bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the use of a slice‐selective 270° self‐refocusing Gaussian pulse for magnetic resonance imaging: Comments on the note by D. M. Doddrell et al.
Authors: Emsley Lyndon , Bodenhausen Geoffrey 
Published: March 2007

AbstractIt is shown that the results obtained by D. M. Doddrell, G. J. Galloway, S. E. Rose, P. J. Moulds, and I. M. Brereton (Magn. Reson. Med. 19, 1991) using self‐refocusing 270° Gaussian pulses for slice selection are consistent with our predictions (Magn. Reson. Med. 10, 273, 1989). © 1991 Academic Press, Inc.
Cerebral glucose is detectable by localized proton NMR spectroscopy in normal rat brain in Vivo
Authors: Gyngell M. L. , Michaelis T. , Hörstermann D. , Bruhn H. , Hänicke W. , Merboldt K. D. , Frahm J. 
Published: March 2007

AbstractThis contribution reports the first direct and noninvasive observation of cerebral glucose in normal anesthetized rats (n = 16) using short‐echo‐time localized proton NMR spectroscopy (2.35 T, STEAM, TR = 6000 ms, TE = 20 ms, 125 μl). In addition to resonances from N‐acetyl aspartate (NAA), glutamate, total creatine, cholines, taurine, and myo‐inositol, all spectra exhibit strongly coupled resonances from glucose (3.43, 3.80 ppm) that are readily identifiable using model solutions. The observed level of cerebral glucose in fasted rats covered a range of 15–4096 of that of NAA giving absolute concentrations of 1.1–2.8 mM when NAA is taken to be 7 mM. The arterial blood glucose concentration was 7.7 ± 0.8 mM in the same group Of animals.
Double‐volume 1H spectroscopy with interleaved acquisitions using tilted gradients
Authors: Ernst Th. , Hennig J. 
Published: March 2007

AbstractA method is presented by which volume selective in vivo 1H spectra of two different voxels can be acquired in an interlaced mode using PRESS or STEAM spectroscopy. Spatially tilted gradients are employed for voxel definition so as to avoid mutual saturation. Independent volume selective shimming of the voxels is possible. Two spectra of volumes as small as (1.5 cm)3 can be acquired from human brain within 14 min even from very disadvantageous locatins close to air‐bone interfaces. © 1991 Academic Press, Inc.
Correlation of lactate and pH in human skeletal muscle after exercise by 1H NMR
Authors: Pan J. W. , Hamm J. R. , Hetherington H. P. , Rothman D. L. , Shulman R. G. 
Published: March 2007

AbstractWe have made in vivo 1H NMR measurements of the time course of pH and lactate in human skeletal muscle after exercise. Spectra were obtained in a 4.7‐T 30 cm bore Bruker Biospec spectrometer with a 2.5‐cm diameter single surface coil. pH was determined from the shift of the endogenous carnosine H‐C2 peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 mM/ kg wet wt. Fitting the data shows that the exponential decay of lactate (‐0.094 ± 0.014 min ‐1, t 1/2 = 10.6 min) is slower than that of pH (‐0.147 ± 0.015 min‐1, t1/2 = 4.7 min), n = 7 with two different volunteers. These values are significantly different with P < 0.0005. Relaxation times of lactate and creatine were also measured for lactate quantitation: creatine Tl. 1.23 ± 12 s. T2, 136.2 ± 26.4 ms (both in resting human muscle); lactate Tl (in postmortem rabbit muscle), 1.0 ± 11 s and T2, 80 ms (in postexercise human muscle). At the end of intense exercise, the lactate level reached was 25.3 ± 4.0 m M and the average pH drop was 1.0 pH unit. We discuss the implicaions of these measurements in conjunction with existing data on other sources of H+ flux, phosphocreatine resynthesis, H+ transport, and contribution of inorganic phosphate to buffering. © 1991 Academic Press, Inc.
Application of missing pulse steady state free precession to the study of renal microcirculation
Authors: Stromski M. E. , Brady H. R. , Gullans S. R. , Patz S. 
Published: March 2007

