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Journal Cover   Magnetic Resonance Materials in Physics, Biology and Medicine
  [SJR: 0.928]   [H-I: 40]   [1 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0968-5243 - ISSN (Online) 1352-8661
   Published by Springer-Verlag Homepage  [2302 journals]
  • Free breathing 1 H MRI of the human lung with an improved radial turbo
           spin-echo
    • Abstract: Objective To optimize a radial turbo spin-echo sequence for motion-robust morphological lung magnetic resonance imaging (MRI) in free respiration. Materials and methods A versatile multi-shot radial turbo spin-echo (rTSE) sequence is presented, using a modified golden ratio-based reordering designed to prevent coherent streaking due to data inconsistencies from physiological motion and the decaying signal. The point spread function for a moving object was simulated using a model for joint respiratory and cardiac motion with a concomitant T2 signal decay and with rTSE acquisition using four different reordering techniques. The reordering strategies were compared in vivo using healthy volunteers and the sequence was tested for feasibility in two patients with lung cancer and pneumonia. Results Simulations and in vivo measurements showed very weak artifacts, aside from motion blur, using the proposed reordering. Due to the opportunity for longer scan times in free respiration, a high signal-to-noise ratio (SNR) was achieved, facilitating identification of the disease as compared to standard half-Fourier-acquisition single-shot turbo spin-echo (HASTE) scans. Additionally, post-processing allowed modifying the T2 contrast retrospectively, further improving the diagnostic fidelity. Conclusion The proposed radial TSE sequence allowed for high-resolution imaging with limited obscuring artifacts. The radial k-space traversal allowed for versatile post-processing that may help to improve the diagnosis of subtle diseases.
      PubDate: 2015-06-01
       
  • Proton spectroscopic imaging of brain metabolites in basal ganglia of
           healthy older adults
    • Abstract: Object We sought to measure brain metabolite levels in healthy older people. Materials and methods Spectroscopic imaging at the level of the basal ganglia was applied in 40 participants aged 73–74 years. Levels of the metabolites N-acetyl aspartate (NAA), choline, and creatine were determined in "institutional units" (IU) corrected for T1 and T2 relaxation effects. Structural imaging enabled determination of grey matter (GM), white matter (WM), and cerebrospinal fluid content. ANOVA analysis was carried out for voxels satisfying quality criteria. Results Creatine levels were greater in GM than WM (57 vs. 44 IU, p < 0.001), whereas choline and NAA levels were greater in WM than GM [13 vs. 10 IU (p < 0.001) and 76 versus 70 IU (p = 0.03), respectively]. The ratio of NAA/cre was greater in WM than GM (2.1 vs. 1.4, p = 0.001) as was that of cho/cre (0.32 vs. 0.16, p < 0.001). A low voxel yield was due to brain atrophy and the difficulties of shimming over an extended region of brain. Conclusion This study addresses the current lack of information on brain metabolite levels in older adults. The normal features of ageing result in a substantial loss of reliable voxels and should be taken into account when planning studies. Improvements in shimming are also required before the methods can be applied more widely.
      PubDate: 2015-06-01
       
  • Multiparametric oxygen-enhanced functional lung imaging in 3D
    • Abstract: Objective To develope a self-gated free-breathing 3D sequence allowing for simultaneous T 1-weighted imaging and quantitative \(T_{2}^{ *}\) mapping in different breathing phases in order to assess the feasibility of oxygen-enhanced 3D functional lung imaging. Materials and methods A 3D sequence with ultrashort echo times and interleaved double readouts was implemented for oxygen-enhanced lung imaging at 1.5 T. Six healthy volunteers were examined while breathing room air as well as 100 % oxygen. Images from expiratory and inspiratory breathing phases were reconstructed and compared for the two breathing gases. Results The average \(T_{2}^{*}\) value measured for room air was 2.10 ms, with a 95 % confidence interval (CI) of 1.95–2.25 ms, and the average for pure oxygen was 1.89 ms, with a 95 % CI of 1.76–2.01 ms, resulting in a difference of 10.1 % (95 % CI 8.9–11.3 %). An 11.2 % increase in signal intensity (95 % CI 10.4–12.1 %) in the T 1-weighted images was detected when subjects were breathing pure oxygen compared to room air. Furthermore, a significant change in signal intensity (26.5 %, 95 % CI 18.8–34.3 %) from expiration to inspiration was observed. Conclusions This study demonstrated the feasibility of simultaneous \(T_{2}^{*}\) mapping and T 1-weighted 3D imaging of the lung. This method has the potential to provide information about ventilation, oxygen transfer, and lung expansion within one experiment. Future studies are needed to investigate the clinical applicability and diagnostic value of this approach in various pulmonary diseases.
      PubDate: 2015-06-01
       
