**Core Concept**
Myelography is a radiographic imaging technique used to visualize the spinal cord and nerve roots. It involves the injection of a contrast agent into the cerebrospinal fluid (CSF) surrounding the spinal cord to enhance visualization of the neural structures.

**Why the Correct Answer is Right**
The correct answer is **Iodinated contrast agents**, specifically water-soluble iodinated contrast media such as iohexol or metrizamide. These agents are used for myelography because they remain in the CSF for an extended period, allowing for optimal visualization of the spinal cord and nerve roots. The iodine in these agents absorbs X-rays, making the neural structures more visible on radiographs.

**Why Each Wrong Option is Incorrect**
**Option A:** **Air** is not used for myelography because it does not provide sufficient contrast to visualize the neural structures. Air myelography was used in the past, but it has largely been replaced by iodinated contrast agents.
**Option B:** **Gadolinium-based contrast agents** are used in MRI (Magnetic Resonance Imaging) procedures, not myelography. They are not suitable for myelography because they are not water-soluble and may cause toxicity at high concentrations.
**Option C:** **Barium sulfate** is used as a contrast agent in gastrointestinal imaging procedures, such as barium swallow or barium enema. It is not suitable for myelography because it is not water-soluble and may cause toxicity at high concentrations.

**Clinical Pearl / High-Yield Fact**
When performing myelography, it is essential to use water-soluble iodinated contrast agents to avoid the risk of arachnoiditis, a condition characterized by inflammation of the arachnoid membrane surrounding the spinal cord.

**Correct Answer: C. Iodinated contrast agents**