Magnetic resonance (MR) imaging typically has excellent spatial resolution, but relatively poor temporal resolution. In contrast, positron emission tomography (PET) typically has excellent temporal resolution, but poor spatial resolution relative to MR. Resultantly, it is advantageous to use combined PET-MR imaging sequences to create hybrid or enhanced images that reap the benefits of both modalities. A contrast agent (80) that includes both a PET tracer (82) and MR contrast enhancement (86) can be used in such a combined modality setting. The contrast agent (80) also includes a targeting system (84) that allows the contrast agent (80) to pool in a region of interest.