Efficiency and reproducibility in pulmonary nodule detection in simulated dose reduction lung CT images

Abstract

Purpose: To determine the reproducibility and productivity of reduced dose chest computed tomography (CT) using a nodule detection task.

Materials and methods: Eighty-eight consecutive non-contrast CT examinations were performed using an automatic exposure system with a reference standard deviation of 8.5. Simulated raw data of a reduced dose scan (standard deviation at 21 and 29) were generated with a dose simulator. Original and simulated raw data were reconstructed to series of 7-mm-thick images (Original, Simulation A, Simulation B). In the first part of the reading experiment, three readers independently interpreted these images (88 cases × 3 series) and recorded the size, type, and location of the pulmonary nodules. The reading time for every case was recorded. In the second part of the experiment, the repeated interpretation of standard dose images was performed by two readers. Concordance or discordance of nodule detection between the first and the repeated reading result was assessed.

Results: A statistically significant difference in the detected nodule counts for lesions less than 5 mm by one reader was observed in simulation B images. Discordance of the interpretation result was found only in ground-glass nodules larger than 5 mm detected by one reader in simulation B images. There was no statistically significant difference in the reading time among the three image types.

Conclusion: Simulated standard deviation 21 images can reproduce the image interpretation result of original images, whereas simulated standard deviation 29 images may compromise the accuracy of nodule assessment. The effect on the reading time was not observed with dose reduction simulation.

Keywords: Automatic exposure control; Computed tomography; Pulmonary nodules; Radiation dose reduction.

Fig. 1

Area of ground-glass opacity in the right lower lobe measuring 7 mm was detected by a reader on the original image (left) but missed on the simulation A image (middle) and simulation B image (right). Another 5-mm solid nodule (not shown) is found in the right middle lobe and identified on both original and simulation images.

Fig. 2

Area of ground-glass opacity measuring 21 mm in the left upper lobe was detected by a reader on the original image (left) and simulation A image (middle) and missed on simulation B image (right). The increased noise and streak artifacts decrease disease conspicuity.

Fig. 3

A solid 5-mm nodule in the left upper lobe is depicted in the original image (left) with a well-defined border. The margin of the nodule become blurred by the overlapping streak artifacts in simulation A image (middle) and almost effaced in simulation B image (right).