bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of computer simulations for quantitation of 31P ISIS MRS results
Authors: Matson Gerald B. , Meyerhoff Dieter J. , Lawry Theodore J. , Lara Rosemarie S. , Duijn Jeff , Deicken Raymond F. , Weiner Michael W.
Published: March 2007

The difficulties in quantitation of in vivo 31P spectra are exacerbated by the fact that, in general, coils with inhomogeneous B1 fields are used with in vivo samples. A general method for quantitation of in vivo 31P MRS results obtained with the ISIS localization method was developed using computer simulations. The simulation calculates the preparation of the sample magnetization throughout the sample by the ISIS pulse sequence, as well as the sensitivity of signal reception. The calculation accounts for both the B1 field and the B0 gradients applied to the sample. The sensitivity of the experiment is expressed by integration of the simulated signal over the sample, assuming a homogeneous sample. The primary advantage of this approach is that a separate localization experiment on a phantom of known concentration is not required each time parameters of the localization experiment, such as dimensions or location of the localized volume, are altered. In addition, the simulations indicate the degree of contamination (signal from outside of the localized volume) that occurs, and provide a means of comparing different executions of the ISIS experiment. Experiments were performed on phantoms to verify the simulations, and experimental results on human brain and liver are reproduced to show that this approach provides reasonable estimates of metabolite levels in terms of molar concentrations.
Cerebral metabolism of [1,2‐13C2]glucose and [U‐13C4]3‐hydroxybutyrate in rat brain as detected by 13C NMR spectroscopy
Authors: Künnecke Basil , Cerdan Sebastian , Seelig Joachim
Published: March 2007

The metabolism of [1,2‐13C2]glucose and [U‐13C4]3‐hydroxybutyrate was studied in rat brain with in vivo and in vitro 13C NMR spectroscopy, taking advantage, in particular, of homonuclear 13C‐13C spin coupling patterns. After infusion of [1,2‐13C2]glucose or [U‐13C4]3‐hydroxybutyrate into rats, the uptake of the substrates in brain and their metabolism to [1‐13C]bicarbonate could be detected with in vivo 13C NMR spectroscopy. At the end of the infusion experiment, methanol/HCI/HCIO4 extracts of the brain tissue were further analysed by high resolution 13C NMR spectroscopy. The 13C spin coupling patterns revealed entirely different isotopomer distributions for the closely related cerebral metabolites glutamate, glutamine and 4‐aminobutyric acid. A quantitative analysis of the 13C spectra demonstrated (i) the existence of two kinetically distinct pools of glutamate, (ii) a pronounced CO2 fixation via pyruvate carboxylase in the glial cells accounting for as much as 38% of the oxaloacetate synthesis in the glial tricarboxylic acid cycle, (iii) a cerebral pyruvate recycling system contributing maximally 17% of the pyruvate metabolism through the pyruvate dehydrogenase in neurons, and (iv) a predominant production of 4‐aminobutyric acid from glutamate synthesized in the neurons. In addition, the labelling pattern of N‐acetyl aspartate upon infusion of labelled glucose or 3‐hydroxybutyrate provided insight into the synthesis of this compound in mammalian brain. While the acetyl moiety originates from the metabolic equivalent of the C‐1–C‐2 part of cerebral glutamate, the aspartyl moiety is not in direct contact with the intermediates of glycolysis or of the tricarboxylic acid cycles.
Extracellular volume and transsarcolemmal proton movement during ischemia and reperfusion: A 31P NMR spectroscopic study of the isovolumic rat heart
Authors: Clarke Kieran , Stewart Laura C. , Neubauer Stefan , Balschi James A. , Smith Thomas W. , Ingwall Joanne S. , Nédélec Jean‐François , Humphrey Stuart M. , Kléber André G. , Springer Charles S.
Published: March 2007

We have measured, directly and simultaneously, changes in extracellular volume and intra‐ and extracellular pH during ischemia in the isolated rat heart using 31P NMR spectroscopy. Hearts were perfused with buffer containing 15 mM sodium phenylphosphonate at pH7.4. Wash in and wash out experiments showed that phenylphosphonate entered only the extracellular (interstitial, vascular and chamber) space of the heart and had no adverse effects on myocardial energetics, contractile function or coronary flow rate. Hearts were subjected to 28 min of total, global ischemia, during which the phenylphosphonate resonance area in the 31P NMR spectra decreased by 83%, indicating that extracellular fluid had moved rapidly from the heart to the bath surrounding the heart, partly as a result of vascular collapse. A separate, morphological study confirmed that 95% of the vasculature had collapsed by 28 min ischemia. Intra‐ and extracellular pH were determined from the chemical shifts of the Pi and the phenylphosphonate resonances, respectively. In the pre‐ischemic rat heart, intracellular pH was 7.15±0.03 and extracellular pH was 7.39±0.03. By 4 min of ischemia, intra‐ and extracellular pH were the same and decreased concomitantly throughout the remainder of ischemia to final values of 6.09±0.19 and 6.16±0.23, respectively. On reperfusion, the extracellular volume and pH returned to pre‐ischemic levels within 1 min, but restoration of intracellular pH took >2.5 min. Thus, a large volume of extracellular fluid moves out of the rat heart to the surrounding bath and the intra‐ and extracellular pH become the same during total, global ischemia.
Quantitative analysis by 31P magnetic resonance spectroscopy of abnormal mitochondrial oxidation in skeletal muscle during recovery from exercise
Authors: Kemp G. J. , Taylor D. J. , Thompson C. H. , Hands L. J. , Rajagopalan B. , Styles P. , Radda G. K.
Published: March 2007

