^<99m>Tc-MAA SPECT in Patients with Pulmonary Thromboembolism

Abstract

Background. Acute pulmonary thromboembolism (APTE) is increasing in Japan. Semiquantification of the number of segments with perfusion defect by ^<99m>Tc-MAA SPECT might allow us to predict aggravation to chronic thromboembolic pulmonary hypertension (CTPH). Purpose. To assess the significance of serial semi-quantitative studies by ^<99m>Tc-MAA SPECT in patients with APTE. Methods. We enrolled 26 patients who had been given a diagnosis of APTE by means of CT pulmonary angiography and/or pulmonary angiography between 2002 and 2006. All patients underwent ^<133>Xe gas ventilation/^<99m>Tc-M A A perfusion SPECT studies or perfusion SPECT study only, every 6 to 12 months, twice or more. Results. Of the 26 patients with APTE, 18 (26.9%) improved after thrombolytic treatment with reduction in mean numbers of perfusion defect segments from 6.75 to 2.80. Complete resolution of embolism on 99mTc-MAA SPECT following the thrombolysis was seen in only 4 patients (15.4%) with APTE. On the other hand, 7 patients with APTE exhibited deterioration or no change, and one showed both improvement and deterioration in the serial SPECT studies. Thus, 8 patients (30.8%) had no improvement of pulmonary perfusion on the serial SPECT studies despite thrombolytic treatment. Conclusion. We believe that serial ^<99m>Tc-MAA SPECT studies are useful in monitoring semi-quantitative assessment of pulmonary perfusion defects and of aggravation to CTPE after thrombolytic treatment.