Lung Ventilation-Perfusion Scan (V/Q Scan) 2015/2016 الدكتور قصي المقبل أستاذ مشارك- قسم الأشعة والطب النووي كلية الطب-جامعة العلوم والتكنولوجيا الأردنية

Pulmonary Embolism The main application of this procedure is in pulmonary embolism investigation. Pulmonary embolism usually causes perfusion defects, which usually occur in more than one segment.

Technique Perfusion scan is usually correlated with ventilation scan. If perfusion scan is normal, ventilation scan can be skipped. If there are segmental perfusion defects, then ventilation scan is needed.

Normal Perfusion Images Normal Scan: A completely normal lung scan rules out the possibility of pulmonary embolism. I am afraid this statement is not true in my experience. Low Probability Scan: This implies that the probability of pulmonary embolism is low. However it does not rule out pulmonary embolism. Indeterminate: High Probability Scan: This is diagnostic of pulmonary embolism. However, it is not absolutely diagnostic of pulmonary embolism. A proper comprehension of terminology and what is implied, is important to know.

Normal Ventilation Scan

Normal Ventilation/Perfusion Brief history: Shortness of breath. Ventilation images (vq009vq2.gif). Sequential 1 minute frames. (ignore the activity outside of the lungs on the single breath image) Findings:Note the impression of the heart and great vessels on the lungs, and the mildly decrease activity at the lung apices. These findings are most apparent on the anterior image.

Perfusion defects usually indicate PE But no all perfusion defects are due to PE. So, they should be correlated with ventilation

Types of Perfusion Defects Mismatched Perfusion defects: -Ventilation is normal in that segment -Indicative of PE. Matched Perfusion defects: -Ventilation defect in that segment. -It is usually seen in parenchymal lung disease.

RESULTS Normal perfusion scan: means that the patient is very unlikely to have acute PE. Low probability V/Q scan: means that the patient has less than 20% probability of having acute PE.

RESULTS-Cont.. High probability V/Q scan: means that the patient has greater than 80% probability of having acute PE. Intermediate probability V/Q scan: means that the patient has between 20 – 80% probabilities of having acute PE.

High Probability for PE Brief history: Normal chest radiograph. The patient presented with recent onset of shortness of breath and chest pain. There was no fever or cough to suggest an infectious process. The chest radiograph was normal. Xe-133 ventilation images : one minute per frame with washout images in the lower row. Findings: Multiple large defects are seen, including the apical-posterior and anterior segments of the left upper lobe, multiple left basilar defects, and a moderate defect at the right apex. Ventilation scintigraphy was normal, as was the chest radiograph. Ffindings easily meet the criteria for "high likelihood for pulmonary embolism" .

High probability for PE

V/Q Scan and CTPA A normal perfusion scan essentially excludes the diagnosis of PE (100% sensitive). A positive perfusion scan does mean 100% PE (lower specificity).

CTPA: Large filling defect in the right main pulmonary artery = PE

V/Q Scan and CTPA V/Q scans are often preferred over CT angiography for patients who have contrast allergies and renal failure as well as in young pregnant women patients. V/Q scan is also indicated if CTPA is negative with persistent high clinical suspicion for PE.

V/Q Scan and CTPA Normal CTPA of the lungs does not 100% exclude PE (less sensitive than V/Q scan). The reason for that is small emboli (subsegmental or perioheral). CTPA is much more specific than V/Q scan. Positive V/Q scan does not mean for sure that the patient has PE (low specificity). Positive CTPA is 100% specific.