Which of the following factors does NOT impact radiographic contrast?

Radiographic contrast, which refers to the difference in density between different areas on a radiographic image, is influenced by several key factors that affect how X-rays interact with the subject being imaged and the image receptor.

Photon energy directly impacts contrast because it determines the penetrability of the X-ray beam. Higher energy photons can penetrate tissues better, which can lead to less variation in exposure among different tissues and lower contrast.

Grid ratio is another critical factor as it enhances contrast by reducing scatter radiation that reaches the image receptor. A higher grid ratio leads to more effective cleaning of scatter, thus increasing radiographic contrast.

Object-to-image distance (OID) plays a role as well; increasing OID can enhance contrast by reducing the amount of scatter that reaches the film, as the scattered rays are more likely to diverge away from the detector due to increased distance.

Focal-spot size, however, does not significantly affect radiographic contrast. It primarily influences spatial resolution and sharpness of the image rather than the contrast itself. While a smaller focal spot can improve resolution, it does not change the interaction of X-rays with the tissues or the film in a way that impacts contrast. Therefore, this factor is correctly identified as NOT impacting radiographic contrast.