Showing papers in "NMR in Biomedicine in 2003"

1H MR spectroscopy of brain tumours and masses.

Abstract: Accurate diagnosis is essential for optimum management and treatment of patients with brain tumours. Proton magnetic resonance spectroscopy (1H MRS) provides information non-invasively on tumour biochemistry and has been shown to provide important additional information to that obtained by conventional radiology. We review the current status of 1H MRS in classifying brain tumour type and grade, for monitoring response to therapy and progression to higher grade, and as a molecular imaging technique for determining tumour extent for treatment planning. Copyright © 2003 John Wiley & Sons, Ltd.

Localized in vivo 13C NMR spectroscopy of the brain.

Abstract: Localized (13)C NMR spectroscopy provides a new investigative tool for studying cerebral metabolism. The application of (13)C NMR spectroscopy to living intact humans and animals presents the investigator with a number of unique challenges. This review provides in the first part a tutorial insight into the ingredients required for achieving a successful implementation of localized (13)C NMR spectroscopy. The difficulties in establishing (13)C NMR are the need for decoupling of the one-bond (13)C-(1)H heteronuclear J coupling, the large chemical shift range, the low sensitivity and the need for localization of the signals. The methodological consequences of these technical problems are discussed, particularly with respect to (a) RF front-end considerations, (b) localization methods, (c) the low sensitivity, and (d) quantification methods. Lastly, some achievements of in vivo localized (13)C NMR spectroscopy of the brain are reviewed, such as: (a) the measurement of brain glutamine synthesis and the feasibility of quantifying glutamatergic action in the brain; (b) the demonstration of significant anaplerotic fluxes in the brain; (c) the demonstration of a highly regulated malate-aspartate shuttle in brain energy metabolism and isotope flux; (d) quantification of neuronal and glial energy metabolism; and (e) brain glycogen metabolism in hypoglycemia in rats and humans. We conclude that the unique and novel insights provided by (13)C NMR spectroscopy have opened many new research areas that are likely to improve the understanding of brain carbohydrate metabolism in health and disease.

Visualizing metabolic changes in breast-cancer tissue using 1H-NMR spectroscopy and self-organizing maps.

Abstract: In-vitro NMR spectroscopic examinations of tissue extracts can be combined with appropriate pattern-recognition and visualization techniques in order to monitor characteristic metabolic differences between tissue classes. In the present study, such techniques are applied to a set of 88 breast-tissue samples with the intention of identifying typical differences between various tissue classes. The set contains 49 breast-tumor samples of various tumor grades and 39 samples of healthy tissue. The metabolite compositions of the tissue extracts were investigated using a dual extraction technique and high-resolution 1H-NMR spectroscopy. The spectra of the hydrophilic and the lipophilic compounds were assigned to three groups according to different malignancy grades of the respective tissue samples. The group characteristics were analyzed using the k-nearest-neighbor method and self-organizing-map visualizations. The results show an increase of UDP-hexose, phosphocholine and phosphoethanolamine concentrations according to the tumor grade. Higher concentrations of taurine were detected in the malignant samples. Myo-inositol and glucose content were elevated in control samples compared with malignant tissue. Both compounds also characterized different subgroups in the pool of unaffected tissue samples depending upon fat content or fibrosis. Several lipid metabolites showed a characteristic elevation with high malignancy. Copyright © 2003 John Wiley & Sons, Ltd.

In vivo 1H-[13C]-NMR spectroscopy of cerebral metabolism.

Abstract: 13C NMR spectroscopy in combination with the infusion of (13)C-labeled precursors is currently the only technique that is capable of quantitatively studying energy metabolism, neurotransmission and other metabolic pathways non-invasively in vivo. (1)H-[(13)C]-NMR spectroscopy is a high-sensitivity alternative to direct (13)C NMR spectroscopy. The development of improved NMR methods for water suppression, spatial localization, broadband decoupling, shimming and signal quantification, together with the availability of high magnetic field strengths, has made (1)H-[(13)C]-NMR spectroscopy the method of choice for the detection of metabolism at a high spatial and/or temporal resolution. (1)H-[(13)C]-NMR spectroscopy can now be used to discriminate glutamatergic (excitatory) and GABAergic (inhibitory) neuronal activity. The improved sensitivity allows the detection of metabolism in different tissues (e.g. gray and white matter) and potentially even in smaller structures, like cortical layers. Finally, (1)H-[(13)C]-NMR spectroscopy allows the detection of energy metabolism and neurotransmission during functional activation, thereby further strengthening our understanding of the neurochemical basis of brain function.

Absolute eigenvalue diffusion tensor analysis for human brain maturation.

