VQ scan

V/Q

Helps measure the gas distribution in the lungs Ventilation Scan and Perfusion scan are done separately Results provide maximum amount of info when used together

Alveolar ventilation -

Movement of air between the environment and lungs via inhalation and exhalation

Perfusion procedure

Patient is injected intravenously with radioactive iodine Serial perfusion scans are made over the lungs as blood perfuses the lungs

Pulmonary perfusion-

Blood flow to lungs available for O2 exchange

When to use VQ scan

Rule out pulmonary emboli Particularly in individuals with DVTs, have a high clinical likelihood of PE, and a positive D-dimer test (rules out PE and DVT) CT scans are used more often and have a greater definitive reliability V/Q scans are nondiagnostic --> less sensitive and specific for PE than CT scans A normal (negative) scan has less than 5% probability of PE However, a high probability scan has 96% predictive value in high risk patients V/Q scans can be used when CT scans are contraindicated such as pregnancy or chronic kidney disease

Ventilation procedure

The patient is positioned in sitting or supine The patient is asked to inhale a normal tidal volume of a closed system of xenon gas and hold the breath while scans are performed Serial scans are made over 10-15 minutes to determine the rate of equilibrium of the gas in the lungs through rebreathing techniques Serial scans are then made to determine the washout rate of the xenon gas, and the patient is instructed to return to atmospheric breathing

Normal results

There will be greater ventilation and perfusion in the bases of the lungs and less in the apices