Investigation of choice for acute SAH is:

**Core Concept**
Non-contrast computed tomography (CT) is the primary imaging modality for acute subarachnoid hemorrhage (SAH) detection due to its high sensitivity for blood in the subarachnoid space. SAH involves bleeding into the space surrounding the brain, necessitating prompt diagnosis.

**Why the Correct Answer is Right**
Non-contrast CT scans are widely available, quick, and highly sensitive for detecting acute SAH. This is because blood in the subarachnoid space appears hyperdense on non-contrast CT scans, making it easily distinguishable from surrounding brain tissue. The sensitivity of CT scans for SAH peaks within the first 24-48 hours after the hemorrhage.

**Why Each Wrong Option is Incorrect**
**Option A:** Magnetic Resonance Imaging (MRI) is less sensitive than CT in the acute phase and may not be readily available in emergency situations.
**Option B:** Angiography is more invasive and typically reserved for identifying the source of the hemorrhage, such as an aneurysm or arteriovenous malformation.
**Option C:** Lumbar puncture (LP) may be used in cases where CT or MRI findings are inconclusive, but it is not the first-line investigation for acute SAH.

**Clinical Pearl / High-Yield Fact**
It's essential to note that a negative non-contrast CT scan does not entirely rule out SAH, especially if the hemorrhage is small or has occurred more than 24 hours prior.

**Correct Answer: C. Lumbar puncture (LP) may be used in cases where CT or MRI findings are inconclusive, but it is not the first-line investigation for acute SAH.