bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sensitivity and localization enhancement in multinuclear in vivo NMR spectroscopy by outer volume presaturation
Authors: Shungu Dikoma C. , Glickson Jerry D. 
Published: March 2007

AbstractSampling of the entire brain tissue in 1H NMR metabolic studies is complicated by the presence of intense pericranial lipid and tissue water resonances, which can obscure metabolite resonances. This study extends the concept of localization by outer volume suppression (OVS) to achieve fully conformal in viuo localization, sampling at least 95% of rat brain with complete elimination of pericranial lipids. This has permitted acquisition of lipid‐free short echo time (7.5 ms), high spatial resolution 2D spectroscopic images exhibiting high sensitivity and information content in relatively short measurement time (68 min). Incorporation of spatially tailored OVS into existing methods (e.g., DRESS, STEAM, PRESS) extends their localization efficiency and performance. Two single spin‐echo localization sequences have been described that attain much shorter echo times or achieve better water suppression than PRESS. One of these sequences allows editing and relaxo‐metric studies of J‐coupled spins. The methods described are suitable for in vivo localization of most tissues and can be applied with any biologically important nucleus.
Estimation of metabolite concentrations from localized in vivo proton NMR spectra
Authors: Provencher Stephen W. 
Published: March 2007

AbstractThe LCModel method analyzes an in vivo spectrum as a Linear Combination of Model spectra of metabolite solutions in vitro. By using complete model spectra, rather than just individual resonances, maximum information and uniqueness are incorporated into the analysis. A constrained regularization method accounts for differences in phase, baseline, and lineshapes between the in vitro and in vivo spectra, and estimates the metabolite concentrations and their uncertainties. LCModel is fully automatic in that the only input is the time‐domain in vivo data. The lack of subjective interaction should help the exchange and comparison of results. More than 3000 human brain STEAM spectra from patients and healthy volunteers have been analyzed with LCModel. N‐acetylaspartate, cholines, creatines, myo‐inositol, and glutamate can be reliably determined, and abnormal levels of these or elevated levels of lactate, alanine, scyllo‐inositol, glutamine, or glucose clearly indicate numerous pathologies. A computer program will be available.
Resolution enhanced NMR spectroscopy in biological systems via magnetic susceptibility matched sample immersion chambers
Authors: Ballon D. , Mahmood U. , Jakubowski A. , Koutcher J. A. 
Published: March 2007

AbstractA technique is described which reduced the magnetic susceptibility induced line broadening in NMR spectra obtained from three biological systems at 4.7 Tesla. Proton spectra from a sealed suspension of HL60 leukemic myeioblasts yielded minimum linewidths of 1.3 Hz at 200 MHz (0.0065 ppm) after 10 min of automated shimming. 31P spectra from an in vivo murine MCa mammary carcinoma yielded a well‐resolved phospharylcholine resonance without proton decoupling and with the resistive shim coil currents set to zero. 31P spectra from a perfused suspension of RIF‐1 fibrosarcoma cells exhibited a γ‐nucleoside triphosphate resonance which was resolved into purine and pyrimidine components.
NMR visibility studies of N‐δ proton of proximal histidine in deoxyhemoglobin in lysed and intact red cells
Authors: Wang Dah‐Jyuu , Nioka Shoko , Wang Zhiyue , Leigh John S. , Chance Britton 
Published: March 2007

AbstractRecent in vivo 1H MRS studies of muscle oxygen levels by means of myoglobin (Mb) oxygenation have necessitated an investigation of the possible contamination from deoxy‐hemoglobin (Hb). To determine the contribution of Hb in these NMR measurements, we studied the NMR visibility of histidyl N‐δ proton of Hb in lysed and intact RBC (red blood cell) suspensions. We found that the visibility of deoxy‐Hb was significantly lower in intact RBCs (ca. 16%) than the solution form at an equivalent concentration of β heme‐iron, even though the visibility of deoxy‐Hb from lysed RBC and deoxy‐Mb was almost identical. Our study also shows that visibility increases with RBC swelling. Based on the difference in concentration and compartmentation, we conclude that less than 17% contribution from Hb is expected in Mb measurements in vivo. The possible mechanisms which cause the low visibility of Hb in RBCs are discussed.
Quantitative characterization of the eddy current fields in a 40‐cm bore superconducting magnet
Authors: Liu Q. , Hughes D. G. , Allen P. S. 
Published: March 2007

