bluuebunny/crossref_metadata_2025_split huggingface dataset:
Imaging of brain tissue pH and metabolites. A new approach for the validation of volume‐selective NMR spectroscopy
Authors: Höhn‐Berlage M. , Okada Y. , Kloiber O. , Hossmann K.‐A. 
Published: March 2007

AbstractFor the validation of volume‐selective 1H and 31P NMR spectroscopy of the brain methods are required that allow high resolution quantitative mapping of tissue pH and metabolites on intact brain slices. The following techniques are proposed for this purpose. Tissue pH is imaged on cryostat sections of in situ frozen brains, using umbelliferone as a fluorescent pH indicator (Csiba et al, Brain Res 289, 334–337 (1983)). Regional tissue ATP content is measured in adjacent cryostat sections, using the luciferine/luciferase system of fireflies for evoking substrate‐specific bioluminescence (Kogure and Furones Alonso, Brain Res. 154, 273–284 (1978)). Lactate content is imaged in a similar way by inducing substrate‐specific bioluminescence with lactate dehydrogenase and luciferase from vibrio Fischeri (Paschen, J. Cereb. Blood Flow Metab. 5, 609–612 (1985)). The spatial resolution of these techniques is better than 100m̈, as exemplified in experimental brain tumors and brain infarct of cats.The applicability of biochemical mapping for the validation of NMR spectroscopy was tested in a global brain ischemia model of cat by correlating surface coil 31P and 1H spectra with the corresponding regional biochemical data, measured in the sensitive volume of the coil. Correlation coefficients were r = 0.907, 0.852 and 0.924 for pH, lactate and ATP, respectively. These results demonstrate that the biochemical measurements obtained by bioluminescence and fluoroscopic imaging correlate closely with the NMR data and, therefore, are appropriate for the validation of more complex applications, such as volume‐selective spectroscopy of brain infarcts or tumors.
Rational approaches to the design of NMR selective pulses
Authors: Morris Peter G. , McLntyre Dominick J. O. , Rourke David E. , Ngo J. Thomas 
Published: March 2007

AbstractThe need for NMR selective pulses in magnetic resonance imaging and spectroscopy is reviewed. The shortcomings of the current generation of pulses are discussed and the need for new categories of pulse identified. Strategies for selective pulse design are outlined and two numerical optimization methods, simulated annealing and SPINCALC (a method recently introduced by us: J. T. Ngo and P. G. Morris, Magn. Reson. Med. 5, 217 (1987)), are discussed in detail. Their use is illustrated and compared for the design of π/2 phase‐compensated pulses. Both methods require substantial amounts of CPU time, with simulated annealing the more demanding. Unconstrained, simulated annealing also tends to produce pulses with discontinuous waveforms. A crude two‐dimensional pulse derived from a low flip angle approximation is illustrated.
Localized 13C‐{1H} NMR of rat liver In vivo using surface‐spoiling gradients
Authors: Chen Wei , Ackerman Joseph J. H. 
Published: March 2007

AbstractAn NMR spectroscopy localization method that employs an inhomogeneous surface‐spoiling magnetic field gradient has been applied to detect the 13C‐{1H} signals from deep‐lying liver tissue of rat in vivo. The method requires small gradient driving currents (less than 1 amp) and short gradient periods (˜0.5–1.6 ms). Thus, it is not likely to suffer from induced eddy currents and can detect short T2 resonances. We demonstrate that by employing a pulsed surface‐spoiling gradient one can eliminate “contaminating” signals from the surface‐lying tissues (muscle, fat and skin) while still maintaining the resonance linewidth resolution for the deep‐lying tissue of interest (liver). The feasibility of using this localization approach to trace glucose conversion into glycogen is shown.
19F chemical shift imaging in perfluorocarbons
Authors: Börnert Peter , Dreher Wolfgang , Schneider Wilfried 
Published: March 2007

AbstractThe use of 19F chemical shift sensitive imaging techniques to monitor the biodistribution of perfluorocarbons (PFC) is discussed. For these experiments one has to study the spectroscopic properties of the PFC to be mapped for choosing high performance NMR imaging sequences. Three techniques used in our laboratory, a chemical shift selective approach, a method using spectrum simplification and a chemical shift sensitive NMR imaging method using adjusted phase encoding are discussed and illustrated by experiments.
Problems and expediencies in human 31P spectroscopy. The definition of localized volumes, dealing with saturation and the technique‐dependence of quantification
Authors: Bottomley Paul A. , Hardy Christopher J. , Roemer Peter B. , Weiss Robert G. 
Published: March 2007