Abstract: The absolute eigenvalues of the diffusion tensor of white matter in sixteen normal subjects in two groups representing the early developmental stage (ages 1–10 years, n = 8) and young adult stage (ages 18–34 years, n = 8) were assessed using a high-field (3.0 T) magnetic resonance (MR) system. All three eigenvalues, including the largest eigenvalue, decreased significantly with brain maturation. The rate of the decline in the two small eigenvalues was, however, much higher than that of the largest eigenvalue, resulting in an actual increase in fractional anisotropy, a commonly measured relative index. The data demonstrate that an increase in anisotropy associated with brain maturation represents a significant decline in the small eigenvalue components, rather than an increase in the largest eigenvalue. The observed pattern of eigenvalue changes is best explained by the simultaneous occurrence of two of several independent phenomena within the axonal microenvironment during the myelination process, namely, (1) decline in unrestricted water content in extra-axonal space, and (2) increase in apparent diffusivity within the axon. Copyright © 2003 John Wiley & Sons, Ltd.

Characterization of oligodendrogliomas using short echo time 1H MR spectroscopic imaging.

Abstract: Oligodendroglial tumors may not be distinguished easily from other brain tumors based on clinical presentation and magnetic resonance imaging (MRI) alone. Identification of these tumors however may have therapeutic consequences. The purpose of this study was to characterize and identify oligodendrogliomas by their metabolic profile as measured by (1)H MR spectroscopic imaging (MRSI). Fifteen patients with oligodendroglial tumors (eight high-grade oligodendrogliomas, seven low-grade oligodendrogliomas) underwent MRI and short echo time (1)H MRSI examinations. Five main metabolites found in brain MR spectra were quantified and expressed as ratios of tumor to contralateral white matter tissue. The level of lipids plus lactate was also assessed in the tumor. For comparison six patients with a low grade astrocytoma were also included in the study. The metabolic profile of oligodendrogliomas showed a decreased level of N-acetylaspartate and increased levels of choline-containing compounds and glutamine plus glutamate compared with white matter. The level of glutamine plus glutamate was significantly higher in low-grade oligodendrogliomas than in low-grade astrocytomas and may serve as a metabolic marker in diagnosis and treatment planning. In high-grade oligodendrogliomas large resonances of lipids plus lactate were observed in contrast to low-grade tumors.

Regulation of glial metabolism studied by 13C‐NMR

Abstract: Glial metabolism and their metabolic trafficking with neurons are essential parts of neuronal function, as they modulate, by this means, neuronal activity. Ex vivo and in vitro (13)C-NMR spectroscopy have been used to monitor neural cellular and tissue metabolism. Special emphasis has been given to the metabolic specialization of astrocytes and its enzymatic regulation. For this purpose primary cell cultures are useful tools to study neuronal-glial metabolic relationships as the extracellular fluid can be investigated and manipulated by various stimuli. In astrocytes, glucose is utilized predominantly anaerobically. Glycolysis is interrelated to the astrocytic TCA cycle via bi-directional signals and metabolic exchange processes between astrocytes and neurons. Besides glucose oxidation, neuronally released glutamate is metabolized through the glial TCA cycle. The flexibility of glutamate metabolism, depending on ammonia and energy homeostasis, and the discovered pyruvate recycling pathway in astrocytes, modulates the glutamine-glutamate cycle. (13)C-NMR studies have extended the concept of the "non-stoichiometric" glutamate-glutamine cycle between neurons and astrocytes. An alanine-lactate shuttle between neurons and astrocytes contributes to nitrogen transfer from neurons to astrocytes, recycles energy substrates for neurons, and in return promotes intercellular glutamine-glutamate cycling. The conversion of alanine to lactate in astrocytes is regulated by intracytosolic pyruvate compartmentation. In essence, the metabolic flexibility and compartmentalized enzymatic specialization of astrocytes buffers the brain tissue against metabolic impairments and excitotoxicity in response to extracellular stimuli, some of them being released by neurons. These in vitro studies using (13)C-NMR spectroscopy provide important knowledge regarding physiological and pathophysiological regulation of neural metabolism to improve our understanding of general brain function.

Clinical experience with 13C MRS in vivo

Abstract: 13C MRS was installed on a clinical scanner at 15 T in order to facilitate integrated MR examinations of human brain disorders Using a simplified protocol, (1-(13)C) glucose and/or (1-(13)C) acetate were administered orally or by intravenous infusion (13)C spectra of diagnostic quality were acquired in more than 100 consecutive studies Novel (13)C neurochemical data contributed to the understanding of Alzheimer's, Canavan's, mitochondrial and hepatic encephalopathy, epilepsy and normal brain development (13)C MRS uncovered hitherto unknown disorders of NAA-synthesis, glutamate neurotransmission, TCA-cycle and glycolysis Despite low inherent signal-to-noise, natural abundance (13)C MRS showed diagnostic promise (13)C MRS is feasible in a clinical setting, at reasonable cost in neonates, children, adults and elderly patients

Diffusion-weighted MR imaging of the liver of hepatitis C patients.

