**Core Concept**
Contrast nephropathy, also known as contrast-induced nephropathy (CIN), is a common complication of angiography and other radiographic procedures that involve the use of iodinated contrast media. This condition is characterized by a decline in renal function, which can be reversible or, in severe cases, lead to acute kidney injury.

**Why the Correct Answer is Right**
Fenoldopam is a dopamine receptor agonist that increases renal blood flow by causing vasodilation of the renal arteries. However, its effectiveness in preventing contrast nephropathy has not been consistently demonstrated in clinical trials. In fact, some studies have shown that fenoldopam may even increase the risk of CIN. Therefore, it is not recommended as a preventive measure for contrast nephropathy.

**Why Each Wrong Option is Incorrect**
**Option A:** Haemofiltration is a form of renal replacement therapy that can be used to prevent contrast nephropathy, especially in patients with pre-existing renal impairment. It involves the removal of excess fluids and waste products from the blood, which can help to reduce the risk of CIN.

**Option C:** N-acetylcysteine is an antioxidant that has been shown to have a protective effect on the kidneys in patients undergoing procedures that involve the use of contrast media. It is thought to work by reducing oxidative stress and inflammation in the kidneys.

**Option D:** 1/2 N saline is a type of hydration regimen that involves the administration of half-normal saline solution to patients undergoing procedures that involve the use of contrast media. This can help to reduce the risk of CIN by maintaining adequate renal perfusion and preventing dehydration.

**Clinical Pearl / High-Yield Fact**
The American College of Radiology recommends using a combination of hydration and a contrast agent that is less nephrotoxic, such as iodixanol or iohexol, to reduce the risk of contrast nephropathy.

**Correct Answer:**
✓ Correct Answer: B. Fenoldopam