bluuebunny/crossref_metadata_2025_split huggingface dataset:
The design of pulse sequences employing spatial presaturation for the suppression of flow artifacts
Authors: Mugler John P. , Brookeman James R. 
Published: March 2007

AbstractThe use of spatial presaturation to suppress the signal, and therefore also the artifacts, from flowing blood has become an important tool in the arsenal of techniques to suppress pulsatile flow artifacts in magnetic resonance images. However, a detailed theoretical analysis of the behavior of these flow artifact suppression pulses and of the important aspects of implementing suppression pulses in combination with particular imaging sequences has yet to be presented. In this paper we present a general theoretical framework to describe the flow artifact suppression technique. This analysis addresses the following four major issues: (1) the spin washout characteristics of the imaging sequence, (2) the interference between the flow signal suppression pulses and the imaging sequence, (3) the flow velocity range for a single application of the suppression pulse, and (4) the total flow velocity range for a suppression pulse repeated with a constant time interval between applications of the pulse. The predictions of our theoretical model are confirmed by experimental measurements made with stationary and flow phantoms. The results of this investigation provide guidelines for the design of flow artifact suppression pulse sequences and, in addition, should aid in the future development and refinement of the spatial presaturation technique as applied to flow Signal Suppression. © 1992 Academic Press, Inc.
The progression of spermatogenesis in the developing rat testis followed by 31P MR spectroscopy
Authors: van der Grond Jeroen , Laven Joop S. E. , van Echteld Cees J. A. , Dijkstra Grietje , Grootegoed J. Anton , de Rooij Dirk G. , Mali Willem P. Th. M. 
Published: March 2007

AbstractTo evaluate the use of human testicular 31P MR spectroscopy as a diagnostic tool to differentiate between several stages of male infertility, we have studied the testicular levels of several phosphorus containing compounds in the rat in relation to the condition of spermatogenesis and the cell types present in the seminiferous tubules of the testis. During testicular maturation several characteristic changes occur in the 31P MR spectrum of the testis of male Wistar rats. The phosphomonoester/adenosine triphosphate (PM/ATP) ratio shows a decline from 1.61 to 1.02 between the age of 3 and 12 weeks, whereas the phosphodiester (PD)/ATP ratio increases from 0 to 0.72. The testicular pH increases in the same time from 7.06 to 7.32. Testicular MR data obtained after 12 weeks of age onward do not show significant change anymore. The high PM/ATP ratio is associated by a relative high amount of proliferating spermatogonia and spermatocytes during meiosis in the testis, whereas the PD peak seems to be correlated with the release and maintenance of spermatozoa. The MR spectra show a specific fingerprint in all developmental stages of the rat testis as a result of the different cell types in the testis. © 1992 Academic Press, Inc.
Effects of local irradiation on spin‐lattice relaxation time of phosphate metabolites in mouse tumors monitored by 31P magnetic resonance spectroscopy
Authors: Li Shi‐Jiang , Jin Guan‐Yuan , Moulder John E. 
Published: March 2007

AbstractAn inversion‐recovery pulse sequence and solenoidal surface coil were employed to determine the spin‐lattice relaxation time (T1) in murine tumors (RIF‐1 and SCCVII). Reduction in T1s of inorganic phosphate (Pi) and nucleotide triphosphates (NTP) has been observed in irradiated tumors compared with unirradiated tumors. The reduction is accompanied by tumor regression and improved tumor energetic status in both tumor lines. The results of the TI measurement of phosphate metabolites in tumors suggest that partial saturation effects may exist in spectra and could effect quantitative analysis when short repetition time is used. The reduction in T1s of Pi and NTP may be attributed to the active biochemical exchange and better tumor oxygenation in irradiated tumors. © 1992 Academic Press, Inc.
Tissue conductivity modifies the magnetic resonance intrinsic signal‐to‐noise ratio at high frequencies
Authors: Foster Thomas H. 
Published: March 2007

AbstractInclusion of a frequency‐dependent tissue conductivity in the calculation of the magnetic resonance imaging signal‐to‐noise ratio is considered. The linear dependence of field strength described previously by Edelstein is preserved for frequencies up to ≈60 MHz. At higher frequencies, tissue conductivity effects become significant. © 1992 Academic Press, Inc.
Proton nuclear magnetic resonance studies on water structure in peritumoral edematous brain tissue
Authors: Iwama T. , Yamada H. , Era S. , Sogami M. , Andoh T. , Sakai N. , Kato K. , Kuwata K. , Wataris H. 
Published: March 2007

