This invention includes agents and compositions having MRI, PET, CT, X-ray, SPECT or optical signals, and methods for their use in the determination of a target. In some cases, a MRI, PET, CT, X-ray, SPECT, optical or other signal produced by the agent or composition can be affected by the presence of the target. Examples of targets that can be determined by this invention include, but are not limited to zinc, copper, iron ions and other biological targets. Example of application for imaging in vivo includes the function of pancreas and other organs.
