Glossary of terms used on this site
C
- Contrast
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Radiographic contrast describes the differences in photographic density in a radiograph. The larger the difference in thickness or density between to areas of the subject, the larger the difference in radiographic density or contrast, the more visible features become. Contrast is caused by the fact that different parts of the object absorb X-rays differently. How great a difference in radiation absorption is necessary depends on the detector. With two parts of an object with radiation intensities I[A] and I[B], the difference in contrast is defined as 2*| I[A] � I [B] | / ( I[A] + I [B] ). As a rule of thumb, a difference in radiation absorption of 2% (0.5% for a digital detector) is needed in order for an image intensifier to produce a visible image. Moreover, contrast depends on the wavelength of the primary radiation.