AbstractSpin–lattice relaxation times (T1) of water protons and cross‐relaxation times (TIS) between irradiated protein and water protons were measured to study the water structure in peritumoral edematous brain tissue of rats. Despite small changes in T1, water, and electrolyte contents, TIS values of water protons were significantly reduced in peritumoral edematous brain tissue when compared to those of the controls. Results indicate that the water structure in brain tissues may become altered at an early stage of edemic formation without causing any significant changes in cellular hydration. TIS, might serve as a sensitive parameter for studying the water structure in a variety of tissues, such as in edematous brain tissue. © 1992 Academic Press, Inc.
Noise correlation in multicoil receiver systems
Authors: Redpath T. W. 
Published: March 2007

AbstractWhen two or more rf coils are used to receive NMR signals from the same part of the patient, the overall sensitivity of an image formed from some combination of these signals may be degraded if noise voltages in the coils are correlated. Whereas it is straightforward to calculate correlation caused by noise sources in the coils themselves, there is disagreement about noise correlation when that noise arises from thermally driven currents within the body itself. A general analysis based on the principles of reciprocity, superposition, and energy conservation yields an equation for sample‐induced noise correlation in terms of circuit impedances. Furthermore, the analysis yields a very simple expression for the total noise correlation (i.e., noise from patient and coil elements) between the coils. This latter expression is applicable to any two‐port receiver coil assembly, including single coils with two modes, such as a birdcage coil, and in general, to any two ports of an n‐port receiver system. © 1992 Academic Press, Inc.
T1ρ dispersion imaging and localized T1ρ dispersion relaxometry: Application in vivo to mouse adenocarcinoma
Authors: Rommel E. , Kimmich R. , Körperich H. , Kunze C. , Gersonde K. 
Published: March 2007

AbstractThe dispersion (frequency dependence) of the spin‐lattice relaxation time in the rotating frame, T1ρ, is considered for tissue characterization. Methods for the volume‐selective determination of the proper T1ρ, dispersion and for imaging of parameters characterizing this frequency dependence are described. On‐ and off‐resonance versions of the techniques are demonstrated. In vitro studies of excised rat tissues and in vivo applications to mice with implanted adenocarcinoma are reported. T1ρ, dispersion images show clear contrasts of the malignant tissue, whereas muscle tissue is completely suppressed. No contrast agent is required. The measuring time is only twice as long as that for conventional magnetic resonance images. The results suggest that the T1ρ, dispersion is less susceptible to the biological variability than the absolute values of the relaxation times. © 1992 Academic Press, Inc.
A hybrid bird cage resonator for sodium observation at 4.7 T
Authors: Pimmel P. , Briguet A. 
Published: March 2007

AbstractA bird cage resonator operating at 52.9 MHz is described. The particularity of the presented design is due to fixed capacitors between conductors. Tuning is performed by adjusting a self‐capacitance system without breaking the coil symmetry. This structure denoted as “hybrid” is suitable for biological lossy samples. © 1992 Academic Press, Inc.
Measurement of blood‐brain barrier permeability using dynamic Gd‐DTPA scanning—a comparison of methods
Authors: Larsson H. B. W. , Tofts P. S. 
Published: March 2007

AbstractTwo recently published methods of blood‐brain barrier permeability measurement using Gd‐DTPA scanning are compared by authors representing each group. The physiological models are reconciled. Results from both groups agree. These show that the transfer constant (the permeability surface area product per unit volume of tissue) of the defective blood‐brain barrier in multiple sclerosis is in the range 1‐12·10−4s−1 © 1992 Academic Press, Inc.
ECG‐optimized phase contrast line‐scanned MR angiography
Authors: Korosec F. R. , Mistretta C. A. , Turski P. A. 
Published: March 2007

AbstractWe describe a rapid phase contrast line scan MR angiographic imaging technique. A projection angiogram is obtained by sequentially imaging a series of thin slices oriented perpendicular to the primary flow direction. Bipolar gradient subtraction is employed to suppress signal from static tissues, which in turn allows elimination of phase encoding in the depth dimension. The sequence is cardiac gated to improve image quality and to allow observation of hemodynamics. To further improve image quality, the amplitude of the bipolar gradient is altered throughout the cardiac cycle to provide maximum vessel signal at all cardiac phases. The ECG‐gated phase contrast line scan sequence has been used to image regions where cardiac pulsatility and respiratory motion compromise the quality of images obtained using standard spin warp angiographic methods. © 1992 Academic Press, Inc.
Selective intracellular lactate invisibility in Enterococcus faecalis
Authors: Hockings P. D. , Bendall M. R. , Rogers P. J. 
Published: March 2007