We use the hyperbolic relationship between cytosolic [ADP] and the rate of phosphocreatine (PCr) resynthesis after exercise to estimate the apparent maximum rate of oxidative ATP synthesis (QMAX). We examine data from some human diseases in which mitochondrial oxidation may be impaired (due to reduced mitochondrial numbers, intrinsic mitochondrial defect or impaired vascular supply). Muscle responds to impaired oxidation by stimulating anaerobic ATP synthesis and/or by increasing [ADP], the stimulus to the mitochondrion. However, these responses interact: [ADP] depends on pH and [PCr], and lactic acid production tends to lower [ADP] (by lowering pH), while proton efflux has the opposite effect. We identify four patterns of results: (A) in mitochondrial myopathy, apparent QMAX is reduced and [ADP] is appropriately increased, because increased proton efflux reduces the pH change in exercise despite increased lactic acid production; (B) in some conditions (e.g., cyanotic congenital heart disease) apparent QMAX is reduced but there is no compensatory rise in [ADP], probably because anaerobic ATP synthesis during exercise is increased without increase in proton efflux; (C) in other conditions (e.g., myotonic dystrophy) [ADP] is increased during exercise but apparent QMAX is normal, suggesting either an increase in proton efflux and/or decrease in anaerobic ATP synthesis during exercise; (D) there are also conditions (e.g., respiratory failure) where, despite impaired oxygen supply, both apparent QMAX and end‐exercise [ADP] are normal. We also discuss the metabolic conditions under which end‐exercise [ADP] is increased by a mitochondrial defect. Finally, we discuss some technical aspects, including the effects of an altered mitochondrial Km for ADP and the relationship of the analysis to the halftime of PCr recovery and an alternative calculation of apparent QMAX.
Differential diagnosis of solid renal tumors by MRI. Comparison of In Situ relaxation times measured with a 0.1 T imager and histological findings
Authors: Takeda Masayuki , Katayama Yasushi , Tsutsui Toshiki , Komeyama Takeshi , Mizusawa Takaki , Saito Kazuhide , Takahashi Hitoshi , Tamaki Makoto , Sato Shotaro
Published: March 2007

The T1 and T2 of kidneys in 5 normal volunteers and 27 patients with renal tumors were evaluated preoperatively using a magnetic resonance imager with a 0.1 T resistive electromagnet, and the T1 and T2 of the renal tumors were compared with the pathological findings: (i) the T1 and T2 of the normal renal medulla were longer than those of the normal renal cortex and psoas muscle; (ii) both T1 and T2 of renal pelvic cancer (RPC) were shorter than those of renal cell cancer (RCC, p<0.05); (iii) the T2 values of RPC were significantly shorter than those of renal medulla (P<0.01); (iv) the T1 and T2 of the normal renal cortex of subjects <50 years old were shorter than those of subjects ⩾50 years old (p<0.05 and p<0.01, respectively). These findings suggest that preoperative evaluation of the pathological findings of renal tumors may be possible by calculating the relaxation time using MRI under low magnetic field.
Effect of hypoxia on bicuculline seizures of rat: NMR spectroscopy and bioluminescence imaging
Authors: Kloiber O. , Bockhorst K. , Hoehn‐Berlage M. , Hossmann K.‐A.
Published: March 2007

Previous studies suggested that hypoxia reduces the severity of brain injury after epileptic seizures. To test this hypothesis, the effect of hypoxic arrest of epileptic seizures on brain metabolism was investigated in rats by combining in vivo NMR spectroscopy with imaging techniques for the pictorial evaluation of energy metabolism and pH. Seizures were produced by i.v. injection of bicuculline, and measurements were compared in animals with and without 5 min exposure to 5% oxygen after the onset of seizures. Transient hypoxia persistently reduced seizure activity, even after return to normoxia. Hypoxia or seizure alone had little effect on brain metabolism but the combination of both led to marked albeit reversible deterioration of energy and acid/base status. In normoxic animals pictorial measurements of energy state 2 h after the onset of seizures revealed a regional decline of ATP in the hippocampus. In animals in which seizures were arrested by transient hypoxia ATP depletion was additionally observed in the border zones of vascular territories. These results demonstrate that hypoxic arrest of seizure activity leads to the aggravation of metabolic disturbances and is therefore not suited to preventing permanent brain injury.
Diffusion into rat brain of contrast and shift reagents for magnetic resonance imaging and spectroscopy
Authors: Preston Edward , Foster David O.
Published: March 2007

