In Medical Situations, What are Gamma Rays used for? Where do they Excel and Fail in?

-Gamma Rays are Transmitted by Pretty much every part of the Body, so that means you can Detect it from Outside the Body -This can be done via Radio tracers, Radioactive Isotopes that can be Injected or Swollen, and can Emit Gamma Rays -This means, for examples, if you put the Tracer in a Molecule, Glucose, it can see how much Absorption of that Molecule is happening, giving you Answers