AbstractIn this article we will demonstrate that differences in Hahn T2, relaxation of the 1H NMR signal from cytosolic and extracellular lactate can be exploited to monitor lactate concentration gradients in bacterial cells and provide information on lactate transport mechanisms. As a by‐product of this study we have determined that there are at least three pools of lactate in bacterial cells with differing visibility in the NMR experiment. This has serious implications for the spectral editing techniques that are so vital for in vivo spectrocopy. © 1992 Academic Press, Inc. © 1992 Academic Press, Inc.
Water‐suppressed one‐dimensional 1H NMR spectroscopic imaging of myocardial metabolites in vivo
Authors: Balschi James A. , Hetherington Hoby P. , Pohost Gerald M. 
Published: March 2007

AbstractExcitation by conventional B1 pulses in surface coil chemical‐shift imaging experiments yields resonance intensities that vary greatly with position. B1 compensated semi‐selective pulses overcome much of this problem. These pulses are employed for excitation and refocusing in 1H NMR spectroscopic localization in the intact heart.
Correlations between in vivo31P MRS measurements, tumor size, cell survival, and hypoxic fraction in the murine EMT6 tumor
Authors: Wendland Michael F. , Iyer Sujata B. , Fu Karen K. , Lam Kitty N. , James Thomas L. 
Published: March 2007

AbstractPhosphorus metabolite ratios were measured using 31P magnetic resonance spectroscopy shortly before measurement of cell survival and radiobologic hypoxic fraction (HF) in EMT6/SF tumors, transplanted into a hindlimb of Balb/c mice. A total of 58 tumors with a volume range of 180 to 1250 mm3 were examined in experiments entailing no anesthesia. Postirradiation tumor cell viability was measured using an in vitro clonogenic assay. Correlations between tumor volume, surviving fraction (SF), HF, phosphorus metabolite ratios, and intracellular pH were computed. Both SF and HF increased significantly with tumor volume as did the metabolite ratios of inorganic phosphorus and phosphomonoesters to nucleoside triphosphates (Pi/NTP and PME/NTP, respectively), as well as Pi to phosphocreatine (Pi/PCr). In comparison to HF, the ratios of PiNTP, Pi,/PCr, and PME/NTP each yielded significant positive correlations (Kendall correlation coefficients (τ) = 0.25 to 0.33). However, these were not significantly stronger than the correlation between HF and volume (τ = 0.21). Apparent values of tumor pH did not correlate with any other measured parameter. While these results indicate a statistical relationship between HF and the measured metabolite ratios, the widely scattered data, as reflected by |τ| < 0.35, made metabolite ratios poor predictors of HF in individual tumors. © 1992 Academic Press, Inc.
Metabolic response of the human heart to inotropic stimulation: In vivo phosphorus‐31 studies of normal and cardiomyopathic myocardium
Authors: Schaefer Saul , Schwartz Gregory G. , Steinman Sean K. , Meyerhoff Dieter J. , Massie Barry M. , Weiner Michael W. 
Published: March 2007

AbstractIn order to determine if an increase in myocardial oxygen consumption is accompanied by changes in high energy phosphates in normal subjects and patients with dilated cardio‐myopathy, phosphorus‐31 spectra were acquired under resting conditions and during do‐butamine infusion. In seven normal subjects, dobutamine raised the rate‐pressure product to 226% of control. The ratio of PCr/ATP was 1.86 ± 0.17 (mean ± SE) under resting conditions and 1.90 ± 0.22 (P = 0.44) with dobutamine infusion. In eight patients with dilated cardiomyopathy, dobutamine raised the rate‐pressure product to 161% of control. As in the normal subjects, the ratio of PCr/ATP under resting conditions (1.63 ± 0.24) was unchanged during dobutamine infusion (1.57 ± 0.24, P = 0.38). These data indicate that increases in cardiac work do not have a major effect on high energy phosphate concentrations in normal subjects or in patients with clinically compensated dilated cardiomyopathy. © 1992 Academic Press, Inc.
Elimination of oblique flow artifacts in magnetic resonance imaging
Authors: Frank Lawrence R. , Crawley Adrian P. , Buxton Richard B. 
Published: March 2007

