Publications by authors named "Ralf Mekle"

34 Publications

Magnetic resonance imaging-based changes in vascular morphology and cerebral perfusion in subacute ischemic stroke.

J Cereb Blood Flow Metab 2021 Apr 17:271678X211010071. Epub 2021 Apr 17.

Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Center for Stroke Research Berlin, Berlin, Germany.

MRI-based vessel size imaging (VSI) allows for assessment of cerebral microvasculature and perfusion. This exploratory analysis of vessel size (VS) and density (Q; both assessed via VSI) in the subacute phase of ischemic stroke involved sixty-two patients from the BAPTISe cohort ('Biomarkers And Perfusion--Training-Induced changes after Stroke') nested within a randomized controlled trial (intervention: 4-week training relaxation). Relative VS, Q, cerebral blood volume (rCBV) and -flow (rCBF) were calculated for: ischemic lesion, perilesional tissue, and region corresponding to ischemic lesion on the contralateral side (mirrored lesion). Linear mixed-models detected significantly increased rVS and decreased rQ within the ischemic lesion compared to the mirrored lesion (coefficient[standard error]: 0.2[0.08] p = 0.03 and -1.0[0.3] p = 0.02, respectively); lesion rCBF and rCBV were also significantly reduced. Mixed-models did not identify time-to-MRI, nor training as modifying factors in terms of rVS or rQ up to two months post-stroke. Larger lesion VS was associated with larger lesion volumes (β 34, 95%CI 6.2-62; p = 0.02) and higher baseline NIHSS (β 3.0, 95%CI 0.49-5.3;p = 0.02), but was not predictive of six-month outcome. In summary, VSI can assess the cerebral microvasculature and tissue perfusion in the subacute phases of ischemic stroke, and may carry relevant prognostic value in terms of lesion volume and stroke severity.
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http://dx.doi.org/10.1177/0271678X211010071DOI Listing
April 2021

Contribution of macromolecules to brain H MR spectra: Experts' consensus recommendations.

NMR Biomed 2021 May 25;34(5):e4393. Epub 2020 Nov 25.

High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.

Proton MR spectra of the brain, especially those measured at short and intermediate echo times, contain signals from mobile macromolecules (MM). A description of the main MM is provided in this consensus paper. These broad peaks of MM underlie the narrower peaks of metabolites and often complicate their quantification but they also may have potential importance as biomarkers in specific diseases. Thus, separation of broad MM signals from low molecular weight metabolites enables accurate determination of metabolite concentrations and is of primary interest in many studies. Other studies attempt to understand the origin of the MM spectrum, to decompose it into individual spectral regions or peaks and to use the components of the MM spectrum as markers of various physiological or pathological conditions in biomedical research or clinical practice. The aim of this consensus paper is to provide an overview and some recommendations on how to handle the MM signals in different types of studies together with a list of open issues in the field, which are all summarized at the end of the paper.
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http://dx.doi.org/10.1002/nbm.4393DOI Listing
May 2021

T relaxation times of macromolecules and metabolites in the human brain at 9.4 T.

Magn Reson Med 2020 08 31;84(2):542-558. Epub 2020 Jan 31.

High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.

Purpose: Relaxation times can contribute to spectral assignment. In this study, effective T relaxation times ( ) of macromolecules are reported for gray and white matter-rich voxels in the human brain at 9.4 T. The of macromolecules are helpful to understand their behavior and the effect they have on metabolite quantification. Additionally, for absolute quantification of metabolites with magnetic resonance spectroscopy, appropriate T values of metabolites must be considered. The T relaxation times of metabolites are calculated after accounting for TE/sequence-specific macromolecular baselines.

Methods: Macromolecular and metabolite spectra for a series of TEs were acquired at 9.4 T using double inversion-recovery metabolite-cycled semi-LASER and metabolite-cycled semi-LASER, respectively. The T relaxation times were calculated by fitting the LCModel relative amplitudes of macromolecular peaks and metabolites to a mono-exponential decay across the TE series. Furthermore, absolute concentrations of metabolites were calculated using the estimated relaxation times and internal water as reference.

Results: The of macromolecules are reported, which range from 13 ms to 40 ms, whereas, for metabolites, they range from 40 ms to 110 ms. Both macromolecular and metabolite T relaxation times are observed to follow the decreasing trend, with increasing B . The linewidths of metabolite singlets can be fully attributed to T and B components. However, in addition to these components, macromolecule linewidths have contributions from J-coupling and overlapping resonances.

Conclusion: The T relaxation times of all macromolecular and metabolite peaks at 9.4 T in vivo are reported for the first time. Metabolite relaxation times were used to calculate the absolute metabolite concentrations.
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http://dx.doi.org/10.1002/mrm.28174DOI Listing
August 2020

Advanced single voxel H magnetic resonance spectroscopy techniques in humans: Experts' consensus recommendations.

NMR Biomed 2020 Jan 10:e4236. Epub 2020 Jan 10.

Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, USA.

Conventional proton MRS has been successfully utilized to noninvasively assess tissue biochemistry in conditions that result in large changes in metabolite levels. For more challenging applications, namely, in conditions which result in subtle metabolite changes, the limitations of vendor-provided MRS protocols are increasingly recognized, especially when used at high fields (≥3 T) where chemical shift displacement errors, B and B inhomogeneities and limitations in the transmit B field become prominent. To overcome the limitations of conventional MRS protocols at 3 and 7 T, the use of advanced MRS methodology, including pulse sequences and adjustment procedures, is recommended. Specifically, the semiadiabatic LASER sequence is recommended when T values of 25-30 ms are acceptable, and the semiadiabatic SPECIAL sequence is suggested as an alternative when shorter T values are critical. The magnetic field B homogeneity should be optimized and RF pulses should be calibrated for each voxel. Unsuppressed water signal should be acquired for eddy current correction and preferably also for metabolite quantification. Metabolite and water data should be saved in single shots to facilitate phase and frequency alignment and to exclude motion-corrupted shots. Final averaged spectra should be evaluated for SNR, linewidth, water suppression efficiency and the presence of unwanted coherences. Spectra that do not fit predefined quality criteria should be excluded from further analysis. Commercially available tools to acquire all data in consistent anatomical locations are recommended for voxel prescriptions, in particular in longitudinal studies. To enable the larger MRS community to take advantage of these advanced methods, a list of resources for these advanced protocols on the major clinical platforms is provided. Finally, a set of recommendations are provided for vendors to enable development of advanced MRS on standard platforms, including implementation of advanced localization sequences, tools for quality assurance on the scanner, and tools for prospective volume tracking and dynamic linear shim corrections.
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http://dx.doi.org/10.1002/nbm.4236DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7347431PMC
January 2020

Brain iron and metabolic abnormalities in C19orf12 mutation carriers: A 7.0 tesla MRI study in mitochondrial membrane protein-associated neurodegeneration.

