X-ray film must be characteristically different from film used in photography, since
x-ray exposure is different from light exposure. Because of its importance to medicine,
x-ray film is manufactured with consistent uniformity and quality, which facilitates
standardization of exposure and processing.
CHEMICAL COMPONENTS OF FILM
In general, x-ray film is a double-emulsion film consisting of a transparent base
with adhesive subcoating, sensitized emulsion, and protective coating on both surfaces
Figure 1-2. Magnified cross-section of x-ray film.
a. Film Base. The film base supports the emulsion and provides the correct
degree of stiffness for handling purposes. It is composed of either cellulose acetate or
polyester, both of which are transparent and blue-tinted.
(1) Cellulose acetate. Dissolving cotton in acetic acid makes cellulose
acetate. The cotton cellulose combines with the acid to form cellulose acetate, which is
then dissolved in a volatile solvent containing blue dye. The solution of cellulose
acetate is poured onto huge heated drums where it solidifies to a thickness of about
0.008 inch. Cellulose acetate does have a tendency to become saturated with liquids
during processing, which results in frequent problems in automatic processors.
(2) Polyester. The polyester base is made by "cracking" crude oil forming
the substance parazylene. When this substance is mixed with methyl alcohol and other
chemicals, a product of dimethyl-terebthalate (DMT) is formed. This DMT is one-half of