bluuebunny/crossref_metadata_2025_split huggingface dataset:
Small animal imaging with a clinical magnetic resonance imager
Authors: Henkelman R. Mark , van Heteren John G. , Bronskill Michael J. 
Published: March 2007

AbstractAny clinical whole‐body MR imager can be adapted for experimental small animal imaging. The design of an if receiver coil and an efficient magnified imaging technique are presented. Application of this small animal imaging technique is illustrated using a study of paramagnetic contrast enhancement of a tumor in the mouse. © 1987 Academic Press, Inc.
Flow velocity measurement with ac gradients
Authors: Walton J. H. , Conradi Mark S. 
Published: March 2007

AbstractTwo NMR experiments are described that use ac field gradients to measure flow velocities. Both experiments perform no spacial localization; instead, fluid velocity is converted to a resonance frequency shift. Thus, by Fourier transformation of a single FID or echo train the distribution of velocities is available. The first experiment uses only one of pulse but requires a homogeneous static field. The second experiment uses the CPMG multiple‐pulse sequence to refocus the effects of field inhomogeneity and chemical shifts. Results are shown for both experiments using a simple flowing phantom. Applications of the techniques to time‐resolved blood flow measurement are discussed. © 1987 Academic Press, Inc.
Simplified mathematical description of longitudinal recovery in multiple‐echo sequences
Authors: Conturo Thomas E. , Beth Albert H. , Arenstorf Richard F. , Price Ronald R. 
Published: March 2007

AbstractThe intensity of multiple echoes separated by a time 2τ has been modeled using the closed form of a finite geometric series. This eliminates long exponential series, introduces the number of echoes as an independent parameter, and corrects for the net T1 relaxation during the echo train. Other sequences having echo trains can be modeled similarly. © 1987 Academic Press, Inc.
Spin‐echo proton NMR spectroscopy of urine samples. Water suppression via a urea‐Dependent T2 relaxation process
Authors: Connor S. , Everett J. , Nicholson J. K. 
Published: March 2007

AbstractSpin‐echo methods have been used to effect solvent suppression during the collection of 400 and 500 MHz 1H NMR spectra of urine samples containing urea in the concentration range 0.7–1.2 M. There was a marked trough of water T values in the pH* range 2.6 to 4.1, due to acidcatalyzed proton exchange between urea and the solvent water. Minimum values of T (9 ms at 500 MHz) of water were obtained at about pH* 3.2 in urine samples containing 1.2 M urea. However, good solvent suppression factors were obtained with endogenous urea concentrations of only 0.7 M. There was a strong field dependence on the water, T2 over the pH range 2 to 4. Attenuation of the water signal was estimated to be at least an order of magnitude greater at 500 MHz rather than at 400 MHz. Using the Cam‐Purcell‐Meiboom‐Gill spin‐echo pulse sequence, water signals broader than 13 Hz were attenuated by factors of > 103, and factors of > 104 were possible with water linewidths greater than 20 Hz, thus allowing the signals from metabolites in the sample to be efficiently digitized. This approach allowed metabolite signals at or near the water resonance to be observed without serious distortion of their intensities. The utility of this approach to solvent suppression in real systems is illustrated by observation of paracetamol and benzyl penicillin metabolites in human urine samples. © 1987 Academic Press, Inc.
The fate of inorganic phosphate and pH in regional myocardial ischemia and infarction: A noninvasive 31P NMR study
Authors: Bottomley P. A. , Smith L. S. , Brazzamano S. , Hedlund L. W. , Redington R. W. , Herfkens R. J. 
Published: March 2007

