Applications and Imaging Principles of Medical Films

1. Imaging Principle of Black-and-White Medical Films

The bright (thin) areas correspond to the parts with less exposure; the fully transparent areas are the parts that have not been exposed to light. This is the basic process of image recording by black-and-white medical films.

2. Imaging Principle of Color Medical Films

Color medical films have three layers of photosensitive emulsion, each containing different organic compounds capable of producing dyes, known as color couplers. These couplers are colorless in their natural state, but can couple with oxides of color developers to form colored dyes during color development.

For negative medical films, the couplers in the top panchromatic emulsion layer form yellow during color development, the middle layer forms magenta, and the bottom layer forms cyan — this is the processed color medical film we obtain. When the image is projected onto photographic paper through enlargement or onto reversal film through reversal processing, the yellow in the top layer of the medical film is converted to its complementary color (blue), the middle layer to green, and the bottom layer to red. Thus, we get color photographs or transparent reversal films that match the natural state of the subject.

This is the basic process of image recording by color medical films. The result is that the dark (thick) areas on the negative image correspond to parts with more exposure; the bright (thin) areas are parts with less exposure; and the fully transparent areas are parts that have not been exposed to light — the same basic principle as black-and-white medical film recording.