Purpose We propose a new slab-wise framework to design parallel transmit multiband pulses for volumetric simultaneous multislice imaging with a large field of view along the slice direction (FOVs). Theory and Methods The slab-wise framework divides FOVs into a few contiguous slabs and optimizes pulses for each slab. Effects of relevant design parameters including slab number and transmit B1 (B1+) mapping slice placement were investigated for human brain imaging by designing pulses with global or local SAR control based on electromagnetic simulations of a 7T head RF array. Pulse design using in vivo B1+ maps was demonstrated and evaluated with Bloch simulations. Results RF performance with respect to SAR reduction or B1+ homogenization across the entire human brain improved with increasing slabs; however, this improvement was nonlinear and leveled off at ∼12 slabs when the slab thickness reduced to ∼12 mm. The impact of using different slice placements for B1+ mapping was small. Conclusion Compared with slice-wise approaches where each of the many imaging slices requires both B1+ mapping and pulse optimization, the proposed slab-wise design framework attained comparable RF performance while drastically reducing the number of required pulses; therefore, it can be used to increase time efficiency for B1+ mapping, pulse calculation, and sequence preparation.
Bibliographical noteFunding Information:
National Institutes of Health; Grant numbers: P41EB015894; R21-EB009133; R01-EB006835; R01-EB007327. We thank Jinfeng Tian for running the electromagnetic modeling of the RF array, John Strupp and Brian Hanna for assistance with setting up the computation resources, and Julien Sein for creating binary brain masks in FreeSurfer.
© 2015 Wiley Periodicals, Inc.
- high-field MRI
- multiband RF pulse design
- parallel excitation
- simultaneous multislice imaging
- transmit B1 homogenization