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Journal Cover   Magnetic Resonance Materials in Physics, Biology and Medicine
  [SJR: 0.928]   [H-I: 40]   [3 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  [2303 journals]
  • Adaptive speech enhancement using directional microphone in a 4-T MRI
    • 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
    • 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
    • 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
  • Volumetric velocity measurements in restricted geometries using spiral
           sampling: a phantom study
    • Abstract: Object The aim of this study was to evaluate the accuracy of maximum velocity measurements using volumetric phase-contrast imaging with spiral readouts in a stenotic flow phantom. Materials and methods In a phantom model, maximum velocity, flow, pressure gradient, and streamline visualizations were evaluated using volumetric phase-contrast magnetic resonance imaging (MRI) with velocity encoding in one (extending on current clinical practice) and three directions (for characterization of the flow field) using spiral readouts. Results of maximum velocity and pressure drop were compared to computational fluid dynamics (CFD) simulations, as well as corresponding low-echo-time (TE) Cartesian data. Flow was compared to 2D through-plane phase contrast (PC) upstream from the restriction. Results Results obtained with 3D through-plane PC as well as 4D PC at shortest TE using a spiral readout showed excellent agreements with the maximum velocity values obtained with CFD (<1 % for both methods), while larger deviations were seen using Cartesian readouts (−2.3 and 13 %, respectively). Peak pressure drop calculations from 3D through-plane PC and 4D PC spiral sequences were respectively 14 and 13 % overestimated compared to CFD. Conclusion Identification of the maximum velocity location, as well as the accurate velocity quantification can be obtained in stenotic regions using short-TE spiral volumetric PC imaging.
      PubDate: 2015-04-01
  • K-t GRAPPA-accelerated 4D flow MRI of liver hemodynamics: influence of
           different acceleration factors on qualitative and quantitative assessment
           of blood flow
    • Abstract: Objective We sought to evaluate the feasibility of k-t parallel imaging for accelerated 4D flow MRI in the hepatic vascular system by investigating the impact of different acceleration factors. Materials and methods k-t GRAPPA accelerated 4D flow MRI of the liver vasculature was evaluated in 16 healthy volunteers at 3T with acceleration factors R = 3, R = 5, and R = 8 (2.0 × 2.5 × 2.4 mm3, TR = 82 ms), and R = 5 (TR = 41 ms); GRAPPA R = 2 was used as the reference standard. Qualitative flow analysis included grading of 3D streamlines and time-resolved particle traces. Quantitative evaluation assessed velocities, net flow, and wall shear stress (WSS). Results Significant scan time savings were realized for all acceleration factors compared to standard GRAPPA R = 2 (21–71 %) (p < 0.001). Quantification of velocities and net flow offered similar results between k-t GRAPPA R = 3 and R = 5 compared to standard GRAPPA R = 2. Significantly increased leakage artifacts and noise were seen between standard GRAPPA R = 2 and k-t GRAPPA R = 8 (p < 0.001) with significant underestimation of peak velocities and WSS of up to 31 % in the hepatic arterial system (p <0.05). WSS was significantly underestimated up to 13 % in all vessels of the portal venous system for k-t GRAPPA R = 5, while significantly higher values were observed for the same acceleration with higher temporal resolution in two veins (p < 0.05). Conclusion k-t acceleration of 4D flow MRI is feasible for liver hemodynamic assessment with acceleration factors R = 3 and R = 5 resulting in a scan time reduction of at least 40 % with similar quantitation of liver hemodynamics compared with GRAPPA R = 2.
      PubDate: 2015-04-01
  • An L1-norm phase constraint for half-Fourier compressed sensing in 3D MR
    • Abstract: Objective In most half-Fourier imaging methods, explicit phase replacement is used. In combination with parallel imaging, or compressed sensing, half-Fourier reconstruction is usually performed in a separate step. The purpose of this paper is to report that integration of half-Fourier reconstruction into iterative reconstruction minimizes reconstruction errors. Materials and methods The L1-norm phase constraint for half-Fourier imaging proposed in this work is compared with the L2-norm variant of the same algorithm, with several typical half-Fourier reconstruction methods. Half-Fourier imaging with the proposed phase constraint can be seamlessly combined with parallel imaging and compressed sensing to achieve high acceleration factors. Results In simulations and in in-vivo experiments half-Fourier imaging with the proposed L1-norm phase constraint enables superior performance both reconstruction of image details and with regard to robustness against phase estimation errors. Conclusion The performance and feasibility of half-Fourier imaging with the proposed L1-norm phase constraint is reported. Its seamless combination with parallel imaging and compressed sensing enables use of greater acceleration in 3D MR imaging.
