**Core Concept**
Pheochromocytoma is a rare, usually benign, tumor of the adrenal gland that secretes excess catecholamines, leading to hypertension and other symptoms. The diagnostic procedure for pheochromocytoma must be carefully chosen to avoid precipitating a potentially life-threatening hypertensive crisis.

**Why the Correct Answer is Right**
The correct answer is **A. Intravenous pyelography (IVP)** because it involves the use of contrast agents, which can cause a sudden release of catecholamines from the tumor, leading to a hypertensive crisis. This is a contraindication for IVP in the diagnosis of pheochromocytoma.

**Why Each Wrong Option is Incorrect**
**Option B:** **MRI** is actually a preferred imaging modality for pheochromocytoma due to its high sensitivity and ability to detect small tumors. It does not involve the use of contrast agents that could precipitate a hypertensive crisis.

**Option C:** **CT scan** can be used to diagnose pheochromocytoma, but it should be performed with non-ionic contrast agents, which carry a lower risk of triggering a hypertensive crisis compared to ionic agents.

**Option D:** **MIBG scintigraphy** is a nuclear medicine test that can help diagnose pheochromocytoma by detecting the uptake of the radiolabeled compound in the tumor.

**Clinical Pearl / High-Yield Fact**
When managing pheochromocytoma, it is essential to use alpha-blockers before beta-blockers to prevent a hypertensive crisis.

**Correct Answer:** A. IVP