bluuebunny/crossref_metadata_2025_split huggingface dataset:
MRI Measurement of Hepatocyte Toxicity Using the New MRI Contrast Agent Manganese Dipyridoxal Diphosphate, a Manganese/Pyridoxal 5‐Phosphate Chelate
Authors: Young Stuart W. , Simpson Beverly B. , Ratner Adam V. , Matkin Chantal , Carter Edward A. 
Published: March 2007

AbstractThis study reports the first in vivo results using an MR contrast agent manganese dipyridoxal diphosphate (Mn‐DPDP) designed to estimate the functional status of the hepatocyte. Thirty New Zealand white rabbits were studied in groups of 5 as follows: No. 1, control, MRI scans only; No. 2 MRI before and up to 90 min following 50 μmol/kg of Mn‐DPDP iv; No. 3, rabbits received 9.3 g ethanol/kg and MRI; No. 4, as in No. 3 but following Mn‐DPDP; No. 5, MRI as in No. 2 but 18 h. following 1000 mg/kg Dgalactosamine used to induce hepatocyte necrosis; and No. 6, rabbits received D‐galactosamine and Mn‐DPDP. In this study significant ethanol‐and D‐galactosamine‐induced hepatocyte damage was indicated by the increased SGPT serum levels in the rabbit. The use of Mn‐DPDP allowed detection of early hepatocyte necrosis in these animals whereas conventional spin‐echo MRI did not. The fact that D‐galactosamine curves with and without Mn‐DPDP were not significantly different indicated virtually no membrane transport or metabolism of Mn‐DPDP in the liver. Ethanol curves were not normal, but there was still considerable residual Mn‐DPDP metabolism. Mn‐DPDP appears to be an attractive agent in assessing hepatocyte function. © 1989 Academic Press, Inc.
Improvements in MR Angiography Using Phase‐Corrected Data Sets
Authors: Chenevert Thomas L. , Fechner Klaus P. , Gelblum Daphna Y. 
Published: March 2007

AbstractThe objective of this work is refinement of an MR angiography technique via postprocessing removal of phase errors which inhibit static signal subtraction. Projective views of the object are obtained using interleaved flow‐compensated and noncompensated gradient waveforms. Complex subtraction of data sets is required since a projection dephase pulse is used for static signal suppression. This renders the difference image susceptible to systematic phase errors which are modeled asa smoothly varying multiplicative phase function. The error function is estimated by comparison of heavily spatial filtered renditions of the object acquired without projection dephasing in order to minimize influence of flow. The phase correction is then applied to high‐resolution data sets collected with projection dephasing to enhance flow sensitivity. The technique is demonstrated by improvement of MR angiograms of rats acquired on a 2‐T, 31‐cm‐bore system. © 1989 Academic Press. Inc.
Simultaneous Multislice imaging (SIMUSIM) for improved cardiac imaging
Authors: Müller S. 
Published: March 2007

AbstractIn conventional ECG gated multislice imaging of the heart, slice position and phase in the heart cycle are not independent parameters. This drawback is removed by simultaneous imaging of multiple slices. This paper describes a technique which is based on simultaneous excitation of several slices by multifrequency selective rf pulses. In comparison to conventional cardiac multislice imaging an improved quality of heart images is obtained, because more acquisitions are attributed to the MR signal of the slices. The gain in signal‐to‐noise ratio per measurement time increases with the square root of the number of slices investigated simultaneously. This is demonstrated using phantom experiments and cardiac images. © 1989 Academic Press, Inc.
Preliminary results of nuclear magnetic resonance studies of healthy human saliva
Authors: Coudert J. L. , Lissac M. , Teyssier R. , Bejat C. , Magnin P. , Peyrin J. O. , Bene G. J. 
Published: March 2007

AbstractRelaxation times T1 and T2 of water protons for stimulated and unstimulated parotid and submandibular saliva from healthy patients were measured in the conventional way using the Bruker PC 20 Minispec. Some measurements of dispersion were also carried out. An interpretation of the average values for T1 and T2, observed in the 20 MHz range is proposed for these types of saliva in relation to biochemical composition (total proteins, amylase activity, sialic acids and hexosamins) and viscosity. For parotid saliva T−12−T−11 correlates significantly with amylase activity. In the submandibular saliva T−12−T−11 correlates significantly with both mucins and α‐amylase activity. © 1989 Academic Press, Inc.
1H and 31P NMR measurement of cerebral lactate, high‐energy phosphate levels, and pH in humans during voluntary hyperventilation: associated EEG, capnographic, and doppler findings
Authors: van Rijen P. C. , Luyten P. R. , Van der Sprenkel J. W. Berkelbach , Kraaier V. , van Huffelen A. C. , Tulleken C. A. F. , den Hollander J. A. 
Published: March 2007

