bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional MRI of CO2 induced increase in cerebral perfusion
Authors: Rostrup Egill , Larsson Henrik B. W. , Toft Peter B. , Garde Kim , Thomsen Carsten , Ring Poul , Søndergaard Lars , Henriksen Ole 
Published: March 2007

AbstractThe sensitivity of MR gradient echo imaging towards CO2 induced changes in cerebral blood flow was investigated in 10 normal subjects. The subjects were inhaling 5% and 7% CO2 and the experiments were carried out at 1.5T (n=6) and 2.0 T (n=5), allowing a comparison of field strengths. Additional experiments were carried out using a higher spatial resolution. The largest signal increases were noted in areas corresponding to larger vessels, but significant changes were also conspicuous in deeper cortical and central grey matter. The changes appeared linearly related to the arterial CO2 tension, within the range of PaCO2 studied. In white matter, the changes were not statistically significant.
Comparison of EPI gradient‐echo contrast changes in cat brain caused by respiratory challenges with direct simultaneous evaluation of cerebral oxygenation via a cranial window
Authors: Jezzard Peter , Heineman Frederick , Taylor Joni , Despres Daryl , Wen Han , Balaban Robert S. , Turner Robert 
Published: March 2007

AbstractA gradient‐echo echo planar imaging (EPI) sequence has been used to generate images of cat brain during respiratory challenges. Direct spectrophotometric measurements have been made simultaneously in order to correlate the changes in oxygen saturation as measured by spectrophotometry with the image intensity changes seen in the gradient‐echo images. When blood volume remains approximately constant, as derived from the spectrophotometry data, good correlation is seen between calculated plots made of changes in the transverse relaxation rate, ΔR, and the oxygen saturation as measured by spectrophotometry for much of the time course of the respiratory challenges of anoxia, apnea and hypercapnia. In some cases, the correlation is poorer during the recovery periods of the apnea and anoxia challenges. Those lower correlations can often be accounted for by changes in blood volume, which also affects the NMR relaxation rate. These results contribute to the understanding of the image intensity changes seen during functional brain imaging studies in humans.
Brain or veinoxygenation or flow? On signal physiology in functional MRI of human brain activation
Authors: Frahm Jens , Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Kleinschmidt Andreas , Boecker Henning 
Published: March 2007

AbstractStimulus‐related signal changes in functional MRI of human brain activation not only reflect associated adjustments of cerebral blood flow and oxygen consumption, but strongly depend on the MRI technique chosen and the actual experimental setting. A list of relevant parameters includes static field homogeneity of the magnet, MR pulse sequence and signal type, TE, TR, flip angle, gradient strengths, gradient waveforms, receiver bandwidth and voxel size. In principle, a local signal increase during functional activation may reflect a regional change in cerebral blood flow or deoxyhemoglobin concentration or both. This ambiguity was demonstrated using long TE FLASH MRI at high spatial resolution. Subsequently, experimental strategies were evaluated that either discriminate MRI effects in large vessels from those in the cortical microvasculature or separate changes in blood flow velocity from those in blood oxygenation. Examples comprise studies of the human visual and motor cortex.
Spatial patterns of functional activation of the cerebellum investigated using high field (4 T) MRI
Authors: Ellerman J. M. , Flament D. , Kim S.‐G. , Fu Q.‐G. , Merkle H. , Ebner T. J. , Ugurbil K. 
Published: March 2007

AbstractUsing single and multislice functional MRI at high field strength (4 T) we studied cerebellar activation in 12 subjects making a series of alternating wrist flexion and extension movements against constant inertial loads. Three spatial patterns of activation were observed: (i) parasagittal bands of activity localized primarily in the ipsilateral intermediate and lateral zones of the cerebellar hemispheres, (ii) medio‐lateral bands which in some subjects followed the contour of individual folia and (iii) fragmented regions of activation covering extensive areas of the cerebellum. Bilateral activation of the cerebellum was observed in all subjects with measurable activity. Mean statistically significant activation intensity ranged from 2.34 to 13.54% above baseline.
Inflow versus deoxyhemoglobin effects in bold functional MRI using gradient echoes at 1.5 T
Authors: Duyn Jeff H. , Moonen Chrit T. W. , van Yperen Gert H. , de Boer Ruud W. , Luyten Peter R. 
Published: March 2007

