bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of factors affecting the design of NMR contrast agents: manganese in blood as a model system
Authors: Kang Young S. , Gore John C. , Armitage Ian M. 
Published: March 2007

AbstractSome factors affecting the performance of paramagnetic ions as contrast agents for proton NMR imaging have been studied. It is demonstrated that the relaxation rate of an aqueous solution of the ion is not reliably predicted by its magnetic moment, but that significant relaxation enhancement may result when the ion is complexed with large molecules, which increases the dominant correlation time. This enhancement in turn can be altered by factors such as pH and competition for binding. Chelation of the paramagnetic ion, which may be implemented to lower its toxicity, can considerably reduce its efficacy by not only limiting its access to water but also by preventing the enhancement from associations and macromolecules. For manganese the ratio T1/T2 is a useful parameter which is sensitive to the degree of metal binding. These features of paramagnetic relaxation enhancement in tissue are demonstrated in a series of experiments on systems consisting of blood components and manganese.
In vivo measurements of NMR relaxation times
Authors: Kroeker Randall M. , Mcveigh Elliot R. , Hardy Peter , Bronskill Michael J. , Mark Henkelman R. 
Published: March 2007

AbstractA series of solenoidal NMR probes were built to measure T1 and T2 relaxation times in vivo in the mouse, over the frequency range of 5 to 60 MHz, using inversionrecovery and spin‐echo pulse sequences. KHT tumors growing in the legs of C3H mice were studied and compared with normal mouse legs. The tumor relaxation times were studied at 10 MHz during the course of tumor growth and as a function of frequency when the course of tumor growth and as a function of frequency when the tumor had a mass of approximately 0.9 g. Mouse legs with tumors have higher T1 and T2 values than those without tumors over the frequency range of 5 to 60 MHz. Significant changes in both relaxation times were detected before a palpable mass could be detected. T1 contrast between normal and tumor‐bearing legs decreased with increasing frequency, while T2 contrast remained nearly constant. A comparison between in vivo and in vitro measurements was done using four different types of sample preparation: live mouse, dead mouse, excised whole mouse leg, and tissue sample. These studies showed small but significant differences between the relaxation times measured in vivo and those measured in vitro.
The slotted cylinder: An efficient probe for NMR imaging
Authors: Leroy‐Willig Anne , Darrasse Luc , Taquin Jacques , Sauzade Michel 
Published: March 2007

AbstractThe slotted cylinder, and inductive structure with low self‐inductance, low electric field, has been studied as a probe for NMR imaging applications. A theoretical calculation allows us to map the magnetic field and to evaluate electrical parameters of the structure. Several implementations, including new designs, have been experimentally tested over a wide range of frequencies (4–40 MHz), and compared to a classical coil probe. This study demonstrates the efficiency of the slotted cylinder for NMR imaging. It is optimized for large conductive samples when imaging at high frequencies (for human head, above 20 MHz).
Theoretical description of depth pulse sequences, on and off resonance, including improvements and extensions thereof
Authors: Bendall M. Robin , Pegg David T. 
Published: March 2007

AbstractA general mathematical description of depth pulse sequences in terms of rotation matrices permits a single matrix, known as a cycle matrix, to be written down for each phase‐cycled pulse in the overall sequence, such that the result for the total phase‐cycled sequence is the product of the individual cycle matrices. It is straightforward to include the effect of the tilted rf axis off resonance and obtain exact solutions. The two types of phase‐cycled pulse used in a depth pulse scheme are 2θ[±x] and 2θ[±x, ± y] and for the general off‐resonance case, four of the off‐diagonal elements in the 2θ[±x] cycle matrix, and all of the off‐diagonal elements in the 2θ[±x, ± y] cycle matrix, are zero. These simplifications enable important improvements of depth pulse schemes for the elimination of high‐flux signals, the reduction of signals from sample regions experiencing pulse angles differing from 90°, and the avoidance of deletrious off‐resonance effects such as the production of dispersion signals. In all cases, the dependence of signal intensity off resonance can be easily and exactly calculated. There are important applications in in vivo spectroscopy.
Shielded solenoidal probe for in Vivo NMR studies of solid tumors
Authors: Ng Thian C. , Glickson Jerry D. 
Published: March 2007

