Array-optimized composite pulse for excellent whole-brain homogeneity in high-field MRI
Corresponding Author
Christopher M. Collins
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
NMR/MRI Building, H066, 500 University Drive, Hershey, PA 17033===Search for more papers by this authorZhangwei Wang
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorWeihua Mao
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorJieming Fang
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorWanzhan Liu
Center for MR Research, University of Minnesota, Minneapolis, Minnesota, USA
Search for more papers by this authorMichael B. Smith
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorCorresponding Author
Christopher M. Collins
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
NMR/MRI Building, H066, 500 University Drive, Hershey, PA 17033===Search for more papers by this authorZhangwei Wang
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorWeihua Mao
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorJieming Fang
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorWanzhan Liu
Center for MR Research, University of Minnesota, Minneapolis, Minnesota, USA
Search for more papers by this authorMichael B. Smith
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA
Search for more papers by this authorAbstract
A number of methods to improve excitation homogeneity in high-field MRI have been proposed, and some of these methods rely on separate control of radiofrequency (RF) coils in a transmit array. In this work we combine accurate RF field calculations and the Bloch equation to demonstrate that by using a sequence of pulses with individually optimized current distributions (i.e., an array-optimized composite pulse), one can achieve remarkably homogeneous distributions of available signal intensity over the entire brain volume. This homogeneity is greater than that achievable using the same transmit array to produce either a single optimized (or RF shimmed) pulse or a single RF shimmed field distribution in a standard 90x-90y composite pulse arrangement. Simulations indicate that with a very simple array-optimized composite pulse, excellent whole-brain excitation homogeneity can be achieved at up to 600 MHz. Magn Reson Med 57:470–474, 2007. © 2007 Wiley-Liss, Inc.
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