In a method and apparatus to enable increased RF duty cycle in high field MR scans, a specific energy absorption rate (SAR) calculation processor (36) calculates the local and global SAR or even a spatial SAR map. The efficient implementation by using pre- averaged data (based on E-fields) makes a fast and accurate SAR estimation possible. By incorporating additional information as e.g. patient position the SAR calculation accuracy can be increased as well as by using more patient specific precalculated information (e.g. based on different bio meshes), the so called Q-matrices. Optionally, a sequence controller (24) creates a global SAR optimal RF pulse. After the optimal RF pulse is applied, the SAR and its spatial distribution are determined. SAR hotspots are also determined. Q-matrices within an appropriate radius around the hotspots are averaged and added to a global Q-matrix in a weighted fashion. After the global Q-matrix is updated, a new optimal RF pulse is created. One or more of the steps can be repeated to converge the SAR to a minimum.