Doctors, what is the difference between diagnostic radiography and nuclear medicine?

Nuclear medicine : Diagnostic radiology usually involves a source of radiation which begins outside the body (such as X-ray) which then passes through the body and is sensed by detectors. Nuclear medicine is sort of "inside out" imaging where a radionuclide source is injected into the body and the gamma rays which are emitted from the tracer are detected by the gamma camera outside of the body.

Both radiation: Nuclear medicine radiation is given internally via IV injection, ingestion, or inhalation for determination of function of organs of body. Isotopes have different half lives and decay at different rates.Ct/xray is external radiation for visualization of anatiomy and pathology. Both contribute to radiation dose. Both are ionizing radiation. Ultrasound and MRI do not involve irradiation.