Which type of x-ray photons are present in the remnant x-ray beam, but not in the primary beam?

• A. Unattenuated.
• B. Bremsstrahlung.
• C. Characteristic.
• D. Scattered.

Answer: (D)

Scattered photons are the ones produced inside the patient due to interactions with matter (like Compton scattering). The remnant beam is what exits the patient and travels to the image receptor, so it includes photons that were transmitted without interaction and photons that were scattered inside the body. The primary beam, however, is the set of photons that leave the x-ray tube before they reach the patient and encounter any matter. Since scattered photons are created by tissue interactions after the beam has left the tube, they do not exist in the primary beam. Bremsstrahlung and characteristic photons come from the tube itself and are part of the primary beam. Unattenuated photons can pass through the patient and appear in remnant, so they aren’t exclusive to the remnant. Therefore, scattered photons are present in the remnant beam but not in the primary beam.