Tracers- Nuclear Medicine please help?

is this information correct (concerning tracers in nuclear medicine)

- a radioactive substance is inject into shoulder [or body], or swallowed through mouth
- radioactive substances are generally gamma emitters
- We use a gamma camera to detect the tracer
- We use gamma rays for tracing as they can easily pass through the body without damaging it. Secondly we use a substance with a relativity short half-life (a few hours), long enough to take measurements but short enough not to cause damage.
- Tracers are used to create a picture of an organ or an organ system by detecting where the strongest readings are coming from
- Along with the tracer, a radionuclide is injected, to guide the tracer to a certain part of the body

The most important part of this thing is the last bullet point (Is that correct?)