bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactions of nitroxides with plasma and blood: Effect on 1/T1 of water protons
Authors: Bennett Harold F. , Brown Rodney D. , Keana John F. W. , Koenig Seymour H. , Swartz Harold M. 
Published: March 2007

AbstractNitroxide stable free radicals (nitroxides) have potential utility as MRI contrast‐enhancing agents with the additional capability of reflecting redox metabolism. In order to gain a better understanding of their potential interactions in vivo, we have studied the longitudinal NMRD profiles (1 / T1 as a function of field strength) and ESR spectra for lipophilic and aqueous‐soluble nitroxides in blood, plasma, and plasma components. Typical water‐soluble nitroxides do not interact appreciably with blood, plasma, or plasma proteins. Fatty acid nitroxides do interact physically with blood, predominantly by intercalation within red blood cell membranes and binding to albumin. The latter interaction results in significantly enhanced relaxivity for the nitroxide/HSA complex. Relaxation of water protons in this case is dominated by inner sphere processes, ostensibly due to water molecules hydrogen bonded to nitroxide moieties. The rotational reorientation time for the complex, the electronic relaxation time, and the exchange time for the water molecule reversably bound to the nitroxide, all appear significantly to influence the correlation time (∼ 16 ns) for this inner sphere contribution. Inc. © 1990 Academic Press, Inc.
Regional phase correction of inversion‐recovery MR images
Authors: Borrello Joseph A. , Chenevert Thomas L. , Aisen Alex M. 
Published: March 2007

AbstractMany MR imaging systems are limited in their ability to successfully display inversion‐recovery images. The reason is that part of the contrast is encoded as phase differences between pixels, whereas in the more commonly used spin‐echo pulse sequence all the information is contained in the pixel magnitude. Inversion‐recovery images are often displayed in magnitude form, resulting in loss of potentially useful phase information contained in the data. Before this phase information can be used, phase errors which result from scanner imperfections must be removed. While most of the necessary correction can be accomplished using data obtained by scanning a uniform phantom, this approach has several disadvantages. An alternative method by which phase errors can be readily removed without phantom data is described. This method has been applied to images of the head, knee, and liver with good results. It is concluded that this technique is useful for producing phase corrected inversion‐recovery MR images © 1990 Academic Press, Inc.
Mechanics and imaging of the macrocirculation
Authors: Caro C. G. , Parker K. H. 
Published: March 2007

AbstractThe mechanics of the macrocirculation are examined as a basis for imaging blood flow within the system. The macrocirculation is denned as that part of the circulation in which inertial forces are not negligible compared to viscous forces and as such in human subjects comprises the heart and large blood vessels. Because the flow in the system is so complicated, understanding is built up piecemeal by considering various relatively well‐characterized flows which can be seen as approximations to the actual flow. © 1990 Academic Press, Inc.
Time‐of‐flight effects in MR imaging of flow
Authors: Wehrli Felix W. 
Published: March 2007

AbstractThis article provides a brief overview of one of the two fundamental physical principles which lead to a modulation of the magnetic resonance signal of moving spins: the time‐of‐flight effect. It then discusses some of its characteristic manifestations in spin‐echo imaging and reviews strategies for exploiting the effect to quantitate vascular flow. © 1990 Academic Press, Inc.
Optimizing blood vessel contrast in fast three‐dimensional MRI
Authors: Haacke E. M. , Masaryk T. J. , Wielopolski P. A. , Zypman F. R. , Tkach J. A. , Amartur S. , Mitchell J. , Clampitt M. , Paschal C. 
Published: March 2007