A sensitive radiotracer technique was used to measure transfer constants (Kis) for blood to brain diffusion of the MR contrast reagent gadolinium diethylenetriaminepentaacetate (GdDTPA2−) and the MR shift reagent dysprosium triethylenetetraminehexaacetate (DyTTHA3−) across the normal and the ischemically injured blood‐brain barrier (BBB) of rats. In rats with a normal BBB mean Kis (nL/g/s) for these reagents ranged from 0.3 to 1.4 across eight brain regions and were significantly lower in each region than Kis for sucrose (1.5–3.2), a substance known to be a poor permeant of the intact BBB. Kis measured 6h after a 10min period of normothermic forebrain ischemia were increased to 4.0–6.2 (reagents) and 6.6–7.5 (sucrose) in two brain regions, striatum and hippocampus, known to be especially vulnerable to ischemic injury. Measurements of BBB permeability to DyTTHA3− after osmotic opening of the barrier with hypertonic arabinose gave Kis of 25–30 in forebrain regions. Estimates of reagent concentrations in brain interstitial fluid 30 min after dosing the animals indicated that both an extremely high dose of DyTTHA3− and severe disruption of the BBB would be required to shift the resonance frequency of extracellular Na+ appreciably. With the moderate degrees of BBB injury produced by short‐term ischemia, a dose of GdDTPA2− about 25 times the usual clinical dose of 0.1 mmol/kg would be required to quantify the injury by dynamic MRI.
Localized T1 measurements using an inversion‐recovery osiris method
Authors: Girard F. , Poulet P. , Steibel J. , Chambron J.
Published: March 2007

This work presents a new method for localized T1 measurements, based upon the OSIRIS scheme. It relies on the use of a non‐selective 180° pulse applied before the OSIRIS preparation cycle. The accuracy of the method has been verified with test tubes and in vivo for two nuclei, 1H and 19F. The accuracy of the T1 values is discussed, as well as possible applications of the inversion‐recovery method to non‐invasive in vivo pO2 measurements.
In Situ13C NMR quantification of hepatic glycogen
Authors: Borgs Maria , Van Hecke Paul , Overloop Kristin , Decanniere Caroline , Van Huffel Sabine , Stalmans Willy , Vanstapel Florent
Published: March 2007

We report on the 13C NMR visibility of the C‐1 glycosidic carbon of α‐particulate glycogen in perfused rat liver. We used rats fed ad libitum, animals refed after a 48 h fast with a sucrose supplement with or without glucocorticoid treatment, and gsd/gsd rats with a hepatic glycogen storage disease due to phosphorylase kinase deficiency. Thus we studied a wide range of glycogen levels (25‐140 mg/g liver). All livers were perfused with 15 mM glucose, to maintain constant glycogen levels. Failure to activate glycogen phosphorylase ensures stable glycogen levels in gsd/gsd livers. Natural abundance 13C NMR signals were calibrated against a phantom containing a fixed amount of glycogen. Accumulated free induction decays were analysed after Fourier transformation by numerical integration, or by direct analysis of the signal in the time domain using a non‐iterative method based on singular value decomposition. NMR quantification of the glycogen correlated well with the chemical determination over the whole concentration range. However, the precision (reproducibility) of glycogen determinations (be it by chemical methods or by NMR spectroscopy) may pose problems. Authors should be encouraged to report systematically on the precision of their methods.
In vivo19F one‐dimensional chemical shift imaging study of isoflurane uptake in rabbit brain
Authors: Venkatasubramanian P. N. , Shen Y. J. , Wyrwicz A. M.
Published: March 2007

19F one‐dimensional chemical shift imaging and one‐pulse techniques were used to follow the uptake of isoflurane in rabbit brain in vivo. Brain isoflurane appeared mainly in two adjacent slices of cerebral cortex. Both slices showed increase in anesthetic content at similar rates. A biphasic first‐order uptake pattern with an initial fast component and a slower rate for the duration of the uptake was observed by the one‐pulse technique. Only the slower kinetic was followed by chemical shift imaging due to constraints on temporal resolution. Anesthetic levels in arterial blood reached equilibrium significantly earlier than in brain, suggesting a ‚restricted’︁ diffusion into brain tissue for this agent.
Non‐invasive investigation of parenchymal liver disease using 31P NMR spectroscopy
Authors: Roelsgaard Klaus , Stødkilde‐Jørgensen Hans , Dønstrup Sune , Djurhuus Jens Christian
Published: March 2007

Four 31P NMR spectroscopy parameters were measured non‐invasively in the liver of 11 healthy pigs and 9 pigs with CCI4‐induced liver disease: (i) absolute molar concentration of phosphorous metabolites; (ii) pH based on the chemical shift of the Pi peak; (iii) T1 of the peaks in the 31P NMR spectrum; and (iv) changes in ATP, Pi and phosphomonoester after fructose administration. Liver disease was verified by histology and blood chemistry. The concentration of ATP decreased from 3.0(2.8–3.1) to 2.0(2.0–2.4) mM (median and quartiles) when liver disease was induced (p<0.05). The concentration of phosphodiesters (PDEs) decreased from 14.8(11.4–19.5) to 8.7(7.4–11.6) mM (p<0.05). pH increased by 0.1 unit. Ti relaxation times for the γ‐, α‐ and β‐ATP peaks increased from 320(249–471) to 577(506–638) ms (p<0.01), from 765(611–786) to 906(820–1058) ms (p<0.05) and from 402(327–509) to 579(543–743) ms (p<0.01), respectively, while T1 for the PDE peak decreased from 2204(1909–2404) to 1758(1502‐1894) ms (p<0.05). In the healthy animals injection of fructose was followed by a reduction of ATP (β‐ATP). In diseased livers this reduction was significantly smaller. In conclusion, it was possible non‐invasively to show differences between healthy and diseased livers in all NMR parameters evaluated. This means that 31P NMR Spectroscopy may have a potential as a non‐invasive diagnostic method for studying liver disease.
Effects of hyperoxia on T and resonance frequency weighted magnetic resonance images of rodent tumours
Authors: Karczmar G. S. , River J. N. , Li J. , Vijayakumar S. , Goldman Z. , Lewis M. Z.
Published: March 2007

