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Morgan Mercredi, Melanie Martin
OBJECT: Recent advances have allowed oscillating gradient (OG) diffusion MRI to infer the sizes of micron-scale axon diameters. Here the effects on the precision of the inferred diameters are studied when reducing the number of images collected to reduce imaging time for clinical feasibility. MATERIALS AND METHODS: Monte Carlo simulations of cosine OG sequences (50-1000 Hz) using a two-compartment model on a parallel cylinder (diameters 1-5 μm) geometry were conducted...
March 7, 2018: Magma
Lukas Reinhold Buschle, Christian H Ziener, Ke Zhang, Volker J F Sturm, Thomas Kampf, Artur Hahn, Gergely Solecki, Frank Winkler, Martin Bendszus, Sabine Heiland, Heinz-Peter Schlemmer, Felix T Kurz
OBJECTIVES: Spin dephasing of the local magnetization in blood vessel networks can be described in the static dephasing regime (where diffusion effects may be ignored) by the established model of Yablonskiy and Haacke. However, for small capillary radii, diffusion phenomena for spin-bearing particles are not negligible. MATERIAL AND METHODS: In this work, we include diffusion effects for a set of randomly distributed capillaries and provide analytical expressions for the transverse relaxation times T2* and T2 in the strong collision approximation and the Gaussian approximation that relate MR signal properties with microstructural parameters such as the mean local capillary radius...
February 24, 2018: Magma
Felix Schyboll, Uwe Jaekel, Bernd Weber, Heiko Neeb
OBJECTIVE: Recent MRI studies have shown that the orientation of nerve fibres relative to the main magnetic field affects the R2 *(= 1/T2 *) relaxation rate in white matter (WM) structures. The underlying physical causes have been discussed in several studies but are still not completely understood. However, understanding these effects in detail is of great importance since this might serve as a basis for the development of new diagnostic tools and/or improve quantitative susceptibility mapping techniques...
February 20, 2018: Magma
Dounia El Hamrani, Amandine Chepied, William Même, Marc Mesnil, Norah Defamie, Sandra Même
OBJECTIVE: Using non-invasive magnetic resonance (MR) techniques and a histological approach, we assessed the outcomes of perinatal exposure at a low dose of 3,3'-DCBPA (2-chloro-4-[1-(3-chloro-4-hydroxyphenyl)-1-methylethyl]phenol) and/or 3,5-DCBPA (2,6-dichloro-4-[1-(4-hydroxyphenyl)-1-methylethyl]phenol) on mice livers. MATERIALS AND METHODS: Fertilized female Swiss mice were injected intraperitoneally during gestation and lactation with either vehicle control, 20 μg/kg/day of BPA, 3,5-DCBPA, 3,3'-DCBPA or a mixture (mix-DCBPA)...
February 20, 2018: Magma
Tim Leiner, Gustav Strijkers
No abstract text is available yet for this article.
February 6, 2018: Magma
Manohar Latha, Ganesan Kavitha
OBJECTIVE: Schizophrenia (SZ) is a psychiatric disorder that especially affects individuals during their adolescence. There is a need to study the subanatomical regions of SZ brain on magnetic resonance images (MRI) based on morphometry. In this work, an attempt was made to analyze alterations in structure and texture patterns in images of the SZ brain using the level-set method and Laws texture features. MATERIALS AND METHODS: T1-weighted MRI of the brain from Center of Biomedical Research Excellence (COBRE) database were considered for analysis...
February 3, 2018: Magma
Alejandro Santos-Díaz, Sergei I Obruchkov, Rolf F Schulte, Michael D Noseworthy
OBJECT: To present and evaluate a fast phosphorus magnetic resonance spectroscopic imaging (MRSI) sequence using echo planar spectroscopic imaging with flyback readout gradient trajectories. MATERIALS AND METHODS: Waveforms were designed and implemented using a 3 Tesla MRI system. 31P spectra were acquired with 2 × 2 cm2 and 3 × 3 cm2 resolution over a 20- and 21-cm field of view and spectral bandwidths up to 1923 Hz. The sequence was first tested using a 20-cm-diameter phosphate phantom, and subsequent in vivo tests were performed on healthy human calf muscles and brains from five volunteers...
