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JPEG2000 Compression of Thin-Section CT Images of the Lung: Effect of Compression Ratio on Image Quality¹

¹ From the Department of Radiology, University Hospital Vienna, AKH Wien, Währinger Gürtel 18-20, A-1090, Vienna, Austria (H.R., R.E.S., A.A.B., M.W., C.J.H., C.S.); and Department of Radiology, Utrecht Medical Center, Utrecht, the Netherlands (M.P.). Received March 29, 2005; revision requested May 25; revision received September 2; accepted September 12; final version accepted November 23. Address correspondence to H.R. (e-mail: helmut.ringl{at}meduniwien.ac.at).

Purpose: To assess retrospectively the effect of the Joint Photographic Experts Group 2000 (JPEG2000) compression ratio on the quality of thin-section computed tomographic (CT) images.

Materials and Methods: In this institutional review board–approved investigation (protocol 238/2004), thin-section CT images were subjected to irreversible JPEG2000 compression by using five compression ratios (3:1, 5:1, 7:1, 9:1, and 11:1). Three radiologists independently evaluated 60 thin-section CT images, of various diseases, that were obtained with single-detector (weighted dose index, 14.4 mGy) and multidetector (weighted dose index, 9.8 mGy) CT. Toggling between the original and compressed images, readers had to identify the original image by using a forced-choice two-alternative model and to subjectively rank the quality of what they believed to be the compressed image. To assess the reader's ability to distinguish the compressed from the original image, a binomial test was used. Bonferroni correction was applied for all multiple tests.

Results: Images compressed with a ratio of 3:1 were not distinguishable from original images (P > .2 for all readers). With use of the 5:1 ratio, minor differences in appearance between the compressed and original images were seen by one of the three readers. With use of higher compression ratios (7:1), all readers (P < .001) recognized the original image. The quality of more than 90% of the images compressed with a 7:1 or higher ratio was substantially degraded. Single-detector and multidetector CT results were not significantly different.

Conclusion: The highest ratio that yielded visually lossless compression of thin-section CT images was 3:1. With the 5:1 ratio, there was minor image quality loss, while use of higher compression ratios (7:1) caused substantial degradation of image quality and potential loss of diagnostic information.

© RSNA, 2006