COMPARISON OF TC-99M AEROSOL AND KRYPTON-81M IN VENTILATION STUDIES FOR THE DIAGNOSIS OF PULMONARY-EMBOLISM

A new method of producing aerosols (technegas) in which99Tcmis bound to carbon atoms (99Tcm-C) was evaluated by comparing99Tcm-C images with those obtained with81Krmin the same patients. Twenty-five patients with suspected pulmonary embolism (PE) were studied. Immediately after the last99Tcm-C view, the patients remained in supine position and inhaled81Krmat tidal volume. Immediately after the81Krmventilation views were recorded, 4-7 mCi of MAA were injected IV. The same four views (ant, lop, rop, post) were recorded after inhalation of99Tcm-C and 81Krm (200 kcounts) and99TcmMAA injection (400 kcounts). The mean penetration index of99Tcm-C (0.91) was lower than that of81Krm(1.04) (P<0.03). The apex to base lung distribution of99Tcm-C and81Krmappeared to be similar. The mean heterogeneity of 99Tcm distribution was 23, greater than that of81Krm(14) (P = 10-4). The99Tcm-C ventilation image quality was considered very good for 16 patients and good for 6 others. Significant foci of high bronchial uptake were infrequent. Interpretation of the examinations performed after inhalation of99Tcm-C and81Krmwas concordant in all cases. No patient had an81Krm/99TcmMAA examination suggestive of PE when99Tcm-C/99TcmMAA indicated a low probability of PE, and vice versa.99Tcm-C aerosols enable good quality ventilation images to be obtained in nearly all cases. Thus99Tcm-C aerosols could be used in preference to81Krmin ventilation studies for the diagnosis of PE. © 1990 Chapman and Hall Ltd.