Abstract: Magnetic resonance diffusion-weighted imaging (DWI) of the liver was investigated to determine whether this method could be used to differentiate between the stages of fibrosis and inflammation for hepatitis C viral infection. DWI data were recorded for 18 hepatitis C patients and 10 control subjects using a modified pulse sequence allowing a 52 ms echo time delay. Acquisitions were performed with breath holding using five different b gradient factor values ranging between 50 and 250 s/mm(2) and in the three axes. Apparent diffusion coefficient (ADC) values were measured from a 5.7 cm(2) area in the central region of the liver. The inflammation and fibrosis grades were evaluated histologically on a biopsy sample. The mean ADC values were 2.30 +/- 1.28 x 10(-3) and 1.79 +/- 0.25 x 10(-3) mm(2)/s for hepatitis C patients and control subjects, respectively. Using our technique, no correlation could be found between the ADC values and the inflammation or fibrosis scores, indicating that tissue changes produced by hepatitis C do not appear to be quantifiable by DWI.

Diffusion tensor imaging in fixed brain tissue at 7.0 T

Abstract: The purpose of this work is to assess the feasibility of performing quantitative in vitro brain tissue diffusion tensor imaging (DTI) measurements and to examine their comparability to in vivo measurements DTI of fixed tissue at high field strength is potentially a very valuable investigative tool as very high spatial resolution can be achieved DTI was applied to human and mouse brain fixed tissue samples as well as in vivo measurements of the mouse brain T1 and T2 relaxography of the fixed tissue samples was also performed to provide further characterization of the tissue All experiments were performed at 7 T The fractional anisotropy (FA) of the human fixed brain tissue samples is found to be higher in the corpus callosum than in the occipital white matter region, consistent with in vivo measurements reported in the literature Our FA measurements of the corpus callosum of a mouse brain are also found to be the same both in vitro and in vivo This preliminary work supports the use of DTI in both fixed human and fixed animal brain tissue as a valid investigative tool With the increased availability of brain banks in different brain disorders, DTI in fixed tissue may prove to be a very useful method for the study of white matter abnormalities Copyright © 2003 John Wiley & Sons, Ltd

Evaluation of two-dimensional L-COSY and JPRESS using a 3 T MRI scanner: from phantoms to human brain in vivo.

Abstract: Localized versions of two-dimensional (2D) magnetic resonance spectroscopic (MRS) sequences, namely JPRESS and L-COSY, have been implemented on a whole-body 3T MRI/MRS scanner. Volume selection was achieved using three slice-selective radio-frequency (RF) pulses: 90 degrees-180 degrees-180 degrees in JPRESS and 90 degrees-180 degrees-90 degrees in L-COSY with a CHESS sequence prior to voxel localization for global water suppression. The last 180 degrees RF pulse was used for resolving the J-coupled cross peaks in JPRESS, whereas the last 90 degrees RF pulse was used for coherence transfer between J-coupled metabolites in L-COSY. A head MRI coil for 'transmission' and a 4 inch receive surface coil for 'reception' or a head coil transmit/receive were used. A total of 16 healthy volunteers were investigated using these 2D MRS sequences. Voxel sizes of 18 and 27 ml were localized in the occipito-parietal gray and white matter regions and the total duration for each 2D signal acquisition was typically 35 min. Compared with 2D L-COSY, reduced spectral width along the second spectral dimension and shorter 2D spectral acquisition were the major advantages of 2D JPRESS. In contrast, increased spectral width along the new spectral dimension in L-COSY resulted in an improved spectral dispersion enabling the detection of several brain metabolites at low concentrations that have not been resolved using the conventional one-dimensional (1D) MRS techniques. Due to increased sampling rate, severe loss of metabolite signals due to T2 during t1 was a major drawback of 2D JPRESS in vivo.

Animal anaesthesia for in vivo magnetic resonance

Abstract: Almost all animal patients, including research subjects, presented for MRI/MRS studies are anesthetized. As MR moves rapidly beyond simple anatomic studies, becoming a powerful tool for defining physiologic processes, it is imperative that investigators become familiar with the physiologic effects of the anaesthetic drugs. This decreases confounding variables, making data interpretation more accurate and more applicable to future uses. This article is intended to be a basic resource for investigators wishing to increase their understanding of the anesthetic drugs. The following is a general discussion describing the mechanism of action and physiologic effects of the more common anaesthetic drugs used in laboratory animals. A dosing table of common anaesthetics and analgesics used in mice and rats is included because these two species comprise a great majority of MRI/MRS research subjects.

Correlation between the occurrence of 1H-MRS lipid signal, necrosis and lipid droplets during C6 rat glioma development.