      PubDate: 2015-02-26
  • Monoplanar gradient system for imaging with nonlinear gradients
    • Abstract: Object In this paper we present a monoplanar gradient system capable of imaging a volume comparable with that covered by linear gradient systems. Such a system has been designed and implemented. Materials and methods Building such a system was made possible by relaxing the constraint of global linearity and replacing it with a requirement for local orthogonality. A framework was derived for optimization of local orthogonality within the physical boundaries and geometric constraints. Spatial encoding of magnetic fields was optimized for their local orthogonality over a large field of view. Results A coil design consisting of straight wire segments was optimized, implemented, and integrated into a 3T human scanner to show the feasibility of this approach. Initial MR images are shown and further applications of the derived optimization method and the nonlinear planar gradient system are discussed. Conclusion Encoding fields generated by the prototype encoding system were shown to be locally orthogonal and able to encode a cylindrical volume sufficient for some abdomen imaging applications for humans.
      PubDate: 2015-02-17
  • Motion correction of multi-contrast images applied to T 1 and T 2
           quantification in cardiac MRI
    • Abstract: Object The ability to manipulate image contrast and thus to obtain complementary information is one of the main advantages of MRI. Motion consistency within the whole data set is a key point in the context of multi contrast imaging. In cardiac and abdominal MRI, the acquisition strategy uses multiple breath-holds and often relies on acceleration methods that inherently suffer from a signal-to-noise ratio loss. The aim of this work is to propose a free-breathing multi-contrast acquisition and reconstruction workflow to improve image quality and the subsequent data analysis. Materials and methods We extended a previously proposed motion-compensated image reconstruction method for multi-contrast imaging. Shared information throughout the imaging protocol is now exploited by the image reconstruction in the form of an additional constraint based on image gradient sparsity. This constraint helps to minimize the amount of data needed for efficient non-rigid motion correction. T1 and T2 weighted images were reconstructed from free-breathing acquisitions in 4 healthy volunteers and in a phantom. The impact of multi-contrast motion correction was evaluated in a phantom in terms of precision and accuracy of T1 and T2 quantification. Results In the phantom, the proposed method achieved an accuracy of 97.5 % on the quantified parameters against 88.0 % before motion correction. In volunteers, motion inconsistency in T1 and T2 quantification were noticeably reduced within 5 min of free-breathing acquisition. Conclusion An efficient, free-breathing, multi-contrast imaging method has been demonstrated that does not require prior assumptions about contrast and that is applicable to a wide range of examinations.
      PubDate: 2015-02-01
  • Measuring short-term liver metabolism non-invasively: postprandial and
           post-exercise 1 H and 31 P MR spectroscopy
    • Abstract: Object The objective of this study was to determine the effects of a standardized fat rich meal and subsequent exercise on liver fat content by 1H MRS and on liver adenosine triphosphate (ATP) content by 31P MRS in healthy subjects. Materials and methods Hepatic 1H and proton decoupled 31P MRS were performed on nine healthy subjects on a clinical 3.0 T MR imager three times during a day: after (1) an overnight fast, (2) a following standardized fat rich meal and (3) a subsequent exercise session. Blood parameters were followed during the day to serve as a reference to MRS. Results Liver fat content increased gradually over the day (p = 0.0001) with an overall increase of 30 %. Also γ-NTP changed significantly over the day (p = 0.005). γ-NTP/tP decreased by 9 % (p = 0.019, post hoc) from the postprandial to the post-exercise state. Conclusion Our study shows that in vivo MRS can depict short lived physiological changes; entering of fat into liver cells and consumption of ATP during exercise can be measured non-invasively in healthy subjects. The physiological state may have an impact on fat and energy metabolite levels. Hepatic 1H and 31P MRS studies should be performed under standardized conditions.