AbstractMagnetic resonance angiography has matured to the point where clinically useful images can be acquired in half an hour or less. In this paper, the role of 3D imaging techniques is primarily considered. Specifically, the optimal imaging parameters, sequences, and reconstruction techniques are evaluated for moving spins. A variant of FISP known as ROAST with low flip angles, short repeat times, and a thick slab has been found to yield the best 3D survey scan of the cranial vessels with roughly 1 × 1 × I‐mm3 resolution in each of the processed images (slices). For the faster flowing carotids, a sagittal scout with as short a TE as possible is required to avoid spin dephasing. Localization is accomplished in both cases by acquiring thin slab 3D, thin partition, larger flip angle, longer repeat time FLASH sequences. Different choices of dephaseirephase sequences and directions are also reviewed. These choices are discussed from a practical and theoretical perspective. In particular, improvements in contrast and resolution are evaluated using half‐Fourier, 512 acquisition, small fields of view and constrained reconstruction for both rephased gradient echo sequences and dephased thin slice long TR spin‐echo sequences. A resolution of 0.5‐0.75 mm is recommended to obtain sufficient image quality for consistent clinical interpretation of stenoses and vessel abnormalities. © 1990 Academic Press, Inc.
Early detection of regional cerebral ischemia in cats: Comparison of diffusion‐ and T2‐weighted MRI and spectroscopy
Authors: Moseley M. E. , Cohen Y. , Mintorovitch J. , Chileuitt L. , Shimizu H. , Kucharczyk J. , Wendland M. F. , Weinstein P. R. 
Published: March 2007

AbstractDiffusion‐weighted MR images were compared with T2‐weighted MR images and correlated with 1H spin‐echo and 31P MR Spectroscopy for 6‐8 h following a unilateral middle cerebral and bilateral carotid artery occlusion in eight cats. Diffusion‐weighted images using strong gradient strengths (b values of 1413 s/mm2) displayed a significant relative hyperintensity in ischemic regions as early as 45 min after onset of ischemia whereas T2‐weighted spin‐echo images failed to clearly demonstrate brain injury up to 2‐3 h postocclusion. Signal intensity ratios (SIR) of ischemic to normal tissues were greater in the diffusion‐weighted images at all times than in either TE 80 or TE 160 ms T2‐weighted MR images. Diffusion‐ and T2‐weighted SIR did not correlate for the first 1‐2 h postocclusion. Good correlation was found between diffusion‐weighted SIR and ischemic disturbances of energy metabolism as detected by 31P and 1H MR Spectroscopy. Diffusion‐weighted hyperintensity in ischemic tissues may be temperature‐related, due to rapid accumulation of diffusion‐restricted water in the intracellular space (cytotoxic edema) resulting from the breakdown of the transmembrane pump and/or to microscopic brain pulsations. © 1990 Academic Press, Inc.
Differentiation of proliferating from resting cartilage in human fetal nasal septum by magnetic resonance imaging
Authors: Allegrini Peter R. , van Velzen Dick , van Loosen John , Bullock Gillian R. 
Published: March 2007

AbstractMagnetic Resonance Imaging (MRI) has been used for the characterization of human fetal nasal septa. The images were made from fixed fetal heads from spontaneous abortions of different gestational age. The “in‐plane” resolution of the images (at a pixel size of 312 × 312 μm2) allowed a detailed anatomical analysis of the midfacial structures of the fetal heads. In T2 ‐weighted midsagittal sections a low signal intensity region of the septal cartilage could be seen. This part was shown to consist of immature proliferating cartilage by histochemical methods and contrasted to mature resting tissue at the rim of the septum. Direct comparison of the MR images with histological sections demonstrated the potential of MRI in pre‐ and postoperative evaluation of patients requiring surgical reconstruction of either traumatic or congenital defects of the face. © 1990 Academic Press, Inc.
Measurement of regional cerebral blood flow in cat brain using intracarotid 2H2O and 2H NMR imaging
Authors: Detre J. A. , Subramanian V. H. , Mitchell M. D. , Smith D. S. , Kobayashi A. , Zaman A. , Leigh J. S. 
Published: March 2007

AbstractCerebral blood flow (CBF) was measured in cat brain in vivo at 2.7 T using 2H NMR to monitor the washout of deuterated saline injected into both carotid arteries via the lingual arteries. In anesthetized cats, global CBF varied directly with PaCO2 over a range of 20‐50 mm Hg, and the corresponding global CBF values ranged from 25 to 125 ml‐100 g−1min−1. Regional CBF was measured in a 1‐cm axial section of cat brain using intracarotid deuterated saline and gradient‐echo 2H NMR imaging. Blood flow images with a maximum pixel resolution of 0.3 × 0.3 × 1.0 cm were generated from the deuterium signal washout at each pixel. Image derived values for CBF agreed well with other determinations, and decreased significantly with hypocapnia. © 1990 Academic Press, Inc.
Two‐volume acquisition in image‐guided proton spectroscopy
Authors: Hafner H.‐P. , Radü E. , Seelig J. 
Published: March 2007

