Which expression correctly determines radiographic density?

Radiographic density is a measure of the blackness or darkness of a radiographic film, which is primarily influenced by the amount of radiation that has passed through an object and reached the film. The correct expression for determining radiographic density is based on the relationship between the incident radiation (Io) and the transmitted radiation (It).

The formula log(Io/It) is rooted in logarithmic functions, which are used in radiography to quantify differences in intensity of radiation. In this context, Io represents the intensity of the radiation before it passes through the object, while It represents the intensity after it has traversed the object. By taking the logarithm of the ratio of these two intensities, we account for the exponential nature of attenuation that occurs as the radiation passes through materials. Essentially, the greater the difference between Io and It, the denser the image appears, and the logarithmic function allows for a more manageable numerical representation of this relationship.

This formulation is vital because it translates the physical realities of radiation transmission into a measurable quantity on the film, enabling radiographers to assess the density of the resulting radiograph effectively.