V/Q scan is used as an alternative to CT in PE for patients in which situation?

• A. Alternative to CT when CT is contraindicated due to renal insufficiency
• B. Primary test for DVT
• C. Not used in PE
• D. Used to monitor anticoagulation

Answer: (A)

When IV contrast for CT pulmonary angiography is risky because of kidney problems, a ventilation-perfusion scan offers a safe alternative to evaluate for pulmonary embolism. It uses two parts: ventilation, with an inhaled radiotracer to image air reaching the alveoli, and perfusion, with an IV radiotracer to show blood flow. A PE typically creates a mismatch where ventilation is good but perfusion is reduced in the same region of the lung. A high-probability V/Q result supports PE, while a normal scan can effectively exclude PE in many patients without underlying lung disease; nondiagnostic results may require further testing.

This approach isn’t used to diagnose DVT—that’s usually done with ultrasound—nor is it used to monitor anticoagulation. Its key advantage here is avoiding iodinated contrast in patients with renal insufficiency.