AbstractMissing pulse steady state free precession (MP‐SSFP), an extension of steady state free precession (SSFP), was evaluated for its ability to measure slow fluid flows. In experiments using flow phantoms, the MP‐SSFP signal was sensitive to fluid velocities in the millimeters per second range. Isolated perfused rabbit kidneys were then used to determine if MP‐SSFP could measure perfusion in a biological tissue. The signal intensities in the different anatomical regions of the kidney were observed to be related to the total flow to the organ. Furthermore, increasing the flow sensitivity of the pulse sequence by increasing the gradient strength resulted in decreases in the image signal intensity. The MP‐SSFP signal was more sensitive to flow in the medulla than in the cortex. This can be related to slow flow sensitivity of MP‐SSFP and the known differences in velocity profiles between these two regions. These results suggest that MP‐SSFP may be a powerful tool for the noninvasive measurement of slow fluid flows in different regions of the kidney. © 1991 Academic Press, Inc.
Regional 1H transverse magnetization studies in perfused rabbit kidney
Authors: Mulkern R. V. , Stromski M. E. , Brady H. R. , Gullans S. R. , Sandor T. , Jolesz F. A. 
Published: March 2007

AbstractA Carr‐Purcell‐Meiboom‐Gill imaging sequence consisting of 128 echoes is used to extract transverse magnetization decay curves (TDCs) at 1.9 T from 1.7 × 1.7 × 5‐mm3 voxels within the cortex, outer medulla, and inner medulla of perfused rabbit kidneys. The spatially localized TDCs within each tissue type are found to be better approximated by biexponential, as opposed to monoexponential, functions. The biexponential parameters characterizing the TDCs demonstrate an improved degree of tissue specificity over that available from monoexponential analyses. The fraction of the quickly relaxing TDC component and the relaxation rate of this component are observed to decrease from cortex to inner medulla. A two‐site exchange analysis is used to convert biexponential TDC parameters into water volume fractions and exchange rates. The exchange rates between the fast and slowly relaxing pools increased from cortex to inner medulla. All exchange rates were less than 1.5 Hz, indicating a relatively slow water exchange process. The imaging methods and subsequent analyses offer the potential to generate unconventional MR images with tissue contrast dependent upon water compartmentation and exchange. © 1991 Academic Press, Inc.
Application of continuous relaxation time distributions to the fitting of data from model systmes and excised tissue
Authors: Menon R. S. , Allen P. S. 
Published: March 2007

AbstractBiological systems exhibit heterogeneity at many different levels, leading to the expectation of multiple relaxation time components for water protons in tissue samples. Traditional methods which fit the relaxation data to an a priori number of discrete components are open to observer bias in their interpretation of this data, and moreover, are intutively less realistic for heterogeneous systems than methods which produce continuous relaxation time distributions. Previous validations of continuous distribution techniques have been made on simulated data assuming uniform Gaussian noise. In the current work we have investigated the ability of one particular linear inverse theory technique to reproduce known relaxation time distributions from the data on a controllable model system. Furthermore, using the experience gained on the model system, we have applied this same technique to the analysis of in vitro relaxation time measurements on excised brain tissue and found for water protons in white matter, four reproducible components for the transverse relaxation, whereas gray matter gave rise to only two. The lougitudinal relaxation displayed only one component in either white matter or gray matter. © 1991 Academic Press, Inc.
Evaluation of ba1112 rhabdomyosarcoma oxygenation with microelectrodes, optical spectrophotometry, radiosensitivity, and magnetic resonance spectroscopy
Authors: Sostman H. Dirk , Rockwell Sara , Sylvia Avis L. , Madwed David , Cofer Gary , Charles H. Cecil , Negro‐Vilar Rosa , Moore Deborah 
Published: March 2007

