabolic state of the tissues. © 1987 Academic Press, Inc.
An estimation and correction scheme for system imperfections in multiple‐echo magnetic resonance imaging
Authors: Majumdar S. , Gmitro A. , Orphanoudakis S. C. , Reddy D. , Gore J. C. 
Published: March 2007

AbstractMultiecho sequences are widely used in MRI because they are an efficient means of acquiring data and they can be used to quantitatively estimate T2. However, the uniformity of each image and the accuracy of each T2 estimate may be corrupted by several instrumental factors such as rf pulse imperfections and static field inhomogeneities. We propose a scheme based on our prior knowledge of the effects of such factors and using the Lexenberg‐Marquardt method of nonlinear estimation that produces accurate estimates of T2 even in the presence of substantial system imperfections and improves the image quality of later echo images in a multiecho sequence. A further extension of this scheme permits mapping the distribution of the static magnetic field from a single multiecho imaging study of a uniform object. Simulations have been performed to test the efficacy of this scheme and the results are substantiated with experiments performed on a whole‐body imager operating at 6.35 MHz. © 1987 Academic Press, Inc.
The anomalous relaxivity of Mn3+(TPPS4)
Authors: Koenig Seymour H. , Brown Rodney D. , Spiller Marga 
Published: March 2007

AbstractIt was recently reported (C‐W. Chen et al., FEBS Lett. 168, 70 (1984)) that water solutions of Mn3+(TPPS4) have a surprisingly high relaxivity at 20 MHz and 37oC, greater than most Mn2+ complexes including the hexaaquoion. Because Mn3+(TPPS4) is highly stable, and porphyrins in general are tumor‐seeking, we have sought to understand the origin of the large relaxivity by comparing the 1/Tl NMRD profiles (magnetic field dependence of 1/T1 of solvent protons) of Mn3+(TPPS4) solutions with those of a number of other small Fe3+ and Mn2+ complexes. By relating the measured NMRD profiles to the theory of relaxation by magnetic dipolar interactions, in a form appropriate for small paramagnetic solute molecules, we establish that the theory affords an excellent quantitative description of the relaxation behavior of all the samples, and confirm that the relaxivity of Mn3+(TPPS4) is anomalously high. The effect is attributed, in part, to the anisotropy of the ground‐state wavefunction of Mn3+ in the porphyrin complex, effectively bringing the spin density of the Mn3+ ions closer to the protons of the coordinated water molecules than would a spherically symmetric S‐state ion. In addition, the paramagnetic relaxation time of the Mn3+ spins, though short, is longer than would be anticipated for a non‐S‐state ion, and increases substantially with magnetic field above about 2 MHz. In this regard, Mn3+(TPPs4) may be one of a class of molecules with properties particularly favorable for use as contrast‐enhancing agents in magnetic resonance imaging. © 1987 Academic Press, Inc.
Feasibility study of imaging a living murine tumor by electron paramagnetic resonance
Authors: Berliner Lawrence J. , Fujii Hirotada , Wan Xiaoming , Lukiewicz S. J. 
Published: March 2007

AbstractAn electron paramagnetic resonance image was measured for the first time from in vivo field gradient spectra of a living murine tumor (Cloudman S‐91 melanoma in the tail of a DBA‐2J mouse) using the paramagnetic nitroxide imaging agent 3‐carboxamido‐2,2,5,5‐tetramethylpyrroline‐l‐oxyl injected into the tail vein. The experiments were accomplished at L‐band frequency (1.55 GHz) with a single‐turn flat‐loop coil. A cross‐sectional image was obtained perpendicular to the tail axis, which clearly distinguished features to the submillimeter resolution level. © 1987 Academic Press, Inc.
Edited 31P brain spectra using maximum entropy data processing
Authors: Waller M. L. , Tofts Paul S. 
Published: March 2007

AbstractStrategies for estimating peak areas in 31P brain spectra are discussed, and the widespread convolution difference method is analyzed. The Skilling maximum entropy method (MEM) algorithm is applied to in vivo spectra and provides an estimate of the spectrum that is operator‐independent, although at the expense of some negative bias. It may be possible to overcome this bias. © 1987 Academic Press, Inc.
31P and 1H NMR spectroscopy to study the effects of Gallopamil on brain ischemia
Authors: Ligeti Laszlo , Osbakken Mary D. , Subramanian Harihara V. , Kovach Arisztid G. B. , Leigh John S. , Chance Britton 
Published: March 2007

AbstractStudies were performed on 16 cats to evaluate the potential protective effects of Gallopamil on brain ischemia. Brain energy state was determined by 31P NMR and lactate concentration was determined by 1H NMR. Double‐tuned surface coils (tuned to 35.8 and 88.4, respectively) were placed on the head after skin and muscle were removed from the calvarium. A 2.1‐T, 25‐cm‐bore Oxford magnet interfaced to a Phosphoenergetics 250‐80 spectrometer was used. The cats were bled to 50 mm Hg for 10 min with subsequent application of bilateral carotid occlusion for 10 min to produce ischemia. In all animals, brain energy state as measured by P/PCr and lactate concentrations were determined over 5‐min intervals (before, during, and after the onset of ischemia). While Gallopamil did not prevent decreases in brain energy state or attenuate the rise in lactate concentration seen during ischemia, brain from animals treated with Gallopamil had a more rapid return of pHi to baseline during the recovery period. In Gallopamil‐treated cats, higher levels of lactate were necessary to cause a similar decrease in pHi when compared to controls. The rate of lactate recovery to baseline levels was similar in both groups (control = −0.38 ± 0.14 mM/min; Gallopamil = −0.44 ± 0.32 mM/min). In conclusion, Gallopamil appears to lessen the acidosis caused by cerebral ischemia. In addition, we have demonstrated that multinuclear NMR spectroscopy is a powerful tool to study the effects of drugs on cerebral metabolism. © 1987 Academic Press, Inc.
Chemical‐shift imaging with large magnetic field inhomogeneity
Authors: Kim Y. S. , Mun C. W. , Cho Z. H. 
Published: March 2007