Abstract: The aim of this study was to investigate the possible correlation between the 1H MRS mobile lipid signal, necrosis and lipid droplets in C6 rat glioma. First, the occurrence of necrosis and lipid droplets was determined during tumor development, by a histological analysis performed on 34 rats. Neither necrosis nor lipid droplets were observed before 18 days post-implantation. At later stages of development, both necrosis and lipid droplets were apparent, the lipid droplets being mainly located within the necrotic areas. Using a second group of eight rats, a temporal correlation was evidenced between mobile lipid signal detected by in vivo single-voxel one- (136 ms echo time) and two-dimensional J-resolved 1H MR spectroscopy, and the presence of necrosis and lipid droplets on the histological sections obtained from the brains of the same rats. Finally, spatial distribution of the mobile lipid signal was analyzed by chemical-shift imaging performed on a third group of eight animals, at the end of the tumor growth. The spectroscopic image corresponding to the resonance of mobile lipids had its maximum intensity in the center of the tumor where necrotic regions were observed on the histological sections. These necrotic areas contained large amounts of lipid droplets. All these results suggest that mobile lipids detected in vivo by 1H MRS (136 ms echo time) in C6 rat brain glioma arise mainly from lipid droplets located in necrosis.

Neuronal glial interaction in different neurological diseases studied by ex vivo 13C NMR spectroscopy.

Abstract: Nuclear magnetic resonance spectroscopy (NMRS) has been used extensively for several decades to elucidate metabolic pathways in biological systems and has led to new insights into cerebral metabolism. Many of these insights have been gained by NMRS using in vitro models, such as tissue extracts, cell cultures or brain slices. Extracts of cells or tissue provide an excellent basis for metabolic studies and facilitate the interpretation of in vivo spectra. 13C NMRS is at present mostly used for in vitro or animal studies. Conclusions from the epilepsy models presented in this review are that turnover of metabolites is time-dependant in kainate-injected rats with limbic seizures. Early and only temporarily enhanced astrocytic activity is followed by altered metabolism in neurons with an increased turnover of important amino acids such as GABA and glutamate. However, pentylenetetrazole (PTZ) kindling affects astrocytes in younger and glutamatergic neurons in older animals. In the presence of PTZ, phenobarbital decreases labeling of most metabolites in all cell types, except GABAergic neurons, from both labeled precursors in the younger animals. However, in older animals only GABAergic neurons are affected by phenobarbital, as indicated by an increase in GABA labeling. In kaolin-induced hydrocephalus it was shown that astrocyte metabolism is disturbed in the early phase, particularly in the cerebrum. These alterations continue into the chronic period. Only then do the first signs of neuronal metabolic impairment appear, which might explain why dementia is a prominent clinical feature in patients with chronic hydrocephalus. Copyright © 2003 John Wiley & Sons, Ltd.

Toward dynamic isotopomer analysis in the rat brain in vivo: Automatic quantitation of 13C NMR spectra using LCModel

Abstract: The LCModel method was adapted to analyze localized in vivo (13)C NMR spectra obtained from the rat brain in vivo at 9.4 T. Prior knowledge of chemical-shifts, J-coupling constants and J-evolution was included in the analysis. Up to 50 different isotopomer signals corresponding to 10 metabolites were quantified simultaneously in 400 microl volumes in the rat brain in vivo during infusion of [1,6-(13)C(2)]glucose. The analysis remained accurate even at low signal-to-noise ratio of the order of 3:1. The relative distribution of isotopomers in glutamate, glutamine and aspartate determined in vivo in 22 min was in excellent agreement with that measured in brain extracts. Quantitation of time series of (13)C spectra yielded time courses of total (13)C label incorporation into up to 16 carbon positions, as well as time courses of individual isotopomer signals, with a temporal resolution as low as 5 min (dynamic isotopomer analysis). The possibility of measuring in vivo a wealth of information that was hitherto accessible only in extracts is likely to expand the scope of metabolic studies in the intact brain.

Three-dimensional MRI of cerebral projections in rat brain in vivo after intracortical injection of MnCl2.

Abstract: In this study we investigated the potential of in vivo MRI detection of axonal Mn2+ transport for tracing neuronal projections originating in the sensorimotor cortex in healthy and lesioned rat brains. Special attention was given to the potential of visualizing neuronal sprouting of central nervous system across the midline. After injecting unchelated MnCl2 into the forelimb area of sensorimotor cortex of 18 healthy and 10 lesioned rats corticofugal projections could be traced through the internal capsule to the cerebral peduncle and the pyramidal decussation. Although the neuronal tract was visible as early as 6 h after MnCl2 injection, best contrast was achieved after 24–48 h. Beside the cortico-spinal tract, the cortico-thalamic fibres were also visualized by anterograde Mn2+ transport. Cortico-striatal fibres were partially masked by the very high signal near the MnCl2 injection site but could be discerned as well. Slight, diffuse signal enhancement of cortical tissue contralateral to the MnCl2 injection site in healthy rat brains suggests interhemispheric connections or passive diffusion of Mn2+. However, enhanced fibre tract contrast connecting both hemispheres was visible 16 weeks after onset of focal photothrombotic cortical injury. In conclusion our study has shown that we were able to visualize reproducibly the main descending corticofugal projections and interhemispheric connections by non-invasive MRI after localized injection of MnCl2. The appearence of interhemispheric Mn2+-enhanced fibres after photothrombotic focal injury indicates that the method may bear potential to follow non-invasively gross plastic changes of connectivity in the brain after injury. Copyright © 2001 John Wiley & Sons, Ltd.

