67-4

20/90

340criteria in the non-PTE group were labeled as the non-thrombi group. CT attenuation values were then measured on unenhanced CT images. In the thrombi group, attenuation values were measured in relation to the thrombus after referring to its position in the enhanced CT image. The attenua-tion values of the pulmonary trunk were also measured after confirming that there was no thrombus on the enhanced CT image. In the non-thrombi group, the attenuation value of the PAs was evaluated and compared to the attenua-tion value of the thrombi in the thrombi group. The attenuation value of the pulmonary trunk was also evaluated. These measurements were performed by placing the region of interest (ROI) in the scans, after which the computer automatically calculated the average attenuation values (in HU) for the selected foci (Figure 2A, 2B and 3). Each ROI was about 4-6 mm in diameter with an area of 12-28 mm2, which was the maximum diameter possible without exceeding the diameter of the segmental PA. Although no specific window setting was used consistently in this study, results were best seen with narrow window settings (window width=330 HU, window level=30 HU). To reduce bias without affecting the partial volume effect, 3-5 ROIs were placed for each image.Medical records were reviewed to assess the baseline characteristics of patients, including the Figure 2　Placing the region of interest (ROI)(●) on unenhanced computed tomography (CT) in the thrombi group. ROIs were placed on the thrombus (A) after referring to its position in the enhanced CT image (B).presenting signs and symptoms, clinical diagnosis, indications for the procedure, and laboratory workups. The mean (± standard deviation [SD]) attenuation values (in HU) of the thrombus and main PA were compared. The thrombus attenua-tion value on unenhanced CT is related to the Figure 3　Placing the region of interest (ROI) (●) on unenhanced computed tomography (CT) in the non-thrombi group. ROIs were placed on the pulmonary trunk and the left and right main pulmonary arteries.