1. A method of designing a parallel transmission radio frequency (RF) pulse for a magnetic resonance imaging (MRI) system, the method comprising: compressing a model for a subject to be scanned by the MRI system into a plurality of voxel clusters, each voxel cluster defining a virtual observation point with a peak sensitivity to local specific absorption rate (SAR) for the voxel cluster; and defining the parallel transmission RF pulse based on an approximation of a minimization criterion having a local SAR component based on the peak sensitivity of each virtual observation point, the approximation comprising a weighted sum of local SAR values for the virtual observation points.