Hybrid-PUSH pulses for controlled MT bias in T1 mapping at 7T

While standard pulse design methods control the rotation of magnetization (i.e. flip angle), the recently proposed PUSH method aims to control the root-mean-squared B1, to control magnetization transfer (MT) effects. General RF pulses create both effects simultaneously: this is important in T1 mapping, where incidental MT effects introduce bias. We show that using standard pulse design methods to improve flip angle uniformity can actually worsen the bias in T1 measurement by producing uncontrolled spatially variable MT effects. We propose a ‘hybrid-PUSH’ method optimizing both flip angle and B1rms, and demonstrate this improves quality of T1 estimation in-vivo at 7T.