**Question:** The investigation of choice in acute ischemic stroke (AIS) is:

A. CT (Computed Tomography)
B. MRI (Magnetic Resonance Imaging)
C. Angiography
D. Ultrasound

**Core Concept:** Acute ischemic stroke is a medical emergency characterized by a rapid onset of neurological deficits due to cerebral ischemia. The appropriate diagnostic modality would help guide acute management decisions and thrombolysis eligibility.

**Why the Correct Answer is Right:**

Correct Answer: C. Angiography

Angiography is the gold standard investigation for AIS, as it directly visualizes the cerebral vasculature and provides information about the extent and location of the occlusive lesion. Angiography can reveal the presence of intracranial occlusion, stenosis, or aneurysms that may require specific interventions.

**Why Each Wrong Option is Incorrect:**

A. CT (Computed Tomography) is a valuable tool in AIS for initial evaluation, excluding hemorrhagic stroke and assessing the extent of cerebral edema. However, CT lacks the spatial resolution to evaluate intracranial vasculature, making angiography the superior choice for identifying the cause of stroke.

B. MRI (Magnetic Resonance Imaging) is essential in AIS for assessing brain tissue viability, identifying early ischemic changes, and detecting other potential causes of neurological deficits. However, MRI is not as effective as angiography in identifying the occlusive lesion.

D. Ultrasound is primarily used for peripheral vascular evaluation and is not the first-line investigation for AIS. Ultrasound may detect certain vascular occlusions but lacks the spatial resolution for accurate identification of the occlusive lesion in the brain.

**Clinical Pearl:** Early diagnosis and identification of the occlusive lesion in AIS are crucial for prompt initiation of reperfusion therapies, such as intravenous thrombolysis or endovascular interventions, improving patient outcomes.

In summary, while CT and MRI are essential components of the stroke workup, angiography remains the superior investigation to identify the specific cause of stroke and guide appropriate management.