Mov Disord 2020 01 13;35(1):142-150. Epub 2019 Sep 13.

Neurology Department, Ludwig Maximilians-University of Munich, Germany.

Background: Mitochondrial membrane protein-associated neurodegeneration is an autosomal-recessive disorder caused by C19orf12 mutations and characterized by iron deposits in the basal ganglia.

Objectives: The aim of this study was to quantify iron concentrations in deep gray matter structures using quantitative susceptibility mapping MRI and to characterize metabolic abnormalities in the pyramidal pathway using H MR spectroscopy in clinically manifesting membrane protein-associated neurodegeneration patients and asymptomatic C19orf12 gene mutation heterozygous carriers.

Methods: We present data of 4 clinically affected membrane protein-associated neurodegeneration patients (mean age: 21.0 ± 2.9 years) and 9 heterozygous gene mutation carriers (mean age: 50.4 ± 9.8 years), compared to age-matched healthy controls. MRI assessments were performed on a 7.0 Tesla whole-body system, consisting of whole-brain gradient-echo scans and short echo time, single-volume MR spectroscopy in the white matter of the precentral/postcentral gyrus. Quantitative susceptibility mapping, a surrogate marker for iron concentration, was performed using a state-of-the-art multiscale dipole inversion approach with focus on the globus pallidus, thalamus, putamen, caudate nucleus, and SN.

Results And Conclusion: In membrane protein-associated neurodegeneration patients, magnetic susceptibilities were 2 to 3 times higher in the globus pallidus (P = 0.02) and SN (P = 0.02) compared to controls. In addition, significantly higher magnetic susceptibility was observed in the caudate nucleus (P = 0.02). Non-manifesting heterozygous mutation carriers exhibited significantly increased magnetic susceptibility (relative to controls) in the putamen (P = 0.003) and caudate nucleus (P = 0.001), which may be an endophenotypic marker of genetic heterozygosity. MR spectroscopy revealed significantly increased levels of glutamate, taurine, and the combined concentration of glutamate and glutamine in membrane protein-associated neurodegeneration, which may be a correlate of corticospinal pathway dysfunction frequently observed in membrane protein-associated neurodegeneration patients. © 2019 International Parkinson and Movement Disorder Society.
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http://dx.doi.org/10.1002/mds.27827DOI Listing
January 2020

Glutamate Concentration in the Superior Temporal Sulcus Relates to Neuroticism in Schizophrenia.

Front Psychol 2018 7;9:578. Epub 2018 May 7.

Department of Psychiatry and Psychotherapy, St. Hedwig Hospital, Charité - Universitätsmedizin Berlin, Berlin, Germany.

Clinical studies suggest aberrant neurotransmitter concentrations in the brains of patients with schizophrenia (SCZ). Numerous studies have indicated deviant glutamate concentrations in SCZ, although the findings are inconsistent. Moreover, alterations in glutamate concentrations could be linked to personality traits in SCZ. Here, we examined the relationships between personality dimensions and glutamate concentrations in a voxel encompassing the occipital cortex (OCC) and another voxel encompassing the left superior temporal sulcus (STS). We used proton magnetic resonance spectroscopy to examine glutamate concentrations in the OCC and the STS in 19 SCZ and 21 non-psychiatric healthy control (HC) participants. Personality dimensions neuroticism, extraversion, openness, agreeableness and conscientiousness were assessed using the NEO-FFI questionnaire. SCZ compared to HC showed higher glutamate concentrations in the STS, reduced extraversion scores, and enhanced neuroticism scores. No group differences were observed for the other personality traits and for glutamate concentrations in the OCC. For the SCZ group, glutamate concentrations in STS were negatively correlated with the neuroticism scores [ = -0.537, = 0.018] but this was not found in HC [(19) = 0.011, = 0.962]. No other significant correlations were found. Our study showed an inverse relationship between glutamate concentrations in the STS and neuroticism scores in SCZ. Elevated glutamate in the STS might serve as a compensatory mechanism that enables patients with enhanced concentrations to control and prevent the expression of neuroticism.
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http://dx.doi.org/10.3389/fpsyg.2018.00578DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5949567PMC
May 2018

In vivo characterization of the downfield part of H MR spectra of human brain at 9.4 T: Magnetization exchange with water and relation to conventionally determined metabolite content.

Magn Reson Med 2018 06 16;79(6):2863-2873. Epub 2017 Oct 16.

Department of Radiology, Neuroradiology, and Nuclear Medicine, University of Bern, Bern, Switzerland.

Purpose: To perform exchange-rate measurements on the in vivo human brain downfield spectrum (5-10 ppm) at 9.4 T and to compare the variation in concentrations of the downfield resonances and of known upfield metabolites to determine potential peak labels.

Methods: Non-water-suppressed metabolite cycling was used in combination with an inversion transfer technique in two brain locations in healthy volunteers to measure the exchange rates and T values of exchanging peaks. Spectra were fitted with a heuristic model of a series of 13 or 14 Voigt lines, and a Bloch-McConnell model was used to fit the exchange rate curves. Concentrations from non-water-inverted spectra upfield and downfield were compared.

Results: Mean T values ranged from 0.40 to 0.77 s, and exchange rates from 0.74 to 13.8 s . There were no significant correlations between downfield and upfield concentrations, except for N-acetylaspartate, with a correlation coefficient of 0.63 and P < 0.01.