  • Characterizing blood oxygen level-dependent (BOLD) response following
           in-magnet quadriceps exercise
    • Abstract: Object There have been no studies to investigate the effects of cycling exercise protocols, as well as repeated bouts of exercise, on the blood oxygen level-dependent (BOLD) response in the quadriceps muscles. This study characterized BOLD signal recovery following non-ischemic bouts of exercise in the quadriceps muscles of healthy adults in order to provide a basis for application of a protocol for clinical populations. Materials and methods Healthy male subjects (23.7 ± 2.0 years of age, n = 10) completed three cycles of one-minute exercise (65 % of maximum workload), with two  minutes of rest between each bout, on an MRI-compatible ergometer. The BOLD responses during recovery were fitted to a sigmoid model, and response kinetics (post-exercise intensity [S0]), response time (α), change in baseline BOLD signal (κ), and inflection point (β)] were measured. Results The sigmoid function fit well to the post-exercise BOLD data (r 2 = 0.95 ± 0.04). The mean response time was 10.5 ± 3.8 seconds, change in baseline BOLD intensity was 0.15 ± 0.068, and time to half-peak was 20.2 ± 8.6 seconds. Conclusion The proposed sigmoid model is a robust method for quantifying quadriceps BOLD response post-exercise without induced ischemia. Extension of this model to evaluate microvascular responses in patients with chronic disease could improve our understanding of exercise intolerance.
      PubDate: 2015-06-01
       
  • Free-breathing, zero-TE MR lung imaging
    • Abstract: Object The investigation of three-dimensional radial, zero-echo time (TE) imaging for high-resolution, free-breathing magnetic resonance (MR) lung imaging using prospective and retrospective motion correction. Materials and methods Zero-TE was implemented similarly to the rotating-ultra-fast-imaging-sequence, providing 3D, isotropic, radial imaging with proton density contrast. Respiratory motion was addressed using prospective triggering (PT), prospective gating (PG) and retrospective gating (RG) with physiological signals obtained from a respiratory belt and interleaved pencil beam and DC navigators. The methods were demonstrated on four healthy volunteers at 3T. Results 3D, radial zero-TE imaging with high imaging bandwidth and nominally zero echo-time enables efficient capture of short-lived signals from the lung parenchyma and the vessels. Compared to Cartesian encoding, unaccounted for free-breathing respiration resulted in only benign blurring artifacts confined to the origin of motion. Breath holding froze respiration but achieved only limited image resolution (~1.8 mm, 30 s). PT and PG obtained similar quality expiratory-phase images at 1.2 mm resolution in ~6 min scan time. RG allowed multi-phase imaging in ~15 min, derived from eight individually stored averages. Conclusion Zero-TE appears to be an attractive pulse sequence for 3D isotropic lung imaging. Prospective and retrospective approaches provide high-quality, free-breathing MR lung imaging within reasonable scan time.
      PubDate: 2015-06-01
       
  • Automatic voxel positioning for MRS at 7 T
    • Abstract: Object The purpose of this study was to test, for the first time, whether spectroscopy voxels could be positioned automatically with high accuracy and reproducibility in ultrahigh-field longitudinal magnetic resonance spectroscopy (MRS) studies. Materials and methods MRS voxels were automatically positioned in two cingulate subregions of 12 healthy subjects using a vendor-provided automatic voxel positioning (AutoAlign) technique, and were manually placed in the same regions of 10 healthy subjects by an experienced technician in three 7T MRS scan sessions. Different coils were used for manual (24-channel coil) and automatic (32-channel coil) voxel placement, and the effects of signal-to-noise-ratio differences on the spectra were considered. Results Over three scan sessions and two regions scanned for each subject, a mean voxel geometric overlap ratio of 0.91 for automatic positioning reflected accurate voxel alignment, while the geometric overlap ratio was only 0.70 for voxels placed manually. Comparable voxel positions among the three scan sessions (p > 0.05) indicated high reproducibility of automatic voxel alignment. In comparison, significant voxel displacement among scan sessions (p < 0.05) was found using manual voxel positioning. Conclusions In view of the highly accurate and reproducible voxel alignment with automatic voxel positioning, we propose the application of automatic rather than manual voxel positioning in future ultrahigh-field longitudinal MRS studies.
      PubDate: 2015-06-01
       
