title: RF Head Coil Design with Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems.
abstract: Higher magnetic field strength in magnetic resonance imaging (MRI) systems offers higher signal-to-noise ratio (SNR), contrast, and spatial resolution in MR images. However, the wavelength in ultra-high fields (7 tesla and beyond) becomes shorter than the human body at the Larmor frequency with increasing static magnetic field (B0) of MRI system. At short wavelengths, interference effect appears resulting in non- uniformity of the RF magnetic near-field (B1) over the subject and MR images may have spatially anomalous contrast. The B1near-field generated by the transverse electromagnetic (TEM) RF coil's microstrip line element has a maximum near the center of its length and falls off towards both ends. In this study, a double trapezoidal shaped microstrip transmission line element is proposed to obtain uniform B1field distribution by gradual impedance variation. Two multi-channel RF head coils with uniform and trapezoidal shape elements were built and tested with a phantom at 7T MRI scanner for comparison. The simulation and experimental results show stronger and more uniform B1+near-field with the trapezoidal shape.
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota. He is now with Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Sung-Min
authors.initials: SM
authors.lastname: Sohn
authors.affiliation: Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55454.
authors.forename: Lance
authors.initials: L
authors.lastname: DelaBarre
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: Anand
authors.initials: A
authors.lastname: Gopinath
authors.affiliation: Department of Electrical and Computer Engineering and with the Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN 55455 USA.
authors.forename: John Thomas
authors.initials: JT
authors.lastname: Vaughan
keywords: B1 field uniformity; Magnetic Resonance Imaging (MRI); RF coil; Transverse electromagnetic (TEM) resonator