January 30, 2018: Magma
Felix Lugauer, Jens Wetzl, Christoph Forman, Manuel Schneider, Berthold Kiefer, Joachim Hornegger, Dominik Nickel, Andreas Maier
OBJECTIVE: Our aim was to develop and validate a 3D Cartesian Look-Locker [Formula: see text] mapping technique that achieves high accuracy and whole-liver coverage within a single breath-hold. MATERIALS AND METHODS: The proposed method combines sparse Cartesian sampling based on a spatiotemporally incoherent Poisson pattern and k-space segmentation, dedicated for high-temporal-resolution imaging. This combination allows capturing tissue with short relaxation times with volumetric coverage...
January 25, 2018: Magma
Gwenaël Pagé, Jérémie Bettoni, Anne-Virginie Salsac, Olivier Balédent
OBJECTIVE: The objective of the study was to determine how to optimize 2D and 4D phase-contrast magnetic resonance imaging (PC-MRI) acquisitions to acquire flow velocities in millimetric vessels. In particular, we search for the best compromise between acquisition time and accuracy and assess the influence of the principal component analysis (PCA). MATERIALS AND METHODS: 2D and 4D PC-MRI measurements are conducted within two in vitro vessel phantoms: a Y-bifurcation phantom, the branches of which range from 2 to 5 mm in diameter, and a physiological subject-specific phantom of the carotid bifurcation...
January 22, 2018: Magma
David Norris
No abstract text is available yet for this article.
January 8, 2018: Magma
Rita G Nunes, Joseph V Hajnal
OBJECTIVE: Point spread function (PSF) mapping enables estimating the displacement fields required for distortion correction of echo planar images. Recently, a highly accelerated approach was introduced for estimating displacements from the phase slope of under-sampled PSF mapping data. Sampling schemes with varying spacing were proposed requiring stepwise phase unwrapping. To avoid unwrapping errors, an alternative approach applying the concept of finite rate of innovation to PSF mapping (FRIP) is introduced, using a pattern search strategy to locate the PSF peak, and the two methods are compared...
January 3, 2018: Magma
Xin Zhang, Xiangyang Zhu, Christopher Martyn Ferguson, Kai Jiang, Tyson Burningham, Amir Lerman, Lilach Orly Lerman
OBJECTIVE: Low-energy shockwave (SW) therapy attenuates damage in the stenotic kidney (STK) caused by atherosclerotic renal artery stenosis (ARAS). We hypothesized that magnetic resonance elastography (MRE) would detect attenuation of fibrosis following SW in unilateral ARAS kidneys. MATERIALS AND METHODS: Domestic pigs were randomized to control, unilateral ARAS, and ARAS treated with 6 sessions of SW over 3 consecutive weeks (n = 7 each) starting after 3 weeks of ARAS or sham...
December 30, 2017: Magma
Shuo Zhang, Thu Thao Le, Sven Kabus, Boyang Su, Derek J Hausenloy, Stuart A Cook, Calvin W L Chin, Ru San Tan
OBJECTIVE: Our aim was to investigate the technical feasibility of a novel motion compensation method for cardiac magntic resonance (MR) T1 and extracellular volume fraction (ECV) mapping. MATERIALS AND METHODS: Native and post-contrast T1 maps were obtained using modified look-locker inversion recovery (MOLLI) pulse sequences with acquisition scheme defined in seconds. A nonrigid, nonparametric, fast elastic registration method was applied to generate motion-corrected T1 maps and subsequently ECV maps...
December 21, 2017: Magma
Haining Liu, Gregory J Wilson, Niranjan Balu, Jeffrey H Maki, Daniel S Hippe, Wei Wu, Hiroko Watase, Jinnan Wang, Martin L Gunn, Chun Yuan
OBJECTIVES: A postprocessing technique termed 3D true-phase polarity recovery with independent phase estimation using three-tier stacks based region growing (3D-TRIPS) was developed, which directly reconstructs phase-sensitive inversion-recovery images without acquisition of phase-reference images. The utility of this technique is demonstrated in myocardial late gadolinium enhancement (LGE) imaging. MATERIALS AND METHODS: A data structure with three tiers of stacks was used for 3D-TRIPS to directly achieve reliable region growing for successful background-phase estimation...