AbstractTo determine the characteristic appearance of phosphorus (31P) nuclear magnetic resonance spectra in acute and chronic myocardial infarction in situ. cardiac‐gated depth‐resolved surface coil spectroscopy (DRESS) at 1.5 T was used to monitor 31P NMR spectra from localized volumes in the left anterior canine myocardium for up to 5 days following permanent occlusion of the left anterior descending coronary artery. Coronary occlusion initially produced regional ischemia manifested as significant reductions in the phosphocreatine (PCr) to inorganic phosphate (Pi) ratios and intracellular pH (P < 0.05, Student's t test) in endocardially displaced spectra acquired in periods as short as 50 to 150 s postocclusion. Spectra acquired subsequently revealed either (i) restoration of near‐normal phosphate metabolism sometime between 10 and about 50 min postocclusion or (ii) advancing ischemic phosphate metabolism at about an hour postocclusion, and/or (iii) maintenance of depressed PCI/P1 ratios for up to 5 days postocclusion with a return of the apparent pH to near normal values between 6 and 15 h postocclusion. Postmortem examination of animals exhibiting the first type of behavior revealed the existence of coronary collateral vessels. The last type of behavior indicates that P1 remains substantially localized in damaged myocardium for days following infarction. The location and size of infarctions were determined postmortem by staining excised hearts. The smallest infarctions detected by 31P DRESS weighed 4.9 and 7.5 g. The most acidic pH measured in vivo was 5.9 ± 0.2. Infarctions aged 1/2 day to 5 days were characterized by elevated but broad P1 resonances at 5.1 ± 0.2 ppm relative to PCr and significantly depressed PCr/P1 ratios (P < 0.002, Student's t test) relative to preocclusion values. Contamination of P1 resonances by phosphomonoester (PM) components is a significant problem for preocclusion P1 and pH measurements. These results should be applicable to the detection and identification of human myocardial infarction using 31P NMR and DRESS. © 1987 Academic Press, Inc.
Noise reduction in wide‐bore magnets using a patient cage
Authors: Ceckler Toni L. , Bryant Robert G. , Hornak Joseph P. 
Published: March 2007

AbstractSignificant rf noise reduction is demonstrated by enclosing the patient in a conducting cage grounded to the magnet bore in a 22‐cm‐bore spectrometer system capable of examining magnetic images and spectroscopy of human limbs. This method of noise reduction was found to be reliable, simple, and efficient for dealing with ambient rf noise in an unshielded room. © 1987 Academic Press, Inc.
Spectral resolution in clinical magnetic resonance spectroscopy
Authors: Cox I. Jane , Bryant David J. , Ross Brian D. , Young Ian R. , Gadian David G. , Bydder Graeme M. , Williams Stephen R. , Busza Albert L. , Bates Timothy E. 
Published: March 2007

AbstractWe observe linewidths of 0.1–0.4 ppm in 31P spectra of human muscle, liver, and brain. T2 measurements of muscle phosphocreatine, together with previous brain studies, indicate that further improvements in linewidth to 0.02–0.05 ppm might often be achieved, but in same lesions magnetic susceptibility variations may limit spectral resolution. © 1987 Academic Press, Inc.
General solution to the NMR excitation problem for noninteracting spins
Authors: Ngo J. Thomas , Morris Peter G. 
Published: March 2007

AbstractThe design of an NMR excitation scheme, whether selective or nonselective, is essentially the simultaneous inversion of an array of Bloch equations driven by magnetic fields which differ according to well‐defined constraints. We find that if relaxation effects are negligible, nearly exact inversion of the Bloch equations is straightforward when performed in a special time‐varying frame of reference. Repeated inversions of the Bloch equations for small perturbations provide the basis for arbitrarily large, optimal adjustments of the magnetization response to an applied time‐varying magnetic field. Choice of the target response to be sought at each iteration is not trivial if overall adjustments of more than one‐half rotation are required. We present the analysis both formally and in geometric terms and show how it leads to a general algorithm for the optimization of NMR excitation schemes. The unprecedented efficiency of the algorithm and its ability to generate novel pulses from distant starting approximations are demonstrated in the optimization of slice‐selective π/2 pulses for inversion and refocusing, and a prefocused slice‐selective π/2 pulse. Other applications are discussed, including use of the algorithm to compensate for instrumental imperfections such as radiofrequency inhomogeneity. © 1987 Academic Press, Inc.
Real‐time movie imaging from a single cardiac cycle by NMR
Authors: Chapman B. , Turner R. , Ordidge R. J. , Doyle M. , Cawley M. , Coxon R. , Glover P. , Mansfield P. 
Published: March 2007

AbstractUsing a 1‐m‐bore super conductive magnet at 0.1 T, whole‐body transverse images through adult humans have been obtained at repetition times of 57 ms. The techniques used were minor variations of echo‐planar imaging (EPI) employing large pulsed gradients to provide complete coverage of the plane in phase space, and low‐angle RF excitation sequences allowing rapid repetition of the experiment. In addition active magnetic screening of the gradient coils was implemented to protect the surrounding magnet from the eddy currents induced by the necessarily fast switching of the large gradient fields. © 1987 Academic Press, Inc.
The Development of a pH‐sensitive contrast agent for NMR 1H imaging
Authors: Helpern Joseph A. , Curtis Jeff C. , Hearshen David , Smith Jmichael B. , Welch Kenneth M. A. 
Published: March 2007

