UNLABELLED The lung scan is one of the most important diagnostic tests used for selecting candidates for lung volume reduction surgery (LVRS) and for determining the actual percentage of lung to be resected during the surgery (McKenna R, personal communication, 1997). This article describes the anatomical quantitation of the lungs. METHODS We used automatic and manual regions of interest in the posterior, and both posterior obliques of lung perfusion images to calculate the percent function in each individual lung lobe. RESULTS We evaluated 172 patients with this technique. Subsequently 136 of these patients had LVRS. CONCLUSION The anatomical placement of regions of interest in the lung perfusion image aids the thoracic surgeon in selecting LVRS candidates and in determining the amount of lung to be resected during surgery.