Depiction of pulmonary emboli with spiral CT: Optimization of display window settings in a porcine model

PURPOSE: To determine optimal spiral computed tomographic (CT) image display for depiction of pulmonary emboli (PE). MATERIALS AND METHODS: Autologous PE detected in 10 pigs with contrast material-enhanced spiral CT were displayed with six display window settings (standard mediastinal window and five modified windows referenced to attenuation values in pulmonary artery [PA] branches). The thrombus gray level and gray level contrast and separability of PE versus those of the local PA branch were computed for each window setting; results were compared with repeated measured analysis of variance. RESULTS: Of 114 PE detected pathologically, 28 were visible with spiral CT. Two of the 28 PE were not detectable with standard mediastinal windows. Statistically significantly improved gray level contrast and separability were noted with modified windows referenced to the second order PA branch and the local PA branch than with the standard mediastinal and other modified window settings (P < .05). However, thrombus gray level was statistically significantly higher with the standard mediastinal window (P < .05). CONCLUSION: PE are best depicted as filling defects when displayed with a modified window referenced to the right or left main PA attenuation. Standard mediastinal windows are useful for identifying vessels that are occluded completely with PE.