Magnetic resonance imaging (MRI) was used for non-destructive characterization of the pore structure of starch-based extruded products. The samples were obtained by extrusion cooking of corn meal in a twin screw extruder. The samples were extruded at varying mechanical energy input and, subsequently, the pore size distributions were analyzed. Two different sample preparation methods were introduced and discussed. Negative imaging was the favorable technique. In this method, the pores are filled with cyclohexane and the solvent is detected by MRI. The analysis method was validated by glass beads of known size as reference samples. The pore sizes detected by MRI were slightly higher than the real size of the glass beads. When extruded corn meal samples were analyzed, we were able to show, that despite an equal expansion index, samples can have different pore size distributions. Finally, the pore size distributions were compared to analysis via X-ray microtomography and advantages and limitations of both methods were discussed. (C) 2013 Elsevier Ltd. All rights reserved.