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  • Articles  (1,333)
  • 2010-2014  (1,333)
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  • Articles  (1,333)
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  • 1
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    Recommended implementation of arterial spin-labeled perfusion MRI for clinical applications: A consensus of the ISMRM perfusion study group and the European consortium for ASL in dementia (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-25
    Description: This review provides a summary statement of recommended implementations of arterial spin labeling (ASL) for clinical applications. It is a consensus of the ISMRM Perfusion Study Group and the European ASL in Dementia consortium, both of whom met to reach this consensus in October 2012 in Amsterdam. Although ASL continues to undergo rapid technical development, we believe that current ASL methods are robust and ready to provide useful clinical information, and that a consensus statement on recommended implementations will help the clinical community to adopt a standardized approach. In this review, we describe the major considerations and trade-offs in implementing an ASL protocol and provide specific recommendations for a standard approach. Our conclusion is that as an optimal default implementation, we recommend pseudo-continuous labeling, background suppression, a segmented three-dimensional readout without vascular crushing gradients, and calculation and presentation of both label/control difference images and cerebral blood flow in absolute units using a simplified model. Magn Reson Med 73:102–116, 2015. © 2014 Wiley Periodicals, Inc.
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    Electronic ISSN: 1522-2594
    Topics: Medicine
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  • 2
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    Selective magnetic resonance imaging of magnetic nanoparticles by acoustically induced rotary saturation (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-24
    Description: Purpose The goal of this study was to introduce a new method to selectively detect iron oxide contrast agents using an acoustic wave to perturb the spin-locked water signal in the vicinity of the magnetic particles. The acoustic drive can be modulated externally to turn the effect on and off, allowing sensitive and quantitative statistical comparison and removal of confounding image background variations. Methods We demonstrated the effect in spin-locking experiments using piezoelectric actuators to generate vibrational displacements of iron oxide samples. We observed a resonant behavior of the signal changes with respect to the acoustic frequency where iron oxide is present. We characterized the effect as a function of actuator displacement and contrast agent concentration. Results The resonant effect allowed us to generate block-design “modulation response maps” indicating the contrast agent's location, as well as positive contrast images with suppressed background signal. We found that the acoustically induced rotary saturation (AIRS) effect stayed approximately constant across acoustic frequency and behaved monotonically over actuator displacement and contrast agent concentration. Conclusion AIRS is a promising method capable of using acoustic vibrations to modulate the contrast from iron oxide nanoparticles and thus perform selective detection of the contrast agents, potentially enabling more accurate visualization of contrast agents in clinical and research settings. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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    Topics: Medicine
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  • 3
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    Contrast enhancement by combining T1- and T2-weighted structural brain MR Images (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-23
    Description: Purpose In order to more precisely differentiate cerebral structures in neuroimaging studies, a novel technique for enhancing the tissue contrast based on a combination of T1-weighted (T1w) and T2-weighted (T2w) MRI images was developed. Methods The combined image (CI) was calculated as CI = (T1w − sT2w)/(T1w + sT2w), where sT2w is the scaled T2-weighted image. The scaling factor was calculated to adjust the gray- matter (GM) voxel intensities in the T2w image so that their median value equaled that of the GM voxel intensities in the T1w image. The image intensity homogeneity within a tissue and the discriminability between tissues in the CI versus the separate T1w and T2w images were evaluated using the segmentation by the FMRIB Software Library (FSL) and FreeSurfer (Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital, Boston, MA) software. Results The combined image significantly improved homogeneity in the white matter (WM) and GM compared to the T1w images alone. The discriminability between WM and GM also improved significantly by applying the CI approach. Significant enhancements to the homogeneity and discriminability also were achieved in most subcortical nuclei tested, with the exception of the amygdala and the thalamus. Conclusion The tissue discriminability enhancement offered by the CI potentially enables more accurate neuromorphometric analyses of brain structures. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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    Topics: Medicine
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  • 4
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    Concentric rings K-space trajectory for hyperpolarized 13C MR spectroscopic imaging (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-23