AbstractWe studied tumor tissue oxygenation in the BA1112 rhabdomyosarcoma using microelectrode pO2 measurements, optical spectrophotometry, analyses of cell survival after irradiation, and 31 P magnetic resonance spectroscopy (MRS). Studies were carried out in WAG/Rij/Y rats breathing normoxic, hypoxic, and hyperoxic gas mixtures with and without iv administration of perfluorochemical. Significant changes in tissue oxygenation and metabolic status were found when pO2 values, optical measurements of hemoglobin saturation and cytochrome a, a3 reduction‐oxidation, radiation cell survival determinations, and MRS measurements of phosphometabolite ratios were obtained in rats breathing different gas mixtures. Inhalation of 100% O2 caused increases in tumor pO2, hemoglobin saturation, cytochrome a, a3 oxidation, tumor radiosensitivity, and PCr/Pi, NTP/Pi, and PDE/Pi ratios. Such changes were augmented by pretreatment with iv perfluorochemicals. Inhalation of hypoxic gas mixtures resulted in reductions in the above paramenters. These results indicate that tissue oxygenation can be manipulated reproducibly in the BA1112 rhabdomyosarcoma and suggest that 31 P MRS can be used to monitor changes in tumor oxygenation in this model system.
An NMR probe to study function and metabolism simultaneously in isolated human cardiac tissue
Authors: Lareau Sylvain , Moore Rayad , Mainwood Graham W. , Labow Rosalind S. , Keon Wilbert J. , Deslauriers Roxanne 
Published: March 2007

AbstractTrabeculae isolated from human atrial appendages have been used to study preservation of donor hearts for cardiac transplantation. We have developed a perifusion system equipped with a fiber optic strain gauge to study mechanical performance of human atrial trabeculae (10‐20 mg) while simultaneously observing the energetic compounds by 31P NMR spectroscopy. The NMR probe consists of an eight‐turn solenoid coil (2.3 mm i. d. × 5 mm length, 24‐gauge wire) double tuned to allow observation of 1H and 31P nuclei. The probe and the perifusion system are temperature regulated and permit preservation studies using a variety of small muscles at low temperatures (down to 4°C) as well as at physiological temperature (37°C). 31P NMR spectra suitable for quantification can be obtained from ≈︁ 10 mg of human atrial trabeculae in 15 min. Spectra of 8‐to 12‐mg mouse extensor digitalis longus or soleus muscle can be obtained in less than 10 min. © 1991 Academic Press, Inc.
A complete solution to the model describing Carr‐Purcell and Carr‐Purcell‐Meiboom‐Gill experiments in a two‐site exchange system
Authors: Sobol W. T. 
Published: March 2007

AbstractA general solution for the relaxation decay function observed in both CP and CPMG spin‐echo experiments, performed on systems governed by a two‐site chemical exchange mechanism, is presented. This solution not only provides the relaxation time constants, but also supplies complete information about relative component sizes. Solutions are analytical, but results are complex enough to warrant computer‐assisted calculations. Programming suggestions, based on the extensive tests performed, are provided. © 1991 Academic Press, Inc.
An analytical model for the design of RF resonators for MR body imaging
Authors: Foo Thomas K. F. , Hayes Cecil E. , Kang Yoon‐Won 
Published: March 2007

AbstractA closed form, analytical solution describing the RF fields generated by an RF body coil resonator for MR imaging at 1.5 and 4.0 T is presented. This solution extends the results of earlier studies of RF penetration in the body by explicitly including the RF coil, the RF shield, and the field variation along the z axis for high‐pass birdcage coils. A salient feature of this treatment is the calculation of the axial propagation constant, kz, which determines the z dependence of the RF field. We have determined the relative power deposition in the body, the \documentclass{article}\pagestyle{empty}\begin{document}$ \vec B $\end{document}1, field homogeneity, and coil losses, which are functions of the coil‐to‐shield separation and body size. The relative power deposition in the body has been calculated to vary as the 1.58 power of the body radius. The calculations have also predicted that the field homogeneity in the z direction exhibits greater degradation at higher frequencies in a high‐pass coil than in a low‐pass coil. The model predicts an increase in coil losses by a factor of 2.8 as the coil‐to‐shield separation is reduced from 5 to 2 cm in a standard body resonator. Although the results for only a homogeneous cylindrical object or body are presented, the theory can be extended to a multilayered heterogeneous object of varying permittivity and conductivity. © 1991 Academic Press, Inc.
Evaluation of energy metabolism in brain using epimerization of 2‐deoxy‐2‐fluoro‐d‐glucose by 19F NMR: The effect of anesthesia
Authors: Shinohara Shunji , Kanazawa Yoko , Kojima Masaharu 
Published: March 2007

