1. A hybrid medical imaging system comprising: a nuclear medicine imaging subsystem for capturing an image of a target region of a subject; a magnetic resonance imaging (MRI) subsystem for capturing an MRI image of said target region based on at least one MRI parameter; and processing structure communicating with said subsystems, said processing structure processing the MRI image to estimate attenuation within said target region and using the estimated attenuation to correct the image captured by said nuclear medicine imaging subsystem.