bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Localized Polarization Transfer
Authors: Pegg David T. , Robin BENDALL M.
Published: March 2007

Because 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

Isolated 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

A 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

A 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

A 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

The 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

Modulus 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

A 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

An 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

The 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

A 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

Differences 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

Projective 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

The 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

Relative 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

Phosphorus‐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

We 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

Particles 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

A 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.
Use of frequency‐modulated radiofrequency pulses in MR imaging experiments
Authors: Kunz D.
Published: March 2007

With 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

Bovine 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

The 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

NMR 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

Small 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

Nambu 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

23Na 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

Accurate 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

We 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

Copenhagen 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

31P 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

Multiecho 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

It 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

An 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

Strategies 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

Studies 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

A 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

Natural‐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

Proton 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

The 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

Effects 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

The 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.
31P nuclear magnetic resonance study of acute renal dysfunction in rat kidney transplants
Authors: Shapiro J. I. , Haug C. E. , Weil R. , Chan L.
Published: March 2007

31NMR spectroscopy was used to study renal allografts in rats subjected to allograft rejection, cyclosporine toxicity, ischemia, and ureteral obstruction. Parameters of relative peak areas and intracellular pH were accurately distinguished among the different causes of graft dysfunction. Ureteral obstruction was clearly identified by elevations in the phosphodiester/urine phosphate peak. Ischemia and rejection were. both associated with increases in inorganic phosphates and phosphomonesters and decreases in the β‐phosphate peak of adenosine triphosphate but were distinguishable from each other by differences in intracellular pH which was normal in rejected allografts (7.33 ± 0.07, n = 3) but low in ischemic allografts (7.00 ± 0.05, n = 3, P < 0.05). Grafts insulted with cyclosporine toxicity were not distinguishable from normal allografts by any of the parameters studied. These data suggest that 31P NMR spectroscopy may have potential clinical application in differentiating among the causes of graft failure of human rend allografts. © 1987 Academic Press, Inc.
Selective fourier transform localization
Authors: Brooker H. Ralph , Mareci Thomas H. , Mao Jintong
Published: March 2007

We have introduced the selective Fourier transform technique for spectral localization. This technique allows the acquisition of a high‐resolution spectrum from a selectable location with control over the shape and size of the spatial response function. The shape and size of the spatial response are defined during data acquisition and the location is selectable through processing after the data acquisition is complete. The technique uses pulsed‐field‐gradient phase encoding to define the spatial coordinates. In this paper the theoretical basis of the selective Fourier transform technique is developed and experimental results are presented, including comparisons of spectral localization using either the selective Fourier transform method or conventional multidimensional Fourier transform chemical‐shift imaging. © Academic Press, Inc.
Errors in spin–lattice relaxation time measurements from restricted volumes
Authors: Morrone Terry
Published: March 2007

In vivo T1 measurements are usually made from images. In this paper we describe an alternative method in which data are collected from a strip instead of from an entire plane. We will compare the signal‐to‐noise ratios, the time to make a measurement, and the error in T1 as well as other aspects of the two methods. We have found that the strip method has less inherent signal‐to‐noise, but that this may be compensated for by taking measurements at more than the usual two repetition rates. The method employs a selective 180° pulse as well as a selective 90° pulse. It is shown that both pulses effectively isolate the region of interest. © Academic Press, Inc.
New reconstruction technique for echo‐planar imaging to allow combined use of odd and even numbered echoes
Authors: Sekihara Kensuke , Kohno Hideki
Published: March 2007

An image reconstruction technique for echo‐planar imaging is proposed. This technique combines odd and even numbered echo signals. It is thus possible to reduce the frequency of the time‐modulated gradient used in echo‐planar imaging by 5070, and to reduce its amplitude by almost 50% for sinusoidal gradient modulation. © Academic Press, Inc.
Reciprocal space description of MR experiments
Authors: Müller S.
Published: March 2007

The phase space description of Fourier‐based imaging methods is extended to describe imaging of heterogeneous distributions of chemical shift, J coupling, and T1 and T2 relaxation. Simple graphical illustrations for a general class of spectroscopic imaging experiments are provided. © Academic Press, Inc.
Experimental acute pancreatitis: MR relaxation time studies using gadolinium–DTPA
Authors: Paajanen Hannu , Brasch Robert C. , Dean Peter B.
Published: March 2007