February 2018: Magma
Bart R Steensma, Ingmar J Voogt, Tim Leiner, Peter R Luijten, Jesse Habets, Dennis W J Klomp, Cornelis A T van den Berg, Alexander J E Raaijmakers
OBJECTIVE: To demonstrate imaging performance for cardiac MR imaging at 7 T using a coil array of 8 transmit/receive dipole antennas and 16 receive loops. MATERIALS AND METHODS: An 8-channel dipole array was extended by adding 16 receive-only loops. Average power constraints were determined by electromagnetic simulations. Cine imaging was performed on eight healthy subjects. Geometrical factor (g-factor) maps were calculated to assess acceleration performance. Signal-to-noise ratio (SNR)-scaled images were reconstructed for different combinations of receive channels, to demonstrate the SNR benefits of combining loops and dipoles...
February 2018: Magma
Elias Kellner, Irina Mader, Marco Reisert, Horst Urbach, Valerij Gennadevic Kiselev
OBJECT: We aimed to modify our previously published method for arterial input function measurements for evaluation of cerebral perfusion (dynamic susceptibility contrast MRI) such that it can be applied in humans in a clinical setting. MATERIALS AND METHODS: Similarly to our previous work, a conventional measurement sequence for dynamic susceptibility contrast MRI is extended with an additional measurement slice at the neck. Measurement parameters at this slice were optimized for the blood signal (short echo time, background suppression, magnitude and phase images)...
December 9, 2017: Magma
Chengcheng Zhu, Bing Tian, Luguang Chen, Laura Eisenmenger, Esther Raithel, Christoph Forman, Sinyeob Ahn, Gerhard Laub, Qi Liu, Jianping Lu, Jing Liu, Christopher Hess, David Saloner
OBJECTIVE: Develop and optimize an accelerated, high-resolution (0.5 mm isotropic) 3D black blood MRI technique to reduce scan time for whole-brain intracranial vessel wall imaging. MATERIALS AND METHODS: A 3D accelerated T1 -weighted fast-spin-echo prototype sequence using compressed sensing (CS-SPACE) was developed at 3T. Both the acquisition [echo train length (ETL), under-sampling factor] and reconstruction parameters (regularization parameter, number of iterations) were first optimized in 5 healthy volunteers...
December 5, 2017: Magma
Patrick J Cozzone
No abstract text is available yet for this article.
December 2017: Magma
Bora Buyuksarac, Mehmed Ozkan
OBJECTIVE: This research utilizes magnetic resonance angiography (MRA) to identify arterial locations during the parametric evaluation of concentration time curves (CTCs), and to prevent shape distortions in arterial input function (AIF). MATERIALS AND METHODS: We carried out cluster analysis with the CTC parameters of voxels located within and around the middle cerebral artery (MCA). Through MRA, we located voxels that meet the AIF criteria and those with distorted CTCs...
December 2017: Magma
Sascha Brunheim, Sören Johst, Viktor Pfaffenrot, Stefan Maderwald, Harald H Quick, Benedikt A Poser
OBJECTIVE: A new technique for 2D gradient-recalled echo echo-planar imaging (GE-EPI) termed 'variable slice thickness' (VAST) is proposed, which reduces signal losses caused by through-slice susceptibility artifacts, while keeping the volume repetition time (TR) manageable. The slice thickness is varied across the brain, with thinner slices being used in the inferior brain regions where signal voids are most severe. MATERIALS AND METHODS: Various axial slice thickness schemes with identical whole-brain coverage were compared to regular EPI, which may either suffer from unfeasibly long TR if appropriately thin slices are used throughout, or signal loss if no counter-measures are taken...
December 2017: Magma
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