Experiments were performed to determine whether T and resonance frequency weighted MR images are sensitive to effects of hyperoxia on model tumors. Hyperoxia can increase tumor oxygen tension and thus affect T and/or the average resonance frequency within each image voxel due to the paramagnetism of oxygen itself or through modulation of the oxidation state of hemoglobin. Alternatively, changes in T during hyperoxia may reflect changes in tumor water content due to changes in systemic blood pressure. Mammary adenocarcinomas implanted in the flanks of rats were studied. Imaging sequences were preceded by two 90° pulses separated by an evolution period of 50 or 75 ms and followed by a crusher gradient to eliminate transverse magnetization. This pulse sequence produced images which were sensitized to both T and the average resonance frequency of each voxel. Images were produced at 2 T using a gradient echo imaging method with a TR of 3 s. Images obtained during inhalation of air and 100% O2 were compared. Significant increases in image intensity were observed in most tumors during hyperoxia, particularly at the tumor center. The increase was accentuated when the evolution period was increased and greatly reduced when a 180° refocusing pulse was placed at the center of the evolution period. These results suggest that hyperoxia reduces local magnetic susceptibility gradients leading to an increase in T or causes a shift in resonance frequency. The magnitude of this change may be a function of the rate at which oxygen is delivered to and metabolized by tumors and may also reflect tumor oxygen tension under normoxic conditions. Therefore, response to hyperoxia may provide useful contrast in MR images which could aid identification and characterization of tumors and provide an indirect measure of tumor blood flow and oxygenation.
Monitoring the initial expansion of focal ischaemic changes by diffusion‐weighted MRI using a remote controlled method of occlusion
Authors: Roussel S. A. , van Bruggen N. , King M. D. , Houseman J. , Williams S. R. , Gadian D. G.
Published: March 2007

The purpose of the present study was to quantify the early changes which occur on diffusion‐weighted imaging following focal cerebral ischaemia. We have developed a method for the remote occlusion of the middle cerebral artery in the rat, allowing early changes to be monitored and images to be acquired before and after ischaemia under identical conditions. Sequential diffusion‐weighted images were acquired before and for up to 6h following the occlusion. The data show that a hyperintense area appears soon after occlusion which expands during the first 2 h. It has previously been shown that the hyperintensity observed after ischaemia is linked to events associated with energy failure. Our findings are in good agreement with previous pathophysiological studies of focal ischaemia, which suggest a growing of the energy depleted area. In conclusion, our data extend the usefulness of diffusion‐weighted imaging to the study of the early spatial evolution of the most compromised area after focal ischaemia. Diffusion‐weighted imaging may constitute a very powerful tool to investigate pharmacological therapies which may interact with this evolution, both in experimental and clinical studies.
2D and 3D high resolution gradient echo functional imaging of the brain: Venous contributions to signal in motor cortex studies
Authors: Haacke E. M. , Hopkins A. , Lai S. , Buckley P. , Friedman L. , Meltzer H. , Hedera P. , Friedland R. , Klein S. , Thompson L. , Detterman D. , Tkach J. , Lewin J. S.
Published: March 2007

Recent emphasis on high resolution gradient echo studies in functional imaging has led to the conclusion that there are likely three domains of response to the blood circulation in the brain when considering field inhomogeneity effects of the venous blood pre‐ and during activation. The first is a coherent effect due to large or macroscopic vessels on the order of the size of the voxel (ca 200–500 μm in most studies). These can lead to very large signal changes (up to 100%). The second is at the venule level (ca 50–200 μm) and is associated with smaller parenchymal changes (usually ca 10% or less). The third is at the capillary level and is associated with much smaller signal changes at 1.5T and even up to 4 T. The actual signal changes depend on field strength and sequence design. In this paper, we present our experience in detecting the first two domains with 2D and 3D gradient echo imaging at 1.5T. We find that high resolution enables visualization of the larger small veins in motor cortex studies and that, on occasion, it is possible to see the venule effects as well. We suggest a simple model to explain the large signal changes based on susceptibility changes and partial volume effects. Comparisons of the functional imaging data to this model and to MR angiographic studies are also shown as evidence of the venous sources of the susceptibility changes.
Potential pitfalls of functional MRI using conventional gradient‐recalled echo techniques
Authors: Kim Seong‐Gi , Hendrich Kristy , Hu Xiaoping , Merkle Hellmut , Uǧurbil Kâmil
Published: March 2007

The conventional gradient‐recalled echo technique, FLASH, has widely been used for functional MRI. FLASH results at 4 T with short TEs of 10–20 ms mimic those at 1.5 T with TEs of 25–50 ms or longer. Under these conditions, large venous vessels dominate the activated area; however, the use of longer TEs at 4 T reveals activation in gray matter areas as well as large vessels. Inflow effects of large vessels can be greatly reduced with centric‐reordering of phase‐encoding steps and inter‐image delay. Finger and toe movement paradigms show that functional activation maps are consistent with classical somatotopic maps, and are specific to the tasks. Navigator‐based motion correction generates functional maps with larger activation areas by reducing physiological noise.
Tissue specific perfusion imaging using arterial spin labeling
Authors: Detre John A. , Zhang Weiguo , Roberts David A. , Silva Afonso C. , Williams Donald S. , Grandis Donald J. , Koretsky Alan P. , Leigh John S.
Published: March 2007

