Positron Emission Tomography (PET) images need correction for the loss of photons. This loss, or attenuation, is due to interactions with patient tissues. Corrections are currently done with X-ray Computed Tomography (CT), however we are proposing a method whereby Magnetic Resonance Images (MRI) are used. This will be done by creating an attenuation map(?-map). The construction of ?-maps can be divided into two categories, patient specific ?-maps by MRI segmentation, and registration of a predefined atlas to an MRI.