      PubDate: 2015-02-01
  • Data quality in fMRI and simultaneous EEG–fMRI
    • Abstract: Object To evaluate functional magnetic resonance imaging (fMRI) and simultaneous electroencephalography (EEG)–fMRI data quality in an organization using several magnetic resonance imaging (MRI) systems. Materials and methods Functional magnetic resonance imaging measurements were carried out twice with a uniform gel phantom on five different MRI systems with field strengths of 1.5 and 3.0 T. Several image quality parameters were measured with automatic analysis software. For simultaneous EEG–fMRI, data quality was evaluated on 3.0 T systems, and the phantom results were compared to data on human volunteers. Results The fMRI quality parameters measured with different MRI systems were on an acceptable level. The presence of the EEG equipment caused superficial artifacts on the phantom image. The typical artifact depth was 15 mm, and no artifacts were observed in the brain area in the images of volunteers. Average signal-to-noise ratio (SNR) reduction in the phantom measurements was 15 %, a reduction of SNR similar to that observed in the human data. We also detected minor changes in the noise of the EEG signal during the phantom measurement. Conclusion The phantom proved valuable in the successful evaluation of the data quality of fMRI and EEG–fMRI. The results fell within acceptable limits. This study demonstrated a repeatable method to measure and follow up on the data quality of simultaneous EEG–fMRI.
      PubDate: 2015-02-01
  • Transparent thin shield for radio frequency transmit coils
    • Abstract: Objective To identify a shielding material compatible with optical head-motion tracking for prospective motion correction and which minimizes radio frequency (RF) radiation losses at 7 T without sacrificing line-of-sight to an imaging target. Materials and methods We evaluated a polyamide mesh coated with silver. The thickness of the coating was approximated from the composition ratio provided by the material vendor and validated by an estimate derived from electrical conductivity and light transmission measurements. The performance of the shield is compared to a split-copper shield in the context of a four-channel transmit-only loop array. Results The mesh contains less than a skin-depth of silver coating (300 MHz) and attenuates light by 15 %. Elements of the array vary less in the presence of the mesh shield as compared to the split-copper shield indicating that the array behaves more symmetrically with the mesh shield. No degradation of transmit efficiency was observed for the mesh as compared to the split-copper shield. Conclusion We present a shield compatible with future integration of camera-based motion-tracking systems. Based on transmit performance and eddy-current evaluations the mesh shield is appropriate for use at 7 T.
      PubDate: 2015-02-01
  • Erratum to: Quantitative accuracy of attenuation correction in the Philips
           Ingenuity TF whole-body PET/MR system: a direct comparison with
           transmission-based attenuation correction
    • PubDate: 2015-02-01
  • Multi-parametric (ADC/PWI/T2-w) image fusion approach for accurate
           semi-automatic segmentation of tumorous regions in glioblastoma multiforme
    • Abstract: Object Glioblastoma multiforme (GBM) brain tumor is heterogeneous in nature, so its quantification depends on how to accurately segment different parts of the tumor, i.e. viable tumor, edema and necrosis. This procedure becomes more effective when metabolic and functional information, provided by physiological magnetic resonance (MR) imaging modalities, like diffusion-weighted-imaging (DWI) and perfusion-weighted-imaging (PWI), is incorporated with the anatomical magnetic resonance imaging (MRI). In this preliminary tumor quantification work, the idea is to characterize different regions of GBM tumors in an MRI-based semi-automatic multi-parametric approach to achieve more accurate characterization of pathogenic regions. Materials and methods For this purpose, three MR sequences, namely T2-weighted imaging (anatomical MR imaging), PWI and DWI of thirteen GBM patients, were acquired. To enhance the delineation of the boundaries of each pathogenic region (peri-tumoral edema, viable tumor and necrosis), the spatial fuzzy C-means algorithm is combined with the region growing method. Results The results show that exploiting the multi-parametric approach along with the proposed semi-automatic segmentation method can differentiate various tumorous regions with over 80 % sensitivity, specificity and dice score. Conclusion The proposed MRI-based multi-parametric segmentation approach has the potential to accurately segment tumorous regions, leading to an efficient design of the pre-surgical treatment planning.
      PubDate: 2015-02-01
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