Reflections on the application of 13C-MRS to research on brain metabolism.

Abstract: The power of 13C-MRS lies in its unique chemical specificity, enabling detection and quantification of metabolic intermediates which would not be so readily monitored using conventional radiochemical techniques. Examples from animal studies, by examination of tissue extracts from the whole brain, brain slices and cultured cells, include observation of intermediates such as citrate and triose phosphates which have yielded novel information on neuronal/glial relationships. The use of 13C-labelled acetate as a specific precursor for glial metabolism provided evidence in support of the view that some of the GABA produced in the brain is derived from glial glutamine. Such studies have also provided direct evidence on the contribution of anaplerotic pathways to intermediary metabolism. Analogous studies are now being performed on the human brain, where 13C-acetate is used to quantitate the overall contribution of glial cells to intermediary metabolism, and use of 13C-glucose enables direct calculation of rates of flux through the TCA (FTCA) and of the glutamate–glutamine cycle (FCYC), leading to the conclusion that the rate of glial recycling of glutamate accounts for some 50% of FTCA. The rate of 0.74 μmol min−1 g−1 for FTCA is compatible with PET rates of CMRglc of 0.3–0.4 μmol min−1 g−1 (since each glucose molecule yields two molecules of pyruvate entering the TCA). Our brain activation studies showed a 60% increase in FTCA, which is very similar to the increases in CBF and in CMRglc observed in PET activation studies. Copyright © 2003 John Wiley & Sons, Ltd.

Manganese ions as intracellular contrast agents: proton relaxation and calcium interactions in rat myocardium.

Abstract: Manganese as intracellular contrast agents: proton relaxation and calcium interactions in rat myocardium

Tissue-specific differences in 2-fluoro-2-deoxyglucose metabolism beyond FDG-6-P: a 19F NMR spectroscopy study in the rat.

Abstract: 2-Fluoro-[(18)F]-2-deoxy-glucose (FDG) is a positron-emitting analogue of glucose used clinically in positron emission tomography (PET) to assess glucose utilization in diseased and healthy tissue. Originally developed to measure local cerebral glucose utilization rates, it has now found applications in tumour diagnosis and in the study of myocardial glucose uptake. Once taken up into the cell, FDG is phosphorylated to FDG-6-phosphate (FDG-6-P) by hexokinase and was originally believed to be trapped as a terminal metabolite. This 'metabolic trapping' of FDG-6-P forms the basis of the analysis of PET data. In this study, we have used (19)F NMR spectroscopy to investigate FDG metabolism following the injection of a bolus of the glucose tracer into the rat (n=6). Ninety minutes after the (19)FDG injection, the brain, heart, liver and kidneys were removed and the (19)FDG metabolites in each were extracted and quantified. We report that significant metabolism of FDG occurs beyond FDG-6-P in all organs examined and that the extent of this metabolism varies from tissue to tissue (degree of metabolism beyond FDG-6-P, expressed as percentage of total organ FDG content, was brain 45 +/- 3%; heart 29 +/- 2%; liver 22+/-3% and kidney 17 +/- 3%, mean +/- SEM n=6). Furthermore, we demonstrate that the relative accumulation of each metabolite was tissue-dependent and reflected the metabolic and regulatory characteristics of each organ. Such inter-tissue differences may have implications for the mathematical modelling of glucose uptake and phosphorylation using FDG as a glucose tracer.

In vivo characterization of fatty acids in human adipose tissue using natural abundance 1H decoupled 13C MRS at 1.5 T: clinical applications to dietary therapy.

