Asymmetric Spokes : a demonstration of free-breathing pTX in the human torso at 7 T

Introduction: In the recent past several publications have demonstrated parallel transmission (pTX) [1,2] for flip-angle homogenization at ultra-high field in the human brain [3, 4, among others]. For slice selective pTX applications, the popular “spokes” method is often used [5,3]. On conventional scanners asymmetric sincpulses, are commonly adopted to reduce the minimum echo time in fast slab-selective sequences such as the VIBE. To optimize the echo time for these clinically relevant sequences in the pTX framework, we introduce the asymmetric spoke (a-spoke) design. In addition, we present an optimized freebreathing B1-mapping procedure. The comprehensive method is demonstrated by homogenizing the flip-angle on a 6cm axial slab through the human torso at 7T using the 3DVIBE sequence.