Effect of Acute Experimental Pulmonary Arterial Occlusion on the Deposition and Clearance of Technetium-99m-DTPA Radioaerosols

Canine models of autologous PE and balloon occlusion of the pulmonary vasculature were used to evaluate radioaerosol deposition and to quantify radioaerosol clearance in the immediate postembolic period. A total of 28 animals were anesthetized, intubated and studied (central balloon occlusion = 4, peripheral balloon occlusion = 7, autologous PE = 5, various control groups = 12). A gamma camera computer system was used to monitor the distribution and clearance rate of inhaled DTPA radioaerosol. The perfusion defect distribution was determined after the radioaerosol study using 99mTc-MAA. A new radioaerosol deposition defect was seen in 3 of 16 animals in a zone of acute vascular occlusion by a balloon (n = 2) or PE (n = 1). In addition, radioaerosol clearance rates were altered substantially. Peripheral vascular occlusion and PE caused radioaerosol clearance rates to accelerate significantly (control clearance half-time = 33.6 +/- 4.6 min, post-balloon occlusion = 19.0 +/- 8.3 min, post-PE = 12.4 +/_ 3.7 min, both p < 0.05). In only one case did these clearance rate changes create a visible abnormality in the aerosol images. The pulmonary deposition patterns and clearance rates of 99mTc-DTPA radioaerosol can be altered by acute vascular occlusion or PE. These findings should be considered when interpreting radioaerosol images in patients with suspected PE.