Conclusions: Using ultrahigh field allowed improved separation of peaks in the 8.2 to 8.5 ppm amide proton region, and the exchange rates of multiple downfield resonances including the 5.8-ppm peak, previously tentatively assigned to urea, were measured in vivo in human brain. Downfield peaks consisted of overlapping components, and largely missing correlations between upfield and downfield resonances-although not conclusive-indicate limited contributions from metabolites present upfield to the downfield spectrum. Magn Reson Med 79:2863-2873, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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http://dx.doi.org/10.1002/mrm.26968DOI Listing
June 2018

Metabolite-cycled STEAM and semi-LASER localization for MR spectroscopy of the human brain at 9.4T.

Magn Reson Med 2018 04 15;79(4):1841-1850. Epub 2017 Aug 15.

High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.

Purpose: Metabolite cycling (MC) is an MRS technique for the simultaneous acquisition of water and metabolite spectra that avoids chemical exchange saturation transfer effects and for which water may serve as a reference signal or contain additional information in functional or diffusion studies. Here, MC was developed for human investigations at ultrahigh field.

Methods: MC-STEAM and MC-semi-LASER are introduced at 9.4T with an optimized inversion pulse and elaborate coil setup. Experimental and simulation results are given for the implementation of adiabatic inversion pulses for MC. The two techniques are compared, and the effect of frequency and phase correction based on the MC water spectra is evaluated. Finally, absolute quantification of metabolites is performed.

Results: The proposed coil configuration results in a maximum B1 + of 48 μΤ in a voxel within the occipital lobe. Frequency and phase correction of single acquisitions improve signal-to-noise ratio (SNR) and linewidth, leading to high-resolution spectra. The improvement of SNR of N-acetylaspartate (SNR ) for frequency aligned data, acquired with MC-STEAM and MC-semi-LASER, are 37% and 30%, respectively (P < 0.05). Moreover, a doubling of the SNR for MC-semi-LASER in comparison with MC-STEAM is observed (P < 0.05). Concentration levels for 18 metabolites from the human occipital lobe are reported, as acquired with both MC-STEAM and MC-semi-LASER.

Conclusion: This work introduces a novel methodology for single-voxel MRS on a 9.4T whole-body scanner and highlights the advantages of semi-LASER compared to STEAM in terms of excitation profile. In comparison with MC-STEAM, MC-semi-LASER yields spectra with higher SNR. Magn Reson Med 79:1841-1850, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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http://dx.doi.org/10.1002/mrm.26873DOI Listing
April 2018

Effect of age and the APOE gene on metabolite concentrations in the posterior cingulate cortex.

Neuroimage 2017 05 18;152:509-516. Epub 2017 Mar 18.

Department of Psychiatry, University of Oxford, Oxford OX3 7JX, United Kingdom.

Proton magnetic resonance spectroscopy (H-MRS) has provided valuable information about the neurochemical profile of Alzheimer's disease (AD). However, its clinical utility has been limited in part by the lack of consistent information on how metabolite concentrations vary in the normal aging brain and in carriers of apolipoprotein E (APOE) ε4, an established risk gene for AD. We quantified metabolites within an 8cm voxel within the posterior cingulate cortex (PCC)/precuneus in 30 younger (20-40 years) and 151 cognitively healthy older individuals (60-85 years). All H-MRS scans were performed at 3T using the short-echo SPECIAL sequence and analyzed with LCModel. The effect of APOE was assessed in a sub-set of 130 volunteers. Older participants had significantly higher myo-inositol and creatine, and significantly lower glutathione and glutamate than younger participants. There was no significant effect of APOE or an interaction between APOE and age on the metabolite profile. Our data suggest that creatine, a commonly used reference metabolite in H-MRS studies, does not remain stable across adulthood within this region and therefore may not be a suitable reference in studies involving a broad age-range. Increases in creatine and myo-inositol may reflect age-related glial proliferation; decreases in glutamate and glutathione suggest a decline in synaptic and antioxidant efficiency. Our findings inform longitudinal clinical studies by characterizing age-related metabolite changes in a non-clinical sample.
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http://dx.doi.org/10.1016/j.neuroimage.2017.03.031DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5440729PMC
May 2017

Towards a neurochemical profile of the amygdala using short-TE H magnetic resonance spectroscopy at 3 T.

NMR Biomed 2017 May 6;30(5). Epub 2017 Jan 6.

Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.

The amygdala plays a key role in emotional learning and in the processing of emotions. As disturbed amygdala function has been linked to several psychiatric conditions, a knowledge of its biochemistry, especially neurotransmitter levels, is highly desirable. The spin echo full intensity acquired localized (SPECIAL) sequence, together with a transmit/receive coil, was used to perform very short-TE magnetic resonance spectroscopy at 3 T to determine the neurochemical profile in a spectroscopic voxel containing the amygdala in 21 healthy adult subjects. For spectral analysis, advanced data processing was applied in combination with a macromolecule baseline measured in the anterior cingulate for spectral fitting. The concentrations of total N-acetylaspartate, total creatine, total choline, myo-inositol and, for the first time, glutamate were quantified with high reliability (uncertainties far below 10%). For these metabolites, the inter-individual variability, reflected by the relative standard deviations for the cohort studied, varied between 12% (glutamate) and 22% (myo-inositol). Glutamine and glutathione could also be determined, albeit with lower precision. Retest on four subjects showed good reproducibility. The devised method allows the determination of metabolite concentrations in the amygdala voxel, including glutamate, provides an estimation of glutamine and glutathione, and may help in the study of disturbed amygdala metabolism in pathologies such as anxiety disorder, autism and major depression.
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http://dx.doi.org/10.1002/nbm.3685DOI Listing
May 2017

Detection of metabolite changes in response to a varying visual stimulation paradigm using short-TE H MRS at 7 T.

NMR Biomed 2017 Feb 23;30(2). Epub 2016 Dec 23.

Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, and Berlin, Germany.