AbstractWe present an analysis of how flow oblique to the frequency‐encoding direction generates displacement artifacts in MR imaging and show that for flow which has constant velocity between the start of the phase encoding and the center of the echo it is possible to eliminate these artifacts by gradient moment nulling in the phase‐encoding direction. However, unlike the standard moment nulling calculations for flow compensating the frequency‐encode and slice‐selection gradients, the phase‐encoding first moment must be nulled specifically with respect to the echo center. Limitations of this method imposed by finite gradient strengths are analyzed. In 3D volume acquisitions with two axes phase encoded it is possible to correct for oblique flow in all directions, and this is demonstrated in images of a human volunteer. Correction for oblique flow displacement artifacts may be particularly useful in quantitative flow and angiographic applications. © 1992 Academic Press, Inc.
Modification of the carr‐purcell sequence for single‐shot echo‐planar imaging
Authors: Hennel Franciszek 
Published: March 2007

AbstractAn artifact caused by the RF field inhomogeneity in echo‐planar imaging (EPI) with the CPMG sequence is analyzed. A modified sequence is presented, using 90° phase alternation of the π pulses, which suppresses the spurious components of the signal. Thus the phase cycling procedure can be avoided and the π‐pulsed EPI experiment can be reduced to a single shot.
The magnetic properties and water dynamics of the red blood cell: A study by proton‐NMR lineshape analysis
Authors: Gasparovic Charles , Matwiyoff Nicholas A. 
Published: March 2007

AbstractThe magnetic properties and water dynamics of human red blood cells were examined by analysis of the water proton spectra of suspensions of oxygenated, deoxygenated, carbon monoxide‐treated, and methemoglobin‐containing cells at a magnetic field strength of 7.05 T. Total lineshape analysis of spectra from deoxygenated red blood cell suspensions was performed to determine the transmembrane water exchange rate, the contribution of diffusion in local magnetic field gradients to the transverse relaxation rate, and the difference between the intra‐and extracellular chemical shifts of water protons. Mathematical models are proposed to account for the dependence of the chemical shifts and linewidths of these spectra on the magnetic susceptibility or density of the cells.
Spatial heterogeneity of the metabolic response of RIF‐1 tumors to a vasoactive agent evaluated in vivo by one‐dimensional 31P chemical‐shift imaging
Authors: Bhujwalla Z. M. , Blackband S. J. , Wehrle J. P. , Glickson J. D. 
Published: March 2007

AbstractLocalized 31P NMR spectroscopy was used to evaluate the spatial heterogeneity of the metabolic response of RIF‐1 tumors to hydralazine. Volume localized 31P spectra were obtained from subcutaneous RIF‐1 tumors using one‐dimensional chemical‐shift imaging, before and 20 min after treatment with 5 mg/kg hydralazine, administered intravenously. Following treatment all of the tumors showed an overall decrease in the ratio of nucleoside triphosphate (NTP) to inorganic phosphate (Pi) and a decrease in pH. However, spatial localization revealed that the reduction in NTP/Pi was not uniform within some tumors. This was partly due to regional differences in the levels of metabolites existing before treatment. Normal tissue adjacent to the tumor did not show a significant decrease in high‐energy metabolites or pH.
Proton magnetic resonance spectroscopy of human brain: Applications to normal white matter, chronic infarction, and MRI white matter signal hyperintensities
Authors: Sappey‐Marinier Dominique , Calabrese Giovanna , Hetherington Hoby P. , Fisher Sarah N. G. , Deicken Raymond , Dyke Craig Van , Fein George , Weiner Michael W. 
Published: March 2007