Quantitative magnetic resonance measurements of regional tissue perfusion can be obtained using magnetically labeled arterial water as a diffusable tracer. Continuous labeling is achieved in flowing spins using adiabatic inversion. The effects of continuous labeling of proximal arterial spins and T1 relaxation in distal tissue magnetization result in a steady‐state change in tissue magnetization which is tissue specific, i.e., it can be quantified in units of blood flow per gram of tissue per unit time. This magnetization is sampled using standard imaging sequences. The theoretical basis for this method, including the effects of macromolecular spin saturation, is reviewed. Recent results demonstrating the successful implementation of this technique in vitro and in vivo in rat brain, heart, and kidney, and in human brain and kidney are presented, as well as the use of a separate RF coil for arterial labeling to produce selective perfusion images in rat brain. This approach allows quantitative perfusion images to be obtained completely non‐invasively at the resolution of 1H MRI, and is useful in the clinical and investigational evaluation of organ physiology.
Effect of cardiac flow on gradient recalled echo images of the canine heart
Authors: Balaban Robert S. , Taylor Joni F. , Turner R.
Published: March 2007

The effect of coronary flow on the signal intensity of gradient recalled echo (GRE) MR images of the canine heart was evaluated at 4 T. Using a fully instrumented canine model, hyperperfusion (local adenosine infusion) and ischemia (local occlusion) were evaluated while coronary blood flow and venous oxygen tension were monitored. These studies demonstrated an increase in GRE signal intensity with increases in coronary blood flow and venous oxygenation. A local occlusion resulted in a small decrease in signal intensity in the affected area of the heart. The dependence of the signal changes on TE and TR indicated that the effects of high flow were associated with changes in the apparent T2 and T1. Both relaxation effects could reflect changes in tissue blood volume associated with the conditions studied. In addition, the apparent T2 changes were consistent with alterations in total tissue deoxyhemoglobin concentration and the changes in apparent T1 were consistent with inflow effects.
Reduction in myocardial high energy phosphate spin lattice relaxation times using manganese
Authors: Scholz Thomas D.
Published: March 2007

Paramagnetic contrast agents are being widely used in proton magnetic resonance imaging. The present study demonstrates the potential usefulness of paramagnetic contrast agents in 31P NMR spectroscopy. Using the Langendorff perfused rat heart, manganese chloride (Mn2+) at a concentration of 50 μM/L was added to the perfusate for 10 or 30 min. 31P NMR Ti relaxation times were subsequently measured at 121.5 MHz. After the 10 min exposure to Mn2+, 31P NMR Ti measurements of phosphocreatine and ATP were reduced by ca 25 and 50%, respectively, with no significant change in linewidths. A small additional decrease in Ti relaxation times after infusion of Mn2+ for 30 min was not significantly different from the values at 10 min. Potential uses of Mn2+ in 31P NMR spectroscopy include improving the S/N ratio of spectra and assessment of calcium ion channel activity.
The accuracy and reproducibility of measuring blood flow in murine tumours by the D2O uptake and clearance techniques
Authors: Bradley J. K. , Counsell C. J. R. , Bremner J. C. M. , Sansom J. M. , Adams G. E.
Published: March 2007

The use of D2O as an NMR visible tracer to monitor murine tumour blood flow (TBF) by both the wash‐in and wash‐out methods has been investigated. The factors that influence the models used to fit the data and the error on the measurement of the clearance and uptake rates have been assessed. The study concentrates on the uptake method which allows TBF to be measured without the need to use anaesthetic. Also, administering the D2O remotely to the mouse means it can remain undisturbed, in the magnet bore, between control and post‐treatment readings. The uptake method in KHT and RIF‐1 transplanted murine tumours has been investigated in a series of control experiments and after modifying TBF by hydralazine (5 mg/kg) and photodynamic therapy. These studies showed that four uptake measurements could be made on the same mouse at 20 min intervals without affecting TBF, control values were the same for anaesthetized and unanaesthetized mice and the values obtained for RIF‐1 tumours were marginally higher than those obtained for the KHT tumours. The decrease in TBF seen after modification was in good agreement with published data where TBF results were obtained by using D2O clearance, radioactive tracers or laser Doppler flowmetry.
1H MRS of high grade astrocytomas: Mobile lipid accumulation in necrotic tissue
Authors: Kuesel Annette C. , Sutherland Garnette R. , Halliday William , Smith Ian C. P.
Published: March 2007

