Lung Perfusion Scan

Ventilation-perfusion scan also referred to as lung scintigraphy or commonly V/Q scan, is a diagnostic test utilizing radioisotopes to evaluate pulmonary ventilation and perfusion. The history of the V/Q scan dates to 1964, when its initial clinical application in the diagnosis of pulmonary embolism was reported. While CT pulmonary angiography is currently considered the gold standard and is one of the most commonly used modalities for diagnosing pulmonary embolism, a V/Q scan is useful in assessing the likelihood of pulmonary embolism when intravenous contrast is contraindicated, such as in acute or chronic kidney disease and intravenous contrast allergy. Ventilation perfusion scan consists of two portions, a ventilation (V) scintigraphy and a perfusion (Q) scintigraphy. An aerosolized tracer is administered to assess lung ventilation by evaluating the distribution of the tracer to the alveoli. The assessment of lung perfusion involves administering an injectable tracer and its distribution to the pulmonary vasculature. Over time, many criteria were designed to interpret the V/Q scan. These include the McNeil criteria reported in 1984, the Biello criteria, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) criteria reported in 1990, the PIOPED II criteria, the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISAPED) criteria in 1996, and the European Association of Nuclear Medicine (EANM) guidelines published in 2009.  These criteria are aimed at increasing the diagnostic accuracy of the study.