Investigation of choice for focal neurologic deficit in emergency room is –

**Core Concept**
Computed Tomography (CT) scans are widely used in emergency medicine to rapidly evaluate patients with acute neurological symptoms, such as focal neurologic deficits, due to their high sensitivity for detecting hemorrhages and acute changes in brain structure.

**Why the Correct Answer is Right**
The correct answer is a CT scan because it provides rapid and detailed images of the brain, allowing emergency physicians to quickly identify potential causes of focal neurologic deficits, such as ischemic strokes, hemorrhages, or tumors. CT scans are particularly useful in the emergency room setting due to their short scanning time and ability to detect acute changes in brain structure.

**Why Each Wrong Option is Incorrect**
**Option A:** MRI (Magnetic Resonance Imaging) is not the primary investigation of choice for focal neurologic deficits in the emergency room due to its longer scanning time and higher cost compared to CT scans.
**Option B:** Angiography is not typically used as an initial investigation for focal neurologic deficits, as it is more invasive and usually reserved for cases where vascular malformations or dissections are suspected.
**Option C:** Lumbar puncture (LP) is not a primary investigation for focal neurologic deficits, as it is more invasive and typically reserved for cases where meningitis or other central nervous system infections are suspected.

**Clinical Pearl / High-Yield Fact**
In the emergency room, it's essential to remember the "ABCs" of stroke diagnosis: Alertness, Blood pressure, Capillary refill, and Cranial nerves. A thorough examination of these areas can help identify patients at risk for stroke and guide further diagnostic testing.

**Correct Answer:** C. Non-contrast CT scan.