bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acquistion and Accuracy in Rapid NMR Imaging Methods
Authors: Twieg Donald B. 
Published: March 2007

AbstractThe echo‐planar imaging method (EPI) and its variants can acquire data sufficient to form an image in a much shorter time than the Fourier or projection‐reconstruction methods. Fundamental requirements on gradient waveforms and signal sampling are discussed for EPI and SEPI (a variant using sinusoidal gradient waveforms), based on thek‐trajectory formulation of acquisition in NMR imaging. Using a new simulation method, image defects in EPI and SEPI are demonstrated which result from failure to meet these requirements. Faithful rendition of theoretically ideal gradient waveforms places severe demands on gradient system response in rapid imaging. It is shown, however, that nonideal gradient system response need not degrade images if appropriate reconstruction computations are used. Transfer functions and noise power spectra are derived for EPI and SEPI, and the ratio of these two functions is used to derive ideal observer signal‐to‐noise ratios for simple visual interpretive tasks. It is shown that ideal observer performance can differ significantly between EPI and SEPI for some visual tasks, using the same NMR imaging system.© 1985 Academic Press,Inc.
Ferromagnetic contrast agents: A new approach
Authors: Renshaw Perry F. , Owen Charles S. , McLaughlin Alan C. , Frey Terrence G. , Leigh John S. 
Published: March 2007

AbstractMost contrast agents used in NMR imaging studies to date have been paramagnetic. However, it is also possible to obtain selective contrast with a ferromagnetic agent, and these agents are potentially more sensitive than paramagnetic compounds because of their large magnetic moments. The water relaxation ability of ferromagnetic, albumin‐coated magnetite (Fe3O4) particles has been investigated. These particles are quite effective at reducing both T1 and T2 at relatively low particle concentrations. The potential applications of these particles include improved visualization of the liver, gastrointestinal tract, and genitourinary tract, as well as specific targeting and detection of small tumors or other cells with unique surface receptors. © 1986 Academic Press, Inc.
A method for in vivo MR imaging of the short T2 component of sodium‐23
Authors: Ra J. B. , Hilal S. K. , Cho Z. H. 
Published: March 2007

AbstractA magnetic resonance imaging pulse sequence featuring a short echo time of 3.6 ms is described and used clinically for in vivo imaging of sodium‐23 in the human head. In living tissues, sodium exhibits at least two transverse relaxation constants, namely, (a) a short component T2s = 0.7–3.0 ms and (b) a long component T2l = 16–30 ms. Since our first in vivo imaging of sodium, an echo time of 10–15 ms has been used by us and by other investigators. This echo time is adequate for the observation of the long T2 component of sodium. However, a substantial fraction of the sodium, namely, the short T2 component, representing about 40%, has remained undetected by the imaging method with this echo time and is now observable by the new pulse sequence. The proposed method is a hybrid technique combining both projection reconstruction and Fourier encoding schemes. The projection reconstruction is used for the xy plane imaging while the Fourier encoding is used for slice separation. Sodium MR images of the human head produced with a short and a long TE are presented and analyzed. There is an increase in the MR signal and improved visibility of intraparenchymal sodium with the new scheme of short TE. © 1986 Academic Press, Inc.
Multiple field strength in vivo T1 and T2 for cerebrospinal fluid protons
Authors: Hopkins A. L. , Yeung H. N. , Bratton C. B. 
Published: March 2007

AbstractTo estimate the feasibility of measuring in vivo CSF protein, oxygen, or other solutes through their effect on proton relaxation times, the T1 and T2 of CSF protons has been measured within the human lateral ventricles, T1 was measured at 6.25, 25.4, and 60.1 MHz with a two‐point method. T2 was measured at 6.25 and 25.4 MHz using the CPMG sequence to acquire 8 echo images. The T1 was 4.3 s with no evidence of field dependence. The T2 was 2 s. Although these values approach those for water at the same temperature it is possible that the T1 is influenced by the normal oxygen concentration. Calculations based on the relaxivity of dissolved protein indicate that the use of these methods for the detection of elevated levels of CSF protein would be less sensitive than existing methods. © 1986 Academic Press, Inc.
31P NMR studies of adenosine‐stimulated ATP synthesis in perfused luteinized ovaries
Authors: Haseltine F. P. , Arias‐Mendoza F. , Kaye A. M. , Degani H. 
Published: March 2007