AbstractFe(III)meso‐tetra(4‐sulfonatophenyl)porphine (Fe‐TPPS,) has been investigated as a potential pH‐sensitive nuclear magnetic resonance (NMR) proton image contrast agent. Relaxation rates (1/T1, and 1/T2) of water protons were measured as a function of pH and concentration of Fe‐TPPS, in phosphate‐buffered isotonic saline. Transverse relaxation rates (1/T2) did not change appreciably with pH above 6.0. Longitudinal relaxation rates (1/T1) increased significantly between pH 7.75 and 5.75. This effect was more pronounced with the increasing concentration of Fe‐TPPS, from 0.1 to 1. 5 mM and is attributed to a pH‐dependent equilibrium between the high‐spin (S = 5/2) Fe–TPPS4 monomer at low pH and the antiferromagnetically coupled μ‐oxodimer O–(FeTPPS4)2 at high pH. The efficacy of this pH‐dependent contrast agent is demonstrated in vitro. © 1987 Academic Press, Inc.
Measurement of lactate accumulation by in Vivo proton NMR spectroscopy during global cerebral ischemia in rats
Authors: Richards T. L. , Keniry M. A. , Weinstein P. R. , Pereira B. M. , Andrews B. T. , Murphy E. J. , James T. L. 
Published: March 2007

AbstractIn vivo 1H NMR spectral editing techniques were used to monitor cerebral lactate production during remotely controlled temporary forebrain ischemia in rats. The lactate/N‐acetylaspartate (NAA) ratio correlated with survival after ischemia and subsequent reperfusion. The lactate/NAA ratio that predicted death after ischemia in rats was estimated to be approximately 1.3. © 1987 Academic Press, Inc.
Fast three‐dimensional imaging of cerebrospinal fluid
Authors: Hennig J. , Friedburg H. , Ott D. 
Published: March 2007

AbstractThe RARE method is based on the principle of echo imaging to generate images with high T2 contrast. Since RARE is a fast imaging method, it can be used to acquire a high‐resolution three‐dimensional data set in less than 15 min. Thin slices from such a three‐dimensional data set provide detailed information about the ventricular system. © 1987 Academic Press, Inc.
RLSQ: T1, T2, and ρ calculations, combining ratios and least squares
Authors: in den Kleef J. J. E. , Cuppen J. J. M. 
Published: March 2007

AbstractA method is proposed for calculating images of spin density p and relaxation times T1 T2 from MR imaging sequencies with the following characteristics:

it avoids nonlinear iterative techniques and is consequently sufficiently fast to allow calculation ofp, T1 and T2 on a pixel by pixel basis routinely;
it uses all available data simultaneously in an approximately optimal fashion.
The method is applied to the combined SE + IR sequence but can be used for other acquisition Schemes as Well. © Academic Press, Inc.
Triple nuclear NMR studies of cerebral metabolism during generalized seizure
Authors: Schnall M. D. , Yoshizaki K. , Chance B. , Leigh J. S. 
Published: March 2007

AbstractNoninvasive NMR spectroscopy of 1H, 31P, and 23Na is performed simultaneously to study brain metabolism during grand mal seizures. Decreases in PCr and increases in lactate associated with seizure as well as an intracellular shift of the Na+ ion pool are demonstrated. A close correlation between the phosphate potential and the intensity of the seizure, as well as the intra/extracellular ionic gradient, is shown. © 1988 Academic Press, Inc.
An analysis of fast imaging sequences with steady‐state transverse magnetization refocusing
Authors: Zur Yuval , Stokar Saul , Bendel Peter 
Published: March 2007

AbstractRecently, several groups have proposed and demonstrated the use of rapid imaging methods, using short pulse repetition times and gradient‐reversal echoes. Here, we analyze the behavior of the magnetization and the resulting image contrasts in such sequences for the case where the pulse repetition time TR is of the order of, or shorter than, the transverse relaxation time T2, and the transverse magnetization is not destroyed between phase‐encoding cycles. Exact analytical expressions describing the signal evolution between the pulses are derived, taking into account the effects of resonance offsets and flip angles, and examining the influence of constant‐phase or alternate‐phase RF pulse trains. It is shown that for typical imaging sequences two distinct echo signals will develop between pulses, which may have a detrimental effect on image quality if they partially overlap within the sampling window. It is shown that artifact‐free images can be obtained only if the two echo signals overlap precisely, which seems technically close to impossible to achieve, or if they are sufficiently separated in time to allow sampling of only one of the signals. © 1988 Academic Press, Inc.
FADE–A new fast imaging sequence
Authors: Redpath T. W. , Jones R. A. 
Published: March 2007

