Radiographs and Photographs

After reading this section you will be able to do the following:

  • Compare and contrast the differences between radiographs and photographs.

X-ray film is not very widely used anymore and most applications where x-rays are used to produce radiographic images have switched to using digital detectors. However, it is a helpful teaching aid to compare and contrast x-ray film images to photographic images.

Below are a series of photographs and a radiograph of the same objects.

This is a diagram of a person's spine                This is an X-ray of a person's spine

This is an image of retractable measuring tape                This is an X-ray image of retractable measuring tape

This is an image of a lock and key                This is an X-ray image of a lock and key

This is an image of a computer mouse                This is an X-ray image of a computer mouse.

There are several characteristics of the photographs and x-ray photographs that are similar, and yet, there are very distinct differences. Radiography and photography both often use some type of film to record the image. The principle difference is in how the image is recorded on the film.

In photography, the image on the film is produced due to the reflection of light. When you want to take a picture, you use a camera, which has a shutter that opens and closes allowing light to enter and strike the film. The amount of light that interacts with the film determines how the image appears on the film .

In radiography, the process to produce an image is quite different. The camera is actually a radiation source and it operates quite differently than a photographic camera. The film is not placed inside the camera but instead is placed on the opposite side of the object being imaged. The radiation is not reflected to the film, but rather passes through the object and then strikes the film. The image on the film is dependent upon how much of the radiation makes it through the object and to the film. Some materials like bone and metal stop more of the radiation from passing through than do materials like flesh and plastic. The amount of material that the X-rays must travel through also affects how many X-rays reach the film. Differences in the type of material and the amount of material that the X-rays must penetrate are responsible for the details in the image. 

Review:

  1. In photography, reflected light rays from the object expose the film to produce an image.
  2. In radiography, X-rays that pass through the object expose the film to produce an image.
  3. Differences in the types and amounts of the materials that the X-rays must travel through are responsible for the details of the radiographic image.