Biomedical subjects

D Leibfritz

Publications and source records attributed to D Leibfritz.

At least 73 records · Page 4Linked to original sources

PubMed1995

A fast method for in vivo lactate imaging.

A robust method for fast lactate imaging is presented using a combination of a lactate editing sequence and a one-shot imaging experiment. The lactate editing method is based on manipulation of the phase of the lactate CH3 signal via J-modulation. This is applied as a preparation experiment to the U-FLARE imaging sequence. Phantom experiments are presented in which the quality of water and lipid suppression is established. Edited lactate images with a spatial resolution of 3 microL and total measuring time of 15.8 min are shown. These were obtained from a hemispherical ischemia in the gerbil brain. The images are compared with diffusion-weighted water images.

Animals↗

PubMed1995

Changes in organic solutes, volume, energy state, and metabolism associated with osmotic stress in a glial cell line: a multinuclear NMR study.

Diffusion-weighted in vivo 1H-NMR spectroscopy of F98 glioma cells embedded in basement membrane gel threads showed that the initial cell swelling to about 180% of the original volume induced under hypotonic stress was followed by a regulatory volume decrease to nearly 100% of the control volume in Dulbecco's modified Eagle's medium (DMEM) but only to 130% in Krebs-Henseleit buffer (KHB, containing only glucose as a substrate) after 7 h. The initial cell shrinkage to approx. 70% induced by the hypertonic stress was compensated by a regulatory volume increase which after 7 h reached almost 100% of the control value in KHB and 75% in DMEM. 1H-, 13C- and 31P-NMR spectroscopy of perchloric acid extracts showed that these volume regulatory processes were accompanied by pronounced changes in the content of organic osmolytes. Adaptation of intra- to extracellular osmolarity was preferentially mediated by a decrease in the cytosolic taurine level under hypotonic stress and by an intracellular accumulation of amino acids under hypertonic stress. If these solutes were not available in sufficient quantities (as in KHB), the osmolarity of the cytosol was increasingly modified by biosynthesis of products and intermediates of essential metabolic pathways, such as alanine, glutamate and glycerophosphocholine in addition to ethanolamine. The cellular nucleoside triphosphate level measured by in vivo 31P-NMR spectroscopy indicated that the energy state of the cells was more easily sustained under hypotonic than hypertonic conditions.

Animals↗

PubMed1995

Quality assessment in in vivo NMR spectroscopy: I. Introduction, objectives, and activities.

By enabling noninvasive measurements of tissue biochemistry, nuclear magnetic resonance spectroscopy (MRS) provides a unique means of characterizing tissues. Differences in equipment, techniques, and methodology between different laboratories cause major difficulties when comparing results, whether from measurements of tissue metabolism, or from the effects of different therapies. This is of concern in critically evaluating work from different laboratories and centres, causing potential difficulties in reproducing results, limiting the establishment of MRS as a standard method of diagnosis and of characterising disease and response to therapy in the laboratory and clinic. It also poses particular problems in establishing the multicentre clinical trials of MRS that are now required to provide adequate statistical power in confirming the encouraging preliminary clinical observations. These difficulties arise principally from imperfect localization of signal from selected regions of interest in the body, and from the subsequent analyses of the MRS spectra. Improvement is possible by establishing agreed procedures for test measurements and for data analysis, and by using appropriate test objects and test substances to establish the quality of measurements. A concerted research project on characterisation of biological tissues by NMR, principally concerned with MR imaging (MRI), was activated in 1984 by the European Economic Community as part of its third Medical and Health Research Programme, under the auspices of the Biomedical Engineering Concerted Actions' Committee (COMAC-BME). In 1988, this project was prolonged for 5 years, when the programme was expanded to encompass MRS.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗

PubMed1995

Parametric multiecho proton spectroscopic imaging: application to the rat brain in vivo.

A parametric multiecho variant of proton spectroscopic imaging (SI) is presented using a multiecho SI sequence with uniform phase-encoding of all echoes within each echo train. The acquisition of SI data sets at different echo times (TE) increases the amount of information obtained within the same total measuring time as in standard SI measurements. The gain in information can be used: (a) to choose the most appropriate TE for each metabolite signal with respect to T2, spin coupling, or problems caused by peak overlap; (b) to measure the relaxation time T2 of metabolite signals with high spatial resolution; or (c) to improve the signal-to-noise ratio for metabolite signals with long T2 values by adding spectra calculated from consecutive echoes. The method was tested in vivo on healthy rat brain and applied to study metabolic changes in rat brain lesions.

