Efficient Use of Specific Absorption Rate Limits Through Sub-Population Universal Pulses in Parallel Transmission

Universal pulse (UP) design in parallel transmit (pTx) imaging is a calibration-free technique that can effectively mitigate the radiofrequency (RF) field inhomogeneity over a population in ultra-high field MRI. In this work, we explore a middle-ground approach of using sub-population UPs. Assuming the entire population is divided into sub-populations by grouping similar anatomical shapes and positions, UPs can thus be designed with reduced intersubject variability. In this preliminary study of head imaging, it is demonstrated that sub-populations of various sizes centred at the mean shape and position can reduce safety margins and improve UP’s performance.