What is the difference between x rays used in radiography and CT and gamma rays used in nuclear medicine techniques?
X-rays and gamma rays are both types of ionizing electromagnetic radiation (i.e., they are photons that are energetic enough to remove electrons from other atoms or molecules) with wavelengths shorter than those of visible light. X-rays are emitted by electrons located outside of the nucleus of an atom, whereas gamma rays are emitted by unstable nuclei within atoms and have higher energies than x-rays. Diagnostic x-ray imaging is referred to as transmission imaging, since images are formed by the transmission of x-ray photons from an external source (outside the patient) through the patient to external detectors. Nuclear medicine imaging is referred to as emission imaging because images are formed by the emission of gamma ray photons from an internal source (inside the patient) through the patient to external detectors.