The two-fold benefit of H magnetic resonance spectroscopy (MRS) at high B fields - enhanced sensitivity and increased spectral dispersion - has been used previously to study dynamic changes in metabolite concentrations in the human brain in response to visual stimulation. In these studies, a strong visual on/off stimulus was combined with MRS data acquisition in a voxel location in the occipital cortex determined by an initial functional magnetic resonance imaging experiment. However, 1) to exclude the possibility of systemic effects (heartbeat, blood flow, etc.), which tend to be different for on/off conditions, a modified stimulation condition not affecting the target voxel needs to be employed, and 2) to assess important neurotransmitters of low concentration, in particular γ-aminobutyric acid (GABA), it may be advantageous to analyze steady-state, rather than dynamic, conditions. Thus, the aim of this study was to use short-TE H MRS methodology at 7 T to detect differences in steady-state metabolite levels in response to a varying stimulation paradigm in the human visual cortex. The two different stimulation conditions were termed voxel and control activation. Localized MR spectra were acquired using the SPECIAL (spin-echo full-intensity acquired localized) sequence. Data were analyzed using LCModel. Fifteen individual metabolites were reliably quantified. On comparison of steady-state concentrations for voxel versus control activation, a decrease in GABA of 0.05 mmol/L (5%) and an increase in lactate of 0.04 mmol/L (7%) were found to be the only significant effects. The observed reduction in GABA can be interpreted as reduced neuronal inhibition during voxel activation, whereas the increase in lactate hints at an intensification of anaerobic glycolysis. Differences from previous studies, notably the absence of any changes in glutamate, are attributed to the modified experimental conditions. This study demonstrates that the use of advanced H MRS methodology at 7 T allows the detection of subtle changes in metabolite concentrations involved in neuronal activation and inhibition.
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http://dx.doi.org/10.1002/nbm.3672DOI Listing
February 2017

No Effect of Anodal Transcranial Direct Current Stimulation on Gamma-Aminobutyric Acid Levels in Patients with Recurrent Mild Traumatic Brain Injury.

J Neurotrauma 2017 01 16;34(2):281-290. Epub 2016 Aug 16.

1 Department of Neurology, Charité-University Hospital , Berlin, Germany .

In patients in the chronic phase after recurrent mild traumatic brain injury (mTBI), alterations in gamma-aminobutyric acid (GABA) concentration and receptor activity have been reported, possibly mediating subtle but persistent cognitive deficits and increased rate of dementia in older age. We evaluated whether anodal transcranial direct current stimulation (atDCS) over the primary motor cortex reduces GABA concentration and GABA receptor activity in patients with recurrent mTBI. Seventeen patients (mean age 25, two women) in the chronic phase after recurrent mTBI and 22 healthy control subjects (mean age 26, two women) were included. All participants received comprehensive cognitive testing and detailed questionnaires on post-concussive symptoms at baseline. Subsequently, they participated in four experimental sessions, consisting of either magnetic resonance spectroscopy (MRS)/atDCS/MRS, transcranial magnetic stimulation (TMS)/atDCS/TMS, MRS/sham/MRS, or TMS/sham/TMS to determine GABA concentration (from MRS) and GABA receptor activity (from TMS) after atDCS and after sham stimulation. Patients with mTBI scored significantly lower on verbal fluency tasks compared with healthy control subjects. GABA concentration at baseline was associated with the number of mTBI, although no group differences in GABA concentration and GABA receptor activity were found. Moreover, no effects of atDCS on GABA concentration and receptor activity were seen in patients with mTBI or healthy control subjects. GABA concentration may increase with the number of mTBI, but atDCS did not modulate GABA concentration and receptor activity, as has been reported previously. Specifics of experimental design and analysis, but also characteristics of the respective samples, may account for these differential findings, and should be addressed in future larger studies.
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http://dx.doi.org/10.1089/neu.2016.4399DOI Listing
January 2017

A new sequence for shaped voxel spectroscopy in the human brain using 2D spatially selective excitation and parallel transmission.

NMR Biomed 2016 08 2;29(8):1028-37. Epub 2016 Jun 2.

Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.

Spatially selective excitation in two dimensions (2D-SSE) utilizing parallel transmission was applied as a means to acquire signal from voxels adapted to the anatomy of interest for in vivo (1) H MR spectroscopy. A novel method to select spectroscopy voxels with arbitrary shapes in two dimensions was investigated. An on-off scheme with an adiabatic slice selective inversion pulse preceding a 2D-SSE pulse together with a segmented inward spiral excitation k-space trajectory enabled rapid free induction decay acquisitions. Performance of the sequence was evaluated in simulations, phantom experiments, and in vivo measurements at 3 T. High spatial fidelity of the excitation profile was achieved for different target shapes and with little off-resonance deterioration. Metabolite concentrations in human brain determined with the new sequence were quantified with Cramér-Rao lower bounds less than 20%. They were in the physiological range and did not deviate systematically from results acquired with a conventional SPECIAL sequence. In conclusion, a new approach for shaped voxel MRS in the human brain is presented, which complements existing sequences. Simulations show that 2D-SSE pulses yield reduced chemical shift artifact when compared with conventional localization methods. Copyright © 2016 John Wiley & Sons, Ltd.
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http://dx.doi.org/10.1002/nbm.3558DOI Listing
August 2016

Genetic Polymorphism Associated Prefrontal Glutathione and Its Coupling With Brain Glutamate and Peripheral Redox Status in Early Psychosis.

Schizophr Bull 2016 09 11;42(5):1185-96. Epub 2016 Apr 11.

Unit for Research in Schizophrenia, Center for Psychiatric Neuroscience, Department of Psychiatry, Lausanne University Hospital (CHUV), Lausanne, Switzerland;

Background: Oxidative stress and glutathione (GSH) metabolism dysregulation has been implicated in the pathophysiology of schizophrenia. GAG-trinucleotide repeat (TNR) polymorphisms in the glutamate-cysteine ligase catalytic gene (GCLC), the rate-limiting enzyme for GSH synthesis, are associated with schizophrenia. In addition, GSH may serve as a reserve pool for neuronal glutamate (Glu) through the γ-glutamyl cycle. The aim of this study is to investigate brain [GSH] and its association with GCLC polymorphism, peripheral redox indices and brain Glu.

