Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Quantitative susceptibility map (QSM) reconstruction is ill posed due to the zero values on the "magic angle cone" that make the maps prone to streaking artifacts. We propose projection onto convex sets (POCS) in the method of steepest descent (SD) for QSM reconstruction. ⋯ POCS is an alternative method for regularization that can be used in an iterative minimization method such as SD for QSM reconstruction.
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Diffusion contrast in diffusion-weighted steady-state free precession magnetic resonance imaging (MRI) is generated through the constructive addition of signal from many coherence pathways. Motion-induced phase causes destructive interference which results in loss of signal magnitude and diffusion contrast. In this work, a three-dimensional (3D) navigator-based real-time correction of the rigid body motion-induced phase errors is developed for diffusion-weighted steady-state free precession MRI. ⋯ The proposed prospective motion correction method is shown to preserve the phase coherence of the steady state in diffusion-weighted steady-state free precession MRI, thus mitigating signal magnitude losses that would confound the desired diffusion contrast.
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To demonstrate that rotationally invariant measures of the diffusion anisotropy on a microscopic scale can be mapped in human brain white matter in vivo. ⋯ Mapping measures of the microscopic diffusion anisotropy in human brain white matter is feasible in vivo and could help to characterize tissue microstructure in the healthy and pathological brain.
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The combination of MRI and positron emission tomography (PET) offers new possibilities for the development of novel methodologies. In pharmacokinetic image analysis, the blood concentration of the imaging compound as a function of time, [i.e., the arterial input function (AIF)] is required for MRI and PET. In this study, we tested whether an AIF extracted from a reference region (RR) in MRI can be used as a surrogate for the manually sampled (18) F-FDG AIF for pharmacokinetic modeling. ⋯ An AIF derived from an RR in MRI can be accurately converted into a (18) F-FDG AIF and used in PET pharmacokinetic modeling.
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Review
Quantitative susceptibility mapping (QSM): Decoding MRI data for a tissue magnetic biomarker.
In MRI, the main magnetic field polarizes the electron cloud of a molecule, generating a chemical shift for observer protons within the molecule and a magnetic susceptibility inhomogeneity field for observer protons outside the molecule. The number of water protons surrounding a molecule for detecting its magnetic susceptibility is vastly greater than the number of protons within the molecule for detecting its chemical shift. ⋯ Recently, physically meaningful regularizations, including the Bayesian approach, have been developed to enable accurate quantitative susceptibility mapping (QSM) for studying iron distribution, metabolic oxygen consumption, blood degradation, calcification, demyelination, and other pathophysiological susceptibility changes, as well as contrast agent biodistribution in MRI. This paper attempts to summarize the basic physical concepts and essential algorithmic steps in QSM, to describe clinical and technical issues under active development, and to provide references, codes, and testing data for readers interested in QSM.