1. A diagnostic imaging apparatus for contrast enhanced imaging of a patient, the apparatus comprising: a magnetic resonance imaging apparatus including: a main magnetic coil assembly for generating a main magnetic field in an imaging region of the apparatus, a gradient coil assembly for overlaying gradient magnetic fields on the main magnetic field, and an RF coil assembly for at least transmitting RF signals into the imaging region and receiving magnetic resonance signals from the imaging region; a nuclear PET imaging apparatus including: a detector array configured to detect nuclear decay events concurrently with the receiving of the magnetic resonance signals by the RF coil assembly, and at least one reconstruction processor for producing an image representation from the nuclear decay events detected by the detector array that gather in the imaging region and from the detected magnetic resonance; a common PET and MRI agent configured for injection into a patient disposed in the imaging region, the common agent including: a carrier including a fluorine-19 component which is imaged by the magnetic resonance imaging apparatus and a radiopharmaceutical which includes fluorine-18 which decays to generate the nuclear decay events detected by the PET imaging apparatus, the fluorine-18 being imaged concurrently with the imaging of the fluorine-19 component by the magnetic resonance imaging apparatus, a targeting system that takes advantage of biological processes to cause the common agent to collect in a target region, and an MRI contrast agent that is imaged by the magnetic resonance imaging apparatus.