Comprehensive 4D Parallel Transmission Spatial‐Spectral Pulse Design for Slab‐Selective Uniform Water‐Selective Excitation: Demonstration in the Human Brain at 7 Tesla

Purpose To propose a new parallel transmission (pTx) spatial‐spectral (SPSP) pulse design for achieving slab‐selective uniform water‐selective excitation without unwanted out‐of‐slab fat excitation when using bipolar slab‐selective gradients to maintain a sharp slab profile. Methods Our new pTx SPSP pulses were designed by formulating the design problem comprehensively in the 4D space (1D spectral and 3D spatial domains) and by incorporating a SPINS‐like 2D excitation k‐space trajectory for within‐slab flip‐angle homogenization. Our new design was validated at 7 T using simulation, phantom and human experiments with the commercial Nova eight‐channel transmit RF head coil. Its utility was demonstrated by comparing to traditional multi‐spoke pTx SPSP pulses. Results In both simulation and experiments, our design outperformed traditional approaches, producing slab‐selective uniform water‐selective excitation with no out‐of‐slab fat excitation. Quantitatively, coefficient of variation measuring excitation non‐uniformity reduced by up to ∼23%. Conclusion Our proposed new design provides an effective solution for slab‐selective uniform water‐selective excitation, holding a promise to many applications including mesoscale BOLD fMRI and fat‐free body imaging at ultrahigh field.