A magnetic resonance (MR) image segmentation processor (32) is configured to identify one or more geometrical regions of a subject using an MR image of the subject. An emission data reconstruction processor (40) is configured to generate an attenuation map (54) of the subject by assigning initial attenuation values (52) to the geometrical regions of the subject, and to: (i) process (56) emission data acquired from the subject to generate an emission image (58) of the subject, the processing employing the attenuation map of the subject； (ii) update (60) the attenuation map based on corrections calculated using the emission image of the subject； and (iii) iterate operations (i) and (ii) to iteratively generate a reconstructed emission image of the subject.