AbstractBy combining two‐frequency excitation with 1H NMR STEAM spectroscopy, it is possible to measure two volumes of interest simultaneously without an increase in measuring time compared to single‐volume STEAM. Spatial selectivity and spectral resolution of this approach are demonstrated for test solutions and for human 1H NMR brain spectroscopy. First results with a tumor patient are also presented. © 1990 Academic Press, Inc.
A spoiling sequence for suppression of residual transverse magnetization
Authors: Wang Henry Z. , Riederer Stephen J. 
Published: March 2007

AbstractWe present a spoiler sequence which substantially eliminates residual transverse magnetization in rapid magnetic resonance imaging. Such magnetization is due to the repetition time TR being on the order of or shorter than the transverse relaxation time T2. This sequence was designed using computer simulation methods to model the slice profile and signal. The spoiler pulse is applied in the slice‐selecting direction and the magnitude of the gradient spoiler is incremented with each repetition as an arithmetic series. A finite number of different spoiler amplitudes is repeated with a cycle time several times greater than the anticipated T2. Each spoiler is shown to nullify the residual transverse magnetization from the just‐measured signal of the experiment as well as that from preceding repetitions. It is shown experimentally that the spoiler pulse can be as short as 2 ms. This is considerably shorter than existing methods using constant spoiling or phase‐tagged spoiling. This sequence was used to acquire. T1‐weighted images free of the central line artifact of FLASH imaging. Furthermore, images formed with the new spoiled technique are shown to have contrast‐to‐noise comparable if not superior to standard T 1‐weighted spin‐echo images while taking only a fifth of the scan time. © 1990 Academic Press, Inc.
Spin‐labeling angiography of the carotids by presaturation and simplified adiabatic inversion
Authors: Sardashti Maziar , Schwartzberg Daniel G. , Stomp Guido P. , Dixon W. Thomas 
Published: March 2007

AbstractA new adiabatic inversion pulse is tested for a spin‐labeling subtraction angiography method. Adiabatic nature of the pulse is achieved by ramping the gradient during the RF pulse. In addition, with cardiac triggering, any irregularity of the heartbeat would decrease cancelation of the static tissue after subtraction. A 90° presaturation pulse applied to prevent this suppresses the background intensity from the static tissue by a factor greater than 2. Slice angiograms of carotid arteries are presented. © 1990 Academic Press, Inc.
Chronic carbon tetrachloride and phospholipase D hepatotoxicity in rat:In vivo1H magnetic resonance, total lipid analysis, and histology
Authors: Hazle John D. , Narayana Ponnada A. , Dunsford Harold A. 
Published: March 2007

AbstractMagnetic resonance (MR) imaging, localizedin vivoproton spectroscopy, andT1relaxation measurements were obtained from the livers of rats treated chronically with carbon tetrachloride and phospholipase D. The MR data correlated well with lipid changes measured biochemically and histologically. MR images appeared generally hyperintense during fatty infiltration, changing to hypointense mottling during cirrhosis. WaterT1relaxation times showed no statistically significant change at any time during the experiments from the control value of 908 ms (SE = 42 ms). Minor changes in lipidT1values with time were noted. The average lipidT1curve demonstrated a linear relation with time (r= 0.81), increasing from the control value of 283 ms (±16 ms) to 365 ms (±53 ms) at the end of the third week and decreasing slightly through the end of the experiment. Water‐suppressedin vivospectra showed quantitative changes in liver lipids which correlated well with the biochemical and histologic analysis. From the MR images and spectroscopy results it was possible to distinguish early fatty liver from more advanced cirrhosis. © 1990 Academic Press, Inc.
Quantification of fluid changes in rat leg joints with adjuvant arthritis by a one‐dimensional magnetic resonance imaging experiment
Authors: Borah Babul , Szeverenyi Nikolaus M. 
Published: March 2007

