V/Q ventilation-perfusion lung scans

Introduction

V/Q lung scans are performed to help in the diagnosis of pulmonary embolism
patient inhales a radioactive gas in the ventilation phase and a special camera is then used to image these results
patient is then given an intravenous injection of radioactive labelled albumin and then the camera records these perfusion scan images
the radiologist looks for areas where the lung is ventilated but there is reduced perfusion and this is suggestive of a PE

patients with airway infections are generally not permitted to have the ventilation phase
a recent CXR preferably with past 24hrs is required for the interpretation of these images as per PIOPED protocols
- CXR findings such as COPD, cardiomegaly, pleural effusion, consolidation may change the interpretation of the scan
- patients with COPD commonly have matched V/Q abnormalities due to hypoxic vasoconstriction
only 15% of patients with a PE have a high probability scan
a VQ interpreted as being high probability for PE will 90% probability of having a PE
around half of patients with a PE will have an indeterminate scan as there is both reduced ventilation and reduced perfusion and may need CTPA to confirm