American Registry of Radiologic Technologists (ARRT) Practice Exam

What is the effect of increased tissue density on contrast?

1. Contrast increases

2. Contrast decreases

3. Contrast remains the same

4. Contrast fluctuates

The correct answer is: Contrast decreases

Increased tissue density generally leads to a decrease in contrast in imaging. This phenomenon occurs because denser tissues absorb more radiation and therefore result in a narrower range of x-ray intensities reaching the detector. As a result, the differences in attenuation between various tissues become less pronounced. In radiographic imaging, contrast refers to the degree of difference between the light and dark areas on the image, which is crucial for distinguishing between various tissues and structures. When tissue density increases without a corresponding increase in the difference in tissue composition or thickness (for example, fat versus muscle), the overall image may lose the ability to distinguish features effectively. This effect can be particularly pronounced when high-density tissues, such as bone, are imaged alongside lower-density tissues, making differentiation more challenging as they might appear closer in shades on the final image. Therefore, the proper understanding of tissue density's role is essential in radiologic imaging to ensure optimal interpretation and diagnosis.