Array-optimized composite pulse for excellent whole-brain homogeneity in high-field MRI.
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.
Collins
Christopher M
CM
Center for NMR Research, Penn State College of Medicine, Hershey, Pennsylvania, USA. cmcollins@psu.edu
Wang
Zhangwei
Z
Mao
Weihua
W
Fang
Jieming
J
Liu
Wanzhan
W
Smith
Michael B
MB
D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted; D016018:Least-Squares Analysis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*