AbstractThe temporal and spatial dependence of the eddy current fields, generated by switching off x, y, and z gradients in a 40‐cm bore Bruker superconducting magnet, have been studied by measuring the offset frequency of the proton FID obtained from a small spherical sample. The measurements were made with the pre‐emphasis unit deactivated. The data obtained at each location were well fitted to a sum of four exponentially decaying components. The shortest decay is, in each case, associated with the decay of the current in the gradient coil itself, while the other decays are associated with three eddy currents with decay times ranging from 13 to 480 ms. Each of the three eddy currents generates an essentially uniform gradient for at least 4 cm on either side of the isocenter. However, when the eddy currents are generated by either the vertical transverse gradient or the longitudinal gradient, the eddy current gradients are also accompanied by a field shift.
Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain
Authors: Dreher Wolfgang , Norris David G. , Leibfritz Dieter 
Published: March 2007

AbstractThe effect of off‐resonance preirradiation on proton spectra acquired from the healthy rat brain at 4.7 T is examined using a PRESS sequence. The creatin/phosphocreatine (Cr/PCr) signal at 3.0 ppm decreases in signal intensity for offset frequencies between ±10 kHz. This cannot be explained by RF bleedover, but is attributed to magnetization transfer between two pools of Cr/PCr, one with a long T2 relaxation time giving the observed NMR signal, the other corresponding to a broad resonance line being completely or partially saturated by off‐resonance preirradiation. Possible interpretations of these results are discussed.
Methods for reconstructing phase sensitive slice profiles in magnetic resonance imaging
Authors: Devoulon Philippe , Emsley Lyndon , Weber Peter , Meuli Reto , Decorps Michel , Bodenhausen Geoffrey 
Published: March 2007

AbstractThe experimental determination of slice profiles excited by applying radiofrequency pulses in the presence of a gradient generally results in magnitude profiles. The conditions necessary to obtain a phase‐sensitive picture of the profile of a slice are discussed. A distinction is made between the “excitation profile” (distribution of the transverse magnetization immediately after the RF pulse) and the “slice profile” (distribution after refocusing by gradient reversal and/or imperfect gradient switching). Methods are presented that allow one to obtain either the excitation profile or the slice profile. It is shown that phase encoding along the direction of the slice selection gradient provides a convenient protocol for obtaining the distribution of both the real and imaginary parts of the slice profile. The phase sensitive excitation profile can be obtained by frequency encoding. These methods were used to evaluate the performance of various shaped pulses.
Accurate T1 determination from inversion recovery images: Application to human brain at 4 Tesla
Authors: Kim Seong‐Gi , Hu Xiaoping , Ugurbil Kamil 
Published: March 2007

AbstractIt is well known that the signal polarity in inversion‐recovery (IR) images changes with inversion time, complicating the determination of T1 To avoid this problem, a simple subtraction method is implemented. In this method, k‐space data of the longest inversion time are subtracted from the corresponding data of each inversion time. This subtraction yields IR images of same polarity, making it straightforward to derive T1 using a standard fitting routine. Phantom T1 studies with IR Turbo‐FLASH images demonstrate that this technique is robust and accurate. Four Tesla T1 values of the human brain were also determined by this method to demonstrate its in vivo utility.
Rapid monitoring of changes in water diffusion coefficients during reversible ischemia in cat and rat brain
Authors: Davis D. , Ulatowski J. , Eleff S. , Izuta M. , Mori S. , Shungu D. , van Zijl P. C. M. 
Published: March 2007

AbstractChanges in the diffusion constant of water during reversible brain ischemia and cardiac arrest were monitored with a 10‐s time resolution. Results (five cats, three rats) indicate that these changes are reversible and that the bulk of the changes are not caused by temperature or motion related to brain pulsations and blood flow. The rapid time course of the changes corresponds to the known time course for changes in energy state, signal transduction, and ionic homeostasis.
Surface coil cardiac tagging and 31P spectroscopic localization with B1‐insensitive adiabatic pulses
Authors: Hendrich Kristy , Xu Ya , Kim Seong‐Gi , Uǧurbil Kǎmil 
Published: March 2007

