A 58-year-old man with acute onset dyspnea and pleuritic chest pain presents to the emergency department. Clinical suspicion for pulmonary embolism is high. Which imaging modality is the investigation of choice for confirming acute pulmonary embolism?

Explanation

## Investigation of Choice for Acute PE **Key Point:** Computed tomography pulmonary angiography (CTPA) is the gold standard and investigation of choice for confirming acute pulmonary embolism in hemodynamically stable patients. ### Why CTPA is Superior **High-Yield:** CTPA offers: - High sensitivity (94–98%) and specificity (95–98%) for central and segmental emboli - Fast acquisition time (< 1 minute) - Ability to visualize alternative diagnoses (pneumonia, aortic dissection, pneumothorax) - Widely available in most hospitals - Can assess right ventricular strain and guide risk stratification ### Comparison of Imaging Modalities | Modality | Sensitivity | Specificity | Advantages | Disadvantages | |----------|-------------|-------------|-----------|---------------| | **CTPA** | 94–98% | 95–98% | Fast, high accuracy, alternative diagnoses | Radiation, contrast allergy | | V/Q Scan | 80–90% | 80–90% | Lower radiation, no contrast | Slower, high false-positive rate, needs baseline CXR | | MRPA | 90–95% | 95–98% | No radiation, no iodine contrast | Slow, contraindicated with metallic implants, less available | | CXR + D-dimer | Variable | Variable | Initial screening | Low specificity, not diagnostic | **Clinical Pearl:** CTPA is preferred in hemodynamically stable patients with intermediate to high clinical probability. In patients with renal insufficiency or contrast allergy, MRPA or V/Q scan may be alternatives. ### Role of D-dimer **Key Point:** D-dimer is a screening tool with high sensitivity but low specificity. A negative D-dimer in low-risk patients can exclude PE without imaging; however, it cannot diagnose PE and must always be followed by imaging in intermediate/high-risk patients. ### CTPA Protocol Features 1. **Timing:** Bolus tracking or test bolus to optimize pulmonary artery opacification 2. **Reconstruction:** Thin-section (1–2 mm) multiplanar reconstructions improve detection of subsegmental emboli 3. **Right ventricular assessment:** RV/LV ratio > 0.9 indicates RV strain and worse prognosis 4. **Ancillary findings:** Wedge-shaped infarction, pleural effusion, atelectasis **Mnemonic: CTPA GOLD** — CT Pulmonary Angiography is the GOLD standard for PE diagnosis.