Methods: Magnetic resonance spectroscopy was used to measure [GSH] and [Glu] in the medial prefrontal cortex (mPFC) of 25 early-psychosis patients and 33 controls. GCLC polymorphism was genotyped, glutathione peroxidases (GPx) and glutathione reductase (GR) activities were determined in blood cells.

Results: Significantly lower [GSHmPFC] in GCLC high-risk genotype subjects were revealed as compared to low-risk genotype subjects independent of disease status. In male subjects, [GSHmPFC] and blood GPx activities correlate positively in controls (P = .021), but negatively in patients (P = .039). In GCLC low-risk genotypes, [GlumPFC] are lower in patients, while it is not the case for high-risk genotypes.

Conclusions: GCLC high-risk genotypes are associated with low [GSHmPFC], highlighting that GCLC polymorphisms should be considered in pathology studies of cerebral GSH. Low brain GSH levels are related to low peripheral oxidation status in controls but with high oxidation status in patients, pointing to a dysregulated GSH homeostasis in early psychosis patients. GCLC polymorphisms and disease associated correlations between brain GSH and Glu levels may allow patients stratification.
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http://dx.doi.org/10.1093/schbul/sbw038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988744PMC
September 2016

7T MRI in natalizumab-associated PML and ongoing MS disease activity: A case study.

Neurol Neuroimmunol Neuroinflamm 2015 Dec 29;2(6):e171. Epub 2015 Oct 29.

Department of Neurology (T.S., J.O., M.K., I.S., A.K., P.W., P.K., J.F.), Asklepios Fachklinikum Teupitz; NeuroCure Clinical Research Center (T.S., F.P., J.W.), Experimental and Clinical Research Center (T.N., F.P.), Department of Neurology (F.P.), and Clinical and Experimental Multiple Sclerosis Research Center (F.P.), Charité-Universitätsmedizin Berlin; Medical Physics (R.M.), Physikalisch-Technische Bundesanstalt; Berlin Ultrahigh Field Facility (T.N., J.W.) and Experimental and Clinical Research Center (T.N., F.P.), Max Delbrück Center for Molecular Medicine, Berlin; Institute of Neuroradiology (J.W.), Universitätsmedizin Göttingen, Germany; and MIAC AG (J.W.), Basel, Switzerland.

Objective: To assess the ability of ultra-high-field MRI to distinguish early progressive multifocal leukoencephalopathy (PML) from multiple sclerosis (MS) lesions in a rare case of simultaneous presentation of natalizumab-associated PML and ongoing MS activity.

Methods: Advanced neuroimaging including 1.5T, 3T, and 7T MRI with a spatial resolution of up to 0.08 mm(3) was performed.

Results: 7T MRI differentiated between PML-related and MS-related brain damage in vivo. Ring-enhancing MS plaques displayed a central vein, whereas confluent PML lesions were preceded by punctate or milky way-like T2 lesions.

Conclusions: Given the importance of early diagnosis of treatment-associated PML, future systematic studies are warranted to assess the value of highly resolving MRI in differentiating between early PML- and MS-induced brain parenchymal lesions.
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http://dx.doi.org/10.1212/NXI.0000000000000171DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630686PMC
December 2015

GABA concentration in superior temporal sulcus predicts gamma power and perception in the sound-induced flash illusion.

Neuroimage 2016 Jan 4;125:724-730. Epub 2015 Nov 4.

Department of Psychiatry and Psychotherapy, Charité - Universitätsmedizin Berlin, Große Hamburger Straße 5-11, 10115 Berlin, Germany. Electronic address:

In everyday life we are confronted with inputs of multisensory stimuli that need to be integrated across our senses. Individuals vary considerably in how they integrate multisensory information, yet the neurochemical foundations underlying this variability are not well understood. Neural oscillations, especially in the gamma band (>30Hz) play an important role in multisensory processing. Furthermore, gamma-aminobutyric acid (GABA) neurotransmission contributes to the generation of gamma band oscillations (GBO), which can be sustained by activation of metabotropic glutamate receptors. Hence, differences in the GABA and glutamate systems might contribute to individual differences in multisensory processing. In this combined magnetic resonance spectroscopy and electroencephalography study, we examined the relationships between GABA and glutamate concentrations in the superior temporal sulcus (STS), source localized GBO, and illusion rate in the sound-induced flash illusion (SIFI). In 39 human volunteers we found robust relationships between GABA concentration, GBO power, and the SIFI perception rate (r-values=0.44 to 0.53). The correlation between GBO power and SIFI perception rate was about twofold higher when the modulating influence of the GABA level was included in the analysis as compared to when it was excluded. No significant effects were obtained for glutamate concentration. Our study suggests that the GABA level shapes individual differences in audiovisual perception through its modulating influence on GBO. GABA neurotransmission could be a promising target for treatment interventions of multisensory processing deficits in clinical populations, such as schizophrenia or autism.
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http://dx.doi.org/10.1016/j.neuroimage.2015.10.087DOI Listing
January 2016

Neurotransmitter changes during interference task in anterior cingulate cortex: evidence from fMRI-guided functional MRS at 3 T.

Brain Struct Funct 2016 06 15;221(5):2541-51. Epub 2015 May 15.

St. Hedwig-Krankenhaus, Clinic for Psychiatry and Psychotherapy, Charité University Medicine, Große Hamburger Straße 5-11, 10115, Berlin, Germany.

