What is the term used to describe geometric blur or focal spot blur in radiography?

The term used to describe geometric blur or focal spot blur in radiography is penumbra. Penumbra refers to the region at the edges of a shadow where the light is partially blocked, resulting in a gradual transition from light to dark. In the context of radiography, it is an effect caused by the finite size of the x-ray focal spot. If the focal spot were an ideal point source, the image would have perfect sharpness. However, because the focal spot has a certain size, it produces a blurred boundary on the image, impacting the overall resolution.

Understanding penumbra is essential for improving image quality, as minimizing this effect can lead to more accurate diagnostic information. Factors such as the distance between the focal spot and the film, as well as the distance between the object and the film, play a significant role in controlling the size of the penumbra. It is important for radiographers to recognize and manage penumbra to enhance image sharpness and detail.

The other terms, while they relate to imaging, do not specifically refer to the geometric blur produced by the focal spot. Vignetting refers to the gradual darkening of the corners of an image compared to its center, distortion refers to the alteration of