AbstractA technique is presented for MRI tagging in the presence of inhomogeneous B1 fields. A rectangular tagging grid is produced with B1‐insensitive adiabatic pulses in a magnetization preparation period that precedes image acquisition. Phantom results demonstrate that the method is well‐suited to surface coil experiments. The technique is applied to a canine model of myocardial ischemia to track the spatially dependent wall motion of the left ventricle during the cardiac cycle. Transmural 31P spectra are acquired from the same double‐tuned surface coil, with tagging and spectroscopy performed for the first time, during normal, ischemic, and recovery conditions for the same animal.
Quadrupole gradient coil design and optimization: A printed circuit board approach
Authors: Chu Kenneth C. , Rutt Brian K. 
Published: March 2007

AbstractThree different dual‐axis quadrupole gradient coils for quantitative high resolution MR imaging of small animals, phantoms and specimens were designed and built using printed circuit board technology. Numerical optimization of the conductor positions was used to increase the volume of 0.4% gradient uniformity by up to a factor of four. In one coil, the volume of 5% gradient uniformity occupied 88% and 83% of the overall diameter and length of the coil, respectively. A systematic error of 0.5% in the wire placement was shown to cause a reduction in the volume of 0.4% gradient uniformity by a factor of two, though the region of 5% gradient uniformity was not significantly affected. Heat transfer calculations were used to determine maximum peak and root‐mean‐squared currents that could safely be applied to the coils.
Sources of intensity nonuniformity in spin echo images at 1.5 T
Authors: Simmons Andrew , Tofts Paul S. , Barker Gareth J. , Arridge Simon R. 
Published: March 2007

AbstractThis manuscript describes a number of sources of nonuniformity for spin echo images at 1.5 T. Both coil tuning and crosstalk can have significant effects on image nonuniformity. For short repetition times, nonuniformity increases with decreasing TR, possibly due to gradient eddy currents. In sections of RF coils with poor RF uniformity, image nonuniformity varies with both echo time and the number of echoes in a multiecho sequence. For the particular imager used, there are small differences between transverse and sagittal/coronal nonuniformity. The temporal stability of image nonuniformity is very good. The use of uniform oil phantoms is shown to be superior to low pass filtered images for correction of image nonuniformity.
Spreading waves of decreased diffusion coefficient lifter cortical stimulation in the rat brain
Authors: Latour Lawrence L. , Hasegawa Yasuhiro , Formato James E. , Fisher Marc , Sotak Christopher H. 
Published: March 2007

AbstractA method is demonstrated for the noninvasive detection and study of spreading cortical depression. Spreading depression (SD) was elicited in rats by topical application of potassium chloride to the exposed cortex. The apparent diffusion coefficient (Dapp) of water in a region of the cortex, measured using a PFG‐NMR spin echo sequence with an observation time of 40 ms, declines 35% within 30 s and recovers to the normal value within the next 30 s. The region of decreased Dapp was shown to be 2 mm in size and to move in the cortex, away from the point of application, with a uniform velocity of 3.3 ± 0.5 mm/min. The behavior of the affected region is consistent with other reports of the behavior of SD as monitored by electro‐physiological means. The technique can be implemented on currently available MRI equipment and makes possible the noninvasive study of SD in animal models of neurological disorders, their therapeutic intervention, and possibly the study of SD in humans.
Band‐selective spin echoes for in vivo localized 1H NMR spectroscopy
Authors: Shungu Dikoma C. , Glickson Jerry D. 
Published: March 2007

