Structures seen outside the collimated area on a radiograph are results of which type of radiation?

The correct answer highlighting the structures seen outside the collimated area on a radiograph is off-focus radiation.

Off-focus radiation occurs when x-rays are produced at locations other than the target area of the anode within the x-ray tube. Though the primary beam is collimated to limit exposure to the area of interest, off-focus radiation can scatter and appear on the film, leading to unintentional exposure of adjacent areas not meant to be imaged. This phenomenon contributes to the visibility of structures outside the intended field on the radiograph.

The other types of radiation mentioned do not specifically account for this situation in the same way. Backscatter refers to the x-rays that are scattered back towards the source after hitting a surface, secondary radiation involves x-rays that are emitted from the patient after being excited by primary radiation, and filtered radiation pertains to the removal of low-energy photons from the beam to reduce patient dose, but does not explain structures outside the collimated area on the image. Thus, off-focus radiation is the primary explanation for the visibility of structures beyond the intended collimated boundary.