AbstractA shielded solenoidal probe, suitable for in vivo NMR studies of subcutancous solid tumors, is described. The 31P NMR spectra obtained from phantom samples and in vivo subeutaneous solid tumors in mice show that spurious signals from the body are totally eliminated if the proper shield is used.
The placing of many large superconducting magnets in a limited space
Authors: Patz S. , Moore W. S. 
Published: March 2007

AbstractThe problem of minimizing the space needed to house two or three superconducting magnets was studied. Dipolar fields were used to approximate the stray fields. Field contours of a single dipole μ are reviewed. The three‐dimensional contour surface is discussed in terms of its intersection with planes parallel to a base plane containing μ. The area within a field contour H in the base plane was numerically determined to be 142.55 m2{(m̈/m̈0)(H0/H)}2/3 where μ0 = 109 erg/G and H0 = 5 G. For the contours within planes parallel to the base plane, the contour area and its intercepts with the planar x and y axes are given as a function of the distance from the base plane. For two dipoles at one site and for a given mechanical stress, the torque‐free orientations allow closer spacing. Field contours for the four torque‐free orientations are given for μ1 = μ2. For one zero‐torque configuration (μ1 and μ2 antiparallel, but perpendicular to the line joining them) and for a mutual force of 667 N (150 lb), the 5‐G contour area is only 36% greater than that for a single dipole. General expressions for the forces, torques, and field gradients for two dipoles are given. Torque‐free cases of three superconducting magnets (two of which are identical) at one site are described. Contour plots of the linear arrangements of the magnets as well as of two symmetrical triangular arrangements (corner angle is either 70.5 or 109.50) are given.
The magnetic field dependence of transverse water proton relaxation induced by Nitroxide Radicals
Authors: Polnaszek Carl F. , Bryant Robert G. 
Published: March 2007

AbstractThe magnetic field dependence of the water proton T2 is calculated for aqueous solutions of nitroxides based on a detailed analysis of early T1 measurements on nitroxide solutions made as a function of magnetic field. The results parallel those for T1 closely and, unlike metal systems, the implications for magnetic imaging are similar.
Present clinical status of magnetic resonance imaging
Authors: Margulis Alexander R. , Fisher Madeleine R. 
Published: March 2007

AbstractMagnetic resonance imaging has achieved clinical importance and has become the primary tool in the investigation of head, spinal cord, pelvis, cancellous bone, pericaridium (with gating), gallbladder, lymph node masses, and very soon, in the evaluation of joints. In many areas, particularly with respiratory and ECG gating, this method promises to replace all other imaging modalities with the precision of information obtained. Today the exceptions are the alimentary tube and its mesentery, between the esophagus and rectum, and the peripheral lung.
Theory of Localized Polarization Transfer
Authors: Pegg David T. , Robin BENDALL M. 
Published: March 2007

AbstractBecause polarization transfer from one type of nucleus to another can occur only when both types of nuclei are excited, it is possible, by using two separate rf coils for the excitation, to restrict the spatial region of the sample from which a signal can be received to a specific volume of overlap of the two inhomogeneous field patterns. In this paper we develop the theory of this method of localization in a homogeneous static field. The polarization transfer is achieved by a generalized phase‐cycled DEPT sequence, in which case the method has the additional advantage of a gain in sensitivity of a 13C signal associated with the maximum polarization‐transfer enhancement. Localization by means of the inverse‐DEPT sequence is also studied, and off‐resonance effects are calculated. Experimental confirmation of the theoretical expressions is given.© 1985 Academic Press,Inc.
An Improved Perifusion System for NMR Study of Living Cells
Authors: Boulanger Y. , Vinay P. , Phan Viet M. T. , Guardo R. , Desroches M. 
Published: March 2007

AbstractIsolated cells can be kept in steady‐state conditions for very long periods of time when inserted into dialysis microfibers and perifused with a nutrient‐containing solution. Using this system, stable 31PNMR spectra have been obtained on dog kidney tubules for a period of 13 h.© 1985 Academic Press,Inc.
Proton NMR Characteristics of a Biological System Useful for Developing in Vivo Spectroscopy and Imaging Techniques for Tumors
Authors: Block Ronald E. , Parekh Barbara , Menditto Rita 
Published: March 2007