  • An optically coupled sensor for the measurement of currents induced by MRI
           gradient fields into endocardial leads
    • Abstract: Object The gradient fields generated during magnetic resonance imaging (MRI) procedures have the potential to induce electrical current on implanted endocardial leads. Whether this current can result in undesired cardiac stimulation is unknown. Materials and methods This paper provides a detailed description of how to construct an optically coupled sensor for the measurement of gradient-field–induced currents into endocardial leads. The system is based on a microcontroller that works as analog-to-digital converter and sends the current signal acquired from the lead to an optical high-speed, light-emitting diode transmitter. A plastic fiber guides the light outside the MRI chamber to a photodiode receiver and then to an acquisition board connected to a PC laptop. Results The performance of the system has been characterized in terms of power consumption (8 mA on average), sampling frequency (20.5 kHz), measurement range (−12.8 to 10.3 mA) and resolution (22.6 µA). Results inside a 3 T MRI scanner are also presented. Conclusions The detailed description of the current sensor could permit more standardized study of MRI gradient current induction in pacemaker systems. Results show the potential of gradient currents to affect the pacemaker capability of triggering a heartbeat, by modifying the overall energy delivered by the stimulator.
      PubDate: 2015-06-01
       
  • In vivo proton magnetic resonance spectroscopic imaging of the healthy
           human brain at 9.4 T: initial experience
    • Abstract: Object In this study, the feasibility of in vivo proton magnetic resonance spectroscopic imaging (1H MRSI) of the healthy human brain at a field strength of 9.4 T, using conventional acquisition techniques, is examined and the initial experience is summarized. Materials and methods MRSI measurements were performed on a 9.4 T MR scanner (Siemens, Erlangen, Germany) equipped with head-only gradient insert (AC84, Siemens) and custom-developed, 8-channel transmit/24-channel receive, and 16-channel transmit/31-channel receive coils. Spectra were acquired from the superior part of the human brain with a modified STEAM sequence. Spectral quantification was done with LCModel software. Results Reasonable quality and signal-to-noise ratio of the acquired spectra allowed reliable quantification of 12 metabolites (Cramer-Rao lower bounds < 20 %), some of which may be difficult to quantify at field strengths below 7 T due to overlapping resonances or low concentrations. Conclusion While further developments are necessary to minimize chemical shift displacement and homogeneity of the transmit field, it is demonstrated that in vivo 1H MRSI at a field strength of 9.4 T is possible. However, further studies applying up-to-date techniques to overcome high-field specific problems are needed in order to assess the potential gain in sensitivity that may be offered by MRSI at 9.4 T.
      PubDate: 2015-06-01
       
  • Age-related differences in the response of leg muscle cross-sectional area
           and water diffusivity measures to a period of supine rest
    • Abstract: Object The object was to assess whether cross-sectional area (CSA) and water diffusion properties of leg muscles in young and older women change with increased time spent in supine rest. Materials and methods Healthy young (n = 9, aged 20–30 years) and older (n = 9, aged 65–75 years) women underwent MRI scanning of the right leg at baseline, 30 and 60 min of supine rest. Muscle CSA was derived from proton density images. Water diffusion properties [apparent diffusion coefficient (ADC) and fractional anisotropy (FA)] of the tibialis anterior and posterior, soleus, and medial and lateral heads of the gastrocnemius were derived from diffusion tensor imaging (DTI). Repeated measures ANOVAs and Bonferroni post hoc tests determined the effects of time and group on each muscle outcome. Results In both groups, muscle CSA and FA did not significantly change over time, whereas ADC significantly decreased. A greater decline at 30 min for young women was only observed for ADC in the medial gastrocnemius. Conclusion Regardless of age, ADC values decreased with fluid shift associated with time spent supine, whereas CSA and FA were not affected. For leg muscle assessment in young and older women, DTI scanning protocols should consider the amount of time spent in a recumbent position.
      PubDate: 2015-06-01
       