Spin–lattice (T1) and spin–spin (T2) relaxation times of normal and sodium taurocholate‐induced pancreatitis (38 rats) were determined in vitro using a 10.7‐MHz magnetic resonance (MR) spectrometer. The increase in pancreatic T1 time in acute hemorrhagic pancreatitis correlated well with the elevated water content of the organ. Gadolinium–DTPA did not affect significantly the relaxation times of normal pancreas in vitro during 1 to 20 min postinjection, but it decreased the elevated TI times of inflamed pancreas almost to baseline values. MR imaging studies of rat pancreas in vivo (8 rats, 0.35‐T resistive magnet) indicated that the swollen pancreas and associated edema were depicted using a T2‐weighted SE sequence. Fifteen minutes postinjection of gadolinium–DTPA a homogeneous enhancement of inflamed pancreas was detected. The differentiation of pancreatic necrotic foci from surrounding viable tissue and edema could not be detected on Gd–DTPA‐enhanced MR images after 15 min postinjection although microscopical workup indicated these different tissue constituents in the pancreas. © 1988 Academic Press, Inc.
Quantitation of acidosis in neonatal brain tissue using the 31P NMR resonance peak of phosphoethanolamine
Authors: Corbett Ronald J. T. , Laptook Abbot R. , Hassan A. , Nunnally R. L.
Published: March 2007

31P NMR brain spectra were obtained from piglets over a range of mild hypocarbia to severe hypercarbia (PaCO2 25 to 198 mm Hg). The chemical shifts of the phosphoethanolamine and inorganic phosphate were used to calculate intracellular brain pH (pHet and pHpi, respectively). Both pHpi and pHet underwent parallel significant decreases during hypercarbia, corresponding to 51 and 53% pHregulation, respectively. We conclude that the chemical shift of the phosphomonoester peak in vivo can be used to measure decreases in intracellular pH in neonatal brain. © 1988 Academic Press, Inc.
Enhanced proton magnetic resonance imaging of experimental mammary tumors
Authors: Block Ronald E. , Parekh Barbara C.
Published: March 2007

The proton magnetic resonance imaging contrast of experimental mammary tumors in rats has been dramatically improved. The technique developed combines T2 weighting and chemical‐shift imaging in order to suppress the thoracic wall, muscle, and subcutaneous fat contributions to the image. The technique is demonstrated using the R3230AC mammary adenocarcinoma in F344 rats at 4.7 T. © 1988 Academic Press, Inc.
Dynamic imaging with lanthanide chelates in normal brain: Contrast due to magnetic susceptibility effects
Authors: Villringer Arno , Rosen Bruce R. , Belliveau John W. , Ackerman Jerome L. , Lauffer Randall B. , Buxton Richard B. , Chao Yong‐Sheng , Wedeenand Van J. , Brady Thomas J.
Published: March 2007

Using a one‐dimensional rapid imaging technique, we have found that injection of lanthanide chelates such as Gd(DTPA)2− leads to a significant decrease (50%) in rat brain signal intensity at 1.45 T using T2‐weighted pulse sequences; however, no effect of comparable size is observed with T1‐weighted pulse sequences. The transient effect and its kinetics were followed with a temporal resolution of between 1 and 8 s. Experiments with different lanthanide chelates show that the observed decrease in signal intensity correlates with the magnetic moment of each agent but not with their longitudinal relaxivity. Three‐dimensional chemical‐shift resolved experiments demonstrate significant line broadening in brain during infusion with Dy(DTPA)2− Our results show that the cause of this effect is the difference in susceptibility between the capillaries, containing the contrast agent, and the surrounding tissue. As a result of these susceptibility differences, field gradients are produced in the tissue and diffusion of water through these gradients leads to a loss of spin phase coherence and thus a decrease in signal intensity. We propose this as a new type of contrast agent mechanism in NMR. The effect and its kinetics are likely to be related to important physiological parameters such as cerebral blood volume and cerebral blood flow, and do not depend on a breakdown of the blood‐brain barrier as do conventional contrast agent techniques. © 1988 Academic Press, Inc.