**Core Concept**
Trauma imaging involves the evaluation of patients with acute injuries, requiring rapid and accurate assessment of injuries to guide clinical management. The mainstay modality in trauma imaging should be able to quickly identify life-threatening injuries, such as bleeding, pneumothorax, and fractures.

**Why the Correct Answer is Right**
Computed Tomography (CT) is the mainstay in trauma imaging due to its high sensitivity and specificity in detecting a wide range of injuries, including bone fractures, soft tissue injuries, and internal bleeding. CT scans can be performed quickly, often in under 30 minutes, allowing for rapid triage and prioritization of patients. The use of contrast agents can also help identify vascular injuries and bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** Ultrasonography is useful in specific trauma cases, such as detecting free fluid in the abdomen or thorax, but it is not the mainstay modality in trauma imaging due to its limited field of view and lack of comprehensive assessment.

**Option B:** Magnetic Resonance Imaging (MRI) is not commonly used in trauma imaging due to its longer scan times, higher costs, and limited availability in acute settings. MRI is more suitable for evaluating musculoskeletal injuries and certain types of internal injuries.

**Option C:** Plain radiography is often used as an initial screening tool in trauma but is limited in its ability to detect soft tissue injuries and internal bleeding. It is not the mainstay modality in trauma imaging due to its lower sensitivity and specificity compared to CT.

**Option D:** Angiography is a specialized imaging modality used to evaluate vascular injuries and bleeding but is not the mainstay modality in trauma imaging due to its invasive nature and limited availability in acute settings.

**Clinical Pearl / High-Yield Fact**
In trauma imaging, the Focused Assessment with Sonography for Trauma (FAST) exam is a bedside ultrasound examination that can quickly identify free fluid in the abdomen or thorax, helping to guide initial management and triage.

**Correct Answer:** C. Computed Tomography (CT)