AbstractA model system for in vivo proton NMR studies consisting of a transplantable tumor growing on a rat's tail was investigated at 90 MHz using a high‐resolution Fourier transform spectrometer. Spectra were obtained, relaxation times were measured, and the spatial distributions of proton signal intensities were estimated. We conclude that the model could be used for developing both spectroscopy and imaging approaches.© 1985 Academic Press,Inc.
Real‐value representation in inversion‐recovery NMR imaging by use of a phase‐correction method
Authors: Park H. W. , Cho M. H. , Cho Z. H. 
Published: March 2007

AbstractA new technique of real‐value representation in inversion‐recovery (IR) imaging by use of a phase‐correction method is proposed. In this scheme, negative magnetizations at the beginning of the inversion point (T1 ⋍ 0) are correctly represented as negative values rather than positive. By use of this new scheme, a consistent IR image set as a function of several inversion times (T1) can be obtained. The latter, i. e., consistent image set which represents the real value of T1 weighted images at several inversion times is important in the search for tumors and abnormalities since the inversion time (T1) in the pulse sequence strongly affects T1 contrast. © 1986 Academic Press, Inc.
Optimization of signal‐to‐noise ratio in calculated T1 images derived from two spin‐echo images
Authors: Prato F. S. , Drost D. J. , Keys T. , Laxon P. , Comissiong B. , Sestini E. 
Published: March 2007

AbstractA simplified model relating signal intensity in an MR image to spin‐lattice relaxation time (T1), repetition time (TR), number of signal averages and the average tip angle (α) of the protons within the slice has been developed. This model has been used to select the optimal repetition times of two spin‐echo images for a fixed total imaging time to maximize signal to noise in calculated T1 images. Theoretical predictions of T1 are virtually identical to spectroscopically measured values, and the relative noise (δT1) in T1 images calculated from two measured spin‐echo images is in good agreement with the theoretically predicted values of δT1/T1. This model predicts that: (a) for a T1 of approximately 500 ms, the least T1 image noise is obtained with one of the spin‐echo images collected with a TR of 400–500 ms. The longer the TR of the other spin‐echo image, the lower the T1 image noise, but past a TR of approximately 1400 ms, T1 image signal/noise is optimized for the same total imaging time by increasing the number of averages in the shorter TR spin‐echo image rather than increasing the TR of the second spin‐echo image. (b) The error is reduced and the optimum TR1 is reduced as α is increased from 63 to 90°. (c) For a range of T1, optimal selection of TR1 and TR2 based on an intermediate value of T1, results in relatively little increase over optimal values in δT1/T1 for the entire T1 range. © 1986 Academic Press, Inc.
In vivo spectroscopic magnetic resonance imaging using estimation theory
Authors: Macovski Albert , Spielman D. 
Published: March 2007

AbstractThe ability to map spectroscopic components for in vivo application is a highly desirable goal. Thusfar it has been unavailable because of the low SNR inherent in the measurement of each voxel. In this paper we deal with this low SNR in two ways. First, estimation theory, using a priori data, is used to estimate the amplitudes in each voxel. Second, the resultant estimates are presented in an image format so that they are readily correlated with anatomical and physiological patterns. A computer simulation is presented of a case where the SNR is‐10 dB. At this level, conventional Fourier transform spectroscopy provides meaningless results. Using estimation theory and an imaging format, a simulated lesion is readily seen. © 1986 Academic Press, Inc.
Boundary artifact in inversion‐recovery images
Authors: Droege R. T. , Adamczak S. M. 
Published: March 2007

AbstractModulus reconstruction of inversion‐recovery images causes a pixel value to be assigned the absolute magnitude of the signal amplitude. Consequently, contrast between tissues is reduced if they have amplitudes of opposite sign. When contrast is reduced between adjacent tissues, dark line artifacts are created at the tissue boundaries. The artifacts may enable tissues to be spatially distinguished even if there is no contrast between them. However, the artifacts may lead to misinterpretation of the image since they may be difficult to distinguish from real anatomical structures. © 1986 Academic Press, Inc.
1.5 T in vivo31P NMR spectroscopy of the human liver using a sectorial resonator
Authors: Grist Thomas M. , Jesmanowicz Andrzej , Froncisz W. , Hyde James S. 
Published: March 2007

AbstractA novel resonator for receiving 31P NMR signals at 1.5 T, which because of its topology has been named a “sectorial resonator,” exhibits good radio frequency coupling to the adult human liver. Minimal contamination from nonliver tissue (i. e., muscle) was achieved by the use of depth selective pulses and also because the geometry results in cancellation of signals arising from tissues that are close to the two openings of the structure. © 1986 Academic Press, Inc.
The application of steady‐state free precession to the study of very slow fluid flow
Authors: Patz S. , Hawkes R. C. 
Published: March 2007

