Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Blood oxygenation level-dependent (BOLD)-weighted and vessel-encoded arterial spin labeling (VE-ASL) MRI provide complementary information and can be used in sequence to gauge hemodynamic contributions to cerebrovascular reactivity. Here, cerebrovascular reactivity is assessed using dual echo VE-ASL MRI to understand how VE labeling preparations influence BOLD and ASL contrast in flow-limited and healthy perfusion territories. ⋯ Dual echo VE-ASL can provide simultaneous cerebral blood flow and qualitative BOLD contrast consistent with lateralizing disease severity in patients with asymmetric steno-occlusive disease. The methodological strengths and limitations of composite BOLD and VE-ASL measurements in the clinic are discussed.
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To demonstrate the effect of gradient nonlinearity and develop a method for correction of gradient nonlinearity artifacts in prospective motion correction (Mo-Co). ⋯ The combined correction of gradient nonlinearity and sensitivity map variation leads to a pronounced reduction of residual motion artifacts in prospectively motion-corrected data.
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Local specific absorption rate (SAR) limits many applications of parallel transmit (pTx) in ultra high-field imaging. In this Note, we introduce the use of an array element, which is intentionally inefficient at generating spin excitation (a "dark mode") to attempt a partial cancellation of the electric field from those elements that do generate excitation. We show that adding dipole elements oriented orthogonal to their conventional orientation to a linear array of conventional loop elements can lower the local SAR hotspot in a C-spine array at 7 T. ⋯ The dipole elements provide a sufficiently complimentary B1 (+) and electric field pattern to the loop array that can be exploited by the radiofrequency shimming algorithm to reduce local SAR.
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To develop and validate a respiratory motion compensation method for free-breathing cardiac cine imaging. ⋯ Free-breathing cine imaging with Cine-Nav yielded comparable image quality and ventricular measurements to BH, and was superior to 3AVG.
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To investigate the characteristics of nuclear Overhauser enhancement (NOE) imaging signals in the brain at 7T. ⋯ True NOE signals can be detected using MRS sequences, and considerable pseudo NOE imaging signals may be observed using MRI sequences.