Abstract31P NMR spectroscopy was utilized to study phosphate metabolism of perfused ovaries. In luteinized ovaries, a loss in ATP of ∼ 30% with a concomitant acidification was reversed by 50 μM adenosine. The results suggest that in the ovaries, adenosine can serve to regulate ATP concentration during periodic hypoxic challenges. © 1986 Academic Press, Inc.
Nuclear magnetic resonance study of high‐energy phosphate stores in models of adriamycin cardiotoxicity
Authors: Keller Andrew M. , Jackson Jay A. , Peshock Ron M. , Rehr Roger B. , Willerson James T. , Nunnally Ray L. , Buja L. Maximilian 
Published: March 2007

AbstractPrevious studies have suggested that one of the mechanisms of adriamycin (ADR) cardiomyopathy is depletion of high‐energy phosphate stores (HEP). To examine this hypothesis, we used 31P nuclear magnetic resonance to asses the adenosine triphosphate‐to phosphocreatine ratio (ATP‐to‐PCR ratio) in Langendorff‐Perfused rabbit hearts. Using either and acute (5 days of therapy at 5mg/kg /day) or chronic model (7 to 10 weeks of therapy at 1.2 or 1.5mg/kg twice a week) we compared isovolumetric LV systolic pressure, heart rate, ATP‐to‐PCR rations, and histologic lesions between the treated and control animals in each model. In the acute model, there was a significant incraease in the ATP‐to‐PCr ratio (P < 0.02), without significant change in myocardial function. Despite significant hemodynamic and histologic alterations in the chronic model, compared to controle, we were unable to identify significant differences in ATP‐to PCr ratios. We conclude that (a) there appear to be differences in energy metablism between the acute cardiotoxicity and the chronic cardiomyopathy of ADR in the rabbit model and (b) the mechanism of the chronic cardiomyopathy from ADR therpy does not appear to be related to progressive impariment of cellular high‐energy phosphate metabolims as measured by the ATP‐to‐PCr ratio. © 1986 Academic Press, Inc.
Quantitative proton chemical‐shift imaging
Authors: Buxton Richard B. , Wismer Gary L. , Brady Thomas J. , Rosen Bruce R. 
Published: March 2007

AbstractRecently W. T. Dixon (Radiology 153, 189 (1984)) introduced a simple method of proton chemical‐shift imaging which requires only two images, a conventional (in‐phase) image and an image in which fat and water protons are 180° out of phase during signal acquisition, to separate the signals from fat and water protons. We have tested the application of this method to the quantitative determination of fat content and fat and water longitudinal relaxation times, and analyzed the effects of random and systematic errors. Ten phantoms were constructed with a range of fat contents (0–50% by weight) and water T1's (300–800 ms). Fat and water T1's were measured with a 0.6‐T clinical imaging system in two ways: (1) using the system as a spectrometer with all gradients off, and (2) from least‐squares fits to in‐phase and out‐of‐phase image data made with six values of TR. The image‐derived values of water T1 agreed well with spectrometer‐derived values (r = 0.97) and the image derived fat fraction correlated strongly with the fat fraction by weight (r = 0.995). The effects of random and systematic errors were analyzed for a minimum data set of four images: in‐phase and out‐of‐phase images at two values of TR. The pair of TR values which minimize the variance in water T1 were calculated, and for these pulse sequences the effects of two potential systematic errors were calculated: (1) inhomogeneities in the main field, which will reduce the intensity in out‐of‐phase images compared to in‐phase images even for pure water samples, and (2) an incorrect shift of the 180° pulse in the out‐of‐phase pulse sequence, corresponding to an inaccurate assumed chemical shift. With careful attention to such systematic effects the Dixon method is capable of producing reliable quantitative measurements. © 1986 Academic Press, Inc.
A simple fiber optic monitor of cardiac and respiratory activity for biomedical magnetic resonance applications
Authors: Legendre J. P. , Misner R. , Forester G. V. , Geoffrion Y. 
Published: March 2007