AbstractAn NMR imaging technique sensitive to slow flow (∼ 1 mm/s) using a conventional imaging gradient strength (0.025 mT/cm) is described. Two projections with different spatial magnetic periodicity (determined by the SSFP pulse interval), and thus with different flow sensitivities, are subtracted to give signal from flows in a velocity window. © 1986 Academic Press, Inc.
Hypoxia‐sensitive NMR contrast agents
Authors: Swartz Harold M. , Chen Kai , Pals Mark , Sentjurc Marjeta , Morse Philip D. 
Published: March 2007

AbstractThe rate of reduction of nitroxides is shown to be more rapid in hypoxic cells. The rate of reduction and the effect of hypoxia on the reduction rate vary for different nitroxides. These findings indicate that it may be feasible to develop in vivo NMR contrast agents that selectively will indicate areas of hypoxia and thereby aid in the detection of disease processes such as neoplasia, ischemia, and inflammation. © 1986 Academic Press, Inc.
Flow measurement by the development of phase differences during slice formation in mr imaging
Authors: Young I. R. , Bydder G. M. , Payne J. A. 
Published: March 2007

AbstractA method for measuring flow based on the shifting of the rephasing pulse following slice selection in partial saturation is described. The technique is based on a partial saturation sequence and retains much of the high signal which is a feature of the use of this sequence. Images obtained while encoding for the flow signal compared with those when not encoding appear very similar. © 1986 Academic Press, Inc.
Common pharmaceuticals alter tissue proton NMR relaxation properties
Authors: Karlik Stephen J. 
Published: March 2007

AbstractDifferences in the tissue properties of water are the basis for the detailed anatomic visualization of internal body structures produced by NMR imaging. Physiological and pathological events have the potential to alter proton nuclear magnetic resonance relaxation properties through changes in water environment. In this study, the parenteral injection of pharmaceuticals produced significant changes (12–21%) in proton NMR relaxation times in tissues of treated rats. The extent of relaxation time change was both tissue specific and drug specific. Therefore, the effects of common pharmaceuticals should be considered in the interpretation of T1‐and T2‐weighted NMR images. © 1986 Academic Press, Inc.
Projective MRI angiography and quantitative flow‐volume densitometry
Authors: Wedeen Van J. , Rosen Bruce R. , Buxton Richard , Brady Thomas J. 
Published: March 2007

AbstractProjective MR images of vascular anatomy and flow are performed at 0.14 T by using phase contrast to suppress the signal contribution of the stationary background. The source of the contrast is the distinctive phase evolution of moving protons under the influence of the read‐out gradient of a conventional two‐dimensional Fourier transform (2D FT) spin‐echo pulse sequence. By using short echo times, small phase shifts may be obtained. When phase shifts are less than about 45°, the phase contrast assumes a simple and useful form. The flow image intensity at any pixel becomes proportional to the net flux or flow volume of protons which cross the corresponding voxel. This proportionality is demonstrated in images of flow phantoms as is the reproducibility of measured flow volume under a variety of transformations of imaging conditions and of the subject. Projective images gated in vivo produce angiographic views of arteries and veins, in systole and diastole, in the neck of a dog and in the lower extremities of a human subject. © 1986 Academic Press, Inc.
Magnetic field dependence of solvent proton relaxation rates induced by Gd3+ and Mn2+ complexes of various polyaza macrocyclic ligands: Implications for NMR imaging
Authors: Geraldes C. F. G. C. , Sherry A. D. , Brown R. D. , Koenig S. H. 
Published: March 2007