AbstractA new echo‐time‐encoded chemical‐shift imaging technique applicable to dual‐peak spectroscopic imaging with large magnetic field inhomogeneity is proposed and studied. The basic concept and its applications to modest field homogeneity (⋍3.0 ppm) as well as to relatively large field inhomogeneity (⋍10.5 ppm) are discussed. Actual pulse sequences are given and some experimental results on human volunteers obtained with a 2.0‐T KAIS NMR system are also presented. © 1987 Academic Press, Inc.
NMR imaging of 13C in animal tissues
Authors: Kormos Donald W. , Yeung Hong N. 
Published: March 2007

AbstractNatural‐abundance 13C NMR imaging of animal tissues is demonstrated using high‐field (4.7‐T) and surface coil techniques. Undecoupled images of an unfertilized egg yolk and an oxtail are presented. Analysis indicates the images map mainly methylene carbon or lipid signal intensity. © 1987 Academic Press. Inc.
Proton NMR spectroscopy in canine myocardial infarction
Authors: Richards Todd , Tscholakoff Dimiter , Higgins Charles B. 
Published: March 2007

AbstractProton NMR spectroscopy was used to study the relationship between proton relaxation times and other resonances in the proton spectra, such as lipids, creatine, and choline/ carnitine in subacute (8‐day‐old) myocardial infarctions. Eight mongrel dogs received operative ligation of the left anterior descending coronary artery (four were permanently occluded, four were occluded for 1 h and reperfused) and were sacrificed 8 days later so that tissue samples could be prepared for NMR spectroscopy. The results of this study indicate that (for the core of infarcted tissue) the lipids do not contribute directly to the increased bulk relaxation times associated with myocardial infarction and that the lipid peaks (2.3, 1.2, 0.8 ppm) and creatine peak (3.0 ppm) are more specific to the kind of infarct than to the relaxation times. Therefore, analysis of the proton spectrum of myocardial tissue may Serve as a method for tissue characterization. © 1987 Academic Press, Inc.
Chemical‐shift imaging: A hybrid approach
Authors: Doyle M. , Mansfields P. 
Published: March 2007

AbstractThe hybrid technique of projection‐reconstruction echo‐planar (PREP) imaging for obtaining chemical‐shift images is demonstrated experimentally using a fluorine sample. The technique which is a variation on echo‐planar imaging (EPI) relies on a multipass procedure. It is nevertheless quite efficient and consequently chemical‐shift images may be produced in a few minutes. The method produces images in 64 chemical‐shift regions, each region mapped spatially by 64 × 64 pixels. The imaging time was just over 4 min. These 64 chemical‐shifted images can be straightforwardly added together to form an undistorted image of the complete object. In addition the chemical‐shift spectrum can be extracted and the various chemical‐shift images can be unambiguously assigned to the spectral peaks.
Effect of the sampling rate on magnetic resonance imaging
Authors: Vinitski S. , Griffey R. , Fuka M. , Matwiyoff N. , Prost R. 
Published: March 2007

AbstractEffects of the sampling rate on spatial resolution and the signal‐to‐noise ratio in spin‐echo MR imaging were calculated. The theoretical results suggest that as T decreases, due to either static magnetic field inhomogeneitics or shortened T2 relaxation times, the calculated optimum sampling rate increases accordingly. Since biological tissues exhibit wide variations in their magnetic susceptibilities and T2 relaxation times for various isotopes but modern magnets are characterized by good magnetic field homogeneity, the optimum sampling rate should exhibit an observable dependence on the tissue type. Proton and sodium imaging experiments confirm this conclusion. © 1987 Academic Press, Inc.
Deuterium nuclear spin relaxation in biological tissues
Authors: Block Ronald E. , Parekh Barbara C. 
Published: March 2007

AbstractThe deuterium nuclear spin relaxation times have been measured in tissues taken from rats given 20% deuterium oxide in their drinking water. The spin–lattice and spin–spin relaxation times were measured at 13.7 MHz by the inversion–recovery and Carr–Purcell–Meiboom–Gill FT methods, respectively. The reciprocals of the spin–lattice (T1) relaxation times were found to correlate well with those of protons in similar nondeuteriated tissues at a similar frequency (13.6 MHz) measured in a separate study. A least‐squares analysis of the data yields (I/Tl)II = (0.991)(I/T1)D – 3.48 for five tissues (standard deviations of 0.097 for the slope and 0.383 for the intercept with a correlation coefficient of 0.986). Implications with respect to relaxation mechanisms are discussed. 0_1987 Academic Press, Inc.