AbstractA fiber optic reflectometer, capable of monitoring physiological parameters in a high magnetic field without significant disturbance of either rf or static fields, is described. Both cardiac and respiration rates were monitored with this optical device while31P NMR spectra of the liver of an anesthetized rat were acquired. © 1986 Academic Press, Inc.
Cardiac T1 calculations from MR spin‐echo images
Authors: Prato F. S. , Drost D. J. , King M. , Keys T. , Wisenberg G. , Galland C. , Pflugfelder P. W. 
Published: March 2007

AbstractNormally, cardiac triggering in MR spin‐echo imaging restricts repetition times (TR) to integral values of the cardiac period (TC), and introduces irregularities in TR due to variations in TC. We have investigated how much these restrictions decrease the accuracy and precision of spin‐lattice relaxation (T1) values of the myocardium calculated from two cardiac‐triggered spin‐echo images. By introducing additional excitation pulses, TR can effectively be reduced to a fractional value of TC and considerable improvement in T1 precision is possible. For TC = 800 ms, the improvement in T1 precision is 30% when two spin‐echo images of TR = 1/2 TC and TR = 2 TC are used to calculate T1 instead of two images with TR = TC and TR = 2 TC. The irregularities in TR decrease both T1 precision and accuracy. Irregularities of the order of 15% in a mean TR of 800 ms produce a fourfold decrease in precision. Since irregularities in TC easily exceed 15%, MRI data should be acquired when individual TR values are approximately within ± 15% of the subject's mean TC. © 1987 Academic Press, Inc.
Determination of renal molar concentrations of phosphorus‐containing metabolites in vivo using 31P NMR
Authors: Shine Nancy R. , Xuan Jian Ai , Koretsky Alan P. , Weiner Michael W. 
Published: March 2007

AbstractA technique to determine absolute metabolite concentrations of the kidney in vivo using 31P NMR is described. The technique is based on the use of methylphosphonic acid (MPA), which gives rise to a well‐resolved peak upfield from in vivo phosphorous metabolite resonances, as an “internal standard.” The method involves acquisition of a fully relaxed kidney spectrum with an implanted coil followed by intravenous infusion of MPA (4 ml of 150 mM) for a period of 30 min. The animal is then sacrificed to insure a steady state level of renal MPA and another spectrum is obtained. From these two spectra the ratio of intensities of MPA to β‐ATP was derived. In the method used here, no significant contribution from tissues outside the kidney was observed. In addition, a relatively homogenous distribution of MPA throughout the kidney was achieved. The amount of MPA per gram wet weight of kidney was also obtained through NMR methods by placing the excised organ in a phosphate‐calibrated solenoidal coil. The calibration spectra along with the ratio of intensities for MPA/β‐ATP were used to calculate the number of micromoles of ATP per gram wet weight of kidney. Infusion of a higher concentration of MPA (1.25 M) produced a visible MPA resonance in other organs besides the kidney. Thus, MPA could be useful in determining phosphate metabolite concentrations in other tissues. © 1987 Academic Press, Inc.
31P NMR spectroscopy of an experimentally induced intracerebral tumor in mice
Authors: Ross Brian D. , Higgins Robert J. , Conley Frances K. , True Nancy S. 
Published: March 2007

Abstract31P surface coil NMR spectroscopy was used to evaluate in vivo high‐energy phosphorus metabolism in the brains of mice with experimentally induced primary intracranial and subcutaneous KHT sarcomas. 31P spectra of subcutaneous KHT tumors revealed a lack of detectable phosphocreatine (PCr) levels in the tumor as compared to the relatively high endogenous levels of PCr in normal mouse brain. As the intracerebral tumor size increased, there was a reduction in spectral PCr levels over a 23‐day postinoculation period in situ in the brain. No histologic or spectroscopic evidence of tumor‐associated necrosis or hypoxia was found. This study demonstrates that surface coil 31P NMR spectroscopy can be used to monitor changes in highenergy phosphate metabolism associated with progressive growth of an experimentally induced mouse brain tumor in situ. © 1987 Academic Press, Inc.
Gradient reversal technique and its applications to chemical‐shift‐related NMR imaging
Authors: Park H. W. , Kim D. J. , Cho Z. H. 
Published: March 2007