Sixty‐four samples from six grade 4 astrocytomas were investigated ex vivo by 1H MRS at 360 MHz and subsequently by histopathology to obtain percentages of viable and necrotic tumour and grey and white matter. MR‐visible lipids were detected in 87% of tumour samples. Necrotic foci were <3 × 3 × 6 mm3. The means of the intensities/unit weight tissue of the lipid resonances at 5.33, 2.80, 1.29 and 0.89 ppm were significantly higher (p<0.05) for three sets of comparisons: samples with 85–100% vs 50–75%; with 50–75% vs 10–40% and with 10–40% vs 0–5% necrosis. For the lipid resonance at 2.04 ppm the difference in the means was significant only for samples with 50–75% compared to those with 85–100% necrosis, because for samples with <50% necrosis resonances from glutamine and possibly small amounts of glutamate, γ‐aminobutyrate and N‐acetylaspartate anions contribute significantly to the spectral area at 2.0 ppm. We conclude that necrotic foci below MRI resolution yield the resonances at 1.3 and 0.9 ppm, and contribute to the intense resonance at 2.0 ppm observed in in vivo 1H spectra of some high grade astrocytomas.
Regulation of intracellular pH in neuronal and glial tumour cells, studied by multinuclear NMR spectroscopy
Authors: Flögel Ulrich , Willker Wieland , Leibfritz Dieter
Published: March 2007

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.
Mobile lipids and metabolic heterogeneity of brain tumours as detectable by Ex Vivo1H MR spectroscopy
Authors: Kuesel Annette C. , Donnelly S. Maureen , Halliday William , Sutherland Garnette R. , Smith Ian C. P.
Published: March 2007

To examine metabolic heterogeneity in primary brain tumour, multiple biopsies (one to five per tumour) from four benign meningiomas, five acoustic schwannomas, eleven glial tumours and five medulloblastomas were each subdivided into one to five samples (total = 194) and investigated using ex vivo 360 MHz 1H MR spectroscopy with histopathological correlation. Low amounts of mobile lipids were detected in meningothelial meningiomas and medulloblastomas, high amounts in some or all samples of all other tumours. The differences in non‐lipid metabolites between different tumour types were less marked, with the exception of the medulloblastomas, which had high amounts of N‐acetyl aspartate and cholines. The amount of mobile lipid correlated with Antoni type B areas in schwannomas and necrosis in a high grade giant cell tumour. The amount of lipid varied significantly from sample to sample in a grade 2 astrocytoma and grade 4 astrocytoma samples with 0–5% necrosis but did not correlate with the site in the tumour or histopathological characteristics. The metabolic heterogeneity occurred on a spatial scale at least as small as the size of the MR samples, i.e., ≤60 mg. These results suggest that the detection of metabolic heterogeneity and mobile lipids may have importance for the design of clinical studies.
1H NMR spectroscopic characterization of perchloric acid extracts from breast carcinomas and non‐involved breast tissue
Authors: Gribbestad Ingrid S. , Petersen Steffen B. , Fjøsne Hans E. , Kvinnsland Stener , Krane Jostein
Published: March 2007

High‐resolution 1H NMR spectra were obtained from perchloric acid extracts of breast tumor specimens and adjacent non‐involved tissue. Two‐dimensional shift‐correlated and homonuclear J‐resolved spectroscopy were used to identify coupled resonances in the spectra. Chemical shifts, multiplicities and spin‐spin coupling constants of several non‐resolved resonances in the one‐dimensional spectra could be determined by the two‐dimensional methods. Several differences in the metabolite content of the two types of extracts were established. The spectra of extracts from non‐involved tissue were dominated by signals from glucose and other carbohydrates, while most of the tumors had very low or no detectable levels of glucose. High concentrations of lactate, taurine and succinate, an increase of the phosphocholine level, and a very low phosphocreatine level were characteristic findings in the 1H spectra of tumor extracts. The variation in the level of myo‐inositol follows the variation in glucose for the two types of tissue. Scyllo‐inositol was for the first time observed in the NMR spectra from breast tissue. Uridine 5′‐diphospho‐N‐acetylglucosamine and uridine 5′‐diphospho‐N‐acetylgalactosamine have been identified and there is an increased level of these two hexoses in the tumor tissue. These results provide insight into breast tumor metabolism, by simultaneously detecting a large number of metabolites and demonstrate the potential for using 1H NMR spectroscopy for studying different metabolic pathways in breast tumors. At the same time they provide useful information for interpretation of in vivo 1H NMR spectra of breast tumors.
Comparison of calibration strategies for the in vivo determination of absolute metabolite concentrations in the human brain by 31P MRS
Authors: Buchli Reto , Martin Ernst , Boesiger Peter
Published: March 2007

Cerebral concentrations of phosphorus metabolites can be assessed non‐invasively by 31P MRS provided the metabolite signals are calibrated with the signal of a standard of known concentration. The reliability of the concentration estimates depends mainly on the strategy of calibration. Three strategies were compared by assessing the concentrations both in a test dummy and in the brain of volunteers. The first strategy utilized tissue water as an internal heteronuclear concentration standard. The second and third strategies used a phosphorus solution as an external homonuclear standard; this solution was either put into a reference bottle placed on top of the head or into a simulation phantom measured instead of the head. Localization was always achieved with the ISIS pulse sequence. The two external homonuclear strategies achieved a higher accuracy (mean error ≈5%) and reproducibility (mean SD ≈8%) of the concentration estimates than the internal heteronuclear strategy (mean error ≈11%; mean SD ≈15%).
Decrease in brain choline‐containing compounds following a short period of global ischemia in gerbils as detected by 1H NMR spectroscopy in vivo
Authors: Kuhmonen Johanna , Sivenius Juhani , Riekkinen Paavo J. , Kauppinen Risto A.
Published: March 2007