AbstractIn order to explore the sensitivity of spatially resolved 1H and 31P NMR spectroscopy on a whole‐body NMR instrument, cerebral metabolic changes in human volunteers were measured during hyperventilation provocation. During hyperventilation the flow velocity in the middle cerebral artery decreased significantly and the EEG showed a marked increase in slow activity. 1H NMR spectra revealed an increase in cerebral lactate concentration. 31P NMR spectra showed no changes in ATP or PCr peak heights, but a shift toward tissue alkalosis was derived from changes in Pi chemical shift. During subsequent recovery, lactate concentration decreased and a slight intracellular acidosis was detected. In three experiments broadening of the lactate resonance peak resulted in separation into two components at 1.32 and 1.48 ppm, in which the latter signal possibly arose from alanine. © 1989 Academic press. Inc.
Missing pulse steady‐state free precession
Authors: Patz S. , Wong S. T. S. , Roos M. S. 
Published: March 2007

AbstractA fast imaging technique, missing pulse steady‐state free precession (MP‐SSFP), is described. MP‐SSFP is one of a class of steady‐state free precession techniques in which every nth RF pulse is missing. MP‐SSFP has been implemented for the case where every third RF pulse is omitted: {‐θ1,‐τ‐θ2‐echo‐τ‐}. A RF‐refocused echo forms at the time of the missing pulse. This echo is less sensitive to field inhomogeneities than the gradient‐recalled echoes used in most fast imaging methods. An analytical expression is obtained for the signal strength as a function of the flip angles θ1 and θ2, the interpulse interval τ, and the amount of interpulse dephase. The expression shows that θ1 and θ2 provide two degrees of freedom to optimize the signal‐to‐noise ratio and improve tissue contrast. Two different cases, θ1=θ2 and θ1 = ‐θ2, are described to demonstrate the difference in contrast. The first case gives a strong signal from spins with short T1 and short T2 while the second case has contrast very similar to a conventional SSFP technique. The theoretical expression predicts that the signal consists of multiple components which may be observed experimentally by adjusting the gradient pulses.
Implanted coil MR microscopy of renal pathology
Authors: Farmer T. H. R. , Johnson G. A. , Cofer G. P. , Maronpot R. R. , Dixon D. , Hedlund L. W. 
Published: March 2007

AbstractInductively coupled implanted coils have been shown to provide up to a 10‐fold increase in signal‐to‐noise ratio when compared to whole‐body imaging of small animals. The current study was designed to extend the implanted coil imaging technique to a rodent model of renal pathology. Resonant radiofrequency (RF) coils were implanted around the left kidney of four rats and inductively coupled from within a birdcage body coil. All images were acquired at 2 T using a T1‐weighted spin‐echo sequence with TR = 500 ms and TE = 20 ms. In vivo MR microscopy with voxels of 117 × 117 × 2000 μm demonstrated cortex, inner and outer medulla, and major vascular structures on baseline images. Mercuric chloride‐induced nephrotoxic acute tubular necrosis (ATN) diminished cortico‐medullary contrast at 24 h after dosing with pathologic evaluation demonstrating nephrotoxic changes in the inner cortex. The kidney regained a baseline MR appearance 360 h after dosing and resolution of the damage was confirmed with histology. T1 data were gathered on excised kidneys as an adjunct to the images to help correlate the loss and return ofcortico‐medullary contrast with the pathology and pathophysiology of nephrotoxic ATN. With implanted RF coils we were able to demonstrate renal pathology and follow its subsequent resolution. Specifically, loss and return of cortico‐medullary contrast as a result of nephrotoxic ATN were serially documented in four rats. Such serial in vivo studies performed on single animals should further the use of MR microscopy by minimizing the number of animals required for adequate biostatistics. © 1989 Academic Press, Inc.
Effects of intravoxel incoherent motions (IVIM) in steady‐state free precession (SSFP) imaging: application to molecular diffusion imaging
Authors: Bihan D. Le , Turner R. , Macfall J. R. 
Published: March 2007

