Nuclear Medicine studies work by attaching a small amount of a radioactive material to something the body uses or an analog of a natural molecule.  By seeing how the tracer is used in the body, we look at the metabolic function of the organ systems.   We use the same tracer for many of our studies.  The same tracer is attached to different molecules to see different organs.  That makes it often difficult or impossible to do more than one nuclear medicine study on the same day.   Also, our tracers are completely different than iodinated contrast.  Unless your patient is getting a diagnostic CT scan with contrast in conjunction with a PET/CT scan, they will not need to worry about iodine allergies for Nuclear Medicine.