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Analysis of RF transmit performance for a 7T dual row multichannel MRI loop array

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Kozlov,  Mikhail
Department Neurophysics, MPI for Human Cognitive and Brain Sciences, Max Planck Society;

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Turner,  Robert
Department Neurophysics, MPI for Human Cognitive and Brain Sciences, Max Planck Society;

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Citation

Kozlov, M., & Turner, R. (2011). Analysis of RF transmit performance for a 7T dual row multichannel MRI loop array. In 33rd Annual International Conference of the IEEE EMBS.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0012-17AC-A
Abstract
We present a numerical investigation of the RF fields generated inside a human head by single and dual-row loop arrays. For a uniform circular polarization (CP) mode excitation, a dual-row array has no advantage for human brain excitation. Significant improvement of B1+ homogeneity with a simultaneous increase of coverage in the axial direction can be obtained by using a dual-row array together with a static RF shim: that is, excitation of both rows separately in CP mode, while providing the upper row elements with a +90 phase shift relative to axially adjacent lower row elements. For this case the excitation efficiency over the entire brain remains practically unaffected, and the improved B1+ coverage results in a relatively smaller amount of power delivered to brain. To keep the mean B1+ across the brain equal to its value in a uniform CP excitation mode, a larger transmit power level is required. This results in a moderate increase of peak SAR10g. The location of peak SAR10g moves from the brain (uniform CP mode location) to the nose skin. The performance of dual-row arrays in transmit SENSE operation will be explored in future investigations.