AbstractSeveral technological problems in in vivo localized spectroscopy of metabolism are discussed in the context of comparing data obtained by different means. Deficiencies in spectroscopy localization methods can produce spectra that are dominated by artefactual signals derived from outside of selected volumes. Such artefacts are not usually correctly accounted for by representations of the profiles of the transverse magnetization alone. Selected sensitive volumes should be defined in terms of the size of tissue contributing the major fraction of signal to an observed spectrum, which is the integrated response from the sample including any phase cancellation effects. Phase cancellation in one‐dimensional localization techniques employing excitation by an RF field with uniform phase distribution and surface coil detection such as depth resolved surface coil spectroscopy, chemical shift imaging (CSI) and rotating frame zeugmatography (RFZ) can significantly alter the effective radius of the sensitive volumes depending on the sample distribution and the extent of the homogeneous region of the magnet. Also, discrete spatial sampling in RFZ and CSI can radiate signal artefacts of around 25% into adjacent elements depending on the location and distribution of signal sources. Acquisition delays between excitation and detection and partial saturation are other major sources of systematic error. Saturation factors for metabolites are not easily obtainable on localized volumes during clinical exams on an individual basis, but may be expediently obtained as larger‐volume tissue‐averages. Better documentation of saturation effects, acquisition delays and localized volume sizes is needed to compare and validate clinical results and performance.
Clinical magnetic resonance spectroscopy of brain, heart, liver, kidney, and cancer. A quantitative approach
Authors: Weiner Michael W. , Hetherington Hoby , Hubesch Bruno , Karczmar Greg , Massie Barry , Maudsley Andrew , Meyerhoff Dieter J. , Sappey–Marinier Dominique , Schaefer Saul , Twieg Donald B. , Matson Gerald B. 
Published: March 2007

AbstractClinical studies using 31P and 1H MRS with a whole body 2.0 T MRI/MRS system are described. In most cases, techniques to quantitate absolute molar concentrations of metabolites in various organs were used. In the brain, AIDS, chronic stroke, and white matter lesions were associated with alterations of brain 31P metabolites. Epilepsy was associated with increased pH in the seizure focus. In the heart, dilated cardiomyopathy was associated with increased PDE/ATP while PCr/ATP was unchanged. In the liver, alcoholic hepatitis and cirrhosis were associated with diminished hepatic ATP while alcoholic hepatitis had increased pH and cirrhosis had decreased pH. This allowed differentiation of normal liver, alcoholic hepatitis, and alcoholic cirrhosis without biopsy. In the prostate, malignancy was associated with increased PME/ATP and decreased PCr/ATP. The PME/PCr was greatly increased in malignant prostate with no overlap in normals. Other cancers outside the brain had increased PME and effective treatment was often associated with diminished PME. 1H MRS of the brain was performed using ISIS and outer volume suppression pulses for volume localization. Excellent high resolution 1H water‐suppressed spectra were obtained at echo times as short as 30 ms, showing well resolved peaks for lactate, N‐acetylaspartate, glutamate, choline, creatinine, and inositol. 1H MRS demonstrated that the uptake of ethanol by the brain was slower than the rise of ethanol in blood. 31P spectroscopic imaging of the brain with resolution of 2.25 × 2.25 × 2.5 cm produced metabolic images and high resolution spectra from desired regions of interest. The research activities in this laboratory over the past two years demonstrate the wealth of metabolic information that can be obtained clinically with MRS. Technical advances in the area of proton MRS and spectroscopic imaging should improve the ability to detect metabolic alterations produced by human disease.
In vivo1 values of phosphorus metabolites in human liver and muscle determined at 1.5T by chemical shift imaging
Authors: Buchthal S. D. , Thoma W. J. , Taylor J. S. , Nelson S. J. , Brown T. R. 
Published: March 2007

