Metal complexes having radioactive nuclei find many applications in medicine, such as in organ and tissue imaging. Early detection of cancer, for example by selective and imaging of the tumor using a radioactive metal compound, can facilitate surgical removal or chemotherapeutic treatment before the disease reaches an advanced stage. Metals and metal compounds have been used in medicine for several thousands of years. In the past, metal-based compounds were widely used in the treatment of disease conditions, but the lack of clear distinction between the therapeutic and toxic doses was a major challenge.This book discusses the advantages and disadvantages of some of the metals used in radioioimaging and cancer treatment.