AbstractThe effect of anesthesia on the epimerization of 2‐deoxy‐2‐fluoro‐D‐glucose(‐6‐phosphate) to 2‐deoxy‐2‐fluoro‐D‐mannose(6‐phosphate) in mice was demonstrated with 19F NMR spectroscopy of excised tissue specimens from heart, muscle, and brain. Spectra from each of six excised organs confirmed that pretreatment with an anesthetic suppressed the conversion ratio, FDM/(FDG + FDM), in brain at 3 h from 52 ± 5 to 30 ± 6% under the dose of 100 mg/kg. We propose potential applications for NMR monitoring of FDG‐FDM conversion, including the assessment of regional brain metabolism and the evaluation of Various pharmacologic agents. © 1991 Academic Press, Inc.
A lineshape fitting model for 1H NMR spectra of human blood plasma
Authors: Hiltunen Y. , Ala‐Korpela M. , Jokisaari J. , Eskelinen S. , Kiviniitty K. , Savolainen M. , Kesäniemi Y. A. 
Published: March 2007

AbstractA lineshape fitting model was constructed for classifying the overlapping information in the 1H NMR spectrum of human blood plasma. A reliable assignment of the overlapping fatty acid (‐CH2‐)n and ‐CH3 resonances of the various lipoproteins (VLDL, very low density lipoprotein; LDL, low density lipoprotein; HDL high density lipoprotein) is introduced, and for the first time detailed characteristics (chemical shifts, half linewidths, and relative intensities) of the individual lipoprotein components were obtained directly from the whole plasma spectrum. This was achieved by combining the constructed lineshape fitting model and the proper 400 MHz proton NMR measurements from blood plasma of a healthy donor, from fractions of the different lipoproteins, and from plasma samples in which the lipoprotein fractions were separately added. The results suggest fair promise of future applications of the rapid and easy NMR analysis of lipoprotein distribution in various research and clinical situations. © 1991 Academic Press, Inc.
Quantitative measurement of blood flow using cylindrically localized fourier velocity encoding
Authors: Dumoulin Charles L. , Souza Steven P. , Hardy Christopher J. , Ash Stephen A. 
Published: March 2007

AbstractA procedure for the quantitative measurement of blood velocity was developed and evaluated in the portal vein, aorta, and vena cava of healthy volunteers. This procedure utilizes Fourier velocity encoding and can be performed with or without cardiac gating. The accuracy of velocity measurements is determined by the accuracy of the gradient subsystem. How measurements derived from the velocity measurement are further limited in their accuracy by the luminal cross‐section measurement. Spatial localization is accomplished with an excitation pulse having a cylindrical rather than slab geometry. Data are acquired in the presence of a readout gradient to provide resolution along the cylindrical axis. © 1991 Academic Press, Inc.
Sensitivity enhancement and reduction of Gibbs artifact in T2‐ weighted imaging using variable tip angle excitation
Authors: Webb A. G. , Clarkson R. B. 
Published: March 2007

