**Core Concept**
Non-contrast computed tomography (CT) scan is the initial imaging modality of choice for acute stroke, intracranial hemorrhage, and head trauma, particularly when sub-periosteal bleeding is suspected. This is because CT scans can quickly identify acute hemorrhage and bone fractures.

**Why the Correct Answer is Right**
Non-contrast CT scans are particularly useful in identifying acute hemorrhage due to their high sensitivity and speed. In the case of sub-periosteal bleeding, a non-contrast CT scan can help differentiate between hemorrhage and other potential causes of contralateral hemiplegia, such as ischemic stroke or a subdural hematoma. The CT scan will show hyperdensity in the affected area, indicating bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** Magnetic Resonance Imaging (MRI) is not the initial investigation of choice due to its longer scan time and lower availability in emergency settings.
**Option B:** Computed Tomography Angiography (CTA) is not the initial investigation of choice as it involves contrast administration, which is contraindicated in acute hemorrhage.
**Option C:** Magnetic Resonance Angiography (MRA) is not the initial investigation of choice due to its lower sensitivity and specificity compared to CT scans in detecting acute hemorrhage.

**Clinical Pearl / High-Yield Fact**
In emergency settings, a non-contrast CT scan should always be performed first to quickly assess for acute hemorrhage, which is a contraindication to contrast administration.

**Correct Answer:** C. Non-contrast CT scan of the head