Neural activity as indirectly observed in blood oxygenation level-dependent (BOLD) response is thought to reflect changes in neurotransmitter flux. In this study, we used fMRI-guided functional magnetic resonance spectroscopy (MRS) to measure metabolite/BOLD associations during a cognitive task at 3 T. GABA and glutamate concentration in anterior cingulate cortex (ACC) were determined by means of MRS using the SPECIAL pulse sequence before, during and after the performance of a manual Stroop task. MRS voxel positions were centred around individuals' BOLD activity during Stroop performance. Levels of GABA and glutamate showed inverted U-shape patterns across measurement time points (before, during, and after task), glutamine increased linearly and total creatine did not change. The GABA increase during task performance was associated with ACC BOLD signal changes in both congruent and incongruent Stroop conditions. Using an fMRI-guided MRS approach, an association between induced inhibitory neurotransmitter increase and BOLD changes was observed. The proposed procedure might allow the in vivo investigation of normal and dysfunctional associations between neurotransmitters and BOLD signal crucial for cerebral functioning.
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http://dx.doi.org/10.1007/s00429-015-1057-0DOI Listing
June 2016

Eight-channel transceiver RF coil array tailored for ¹H/¹⁹F MR of the human knee and fluorinated drugs at 7.0 T.

NMR Biomed 2015 Jun 27;28(6):726-37. Epub 2015 Apr 27.

Berlin Ultrahigh Field Facility (BUFF), Max Delbrück Center for Molecular Medicine, Berlin, Germany.

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1)H/(19)F MR of the human knee at 7.0 T following application of (19)F-containing drugs. The (1)H/(19)F RF coil array includes a posterior module with two (1)H loop elements and two anterior modules, each consisting of one (1)H and two (19)F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19)F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) – a (19)F-containing non-steroidal anti-inflammatory drug – to determine T1 and T2 and to study the (19)F signal-to-dose relationship. The suitability of the proposed approach for (1)H/(19)F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. Q(L)/Q(U) was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1)H/(19)F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19)F-containing medicinal compounds in vivo.
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http://dx.doi.org/10.1002/nbm.3300DOI Listing
June 2015

Simultaneous dual contrast weighting using double echo rapid acquisition with relaxation enhancement (RARE) imaging.

Magn Reson Med 2014 Dec 17;72(6):1590-8. Epub 2013 Dec 17.

Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany.

Purpose: This work proposes a dual contrast rapid acquisition with relaxation enhancement (RARE) variant (2in1-RARE), which provides simultaneous proton density (PD) and T2 * contrast in a single acquisition.

Theory And Methods: The underlying concept of 2in1-RARE is the strict separation of spin echoes and stimulated echoes. This approach offers independent weighting of spin echoes and stimulated echoes. 2in1-RARE was evaluated in phantoms including signal-to-noise ratio (SNR) and point spread function assessment. 2in1-RARE was benchmarked versus coherent RARE and a split-echo RARE variant. The applicability of 2in1-RARE for brain imaging was demonstrated in a small cohort of healthy subjects (n = 10) and, exemplary, a multiple sclerosis patient at 3 Tesla as a precursor to a broader clinical study.

Results: 2in1-RARE enables the simultaneous acquisition of dual contrast weighted images without any significant image degradation and without sacrificing SNR versus split-echo RARE. This translates into a factor of two speed gain over multi-contrast, sequential split-echo RARE. A 15% broadening of the point spread function was observed in 2in1-RARE. T1 relaxation effects during the mixing time can be neglected for brain tissue.

Conclusion: 2in1-RARE offers simultaneous acquisition of images of anatomical (PD) and functional (T2 *) contrast. It presents an alternative to address scan time constraints frequently encountered during sequential acquisition of T2 * or PD-weighted RARE.
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http://dx.doi.org/10.1002/mrm.25066DOI Listing
December 2014

Unedited in vivo detection and quantification of γ-aminobutyric acid in the occipital cortex using short-TE MRS at 3 T.

NMR Biomed 2013 Nov 22;26(11):1353-62. Epub 2013 May 22.

Douglas Mental Health University Institute and Department of Psychiatry, McGill University, Montreal, QC, Canada; Department of Psychiatry, University of Oxford, Oxford, UK; FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.

Short-TE MRS has been proposed recently as a method for the in vivo detection and quantification of γ-aminobutyric acid (GABA) in the human brain at 3 T. In this study, we investigated the accuracy and reproducibility of short-TE MRS measurements of GABA at 3 T using both simulations and experiments. LCModel analysis was performed on a large number of simulated spectra with known metabolite input concentrations. Simulated spectra were generated using a range of spectral linewidths and signal-to-noise ratios to investigate the effect of varying experimental conditions, and analyses were performed using two different baseline models to investigate the effect of an inaccurate baseline model on GABA quantification. The results of these analyses indicated that, under experimental conditions corresponding to those typically observed in the occipital cortex, GABA concentration estimates are reproducible (mean reproducibility error, <20%), even when an incorrect baseline model is used. However, simulations indicate that the accuracy of GABA concentration estimates depends strongly on the experimental conditions (linewidth and signal-to-noise ratio). In addition to simulations, in vivo GABA measurements were performed using both spectral editing and short-TE MRS in the occipital cortex of 14 healthy volunteers. Short-TE MRS measurements of GABA exhibited a significant positive correlation with edited GABA measurements (R = 0.58, p < 0.05), suggesting that short-TE measurements of GABA correspond well with measurements made using spectral editing techniques. Finally, within-session reproducibility was assessed in the same 14 subjects using four consecutive short-TE GABA measurements in the occipital cortex. Across all subjects, the average coefficient of variation of these four GABA measurements was 8.7 ± 4.9%. This study demonstrates that, under some experimental conditions, short-TE MRS can be employed for the reproducible detection of GABA at 3 T, but that the technique should be used with caution, as the results are dependent on the experimental conditions.
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http://dx.doi.org/10.1002/nbm.2960DOI Listing
November 2013

Net increase of lactate and glutamate concentration in activated human visual cortex detected with magnetic resonance spectroscopy at 7 tesla.

J Neurosci Res 2013 Aug 1;91(8):1076-83. Epub 2013 Feb 1.

Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland.