AbstractIntroduction of a Gaussian weighting function into the phase encoding of the spin‐echo imaging method via variable tip angle excitation, with concomitant optimization of the recycle delay, is shown to increase the sensitivity of T2‐weighted imaging by up to 40%. In addition, the Gibbs artifact associated with sharp boundaries is reduced considerably without the need for postprocessing of the data. © 1991 Academic Press, Inc.
Ferrioxamine B derivatives as hepatobiliary contrast agents for magnetic resonance imaging
Authors: Muetterties Kurt A. , Hoener Betty‐Ann , Engelstad Barry L. , Tongol Jose M. , Wikstrom Mats G. , Wang Shih‐Chang , Eason Robert G. , Moseley Michael E. , White David L. 
Published: March 2007

AbstractSuccinyl (SDF), phenylsuccinyl (PSDF), glutaryl (GDF), and phenylglutaryl (PGDF) derivatives of desferrioxamine B (DF) have been synthesized. In rats given the 59Fe(III) chelates of each these ligands at tracer levels, 82–94% of the 59Fe was eliminated within 1–2 days. 59Fe given as DF, SDF, and GDF chelates was excreted primarily in the urine, while nearly 50% of that given as PSDF and PGDF was excreted in the feces. Correspondingly, Fe‐DF, Fe‐SDF, and Fe‐GDF (0.2 mmol/kg) produced early, marked renal, but no gastrointestinal magnetic resonance imaging (MRI) enhancement. Fe‐PSDF and Fe‐PGDF (0.2 mmol/kg) produced marked and rapid MRI enhancement of the upper small intestine. In animals with cannulated bile ducts, 59Fe for 59Fe‐PGDF (carrier added, 0.1 mmol/kg) appeared rapidly in the collected bile, but not in the intestinal contents, proving that the contrast agent reaches the bowel via the bile. These changes in the excretion and MRI enhancement patterns brought about by the presence of a phenyl substituent apparently were not related to changes in lipophilicity or protein binding. © 1991 Academic Press, Inc.
pH‐lactate dissociation in neonatal anoxia: Proton and 31P NMR spectroscopic studies in rat pups
Authors: Hida Kazutoshi , Suzuki Nobuyuki , Kwee Ingrid L. , Nakada Tsutomu 
Published: March 2007

AbstractThe pH controlling capability of brain of 1‐day‐old rat pups was investigated using proton (1H) and phosphorus‐31 (31P) nuclear magnetic resonance (NMR) in vivo spectroscopy. Despite significantly high levels of lactate accumulation, brain of 1‐day‐old pups showed remarkable capability of maintaining brain pH virtually unchanged throughout 22 min of anoxia. The study supports the concepts that lactic acidosis is one of the important factors determining the outcome of cerebral anoxia and that the significantly higher pH controlling capability of immature brain plays a key role in the higher resistance toward anoxia. © 1991 Academic Press, Inc.
Proton NMR imaging of cerebral blood flow using H217O
Authors: Kwong K. K. , Hopkins A. L. , Belliveau J. W. , Chesler D. A. , Porkka L. M. , McKinstry R. C. , Finelli D. A. , Hunter G. J. , Moore J. B. , Barr R. G. , Rosen B. R. 
Published: March 2007

AbstractCerebral blood flow was quantitatively mapped by monitoring the cerebral washout of H2 17O using rapid, single‐shot proton NMR imaging. H2 17O acts as a freely diffusible contrast agent for proton imaging via its scalar‐coupled term, enhancing T2 relaxation. Measured values for CBF ranged from 29 to 106 ml/min/100 g over a range of arterial pCO2 between 23 and 81 Torr. © 1991 Academic Press, Inc.
Clinical hepatic imaging with paramagnetic positive enhancers
Authors: Bernardino Michael E. 
Published: March 2007

AbstractAt the present time, there are two types of paramagnetic positive enhancers for hepatic imaging in the United States. One is gadolinium (DTPA) and nonionic forms, and the other is manganese DPDP. Gadolinium derivitives cause the liver to become hyperintense relative to tumors. However, the signal intensity may vary with time. Mn‐DPDP causes the liver to be positively enhanced while tumors are negative defects, thus contrasted against the hyperintense background. Both agents have advantages and drawback. During the past 4 years, we have had the opportunity to evaluate both agent. The following will be a clinical summation of our experience with these two compounds. © 1991 Academic Press, Inc.
Development of an in vivo19F magnetic resonance method for measuring oxygen deficency in tumors
Authors: Raleigh J. A. , Franko A. J. , Kelly D. A. , Trimble L. A. , Allen P. S. 
Published: March 2007

