The amount of information contained on a piece of film is enormous making it an excellent storage medium. Film permits the storage of a great deal of information in a very small space and the information can be displayed very inexpensively. As a consequence of the fact that the film is both the detector and the display medium, the actual exposure requirements are dictated by the need to form a viewable image. Film does not respond linearly to incident photons. Since the structures of the breast, and cancers of the breast have similar x-ray attenuation, this limitation can make it difficult to visualize and separate normal from abnormal structures.
Contrast is extremely important.
Although film has high spatial resolution if there is insufficient contrast between two small structures then they will not be separately visible. Another limitation of film is that once the image is developed it is immutable. The information is displayed in only a single presentation, and, if the exposure has not been optimal, then the image will be suboptimal. The film is the only record of the image, and if it is lost or damaged the loss is irretrievable. Storage of x-ray films requires large amounts of space, and studies are, not infrequently lost.