AbstractA procedure for obtaining T1 values for phosphorous metabolites in localized regions of human subjects, using a standard 1.5 T MR imager, is described. 31P spectra and T1 values localized to the liver, and to abdominal and calf muscle of healthy volunteers were obtained by means of a multi‐slice spectroscopy technique, consisting of a chemical shift imaging (CSI) sequence with a B1‐insensitive excitation and one dimension of phase encoding, used in conjunction with a surface coil. An examination consisting of proton imaging, shimming and collection of 31P progressive saturation spectroscopic data for T1 determination required 1h to perform. Shimming on the signal from the body region detected by the surface coil gave spectra of excellent spectral resolution. Quantification of all peaks in the localized 31P spectra was carried out with the PIQABLE algorithm, and T1 values were calculated for inorganic phosphate (Pi), the phosphodiester region, and the ATP α‐, b̃‐ and γ peaks of liver, and for calf muscle Pi, phosphocreatine (PCr), and the three ATP peaks. The precisions of the measurement and of the entire process for obtaining and quantifying localized spectra by one‐dimensional CSI were determined, and the accuracy of T1 values obtained by this means was verified. The temporal variation in T1 values obtained in a series of examinations of a single normal subject was also assessed. The consistency of the T1 values obtained in this study with in vivo T1 values obtained by other techniques is a stringent test of accuracy of localized spectra obtained with CSI.
Metabolic consequences of coronary stenosis. Transmurally heterogeneous myocardial ischemia studied by spatially localized 31P NMR spectroscopy
Authors: Uǧurbil K. , Merkle H. , Robitaille P.‐M. , Hendrich K. , Yoshiyama M. , Path G. , Zhang J. , Tristani M. , From A. H. L. , Bache R. J. , Garwood M. 
Published: March 2007

AbstractCoronary stenosis results in transmurally non‐uniform blood flow with the inner layers of the left ventricular wall typically suffering a more severe hypoperfusion relative to the outer layers. Coupled with numerous other transmural non‐uniformities such as systolic tension development and oxygen needs, the heterogeneous blood flow distribution in the presence of coronary stenosis is expected to result in transmurally heterogeneous ischemia. All previous NMR spectroscopy studies of myocardial metabolism and bioenergetics under normal and ischemic conditions treated the organ as a homogeneous tissue. We have utilized spatially localized 31P NMR spectroscopy together with non‐NMR measurements of regional blood flow to study the myocardium with transmural spatial differentiation under normal and flow‐restricted conditions. 31P NMR and blood flow data obtained concurrently on each heart revealed that sustained coronary artery stenosis resulted in transmurally non‐uniform ischemia which largely paralleled the hypoperfusion pattern. The reduction in creatine phosphate content (with consequent elevation of Pi) and hypoperfusion was tightly correlated in the subendocardium for flow rates less than ∼0.7 mL/min per g wet myocardium. The high energy phosphate and Pi content of the epicardium, however, was responsive not only to the flow to this region but also to the extent of ischemia in the subendocardial layers. These results document the utility of localized NMR spectroscopy in physiologic research and suggest potential biomedical applications due to the tight correlation noted between alterations in blood flow and changes in the phosphorylated metabolite levels detected by 31P NMR.
Some considerations concerning susceptibility, longitudinal relaxation time constants and motion artifacts in In vivo human spectroscopy
Authors: Young I. R. , Cox I. J. , Coutts G. A. , Bydder G. M. 
Published: March 2007

AbstractArtifacts due to localized susceptibility effects, variations in the spin‐lattice relaxation time constants of signals and a mixing of signals arising from tissue motions can contaminate otherwise credible results. The sources and magnitude of some of these are discussed and their likely impact assessed, so that the necessity of incorporating additional measurements in an individual study can be demonstrated.
Amplification or obfuscation: Is localization improving our clinical understanding of phosphorus metabolism?
Authors: Ross Brian , Narasimhan P. T. , Tropp James , Derby Kevin S. 
Published: March 2007

AbstractLocalization techniques are considered an indispensable part of the clinical spectroscopy examination. The results are often a marked improvement in diagnostic information (amplification), but because of the introduction of new artifacts and the more prolonged examination time, some of the undoubted advantage is lost (obfuscation). There is thus an argument for continued development of more rapid methods of clinical spectroscopy and, if necessary, sacrificing some spatial information.
31P NMR of mammalian cells encapsulated in alginate gels utilizing a new phosphate‐free perfusion medium
Authors: Narayan K. Shankar , Moress E. A. , Chatham J. C. , Barker P. B. 
Published: March 2007

AbstractA simple technique permitting long term 31P magnetic resonance spectroscopy of cultured mammalian cells is described. Cells are encapsulated in calcium alginate gels and perfused with a new phosphate‐free medium designed for maintenance of high cell viability. Intracellular pH and β‐NTP/Pi ratios, studied in three cell types, remained stable over a 16–20 h NMR monitoring period. The techniques described may be useful for monitoring cell metabolism with a variety of cell types.
Decoupling technique for transmit coils in NMR spectroscopy and imaging
Authors: Yoda K. 
Published: March 2007

