**Core Concept**
In pulmonary embolism (PE), perfusion scans are a crucial diagnostic tool that detects mismatch between ventilation and perfusion in the lungs. The principle of perfusion scanning relies on the accumulation of radiolabeled particles in areas of lung tissue with adequate blood flow, highlighting areas of potential embolism.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of pulmonary embolism. In PE, the embolus blocks blood flow to a segment of lung tissue, resulting in a perfusion defect. This defect is due to the lack of blood flow to the affected area, which is best visualized on a perfusion scan. The lung scan and radiograph may appear normal because the embolus may not cause significant structural changes to the lung parenchyma. However, the perfusion scan can detect the mismatch between ventilation and perfusion, indicating a potential embolism.

**Why Each Wrong Option is Incorrect**
**Option A:** Perfusion segmental defect - While this is a possible finding in pulmonary embolism, it is not the most specific answer choice. A segmental defect could also be due to other causes such as pneumonia or atelectasis.

**Option B:** Perfusion defect with normal lung scan & radiograph - This is the correct answer because a perfusion defect on a perfusion scan with a normal lung scan and radiograph is a classic finding in pulmonary embolism, indicating a mismatch between ventilation and perfusion.

**Option C:** Tenting of diaphragm - Tenting of the diaphragm is not a finding typically associated with pulmonary embolism. It is more commonly seen in conditions such as pneumothorax or pleural effusion.

**Option D:** Normal chest scan - A normal chest scan would not indicate pulmonary embolism. While a perfusion scan may appear normal in some cases of PE, the combination of a normal lung scan and radiograph with a perfusion defect is highly suggestive of PE.

**Clinical Pearl / High-Yield Fact**
In pulmonary embolism, the presence of a perfusion defect on a perfusion scan with a normal lung scan and radiograph is a key diagnostic clue. This finding is often associated with a high clinical suspicion of PE, and further testing such as CT pulmonary angiography may be warranted.

**Correct Answer:** B. Perfusion defect with normal lung scan & radiograph