AbstractA 19F magnetic resonance spectroscopy (MRS) approach to measuring hypoxia in experimental tumors in rats at a field strength of 2.35 T has been investigated in a combined study of in situ and excised tumors. The detection of tumor hypoxia is based on the hypoxia marker approach which depends on the selective, covalent binding of a fluorinated 2‐nitromidazole to hypoxic cells. The 19F MRS measurement of in vivo hypoxia marker binding was made at a fixed postinjection time when unbound, circulating marker molecule concentrations had dropped below detectable levels. A correlation between 19F MRS and scintillation counting measures of tumor‐bound, tritium‐labeled hypoxia marker was observed. There was no correlation between integrated 19F MRS hypoxia marker signals and the in vivo 31P MRS parameters of hypoxia which have been developed to measure normal tissue ischemia. Radiolabeling studies and previous immunohistochemical studies with the fluorinated hypoxia marker support the conclusion that the 19F MRS approach has promise as a physically noninvasive guide to the use of hypoxia‐dependent therapies at clinically usable MRS field strengths. © 1991 Academic Press, Inc.
In vivo phosphorus NMR spectroscopy of skin using a crossover surface coil
Authors: Chen Yuhchyau , Richards Todd L. , Izenberg Seth , Golden Robert N. , Williams David L. , Nelson James A. , Steen R. Grant 
Published: March 2007

AbstractA modified crossover surface coil with minimal B1 field penetration was used for collection of skin phosphorus NMR spectra. Projection imaging experiments show that the coilsensitive volume is uniform at the phosphorus frequency, but strikingly nonuniform at s the proton frequency. Experiments with an in vitro phosphorus phantom, designed to simulate skin and underlying tissue, demonstrated that 45.1% (±1.2%) of total signal was derived from Sprague‐Dawley rat skin and 19.3% (±1.4%) of total signal was derived from Fischer‐344 rat skin. 31P MR spectra of rat skin in vivo permitted resolution of four phosphorus compounds: nucleoside triphosphates, phosphocreatine (PCr), inorganic phosphate (Pi), and phosphomonoester. Spectra collected after skin flap surgery in Fischer‐344 rats showed a 50.1% (±7.6%) reduction in the ratio of PCr/Pi within 30 min of surgery, compared to presurgical PCr/Pi levels (P < 0.01). Skin phosphorus spectra are potentially useful for assessment of skin flap and skin graft viability. © 1992 Academic Press, Inc.
Contrast‐to‐noise ratios in maximum intensity projection images
Authors: Brown Donna G. , Riederer Stephen J. 
Published: March 2007

AbstractWe present a statistical analysis of the maximum intensity projection (MIP) algorithm, which is commonly used for MR angiography (MRA). The analysis explains why MIP projection images display as much as a twofold increase in signal‐ and contrast‐to‐noise ratios over those of the source image set. This behavior is demonstrated with simulations and in phantom and MRA image sets. © 1992 Academic Press, Inc.
Reduction of susceptibility artifact in gradient‐echo imaging
Authors: Cho Z. H. , Ro Y. M. 
Published: March 2007

AbstractA new technique with which susceptibility artifact in gradient‐echo imaging can be reduced substantially by use of a tailored RF pulse is described. The proposed technique can ideally be applied to the case where high local magnetic field inhomogeneity is dominated by the susceptibility. The signal loss and void phenomena due to susceptibility in a voxel are studied and a correction method is also proposed. The description of the tailored RF pulse and its proposed application are given and experimental results obtained using a human volunteer with a 2.0‐T KAIS NMR system are presented. © 1992 Academic Press, Inc.