AbstractA simple and reliable method for quantifying the fluid content and characterizing the tissue T2 relaxation properties of animal extremities has been devised. This one‐dimensional magnetic resonance imaging experiment, applied to the adjuvant arthritis model in rats, provides a useful, noninvasive monitor of the course of the disease in vivo. Tissue is characterized through the analysis of the biexponential T2 decay of the NMR‐active hydrogen in the rat leg joint tissue. Long and short T2 components are identified, both of which are sensitive to the arthritic process. The long component is suggested to come from edema and increases by a factor of ca. 9 during the course of the disease, whereas the short T2 component may represent cellular influx into the joint and increases by a factor of ca. 3. These changes correlate with the severity of the disease and can be used to monitor therapeutic response. The main advantage of the technique over the more traditional two‐dimensional imaging approach is that only one spatial variable has to be resolved, resulting in shorter imaging time. © 1990 Academic Press, Inc.
Simultaneous spatial and spectral selective excitation
Authors: Meyer Craig H. , Pauly John M. , Macovskiand Albert , Nishimura Dwight G. 
Published: March 2007

AbstractUsing a k‐space interpretation of small‐tip excitation, a single excitation pulse has been designed that is simultaneously selective in space and resonant frequency. An analytic expression for the response of this pulse has been derived. The pulse has been implemented on a 1.5‐T imaging system. The pulse has been applied to a rapid gradient‐echo imaging sequence that forms both water and fat images within a breath‐holding interval. These rapid images are free of the chemical shift artifacts at organ boundaries that typically afflict conventional rapid images. The pulse can be applied to a variety of other sequences, such as multislice water/fat sequences and rapid k‐space scanning. © 1990 Academic Press, Inc.
Multislice snapshot FLASH using SIMUSIM
Authors: Müller S. 
Published: March 2007

AbstractA combination of the SIMUSIM technique and snapshot ITASH which allows efficient multislice snapshot FLASH imaging is described. Simultaneously acquired images of deliberate slice position and thickness are obtained with an increased SNR compared to standard time sequential multislice experiments. Experimental results show four coronal cross sections through the human head measured in four acquisitions. © 1990 Academic Press, Inc.
Development of the “activated” high resolution 1H MR spectrum in murine T cells and B cells occurs in G1 phase of the cell cycle
Authors: Holmes K. T. , Lean C. L. , Hunt N. H. , King N. J. C. 
Published: March 2007

AbstractT and B lymphocytes stimulated with mitogens develop 'HMR spectra characteristic of triglycerides in an isotropic environment. These distinctive signals, which are also observed in malignant cells, cannot be suppressed by compounds which inhibit progression through the cell cycle. Cellular proliferation is thus not essential for the development and maintenance of high resolution lipid spectra in activated cells. © 1990 Academic Press, Inc.
An in vivo NMR imaging determination of multiexponential Hahn T2 of normal lung
Authors: Shioya Sumie , Christman Rebecca , Ailion David C. 
Published: March 2007

AbstractWe describe the first in vivo imaging determination of normal lung tissue's multiexponential transverse magnetization decay. Normal spontaneously breathing rats were used for the measurements. To obtain motion‐insensitive images, we used a modified line scan imaging technique which we call the interleaved line scan (ILS). The ILS overcomes the following difficulties associated with imaging lungs: low signal‐to‐noise ratio (S/N) due to lung's low proton density and short T2 decay, artifacts associated with cardiac and respiratory motion, and excessively long imaging times with conventional line scan techniques. Using the ILS, a 16‐line 32‐average image with an 8‐s repetition time requires 4.3 min. From a series of 16 Hahn spin‐echo images with echo times ranging from 16 to 90 ms, we obtained a two‐component T2 decay for normal peripheml lung tissue. The measured fast and slow T2 components were 9.5 ± 1.0 and 34 ± 5.0 ms for the right lung and 9.0 ± 1.5 and 32 ± 4.5 for the left lung. The relative magnetization for the slow T2 component was 7.0 ± 4.5% for the right lung and 10 ± 3.0% for the left lung. © 1990 Academic Press, Inc.
Magnetohydrodynamics of blood flow
Authors: Keltner John R. , Roos Mark S. , Brakeman Paul R. , Budinger Thomas F. 
Published: March 2007