Animals↗

PubMed1995

Evolution of regional changes in apparent diffusion coefficient during focal ischemia of rat brain: the relationship of quantitative diffusion NMR imaging to reduction in cerebral blood flow and metabolic disturbances.

Middle cerebral artery occlusion was performed in rats while the animals were inside the nuclear magnetic resonance (NMR) tomograph. Successful occlusion was confirmed by the collapse of amplitude on an electrocorticogram. The ultrafast NMR imaging technique UFLARE was used to measure the apparent diffusion coefficient (ADC) immediately after the induction of cerebral ischemia. ADC values of normal cortex and caudate-putamen were 726 +/- 22 x 10(-6) mm2/s and 659 +/- 17 x 10(-6) mm2/s, respectively. Within minutes of occlusion, a large territory with reduced ADC became visible in the ipsilateral hemisphere. Over the 2 h observation period, this area grew continuously. Quantitative analysis of the ADC reduction in this region showed a gradual ADC decrease from the periphery to the core, the lowest ADC value amounting to about 60% of control. Two hours after the onset of occlusion, the regional distribution of ATP and tissue pH were determined with bioluminescence and fluorescence techniques, respectively. There was a depletion of ATP in the core of the ischemic territory (32 +/- 20% of the hemisphere) and an area of tissue acidosis (57 +/- 19% of the hemisphere) spreading beyond that of ATP depletion. Regional CBF (rCBF) was measured autoradiographically with the iodo[14C]antipyrine method. CBF gradually decreased from the periphery to the ischemic core, where it declined to values as low as 5 ml 100 g-1. When reductions in CBF and in ADC were matched to the corresponding areas of energy breakdown and of tissue acidosis, the region of energy depletion corresponded to a threshold in rCBF of 18 +/- 14 ml 100 g-1 min-1 and to an ADC reduction to 77 +/- 3% of control. Tissue acidosis corresponded to a flow value below 31 +/- 11 ml 100 g-1 min-1 and to an ADC value below 90 +/- 4% of control. Thus, the quantification of ADC in the ischemic territory allows the distinction between a core region with total breakdown of energy metabolism and a corona with normal energy balance but severe tissue acidosis.

Adenosine Triphosphate↗

PubMed1994

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: in vivo demonstration in the rat brain.

The effect of off-resonance preirradiation on proton spectra acquired from the healthy rat brain at 4.7 T is examined using a PRESS sequence. The creatine/phosphocreatine (Cr/PCr) signal at 3.0 ppm decreases in signal intensity for offset frequencies between +/- 10 kHz. This cannot be explained by RF bleedover, but is attributed to magnetization transfer between two pools of Cr/PCr, one with a long T2 relaxation time giving the observed NMR signal, the other corresponding to a broad resonance line being completely or partially saturated by off-resonance preirradiation. Possible interpretations of these results are discussed.

Animals↗

PubMed1994

Double-echo multislice proton spectroscopic imaging using Hadamard slice encoding.

Simultaneous multislice proton spectroscopic imaging (SI) is presented using a pulse sequence with multifrequency selective RF excitation and Hadamard encoding in the slice direction, and conventional Fourier phase encoding in the in-plane directions. Double-echo data acquisition is used to increase the spectral information of the experiment. Tests on a phantom demonstrate the quality of the slice selection. Results of in vivo measurements of the healthy rat brain show that spectra with a high signal-to-noise ratio can be acquired from four slices within 32 min. The measurements were performed at 4.7 T using a field of view of 32 x 32 mm2, a slice thickness of 3 mm, and a voxel size of 12 microliters. The proposed method is a useful alternative to sequential multislice SI and 3D SI. Furthermore, it is possible to combine sequential and simultaneous multislice SI.

Animals↗

PubMed1994

Detection of apparent restricted diffusion in healthy rat brain at short diffusion times.