AbstractThis study describes a new single spin‐echo spatial localization sequence, BASSALE or BAnd‐Selective Spin echo Acquisition for Localized Editing, that overcomes a number of the limitations of the STEAM and PRESS volume selection pulse sequences. It achieves conformal volume localization in a single shot by spatially tailored suppression of all magnetization outside a 2D region of interest followed by selection of a single orthogonal slice. This separation of spatial localization from the echo formation process has permitted use of a spectrally selective cosine‐modulated sinc refocusing pulse to acquire localized 1H spectra with the water suppression efficiency of STEAM and the sensitivity of PRESS. Echoes formed by such spectrally selective pulses have been termed bandselective spin echoes. The BASSALE sequence attains shorter echo times than PRESS, inhibits scalar spin‐spin interactions to permit localized editing and T2 relaxometry of metabolites with J‐coupled spins (e.g., lactate), is insensitive to homonuclear multiple‐quantum and polarization transfer effects, and can be made sensitive or insensitive to spin displacement effects. Applications are shown both with phantoms and in situ in the rat brain.
In Vitro and in Vivo13C and 31P NMR analyses of phosphocholine metabolism in rat glioma cells
Authors: Gillies Robert J. , Barry Judith A. , Ross Brian D. 
Published: March 2007

AbstractIn ivivo magnetic resonance spectroscopy (MRS) has revealed that phsophomonoesters (PME) such as phosphocholine (PCho) and phosphoethanolamine (PEth) are elevated in tumalrs and rapidly proliferating tissues. The regulation of PME levels and their relationship to proliferation are not well known. In the present study, we investigated the regulation of PCho and PEth levels in rat glioma cells grown in vivo and in vitro using 31P and 13C MRS. However, the ability of cells to produce choline endogenously is variable. To fully understand regulation of PCho levels, it is necessary to characterize the activity of the endogenous pathway, if it exists. This was first investigated by following the metabolic fate of 13C‐labeled methionine of 9L glioma tumors in vivo. Our results indicate that there is a significant amount of de novo choline synthesis in ivivo. However, similar experiments performed in virro using cells cultured in bioreactors indicated that glioma cells themselves are unable to synthesize choline de novo, suggesting that the in vivo results were due to the involvement of extra‐tunnoral organs, e.g., liver. Further in vitro experiments demonstrated that the uptake and phosphorylation of physiologically relevant concentrations of exogenous choline is very active in these systems. Thus, it appears that the exogenous pathway for PCho biosynthesis predominates and regulates PCho levels in glioma cells. Our results also demonstrate that PCho levels are lowest, and PEth levels are highest, in non‐proliferating cells. These observations indicate that there is a decrease in the biosynthesis of PCho concomitant with a redulction in culture growth. The source of the increased PEth is, as yet, undefined.
Inversion recovery EPI of bolus transit in rat myocardium using intravascular and extravascular gadolinium‐based MR contrast media: Dose effects on peak signal enhancement
Authors: Wendland Michael F. , Saeed Maythem , Yu Kyle K. , Roberts Timothy P. L. , Lauerma Kirsi , Derugin Nikita , Varadarajan John , Watson Alan D. , Higgins Charles B. 
Published: March 2007

AbstractInversion recovery gradient recalled echo planar imaging (TI/TR/TE = 700/2000/10 ms) was used to dynamically monitor the first pass of an intravascular (GdDOTA‐polylysine) and an extravascular (GdDTPA‐BMA) contrast agent through normal rat myocardium. It was found that myocardial enhancement increased with dose of the intravascutar agent to a limiting value of ∼50% of fully relaxed intensity, consistent with enhancement of 40% of myocardial water content during the first pass. Larger doses produced no further increase in peak response. On the other hand, the extravascular agent caused incrementally increased enhancement throughout the dose range examined to a final value of 68 ± 2% of fully relaxed intensity. The profile of dose dependence for both agents was inconsistent with monoexponential T1 relaxation. It was concluded that (a) compartmentalization of myocardial water combined with restricted myocardial water diffusion limits the peak response during bolus transit; (b) extraction of the extravascular agent during transit elevates the peak response over that obtained from agent confined to the vascular volume; and (c) models that assume simple monoexponential r, relaxation to derive timedensity curves do not adequately describe the relationship between changes in signal intensity, R1 and contrast concentration.
Noninvasive measurement of renal hemodynamic functions using gadolinium enhanced magnetic resonance imaging
Authors: Dumoulin Charles L. , Buonocore Michael H. , Opsahl Lorinda R. , Katzberg Richard W. , Darrow Robert D. , Morris Thomas W. , Batey Charlotte 
Published: March 2007