AbstractThe changes in hydrostatic pressure and electrical potentials across vessels in the human vasculature in the presence of a large static magnetic field are estimated to determine the feasibility of in vivo NMR spectroscopy at fields as high as 10 T. A 10‐T magnetic field changes the vascular pressure in a model of the human vasculature by less than 0.2%. An exact solution to the magnetohydrodynamic equations describing a conducting fluid flowing transverse to a static magnetic field in a nonconducting, straight, circular tube is used. This solution is compared to an approximate solution that assumes that no magnetic fields are induced in the fluid and that has led previous investigators to predict significant biological effects from static magnetic fields. Experimental results show that the exact solution accurately predicts the magnetohydrodynamic slowing of 15% NaCl flowing transverse to 2.3‐ and 4.7‐T magnetic fields for fluxes below 0.5 liter/min while the approximate solution predicts a much more retarded flow. © 1990 Academic Press, Inc.
Nuclear relaxation of human brain gray and white matter: Analysis of field dependence and implications for MRI
Authors: Fischer Helmut W. , Rinck Peter A. , van Haverbeke Yves , Muller Robert N. 
Published: March 2007

AbstractThe dependence of 1 / T1 on the magnetic field strength (the relaxation dispersion) has been measured at 37°C on autopsy samples of human brain gray and white matter at field strengths corresponding to proton Larmor frequencies between 10 kHz and 50 MHz (0.0002‐1.2 T). Additional measurements of 1 / T1 and 1 / T2 have been performed at 200 MHz (4.7 T) and 20 MHz (0.47 T), respectively. Absolute signal amplitudes are found to be proportional to the sample water content, not to the “proton density,” and it is concluded that the myelin lipids do not contribute to the signal. Transverse magnetization decay data can be fitted with a triple exponential function, giving characteristic results for each tissue type, and are insensitive to variations of the pulse spacing interval. The longitudinal relaxation dispersion curves show characteristic shapes for each tissue type. The most striking difference is a large dispersion for white matter at very high fields. As a consequence, the relative difference in 1 / T1 between gray and white matter shows a marked maximum around 10 MHz. Possible implications for MRI are discussed. A weighted least‐squares fit of the dispersions has been performed using a four‐parameter function of the form

The quality of the fit is superior to that of other functions proposed previously. The results of these fits are used to predict image contrast between gray and white matter at different field strengths. © 1990 Academic Press, Inc.
In vivo flow 31P FT‐NMR spectroscopy of a nematode parasite
Authors: Thompson S. N. , Platzer E. G. , Lee R. W.‐K. 
Published: March 2007

Abstract31P NMR spectroscopy of a parasitic nematode, Steinernema carpocapsae, is described. In vivo spectra were generated from nematode suspensions continuously circulating through the spectrometer. By flowing the organism, saturation effects were avoided and short in‐terpulse delays significantly reduced spectral generation time. To maximize sensitivity, 90° pulses were employed. Changes in energetic status in response to oxygen availability were easily and rapidly monitored in circulating nematodes. © 1990 Academic Press, Inc.
Does IVIM measure classical perfusion?
Authors: Henkelman R. Mark 
Published: March 2007

AbstractMR measurements based on motion encoding gradients provide interesting information about diffusion in tissues and have also been advanced as a way to measure tissue perfusion. This communication shows why IVIM cannot measure perfusion in the classical sense. Attempts to do so result from an unclear understanding of classical perfusion measurements and from confusion between terminal deposition (or uptake) and blood volume flow. © 1990 Academic Press, Inc.
Gradient coil design using active magnetic screening
Authors: Bowtell R. , Mansfield P. 
Published: March 2007

AbstractActive magnetic screening allows the production of gradient coils which are magnetically decoupled from their surroundings. Using such coils the eddy current problems associated with the generation of large, rapidly switched gradients within the confines of a superconductive magnet can be eliminated. In this paper the principles of active screening are outlined and some of the methods of designing screened gradient coils are described. Problems relating to the construction of screened gradient coils are also addressed. © 1991 Academic Press, Inc.