**Core Concept**
Myelography is a radiographic technique used to visualize the spinal cord and nerve roots. It involves the introduction of a contrast agent into the subarachnoid space to enhance the visibility of the neural structures on imaging studies.

**Why the Correct Answer is Right**
Iohexol, a non-ionic water-soluble contrast medium, is commonly used for myelography. It is injected into the subarachnoid space to outline the spinal cord, nerve roots, and surrounding structures. Iohexol is preferred due to its non-ionic nature, which reduces the risk of neurotoxicity and allergic reactions.

**Why Each Wrong Option is Incorrect**
**Option A:** Gd-DTPA (Gadolinium-DTPA) is a gadolinium-based contrast agent used in MRI, not myelography. It is not suitable for use in the subarachnoid space.
**Option B:** Conray (Iothalamate) is an ionic contrast agent that was previously used for myelography but has been largely replaced by non-ionic agents like Iohexol due to their safer profile.
**Option C:** Omnipaque (Iohexol) is the correct answer, but this option is incomplete. If you meant to list Iohexol, it is the correct answer.

**Clinical Pearl / High-Yield Fact**
Iohexol is a non-ionic contrast agent that is widely used for myelography due to its safety profile and ability to provide high-quality images of the spinal cord and nerve roots.

**Correct Answer: C. Iohexol**