Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Echo planar-based diffusion-weighted MRI (DW-MRI) requires robust suppression of fat signal. Fat suppression techniques such as inversion recovery or spectrally selective excitation with subsequent gradient spoiling can extend scan time or perform suboptimally in the presence of strong main field inhomogeneities. Chemical shift-encoded water-fat separation using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) is robust in areas of main field inhomogeneity but requires accurate phase information, which can be distorted by patient motion during diffusion-weighting gradients. A method is proposed to overcome this with the use of image navigators. ⋯ DW-EPI with IDEAL and an integrated image navigator allows for robust water and fat separation in different body areas and are a time-efficient alternative to standard fat-suppression techniques in DW-MRI.
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MR thermometry (MRT) is a noninvasive method for measuring temperature that can potentially be used for radio frequency (RF) safety monitoring. This application requires measuring absolute temperature. In this study, a multigradient-echo (mGE) MRT sequence was used for that purpose. A drawback of this sequence, however, is that its accuracy is affected by background gradients. In this article, we present a method to minimize this effect and to improve absolute temperature measurements using MRI. ⋯ The corrections offer the possibility to measure RF heating in phantoms more precisely. This allows mGE MRT to become a valuable tool in RF safety assessment.
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To investigate the effects on quantitative susceptibility mapping (QSM) and susceptibility tensor imaging (STI) of the frequency variation produced by the microstructure of white matter (WM). ⋯ Microstructure-related phase offsets in WM yield artifacts in the calculated susceptibility maps. If susceptibility mapping is to become a robust MRI technique, further research should be carried out to reduce the confounding effects of microstructure-related frequency contributions.
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To iteratively correct for deviations in radial trajectories with no need of additionally performed calibration scans. ⋯ The iterative technique introduced in this paper allows for a correction of trajectory errors in radial imaging with no need for additional calibration data.
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To develop a single-slab three-dimensional variable-flip-angle gradient- and spin-echo pulse sequence with phase-independent reconstruction that is highly energy- or encoding-efficient for high resolution isotropic imaging at high magnetic field. ⋯ We successfully demonstrated that the proposed variable-flip-angle gradient- and spin-echo can be a highly promising energy- or encoding-efficient alternative for high resolution isotropic imaging.