Abstract: Natural abundance proton-decoupled 13C magnetic resonance spectroscopy was used to establish the in vivo lipid composition of normal adipose tissue and the corresponding effects of altered lipid diets. Experiments were performed on a standard 1.5 T clinical MR scanner using a double-tuned 1H-13C coil. Peaks from double-bonded and methylene carbons were analyzed. Normal lipid composition was established in 20 control subjects. For comparison, five subjects on altered lipid diets were studied. Four subjects were on a fish oil supplement diet or predominantly seafood diet (polyunsaturated fatty acids), and one subject was on a Lorenzo's oil diet (monounsaturated fatty acids). Well-resolved 13C spectra were obtained from the calf adipose tissue with a total acquisition time of 10 min. Model oil solutions were used to identify specific 13C resonances. Subjects on lipid diets showed significantly elevated levels of monounsaturated and polyunsaturated fatty acids for Lorenzo's and fish oil diets, respectively. We conclude that 13C MR spectroscopy can readily detect changes in lipid composition due to medium- and long-term therapeutic lipid diets. Since the examination is rapid, robust and noninvasive, opportunities arise for large clinical trials of preventive or therapeutic diets to be performed with 13C MRS on a clinical MR scanner. Copyright © 2003 John Wiley & Sons, Ltd.

Proton T1 relaxation times of cerebral metabolites differ within and between regions of normal human brain.

Abstract: Saturation recovery spectra (STEAM) were acquired at 1.5 T with 7 TRs ranging from 530 to 5000 ms and a constant TE of 30 ms in voxels (7.2 ml) located in occipital grey, parietal white and frontal white matter (10 subjects each location). Spectra were also acquired at 7, 21 and 37 degrees C from separate 100 mm solutions of inositol (Ins), choline-containing compounds (Cho), N-acetyl-aspartate (NAA) and creatine. Simulations of T(1) fits with 2, 3 and 7 TRs demonstrated that at typical SNR there is potential for both inaccurate and biased results. In vivo, different metabolites had significantly different T(1)s within the same brain volume. The same order from shortest to longest T(1) (Ins, Cho, NAA, creatine) was found for all three brain regions. The order (Ins, NAA, creatine, Cho) was found in the metabolite solutions and was consistent with a simple model in which T(1) is inversely proportional to molecular weight. For all individual metabolites, T(1) increased from occipital grey to parietal white to frontal white matter. This study demonstrates that, in spectra acquired with TR near 1 s, T(1) weightings are substantially different for metabolites within a single tissue and also for the same metabolites in different tissues.

Role of glial metabolism in diabetic encephalopathy as detected by high resolution 13C NMR

Abstract: The roles of glial energetics and of the glutamine cycle in diabetic encephalopathy have been investigated ex vivo by (13)C NMR in extracts of adult rat brain. Streptozotocin-induced diabetic or euglycemic animals received intravenous infusions of (1-(13)C) glucose in the absence and presence of trifluoroacetic acid or methionine sulfoximine, two selective inhibitors of the glial tricarboxylic acid cycle or of glutamine synthase, respectively. (1-(13)C) glucose infusions resulted in smaller (13)C incorporation in all carbons of cerebral glutamate, glutamine and GABA in the diabetic animals. Co-infusion of trifluoroacetic acid with (1-(13)C) glucose further reduced the (13)C enrichments in cerebral glutamate and glutamine, the decrease being larger in the diabetic animals than in the corresponding euglycemic controls. Methionine sulfoximine decreased to undetectable levels the fractional (13)C enrichment in the carbons of cerebral glutamine in both groups and had no significant effect on (13)C incorporation in glutamate and GABA, suggesting that glutamine is not the main precursor of glutamate and GABA. Additional animals were infused with (1,2-(13)C(2)) acetate, a major substrate of glial metabolism. In this case, (1,2-(13)C(2)) acetate infusions resulted in increased (13)C incorporation in all carbons of glutamate, glutamine and GABA in the diabetic animals. Together, these results reveal that diabetic encephalopathy has an important effect in astroglial metabolism, decreasing glucose transport and metabolism and increasing the relative contribution of glial oxidative metabolism to the support of glutamatergic and GABAergic neurotransmissions.

MRCP in the diagnosis of iatrogenic bile duct injury.

Abstract: Postoperative biliary tract lesions are becoming increasingly common. The diagnosis is made by direct cholangiography via endoscopic retrograde cholangiopancreatography (ERCP) or percutaneous transhepatic cholangiography (PTC). The present comparative study evaluates the diagnostic efficacy of magnetic resonance cholangiopancreatography (MRCP) in application to iatrogenic bile duct injury. A prospective blind study was performed, contrasting MRCP and ERCP in 10 patients with suspected postoperative biliary tract lesions. MRCP was performed less than 72 h before ERCP. Final diagnosis was made on the basis of findings at surgery and ERCP. The presence of biliary dilatation, excision injury, stricture, fluid collection and free fluid was analyzed. The mean patient age was 66.5 years. There were three males and seven females. The type of postoperative lesion (Bergman classification) are five patients type C, three type D, one type B and one type A. Diagnostic failure was recorded in two cases with ERCP, while in five patients it was unable to define a therapeutic approach. In contrast, MRCP correctly diagnosed all patients. MRCP is effective in diagnosing postoperative biliary tract lesions, and can help decide the best therapeutic approach.