The application of bipolar diffusion sensitizing gradient pulses to significantly reduce the diffusion time is described. This approach is combined with the rapid U-FLARE imaging sequence. Three diffusion-sensitized types of experiments are compared and their suitability for detecting restricted diffusion is discussed. Experiments using a modification of the diffusion weighting by varying the diffusion time between 1.6 and 6.0 ms obtained nonmonoexponential signal attenuation curves from both healthy brains and postmortem. This behavior is indicative of restricted diffusion, but as it is detectable only at short diffusion times, in contrast to a restriction due to impermeable barriers, we have termed this "apparent restriction."

Animals↗

PubMed1994

Regulation of intracellular pH in neuronal and glial tumour cells, studied by multinuclear NMR spectroscopy.

The effect of extracellular pH (pHe) on intracellular pH (pHi) and cellular metabolism was examined by multinuclear NMR spectroscopy of cells in vivo and in vitro. A decrease in pHe from 7.4 to 6.4 led to a significant drop in pHi, in both neuronal and glial tumour cells, as detected by in vivo 31P NMR of cells embedded in basement membrane gel threads. A more than 50% decrease in both the phosphocreatine (PCr) level and derivatives of glycolysis (i.e., glycerol 3-phosphate) was observed, concomitantly to the fall in pHi. A 50% decrease in intracellular lactate levels was seen in in vivo 1H NMR spectra under these conditions. Reperfusion with fresh medium (pHe 7.4) resulted in the full recovery of pHi, simultaneously with an increase in both PCr and intracellular lactate back to their control levels. Perchloric acid and lipid extract measurements confirmed the observations made by in vivo 31P and 1H NMR spectroscopy and further showed a decrease both in tricarboxylic acid cycle activity and phospholipid synthesis. The data revealed no significant differences between the neuronal and glial tumour cells investigated. pHi measurements in the presence of inhibitors of the various pH regulatory mechanisms showed that the Na+/H+ exchanger, the carbonic anhydrase and at least one of the bicarbonate-transport systems are involved in pH regulation of both cell types. The results suggest that Na+/H+ exchange is the preferred mechanism by which both neuronal and glial cells regulate their pHi after extracellular acidification.

Animals↗

PubMed1994

Health and infarcted brain tissues studied at short diffusion times: the origins of apparent restriction and the reduction in apparent diffusion coefficient.

The significance of NMR water diffusion measurements performed at short diffusion times (< 10 ms) for brain tissue is examined. An apparent restriction to diffusion for both healthy and cytotoxically edematous tissue is shown: cytotoxic edema lengthens the diffusion time at which this phenomenon is visible. The dramatic reduction in apparent diffusion coefficient (ADC) observed in the core of cytotoxic edema is explained in terms of the enclosure of extracellular water in non-contiguous pockets in conjunction with the shift of water from the extra-to the intracellular space. The model presented provides an explanation for the ADC reduction without recourse to changes in the cell membrane permeability to water, or unrealistic values for the extra- and intracellular diffusion coefficients.

Animals↗

PubMed1994

Incidence of apparent restricted diffusion in three different models of cerebral infarction.

High speed magnetic resonance imaging (MRI) and short diffusion times are used to investigate the appearance of restricted diffusion in three different models of cerebral infarction. The models are: the middle cerebral artery occlusion (MCAO) model in the rat, the carotid occlusion model in the gerbil, and the Rose Bengal microvascular occlusion model in the rat. All three were investigated for 16 b-values equally spaced between 10 and 1510 s/mm2 using two distinct experiments. In the ct (constant time) experiment, the diffusion time was held constant at 11.7 ms while the b-value was varied with the gradient strength. In the cg (constant gradient) experiment, the gradient strength was held constant and the b-value increased by varying the diffusion time from 4.4 to 11.7 ms. A monoexponential decay of the signal intensity with b-value in the ct experiment accompanied by nonmonoexponential (NME) decay in the cg experiment is indicative of restricted diffusion. As this phenomenon is detectable only at short diffusion times, it cannot be due to restriction by impermeable membranes, and we have thus termed this apparent restriction. For the MCAO model and the carotid occlusion model, apparent restriction was found both inside the infarct territory and in some regions outside it. No definite evidence for restriction was found for the Rose Bengal model, which was, however, only studied from 24 h post-insult.

