Browsing by Author "Wu, X."
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Item Open Access In vivo human head MRI at 10.5T: a radiofrequency safety study and preliminary imaging results(Wiley, 2020) Sadeghi-Tarakameh, Alireza; DelaBarre, L.; Lagore, R. L.; Torrado-Carvajal, A.; Wu, X.; Grant, A.; Adriany, G.; Metzger, G. J.; Van de Moortele, P.-F.; Uğurbil, K.; Atalar, Ergin; Eryaman, Y.Purpose: The purpose of this study is to safely acquire the first human head images at 10.5T. Methods: To ensure safety of subjects, we validated the electromagnetic simulation model of our coil. We obtained quantitative agreement between simulated and experimental and specific absorption rate (SAR). Using the validated coil model, we calculated radiofrequency power levels to safely image human subjects. We conducted all experiments and imaging sessions in a controlled radiofrequency safety lab and the whole‐body 10.5T scanner in the Center for Magnetic Resonance Research. Results: Quantitative agreement between the simulated and experimental results was obtained including S‐parameters, maps, and SAR. We calculated peak 10 g average SAR using 4 different realistic human body models for a quadrature excitation and demonstrated that the peak 10 g SAR variation between subjects was less than 30%. We calculated safe power limits based on this set and used those limits to acquire T2‐ and ‐weighted images of human subjects at 10.5T. Conclusions: In this study, we acquired the first in vivo human head images at 10.5T using an 8‐channel transmit/receive coil. We implemented and expanded a previously proposed workflow to validate the electromagnetic simulation model of the 8‐channel transmit/receive coil. Using the validated coil model, we calculated radiofrequency power levels to safely image human subjects.Item Open Access A nine-channel transmit/receive array for spine imaging at 10.5 T: Introduction to a nonuniform dielectric substrate antenna(John Wiley & Sons, Inc., 2021-11-05) Sadeghi-Tarakameh, Alireza; Jungst, S.; Lanagan, M.; DelaBarre, L.; Wu, X.; Adriany, G.; Metzger, G. I.; Moortele, P. F.; Ugurbil, K.; Atalar, Ergin; Eryaman, Y.Purpose: The purpose of this study is to introduce a new antenna element with improved transmit performance, named the nonuniform dielectric substrate(NODES) antenna, for building transmit arrays at ultrahigh- field.Methods: We optimized a dipole antenna at 10.5 Tesla by maximizing the B+1- SAR efficiency in a phantom for a human spine target. The optimization pa-rameters included permittivity variation in the substrate, substrate thickness, antenna length, and conductor geometry. We conducted electromagnetic simu-lations as well as phantom experiments to compare the transmit/receive perfor-mance of the proposed NODES antenna design with existing coil elements from the literature.Results: Single NODES element showed up to 18% and 30% higher B+1- SAR ef-ficiency than the fractionated dipole and loop elements, respectively. The new element is substantially shorter than a commonly used dipole, which enables z- stacked array formation; it is additionally capable of providing a relatively uni-form current distribution along its conductors. The nine- channel transmit/re-ceive NODES array achieved 7.5% higher B+1homogeneity than a loop array with the same number of elements. Excitation with the NODES array resulted in 33% lower peak 10g- averaged SAR and required 34% lower input power than the loop array for the target anatomy of the spine.Conclusion: In this study, we introduced a new RF coil element: the NODES antenna. NODES antenna outperformed the widely used loop and dipole ele-ments and may provide improved transmit/receive performance for future ultra-high field MRI applications.