AbstractA modified ISIS method, for image‐selected localized proton magnetic resonance spectroscopy (1H MRS), was used to determine the ratios and T2 relaxation times of proton metabolites in normal subjects and in patients with chronic infarction and MRI white matter signal hyperintensities (WMSH). First, in patients with cerebral infarctions, increased concentrations of lactate were found in the majority of patients, and N‐acetyl aspartate (NAA) was reduced to a significantly greater extent than choline (Cho) or creatine (Cre). For TE = 270 ms, the raw ratios of Cho/NAA, Cre/NAA, and Lac/NAA were significantly (P < 0.05) increased from 0.23 ± 0.02 (mean ± SE), 0.20 ± 0.01, and 0.05 ± 0.01, respectively in the normal group to 0.39 ± 0.08, 0.37 ± 0.05, and 0.48 ± 0.15 in the stroke group. Also, the T2 relaxation time of creatine was significantly (P = 0.007) increased from 136 ms in normal white matter to 171 ms in cerebral infarcts. Second, in patients with WMSH, no significant change of the proton metabolite concentrations could be detected with the exception of the choline which was significantly (P = 0.003) altered. The Cho/NAA ratio, after T2 and excitation profile correction, increased from 0.47 ± 0.02 in the normal group to 0.64 ± 0.05 in the WMSH group. Third, in normal white matter, the concentration of N‐acetyl aspartate, choline, and lactate was estimated to 11.5, 2.0, and 0.6 mM, respectively, by assuming a total creatine concentration of 10 mM.
31P NMR spectroscopy of the human heart at 4 T: Detection of substantially uncontaminated cardiac spectra and differentiation of subepicardium and subendocardium
Authors: Menon Ravi S. , Hendrich Kristy , Hu Xiaoping , Uǧurbil Kǎmil 
Published: March 2007

Abstract31 P NMR spectroscopy of the human heart was undertaken at 4 T to investigate whether spectra localized exclusively to the myocardium can be obtained. Utilizing a Fourier series window approach to spectroscopic imaging, we find that at least two layers across the anterior left ventricle wall can be detected, with voxel sizes of about 8 cm3.
A nuclear magnetic resonance investigation of the upper airways in ferrets. i. effects of histamine and methacholine
Authors: Reo Nicholas V. , Barnett Jeanne K. C. , Neubecker Thomas A. , Alexander Marise E. , Goecke Carol M. 
Published: March 2007

AbstractAlterations induced in the upper airways of ferrets by intranasal provocation with methacholine (MC) and histamine (HS) were monitored using proton magnetic resonance imaging (MRI) and spin‐spin relaxation rate (R2) measurements. Both MC and HS cause a significant increase in the MRI signal intensity and a decrease in R2 in the nasal turbinates. A dose‐dependent response is observed for 20 to 315 nmol of HS, with a maximum increase in intensity of ca. 50% occurring above 80 nmol. A single unilateral challenge with MC yields a 62 ± 3% increase in intensity. Control animals (saline‐treated) show little change in image intensity. MC and HS cause decreases in the proton R2 by −27.0 ± 5.5% and −17.2 ± 4.3%, respectively. These data are indicative of an accumulation of fluid in the nasal airways. MRI provides an effective means to monitor changes in the nasal airways which occur as a result of pharmacological treatment.
Magnetic resonance imaging of myocardial kinematics. technique to detect, localize, and quantify the strain rates of the active human myocardium
Authors: Wedeen Van J. 
Published: March 2007

AbstractA magnetic resonance imaging (MRI) method is presented to detect, localize, and quantify myocardial kinematics by measuring the material rate‐of‐strain tensor at each pixel in gated NMR images of the heart. The immediate, local effect of muscular activity is self‐deformation, and the strain tensor is the basic mathematical device by which such deformation may be quantified. The present method, called “strain‐phase” MRI (SP‐MRI), entails four steps: (1) the velocity of the myocardium is encoded by means of a set of motion‐sensitive NMR image acquisitions, one image per velocity component; (2) the spatial derivatives of the velocity are computed at each pixel; (3) the velocity‐derivative data are combined to compute an approximation of the strain‐rate tensor of the myocardium at each pixel; and (4) the strain‐rate tensor data are simplified to produce a color‐coded functional image which represents strain‐rate components which are of particular biomedical interest in the myocardium. We present a quantitative SP‐MRI methodology suited to conventional MRI, and in addition present an “echo‐planar” methodology, able to produce qualitative functional images of myocardial kinematics at almost real‐time speeds. Two‐dimensional strain‐phase MRI data acquired in normal human subjects are presented. These data demonstrate the practicability of SP‐MRI in vivo, that SP‐MRI resolves myocardial kinematics at the single‐pixel scale, having resolution comparable to that of conventional MRI, and that SP‐MRI data may have a signal‐to‐noise ratio up to 50% as great as that of the conventional MRI data from which they are produced. SP‐MRI measurements of the local instantaneous strain rates in the human left ventricular myocardium are quantitatively consistent with known transmural average values of myocardial strain.