V/Q Scan (Ventilation-Perfusion Scan): Purpose and Procedure

V/Q scan = Ventilation-Perfusion scan. A nuclear medicine imaging test assessing lung airflow (ventilation) and blood flow (perfusion).

Procedure

1. Ventilation phase: Patient inhales radioactive gas (e.g., Xenon-133 or Technegas) via mask; gamma camera images distribution in airways.
2. Perfusion phase: IV injection of Tc-99m MAA (macroaggregated albumin); particles lodge in pulmonary capillaries; images show blood flow distribution.

Primary Use

Diagnosing pulmonary embolism (PE). Mismatched defects (ventilation normal, perfusion absent) = high probability PE. Matched defects suggest COPD, pneumonia, etc.

Other Uses

• Pre-operative lung resection planning (quantify regional function)
• Chronic thromboembolic pulmonary hypertension (CTEPH) evaluation
• Congenital lung anomalies

Largely replaced by CT pulmonary angiography (CTPA) for acute PE, but still used in pregnancy, contrast allergy, or renal impairment.