AbstractModified gradient‐echo MR techniques were applied to study the effects of inflow on functional brain imaging studies using visual and motor cortex stimulation. The results demonstrate that the large signal changes, seen in previously reported gradient‐echo studies at 1.5–2.0 T, are dominated by direct inflow effects, in particular when using a large flip angle and a thin slice. The findings suggest that inflow‐based functional imaging, along with Blood Oxygenation Level Dependent (BOLD) functional MRI, may play an important role in future research towards the functional organization of the human brain.
Comparison of diffusion‐weighted MRI with changes in cell volume in a rat model of brain injury
Authors: Verheul H. B. , Balazs R. , Berkelbach van der Sprenkel J. W. , Tulleken C. A. F. , Nicolay K. , Tamminga K. S. , van Lookeren Campagne M. 
Published: March 2007

AbstractThe precise mechanisms that underlie acute changes in tissue water diffusion following cerebral ischemia or related insults such as glutamate exposure remain unexplained, but it has been suggested that these may be caused by cell swelling due to water uptake. This study was undertaken to compare the changes observed in diffusion‐weighted MR images with changes in the cellular volume measured by electrical impedance in a model of N‐methyl‐D‐aspartate‐induced brain injury in perinatal rats. The results show that the temporal course of the intensity changes in the diffusion‐weighted images parallelled the progressive shrinkage of the extracellular space measured from the electrical impedance. After administration of the N‐methyl‐D‐aspartate antagonist MK‐801 the signal enhancement in the images was reversed, which paralleled the normalization of the extracellular space observed by the impedance measurements. It was estimated that the extracellular space decreased from 24 to 12% while the apparent diffusion coefficient of water decreased from 0.89×10−9 in normal tissue to 0.42×10−9 m2/s in tissue exposed to N‐methyl‐D‐aspartate. These data indicate that changes in tissue water diffusion are related to changes in cell volume.
pH and temperature effects on kinetics of creatine kinase in aqueous solution and in isovolumic perfused heart. A 31P nuclear magnetization transfer study
Authors: Goudemant J.‐F. , Elst L. Vander , Dupont B. , Van Haverbeke Y. , Muller R. N. 
Published: March 2007

AbstractPhosphorylated metabolites concentrations and creatine kinase kinetics are measured by 31P NMR in solution and in isovolumic perfused rat hearts submitted to hypo‐ and hyperthermia as well as to acidosis (37°C). In the organ, temperature variation from 40 to 25°C induces an increase of phosphocreatine (PCr) stores, a decrease of Pi and ADP concentrations, but does not affect the ATP pool. Creatine kinase forward flux (Vfor) is gradually reduced when the temperature is lowered both in vitro and in perfused heart. In normothermic and hypothermic conditions, a relationship is found between cardiac performance (rate pressure product, RPP), Vfor and ATP synthesis estimated through the myocardial oxygen consumption rate (MVO2). At 40°C however, the RPP is reduced although both Vfor and MVO2 increase. In vitro experiments show an optimum pH of 7.7 for the forward creatine kinase reaction. In perfused heart submitted to acidosis, a decrease of PCr concentration is observed, whereas ATP and ADP contents remain unchanged. Heart creatine kinase flux increased as in hyperthermia. These high fluxes are attributed to the coupling of the creatine kinase reaction with energy consuming or producing reactions: the increase of energy demand related to non‐contractile processes could explain the high MVO2 and Vfor observed in those conditions.
High‐resolution one‐and two‐dimensional 1H MRS of human brain tumor and normal glial cells
Authors: Kotitschke Klaus , Jung Hans , Nekolla Stephan , Haase Axel , Bauer Albrech , Bogdahn Ulrich 
Published: March 2007