    Description: Purpose To develop a robust and rapid imaging technique for hyperpolarized 13 C MR Spectroscopic Imaging and investigate its performance. Methods A concentric rings readout trajectory with constant angular velocity is proposed for hyperpolarized 13 C spectroscopic imaging and its properties are analyzed. Quantitative analyses of design tradeoffs are presented for several imaging scenarios. The first application of concentric rings on 13 C phantoms and in vivo animal hyperpolarized 13 C MR Spectroscopic Imaging studies were performed to demonstrate the feasibility of the proposed method. Finally, a parallel imaging accelerated concentric rings study is presented. Results The concentric rings MR Spectroscopic Imaging trajectory has the advantages of acquisition timesaving compared to echo-planar spectroscopic imaging. It provides sufficient spectral bandwidth with relatively high efficiency compared to echo-planar spectroscopic imaging and spiral techniques. Phantom and in vivo animal studies showed good image quality with half the scan time and reduced pulsatile flow artifacts compared to echo-planar spectroscopic imaging. Parallel imaging accelerated concentric rings showed advantages over Cartesian sampling in g -factor simulations and demonstrated aliasing-free image quality in a hyperpolarized 13 C in vivo study. Conclusion The concentric rings trajectory is a robust and rapid imaging technique that fits very well with the speed, bandwidth, and resolution requirements of hyperpolarized 13 C MR Spectroscopic Imaging. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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  • 5
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    Feasibility and reproducibility of measurement of whole muscle blood flow, oxygen extraction, and VO2 with dynamic exercise using MRI (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-23
    Description: Purpose Develop an MRI method to estimate skeletal muscle oxygen consumption (VO 2 ) with dynamic exercise using simultaneous measurement of venous blood flow (VBF) and venous oxygen saturation (SvO 2 ). Methods Real-time imaging of femoral VBF using a complex-difference method was interleaved with imaging of venous hemoglobin oxygen saturation (SvO 2 ) using magnetic susceptometry to estimate muscle VO 2 (Fick principle). Nine healthy subjects performed repeated 5-watt knee-extension (quadriceps) exercise within the bore of a 1.5 Tesla MRI scanner, for test/re-test comparison. VBF, SvO 2 , and derived VO 2 were estimated at baseline and immediately (〈1 s) postexercise and every 2.4 s for 4 min. Results Quadriceps muscle mass was 2.43 ± 0.31 kg. Mean baseline values were VBF = 0.13 ± 0.06 L/min/kg, SvO 2 = 69.4 ± 10.1%, and VO 2 = 6.8 ± 4.1 mL/min/kg. VBF, SvO 2 , and VO 2 values from peak exercise had good agreement between trials (VBF = 0.9 ± 0.1 versus 1.0 ± 0.1 L/min/kg, R 2 = 0.83, CV = 7.6%; SvO 2 = 43.2 ± 13.5 versus 40.9 ± 13.1%, R 2 = 0.88, CV = 15.6%; VO 2 = 95.7 ± 18.0 versus 108.9 ± 17.3 mL/min/kg, R 2 = 0.88, CV = 12.3%), as did the VO 2 recovery time constant (26.1 ± 3.5 versus 26.0 ± 4.0 s, R 2 = 0.85, CV = 6.0%). CV = coefficient of variation. Conclusion Rapid imaging of VBF and SvO 2 for the estimation of whole muscle VO 2 is compatible with dynamic exercise for the estimation of peak values and recovery dynamics following exercise with good reproducibility. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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  • 6
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    STEAM-MiTiS: An MR spectroscopy method for the detection of scalar-coupled metabolites and its application to glutamate at 7 T (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-23
    Description: Purpose We herein present a spectroscopic technique for the detection of scalar-coupled metabolites based on stimulated echo acquisition mode (STEAM). The method is based on the time evolution of scalar-coupled metabolites at different mixing times and a constant echo time. The technique is optimized for targeting the metabolite glutamate at 7T. Methods Numerical simulations were used to optimize the parameters to maximize the chosen metabolite signal. The maximum detection efficiency and metabolite signal as a function of echo time were used to identify the optimal parameters. In vitro and in vivo validations of the method were also performed. Results This method canceled all the strong singlet lines and signals from macromolecules and preserved signals originating from the scalar-coupled metabolites. The subtracted spectrum was strongly simplified, but the complete spectral information of the traditional STEAM acquisition was retained in the sum spectrum. Conclusions The simulations performed in this study were in agreement with the experimental results, and a clear detection of the metabolite of interest was obtained. The applicability in vivo was also demonstrated, with the selective detection of glutamate in human brain. This technique is simple, suitable for standard MR systems without sequence programming and could be used to detect other metabolites. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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  • 7
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    Highly undersampled contrast-enhanced MRA with iterative reconstruction: Integration in a clinical setting (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-19
