The radiation that forms the diagnostic image on the film is called remnant radiation.

• A. Primary radiation
• B. Scatter radiation
• C. Remnant radiation
• D. Leakage radiation

Answer: (C)

Remnant radiation is the radiation that forms the diagnostic image on the film because it is the portion of the X-ray beam that exits the patient and reaches the image receptor. After passing through the body, many photons are absorbed or scattered, but the photons that survive and travel toward the receptor—both transmitted primary photons and scatter—constitute the remnant radiation. It is this remnant that exposes the film and creates the image. Primary radiation refers to the original beam before tissue interaction and does not itself form the image unless it emerges, while leakage radiation is radiation that escapes the housing and is not responsible for the image on the film.