What is the primary cause of penumbra in radiographs?

The primary cause of penumbra in radiographs is the distance between the object and the film. Penumbra refers to the blurred edge that surrounds the image of an object in a radiograph, which can occur when there is a discrepancy in the distance between the radiation source, the object being imaged, and the film or detector.

When the object is farther away from the film, the rays of radiation that interact with the object can diverge more, leading to a less distinct, blurry edge. This effect results in the penumbra, which is especially significant in the case of larger objects or when imaging techniques do not optimize the distance relationships. Understanding this concept is crucial for enhancing image sharpness and minimizing blurring, thereby improving the diagnostic quality of radiographs.

The other factors listed, such as inadequate exposure time or improper collimation, may affect image quality but do not directly cause the penumbra effect. Higher voltage can also influence image contrast and penetration but is not related to the penumbral effect specifically.