**Core Concept**
Contrast nephropathy, also known as contrast-induced nephropathy (CIN), is a condition where kidney function is impaired following the administration of contrast media during radiographic procedures. Preventive measures are crucial to minimize this risk, particularly in patients with pre-existing renal dysfunction.

**Why the Correct Answer is Right**
Fenoldopam, a dopamine receptor agonist, is primarily used to manage severe hypertension. Although it has vasodilatory properties, there is no substantial evidence to support its effectiveness in preventing contrast nephropathy. In fact, fenoldopam may even increase the risk of renal dysfunction due to its potential to cause renal vasodilation and reduce renal perfusion.

**Why Each Wrong Option is Incorrect**
**Option B:** N-acetylcysteine (NAC) has been widely studied as a potential preventative measure for contrast nephropathy. Its mechanism involves the replenishment of glutathione stores, which helps to reduce oxidative stress and protect renal function. While its efficacy is still a topic of debate, NAC remains a commonly used agent in the prevention of contrast nephropathy.

**Option C:** Infusion of normal saline is a well-established method for preventing contrast nephropathy. The rationale behind this approach is to maintain adequate hydration, which helps to reduce the concentration of contrast media within the kidneys and minimize the risk of renal damage.

**Option D:** Hemodialysis is an effective method for removing contrast media from the bloodstream and can be used to prevent or treat contrast nephropathy in patients with severe renal impairment.

**Clinical Pearl / High-Yield Fact**
In patients at high risk of contrast nephropathy, it is essential to maintain adequate hydration using intravenous fluids, such as normal saline, to reduce the risk of renal damage.

**✓ Correct Answer: A. Fenoldopam. Fenoldopam is not used to prevent contrast nephropathy.**