AbstractAstrocytoma (WHO grade II, III), glioblastoma, malignant melanoma, and normal glial cell cultures, established from biopsies, were investigated by 1H MRS. At a 1H resonance frequency of 500 MHz (11.75 T) a high spectral resolution was achieved in 1D 1H spectra; in conjunction with 2D shift‐correlated (COSY) MRS, resonances of alanine, aspartate, choline, creatine, glutamate, glutamine, hypotaurine, myo‐inositol, phosphocreatine, phosphoryl‐ethanolamine, phosphoryl‐choline, lactate, lysine, N‐acetylaspartate, taurine, threonine and valine could be identified. T1 relaxation times for the most prominent compounds are presented. T1 values of lactate ranged between 450 ms and 850 ms. The intensity of the lactate signal revealed differences between individual spectra, but exhibited no correlation between different tumor specimens or degree of malignancy. It was shown that the lactate signal at 1.3 ppm is covered by peaks arising from threonine and fatty acids. The choline signal level varied among spectra of different tumors, among tumors with similar degree of malignancy, and within the same tumor. Further preliminary differences due to aspartate, inositol and glutamine/glutamate were found in 1D and 2D COSY spectra between normal glial cells as well as different tumors. These results indicate that some differences observed in in vivo spectra may be attributable to secondary macroscopic structural changes (hypoxia, necrosis) and not to tumor inherent characteristics. Further correlation between in vivo and in vitro spectroscopy is therefore required.
Characterization of a phosphonium analog of choline as a probe in 31P NMR studies of phospholipid metabolism
Authors: Szwergold Benjamin S. , Kappler Francis , Moldes Milagros , Shaller Calvin , Brown Truman R. 
Published: March 2007

AbstractTumors and transformed cells have been shown by 31P NMR to contain elevated concentrations of two phosphomonoesters, phosphorylcholine and phosphorylethanolamine, involved in phospholipid metabolism. In order to understand the biochemical basis for these phenomena new methods are needed to allow for analysis of the relevant metabolic pathways in intact cells. One such promising tool may be phosphonium‐choline, a 31P NMR‐visible analog of choline in which the trimethyl‐ammonium group of choline has been replaced with a trimethyl‐phosphonium moiety. As shown previously [Sim et al. Biochem. J. 154, 303 (1976)], this compound is non‐toxic and readily metabolized by cultured cells into phospholipids. In this paper we describe in greater detail some of the chemical and NMR spectroscopic properties of this material. Most significantly we show here that the chemical shift of phosphonium‐choline is sensitive to the phosphorylation state of the analog and that the phosphonium nucleus is NMR‐visible even after its incorporation into phospholipid. The unique properties of this analog should make it possible to use high‐field 31P NMR to follow the flux of phosphonium‐choline through the Kennedy pathway in intact perfused cells cultures.
Intracellular acidosis in murine fibrosarcomas coincides with ATP depletion, hypoxia, and high levels of lactate and total Pi
Authors: Vaupel P. , Schaefer C. , Okunieff P. 
Published: March 2007

AbstractBioenergetic and metabolic status of murine FSaII tumours were evaluated using 31P MRS, acid extracts (‘global’ techniques) and quantitative bioluminescence (‘microregional’ assay). Data obtained from s.c. tumours of varying sizes (44–600 mm3) have been correlated with the oxygenation status evaluated using O2‐sensitive needle electrodes. β‐NTP/Pi and phosphocreatine (PCr)/Pi ratios derived from 31P MRS were positively correlated to the median tissue pO2 values. pH declined during growth with intracellular acidosis being evident in tumours >350 mm3. Whereas lactic acid formation greatly contributed to this decline in small‐ and medium‐sized tumours, ATP hydrolysis and slowing down of the activities of pumps involved in pHi regulation seem to be major factors responsible for intracellular acidification in bulky tumours. PCr levels decreased at an early growth stage, whilst ATP concentrations dropped in bulky malignancies only, coinciding with a decrease in adenylate energy charge and a substantial rise in the levels of total Pi. MRS observable (mobile) Pi was consistently lower than [Pi] measured in acid extracts. On average, median pO2 values of ca 10 mmHg represent a critical threshold for energy metabolism. At higher median O2 tensions, levels of ATP, phosphomonoester and total Pi were relatively constant. This coincided with intracellular alkalosis or neutrality and stable adenylate ratios. On average, median pO2 values < 10 mmHg coincided with intracellular acidosis, ATP depletion, a drop in energy charge and rising Pi levels.
31P MRS of tumour metabolism in anaesthetized vs conscious mice
Authors: Sansom J. M. , Wood P. J. 
Published: March 2007

