Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Heterogeneity of the static magnetic field in magnetic resonance imaging may cause image artifacts and degradation in image quality. The field heterogeneity can be reduced by dynamically adjusting shim fields or dynamic shim updating, in which magnetic field homogeneity is optimized for each tomographic slice to improve image quality. A limitation of this approach is that a new magnetic field can be applied only once for each slice, otherwise image quality would improve somewhere to its detriment elsewhere in the slice. ⋯ A theoretical description of the method is detailed, simulations and a proof-of-principle experiment are performed using a magnet coil with a known field geometry. The method is shown to remove artifacts associated with magnetic field homogeneity in balanced steady-state free-precession pulse sequences. We anticipate that this method will be useful to improve the quality of magnetic resonance images by removing deleterious artifacts associated with a heterogeneous static magnetic field.
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To correct gradient-induced phase errors in radial MRI. ⋯ The proposed method does not require additional reference measurements and separately corrects for phase errors induced by eddy currents, while retaining the residual phase of the object which may carry physiologic information.
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To improve the visualization of fibrous tissues as tendons, ligaments and fibrocartilage structures as menisci by positive contrast using a new 3D Double Echo Steady State (DESS) sequence. ⋯ Positive contrast of fibrous tissue as demonstrated by the proposed sub-DESS approach provides improved conspicuity and allows for three-dimensional reconstruction especially of structures with curved geometry.
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Radial trajectories facilitate high-resolution balanced steady state free precession (bSSFP) because the efficient gradients provide more time to extend the trajectory in k-space. A number of radial bSSFP methods that support fat-water separation have been developed; however, most of these methods require an environment with limited B0 inhomogeneity. In this work, high-resolution bSSFP with fat-water separation is achieved in more challenging B0 environments by combining a 3D radial trajectory with the IDEAL chemical species separation method. ⋯ The sampling of a unique set of radial lines at each echo time is investigated as a means to circumvent the longer scan time that IDEAL incurs as a multiecho acquisition. The manifestation of undersampling artifacts in this trajectory and their effect on chemical species separation are investigated in comparison to the case in which each echo samples the same set of radial lines. This new bSSFP method achieves 0.63 mm isotropic resolution in a 5-min scan and is demonstrated in difficult in vivo imaging environments, including the breast and a knee with ACL reconstruction hardware at 1.5 T.
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To describe and characterize a new approach to first-pass myocardial perfusion utilizing balanced steady-state free precession acquisition without the use of saturation recovery or other magnetization preparation. ⋯ A new approach to first-pass myocardial perfusion is presented that obviates the need for magnetization preparation and provides high signal-to-noise ratio.