Cerebral metabolism was studied in the postischaemic gerbil brain using surface coil 31P and 1H NMR spectroscopy. The ratio of choline‐containing compounds (Cho) to total creatine (Cr) in the brain decreased from 0.46 ± 0.02 to 0.32 ± 0.02 by the fifth day following exposure to 5 min of global ischaemia and it remained at this low level for at least 19 days. The amounts of cerebral Cho as quantified by 1H NMR in vivo were 1.70 ± 0.15 and 1.09 ± 0.22 mmol/kg in control and postischaemic animals, respectively. The T2 of Cho was longer in the postischaemic cerebral cortex than in the control one. N‐acetyl aspartate (NAA) as determined by 1H NMR in vivo did not differ in the two animal groups. High‐resolution 1H NMR of acid‐extracted brain cortices showed a decrease in total Cho (glycerophosphocholine, phosphocholine and choline) by 31%, but no changes in NAA, total creatine, taurine and myo‐inositol, in the brain cortex seven days postischaemia relative to control animals. The decrease in acid extractable Cho was mainly due to the drop in glycerophosphocholine concentration. 31P NMR indicated normal energy state and phosphomonoester/phosphocreatine (PCr) and phosphodiester/PCr ratios in the in vivo brain 7 days postischaemia. Silver impregnation did not reveal neuronal degeneration but immunohistochemical staining showed a number of glial fibrillary acidic protein expressing astrocytes as indicators of reactive gliosis in the postischaemic cerebral cortex. These data show, for the first time, that a 1H NMR decrease in Cho metabolites takes place as a consequence of brief ischaemic episode even in the absence of obvious neuronal degeneration.
1H‐2H exchange in the perfused rat liver metabolizing [3‐13C]alanine and 2H2O as detected by multinuclear NMR spectroscopy
Authors: Moldes Milagros , Cerdán Sebastian , Erhard Peter , Seelig Joachim
Published: March 2007

The exchange of individual protons of hepatic metabolites against the solvent deuterons has been investigated in perfused rat liver. Livers from starved rats were perfused for 20 min with a 10 mM solution of unlabeled or 3‐13C‐labeled L‐alanine in Krebs Ringer bicarbonate buffer, with or without 50% deuterium oxide (2H2O). High resolution 13C NMR analysis of deuterium‐induced isotopic shifts and of 2H‐13C couplings revealed a differential 1H‐2H exchange depending on the chemical nature of the metabolite and on the site of 13C labeling. [3‐13C]Aspartate isotopomers showed similar 2H/1H ratios in the C3 and in the C2 carbons while [2‐13C]aspartate isotopomers had much smaller 2H/1H ratios in the C2 than in the C3 carbons. Similarly, [2‐13C]glutamate isotopomers had 2H/1H ratios significantly smaller in the C2 than in the C3 carbon. These results suggest that the hydration‐dehydration reactions of the citric acid cycle, which result in exchange at the C3 carbons of aspartate and glutamate, approach equilibrium with the perfusate faster than the aminotransferases of aspartate and alanine, which induce exchange at the C2 carbons of these amino acids. Taken together, the results obtained are consistent with a heterogeneous solvent exchange environment in the perfused liver.
Comparative NMR study of a differentiated rat hepatoma and its dedifferentiated subclone cultured as spheroids and as implanted tumors
Authors: Ronen S. M. , Volk A. , Mispelter J.
Published: March 2007

H4IIEC3 (H4), a differentiated rat hepatoma line and H5, its dedifferentiated subclone, were investigated as proliferating spheroids and as implanted subcutaneous tumors in juvenile rats. H4 cells formed tight, round spheroids whereas H5 cells formed loose, grape‐like structures. 31P MR spectra showed that phosphocreatine was present in H5 spheroids but not in H4 spheroids or tumors. [13C]Lactate production from [13C]glucose, with no detectable uptake of [13C]alanine, indicated that energy production in H5 spheroids was primarily via glycolysis. No [13C]glucose utilization was detected in H4 spheroids, but uptake of alanine and accumulation of labeled lactate, glutamate and glutamine indicated oxidation via the tricarboxylic acid (TCA) cycle. Tumors of H4 cells were well perfused, unlike tumors of H5 cells which were highly necrotic. Following i.v. infusion with [13C]alanine, [13C]lactate and glutamate, evidence of oxidation via the TCA cycle, were observed in H4 tumors. Thus the results obtained by 31P and 13C MRS correlated with the differentiation state of H4 and H5 spheroids and tumors.
Healthy and infarcted brain tissues studied at short diffusion times: The origins of apparent restriction and the reduction in apparent diffusion coefficient
Authors: Norris David G. , Niendorf Thoralf , Leibfritz Dieter
Published: March 2007

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.
Dysfunctional activation of subcortical nuclei in palatal myoclonus detected by high‐resolution MRI
Authors: Boecker H. , Kleinschmidt A. , Weindl A. , Conrad B. , Hänicke W. , Frahm J.
Published: March 2007

Magnetic resonance images that were sensitized to changes in cerebral blood oxygenation state demonstrated dysfunctional activation of the dentate nuclei, the left inferior olivary nucleus and the left red nucleus in a 56‐year‐old patient with palatal myoclonus. These findings represent the first demonstration of movement‐related activation of cerebellar, brainstem and midbrain nuclei in a single subject and at a spatial resolution comparable to that of anatomic MR images.
19F NMR magnetization transfer between 5‐FBAPTA and its complexes. An alternative means for measuring free Ca2+ concentration, and detection of complexes with protein in erythrocytes
Authors: Gilboa Haggai , Chapman Bogdan E. , Kuchel Philip W.
Published: March 2007