Animals↗

PubMed1993

Fast perfluorocarbon imaging using 19F U-FLARE.

The application of an ultra-fast low angle RARE technique for the 19F imaging of perfluorocarbons (PFCs) used as temporary blood substitutes is described. This sequence is attractive for fast 19F imaging studies that measure the biodistribution of PFCs in vivo, due to its high signal-to-noise ratio. Extensions of this technique for the chemical shift selective measurement of fluorine T1 values are presented. Using the linear dependence between the oxygen partial pressure (pO2) and the T1 relaxation rate of PFC resonances this technique makes possible the fast in vivo measurement of oxygen tension. Using the sequence in a diffusion sensitized form 19F measurements of the diffusion constants of PFCs are also presented. Phantom experiments to test the methods, and in vivo images obtained in rat studies are given and discussed.

Animals↗

PubMed1993

High-resolution 1H NMR spectroscopy of cerebrospinal fluid in spinal diseases.

Twenty-nine patients with disk herniations, 7 patients with intraspinal tumors, 4 patients with multiple sclerosis and one patient with infection by borrelia have been studied by CT, myelography and/or MR. To gain information on the metabolism of central nervous system disease (CNS), and thus, to improve diagnosis the cerebrospinal fluid (CSF) was studied in all cases using high-resolution 1H NMR spectroscopy at 360 MHz. Seventeen metabolites could be identified in CSF in addition to the usual clinical chemical parameters. As compared to a control group discrimination of tumors from inflammation was possible by means of different metabolites and/or metabolite concentration. The CSF in disk herniations differed in the concentration of acetate from the control group. In CSF of tumors, multiple sclerosis and of infection by borrelia distinct differences in the concentrations of putrescine, citrate, valine, alpha-alanine, acetate, creatinine, glucose, beta-hydroxy-butyric acid, glutamine and creatine have been observed both as compared directly and in comparison to the control group. Thus, high-resolution 1H NMR spectroscopy of CSF gives speedy information on metabolism, since a variety of metabolites, usually examined only in different tests, can be studied in one single step. Thus, high-resolution 1H NMR spectroscopy supports imaging, especially MR, as morphological changes in diseases may be differentiated by means of different metabolite profiles. This assumption needs further confirmation on a prospective study with a larger patient population.

Borrelia Infections↗

PubMed1993

Tissue characterization by magnetic resonance spectroscopy and imaging: Results of a concerted research project of the European Economic Community. Introduction, objectives, and activities.

The multi-parameter dependence of magnetic resonance (MR) images allows a unique flexibility of soft tissue contrast and gives access to peculiar sources of in vivo tissue characterization, mainly associated with magnetic relaxation properties. However, MR methodologies have not yet expressed their full potential in terms of tissue characterization for several reasons: a) problems of quality control and quantitation have generally not been addressed by centers using MRI equipment, nor in most of the published literature; and b) data scattering of quantitative measurements obtained from tissues in vitro and in vivo appear to be a major factor in inhibiting or limiting the clinical utility of MRI, for a possible in vivo characterization of pathological tissues. An international project, aimed at evaluating the clinical significance of tissue characterization by MR, was activated in 1984 by the Biomedical Engineering Advisory Committee of the European Communities (EC COMAC-BME) within the 3rd EC Medical and Health Research Programme (MHRP). The scientific achievements of this first project (Magn. Reson. Imaging, 6:171-222; 1988) represented the basis for launching and performing a second Concerted Action, in the frame of the 4th MHRP (1988-1992). Main areas of research of this second project were: a) development of standard methodologies for quantitative measurements of MR parameters and correlation with histo- and physiopathology; b) performance assessment and calibration of MR clinical equipment; c) harmonization of test procedures with other centers and industry; and d) pilot multi-center collections of data.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Dynamic imaging with T2* contrast using U-FLARE.

Dynamic changes in T2* in the rat brain induced by the injection of Gd-DTPA are monitored using the U-FLARE sequence. Sensitivity to T2* is easily introduced into this sequence and may be freely varied. The images obtained display an adequate spatial resolution and contrast, for a temporal resolution of 1 s. Intensity-time curves and parametric images of regional cerebral blood flow (rCBV) are presented for three different blood pCO2 values. The results presented clearly demonstrate that U-FLARE is a viable method for dynamically measuring changes in T2*, and thus has application in imaging of both perfusion and functional activation.