AbstractA theoretical analysis of the effects of diffusion and perfusion in steady‐state free precession (SSFP) imaging sequences sensitized to intravoxel incoherent motions by magnetic field gradients is presented and supported by phantom studies. The capability of such sequences to image diffusion and perfusion quickly was recently demonstrated. The possible residual effects of T1 and T2 in diffusion measurements are evaluated, as are the effects of the sequence design and the acquisition parameters (repetition time, flip angle, gradient pulses). It is shown theoretically and confirmed by experiments on phantoms that diffusion coefficients can be directly measured from SSFP images when large enough diffusion gradient pulses are used. © 1989 Academic Press, Inc.
Power deposition and noise correlation in NMR samples
Authors: Carlson J. W. 
Published: March 2007

AbstractA general solution for the power deposited in an NMR sample by an rf coil is presented. The result is simplified in the long wavelength, long skin depth approximation. This formalism is used to derive an expression for noise correlation in two independent receiver coils. © 1989 Academic press, Inc. © 1989 Academic Press, Inc.
Double‐quantum filtered volume‐selective NMR spectroscopy
Authors: üttel A. Kn , Kimmich R. 
Published: March 2007

AbstractAn RF and field‐gradient pulse sequence is presented, permitting the recording of localized double‐quantum filtered proton spectra. In this way distinction between overlapping resonances of coupled and uncoupled spins is possible. The editing of the lactate methyl line is demonstrated in a test experiment. © 1989 Academic Press, Inc.
Localized proton NMR spectroscopy in different regions of the human brain in vivo. Relaxation times and concentrations of cerebral metabolites
Authors: Frahm J. , Bruhn H. , Gyngell M. L. , Merboldt K. D. , Hänicke W. , Sauter R. 
Published: March 2007

AbstractHigh‐resolution proton NMR spectra of normal human brain in vivo have been obtained from selected 27‐ and 64‐ml volumes‐of‐interest (VOI) localized in the insular area, the occipital area, the thalamus, and the cerebellum of normal volunteers. Localization was achieved by stimulated echo (STEAM) sequences using a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). The proton NMR spectra show resonances from lipids, lactate, acetate, Nacetylaspartate (NAA), γ‐aminobutyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. While T1 relaxation times of most of these metabolites were about 1100–1700 ms without significant regional differences, their T2 relaxation times varied between 100 and 500 ms. The longest T2 values of about (500 ± 50) ms were observed for the methyl protons of NAA in the white matter of the occipital lobe compared to (320 ± 30) ms in the other parts of the brain. No significant regional T2 differences were found for choline and creatine methyl resonances. The relative concentrations of NAA in gray and white matter were found to be 35% higher than those in the thalamus and cerebellum. Assuming a concentration of 10 mM for total creatine the resulting NAA concentrations of 13–18 mMare by a factor of 2–3 higher than previously reported using analytical techniques. Cerebral lactate reached a maximum concentration of about 1.0 mM. © 1989 Academic Press, Inc.
31P NMR studies of the thermodynamics and kinetics of the creatine kinase reaction
Authors: Eldar H. , Degani H. 
Published: March 2007

AbstractThe thermodynamic and kinetic parameters of the reaction catalyzed by creatine kinase (CK) were measured in vitro in the temperature range 13 to 35°C, using 31P NMR spectroscopy, including magnetization transfer methods. The apparent equilibrium constant of the reaction and the associated enthalpy for the formation of ATP at 35°C, pH 8.2, and excess [Mg2+] were 3.5 × 109 M−1 and −2.4 ± 0.5 kcal/mol, respectively. The rates at equilibrium at 35°C catalyzed by 1 unit/ml CK were 12.4 and 10.7 μM /s at pH 7 and 8, respectively. The rate constants per 1 unit CK/ 1 ml at 35°C, pH 7, were 1.3 × 108 s−1M−2 and 9.9 × s−1 M−1 in the direction of ATP and PCr formation, respectively. The activation energies in both directions were similar and corresponded to 15 ± 2 kcal/mol at pH 7 and 17.5 ± 1.5 kcal/mol at pH 8. Comparison of in vivo results with the above in vitro data may provide information regarding the activity and kinetics of the CK reaction.
Relaxation measurements at 300 MHz using MR microscopy
Authors: Dockery S. E. , Suddarth S. A. , Johnson G. A. 
Published: March 2007