Involvement of brain lactate in neuronal metabolism.

Abstract: The involvement of brain lactate in neuronal metabolism was analyzed by ex vivo NMR spectroscopy with rats under the effects of pentobarbital, alphachloralose or morphine, which were infused with a solution of either [1-(13)C]glucose+lactate or glucose+[3-(13)C]lactate for 20 min. Electroencephalogram recordings indicated different brain electrical activity levels under the three drugs with a clear distinction between pentobarbital, on the one hand, and alphachloralose and morphine on the other. Labeling of metabolites in brain perchloric acid extracts and of blood glucose and lactate was determined by (13)C- and/or (1)H-observed/(13)C-edited-NMR spectroscopy. The following were found: (i) the ratio between glutamate C3 and C4 (13)C-enrichments increased from pentobarbital to alphachloralose and morphine whatever the labeled precursor, indicating a link between metabolic and electrical activity; (ii) under glucose+[3-(13)C]lactate infusion, alanine C3 and acetyl-CoA C2 enrichments were higher than that of lactate C3, revealing the occurrence of an isotopic dilution of the brain exogenous lactate (arising from blood) by lactate from brain (endogenous lactate); the latter was synthesized from glycolysis in a compartment other than the neurons; (iii) the contributions of labeled glucose and lactate to acetyl-CoA C2 enrichment indicated that the involvement of blood glucose relative to that of blood lactate to brain metabolism was correlated with brain activity. It can therefore be concluded that the brain electrical activity-dependent increase in the contribution of blood glucose relative to that of blood lactate to brain metabolism occurred partly via the increase in the metabolism of lactate generated from astrocytic glycolysis. This conclusion supports the hypothesis of an astrocyte-neuron lactate shuttle component in the coupling mechanism between cerebral activity and energy metabolism.

Integration of [U‐13C]glucose and 2H2O for quantification of hepatic glucose production and gluconeogenesis

Abstract: Glucose metabolism in five healthy subjects fasted for 16 h was measured with a combination of [U-13C]glucose and 2H2O tracers. Phenylbutyric acid was also provided to sample hepatic glutamine for the presence of 13C-isotopomers derived from the incorporation of [U-13C]glucose products into the hepatic Krebs cycle. Glucose production (GP) was quantified by 13C NMR analysis of the monoacetone derivative of plasma glucose following a primed infusion of [U-13C]glucose and provided reasonable estimates (1.90 +/- 0.19 mg/kg/min with a range of 1.60-2.15 mg/kg/min). The same derivative yielded measurements of plasma glucose 2H-enrichment from 2H2O by 2H NMR from which the contribution of glycogenolytic and gluconeogenic fluxes to GP was obtained (0.87 +/- 0.14 and 1.03 +/- 0.10 mg/kg/min, respectively). Hepatic glutamine 13C-isotopomers representing multiply-enriched oxaloacetate and [U-13C]acetyl-CoA were identified as multiplets in the 13C NMR signals of the glutamine moiety of urinary phenylacetylglutamine, demonstrating entry of the [U-13C]glucose tracer into both oxidative and anaplerotic pathways of the hepatic Krebs cycle. These isotopomers contributed 0.1-0.2% excess enrichment to carbons 2 and 3 and approximately 0.05% to carbon 4 of glutamine.

Prior knowledge for time domain quantification of in vivo brain or liver 31P MR spectra.

Abstract: Prior knowledge is required when quantifying in vivo31P magnetic resonance spectra from the brain or liver. The prior knowledge system we have used models both the phosphomonoester and phosphodiester resonances as two peaks of equal linewidth and fixed relative chemical shift. The analysis of the data is carried out in the time domain, which allows the broad component of the spectra to be modelled. This prior knowledge method has been tested for analysis of in vivo31P MR spectra from the liver and brain and gives results consistent with other methods that are also used to analyse the spectra, but with reduced variability. This technique may be utilized for studies requiring serial MR spectroscopy examinations, before and after patient treatment. Copyright © 2003 John Wiley & Sons, Ltd.

Detecting early response to cyclophosphamide treatment of RIF-1 tumors using selective multiple quantum spectroscopy (SelMQC) and dynamic contrast enhanced imaging.

