Approx. 5% of the incident x-ray photons emerge from the patient to form the radiographic image, which is termed___________?

• A. Secondary beam
• B. Primary beam
• C. Remnant radiation
• D. Stray radiation

Answer: (C)

Remnant radiation is the radiation that emerges from the patient and forms the image on the receptor. After the beam enters the body, many photons are absorbed or scattered, and only a small fraction—about 5% in typical diagnostic imaging—exit the patient to reach the image receptor. These exiting photons, whether unattenuated or scattered within the body, carry the attenuated structural information and actually create the radiographic image. The primary beam is the original, unmodified beam before it interacts with the patient. Stray radiation refers to photons outside the intended beam, such as leakage from the tube housing, which does not contribute to the image. Secondary radiation describes photons produced by interactions within the patient (like scatter), but the photons that pass through to form the image are the remnant radiation.