  • Recreational alcohol use induces changes in the concentrations of
           choline-containing compounds and total creatine in the brain: a 1 H MRS
           study of healthy subjects
    • Abstract: Objective It has previously been reported that even social alcohol consumption affects the magnetic resonance spectroscopy (MRS) signals of choline-containing compounds (tCho). The purpose of this study was to investigate whether the consumption of alcohol affects the concentrations of the metabolites tCho, N-acetylaspartate, creatine, or myo-inositol and/or their T 2 relaxation times. Materials and methods 1H MR spectra were obtained at 3 T from a frontal white matter voxel of 25 healthy subjects with social alcohol consumption (between 0 and 25.9 g/day). Absolute brain metabolite concentrations and T 2 relaxation times of metabolites were examined via MRS measurements at different echo times. Metabolite concentrations and their T 2 relaxation times were correlated with subjects’ alcohol consumption, controlling for age. Results We observed positive correlations of absolute tCho and phosphocreatine and creatine (tCr) concentrations with alcohol consumption but no correlation between any metabolite T 2 relaxation time and alcohol consumption. Conclusions This study shows that even social alcohol consumption affects the concentrations of tCho and tCr in cerebral white matter. Future studies assessing brain tCho and tCr levels should control for the confounding factor alcohol consumption.
      PubDate: 2015-05-16
       
  • Adaptive speech enhancement using directional microphone in a 4-T MRI
           scanner
    • Abstract: Objective To evaluate the effectiveness of the proposed adaptive speech enhancement (ASE) system for the magnetic resonance imaging (MRI) environment to reduce the loud scanning noise without disrupting the communication between patients and MRI operators. Materials and methods The developed system employed the idea of differential directional microphones for measuring and distinguishing the speech signals and MRI acoustic noises simultaneously. Two-stage adaptive filters with normalized least mean square algorithms were adopted. Two common MRI scanning sequences, echo planar imaging (EPI) and gradient echo multi-slice (GEMS), were tested using a 4T MRI scanner. Results A total of 1.4 and 3.3 dB speech enhancements quantified by the cepstral distance assessment were achieved for the speech signal contaminated with the EPI and GEMS noises, respectively. The speech signal was noticeably recovered, and a clear speech waveform was observed after treated with the ASE system. Furthermore, a non-adaptive post-processing approach [i.e. simply using spectral subtraction (SS) technique] was also adopted to process the abovementioned results. Additional reductions were achieved for the non-coherent MRI acoustic noises. Conclusion The results showed that combining the proposed ASE system along with the SS approach has a great potential for treating MRI acoustic noise to guarantee an effective communication from patient to MRI operators.
      PubDate: 2015-04-18
       
  • Physiological noise in human cerebellar fMRI
    • Abstract: Objectives To compare physiological noise contributions in cerebellar and cerebral regions of interest in high-resolution functional magnetic resonance imaging (fMRI) data acquired at 7T, to estimate the need for physiological noise removal in cerebellar fMRI. Materials and methods Signal fluctuations in high resolution (1 mm isotropic) 7T fMRI data were attributed to one of the following categories: task-induced BOLD changes, slow drift, signal changes correlated with the cardiac and respiratory cycles, signal changes related to the cardiac rate and respiratory volume per unit of time or other. \(R_{\text{adj}}^{2}\) values for all categories were compared across regions of interest. Results In this high-resolution data, signal fluctuations related to the phase of the cardiac cycle and cardiac rate were shown to be significant, but comparable between cerebellar and cerebral regions of interest. However, respiratory related signal fluctuations were increased in the cerebellar regions, with explained variances that were up to 80 % higher than for the primary motor cortex region. Conclusion Even at a millimetre spatial resolution, significant correlations with both cardiac and respiratory RETROICOR components were found in all healthy volunteer data. Therefore, physiological noise correction is highly likely to improve the temporal signal-to-noise ratio (SNR) for cerebellar fMRI at 7T, even at high spatial resolution.
      PubDate: 2015-04-18
       
