Scintigraphic analysis as a diagnostic tool in canine experimental lung embolism

Scintigraphic changes occurring after lung embolism induced by intravenous administration of agar were assessed in 10 anesthetized prone dogs. Using 99mTc aerosol inhalation combined with 99mTc perfusion scintigraphy, parameters quantifying the regional distribution of the inhalation-to-perfusion ratio (I/P) and the degree of intraregional I-P mismatching were calculated from dorsoventral views (DV) for 6 equidistant cranial-to-caudal left and right lung zones before (B) and after acute embolism (PE). Postmortem examination was performed in 7 dogs. Several perfusion defects could be detected in either the conventional or the functional (I-P) lung scintigrams. Nevertheless, PE did not induce significant changes in blood gases. On the scintigrams, the outer zones appeared to be the most heavily embolized. The regional I/P ratio was increased in the more caudal and cranial parts of both lungs. However, postmortem examination of the lungs showed the presence of emboli diffuse in all lobes. Their presence was revealed in all zones by a significant increase of an intraregional mismatching index rho and especially of an intraregional mismatching factor mean value of gamma. After acute embolism, blood was redistributed to perihilar regions, especially in the right lung. This redistribution process continued during the experiment. In conclusion, the use of combined aerosol inhalation/perfusion lung scintigraphy with quantitative analysis provides a sensitive method for the detection of pulmonary embolism.