Computer processing of perfusion, ventilation, and V/Q images to highlight pulmonary embolism

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Abstract
A method is described for generating regional ventilation/perfusion (V/Q) images of the lung to aid assessment of suspected pulmonary embolism, especially in patients with obstructive airways disease. The radionuclide scans used for this are stored on a computer and comprise: lung perfusion (P) with Tc-99 m MAA, lung ventilation at equilibrium (E) with Xe-127, and the sum of the Xe-127 washout images (W). A functional ventilation image is calculated as V=E/W and a functional perfusion image as Q=P/E. Finally a ventilation perfusion ratio image is obtained by taking V/Q. This is normalised by a factor determined from the cumulative frequency distributions of the counts per pixel in the Q and V images so that areas which are well ventilated and perfused are given a V/Q value of 1.0. Areas with normalised V/Q values>1.5 suggest pulmonary embolism. In 100 studies on patients with abnormal perfusion scans this method proved very helpful by assisting the recognition or exclusion of areas with abnormally high V/Q values.