• In x-ray procedures, x rays pass through the body to form pictures on film or on a computer or television monitor, which are viewed by a radiologist. If you have an x-ray test, it will be performed with a standard x-ray machine or with a more sophisticated x-ray machine called a CT or CAT scan machine.
• In nuclear medicine procedures, a very small amount of radioactive material is inhaled, injected, or swallowed by the patient. If you have a nuclear medicine exam, a special camera will be used to detect energy given off by the radioactive material in your body and form a picture of your organs and their function on a computer monitor. A nuclear medicine physician views these pictures. The radioactive material typically disappears from your body within a few hours or days.
Do magnetic resonance imaging (MRI) and ultrasound use radiation?
MRI and ultrasound procedures do not use ionizing radiation. If you have either of these types of studies, you are not exposed to radiation.
There is no conclusive evidence of radiation causing harm at the levels patients receive from diagnostic xray exams. Although high doses of radiation are linked to an increased risk of cancer, the effects of the low doses of radiation used in diagnostic imaging are not known.
Read more: https://hps.org/documents/meddiagimaging.pdf