AbstractThe chemical‐shift effect often degrades slice selectivity thereby degrading the contrast and spatial resolutions in a high‐field NMR imaging. We propose a new pulse sequence which can compensate for this chemical‐shift effect during slice selection. This technique provides correct slice definition as well as clear separation between water and lipid protons in high‐field proton NMR imaging. Particular applications of this technique are 2D imaging with a thin‐slice selection and chunk 3D imaging, where correction of the chemical‐shift effect in slice selection is important. Another interesting application of the technique is chemical‐shift‐selective (CHESS) imaging. This technique does not require spectral‐selective rf pulses and it takes advantage of the chemical‐shift effect during slice selection. The latter is found to be useful for human in vivo chemical‐shift imaging in high‐field NMR. In this paper, the theoretical derivation of the proposed gradient reversal technique, its applications, and related experimental results are presented. © 1987 Academic Press, Inc.
Magnetic resonance imaging of experimental mumps meningoencephalitis in suckling hamsters
Authors: Narayana P. A. , Wolinsky J. S. , Jensen D. J. 
Published: March 2007

AbstractMumps virus‐infected and normal newborn hamster brains were imaged with magnetic resonance (MR) within 24 h after birth and serially scanned. Hydrocephalus developed explosively on Day 6 postinfection and progressed until death occurred soon after Day 10. This study demonstrates the utility of MR in the investigation of experimental viral encephalitis in very small laboratory animals. © 1987 Academic press Inc.
The contrast‐to‐noise in relaxation time, synthetic, and weighted‐sum MR images
Authors: Lee James N. , Riederer Stephen J. 
Published: March 2007

AbstractThe contrast‐to‐noise ratio (CNR) in three types of computed MR images is compared in a computer simulation. The original data consist of two spin‐echo or two saturationrecovery images. Each pair of images is used to generate a relaxation time image, a synthetic image at arbitrary echo or repetition time, and an image which is a weighted sum of the original images. The CNR produced by these three methods is compared for signals spanning a wide range of relaxation times. In every comparison an optimally weighted sum produces the highest CNR that is statistically attainable. The CNR in the optimum synthetic image equals this bound only if contrast reversal does not occur in the original images. The CNR in relaxation time images is always less than the statistical bound and can be less than the CNR in the original images. © 1987 Academic Press, Inc.
Metabolic fate in the dog of the nitroxide moiety in a compound with potential utility as a contrast agent in MRI
Authors: Erikson Ulf G. , Ogan Marc D. , Peng Chin‐Tzu , Brasch Robert C. , Tozerc Thomas N. 
Published: March 2007

AbstractNitroxides, paramagnetic compounds with demonstrated effectiveness as contrast agents in proton magnetic resonance imaging, shorten the relaxation times of protons and therefore cause an increase in image intensity in tissues into which they distribute. In this study, the metabolic fate of the nitroxide moiety was examined in the dog using a pyrrolidine nitroxide derivative, 2,2,5,5‐tetramethylpyrrolidine‐l‐oxyl‐3‐carbxylic acid, for which contrast‐enhancing properties have been previously studied in animals. After radiolabeling by microwave discharge in the presence of tritium gas, the compound was administered intravenously to a dog. Ninety‐four percent of the radioactivity injected was recovered in urine within 3 days; the majority (90%) was excreted during the first 6 h. The radioactivity in the urine was identified as either the unchanged nitroxide or its corresponding hydroxylamine. Neither complete reduction of the nitroxide moiety to the amine nor any other metabolic transformation was observed. © 1987 Academic Press, Inc.
Random noise selective excitation pulses
Authors: Ordidge Roger J. 
Published: March 2007

AbstractSeveral methods for the spatial localization of NMR signals from well‐defined regions of tissue within extended specimens have been proposed. Most of these techniques are prone to signal error which can arise from large volumes of sample that surround the region of interest. These errors can theoretically be reduced by several orders of magnitude by the application of a radiofrequency prepulse. The pulse acts to randomize the unwanted spin magnetization prior to the application of a spatial localization technique.
MR in renal disease: Importance of cortical–medullary distinction
Authors: Marotti Miljenko , Hricak Hedvig , Terrier Francois , McAninch Jack W. , Thuroff Joachim W. 
Published: March 2007

