**Core Concept**
Non-contrast computed tomography (NCCT) is the investigation of choice for diagnosing acute subdural hemorrhage, particularly in the initial stages. This is due to its high sensitivity and specificity for detecting acute hemorrhage, as well as its rapid availability and low cost.

**Why the Correct Answer is Right**
NCCT is superior for detecting acute hemorrhage because it can identify the hyperdensity of blood within the subdural space. This is achieved through the use of X-rays to generate images of the brain, which are then reconstructed using computer algorithms. The absence of contrast agents allows for the detection of blood without the potential for artifacts or interference from contrast material. Additionally, NCCT is widely available and can be performed quickly, making it an ideal initial imaging modality for acute subdural hemorrhage.

**Why Each Wrong Option is Incorrect**
**Option A:** Angiography is not typically used as an initial imaging modality for subdural hemorrhage, as it is more invasive and not as sensitive for detecting acute hemorrhage.
**Option C:** Contrast-enhanced CT (CECT) is not necessary for diagnosing subdural hemorrhage, as the presence of blood can be detected without the use of contrast agents.
**Option D:** MRI may be used in certain situations, such as when there is a need for better characterization of the hemorrhage or when there are concerns for other types of pathology. However, it is not the initial investigation of choice for acute subdural hemorrhage due to its lower availability and longer scanning time compared to NCCT.

**Clinical Pearl / High-Yield Fact**
In the setting of acute head trauma, a non-contrast CT scan should be performed as soon as possible to evaluate for hemorrhage, with a focus on identifying signs of subdural hemorrhage, such as a crescent-shaped hyperdensity in the subdural space.

**✓ Correct Answer: B. NCCT**