Why do radioactive materials are required for diagnose and treatment of diseases?

In order to investigate the events happening inside the human body before they cause a damage and/or discomfort, an agent which sends signal from inside the body is required. The gamma and positron radiations of the given radioactive materials can be determined and measured from outside the body; thus, the movements of the molecules labeled with a radioactive material can be tracked and reflected as images. Due to the mentioned characteristics of the radioactive materials,

Nuclear Medicine applications;

1) are non-invasive (i.e. do not harm the patient or inflict any kind of discomfort), do not inflict any side effect or allergy;
2) are very sensitive methods
3) are purpose-customized methods;
4) provide data at physiological, metabolic, and molecular levels which can not be obtained by any other methods;
5) provide datas which are digital, so they can be compared and when repeated, those applications provide a great facility for determining normal and abnormal values.