AbstractA decoupling structure using an additional LC resonant configuration for NMR transmit coils is analysed and the probe sensitivity of the receive coil with the decoupled transmit coil is calculated using simple circuit models. An adjustment‐free technique for the decoupling circuit under different loading conditions is proposed using the calculated results and demonstrated by experiments. The proposed method can simplify the probe operation.
In vivo magnetic resonance imaging and spectroscopy of humans with a 4 t whole‐body magnet
Authors: Barfuss H. , Fischer H. , Hentschel D. , Ladebeck R. , Oppelt A. , Wittig R. , Duerr W. , Oppelt R. 
Published: March 2007

AbstractA research‐type 4 T whole‐body magnet, built by Siemens AG, Erlangen, FRG, was used to investigate magnetic resonance at high field strengths. Designs for head and body coils operating at 170 MHz are described. Proton images of the human head and body are degraded by dielectric resonances and penetration effects. The nature of the dielectric resonances was demonstrated in phantoms containing distilled and saline doped water. Radiation damping at 170 MHz generates secondary echoes after a spin echo sequence. This effect was observed in phantoms and with reduced amplitude in the human head. Hydrogen spectra of the human head were selected utilizing stimulated and spin echoes. The latter technique allows the volume size to be reduced to 1 cm3. Examples of brain tumors that have been routinely investigated with volumes of 8 cm3 are given. Natural abundance carbon and phosphorus spectra of muscle and liver demonstrate the expected increase in spectral resolution and signal to noise ratio. Carbon spectra from the liver show the glycogen signal. Fluorine spectroscopy was used to study the time course of the absorption and emptying of a fluorinated antibiotic from the human stomach.
31P and 23Na NMR spectroscopy of normal and ischemic rat skeletal muscle. Use of a shift reagent in vivo
Authors: Balschi James A. , Bittl John A. , Springer Charles S. , Ingwall Joanne S. 
Published: March 2007

Abstract23Na NMR spectroscopy was used 1, to define the distribution of the shift reagent for cations, triethylenetetraminehexaacetatedysprosium(III), DyTTHA3−, in the living rat; 2, to define the characteristics of the Na resonances reporting intra‐ and extracellular Na+ in skeletal muscle in vivo; and 3, to calculate the Na+ concentrations in the intra‐ and extracellular spaces of the gastrocnemius muscle during well‐perfused and ischemic conditions. The concentration of DyTTHA3− infused intravenously into the jugular vein of the living rat reached a maximum value of 8–9 mM in the extracellular space of the muscle after ca 40 min of infusion. This allowed excellent discrimination of extra‐ and intracellular Na signals (Nao and Nai, respectively) and did not spoil the resolution of concurrent 31P NMR spectra. Infusion of shift reagent changed neither hemodynamic performance of the rat nor the high‐energy phosphate content of skeletal muscle. Shift reagent enters ca 15% (v/w) of the rat body weight; this corresponds to almost all of the “fast” or rapidly permeable extracellular space. It is excreted from the body with a pseudo‐first order rate constant of 0.0158 min−1. In resting muscle, we estimate that [Na+]i is 3–5 mM and, in muscle perfused with the sodium salt of the shift reagent, that [Na+]o in the fast exchangeable extracellular space is 166 mM. During 11 h of ischemia at 37°C, the area of the Nai+ signal area monotonically increased sixfold. Based on estimates for maximum changes in fluid shifts reported by the decrease in the area of the Nao signal area, we calculate that the lower limit for [Na+]i after 11 h of ischemia is 27 mM. The NMR‐visibility factors for the extracellular and intracellular Na+ signals are essentially the same. This study demonstrates that the shift reagent DyTTHA3− is acutely non‐toxic and that the 23Na NMR spectra obtained can be used to quantitate [Na+]o and [Na+]i in tissues in vivo. Using this technique, we found that the transmembrane sodium gradient fell from ca 35 in well‐perfused skeletal muscle to <6 during prolonged ischemia.
Hypophosphite transport in human erythrocytes studied by overdetermined one‐dimensional NMR exchange analysis
Authors: Price William S. , Kuchel Philip W. 
Published: March 2007