AbstractThe injectable anaesthetics Hypnorm/Hypnovel, chloral hydrate and etomidate, were examined for their effects on C3H/He mouse core temperature and on the in vivo 31P MR spectra of KHT and SCCVII/Ha transplantable tumours, compared with conscious mice gently restrained in jigs. Hypnorm/Hypnovel at 0.1 mL/mouse i.p. reduced core temperature by 6°C at 30 min after injection, returning to control levels by 100 min, but did not significantly alter the 31P MR spectra of either KHT or SCCVII/Ha tumours. Chloral hydrate at 300 mg/kg i.p. produced a 5°C fall in mouse core temperature, at 25 min after injection, again returning to control levels by 100 min. This agent increased the Pi/total ratio to 155% of control at 15 min after injection in the KHT tumour, and to 170% of control at 45 min in SCCVII/Ha. Etomidate at 25 mg/kg i.p. reduced mouse core temperature by 7.5°C by 20 min after injection, returning to only 84% of control by 100 min. This agent increased the Pi/total ratio by 260% in the KHT tumour 15 min after injection, without recovery to control values by 100 min. In SCCVII/Ha, a maximum increase in Pi/total of 360% was observed at 15 min after injection, with a return to control levels by 60 min. In addition, etomidate caused convulsions in the mice during the induction phase, and myoclonic jerking within 15 min of anaesthesia.
31P NMR in vivo study of the acute effects of different doses of γ‐radiation on rat brain phosphate metabolism
Authors: Semenova Nataly A. , Yushmanov Victor E. , Konradov Alexander A. 
Published: March 2007

AbstractChanges in relative levels of brain phosphates and intracellular pH at selected time intervals after total γ‐irradiation of a rat at a single dose of 6.5 or 300 Gy were studied by 31P NMR in vivo. Irradiation yielded only minor changes in the spectra. Irradiation at a dose of 6.5 Gy caused a reversible decrease in Pi and an alkaline pH shift of 0.2 units after day 1, with no change in ATP. The signal, which consisted of α‐ATP, α‐ADP, NAD+/NADH and diphosphodiesters, declined after day 6, possibly due to a fall in NAD+/NADH concentration. Irradiation at a dose of 300 Gy led to an increase in ATP from 10 to 13% of total phosphates after day 1. Homeostasis of brain energy metabolism was characterized by the Z‐index (normalized sample correlation coefficients averaged over the correlation matrix for NMR‐measured phosphomonoesters, Pi, pH, phosphocreatine, γ‐ATP+β‐ADP,α‐ATP+α‐ADP+NAD+/NADH + diphosphodiesters and β‐ATP). The Z value rose from −0.18 ± 0.02 to −0.02 ± 0.02 by day 6 or from −0.19 ± 0.02 to −0.07 ± 0.02 by day 1 after irradiation at a dose of 6.5 or 300 Gy, respectively. This may indicate a pathological state of brain energetics as a system and a decrease in its stability.
13C NMR kinetic studies of the rapid stimulation of glucose metabolism by estrogen in immature rat uterus
Authors: Shinkarenko Leonid , Kaye Alvin M. , Degani Hadassa 
Published: March 2007

AbstractGlucose metabolism in control and estrogen stimulated rat uteri was investigated using 13C NMR spectroscopy. By employing an NMR adapted perifusion system, and developing protocols and methods based on the application of [1‐13C]glucose labeling, it was possible to measure, with a temporal resolution of 10 min, the kinetics of glucose consumption, lactate production and 13C incorporation into glutamate, alanine and glycogen. In control immature rat uteri, under aerobic conditions, the rates (±SEM) of [1‐13C]glucose consumption and [3‐13C]lactate production were 24±2 and 7.5±0.5mmol/g wet weight/h. The rates of synthesis of [4‐13C]glutamate, [3‐13C]alanine and 13C labeling of glycogen at C1 of its glucose moieties were significantly lower and were in the range 0.3–0.6 mmol/g wet weight/h. Thus, ca 35% of the labeled glucose was accounted for by the glycolytic and other observed pathways. In vitro stimulation of the uteri by estrogen was found to increase significantly, within 1 h, glucose consumption by 80%, lactate production by 150% and glutamate and glycogen synthesis by 150%, in parallel to a rapid hormonal induction of mRNA for the brain type isozyme of creatine kinase.
Saturation correction in human cardiac 31P MR spectroscopy at 1.5 T
Authors: van Dobbenburgh J. O. , Lekkerkerk C. , van Echteld C. J. A. , de Beer R. 
Published: March 2007

