Ba ckground The a sse ssment of regional pulmonary ventilation and perfusion is e ssential for theevaluation of a variety of lung disorders1 Pulmonary ventilation MRI using inhaled oxygen a s a contra stmedium can be obtained with a clinical MR scanner, without additional equipment, and ha s beendemonstrated to be a fea sible means of a sse ssing ventilation in animal models and some clinical patient s1However, few studie s have reported on MR ventilation-perfusion imaging1 In this study, we evaluated theusefulne ss of oxygen-enhanced ventilation in combination with first-pa ss Gd-DTPA-enhanced perfusion MRIin a canine model of pulmonary embolism and airway obstruction1Met h o ds Peripheral pulmonary embolisms were produced in eight dogs by intravenous injection of gelfoamstrip s at the pulmonary segmental arterial level, and airway obstructions were created in five of the dogs byinserting a self-de signed balloon catheter into asecondary bronchus1 Oxygen-enhanced MR ventilationimages were produced by subtracting images from before and after inhalation of pure oxygen1 Pulmonaryperfusion MR images were acquired with a dynamic three-dimensional fast gradient2echo sequence1 MRventilation and perfusion image swere read and contra sted with re sult s from general examinations ofpathological anatomy, ventilation2perfusion scintigraphy, and pulmonary angiography Results Regions identified as having airway obstructions matched using both MR ventilation and perfusionimaging, but regions of pulmonary embolisms were mismatched1 The area of airway obstruction defect swa s smaller using MR ventilation imagery than that using ventilation scintigraphy1 Abnormal perfusionregions due to pulmonary embolisms were divided into defective regions and reduced regions ba sed on thetime course of signal intensity change s1 In the diagno sis of pulmonary embolisms with the technique ofventilation and perfusion MRI, sensitivity and specificity were 75.0% and 98.1%, re spectively, and thediagno stic re sult s of this MRI technique were in agreement with the results of ventilation-perfusionscintigraphy and pulmonary angiography (K: 01899, 01743) Conclusions Oxygen-enhanced ventilation in combination with pulmonary perfusion MRI can be used todiagno se abnormalitie s of airways and blood ve ssels in the lungs, and can provide regional functionalinformation with high spatial and temporal re solution1 This method possesses great potential value forclinical applications1