AbstractThe membrane transport kinetics of the disubstituted phosphorus oxyacid, hypophosphite, were studied in human red cells under equilibrium exchange conditions. Hypophosphite is an analogue of both the bicarbonate and phosphate ions and is known to be rapidly transported across the human red cell membrane via the anion transport protein, Band 3. The hypophosphite ion is a particularly useful probe of Band 3‐mediated membrane transport as the intracellular and extracellular species occur as distinct resonances in the 31P NMR spectrum; as a result the membrane potential may also be readily inferred. We applied ‘overdetermined’ one‐dimensional exchange analysis to estimate the rates of exchange for influx and efflux. The apparent equilibrium exchange (ee) values K for the hypophosphite efflux and influx were different and while the efflux parameters were not able to be unambiguously defined, the measured apparent influx kinetic transport parameters were V = 1600 ± 190 amol cell−1 s−1, and K = 75±16 mM.
31P Magnetic resonance spectroscopy of the human paediatric liver
Authors: Iles R. A. , Cox I. J. , Bell J. D. , Dubowitz L. M. S. , Cowan F. , Bryant D. J. 
Published: March 2007

AbstractLocalized 31P NMR spectroscopy was used to study the developing human liver in three neonates and one infant, all with neonatal intracranial problems, but normal liver function. A prominent resonance was present in the phosphomonoester (PME) region of the spectrum of the neonates; the PME/ATP ratio was 1.0 ± 0.4 (repetition time 1 s), compared to the mean adult liver value of 0.2 ± 0.1. The saturation factor of PME in the neonates was large, indicating that the increase in PME/ATP reflected an increase in relative PME concentration. The chemical shift of the PME peak in the neonatal liver (6.8 ± 0.1) was similar to that found in neonatal brain, suggesting that phosphorylethanolamine may be a major constituent. The phosphodiester (PDE)/ATP ratio in these patients (0.4 ± 0.1) was decreased compared with the mean adult value (1.3 ± 0.2), and the saturation factor of PDE was small. The results from the infant were different from both the neonates and adults; PME/ATP was decreased compared to the neonates, but increased compared to adults. The saturation factor of PDE was increased compared to neonates. The biochemical implications of the observed changes in PME and PDE in paediatric liver are discussed in relation to membrane turnover.
Lipid characterization in an animal model of atherosclerosis using NMR spectroscopy and imaging
Authors: Booth R. F. G. , Honey A. C. , Martin J. F. , Lindon J. C. , Farrant R. D. , Carpenter T. A. , Hall L. D. 
Published: March 2007

AbstractHigh resolution 1H and 13C NMR spectroscopic measurements including 1H/13C 2D correlation and magnetic resonance imaging (MRI) studies, have been carried out on intact rabbit aortic tissues ex vivo using animals fed both normal and high cholesterol diets. The results show that 1H and 13C NMR spectroscopy can distinguish mobile lipids and can differentiate between normal triglyceride content and cholesterol‐enriched lipids, in intact tissue. There were considerable differences in the level of deposition of cholesteryl esters in animals all fed on the same diet. Confirmation is presented of temperature‐dependent differences in mobility and organization between the triglycerides found in control tissue and the cholesteryl esters found in aortas from high lipid diet animals. Water‐suppressed MRI showed evidence of lipid accumulation in the aortas of high cholesterol diet rabbits. It is concluded that the hypercholesterolaemic rabbit model of atherosclerosis, coupled with such NMR methods, may offer a noninvasive method of monitoring disease development, allowing the evaluation of the effect of therapeutic agents on the progress of atherosclerosis.
Spin‐exchange NMR spectroscopy in studies of the kinetics of enzymes and membrane transport
Authors: Kuchel Philip W. 
Published: March 2007

AbstractSpin‐exchange NMR techniques enable the measurement of the rates of exchange of solutes between chemically or physically distinct sites in reactions taking place at chemical equilibrium. The time scale of the events that are able to be investigated lies in the neighbourhood of 1 s. The earliest studies in this area of NMR spectroscopy involved chemical reactions in vitro but the procedures have been adapted to the study of enzyme‐catalysed reactions both in vitro and in vivo, and more recently to transmembrane exchange processes. The emphasis in this review is on the various types of spin‐exchange experiments, the analysis of data derived from them, estimates of uncertainty in measured rate constants, and their shortcomings. Those methods given special attention are saturation transfer, two‐dimensional exchange spectroscopy (2D EXSY), the ‘accordion’ experiment and ‘overdetermined’ one‐dimensional exchange spectroscopy.