After the landmark studies reporting changes in the cerebral metabolic rate of glucose (CMRGlc ) in excess of those in oxygen (CMRO2 ) during physiological stimulation, several studies have examined the fate of the extra carbon taken up by the brain, reporting a wide range of changes in brain lactate from 20% to 250%. The present study reports functional magnetic resonance spectroscopy measurements at 7 Tesla using the enhanced sensitivity to study a small cohort (n = 6). Small increases in lactate (19% ± 4%, P < 0.05) and glutamate (4% ± 1%, P < 0.001) were seen within the first 2 min of activation. With the exception of glucose (12% ± 5%, P < 0.001), no other metabolite concentration changes beyond experimental error were significantly observed. Therefore, the present study confirms that lactate and glutamate changes during physiological stimulation are small (i.e. below 20%) and shows that the increased sensitivity allows reproduction of previous results with fewer subjects. In addition, the initial rate of glutamate and lactate concentration increases implies an increase in CMRO2 that is slightly below that of CMRGlc during the first 1-2 min of activation.
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http://dx.doi.org/10.1002/jnr.23194DOI Listing
August 2013

Magnetization transfer-based 3D visualization of foot peripheral nerves.

J Magn Reson Imaging 2013 May 28;37(5):1234-7. Epub 2012 Sep 28.

Laboratory of Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Purpose: To investigate magnetization transfer (MT) effects as a new source of contrast for imaging and tracking of peripheral foot nerves.

Materials And Methods: Two sets of 3D spoiled gradient-echo images acquired with and without a saturation pulse were used to generate MT ratio (MTR) maps of 260 μm in-plane resolution for eight volunteers at 3T. Scan parameters were adjusted to minimize signal loss due to T2 dephasing, and a dedicated coil was used to improve the inherently low signal-to-noise ratio of small voxels. Resulting MTR values in foot nerves were compared with those in surrounding muscle tissue.

Results: Average MTR values for muscle (45.5 ± 1.4%) and nerve (21.4 ± 3.1%) were significantly different (P < 0.0001). In general, the difference in MTR values was sufficiently large to allow for intensity-based segmentation and tracking of foot nerves in individual subjects. This procedure was termed MT-based 3D visualization.

Conclusion: The MTR serves as a new source of contrast for imaging of peripheral foot nerves and provides a means for high spatial resolution tracking of these structures. The proposed methodology is directly applicable on standard clinical MR scanners and could be applied to systemic pathologies, such as diabetes.
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http://dx.doi.org/10.1002/jmri.23828DOI Listing
May 2013

Magnetic resonance imaging of peripheral nerves: differences in magnetization transfer.

Muscle Nerve 2012 Jan;45(1):13-7

Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Station 6, Lausanne CH 1015, Switzerland.

Introduction: Magnetic resonance imaging (MRI) is an excellent imaging modality for soft tissues. Magnetization transfer (MT) imaging is an MRI technique that is sensitive to the bound protons of macromolecules and therefore can aid in the assessment of nerve damage.

Methods: Measurements of the MT ratio (MTR), which provides an index of the MT effects in tissues, were performed in the wrist and foot of 5 volunteers.

Results: The MTR of foot (interdigital) nerves (22.2 ± 2.1%) was smaller than that of the median nerve (41.1 ± 1.4%). No difference was observed between MTR in muscles adjacent to foot nerves (46.0 ± 1.5%) and muscles adjacent to the median nerve (44.2 ± 1.9%).

Conclusions: In this study we demonstrate the feasibility of measuring the MTR of foot nerves. The difference of MTR between median and foot nerves indicates a difference in structure/composition. The MTR of peripheral nerves may serve as a biomarker of nerve damage, collagen integrity, and demyelination.
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http://dx.doi.org/10.1002/mus.22240DOI Listing
January 2012

Echo-time independent signal modulations for strongly coupled systems in triple echo localization schemes: an extension of S-PRESS editing.

J Magn Reson 2010 Mar 29;203(1):108-12. Epub 2009 Dec 29.

Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.

The double spin-echo point resolved spectroscopy sequence (PRESS) is a widely used method and standard in clinical MR spectroscopy. Existence of important J-modulations at constant echo times, depending on the temporal delays between the rf-pulses, have been demonstrated recently for strongly coupled spin systems and were exploited for difference editing, removing singlets from the spectrum (strong-coupling PRESS, S-PRESS). A drawback of this method for in vivo applications is that large signal modulations needed for difference editing occur only at relatively long echo times. In this work we demonstrate that, by simply adding a third refocusing pulse (3S-PRESS), difference editing becomes possible at substantially shorter echo times while, as applied to citrate, more favorable lineshapes can be obtained. For the example of an AB system an analytical description of the MR signal, obtained with this triple refocusing sequence (3S-PRESS), is provided.
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http://dx.doi.org/10.1016/j.jmr.2009.12.006DOI Listing
March 2010

Eddy current effects on a clinical 7T-68 cm bore scanner.

MAGMA 2010 Feb 9;23(1):39-43. Epub 2009 Dec 9.

Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.

Introduction: Eddy currents induced by switching of magnetic field gradients can lead to distortions in short echo-time spectroscopy or diffusion weighted imaging. In small bore magnets, such as human head-only systems, minimization of eddy current effects is more demanding because of the proximity of the gradient coil to conducting structures.

Methods: In the present study, the eddy current behavior achievable on a recently installed 7 tesla-68 cm bore head-only magnet was characterized.

Results: Residual effects after compensation were shown to be on the same order of magnitude as those measured on two whole body systems (3 and 4.7 T), while using two to three fold increased gradient slewrates.
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http://dx.doi.org/10.1007/s10334-009-0192-0DOI Listing
February 2010

Initial in vivo studies with a polymer-based MR-compatible guide wire.

J Vasc Interv Radiol 2009 Oct 21;20(10):1384-9. Epub 2009 Aug 21.

Division of MR Physics, Department of Medical Radiology, University Hospital Basel, Basel, Switzerland.

The purpose of this study was to evaluate a new polymer-based and magnetic resonance (MR) imaging-compatible guide wire for its application in MR-guided endovascular interventions, particularly for interventional peripheral MR angiography in swine experiments in vivo. A passive device tracking method tailored to the specific conditions of peripheral MR angiography was developed. Near-real-time visualization of the guide wire was accomplished in vivo in the carotid artery, aorta, heart, and iliac arteries of two domestic pigs. Results show great potential for this guide wire in aiding the realization of interventional peripheral MR angiography in humans.
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http://dx.doi.org/10.1016/j.jvir.2009.07.001DOI Listing
October 2009

MR spectroscopy of the human brain with enhanced signal intensity at ultrashort echo times on a clinical platform at 3T and 7T.