Abstract: The purpose of this study was to develop a reliable, noninvasive method for early detection of tumor response to therapy that would facilitate optimization of treatment regimens to the needs of the individual patient. In the present study, the effects of cyclophosphamide (Cp, a widely used alkylating agent) were monitored in a murine radiation induced fibrosarcoma (RIF-1) using in vivo (1)H NMR spectroscopy and imaging to evaluate the potential of these techniques towards early detection of treatment response. Steady-state lactate levels and Gd-DTPA uptake kinetics were measured using selective multiple quantum coherence (Sel-MQC) transfer spectroscopy and dynamic contrast enhanced imaging, respectively in RIF-1 tumors before, 24 and 72 h after 300 mg/kg of Cp administration. High-resolution (1)H NMR spectra of perchloric acid extracts of the tumor were correlated with lactate and glucose concentrations determined enzymatically. In vivo NMR experiments showed a decrease in steady-state lactate to water ratios (5.4 +/- 1.6 to 0.6 +/- 0.5, p < 0.05) and an increase in Gd-DTPA uptake kinetics following treatment response. The data indicate that decreases in lactate result from decreased glycolytic metabolism and an increase in tumor perfusion/permeability. Perchloric acid extracts confirmed the lower lactate levels seen in vivo in treated tumors and also indicated a higher glycerophosphocholine/phosphocholine (GPC/PC) integrated intensity ratio (1.39 +/- 0.09 vs 0.97 +/- 0.04, p < 0.01), indicative of increased membrane degradation following Cp treatment. Steady-state lactate levels provide metabolic information that correlates with changes in tumor physiology measured by Gd-DTPA uptake kinetics with high spatial and temporal resolution. Both of these parameters may be useful for monitoring early tumor response to therapy.

In-vivo high resolution three-dimensional MRI studies of rat joints at 7 T.

Abstract: It is important to obtain high resolution images of joints for the study of disease, especially in rodent experimental models. We optimized 1H magnetic resonance imaging three-dimensional sequences at 7 T, with lipid signal suppression, and T1 and T2 measurements for in-vivo experiments on rat joints, in order to assess the effectiveness of high-field MRI. The method was validated by applying it to the early diagnosis of arthritis. We studied the progress of rheumatoid arthritis in an arthritic rat model. We observed the rats' knees for 21 days after inducing arthritis. The images acquired over one hour had a high resolution of 1.75 × 10−3 mm3, (105 × 105 × 145 μm3) which allowed us to spot the early stages of joint degeneration, such as bone erosion, and to observe an apparent ‘MRI’ loss of cartilage thickness, attributed to dehydration of the cartilage tissue. The MR images obtained during the early stages of rheumatoid arthritis enabled us to study joint changes accurately before any histological signs of attack were visible. Copyright © 2003 John Wiley & Sons, Ltd.

A new dimension of 1H-NMR spectroscopy in assessment of liver graft dysfunction.

Abstract: High-resolution 1H-NMR spectroscopy of serum and urine samples of an 11-year-old male living related orthotopic liver transplant recipient is reported. Serum glutamine increased to abnormal levels along with simultaneous abnormal excretion of urinary glutamine post-transplantation. High levels of glutamine in both blood and urine and concomitant reduced urea levels in urine were found to be evidence of impairment in urea cycle and compatible with persistently abnormal graft function. Thus glutamine levels in serum and urine, and urea in the urine as observed by 1H-NMR spectroscopy highlight their important roles in monitoring liver graft function; increased glutamine levels lead to brain damage, if untreated. Copyright © 2003 John Wiley & Sons, Ltd.

Two-dimensional NMR spectroscopy of urinary glycosaminoglycans from patients with different mucopolysaccharidoses.

Abstract: Patients with different types of mucopolysaccharidoses (MPS) lack specific lysosomal enzymes, which leads to tissue accumulation and urinary excretion of glycosaminoglycans (GAGs). Since little is known about the molecular composition of the excreted GAG fragments, we used two-dimensional [1H,13C]-correlation nuclear magnetic resonance (NMR) spectroscopy for a detailed analysis of the urinary GAGs of patients with MPS types I, II, IIIA, IVA and VI. The method revealed that the molecular structures of the excreted GAGs, i.e. heparan sulfate (HS), dermatan sulfate (DS), chondroitin sulfate (CS), and keratan sulfate (KS) are clearly distinct for the different MPS types. The chain terminal residues that are the normal substrates for the defective enzymes constitute characteristic sets of signals for each MPS type. The GAG chains show variations in carbohydrate composition and sulfation patterns that can be related to the different MPS types and clinical features. For example, two patients with MPS IIIA (M. Sanfilippo) with signs of CNS degeneration but only mild somatic features excrete a highly sulfated variant of HS, resembling HS in porcine brain, whereas a patient with MPS I (M. Scheie) and two patients with MPS II (M. Hunter), who present primarily with coarse facial features, joint contractures and skeletal deformities excrete a different type of HS with lower sulfation. In another case study, a patient with MPS IVA (M. Morquio), who presented mainly with skeletal dysplasia, excreted not only excessive amounts of KS but also a highly sulfated CS variant, resembling CS in articular cartilage. The high-resolution NMR analysis of urinary GAGs presented here for the first time provides a solid basis for future studies with a larger number of patients to further explore pathogenesis and course of the MPS diseases.