Multi-slice magnetic resonance imaging of a region of interest of an imaging subject (16) is performed using a radio frequency coil (40) arranged to generate a B.sub.1 magnetic field in the region of interest. One or more processors (44, 82, 88, 110) determine a B1 field value for each slice that is representative of the B1 field over a selected area of the slice, accounting for subject effects on the BI field, and determine an adjusted per-slice radio frequency excitation for each slice that adjusts the B.sub.1 field value for the slice to a selected value. A magnetic resonance imaging system (10, 44, 46, 50, 52) acquires magnetic resonance imaging data for each slice using the adjusted per-slice radio frequency excitation for that slice. A reconstruction processor (58) reconstructs the acquired magnetic resonance imaging data into a reconstructed image representation.