Magn Reson Med 2009 Jun;61(6):1279-85

Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland.

Recently, the spin-echo full-intensity acquired localized (SPECIAL) spectroscopy technique was proposed to unite the advantages of short TEs on the order of milliseconds (ms) with full sensitivity and applied to in vivo rat brain. In the present study, SPECIAL was adapted and optimized for use on a clinical platform at 3T and 7T by combining interleaved water suppression (WS) and outer volume saturation (OVS), optimized sequence timing, and improved shimming using FASTMAP. High-quality single voxel spectra of human brain were acquired at TEs below or equal to 6 ms on a clinical 3T and 7T system for six volunteers. Narrow linewidths (6.6 +/- 0.6 Hz at 3T and 12.1 +/- 1.0 Hz at 7T for water) and the high signal-to-noise ratio (SNR) of the artifact-free spectra enabled the quantification of a neurochemical profile consisting of 18 metabolites with Cramér-Rao lower bounds (CRLBs) below 20% at both field strengths. The enhanced sensitivity and increased spectral resolution at 7T compared to 3T allowed a two-fold reduction in scan time, an increased precision of quantification for 12 metabolites, and the additional quantification of lactate with CRLB below 20%. Improved sensitivity at 7T was also demonstrated by a 1.7-fold increase in average SNR (= peak height/root mean square [RMS]-of-noise) per unit-time.
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http://dx.doi.org/10.1002/mrm.21961DOI Listing
June 2009

NMR properties of human median nerve at 3 T: proton density, T1, T2, and magnetization transfer.

J Magn Reson Imaging 2009 Apr;29(4):982-6

Laboratory of Functional and Metabolic Imaging , Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.

Purpose: To measure the proton density (PD), the T1 and T2 relaxation time, and magnetization transfer (MT) effects in human median nerve at 3 T and to compare them with the corresponding values in muscle.

Materials And Methods: Measurements of the T1 and T2 relaxation time were performed with an inversion recovery and a Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence, respectively. The MT ratio was measured by acquiring two sets of 3D spoiled gradient-echo images, with and without a Gaussian saturation pulse.

Results: The median nerve T1 was 1410 +/- 70 msec. The T2 decay consisted of two components, with average T2 values of 26 +/- 2 msec and 96 +/- 3 msec and normalized amplitudes of 78 +/- 4% and 22 +/- 4%, respectively. The dominant component is likely to reflect myelin water and connective tissue, and the less abundant component originates possibly from intra-axonal water protons. The value of proton density of MRI-visible protons in median nerve was 81 +/- 3% that of muscle. The MT ratio in median nerve (40.3 +/- 2.0%) was smaller than in muscle (45.4 +/- 0.5%).

Conclusion: MRI-relevant properties, such as PD, T1 and T2 relaxation time, and MT ratio were measured in human median nerve at 3 T and were in many respects similar to those of muscle.
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http://dx.doi.org/10.1002/jmri.21738DOI Listing
April 2009

In vivo measurement of glycine with short echo-time 1H MRS in human brain at 7 T.

MAGMA 2009 Feb 24;22(1):1-4. Epub 2008 Oct 24.

Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Object: To determine whether glycine can be measured at 7 T in human brain with (1)H magnetic resonance spectroscopy (MRS).

Materials And Methods: The glycine singlet is overlapped by the larger signal of myo-inositol. Density matrix simulations were performed to determine the TE at which the myo-inositol signal was reduced the most, following a single spin-echo excitation. (1)H MRS was performed on an actively shielded 7 T scanner, in five healthy volunteers.

Results: At the TE of 30 ms, the myo-inositol signal intensity was substantially reduced. Quantification using LCModel yielded a glycine-to-creatine ratio of 0.14 +/- 0.01, with a Cramér-Rao lower bound (CRLB) of 7 +/- 1%. Furthermore, quantification of metabolites other than glycine was possible as well, with a CRLB mostly below 10%.

Conclusion: It is possible to detect glycine at 7 T in human brain, at the short TE of 30 ms with a single spin-echo excitation scheme.
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http://dx.doi.org/10.1007/s10334-008-0152-0DOI Listing
February 2009

Comparison of three commercially available radio frequency coils for human brain imaging at 3 Tesla.

MAGMA 2008 Mar 10;21(1-2):53-61. Epub 2008 Jan 10.

Centre d'Imagerie BioMedicale, Ecole Polytechnique Federale de Lausanne, EPFL SB IPMC LIFMET, CH F0 572 (Batiment CH), Station 6, 1015 Lausanne, Switzerland.

Objective: To evaluate a transverse electromagnetic (TEM), a circularly polarized (CP) (birdcage), and a 12-channel phased array head coil at the clinical field strength of B0 = 3T in terms of signal-to-noise ratio (SNR), signal homogeneity, and maps of the effective flip angle alpha.

Materials And Methods: SNR measurements were performed on low flip angle gradient echo images. In addition, flip angle maps were generated for alpha(nominal) = 30 degrees using the double angle method. These evaluation steps were performed on phantom and human brain data acquired with each coil. Moreover, the signal intensity variation was computed for phantom data using five different regions of interest.

Results: In terms of SNR, the TEM coil performs slightly better than the CP coil, but is second to the smaller 12-channel coil for human data. As expected, both the TEM and the CP coils show superior image intensity homogeneity than the 12-channel coil, and achieve larger mean effective flip angles than the combination of body and 12-channel coil with reduced radio frequency power deposition.

Conclusion: At 3T the benefits of TEM coil design over conventional lumped element(s) coil design start to emerge, though the phased array coil retains an advantage with respect to SNR performance.
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http://dx.doi.org/10.1007/s10334-007-0100-4DOI Listing
March 2008