AbstractA series of rapid, equally spaced rf pulses of constant amplitude produces two distinct components of transverse magnetization. FADE (fast acquisition double echo) is a new Fourier steady‐state free precession (SSFP) imaging sequence which images both components separately in each interpulse interval. The first component gives more signal than the second but lacks contrast while the second is strongly T2 weighted. © 1988 Academic Press, Inc.
A simple high‐frequency antenna for NMR imaging
Authors: Sergiadis George 
Published: March 2007

AbstractThe classic whole‐body or head antennas for NMR imaging do not resonate properly at higher frequencies. The high‐frequency antenna presented is constructed from segments of transmission lines and is treated as a distributed parameter system. It has an RF magnetic response similar to that of the classic saddle‐shaped antenna, has low exposed impedance to avoid dielectric losses in the patient, and does not disturb the magnetic field gradients. The implementation of a whole‐body antenna for 64 MHz is described and tested. © 1988 Academic Press, Inc.
Nuclear magnetic resonance relaxation in experimental brain edema: Effects of water concentration, protein concentration, and temperature
Authors: Kamman R. L. , Go K. G. , Brouwer W. , Berendsen H. J. C. 
Published: March 2007

AbstractProton relaxation times T1 and T2 of macromolecular solutions, bovine brain tissues, and experimental cat brain edema tissues were studied as a function of water concentration, protein concentration, and temperature. A linear relation was found between the inverse of the weight fraction of tissue water and the spin‐lattice relaxation rate, R1, based on a fast proton exchange model for relaxation. This correlation was also found for the spin‐spin relaxation rate, R2, of gray matter samples and macromolecular solutions at low concentrations. Concentrated solutions of protein‐water samples showed an enhanced relaxation due to viscosity effects. The T2 of white matter was considerably lengthened with elevated water concentration, but showed no straightforward relation with the total tissue water content. The relaxation times of all samples increased with temperature, supporting the assumption of fast proton exchange in the model for relaxation. This was not found for white matter, in which T2 decreased with increasing temperature, which indicated that intermediate or even slow exchange was present. The relation found between relaxation times and tissue water content can be used to predict the amount of and/or increase in tissue water due to water‐elevating processes such as edema. © 1988 Academic Press, Inc.
Multifrequency selective rf pulses for multislice MR imaging
Authors: Müller S. 
Published: March 2007

AbstractA method is described for multislice imaging by means of rf pulses which contain a multifrequency excitation spectrum. These pulses label each slice by an individual signal phase and allow the separation of the signals from all the slices by subsequent add/substract procedures. The image sensitivity corresponds to the total number of acquisitions. Sequences for the imaging of an arbitrary number of slices with a minimum number of experiments are described. © 1988 Academic Press, Inc.
High‐resolution H NMR spectral signature from human atheroma
Authors: Pearlman Justin D. , Zajicek Jaroslav , Merickel Michael B. , Carman Charles S. , Ayers Carlos R. , Brookeman James R. , Brown Michael F. 
Published: March 2007

AbstractCoronary artery disease due to atherosclerosis takes the lives of approximately 550,000 Americans each year—an enormous toll. Put in economic terms, the cost to the United States alone has been estimated to exceed 60 billion dollars annually. We have found that well‐resolved proton (1H) NMR spectra can be obtained from human atheroma (fatty plaque), despite its macroscopic solid appearance. The fraction of the total spectral intensity corresponding to the sharp 1H NMR signals is temperature dependent and approaches unity at body temperature (37°C). Studies of the total lipids extracted from atheroma and cholesteryl esters were conducted to identify the chemical and physical origin of the spectral signature. The samples were characterized through assignment of their chemical shifts and by measurement of their T1 and T*2 relaxation times as a function of magnetic field strength. The results suggest that the relatively sharp 1H NMR signals from human atheroma (excluding water) are due to a mixture of cholesteryl esters, whose liquid‐crystalline to isotropic fluid phase transition is near body temperature. Preliminary applications to NMR imaging of human atheroma are reported, which demonstrate early fatty plaque formation within the wall of the aorta. These findings offer a basis for noninvasive imaging by NMR to monitor early and potentially reversible stages of human atherogenesis. © 1988 Academic Press, Inc.
Metabolic changes in human muscle denervation: Topical 31P NMR spectroscopy studies
Authors: Zochodne D. W. , Thompson R. T. , Driedger A. A. , Strong M. J. , Gravelle D. , Bolton C. F. 
Published: March 2007

