After injection of 131I-MAA (macro-aggregated human serum albumin), the authors obtained pulmonary scans from 500 patients with various pulmonary diseases. The results of scanning and of standard roentgenographic examination are compared on the basis of 138 cases with definitely diagnosed malignant pulmonary tumors. I n all cases with central tumors, i.e., tumors that were located near the hilus, the scan was abnormal and thus indicated a disorder of pulmonary perfusion. In contrast to this, radiologic examination (thoracic films in two planes and, if indicated, fluoroscopy) only disclosed direct or indirect signs of cancer in 88% of these cases. Therefore, lung scanning as a screening method for central pulmonary tumors is a more sensitive diagnostic tool than standard roentgenographic examination. I n cases of peripheral pulmonary tumors, a perfusion disorder which is larger than the radiologically recognizable lesion indicates central metastases.
HE V.4LUE OF THE PULMONARY SCINTIGRAM,
T after injection of labelled MAA, has been demonstrated in the diagnosis and localization of pulmonary blood-distribution disorders. This method is primarily suited for the diagnosis of embolism.3~ 4, 8 , 11, 13, 15-18, 21 T h e area of lung which is excluded from functional perfusion by the embolus remains free of radioactivity and appears in the scan as a "cold area." T h e same mechanism of vascular occlusion may be produced by compression or very rarely by tumor invasion into the pulmonary vessels as observed in two of our cases at autopsy. T h e result of this mechanism is a direct perfusion disorder, i.e., primary due to vascular causes. As has been shown by pathologico-anatomic, angiographic and experimental studies (occlusion of a bronchus, local ventilation with oxygen-poor gas-mixtures), blood-distribution disorders also occur indirectly as a result of ventilation disorders. Any local impediment to ventilation or any decrease of the partial pressure of the alveolar oxygen tension results in a corresponding decrease of the regional functional perfusion-a decrease of alveolar oxygen tension produces contraction of the precapillaries and because of that the peripheral resistance is increased, whereas the flow-rate is decreased. This process, which has been designated by