AbstractPrevious data on changes in tissue TI with field have suggested the convergence of tissue TI values toward a common value at high (>4.0 T) fields. Measures of T2 dependence have suggested reduction of T2 with field. The purpose of this study was to observe the T1 and T2 at 85.5 and 300 MHz of microstructures in excised rat kidneys by employing MR microscopy. This study represents the first attempt of MR microscopy at 7.0 T with regard to the subject of magnetic field dependence of TI and T2 As expected, TI did increase with increasing field strength but not as dramatically as might be expected. Subtle differences in the microstructures of the kidney and the binding of water in those structures were discernible on the basis of T1 differences at 300 MHz. T2 values decreased, raising speculation concerning the mechanism for this dependence. The improved SNR permits smaller samples to be examined at much higher resolutions (< 30 ± 30 ± 200 μm), further extending the potentials for MR microscopy.
High‐Resolution NMR imaging of an antigen‐induced arthritis in the Rabbit Knee
Authors: Checkley David , Johnstone Donna , Taylor Kay , Waterton John C. 
Published: March 2007

AbstractHigh‐resolution, serial, spin‐echo images were obtained for an antigen‐induced knee arthritis in six rabbits. The animals were imaged prior to intra‐articular challenge and at various time points up to 14 weeks after challenge. Extensive high‐signal inflammatory changes were seen at Day 1 in the lymph node, capsule, and surrounding muscle. The muscle and lymph node response decreased rapidly after the first week. The capsule high‐signal area reached a maximum at Day 10, but was still extensive at Day 39. The infrapatellar fat pad was replaced more slowly by high signal and the appearance of high signal in both the tibia and femur was a late change. Terminal histological examination showed that the capsule and fat pad high‐signal areas corresponded to fibrous and synovial proliferation. The bone changes were a result of edema and cyst formation. The separation of the various time courses of the inflammatory changes may be of value in understanding the model and evaluating potential anti‐arthritic drugs. © 1989 Academic Press, Inc.
Precise relaxation time measurements of normal‐appearing white matter in inflammatory central nervous system disease
Authors: Miller D. H. , Johnson G. , Tofts P. S. , Macmanus D. , McDonald W. I. 
Published: March 2007

AbstractPrecise relaxation time (RT) measurements have been made, with a standard deviation of 3% for T1 and T2 in white matter in normal volunteers. This sets an upper limit to the instrumental random errors (imprecision). Achieving this precision requires careful adjustment and use of the imager. The wide variation in RTs seen by other workers may be in part due to larger instrumental errors. We have measured RTs (both T1 and T2) in normal‐appearing white matter in 16 normal controls and patients with multiple sclerosis (MS, 18), systemic lupus erythematosis (SLE, 16) and cerebral sarcoidosis (8). Both RTs were significantly higher in MS than in other patient groups and controls (P < .05), possibly caused by microscopic lesions. T2 was elevated in SLE, patients relative to controls and sarcoidosis patients (P < .05), possibly because of microhemorrhages. Lesion RTs were abnormal but more variable and no significant differences between diseases were found.
Exposure to a 1.5‐T static magnetic field does not alter body and skin temperatures in man
Authors: Shellock Frank G. , Schaefer Daniel J. , Crues John V. 
Published: March 2007

AbstractThe literature has conflicting reports concerning the effect of static magnetic fields on body and skin temperatures in mammals. Since temperature changes induced by static magnetic fields would have important safety implications for clinical magnetic resonance imaging, body (sublingual pocket) and skin (abdomen, forehead, chest, upper arm, forearm, thigh, and calf) temperatures were determined in six normal subjects using a fluoroptic thermometry system during a 20‐min exposure to a 1.5‐T static magnetic field. Ambient conditions were controlled and held constant. An analysis of variance for re‐ peated measures revealed that there were no statistically significant changes in body or any of the skin temperatures recorded. We conclude that exposure for 20 min to a 1.5‐T static magnetic field does not alter body and skin temperatures in man.
Flow‐compensated limited flip angle MR angiography
Authors: Lee James N. , Riederer Stephen J. , Pelc Norbert J. 
Published: March 2007

AbstractA method of subtraction angiography that has an acquisition time of 8 s per slice is described. Flow‐compensated and uncompensated measurements are acquired in an interleaved fashion using limited flip angles and gradient refocusing. Magnitude images are reconstructed and subtracted to generate the angiogram. Results were generated in vivo in the imaging of the carotid bifurcation of several human volunteers. Susceptibility and inhomogeneity induced artifacts are prominent in thick slices, but can be greatly reduced by imaging several thin slices and adding them together. Thin slices do not require de‐phasing gradients to reduce the dynamic range, and there is no signal cancellation in overlapping vessels. The method is ideal for acquiring scout angiograms, and with averaging may produce images of diagnostic quality. © 1989 Academic Press, Inc.
The use of finite impulse response filters in pulse design
Authors: Shinnar Meir , Bolinger Lizann , Leigh John S. 
Published: March 2007