AbstractA technique for the assessment of single kidney hemodynamic functions utilizing a novel MR pulse sequence in conjuinction with MR contrast material administration is described. Renal extraction fraction (EF) is derived by measuring the concentration of the incoming contrast agent in the renal artery and the outgoing concentration in the renal vein. The glomerular filtration rate (GFR) can then be determined by the product of EF and renal plasma flow. A modified iniversion recovery MR pulse sequence is used to measure the T1 of moving blood. This pulse sequence uses a spatially nonselective inversion pulse. A series of small flip angle detection pulses are then used to monitor the recovery of longitudinal spin magnetization in an image plane intersecting the renal vessels. The recovery rate is measured in each vessel and the T1 of blood determined. These T1 measurements are then used to determine the ratio of contrast concentration in the renal arteries and veins. Blood flow measurements can be obtained simultaneously with T1 measurements by inserting flow‐encoding magnetic field gradients into the pulse seqiuence. Preliminary results in human volunteers suggest the feasibility of noninvasively determining hemodynamic functions with magnetic resonance.
Cholesterol effects on nonelectrolyte membrane transport in human erythrocytes: NMR magnetization transfer studies
Authors: Nouri‐Sorkhabi M. Hossein , Chapman Bogdan E. , Sullivan David R. , Kuchel Philip W. 
Published: March 2007

AbstractThe cholesterol content of human erythrocytes was altered by incubating them with sonicated dispersions of cholesterol/phosphatidylcholine at 37°C. 31P NMR saturation transfer experiments were used to measure the rate constant for efflux of dimethyl methylphosphonate (DMMP) from the cells, and thereby gain an estimate of the permeability coefficient. It was shown that up to 39% depletion of membrane cholesterol (cholesterol/phospholipid molar ratio of 0.46) increased the efflux rate constant and permeability coefficient of DMMP 1.55‐and 1.86‐fold, respectively. Enrichment of the membranes with cholesterol by 45% (cholesterol/phospholipid molar ratio of 1.57) on the other hand, decreased the efflux rate constant and permeability coefficient 1.63‐and 1.79‐fold, respectively. It was concluded that DMMP may be used as a probe molecule to study the functional consequences of changes in the lipid composition of erythrocytes in diseases that are associated with disorders of lipid metabolism.
Three‐dimensional time‐of‐flight MR angiography with variable TE (VARIETE) for fat signal reduction
Authors: Lin Weili , Haacke E. Mark , Tkach Jean A. 
Published: March 2007

AbstractUniform fat saturation over a large region of interest remains a problem in time‐of‐flight (TOF) magnetic resonance angiography applications. We demonstrate that a variable echo time with an opposed phase value at low spatial slice select frequencies can effectively reduce most of the fat signal in an otherwise standard three‐dimensional TOF acquisition. We evaluated this method at 1.5 T using a short TE = 5.3 ms and a long TE = 6.75 ms for different values of the slice encoding gradient (i.e., different k2 values). Shorter echo time (TE = 5.3 msec) was used at higher spatial slice select frequencies, but all echoes have the same gradient structures. By keeping the number of slice encoding steps with longer echoes to a minimum, field inhomogeneity effects on flow compensation remained small. A magnetization transfer saturation pulse was used to suppress signal of brain parenchyma. Overall, highly uniform and selective fat signal reduction was obtained while maintaining superior flow compensation in all volunteer studies.
Incorporation of Lactate Measurement in Multi‐Spin‐Echo Proton Spectroscopic Imaging
Authors: Duyn Jeff H. , Frank Joseph A. , Moonen Chrit T. W. 
Published: March 2007

AbstractAn improved multi‐slice, multi‐spin‐echo proton spectro‐scopic imaging method for human brain is presented. The technique allows the reconstruction of lactate images, along with choline plus creatine, N‐acetylaspartate, and lipid images from one single data set processed in three separate ways. The discrimination between resonances of lipid protons and lactate methyl protons is based on homonuclear spin‐spin coupling. The reliability of the separation of the lipid and lactate contribution depends on the T2 of the lipid resonances. Measurements were performed on a standard 1.5 Tesla clinical scanner on healthy volunteers and a patient with high grade CNS lymphoma, demonstrating the ability to obtain high quality metabolite maps within 11 min.