Final answer:
Positive contrast agents, such as barium or iodine, absorb X-rays more than surrounding tissues, which enhances visibility of specific structures.
Step-by-step explanation:
Positive contrast agents, such as barium or iodine, are used in medical imaging to enhance the visibility of certain structures.
They absorb X-rays more than the surrounding tissues, which helps to differentiate and highlight specific areas of interest. This increased absorption of X-rays leads to a decrease in radiographic contrast, making the structures more visible.
Additionally, barium and iodine have high atomic numbers, which means that they have a greater number of electrons and can effectively attenuate X-rays. This allows for better image contrast and clarity.