AbstractThe diagnostic value of MR contrast between renal cortex and medulla (CMC) as an indicator of renal disease was retrospectively studied in 51 patients (9 patients with obstructive disease, 7 with inflammatory disease, 12 with various noninfectious parenchymal medical disease, 5 with vascular disease, 2 with diffuse neoplastic disease, 7 with hemosiderosis, and 10 with renal trauma [blunt trauma and 9 postlithotripsy]). Additionally, normal kidneys from 20 control subjects were studied. On T1‐weighted spin‐echo images (SE 500/30), CMC was visible in all the normal kidneys (19% contrast ± 2% SD). A decrease in or an absence of CMC on T1‐weighted images (SE 500/28) was found to be a sensitive but nonspecific sign in most of the renal diseases studied. CMC was visibly preserved at normal levels in 7 of the 9 kidneys traumatized by lithotripsy and in all 4 kidneys with acute renal obstruction; CMC was above normal in kidneys with hemosiderosis. In conclusion, alteration in CMC is a sensitive but nonspecific indicator of renal disease. Furthermore, normal CMC can be seen in the presence of renal pathology. © 1987 Academic Press, Inc.
An MRI phantom material for quantitative relaxometry
Authors: Kraft K. A. , Fatouros P. P. , Clarke G. D. , Kishore P. R. S. 
Published: March 2007

AbstractMost phantom media in current use exhibit T1 relaxation times that are significantly dependent on both temperature and operating frequency. This can introduce undesirable variability into relaxation measurements due to temperature fluctuations, and complicates direct comparison of imagers operating at different magnetic field strengths. Our investigations of a nickel‐doped agarose gel system have demonstrated near independence of the proton relaxation rates to a wide range of temperatures and frequencies. We therefore propose the adoption of Ni2+ as a relaxation modifier for phantom materials used as relaxometry standards. © Academic Press, Inc.
Functional evaluation of the heart with magnetic resonance imaging
Authors: Higgins Charles B. , Holt William , Pflugfelder Peter , Sechtem Udo 
Published: March 2007

AbstractThis review examines the capability of cine MRI for evaluation of cardiovascular function and shows early results in valvular, ischemic, and congenital heart disease. MR assessment of left and right ventricular volumes is independent of geometrical models; dimensional values have been defined for normal individuals. Noninvasive measurement of peak and end systolic pressure along with cine MR imaging can be used to calculate left ventricular meridional wall stress which can be used for monitoring of myocardial diseases and evaluation of therapeutic intervention. Cine MR may be more accurate than angiography for identifying regional LV dysfunction since it can measure wall thickening as well as inward wall motion. Regurgitant jets due to valvular lesions are readily seen and their characteristics may be used to define the severity of aortic or mitral regurgitation. Calculation of the regurgitant volume separates patients with mild, moderate, or severe disease. Likewise, the shunt flow across ventricular and atrial septal defects has been visualized in cine MR images and shunt flow calculated. Cine MRI serves as a three‐dimensional imaging technique with high temporal resolution. It extends the capability of MRI in cardiac disease beyond the depiction of anatomy and renders a comprehensive cardiac imaging technique for quantitation of cardiac anatomy and function. © 1988 Academic Press, Inc.
Metabolic profiling of body fluids by proton NMR: Self‐poisoning episodes with paracetamol (acetaminophen)
Authors: Bales J. R. , Bell J. D. , Nicholson J. K. , Sadler P. J. , Timbrell J. A. , Hughes R. D. , Bennett P. N. , Williams R. 
Published: March 2007

AbstractIH NMR spectra of urine and plasma from subjects who had taken paracetamol (acetaminophen) at a therapeutic dose or in self‐poisoning episodes (both fatal and nonfatal) are compared. They provide convenient metabolic profiles. For overdose cases, intense resonances corresponding to high levels of both drug and endogenous metabolites are observed. The ratios of glucuronide to sulfate conjugates are unusually high in urine from overdose cases. Elevated levels of the cysteinyl and N‐acetyl cysteinyl conjugates reflect increased glutathione conjugation in the liver. The observed excretion of high levels of amino acids by overdose subjects is suggestive of drug‐induced hepatic damage. No resonances for drug metabolites are detected in plasma samples. However, characteristic and abnormally intense resonances for the amino acids Phe, Tyr, His, Gin, Pro, Ala, Val, Lys, Met, Ser, and Thr are indicative of severe liver failure and disruption of normal deamination and transamination processes. © 1988 Academic Press, Inc.