Subject contrast in radiography refers to which of the following?

Subject contrast in radiography refers to which of the following?

• A. Range of exposures that can be captured by a detector
• B. Magnitude of signal difference in the remnant beam
• C. Total number of brightness levels available in radiography computer system
• D. Range of brightness levels that can be produced by the display monitor

Answer: (B)

Subject contrast is about how much the x-ray signal changes between different tissues as it passes through the body. The remnant beam that reaches the detector carries this information, and tissues with different densities and atomic numbers attenuate the beam by different amounts. For example, bone attenuates much more than soft tissue, so the remnant signal varies considerably between those areas, producing noticeable differences on the image. The larger that difference in the remnant signal, the higher the subject contrast and the easier it is to distinguish structures. The other options describe capabilities of the imaging chain rather than the tissue-induced signal differences: dynamic range of the detector (how many exposure levels can be captured), the computer system’s bit depth or brightness levels (how many tonal values can be stored), and the display monitor’s range of brightness (how many levels can be shown on screen).

Subject contrast is about how much the x-ray signal changes between different tissues as it passes through the body. The remnant beam that reaches the detector carries this information, and tissues with different densities and atomic numbers attenuate the beam by different amounts. For example, bone attenuates much more than soft tissue, so the remnant signal varies considerably between those areas, producing noticeable differences on the image. The larger that difference in the remnant signal, the higher the subject contrast and the easier it is to distinguish structures.

The other options describe capabilities of the imaging chain rather than the tissue-induced signal differences: dynamic range of the detector (how many exposure levels can be captured), the computer system’s bit depth or brightness levels (how many tonal values can be stored), and the display monitor’s range of brightness (how many levels can be shown on screen).