Final answer:
The substance that determines the radiodensity of contrast media is iodine. This is because the radiodensity is related to the atomic number of the element, with higher atomic numbers providing better contrast on radiographic images. Barium and gadolinium are other contrast agents used for different imaging purposes. The correct option is (b)
Step-by-step explanation:
The substance that determines the radiodensity of contrast media is iodine. When it comes to imaging modalities such as CT scans and X-rays, contrast agents are crucial for enhancing the visibility of internal structures. Iodine is utilized in these contrast agents because of its high atomic number, which ensures efficient absorption of X-rays and therefore good contrast on radiographic images. This is because the radiodensity, which refers to the ability of a substance to attenuate X-rays, is directly related to the atomic number of the element constituting the contrast medium. Elements with higher atomic numbers will have greater radiodensity and thus provide better contrast. Barium is also a common contrast agent, especially in gastrointestinal studies, due to its high atomic number as well, whereas gadolinium is typically used in Magnetic Resonance Imaging (MRI) as a contrast agent. Gadolinium is not typically used in X-ray or CT imaging due to its different properties relevant to MRI.
Additionally, materials for radiation shielding are arranged in terms of effectiveness as follows:
- A solid with high density composed of high-mass atoms. (Best)
- A gas composed of high-mass atoms.
- A solid material with low density composed of low-mass atoms.
- A gas composed of low-mass atoms. (Worst)
This ordering is based on how radiation loses its energy in matter; denser materials with higher-mass atoms are more effective in absorbing radiation, making them better shields.