The image receptor refers to the part of the x-ray system that intercepts the x-ray photons exiting the patient. It is the component that captures the image. This can refer to film/screen, computed radiography, or direct digital imaging.
In film/screen imaging, film is enclosed in a light tight cassette. Within the cassette, there are screens that fluoresce (glow), when struck by x-rays. It is this light, not the x-rays, that contribute to the majority of the image. At this point, the image is on the film, but you can't see it. This is called a Latent Image. After processing, which we will get into later, the image can now be seen and is called the Manifest Image.
In Computed Radiography, the x-rays are captured on a cassette that looks very much like the film cassette. There is no film to capture the image. Instead, the inside of the cassette has a screen, much like the film cassette. Instead of fluorescing when struck by x-rays, it absorbs the x-rays. Just like film/screen, the image is there, but we cannot see it. The energy absorbed by the screen must be released somehow. By placing the cassette in a CR Reader, we are able to convert the latent image into a manifest image. A laser scans the screen, which releases the energy in the form of light when struck. A detector measures the light released and converts it to a digital image.
Direct digital imaging consists of detectors that, when struck by x-rays, converts the x-ray directly into a digital signal. This signal is processed by software that constructs the image.
Digital imaging, both CR and direct digital, are becoming increasingly popular as technology develops and systems become more affordable. Although all 3 modalities certainly do the job, there have been notable benefits to digital imaging. For rural facilities, being able to instantly send image files electronically so an expert physician can interpret them has become invaluable, especially in emergency situations. In the case of direct digital imaging, there is also a notable potential for reduced patient exposure. The word potential is used here because digital imaging also has the ability to grossly overexpose patients without even realizing it.