**Core Concept**
Myelography is a type of radiographic imaging used to visualize the spinal cord and nerve roots. It involves injecting a contrast agent into the spinal canal to enhance the visibility of the spine and surrounding structures on X-rays or CT scans. The contrast agent used in myelography must be non-toxic, non-irritating, and able to remain in the subarachnoid space for an extended period.

**Why the Correct Answer is Right**
Iohexol, the correct answer, is a non-ionic, water-soluble iodinated contrast agent that is commonly used for myelography. It is able to remain in the subarachnoid space for several hours, providing a clear image of the spinal cord and nerve roots. Iohexol is also non-toxic and non-irritating, making it an ideal choice for myelography.

**Why Each Wrong Option is Incorrect**
* **Option A:** Gd-DTPA is a gadolinium-based contrast agent used primarily in MRI scans to enhance the visualization of soft tissues. It is not suitable for myelography due to its gadolinium content, which can cause toxicity if not properly cleared from the body.
* **Option B:** Diatrizoate meglumine is an ionic, water-soluble iodinated contrast agent used for various imaging procedures, including X-rays and CT scans. However, it is not the preferred choice for myelography due to its potential to cause irritation and toxicity in the subarachnoid space.
* **Option C:** Iopamidol is another non-ionic, water-soluble iodinated contrast agent used for various imaging procedures. While it is generally safe, it is not the preferred choice for myelography due to its potential to cause contrast-induced nephropathy.

**Clinical Pearl / High-Yield Fact**
When performing myelography, it is essential to use a non-ionic, water-soluble contrast agent to minimize the risk of toxicity and irritation in the subarachnoid space. Iohexol is a safe and effective choice for myelography due to its non-toxic and non-irritating properties.

**Correct Answer:** C. Iopamidol is incorrect, the correct answer is actually Iohexol, but it was not among the options provided.