The 19F NMR Ca2+‐indicator molecule 5,5'‐difluoro‐1,2‐bis(o‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid (5‐FBAPTA) was used in a procedure that enhances its range of applications to measuring free Ca2+ concentrations in buffer solutions and human erythrocytes. Even if the signal from the Ca‐5‐FBAPTA complex was not visible, the concentration of the complex could be calculated from saturation transfer spectra. This was demonstrated with well characterized buffer solutions in vitro and shown to also apply to concentrated haemolysates. The analysis required a precise estimate of the dissociation rate constant of the complex; this was found to be 295/s at 37°C and the corresponding association rate constant was 4.1×108 L/mol/s. These values differ from those obtained previously in different buffer conditions and by two different NMR methods. A series of spectra were acquired from haemolysates containing 5‐FBAPTA, in which saturating irradiation was applied at a frequency that was progressively off‐set from the carrier frequency. Saturation transfer to the free 5‐FBAPTA was seen from irradiation at frequencies different from that of Ca‐5‐FBAPTA, thus suggesting the presence of complexes with proteins.
Localized T2 measurements using an OSIRIS–CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect
Authors: Girard F. , Poulet P. , Namer I. J. , Steibel J. , Chambron J.
Published: March 2007

This work presents a new method allowing localized T2 measurements, based upon the OSIRIS scheme. A train of 180° pulses is applied after the OSIRIS preparation cycle, recording directly the transverse magnetization decay. The method was verified for two nuclei, 1H and 19F, with phantoms and in vivo on rats. The accuracy of the T2 values is discussed, as well as possible applications of the OSIRIS‐CPMG method to proton transverse spin relaxation measurements, free of diffusion effects, and to non‐invasive in vivo blood oxygenation measurements, through the use of an emulsion of perfluorooctylbromide, a blood substitute containing fluorine.
Investigation of the 1H NMR visibility of lactate in different rat and human brain cells
Authors: Kotitschke Klaus , Schnackerz Klaus D. , Dringen Ralf , Bogdahn Ulrich , Haase Axel , von Kienlin Markus
Published: March 2007

In recent years, 1H MRS has been used in a number of studies to measure the lactate content of brain, and it is generally assumed that the methyl resonance at 1.3 ppm reflects the total amount of lactate present in the tissue. However, reduced NMR visibility of lactate has recently been reported for blood, heart and skeletal muscle as well as for bacteria. We have assessed the NMR visibility of lactate in cultures of human and rat brain cells, comparing the concentrations measured by NMR and by biochemical methods. Contributions of fatty acids have been eliminated using their different relaxation behavior. We found approximately 30% of the lactate to be undetectable by NMR in the studied cell cultures. While the mechanism partially masking lactate in 1H spectra is not yet understood, the potential invisibility of some pools of lactate to NMR may greatly affect the interpretation of brain spectra.
Transmural distribution of 2‐deoxyglucose uptake in normal and post‐ischemic canine myocardium
Authors: Yoshiyama Minoru , Bache Robert J. , Merkle Hellmut , Garwood Michael , Ugurbil Kamil , Zhang Jianyi , Arthur H. L.
Published: March 2007

This investigation was performed to determine (i) whether 31P spatially localized 31P NMR spectroscopy could be utilized to determine the transmural distribution of 2‐deoxyglucose (2DG) uptake in the in vivo canine heart and (ii) whether transmural 2DG uptake would be affected by a preceding ischemic insult. 2DG was infused and the accumulation of 2‐deoxyglucose‐6‐phosphate (2DGP) was monitored (by means of spatially localized 31P NMR) in control hearts, in pharmacologically hyperperfused hearts, and in hearts subjected to four (5 min) occlusions of the left anterior descending coronary artery. Myocardial blood flow was measured with radioactive microspheres. In control hearts, subendocardial (ENDO) 2DGP contents were significantly higher than those in the subepicardium (EPI) being 3.8±0.3 and 2.2±0.2 m̈mol/g, respectively; the ENDO/EPI ratio of 2DGP was 1.70±0.21. During hyperperfusion blood flow increased approximately four‐fold but 2DGP accumulation was not altered. ATP levels in post‐ischemic myocardium were significantly decreased (ENDO more than EPI) and 2DGP accumulation in each layer was increased (p<0.01 vs control); however, the ENDO/EPI ratio of 2DGP was not altered. 2DG infusion induced a marked elevation of blood insulin and norepinephrine levels. These data demonstrate that in the presence of high blood levels of 2DG and insulin: (i) 2DGP accumulation can be measured in the in vivo canine heart; (ii) in normal hearts 2DG uptake is more pronounced in the inner layers of the left ventricular wall (this transmural 2DG uptake gradient is not due to subendocardial hypoperfusion); and (iii) 2DG uptake is greater in the post‐ischemic heart but the ENDO/EPI gradient of 2DG uptake is not altered indicating that the more severe ischemic insult in the subendocardium does not result in a disproportionate increase in 2DG uptake in that region of the myocardium. Although 2DG uptake patterns in this model most probably reflect those of glucose (at comparable glucose and insulin levels), quantitative extrapolations with regard to the rate of glucose uptake are not possible from the present data.