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Regional Difference in Compression Artifacts in Low-Dose Chest CT Images: Effects of Mathematical and Perceptual Factors

Kil Joong Kim1,2, Bohyoung Kim1, Kyoung Ho Lee1, Tae Jung Kim1, Rafal Mantiuk3, Heung-Sik Kang1 and Young Hoon Kim1

1 Department of Radiology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Institute of Radiation Medicine, and Seoul National University Medical Research Center, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi-do, Seoul 463-707, Korea.
2 Department of Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Korea.
3 Department of Computer Science, University of British Columbia, Vancouver, BC, Canada.


Figure 1
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  		Fig. 1 —Example of masking procedure. Bottom left image has pixels from compressed image (top right) inside lungs, and pixels from original image (top left) outside lungs. Bottom right image has pixels from compressed image inside chest wall and mediastinum region and pixels from original image outside region. To better present masking procedure, we used compression level of 500:1 for these images, which was not tested in our experiment.

 

Figure 2
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  		Fig. 2A —Individual readers' responses at each compression level. Grading results for compression artifacts by readers 1 (A), 2 (B), and 3 (C). For each compression level, left and right bars represent radiologists' responses for lungs and chest wall and mediastinum, respectively. Different colors of bars represent different grades of perceived artifacts: grade 0 (white), none, indistinguishable; grade 1 (light gray), barely perceptible; grade 2 (dark gray), subtle; or grade 3 (black), significant.

 

Figure 3
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  		Fig. 2B —Individual readers' responses at each compression level. Grading results for compression artifacts by readers 1 (A), 2 (B), and 3 (C). For each compression level, left and right bars represent radiologists' responses for lungs and chest wall and mediastinum, respectively. Different colors of bars represent different grades of perceived artifacts: grade 0 (white), none, indistinguishable; grade 1 (light gray), barely perceptible; grade 2 (dark gray), subtle; or grade 3 (black), significant.

 

Figure 4
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  		Fig. 2C —Individual readers' responses at each compression level. Grading results for compression artifacts by readers 1 (A), 2 (B), and 3 (C). For each compression level, left and right bars represent radiologists' responses for lungs and chest wall and mediastinum, respectively. Different colors of bars represent different grades of perceived artifacts: grade 0 (white), none, indistinguishable; grade 1 (light gray), barely perceptible; grade 2 (dark gray), subtle; or grade 3 (black), significant.

 

Figure 5
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  		Fig. 3 —Joint Photographic Experts Group (JPEG) 2000 compression artifacts in transverse low-dose chest CT images in 50-year-old man with ground-glass opacity nodule. Although lungs and chest wall and mediastinum were segmented in our experiment, unsegmented original image (top left) and Fig. S3A, which can be viewed from the information box in the upper right corner of the article at www.ajronline.org, and 10:1 compressed image (top right and Fig. S3B) are presented here and in Figures S3A and S3B to better depict regional difference in artifacts. Blurring artifacts are more prominent in chest wall than in lung. Note that this regional difference in perceptual artifacts is better reproduced by High–Dynamic Range Visual Difference Predictor (HDR-VDP) map (bottom right) than by mathematical subtraction image (bottom left). Region of interest for original and compressed images is smaller than that of subtraction image and HDR-VDP map. Arrow points to ground-glass opacity nodule.

 

Figure 6
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  		Fig. 4 —Joint Photographic Experts Group (JPEG) compression artifacts in transverse low-dose chest CT image in 72-year-old man with solid nodule. Although lungs and chest wall and mediastinum were segmented in our experiment, unsegmented original image (top left) and Fig. S4A, which can be viewed from the information box in the upper right corner of the article at www.ajronline.org, and 10:1 compressed image (top right and Fig. S4B) are presented here and in Figures S4A and S4B to better depict regional difference in artifacts. Blurring artifacts are more prominent in chest wall than in lung. Note that this regional difference in perceptual artifacts is better reproduced by High–Dynamic Range Visual Difference Predictor (HDR-VDP) map (bottom right) than by mathematical subtraction image (bottom left). Region of interest for original and compressed images is smaller than that of subtraction image and HDR-VDP map. Arrow points to solid nodule.

 

Figure 7
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  		Fig. 5 —Box-and-whisker plots of peak signal-to-noise ratio (PSNR). For each compression level, white and gray graphs represent data for lungs and chest and mediastinum, respectively. Middle lines of boxes show medians, and upper and lower margins of boxes show upper and lower quartiles, respectively. Ends of vertical lines show 5 and 95 percentiles.

 

Figure 8
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  		Fig. 6 —Box-and-whisker plots of High–Dynamic Range Visual Difference Predictor (HDR-VDP) results. For each compression level, white and gray graphs represent data for lungs and chest and mediastinum, respectively. Middle lines of boxes show medians, and upper and lower margins of boxes show upper and lower quartiles, respectively. Ends of vertical lines show 5 and 95 percentiles.

 

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