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Antenna arrays, Biomedical imaging, Computational electromagnetics
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.