AbstractThis study was conducted to verify the validity of using saturation factors obtained from unlocalized 31P spectra containing both chest wall and heart muscle signals for correcting human heart muscle phosphocreatine/β‐adenosine triphosphate (PCr/β‐ATP) ratios. Saturation factors and T1 relaxation times were determined from 31 P magnetic resonance spectra of human chest wall and heart muscle simultaneously in healthy volunteers using one‐dimensional spectroscopic imaging in combination with a two‐dimensional ISIS sequence by using adiabatic 180° inversion and adiabatic 90° excitation pulses at 1.5 T. Blood corrected saturation factors for PCr/β‐ATP at a TR of 2.4s were significantly different in heart muscle and chest wall muscle, 1.30 ± 0.25 and 1.73 ± 0.31, respectively (p < 0.05). T1 values for PCr and β‐ATP in heart muscle were 4.28 ± 0.72 and 2.99 ± 0.52 and in chest wall muscle 6.82 ± 1.07 and 3.39 ± 0.48, respectively. The T1(PCr)/T1(β‐ATP) ratios in chest wall and heart muscle were not identical. The mean PCr/β‐ATP ratios in heart and chest wall muscle of six healthy volunteers were 1.23 ± 0.17 and 3.71 ± 0.53, respectively.
Investigation of broad resonances in 31P NMR spectra of the human brain in vivo
Authors: McNamara R. , Arias‐Mendoza F. , Brown T. R. 
Published: March 2007

AbstractBroad resonances that lie underneath the familiar small molecule profile of in vivo 31P NMR spectra can make accurate spectral integration of these mobile phosphates difficult. The two major broad components are the phosphate contained in the hydroxyapatite in cranial bone and the phosphodiester moiety in partially mobile membrane phospholipids. They can be removed with post‐acquisition processing but this results in distortion of lineshapes and intensities and interferes with accurate quantitation. We have employed an off‐resonance saturation procedure to eliminate the bone resonance and isolate the signal from the membrane phospholipids by subtraction. Selective saturation of the phospholipid resonance increases the clarity of the sharp peaks downfield from the phosphocreatine peak. Selective saturation 3‐D chemical shift imaging techniques were used to create a localized phospholipid profile of the entire brain simultaneously. Monitoring localized phospholipid concentration may be important in studying demyelinating diseases.
Internal temperature calibration for 1H NMR spectroscopy studies of blood plasma and other biofluids
Authors: Farrant R. Duncan , Lindon John C. , Nicholson Jeremy K. 
Published: March 2007

AbstractA method for temperature calibration of human blood plasma and cerebrospinal fluid (CSF) samples inside a high resolution NMR spectrometer is presented. This calibration is based on the temperature dependence of the chemical shift difference between the water signal and that from the H‐1 proton of endogenous α‐glucose or, in some circumstances, β‐glucose. This dependence can be fitted using a second‐order polynomial equation and functions for both human blood plasma and human CSF are given. Similar graphs could easily be generated for other fluids. The blood plasma calibration appears to be accurate to ±0.9 K in test samples. The use of the blood plasma calibration graph has also been evaluated using the 1H NMR spectra of CSF and shown to overestimate the CSF internal temperature by ca 1.3 K. This approach should have a general applicability to blood plasma and CSF samples from normal and pathological situations or from other species, because there are unlikely to be large changes in ionic strength or pH even in disease states. Knowledge of the exact internal temperature of plasma samples is likely to be of particular importance in the investigation of lipid and lipoprotein interactions because of the significant temperature dependence of lipid and lipoprotein NMR linewidths in such samples.
Non‐invasive measurement of steady‐state vitreous lactate concentration
Authors: Berkowitz Bruce A. , Bansal Navin , Wilson Charles A. 
Published: March 2007

AbstractThe cellular events leading to the proliferation of new preretinal blood vessels into the vitreous are unknown. It has been hypothesized that a metabolic trigger, such as increased lactate concentration, induces ambient growth factors to initiate this neovascularization. However, this hypothesis has not been tested in vivo because non‐invasive methods for measuring vitreous lactate concentration have not been available. In this study, we identified lactate as the dominant resonance in normal rabbit vitreous using a water‐suppressed, localized proton NMR method; negligible spectral contamination from lipid, alanine and threonine was demonstrated. The steady‐state vitreous lactate concentration in vivo was 11.3 ± 4 mM (mean ± SD, n = 7 eyes) which was not statistically different (p = 0.498) to the enzymatically determined lactate content in vitreous from a parallel group of animals [12.1 ± 0.6 mM (n = 6 eyes)]. Non‐invasive measurement of steady‐state vitreous lactate concentration using localized proton NMR represents the necessary first step in understanding the role of lactate in neovascularization.