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Automated Detection of Pulmonary Nodules on CT Images: Effect of Section Thickness and Reconstruction Interval—Initial Results¹

¹ From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63110. Received July 23, 2004; revision requested September 29; revision received October 23; accepted December 10. J.H.K. supported by a postdoctoral fellowship program from the Korea Science and Engineering Foundation (KOSEF). Address correspondence to K.T.B. (e-mail: baet{at}mir.wustl.edu).

View larger version (145K): [in a new window]   Figure 1a. (a, b) Two thin-group transverse CT images from two patients with a nodule (arrow) detected in each patient. These images of 1-mm section thickness are slightly noisier (more apparent in the thoracic soft-tissue body wall) than the 5-mm-thick CT images in Figure 2, but the pulmonary vessels are more sharply delineated, particularly in b. No false-negative or false-positive nodules were observed on these two images.

View larger version (162K): [in a new window]   Figure 1b. (a, b) Two thin-group transverse CT images from two patients with a nodule (arrow) detected in each patient. These images of 1-mm section thickness are slightly noisier (more apparent in the thoracic soft-tissue body wall) than the 5-mm-thick CT images in Figure 2, but the pulmonary vessels are more sharply delineated, particularly in b. No false-negative or false-positive nodules were observed on these two images.

View larger version (143K): [in a new window]   Figure 2a. (a, b) Two transverse CT images from two patients in the overlap group with a nodule (arrow) detected in each patient. These images of 5-mm section thickness are less noisy but are slightly blurrier than the 1-mm-thick CT images in Figure 1. No false-negative or false-positive nodules were observed on these two images.

View larger version (146K): [in a new window]   Figure 2b. (a, b) Two transverse CT images from two patients in the overlap group with a nodule (arrow) detected in each patient. These images of 5-mm section thickness are less noisy but are slightly blurrier than the 1-mm-thick CT images in Figure 1. No false-negative or false-positive nodules were observed on these two images.

View larger version (143K): [in a new window]   Figure 3a. (a, b) Two transverse CT images from two patients in the thick group with missed nodules (arrow) and false-positive findings (arrowheads). On these images of 5-mm section thickness without an overlap, pulmonary vessels that were fragmented as a result of volume averaging and incomplete segmentation were falsely detected as nodules. Two true nodules that were identified with CAD on CT images in the thin and overlap groups (Figs 1, 2) were not detected (ie, false-negative findings). Although the CT images in Figures 2 and 3 have the same section thickness and look similar, the images in Figure 2 were reconstructed slightly differently from those in Figure 3 (Fig 2a at 2 mm craniad to Fig 3a, and Fig 2b at 1 mm caudad to Fig 3b). The section positions were selected to best illustrate the findings in each image group.

View larger version (151K): [in a new window]   Figure 3b. (a, b) Two transverse CT images from two patients in the thick group with missed nodules (arrow) and false-positive findings (arrowheads). On these images of 5-mm section thickness without an overlap, pulmonary vessels that were fragmented as a result of volume averaging and incomplete segmentation were falsely detected as nodules. Two true nodules that were identified with CAD on CT images in the thin and overlap groups (Figs 1, 2) were not detected (ie, false-negative findings). Although the CT images in Figures 2 and 3 have the same section thickness and look similar, the images in Figure 2 were reconstructed slightly differently from those in Figure 3 (Fig 2a at 2 mm craniad to Fig 3a, and Fig 2b at 1 mm caudad to Fig 3b). The section positions were selected to best illustrate the findings in each image group.