  • Localized semi-LASER dynamic 31 P magnetic resonance spectroscopy of the
           soleus during and following exercise at 7 T
    • Abstract: Objectives This study demonstrates the applicability of semi-LASER localized dynamic 31P MRS to deeper lying areas of the exercising human soleus muscle (SOL). The effect of accurate localization and high temporal resolution on data specificity is investigated. Materials and methods To achieve high signal-to-noise ratio (SNR) at a temporal resolution of 6 s, a custom-built human calf coil array was used at 7T. The kinetics of phosphocreatine (PCr) and intracellular pH were quantified separately in SOL and gastrocnemius medialis (GM) muscle of nine volunteers, during rest, plantar flexion exercise, and recovery. Results The average SNR of PCr at rest was \(64\pm 15\) in SOL ( \(83\pm 12\) in GM). End exercise PCr depletion in SOL ( \(19\pm 9\)  %) was far lower than in GM ( \(74\pm 14\)  %). The pH in SOL increased rapidly and, in contrast to GM, remained elevated until the end of exercise. Conclusion 31P MRS in single-shots every 6 s localized in the deeper-lying SOL enabled quantification of PCr recovery times at low depletions and of fast pH changes, like the initial rise. Both high temporal resolution and accurate spatial localization improve specificity of Pi and, thus, pH quantification by avoiding multiple, and potentially indistinguishable sources for changing the Pi peak shape.
      PubDate: 2015-04-18
       
  • Characterization of metabolites determined by means of 1 H HR MAS NMR in
           intervertebral disc degeneration
    • Abstract: Object The objective of this study is the identification of metabolites by means of 1H high resolution magic angle spinning nuclear magnetic resonance (1H HR MAS NMR) spectroscopy and the evaluation of their applicability in distinguishing between healthy and degenerated disc tissues. Materials and methods Differences between the metabolic profiles of healthy and degenerated disc tissues were studied by means of 1H HR MAS NMR. Analysis was performed for 81 disc tissue samples (control samples n = 21, degenerated disc tissue samples n = 60). Twenty six metabolites (amino acids, carbohydrates, and alcohols) were identified and quantified. Results The results indicate that the metabolic profile of degenerated discs is characterized by the presence of 2-propanol and the absence of scyllo-inositol and taurine. The concentrations of 2-propanol and lactate increase with age. Conclusion PCA analysis of ex vivo 1H HR MAS NMR data revealed the occurrence of two groups: healthy and degenerative disc tissues. The effects of insufficient nutrient supply of discs, leading to their degeneration and back pain, are discussed.
      PubDate: 2015-04-01
       
  • Influence of blood/tissue differences in contrast agent relaxivity on
           tracer-based MR perfusion measurements
    • Abstract: Purpose Perfusion assessment by monitoring the transport of a tracer bolus depends critically on conversion of signal intensity into tracer concentration. Two main assumptions are generally applied for this conversion; (1) contrast agent relaxivity is identical in blood and tissue, (2) change in signal intensity depends only on the primary relaxation effect. The purpose of the study was to assess the validity and influence of these assumptions. Materials and methods Blood and cerebral tissue relaxivities r1, r2, and r2* for gadodiamide were measured in four pigs at 1.5 T. Gadolinium concentration was determined by inductively coupled plasma atomic emission spectroscopy. Influence of the relaxivities, secondary relaxation effects and choice of singular value decomposition (SVD) regularization threshold was studied by simulations. Results In vivo relaxivities relative to blood concentration [in s−1 mM−1 for blood, gray matter (GM), white matter (WM)] were for r1 (2.614 ± 1.061, 0.010 ± 0.001, 0.004 ± 0.002), r2 (5.088 ± 0.952, 0.091 ± 0.008, 0.059 ± 0.014), and r2* (13.292 ± 3.928, 1.696 ± 0.157, 0.910 ± 0.139). Although substantial, by a nonparametric test for paired samples, the differences were not statistically significant. The GM to WM blood volume ratio was estimated to 2.6 ± 0.9 by r1, 1.6 ± 0.3 by r2, and 1.9 ± 0.2 by r2*. Secondary relaxation was found to reduce the tissue blood flow, as did the SVD regularization threshold. Conclusion Contrast agent relaxivity is not identical in blood and tissue leading to substantial errors. Further errors are introduced by secondary relaxation effects and the SVD regularization.
      PubDate: 2015-04-01
       