AbstractWe develop a new way of synthesizing pulse sequences with desirable frequency characteristics. By combining our previous results with techniques from the theory of finite impulse response filters, we can specify (1) the total duration of the pulse sequence, (2) the frequency ranges it is desired to perturb, (3) the desired perturbation, and (4) the frequency range it is desired not to perturb. We can then synthesize a hard pulse sequence which will yield that desired perturbation with the minimal possible error. The minimum error is global, in the sense that no pulse sequence can do better at achieving the specifications, and is not just a local minimum, around the pulse sequences close to the derived pulse. © 1989 Academic Press, Inc.
Compensation for effects of linear motion in MR imaging
Authors: Korin Hope W. , Farzaneh Farhad , Wright Ronald C. , Riederer Stephen J. 
Published: March 2007

AbstractVarious compensation methods for different types of motion during MR image acquisition have been proposed. Presented here is a postprocessing scheme for eliminating artifacts due to linear, intra‐slice motion of known velocity. The data for each phase encoding or “view” acquired from a moving object are shown to differ from those which would be measured from the stationary object by a phase factor which depends on the object's displacement from a reference point. This derivation is then used to propose a correction scheme for linear motion in which all phase encodings measured at different positions of the moving object are collapsed onto the same reference position. After subsequent reconstruction, the object appears perfectly “focused.” By selection of different reference positions, the method permits positioning of the compensated object as desired within the field of view of the image. This property allows the method to be extended to create sequences of corrected images with smooth object motion between frames of the sequence. The basic correction scheme and its variations were tested experimentally in phantom studies with velocities as large as 8 cm/s. © 1989 Academic Press, Inc.
Regional effects of repetition time on NMR quantitation of water in normal and edematous lungs
Authors: Cutillo Antonio G. , Morris Alan H. , Ganesan Krishnamurthy , Ailion David C. , Case Thomas A. , Durney Carl H. , Watanabe Fumi 
Published: March 2007

AbstractIt is well known that pulmonary edema is, in general, spatially nonuniform. Since the NMR spin‐lattice relaxation time (T1) is increased by lung edema, the spatial distribution of T1 will be nonuniform. When the repetition time (TR) is short relative to the T1 of edematous lung, lung water content will be underestimated and this underestimation will be spatially nonuniform as well. Therefore, technical artifacts which are a complex function of lung edema and its spatial distribution are expected. We compared overall and regional (topographic) lung water density measurements obtained from living rats (with normal or edematous lungs) using repetition times of 2.0 and 6.2 s (at a magnetic field of 1 T), to quantify this uneven T1 effect for normal and edematous lungs. NMR measurements at TR = 2.0 s underestimated whole lung water density (ρ―H2O) (at TR = 6.2 s) by an average of 7.2% in normal rats and 22.5% in rats with pulmonary edema. Regional ρ―H2O underestimation (%Δρ―H2O) varied from 2.2 to 8.8% (group means) in normal lungs and from 7.3 to 30.8% in edematous lungs. As a result, the interquartile range (of the voxel distribution as a function of pH2O) underestimated the spatial nonuniformity of lung water density by 28.0% in edematous lungs, likely because of greater loss of NMR signal from high‐water‐density, long‐T1 lung regions. Both %ΔpH2O and T1, were significantly correlated with ρ―H2O at TR = 6.2 s. Artifactual distortion of the spatial distribution of NMR signal intensity cannot be predicted from average T1 values characterizing the whole lung, but rather requires a knowledge of the spatial distribution of T1. © 1989 Academic Press, Inc.
Correction of distortions due to the pulsed magnetic field gradient‐induced shift in B0 field by postprocessing
Authors: Jehenson P. , Syrota A. 
Published: March 2007

AbstractGradient pulses used in most localization techniques induce time‐dependent shifts in B0 that strongly distort NMR signals. A postprocessing correction method requiring no additional hardware is proposed. The phase shift produced by the B0 shift is calculated from a reference free induction decay (FID) and used to correct any FID acquired with the Same sequence. © 1989 Academic Press, Inc.