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DOI:10.2214/AJR.07.3462
AJR 2008; 191:W30-W37
© American Roentgen Ray Society

Original Research

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.

OBJECTIVE. The objective of our study was to investigate the difference of perceptible artifacts between the lungs and the chest wall and mediastinum in Joint Photographic Experts Group (JPEG) 2000–compressed low-dose chest CT images and to show that a perceptual image quality metric—the High–Dynamic Range Visual Difference Predictor (HDR-VDP)—can reproduce this regional difference.

MATERIALS AND METHODS. Twenty images were compressed reversibly and irreversibly to 6:1–30:1. To analyze the two regions separately (lungs; and chest wall and mediastinum), the compressed pixels outside each tested region were replaced with the original pixels. By comparing the compressed and original images, three radiologists independently rated the compression artifacts as grade 0, none, indistinguishable; 1, barely perceptible; 2, subtle; or 3, significant. At each compression level, the two regions were compared for the readers' responses, peak signal-to-noise ratio (PSNR), and HDR-VDP results. Wilcoxon's signed rank tests and exact tests for paired proportions were used with a p value threshold of 0.05.

RESULTS. Artifacts were rated as lower grades in the lungs than in the chest wall and mediastinum, showing statistical significances at 10:1–20:1 for reader 1, 8:1–15:1 for reader 2, and 8:1–20:1 for reader 3. Grade 0 was more frequent in the lungs, showing statistical significances at 10:1 for reader 1 and at 8:1–10:1 for readers 2 and 3. The results of PSNR indicated greater artifacts in the lungs (p < 0.001), whereas HDR-VDP results indicated fewer artifacts in the lungs (p < 0.001).

CONCLUSION. Although compression artifacts are mathematically greater in the lungs than in the chest wall and mediastinum, radiologists' artifact perceptions are the opposite, which can be successfully reproduced by HDR-VDP.

Keywords: artifacts • CT • data compression • image quality metric • low-dose CT • lung cancer screening • visually lossless threshold


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