  • An in vivo comparison of the DREAM sequence with current RF shim
           technology
    • Abstract: Object In the present study the performance of the dual refocusing echo acquisition mode (DREAM) B1 + mapping sequence is evaluated for RF shimming in the abdomen at 3 T and validated against existing RF shim technology. Materials and methods In vivo experiments were performed on 19 normal volunteers using a clinical 3 T dual channel MRI system. For each volunteer three different B1 + mapping techniques [DREAM, actual flip angle imaging (AFI) and saturated double angle method (SDAM)] were employed for RF shimming of the liver and to subsequently assess the quality of the obtained RF shim settings in terms of the achieved B1 + homogeneity and accuracy of the mean B1 +. Results DREAM-based B1 + calibration led to an average homogeneity improvement of 39.1 % (AFI = 38.7 %, SDAM = 38.1 %) and a mean B1 + of 90.9 % of the prescribed B1 + (AFI = 88.9 %, SDAM = 92.0 %). The duration of the B1 + calibration scan was reduced from 30 s (AFI) and 15 s (SDAM) to 2.5 s (DREAM). Conclusion DREAM accelerates RF shimming of the liver by an order of magnitude without compromising RF shimming performance.
      PubDate: 2015-04-01
       
  • Tracking metabolite dynamics in plants via indirect 13 C chemical shift
           imaging with an interleaved variable density acquisition weighted sampling
           pattern
    • Abstract: Objective Developing and evaluating an improved sampling pattern to track the dynamics of labeled substances in plants using indirect 13C chemical shift imaging. Materials and methods An algorithm to split an acquisition weighted sampling pattern into several undersampled sub-images is presented. The sampling patterns are used in CSI moving phantom experiments as well as in in vivo POCE-CSI experiments on barley stem and grain. Reconstruction is performed traditionally or by compressed sensing. Results The moving phantom experiments show that the sampling pattern can reduce motion artifacts at the cost of an increased overall noise. The in vivo experiments demonstrate the feasibility of extracting a time series from a single imaging experiment. Conclusion The sampling pattern is suitable for tracking the uptake of label substances into plant material. The use of compressed sensing allows an increased spatial and temporal resolution.
      PubDate: 2015-04-01
       
  • Artefacts in 1 H NMR-based metabolomic studies on cell cultures
    • Abstract: Object Metabolomic studies on cultured cells involve assays of cell extracts and culture medium, both of which are often performed by 1H NMR. Cell culture is nowadays performed in plastic dishes or flasks, and the extraction of metabolites from the cells is typically performed with perchloric acid, methanol–chloroform, or acetonitrile, ideally while the cells are still adherent to the culture dish. We conducted this investigation to identify contaminants from cell culture plasticware in metabolomic studies. Materials and methods Human diploid fibroblasts (IMR90) (n = 6), HeLa cells (n = 6), and transformed astrocytes with HIF-1 knockout (Astro-KO) (n = 6) were cultured. Cells were seeded in 100 mm Petri dishes with 10 ml complete growth medium (Dulbecco’s minimum essential medium) containing 10 % foetal bovine serum (FBS). Cell cultures were incubated at 37 °C in 5 % CO2 for approximately 3 days. Metabolites were extracted by use of a perchloric acid procedure. 1H NMR spectroscopy was used for metabolite analysis. “Null sample” (i.e. cell-free) experiments were performed by either rinsing dishes with medium or incubating the medium in Petri dishes from five different manufacturers for 72 h and then by performing a dummy “extraction” of each Petri dish by the perchloric acid, methanol–chloroform, or acetonitrile procedures. Principal components analysis was used for classification of samples and to determine the contaminants arising from plasticware. Results We found that even brief rinsing of cell culture plasticware with culture medium elutes artefactual chemicals, the 1H NMR signals of which could confound assays of acetate, succinate, and glycolate. Incubation of culture medium in cell-culture dishes for 72 h (as in a typical cell-culture experiment) followed by perchloric extraction in the dishes enhanced elution of the artefacts. These artefacts were present, but somewhat less pronounced, in the 1H NMR spectra of null samples extracted with methanol and acetonitrile. Ethanol, lactate, alanine, fructose, and fumarate signals that appear in the 1H NMR spectrum of the unused (pure) medium originate from FBS. Conclusions Plastic Petri dishes from five different manufacturers gave rise to essentially identical artefactual peaks. Use of a pH indicator to assist neutralisation introduced still more artefactual signals in the aromatic region, as well as methanol and ethanol signals. Methanol and acetonitrile extracts also contained artefacts arising from the plasticware, although the amounts were less than in the perchloric acid extracts. Finally, we provide suggestions for minimizing these artefacts. The best practice would be to run a “null” extraction with every batch of cellular metabolomics experiments to test for contamination and to provide a “background” spectrum.
      PubDate: 2015-04-01
       