Animals↗

PubMed1993

Comparative conformational analysis and in vitro pharmacological evaluation of three cyclic hexapeptide NK-2 antagonists.

The conformational analysis of three cyclic hexapeptides is presented. Cyclo-(-Gln6-Trp7-Phe8-Gly9-Leu10-D-Met11-) (1) and cyclo-(-Gln6-Trp7-Phe8-Gly9-Leu10-Met11-) (2) are NK-2 antagonists in the hamster trachea assay, whereas cyclo-(-Gln6-Trp7-Phe8-(R)-Gly9-[ANC-2]Leu10-Met11+ ++-) (3), where Gly9[ANC-2]Leu10 represents (2S)-2-((3R)-3-amino-2-oxo-1-pyrrolidinyl)-4-methylpentanoyl, is inactive as agonist and antagonist in this assay. In DMSO, the NMR results cannot be interpreted as being consistent with a single conformation. However, the combined interpretation of results from NMR spectroscopy, restrained molecular dynamics simulations with application of proton-proton distance information from ROESY spectra, and pharmacological results leads to a reduced number of conformational domains for each peptide, which can be compared with each other and may be classified as responsible for their biological activity. Trying to match the conformational domains approximately with regular beta- and gamma-turns, we find a gamma n-turn at the position of the methionine occurring in all peptides. For the active peptides 1 and 2 we arrive at an inverse gamma i-turn at Phe8, and beta I'- or beta II-turns with Gly9 and Leu10 at the corner positions, these beta-turns having a similar topology with respect to the linking peptide unit. Other conformational domains common to only 1 and 2 support their classification as responsible for the biological activity.

Amino Acid Sequence↗

PubMed1993

Multinuclear NMR studies on the energy metabolism of glial and neuronal cells.

In this multinuclear NMR study myo-inositol is identified as a glia-specific marker for in vivo NMR studies. The unusually high inositol concentration may participate in the osmoregulatory system in astrocytes. Primary astrocytes also synthesize and export high amounts of hypotaurine, an intermediate of taurine synthesis. Taurine--another osmolyte--is synthesized from cysteine by astrocytes but not by primary neurons. Taurine as well as hypotaurine is accumulated by neurons from the extracellular medium. 13C NMR labelling results with 2-13C pyruvate indicate a considerable contribution of the anaplerotic pathway in primary neurons from rat. The activity is only half of the activity in primary astrocytes. The ratio of pyruvate carboxylase/malic enzyme activity versus pyruvate dehydrogenase activity reflects the degree of maturation. The 13C isotopomer ratio of glutamate and glutamine is different for pure astrocyte cultures. Therefore, the different isotopomer ratios of glutamate to glutamine obtained from intact brain studies alone do not prove TCA cycle compartimentation in the brain. Finally, the PCr/ATP ratio in primary astrocytes is 3 times higher than in primary neurons. This has to be considered in case of recovery from ischemic insults.

Amino Acids↗

PubMed1993

Response of 3T3 cells on stimulation of adenylate cyclase by forskolin, studied by multinuclear NMR spectroscopy.

Stimulation of 3T3 cells by forskolin (30 microM) led to an increase in cellular cAMP levels, as detected by 31P-NMR, in both PCA extracts and living cells incorporated in basement membrane gel (BMG) threads. At the same time cAMP was exported in large amounts to the extracellular space. The in vivo experiments showed a decrease of more than 50% in both the PCr and ATP levels within 90 min of stimulation with forskolin. Reperfusion with fresh medium without the drug resulted in the full recovery of the phosphorus energy metabolism. A significant increase in phosphocholine (PC) was observed in 1H and 31P spectra of the PCA extracts concomitant to the rise in cAMP level. 13C spectra of PCA extracts prepared after forskolin stimulation in the presence of [1-13C]glucose indicated a serious inhibition of glycolysis, which was followed by a disordering of the phosphorus energy metabolism. Our results show a significant imbalance in the metabolic homeostasis during stimulation of 3T3 cells with forskolin.

3T3 Cells↗