RespiratoryTier 2Topic

Imaging - V / Q scan

Role

Nuclear medicine ventilation-perfusion scan - compares regional airflow (inhaled radiolabelled gas/aerosol) to regional blood flow (IV radiolabelled albumin) - a "mismatch" (ventilated but not perfused) suggests pulmonary embolism
An alternative to CTPA, preferred when contrast/radiation to the breast is a specific concern (younger patients, pregnancy) or renal impairment precludes contrast

Principle

PE causes perfusion defects with preserved ventilation in the same segment (mismatch); parenchymal lung disease (e.g. pneumonia, COPD) causes matched V/Q defects (both reduced together) - not indicative of PE

Reporting

Reported as low/intermediate/high probability (PIOPED criteria) rather than a binary result - an intermediate-probability result requires further testing, unlike the largely binary result of CTPA

Requirements

Requires a reasonably normal baseline CXR for reliable interpretation - significant underlying lung disease (COPD, ILD) makes V/Q scanning harder to interpret, favouring CTPA instead

Indications

Pulmonary embolism, chronic thromboembolic pulmonary hypertension (V/Q remains the screening test of choice here even with CTPA available, given superior sensitivity for chronic/small peripheral emboli)

A normal scan

A normal perfusion scan effectively excludes clinically significant PE

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.

Get premium access