**Core Concept**
Intracranial bleeding, also known as intracranial hemorrhage, is a life-threatening condition that requires prompt diagnosis and management. The ability to detect intracranial bleeding is crucial in the initial assessment of patients with head injuries, and the choice of imaging modality is critical in this context.

**Why the Correct Answer is Right**
CT-scan is the most sensitive investigation for detecting intracranial bleeding in patients with head injuries due to its high sensitivity and rapid availability. CT scans can quickly identify acute hemorrhages, which appear as hyperdense (bright) areas on the scan. This is because blood is denser than brain tissue, making it easily detectable on CT scans. Additionally, CT scans can be performed quickly, even in emergency situations, allowing for timely decision-making and intervention.

**Why Each Wrong Option is Incorrect**
**Option A:** MRI is less sensitive than CT scans for detecting acute intracranial bleeding, especially in the first few hours after injury. While MRI can provide more detailed images, its longer scanning time and lower availability make it less suitable for emergency situations.
**Option B:** X-rays are not suitable for detecting intracranial bleeding, as they are unable to penetrate bone and soft tissue effectively. X-rays are more useful for detecting fractures and other bony injuries.
**Option D:** Ultrasound is not typically used for detecting intracranial bleeding, as it is not sensitive enough to detect hemorrhages within the skull. Ultrasound is more commonly used for assessing soft tissue injuries and other conditions outside the skull.

**Clinical Pearl / High-Yield Fact**
In patients with head injuries, it is essential to perform a rapid and thorough neurological examination, including assessment of level of consciousness, pupillary response, and motor function. This examination can help identify patients at risk of intracranial bleeding and guide the choice of imaging modality.

**✓ Correct Answer: C. CT-scan**