AbstractMetabolic changes in human forearm flexor muscle following partial or complete denervation were studied using 31P nuclear magnetic resonance spectroscopy. In resting muscle, patients with electromyographically verified forearm flexor denervation had a lower ratio of PCr/Pi than healthy controls [4.76 ± 2.50 (SD) versus 6.50 ± 1.55 (SD); P < 0.01] and a higher intracellular pH [7.09 ± 0.06 versus 7.05 ± 0.04 (SD); P < 0.01]. These changes were more apparent when the diseased arm was compared to the contralateral healthy arm in patients with strictly unilateral denervation. Five patients with severe denervation had the lowest PCr/Pi ratio (1.94 ± 0.70) and the highest pH (7.15 ± 0.04). Four patients with intact innervation and disuse atrophy as a result of a forearm fracture did not exhibit these changes immediately following removal of the forearm cast. The findings show that denervation leads to a reduction in PCr/P, within muscle and a rise in intracellular pH, and that these changes correlate with the degree of denervation and improve with recovery. 31P MRS may be useful to follow the course of denervation atrophy. © 1988 Academic Press, Inc.
Application of a T2,‐filtered COSY experiment to identify the origin of slowly relaxing species in normal and malignant tissue
Authors: Williams P. G. , Saunders J. K. , Dyne M. , Mountford C. E. , Holmes K. T. 
Published: March 2007

AbstractThe 1H NMR spectrum of whole cells consists of many overlapping resonances which are difficult to resolve into individual components. We have developed a modification of the COSY pulse sequence which filters out resonances on the basis of their T2 relaxation rate. When applied to malignant cells, this technique has helped to identify fucose as the origin of the slowly relaxing species associated with their metastatic capacity. The technique can also be used to obtain T2 relaxation rates for individual resonances in a broad envelope of lines. © 1988 Academic Press, Inc.
Gadolinium‐labeled liposomes containing paramagnetic amphipathic agents: Targeted MRI contrast agents for the liver
Authors: Kabalka G. W. , Buonocore E. , Hubner K. , Davis M. , Huang L. 
Published: March 2007

AbstractUnique paramagnetic liposomal contrast agents were synthesized and utilized for se lective augmentation of TI MR imaging of the livers of normal Balb/c mice. Amphipathic gadolinium complexes, which mimic phospholipids, were incorporated into the lamella of small unilamellar liposomes (SUV) such that they became an integral part of its surface. T 1 signal enhancement of normal liver approached 150% after iv administra‐ tion of the paramagnetic liposomes, determined by experiments performed on a 1.9‐T, experimental whole‐body MRI unit. Tracer studies utilizing gadolinium‐ 153‐tagged SUV revealed that the agents exhibited excellent in vivo stability, compared to liposomal preparations in which paramagnetic agents are simply entrapped in the aqueous core of the liposome vesicle. © 1988 Academic Press, Inc.
Magnetic resonance angiography by selective inversion recovery using a compact gradient echo sequence
Authors: Nishimura Dwight G. , Macovski Albert , Jackson John I. , Hu Robert S. , Stevick C. Andrew , Axel Leon 
Published: March 2007

AbstractWe have studied a pulse sequence using compact imaging gradients for MR angiography by selective inversion recovery. By acquiring signals approaching a half‐echo, we achieve significant immunity to artifacts from flow‐induced dephasing. Initial clinical results on carotid arteries accurately depict stenoses without the problems of signal dephasing. © 1988 Academic Press, Inc.
In vivo31P NMR studies of rat salivary glands at 6.3 tesla
Authors: Heerschap A. , van Vaals J. J. , Bergman A. H. , den Boef J. H. , van Gerwen P. H. J. , Gravenmade E. J.'S 
Published: March 2007

AbstractIn vivo31P NMR spectra of rat submandibular glands were obtained. The glands were exposed, leaving the neurovascular system intact, and placed in a solenoidal coil. Resonances of nine phosphate metabolites were identified in the spectra and metabolite concentrations were estimated from the corresponding integrals ([ATP] = 3.4 ± 0.7 mM). Tissue pH, as deduced from the chemical shift ofthe inorganic phosphate resonance, was 7.26 (±0.07). T1 relaxation times of ATP, phosphocreatine, inorganic phosphate, and phosphomonoester 31P spin systems were examined. The effect of hypoxia was followed as a function of time. 31P NMR spectra of the glands have also been obtained noninvasively by the use of a surface coil, adapted to the dimensions of the glands, and depth pulses. © 1988 Academic Press, Inc.