**Core Concept**
Focused Assessment with Sonography for Trauma (FAST) is a rapid ultrasound examination used to detect free intraperitoneal or intrathoracic fluid. It involves scanning specific regions of the abdomen and chest to identify potential sources of bleeding or fluid accumulation.

**Why the Correct Answer is Right**
FAST typically includes scanning of the hepatorenal (right upper quadrant), splenorenal (left upper quadrant), and suprapubic regions. However, it does not involve scanning of the lower limbs. This is because FAST is primarily focused on detecting free fluid in the abdominal cavity, and the lower limbs are not directly relevant to this assessment.

**Why Each Wrong Option is Incorrect**
**Option A:** Scanning of the thoracic cavity is a part of FAST, specifically looking for fluid in the pericardial space or pleural spaces.
**Option B:** The lower abdomen and pelvis are included in the suprapubic region, which is a part of the FAST examination.
**Option C:** Scanning of the upper abdomen, including the hepatorenal and splenorenal spaces, is a critical component of FAST.

**Clinical Pearl / High-Yield Fact**
When performing FAST, it's essential to remember that the examination is not a comprehensive assessment of the abdominal or thoracic organs. It's a rapid, targeted evaluation to identify free fluid or other life-threatening conditions.

**Correct Answer: D. Lower limbs. Lower limbs are not included in the FAST examination.**