Abstract: A solid fiduciary marker for registering at least two images when imaging the same subject using distinct imaging devices is disclosed. The solid fiduciary marker is visible in at least two of a Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Planar gamma camera, X-ray CT, planar X-ray, Magnetic Resonance Imaging (MRI), and optical imager. The marker includes at least two of various doping compounds to be detected by the various imaging systems. The doping compounds include a positron emitting nuclide, a gamma emitting nuclide, a doping compound, metal, and a silicone-based polymer is used in association with an MRI device.