AbstractThe magnetic field dependence of the solvent water proton longitudinal relaxation rate 1/T1 (the NMRD profile) has been measured for solutions of chelates of Gd3+ and Mn2+ ions with two different polyaza macrocyclic ligands: 1, 4, 7‐triazacyclononane‐N, N′, N″,‐triacetic acid (NOTA) and 1, 4, 7, 10‐tetraazacyclododecane‐N, N′, N″, N‴,‐tetraacetic acid (DOTA). Studies were carried out mainly near physiological pH, but the pH dependence was also examined in some cases. The results are compared with published data for complexes of Gd3+ and Mn2+ ions with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetie acid (DTPA). Competition experiments for the NOTA and DOTA chelates with EDTA and DTPA were also performed. It is found that, over the field range in which NMR imaging is currently being done, different symmetries of otherwise similar chemical ligands can alter 1/T1 of solvent protons by factors of up to three. The ligand environment can influence the relaxation times of the electronic spin moments of the ions, as well as their coordination number, thereby changing both the inner and outer sphere contributions to the relaxivities of the complexes. The relevance of these results to questions of efficiency and toxicity of these chelates as agents for enhancement of contrast in NMR images is discussed. © 1986 Academic Press, Inc.
Localization of phosphorus metabolites and sodium ions in the rat kidney
Authors: Bogusky Ronald T. , Garwood Michael , Matson Gerald B. , Acosta Galo , Cowgill Larry D. , Schleich Thomas 
Published: March 2007

AbstractRelative amounts of phosphorus‐containing metabolites and sodium ions present in different regions of the in vivo rat kidney were obtained using a surface‐coil probe and recently developed NMR rotating‐frame methods. During altered physiologic states, changes in distribution of metabolites and sodium ions within the kidney were identified in one‐dimensional metabolite maps. This technique may have important applications to disorders commonly found in clinical medicine. © 1986 Academic Press, Inc.
In vivoevaluation of intracellular pH and high‐energy phosphate metabolities during regional myocardial ischemia in cats using31P nuclear magnetic resonance
Authors: Stein Paul D. , Goldstein Sidney , Sabbah Hani N. , Liu Zhi‐Quan , Helpern Joseph A. , Ewing James R. , Lakier Jeffrey B. , Chopp Michael , Lapenna William F. , Welch Kenneth M. A. 
Published: March 2007

AbstractPhosphorus‐31 nuclear magnetic resonance spectroscopy (31P NMR) was used to asses the temporal changes of high‐energy phosphate metabolites in the region of acute myocardial ischemia of open‐chest cats. Eight anesthetized cats were studied following ligation of the left anterior descending coronary artery. Creatine phosphate showed a 79 ± 16% (mean ± SD) reduction by 4 min after the onset of ischemia. Prominent qualitative reductions of the spectral peak of creatine phosphate occurred by 40 s after ischemia. Adenosine triphosphate measured under the beta spectral peak (β‐ATP) decreased 37 ± 9% by 20–25 min after ligation of the left anterior descending coronary artery. These reductions developed more slowly and were of smaller magnitude than those of creatine phosphate. Intracellular pH decreased from 7.39 ± 0.07 to 7.13 ± 0.09 units by 40 s after ischemia. By 30 min, pH decreased to 6.07 ± 0.40 units. The study shows, therefore, the temporal changes of high‐energy phosphate metabolites during ischemia in localized regions of the myocardium of open‐chest animals. © 1986 Academic Press, Inc.
Rapid average‐flow velocity measurement by NMR
Authors: Altobelli S. A. , Caprihan A. , Davis J. G. , Fukushima Eiichi 
Published: March 2007

AbstractWe describe an NMR method to make a quick determination of average fluid velocity by monitoring the change in phase of the magnetization during a transient signal. We give an example utilizing the second Carr‐Purcell‐Meiboom‐Gill echo in which we measured the velocity of water up to 54 cm/s where each velocity was determined by data taken over 2.5 ms. © 1986 Academic Press, Inc.
Ferromagnetic particles as contrast agents for magnetic resonance imaging of liver and spleen
Authors: Dias M. Helena Mendonca , Lauterbur Paul C. 
Published: March 2007

AbstractParticles of magnetite, Fe3O4, accumulate preferentially in the liver and spleen after intravenous injection. Their magnetic fields drastically decrease echo intensities in spinecho proton magnetic resonance imaging sequences, as demonstrated by experiments on dogs injected with 10 mg/kg of 0.05‐μm particles. © 1986 Academic Press, Inc.
A single acquisition localization technique
Authors: Karczmar Gregory S. , Matson Gerald B. , Weiner Michael W. 
Published: March 2007

AbstractA method is demonstrated for detection of magnetization from a selected region within the sensitive volume of a surface coil in a single acquisition. Composite pulses are described which eliminate signals from regions where magnetization is rotated 270 and 450°. There is a loss of 1.3% or less of signal from regions where magnetization is rotated 90°. © 1986 Academic Press, Inc.