What device is designed to measure the optical density of an exposed and processed radiographic film?

• A. Optical Density Meter
• B. Photodensitometer
• C. Densitograph
• D. Densitometer

Answer: (D)

Measuring optical density on an exposed and processed radiographic film requires an instrument that quantifies how much light passes through the film. The densitometer is designed for this purpose. It shines a beam of light through the film and uses a photodetector to measure the transmitted light. The reading is converted to optical density (OD) using the relation OD = log10(I0/I), where higher densities absorb more light and yield higher OD values. This makes the densitometer ideal for assessing exposure, development quality, and consistency across films.

Other terms describe similar concepts but are not the standard instrument name here. An optical density meter is not the conventional designation in radiography. A photodensitometer is a less common or older term for the same idea, and a densitograph typically focuses on producing a density curve rather than providing a single reading.