A Novel Radiofrequency Pulse Design for Improving Flip-angle Uniformity in Ultra-high Field MRI

Purpose The problem of inhomogeneous B1 + fields in high field MRI has previously been addressed by novel or improved RF pulse designs (e.g. sparse spokes [1] and adiabatic pulses [2]) and hardware modifications (e.g. parallel transmit coils [3]). Existing techniques have practical limitations in that B1 + maps must be acquired for a specific imaging slice prior to the design of the RF pulse, SAR requirements hinder implementation at ultra-high field, or non-standard hardware configurations must be accommodated. The Sequences Of Pulses Optimized for a Range of Inhomogeneities For Imaging Coils (SOPORIFIC) technique introduced here consists of phase and frequency modulated waveforms numerically optimized for B1 + immunity. SOPORIFIC pulses are effective over a specific range of frequency offsets and B1 + variations designated during the design process and thus can be successfully implemented regardless of field strength, transmit coil configuration, or the subject-specific spatial distribution of the B1 + and ΔB0 fields.