    Description: Purpose To integrate, optimize, and evaluate a three-dimensional (3D) contrast-enhanced sparse MRA technique with iterative reconstruction on a standard clinical MR system. Methods Data were acquired using a highly undersampled Cartesian spiral phyllotaxis sampling pattern and reconstructed directly on the MR system with an iterative SENSE technique. Undersampling, regularization, and number of iterations of the reconstruction were optimized and validated based on phantom experiments and patient data. Sparse MRA of the whole head (field of view: 265 × 232 × 179 mm 3 ) was investigated in 10 patient examinations. Results High-quality images with 30-fold undersampling, resulting in 0.7 mm isotropic resolution within 10 s acquisition, were obtained. After optimization of the regularization factor and of the number of iterations of the reconstruction, it was possible to reconstruct images with excellent quality within six minutes per 3D volume. Initial results of sparse contrast-enhanced MRA (CEMRA) in 10 patients demonstrated high-quality whole-head first-pass MRA for both the arterial and venous contrast phases. Conclusion While sparse MRI techniques have not yet reached clinical routine, this study demonstrates the technical feasibility of high-quality sparse CEMRA of the whole head in a clinical setting. Sparse CEMRA has the potential to become a viable alternative where conventional CEMRA is too slow or does not provide sufficient spatial resolution. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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  • 8
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    Spectral-editing measurements of GABA in the human brain with and without macromolecule suppression (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-19
    Description: Purpose The conventional spectral-editing experiment used to measure GABA in the human brain also contains a contribution from macromolecules (MM), and the combined GABA plus MM signal is often referred to as “GABA+”. More recently, methods have been developed to estimate GABA free from MM contamination. In this study, the relationship between GABA acquired with MM suppression and conventional GABA+ measurements was examined. Methods GABA-edited MEGA-PRESS experiments with and without MM suppression were performed in the sensorimotor and occipital cortex of 12 healthy subjects at 3 Tesla. The correlation between GABA+ and MM-suppressed GABA measures was then determined. Results Across all data, a significant correlation between GABA+ and MM-suppressed GABA was found (r = 0.48; P  = 0.02). Regionally, the sensorimotor voxel showed a trend toward a correlation of r = 0.53, P  = 0.07 and the occipital voxel did not show a correlation, r = 0.058, P  = 0.9. Conclusion GABA+ and MM-suppressed GABA are moderately correlated, but statistical power to reveal this relationship may vary regionally. The MM signal, while often assumed to be functionally irrelevant, appears to show inter-individual and inter-regional variance that impacts the correlation of GABA+ and MM-suppressed GABA. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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  • 9
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    Engineering an effective Mn-binding MRI reporter protein by subcellular targeting (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-19
    Description: Purpose Manganese (Mn) is an effective contrast agent and biologically active metal, which has been widely used for Mn-enhanced MRI (MEMRI). The purpose of this study was to develop and test a Mn binding protein for use as a genetic reporter for MEMRI. Methods The bacterial Mn-binding protein, MntR was identified as a candidate reporter protein. MntR was engineered for expression in mammalian cells, and targeted to different subcellular organelles, including the Golgi Apparatus where cellular Mn is enriched. Transfected HEK293 cells and B16 melanoma cells were tested in vitro and in vivo, using immunocytochemistry, MR imaging and relaxometry. Results Subcellular targeting of MntR to the cytosol, endoplasmic reticulum and Golgi apparatus was verified with immunocytochemistry. After targeting to the Golgi, MntR expression produced robust R1 changes and T1 contrast in cells, in vitro and in vivo. Co-expression with the divalent metal transporter DMT1, a previously described Mn-based reporter, further enhanced contrast in B16 cells in culture, but in the in vivo B16 tumor model tested was not significantly better than MntR alone. Conclusion This second-generation reporter system both expands the capabilities of genetically encoded reporters for imaging with MEMRI and provides important insights into the mechanisms of Mn biology which create endogenous MEMRI contrast. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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  • 10
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    Hyperpolarized [U-2H, U-13C]Glucose reports on glycolytic and pentose phosphate pathway activity in EL4 tumors and glycolytic activity in yeast cells (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-19
    Description: Purpose A resonance at ∼181 ppm in the 13 C spectra of tumors injected with hyperpolarized [U- 2 H, U- 13 C]glucose was assigned to 6-phosphogluconate (6PG), as in previous studies in yeast, whereas in breast cancer cells in vitro this resonance was assigned to 3-phosphoglycerate (3PG). These peak assignments were investigated here using measurements of 6PG and 3PG 13 C-labeling using liquid chromatography tandem mass spectrometry (LC-MS/MS) Methods Tumor-bearing mice were injected with 13 C 6 glucose and the 13 C-labeled and total 6PG and 3PG concentrations measured. 13 C MR spectra of glucose-6-phosphate dehydrogenase deficient ( zwf1 Δ) and wild-type yeast were acquired following addition of hyperpolarized [U- 2 H, U- 13 C]glucose and again 13 C-labeled and total 6PG and 3PG were measured by LC-MS/MS Results Tumor 13 C-6PG was more abundant than 13 C-2PG/3PG and the resonance at ∼181 ppm matched more closely that of 6PG. 13 C MR spectra of wild-type and zwf1 Δ yeast cells showed a resonance at ∼181 ppm after labeling with hyperpolarized [U- 2 H, U- 13 C]glucose, however, there was no 6PG in zwf1 Δ cells. In the wild-type cells 3PG was approximately four-fold more abundant than 6PG Conclusion The resonance at ∼181 ppm in 13 C MR spectra following injection of hyperpolarized [U- 2 H, U- 13 C]glucose originates predominantly from 6PG in EL4 tumors and 3PG in yeast cells. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
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