1. An integrated hybrid medical imaging system comprising: a nuclear medicine imaging subsystem configured to capture an image of a target region of a subject; a magnetic resonance imaging (MRI) subsystem configured to capture a plurality of MRI images of said target region, each MRI image being based on a different MRI parameter that highlights a specific tissue type and being captured simultaneously with the image captured by said nuclear medicine imaging subsystem, the different MRI parameters being selected to identify a plurality of different tissue types within said target region; and a processor configured to: process the MRI images to measure the different MRI parameters, estimate attenuation of the different tissue types with said target region from the measured MRI parameters, generate a non-uniform attenuation map of said target region, wherein the non-uniform attenuation map is generated from a combination of individual captures, wherein a first capture of the individual captures is weighted by an MRI parameter including one of longitudinal relaxation weighted, transverse relaxation weighted, proton-density weighted, or proton-density weighted with water suppression, wherein a second capture of the individual captures is weighted by a different MRI parameter than the first capture, and use the non-uniform attenuation map to correct the image captured by said nuclear medicine imaging subsystem.