**Core Concept**
Acute aortic dissection (AAD) is a medical emergency characterized by the intimal tear of the aorta, leading to the formation of a false lumen and potential compromise of aortic branches. The clinical presentation of AAD is often non-specific, requiring a high index of suspicion for diagnosis.

**Why the Correct Answer is Right**
The initial investigation of choice for suspected AAD is non-contrast computed tomography (CT) of the chest (Option C). This imaging modality provides rapid and accurate assessment of the aorta, allowing for the identification of the intimal tear, false lumen, and potential complications such as aortic rupture or branch vessel involvement. The non-contrast CT protocol helps to minimize the risk of contrast-induced nephropathy in patients with potential renal impairment.

**Why Each Wrong Option is Incorrect**
**Option A:** Echocardiography is not the initial imaging modality of choice for AAD, as it may not provide a clear view of the aortic arch and descending aorta.

**Option B:** MRI is not typically used as the initial investigation for AAD, although it may be useful in selected cases where CT is contraindicated or inconclusive.

**Option D:** Chest X-ray is not sensitive for the diagnosis of AAD and may not be performed as an initial investigation.

**Clinical Pearl / High-Yield Fact**
In patients with suspected AAD, it is essential to maintain a high index of suspicion and promptly initiate imaging studies to confirm the diagnosis. A delay in diagnosis can lead to increased morbidity and mortality.

**Correct Answer:** C. Non-contrast computed tomography (CT) of the chest.