  • Effect of acute hyperglycemia on moderately hypothermic GL261 mouse glioma
           monitored by T1-weighted DCE MRI
    • Abstract: Objective We sought to evaluate the effects of acute hyperglycemia induced by intraperitoneal injection of glucose (2.7 g/kg) on vascular delivery to GL261 mouse gliomas kept at moderate hypothermia (~30 °C). Materials and methods Seven GL261 glioma-bearing mice were studied by T1-weighted DCE MRI before and after an injection of glucose (n = 4) or saline (n = 3). Maximum relative contrast enhancement (RCE) and initial area under the enhancement curve (IAUC) were determined in each pixel. Results The mean tumor parameter values showed no significant changes after injecting either saline (RCE −5.9 ± 5.0 %; IAUC −3.7 ± 3.6 %) or glucose (RCE −1.6 ± 9.0 %; IAUC +0.6 ± 6.4 %). Pixel-by-pixel analysis revealed small post-injection changes in RCE and IAUC between the glucose and saline groups, all within 13 % range of their baseline values. Conclusion Perturbing the metabolism of GL261 tumors kept at moderate hypothermia with hyperglycemia did not induce significant changes in the permeability/perfusion of these tumors. This is relevant for future studies with this model since regional differences in glucose accumulation could thus reflect basal heterogeneities in vasculature and/or metabolism of GL261 tumors.
      PubDate: 2015-04-01
       
  • Development and performance of a 129-GHz dynamic nuclear polarizer in an
           ultra-wide bore superconducting magnet
    • Abstract: Objective We sought to build a dynamic nuclear polarization system for operation at 4.6 T (129 GHz) and evaluate its efficiency in terms of 13C polarization levels using free radicals that span a range of ESR linewidths. Materials and methods A liquid helium cryostat was placed in a 4.6 T superconducting magnet with a 150-mm warm bore diameter. A 129-GHz microwave source was used to irradiate 13C enriched samples. Temperatures close to 1 K were achieved using a vacuum pump with a 453-m3/h roots blower. A hyperpolarized 13C nuclear magnetic resonance (NMR) signal was detected using a saddle coil and a Varian VNMRS console operating at 49.208 MHz. Samples doped with free radicals BDPA (1,3-bisdiphenylene-2-phenylallyl), trityl OX063 (tris{8-carboxyl-2,2,6,6-benzo(1,2-d:4,5-d)-bis(1,3)dithiole-4-yl}methyl sodium salt), galvinoxyl ((2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy), 2,2-diphenylpicrylhydrazyl (DPPH) and 4-oxo-TEMPO (4-Oxo-2,2,6,6-tetramethyl-1-piperidinyloxy) were assayed. Microwave dynamic nuclear polarization (DNP) spectra and solid-state 13C polarization levels for these samples were determined. Results 13C polarization levels close to 50 % were achieved for [1-13C]pyruvic acid at 1.15 K using the narrow electron spin resonance (ESR) linewidth free radicals trityl OX063 and BDPA, while 10–20 % 13C polarizations were achieved using galvinoxyl, DPPH and 4-oxo-TEMPO. Conclusion At this field strength free radicals with smaller ESR linewidths are still superior for DNP of 13C as opposed to those with linewidths that exceed that of the 1H Larmor frequency.
      PubDate: 2015-04-01
       
 
 
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