@article{darji_gain_2014,
	title = {Gain of {Imaging} {Fidelity} by {Employing} a {Higher} {Number} of {Independent} {Transmit} {Channels} {Together} with {Slice}-{Selective} {Radio}-{Frequency} ({RF}) {Shimming} at 7T},
	volume = {7},
	issn = {1996-1944},
	url = {http://www.mdpi.com/1996-1944/7/1/30},
	doi = {10.3390/ma7010030},
	abstract = {Dielectric resonance effects and radio-frequency (RF) power deposition have become challenging issues for magnetic resonance imaging at ultrahigh-field (UHF) strengths. The use of transmit (Tx) coil arrays with independently-driven RF sources using a parallel transmission system is a promising method for alleviating the resulting RF inhomogeneities. In this study, the effect on homogeneity and RF-power when employing a higher number of transmit channels with multi-slice acquisition in vivo at high field strength (7T) is scrutinized. An 8-channel head coil array was driven to emulate circular polarized (CP) and 2-, 4-, and 8-channel independent transmit configurations at 7T. Static RF shimming was employed on human subjects in order to homogenize the B1+ field in the excited volume. Slice-selective and global RF shimming methods were applied with CP and 2-, 4-, and 8-channel transmit channel configurations. RF shimming was performed from CP to 2-, 4-, and 8-channel Tx configurations globally and slice-selectively. Systematic improvement in B1+ homogeneity and/or reduction in RF-power were observed. RF shimming in the human brain with 8-channel transmit and slice-selective shimming yields an increase in B1+ homogeneity of 43\% and/or reduces RF-power by 68\% when compared with CP global RF shimming at 7T.},
	number = {1},
	journal = {Materials},
	author = {Darji, Niravkumar and Patel, Gopesh and Speck, Oliver},
	year = {2014},
	pages = {30--43}
}